Aeromodelin And Airplane Design 5d4rd

9/7/2009     

A  REPORT  ON   

 

AERO‐MODELING AND AERODYNAMICS 

SUBMITTED BY | DEBASISH DEVKUMAR PADHY 

INTRODUCTION  As a kid we have always dreamed of flying like a bird or becoming a pilot and flying an airplane. The  thought of flight has always thrilled human race. There are a lot of instances that prove that man was  trying hard to get wings and soar out in the sky just like birds. Ultimately the Wright brothers came up  with the real breakthrough, their Wright Flyer.   There were thousands of attempts before the real flyer came into action. Various concepts and designs  came into contrast before the Wright Brother’s Flyer. Langley and Da Vinci were among the few legends  who gave the preliminary idea about flight.  As a matter of fact, the modern day helicopter still works on  the same principle as given by Da Vinci.   A lot of companies came into action and the requirement for researching and developing a practical  commercial plane came up. And that’s when AERO‐MODELING came into existence.     WHAT EXACTLY IS AEROMODELING??  In the past Aero‐modeling was introduced for rapid R&D and prototype development. Later it was made  available to the public for hobby purpose. At present Aero‐modeling is still in its original form. It  is still  used in R&D and prototyping .  Prototype is an original type, form, or instance of something serving as a typical example, basis, or standard for the things of the same category. Or say prototyping, in a greater extent, practical attempt to simulate the final design, aesthetics, materials and functionality of the intended design. The functional prototype is generally reduced in size (scaled down) in order to reduce costs. The construction of a final and working full-scale prototype and the ultimate test of concept is the engineers' final check for flaws in design and allows last-minute improvements to be made before actual production units are ordered.

   Atlantica plug the prototype developed by NASA   (Source: NASA) 

This whole report is divided into 5  modules.  The report is focused on an introducing to Aero‐modeling and ultimately  deg an Aero‐model. 

  Module one: ­   Introduction to general aerodynamic and  Aero­modeling    Module two: ­   Classification of airplanes  Module three: ­   Deg an Aero­model  Module four: ­   Construction phase  Module five: ­    Flying of the Aero­model     

Module one:  Introduction to aerodynamic  and Aero‐modeling   Before we start off with classification or deg of airplanes, we have to have  ideas of some basic aerodynamic theory and some basic  commonly used in  the field of aviation and aero‐modeling.   But first we will be studying about the airframe. 

Trailing edge  Leading edge 

  Fuselage:   It is the main body of an aircraft over which everything is assembled to make an  airplane. In more generalized way, it is the main body of an aircraft which holds  wings, horizontal stabilizers, vertical stabilizers, crew, etc      

Wing:   It is the main lifting surface of the airplane, it’s the surface where most of the lift  generated acts and its design is the most crucial part of a airplane, to decide its  characteristics.  Leading edge:  The front ends of the wing which is incident to the wind, i.e. which separates the  wind in two section.  Trailing edge:  It is the back end of the wing where the wind after separation meets again. It is  the place where ailerons are located.   Chord:  Chord is the shortest distance between leading edge and trailing edge.  Airfoil:  It is the cross‐sectional view of a wing. It’s shape is responsible for the lifting  action on various lifting surfaces,   Horizontal stabilizer:  A tail plane, also known as horizontal stabilizer, is a small lifting surface located  behind the main lifting surfaces of a fixed‐wing aircraft as well as other non‐fixed  wing aircraft such as helicopters and gyroplanes. The tail plane serves three  purposes: equilibrium, stability and control.   “Note: In short the movement of fuselage up and down along an axis is called pitching  controlled by the elevator attached to the tail plane, more detail later in the text”       

Vertical stabilizer:  The work of vertical stabilizer is same as the work of horizontal stabilizer, but  instead of controlling pitching it controls the yaw moment of the air plane with  the help of rudder.  The image below will show how these things are 

  Rudder:  Its main work is to control the alignment of airframe with respect to runway or  wind. It controls the yaw movement of the airplane. It helps to adjust the heading  of the airplane in case of gust and drifts.  Elevator:  Just as the name says it helps an airplane to elevate up and down and hence  control the altitude of an aircraft. It is located just behind the tail plane.  Angle of attack:  The angle, with which, the wing penetrates the air. As the angle of attack  increases, lift also increases up to a maximum point (along with drag).       

Now let’s jump into basic aerodynamics and flight theory…   Here we will be looking how lift is generated and how an airplane flies.   In today’s date we all know about the principle on which an airplane flies. It is The  Bernoulli’s principle, which in simple words states “Increase in velocity of fluid  results in decrease in pressure.” And decrease in pressure will result in decrease  in gravitational potential energy.   

 

 

  Imagine this way.  You are in a very narrow streets and the number of people  moving on the road is very large. You will observe the people will move slowly  and push each other. That means that the pressure is high. But when the number  of people is less, you will observe that the people will move fast. There will be no  pushing, meaning the pressure is less.   If we assume the people moving in the street as a fluid, then the statement  becomes, “At high speed pressure is low and at low speed pressure is high.”    Now with that we can easily understand the theory behind the lifting of an aero  plane.  All the lifting surfaces present in an aircraft have a unique cross‐sectional shape,  called an aerofoil, whose characteristic is that, air flowing above the wing is faster  than air flowing below the wing.  

  Aerofoil of the wing 

   Now when the wing is incident to wind, the air flowing above the wing has to  cover more distance than the air flowing below the wing. This compels the air  above the wing to move faster than air below the wing. Here Bernoulli’s principle  comes in action “high speed=low pressure; low speed=high pressure”.  Since the  transition of energy is from high to low, the wing generates a lift. When the speed  of the airplane is enough to generate lift equivalent or more than its weight the  airplane lifts off from the ground. 

Now that we have understood how lift is generated, we can go on with other  control surfaces and how they work.   An airplane in stable and straight flight is at dynamic equilibrium, i.e. every force  acting on the body of an aircraft is canceling each other out. The only force that  exists is the forward force by which the aircraft moves forward. Now whenever  there is any disturbance in the equilibrium the airplane responds to it. Any one  flying an airplane uses these disturbances to control all the movement of the  airplane, right from take off to landing.  For example,  for altitude control, the disturbance is made at the pitch of the  aircraft, when the elevator is raised up the wind flowing on the tail plane tries to  push it down as a result the tail goes down and the nose rise up, when nose is up  the thrust due to engine pulls the airplane high in the air. 

Elevator  movement 

 

For banking and direction control use of aileron comes in action, ailerons are  present in both the wing halves so when one aileron is raised and the other is  lowered, the wind flowing above the raised aileron side tries to push that side of  the wing down and the other side where the aileron is lowered the wind below  the wing tries to push it up ward result is a force couple, and the plane banks to  the raised aileron side. The image below illustrates it. 

  Other control are rudder and throttle which aids in skid and speed control of the  airplane.  Another aerodynamic term we should be looking forward is the dihedral of an  airplane…. What is exactly dihedral is?  Dihedral  The dihedral angle is the angle that each wing makes with the horizontal. The  purpose of dihedral is to improve lateral stability. If a disturbance causes one  wing to drop, the unbalanced force produces a sideslip in the direction of the  downgoing wing. This will, in effect, cause a flow of air in the opposite direction to  the slip. This flow of air will strike the lower wing at a greater angle of attack than  it strikes the upper wing. The lower wing will thus receive more lift and the  airplane will roll back into its proper position.  Since dihedral inclines the wing to the horizontal, so too will the lift reaction of  the wing be inclined from the vertical. Hence an excessive amount of dihedral  will, in effect, reduce the lift force opposing weight.  Some modern airplanes have a measure of negative dihedral or anhedral, on the  wings and/or stabilizer. The incorporation of this feature provides some 

advantages in overall design in certain type of airplanes. However, it does have an  effect, probably adverse, on lateral stability.  Also During the design of a fixed‐wing aircraft (or any aircraft with horizontal  surfaces), changing Dihedral Angle is usually a relatively simple way to adjust the  overall Dihedral Effect. This is to compensate for other design elements' influence  on Dihedral Effect. These other elements (such as wing sweep, vertical mount  point of the wing, etc.) may be more difficult to change than Dihedral Angle. As a  result, differing amounts of Dihedral Angle can be found on different types of  fixed‐wing aircraft. For example, the Dihedral Angle is usually greater on low‐wing  aircraft than on otherwise‐similar high‐wing aircraft. This is because "highness" of  a wing (or "lowness" of vertical center of gravity compared to the wing) creates  naturally more Dihedral Effect itself. This leaves less Dihedral Angle needed to  supplement Dihedral Effect and get the amount of Dihedral Effect needed.  How to calculate dihedral?  Well for aeromodelers the answer to this question is “it depends”, It depends on  the characteristics of airplane we want to design, wether the airplane is highly  stable or it is moderately stable, high stable model is less maneuverable and low  stable model is highly maneuverable so it is the requirement which helps us  calculating the dihedral of a airplane. With my experience a dihedral of 7‐ 8degrees is more than enough     

           

        MODULE TWO    This section deals with the general classification of airplane and airframes based on various  distinguishing factors, here the classifications are based on the powerhouse, wing style ,  alignment, purpose etc    ____________________________________ 

      • Classification based on wing styles  • Classification based on wing locations  • Classification based on wing dihedral   • Classification based on powerhouse 

   

       

  Classification: wing styles    There are various aircraft available all over the world and we need to classify them in order to make  deg phase easy and more feasible. The 1st categories is based on the wing style , That is whether  the wing is forward swept or backward swept , the geometry of the wing etc.  So lets start with a forward swept wing:  A forward‐swept wing is an aircraft configuration in which the quarter‐chord line of the wing has a forward sweep.  The configuration was first proposed by some German aircraft designers 

Aircraft with forward‐swept wings are highly maneuverable at transonic speeds because air flows over a  forward‐swept wing and toward the fuselage, rather than away from it.  An example of a forward swept wing concept  

 

  AIRPLANES having this type of wings are called canard airplanes. These are the 3rd generation or say  future style airplanes. For the time being its not in much practical usage    The second style of wing is back swept wings:  The wing angles backwards from the root. This reduces drag at transonic speeds, but can handle badly in or near a  stall, and requires high stiffness to avoid aeroelasticity at high speeds. Common for high‐subsonic and supersonic  designs.   As an aircraft enters the transonic speeds just below the speed of sound, an effect known as wave drag starts to  appear. Using conservation of momentum principles in the direction normal to surface curvature, airflow  accelerates around curved surfaces, and near the speed of sound the acceleration can cause the airflow to reach  supersonic speeds. When this occurs, an oblique shock wave is generated at the point where the flow goes  supersonic. Since this occurs on curved areas, they are normally associated with the upper surfaces of the wing,  the cockpit canopy, and the nose cone of the aircraft, areas with the highest local curvature. Using back swept  wing reduces this problem.  These are the present generation airplanes like the mig‐21,commercial enger airplanes and some military  bombers  

   

Other wing configurations are  ƒ

ƒ

Straight - extends at right angles to the line of flight. The most efficient structurally, and common for low-speed designs. 

M-wing - the inner wing section sweeps forward, and the outer section sweeps backwards. The idea has been studied from time to time, but no example has ever been built.

ƒ

W-wing - the inner wing section sweeps back, and the outer section sweeps forwards. The reverse of the M-wing. The idea has been studied even less than the M-wing and no example has ever been built.

ƒ

Crescent - wing outer section is swept less sharply than the inner section.

ƒ

  ƒ

Swing-wing - also called "variable sweep wing". The left and right hand wings vary their sweep together, usually backwards. Seen in a few types of combat aircraft 

      These styles were important for classification and deg point of view.  Now moving on to the next section of classification I.E classification based on the location of the wing  which will be carried out in the next page 

 

CLASSIFICATION : WING LOCATION    The location of wing with respect to the main airframe is also a deciding factor for the maneuverability  of an aircraft. Typically there are four type of location possible.  ƒ ƒ ƒ ƒ

High wing  Low wing   Shoulder wing  And The parasol wing 

    High wing:  In this configuration the airframe lies below the wing, that is the weight of the whole airframe is  suspended below the wing. This configuration is suitable for stable airplanes like trainers and low  power airplanes. Since the weight of the airplane is suspended below the wing it helps in the auto  correction (for level flight) . it finds application in UAV’s(unmanned aerial vehicle ) and other  autonomous airplanes, enger airplanes and cargo planes.  A typical UAV.  

 

   A typical high wing configuration airplane used in military and defence services.    Low wing configuration:  In this configuration the airframe lies above (over the airframe) the airframe, here the weight of the  airplane is kept over the wing and hence make a bit unstable but more maneuverable. These wing  configuration finds application where high maneuverability is required , that the aircraft is able to  perform precision aerobatics , And we think that you have guessed the probable fields of application  of these, Yes you are right , it’s the defense where fighter aircrafts are used. 

 

  Example: of few combat airplanes. (low wing configuration).    The next wing configuration is a shoulder wing airplane  Shoulder wing airplane:  This style of wing is a combination of high wing and low wing, That means some part of the weight is  above the wing and some part is suspended below the wing, meaning a fussion of stability and  maneuverability. It finds application in the fields of defense and combat.

 

The fifth type of wing configuration is parasol style:  Here the wing is mounted above the airplane body and is held in place by wing struts and dowels, its  like a parachute. This configuration is similar to high wing configuration.   

                 

             

  CLASSIFICATION: WING DIHEDRAL   AS you already know the meaning and physical significance of dihedral, the classification of  airplanes can be done according to there characteristics dihedral.  The characterictic dihedral are of three types  ƒ ƒ ƒ

POSITIVE DIHEDRAL  NEGATIVE DIHEDRAL  or ANHEDRAL  NO DIHEDRAL 

    Positive dihedral:  When the wing tips of a wing are raised to form an angle between the two halves of the wing , its  positive dihedral.  It adds the self correcting ability and stability to the airplane, it is the most  essential part of a stable airplane with predictable behavior.    Negative dihedral:  It’s the opposite of Positive dihedral, the wing tips are dipped towards the ground, to obtain  anhedral, it adds to maneuverability and reduces stability. It finds application in combat airplanes.     NO Dihedral:  As the name says , there is no dihedral present or anhedral present , the angle between the wing  halves is zero degree but still keeps the airplane predictable and a bit stable . Its most widely used  configuration. For some previous jet aircrafts and for some very recent airplanes.         

   

Classification: Power house      By saying power house we mean to say the engine used for aviation.   Commercially airplane uses turbojet, pulse jet, ram jet, etc to power themselves,   In AERO‐MODELING we use  

here IC engines are basically of three types i.e glow, petrol, & diesel. The main difference between  these engines is the fuel they use i.e mixture of “castor and methanol”,” petrol”, and mixture of  “kerosene castor and ether”. Apart from all these the difference is the way the ignition occurs, for   petrol and glow the ignition is initiated with a spark given out by the spark plug or glow plug  respectively, while in the case of diesel engine the fuel air mixture is ignited by subjecting them to  very high pressure in the compression chamber while the compression stroke occurs.     Moving off the IC engines there  is another power house and its called electric motors, which are of  basically of two types, 1st brushed electric motors and second is brushless electric motors. The main  difference between brushed motor and brushless electric motor is that brush motors are less costly  and brushless motor is more costly , apart from it the brushed motors are less efficient and noisy , 

causes more wear and tear. So while deg we have to chose wisely , wethere to chose AN IC  engine or a motor.   Failing to do so will result in poor airplane design.                                         

   

  MODULE 3: DEG AN AEOPLANE       

In the  pages we will be deg an airplane, doing some  calculations and drawing some plans. For this report we will be  deg A “High wing ” Trainer aircraft. Powered by a .25 size glow  engine we will not be focusing on how the formula was derived we will  be using formulas and wherever necessary we will be giving out the  derivations behind each formula, In this section we might be talking  about some advanced aerodynamics which were not discussed earlier.  The deg process will comprise of following steps    • • • •

Laying out specifications.  Analysis of requirements and solutions.   Calculating the required parameters.  Drawing the approx plan.             

LAYING OUT THE SPECIFICATIONS     

A specification allows you to take a vague concept and turn it into specifically what you want. It should detail everything that is important to include and exclude from your design. Since we are deg an aircraft which is supposed to be a trainer we will be looking on the following points.

• • • • • • • • • • • • •

Purpose of the model Style — Modern, Old Timer, Scale, Sleek, etc. Powerplant class Flight time Stability — Should the model be self-stabilizing, neutrally stable or somewhere in between? Airspeed Vertical performance: moderate Control response: predictable Stall characteristics: high speed stalls should be avoided Construction methods — Traditional wood, composite, etc. Control system Landing gear system: tricycle Break-down for transportation

The purpose of the airplane is to behave like a trainer such that a  novice or a beginner can learn how to fly a airplane, style like  modern,old timer etc is not of that importance but the point is that a  very stable aircraft generally is a highwing airplane, being a highwing  model adds the ease with which it can be constructed, Other advantage  of highwing configuration are   •

A high wing aircraft has a shorter landing distance than a low wing  aircraft because the wing stays out of the ground effect. 

•

•

And most importantly it helps in the self correcting ability of an  airplane due to the pendulum stability.

Pendulum stability  Now also since the wing stays high above the ground the  probability of wreaking the wing is highly reduced adding the  crash resistance effect 

 

Now that we have decided the wing location we can proceed to  other section of stability and self correcting ability, for a trainer  airplane the self correcting ability is a must for that we must have  dihedral on our wings. The higher the angle higher is the self  correcting ability to an extent so for our purpose we will go with a 5*  of dihedral.(for more details on dihedral see texts above)  Moving to power plant section , the choice of using a ic engine or a  electric motor depends largely on the way of construction adopted,  like a delicate construction will have to use electric motors despite of  that, purpose of the aircraft is also a deciding factor, it the model has  to be made noise free, then also we have to use electric motors. But  in this case the priority is a high strength trainer airplane, so  choosing a Ic engine powerhouse will not harm anything, also 

electric motors have their own disadvantage like we will have limited  flight time and the RPM of the motor decreases as the battery drains  also we have to carry many battery pack’s if we intend to have some  long day of flying.    The engines and motors rotates different propellers at different  rpm’s  Like   Generally the RPM range of a typical glow engine is from few  thousand to 16,000 or more. The propeller which an engine is  capable to swung for best performance is provided by the engine  manufacturer.  We will be using a .25 cu in glow plug engine for our airplane  swinging a 9x6 size propeller that means a propeller of 9” diameter  and of the pitch 6” that means if this propeller is rotated in a solid  medium of 9 inch then it will move 6” forward, it suggests that the  total weight of our airplane shud be some where between 700gms  to 1.4 kgs, lets fix it to 1kg.    Well the answer is this formula:  Lets say D is the engine size and W is the weight of the aircraft it can  pull happily then   D x 12 = W; or D=W/12  The result comes in lbs then converts it to kgs, 

For our purpose the engine we are using is a .25 cu in hence the  formula is  .25(D) x 12= 3lbs   1lb= 0.4535924 kg   Hence 3 lbs = 1.4 (approx) kg  We keep a margin of 400gm (approx) to compensate the weight  resulting due to repairs and crashes.    Till now what we have decided is       • • • •

A high wing style airplane  Dihedral of 5* initially (can be changed latter)  An engine of .25 cu in  Total weight of 700gms to 1kgs (max) upper limit is 1.4kgs   

    Before we go further we have to leap back into aerofoil section again  because after this is covered we will be deg wing, which will  decide other parameters of the aircraft.   

Back to airfoil    The various related to airfoils are defined below: ƒ

The mean camber line is a line drawn midway between the upper and lower surfaces.

ƒ

The chord line is a straight line connecting the leading and trailing edges of the airfoil, at the ends of the mean camber line.

ƒ

The chord is the length of the chord line and is the characteristic dimension of the airfoil section.

ƒ

The maximum thickness and the location of maximum thickness are expressed as a percentage of the chord.

ƒ

For symmetrical airfoils both mean camber line and chord line from centre of gravity of the airfoil and they touch at leading and trailing edge of the airfoil.

ƒ

The aerodynamic center is the chord wise length about which the pitching moment is independent of the lift coefficient and the angle of attack.

ƒ

The center of pressure is the chord wise location about which the pitching moment is zero.

  Camber is one we need to cover. To an aero engineer, an airfoil is cambered or uncambered, and perhaps reflex. Camber is determined by the mean camber line which is a line halfway between the top and surfaces of the airfoil. Let's say you have a drawing of an airfoil. At several different places, locate the spot which is halfway between the top and bottom surface of the airfoil and make a dot. After you have several dots, connect them up. This is the mean camber line.  

If we see airfoils in very broad category there are three types of airfoil,  1.flat bottom  2.semi‐symitrical. 

3. Symitrical.    FLAT BOTTOM AIRFOILS: This is the airfoil you normally see on a trainer. When you look at a trainer wing, one side of the airfoil is flat. You may think this is a thin airfoil, but if you double the thickness, you would have the corresponding symmetrical airfoil which would be pretty thick. Flat bottom airfoils tend to be very speed sensitive. When you add power and increase speed, they create a lot more lift, making the plane climb. A symmetrical airfoil which is equally curved on both sides, on the other hand, generates very extra lift with a power and speed change. The main characteristics of this type of airfoil are • At Low speed high lift possible ideal for trainer planes • Very bad aerobatics characteristics

Semi-symmetrical airfoils are seem on many "second plane" designs. These are sport planes designed for easy flying or for a person's next plane after a trainer. Most scale planes have semi-symmetrical airfoils because most full size planes have this type airfoil. The semisymmetrical airfoil is much better that the average modeler thinks. They are thinner than most corresponding fully symmetrical airfoils and have less drag, and their inverted performance is not all that bad. We rarely fly the tightest outside loop possible, so the average flier should never notice the difference in inverted flight. • Moderate lift at high speed • Good maneuverability • Good aerobatic capability

  Symmetrical airfoils are the most popular for RC modelers. We fly inverted infinitely more than any full scale pilot. Even the top level competition pilots do not fly inverted for minutes at a time. We also do more outside maneuvers than any except maybe the competition pilots. For these reasons alone, inverted flight and outside performance, symmetrical are the most popular once a person graduates from a trainer. Another reason to select a plane with a symmetrical airfoil, an a compelling one, is the plane tends to maintain its attitude with a change in speed. A symmetrical airfoil is generally thicker, and therefore stronger, from a bending or "g" force direction.

• • • •

High speed low lift  Highly maneuverable   Less fatigue to the G effect and more thicker in size  Best aerobatic capabilities 

  For commercially available database of aerofoil is over 1500 , the  best way to find the best aerofoil is to use personal experience  and peoples reviews, for our purpose the clark‐y flat bottom  aerofoil is best as it have been in practice since the 1st airplane  appeared and is widely used in trainer and other highwing stable  airplanes.  “These are the decisions I make before selecting a specific airfoil: 1. Specify desired flight characteristics (airspeed envelope, aerobatic capabilities, etc.). 2. Specify the wing-loading and power loading ranges. Be disciplined about deg to those goals.

3. Decide on a wing planform (chord(s), span, taper and sweep). 4. Determine the most appropriate airfoil family. Because all designs represent numerous compromises you'll have to use the above to decide which characteristics are more important than others. Select a specific airfoil using whatever information you have.” Almost nobody who designs model airplanes would have a clue how to pick an airfoil for their design based on real airfoil data. We learn from experience knowing that the subtleties between one airfoil and another close to the same shape will make a very small difference — one that would only be noticed by an expert pilot. These behaviors are not different enough to cause any problems in your design unless you do something like change a round leading edge to one that is razor sharp. One of the main concerns of fledgling model airplane designers is how to avoid choosing an airfoil having wicked stall characteristics. All airfoils have a stall angle. This is the angle of the chord line of the wing to the direction of flight. When this angle is at or beyond the stall angle the air breaks away from the wing and the wing stops producing lift. In other words, the aircraft isn't flying any more. It's falling from the sky. The leading edge radius takes the lead role in stall characteristics. A sharp (small radius) leading edge typically has a shallow stall angle. That means it will stall sooner than a blunt leading edge. A tip stall occurs when a wing tip stalls before the wing root. In most cases this causes the aircraft to roll over. If the plane is close to the ground it's usually a total loss. There are several ways to avoid or delay tip stalls. •

Build the wing with washout.

Washout simply means the wing is built with a twist so that the wing tips are at a lower angle of incidence than the wing root. Washout also limits aerobatic capabilities. •

Sand the leading edge such that it becomes more blunt toward the tip.

•

Avoid high aspect ratio wings having a high taper ratio.(will be discussed latter) Taper ratio is the length of the tip chord divided by the length of the root chord. Aspect ratio is the wing span divided by average wing chord. High aspect ratio wings, such as sailplanes, with high taper ratios tend to be more prone to tip stalls than low aspect ratio wings, such as deltas.

Airfoil Thickness  Airfoil thickness is simply the percentage of the wing chord that the airfoil is deep at it's thickest point. For example a wing having a chord of 15" that has a 10% thick airfoil will be 11/2" (1.5") thick. How thick should the airfoil be? I find that wing thickness is a compromise between speed and lift. A thicker wing has more drag but more lift and is capable of slower flight. Thicker wings also tend to "bounce" around more in the air because they can't cut through it as easily. A thinner wing has less lift but is faster. The shape of the leading edge plays a part in this as well. One other thing to note is that as wings get thicker they also become stronger. If a wing is thick it is easy to build it strong using conventional construction techniques. If the wing is thin then more exotic techniques are required to prevent the wing from breaking in flight.

Of course there are limits to everything. I've seen airfoil listings that are thicker than 30%. The thickest wing I have built was about 20% and I didn't like anything about it in flight. From as far back as I can through the 1980's, most sport designs had airfoils in the range of 14% to 16% thick. These airfoils have proven to be safe with few or no bad habits at reasonable wing loadings and can slow down nicely to land. I normally use airfoils from 12% to 18% depending on the airplane. For an extremely fast model I may use an airfoil around 10% thick. In the past several things happened that changed the way we design model airplanes. Pilots came to desire aerobatic models that fly at speeds below Mach 1, four-stroke engines became widely available. A thin airfoil simply isn't going to slow down when the airplane is diving toward the ground even with the engine at idle. More drag was needed, but it had to be smooth, clean (non-turbulent) drag. In other words, airfoil shaped. The easiest way to create this drag was to build a thicker wing which also creates more lift at slower speeds. These models also had to revert to old-time, lightweight construction techniques because lighter planes maneuver better and fly slower. Drag increases exponentially with airspeed. Frontal area, drag and airspeed are inseparable so you need to have a feel for how they work together to decide how thick the wing should be. This is an area where I really can't speak scientifically. I have a good feel for how it works and do pretty well with that knowledge. Carefully match the power plant and propeller to the airframe instead of matching the propeller to the power plant alone. All airplanes have a maximum airspeed at which they will fly smoothly. If the engine has more power available after this speed is reached you won't see more speed, but the model will begin to buffet or worse - something might flutter off.

Airplane 

Engine 

Propeller  Top  Pitch  Speed 

Average weight Stik 

.45 

6"‐7" 

80 MPH

Airfoil 

Flight Characteristics 

15%  symmetrical 

Smooth flying, medium to large  aerobatics, reasonable landing speed.

4"‐5" 

50 MPH

18%  symmetrical 

Slow flight, aerobatics in small area,  very slow landing speed, buffeting at  high speeds and susceptible to gusts  at low speeds. 

.40 

4"‐5" 

16% semi‐ 45 MPH symmetrical 

Hovers in steady winds, very low  flight speeds, minimal aerobatics,  difficult or impossible inverted flight,  landing at a crawl. 

Sport‐Aerobatic Biplane  .60 

6"‐7" 

65 MPH

13% semi‐ symmetrical 

Very aerobatic in a smaller area. Tumbles well.  Requires more "down"  for inverted flight. 

8"‐9" 

100+  MPH 

<12%  symmetrical 

Flies fast, lands fast, extremely large  aerobatics. 

Highly aerobatic  

Lightweight Floating  style 

High speed airplane 

.45 

.40 

 

  Now keeping these data’s in mind we can now predict which type  of aerofoil to use, to be on the safe side we will be using a clark‐y  aerofoil or similar airfoil and use it, we know higher the thickness  the more is drag and hence low flying speeds (we need that for  our trainer plane) also being a flatbottom airfoil it will be having  low speed high lift characteristics,    But how to plot the airfoil, use the ordinate’s of the airfoil and  plot it on the paper,  

So how to use these ordinates, well answer is understand what  actually ordinates are and then follow the steps which we are  going to tell,    Airfoil ordinates are simply points that define the shape of the airfoil. The numbers are given in percentage of the wing chord. There is more than one standard, but they are all easy to figure out. The standards I know of are as follows: 1. Stations from 0% to 100% chord. In this case, multiply the chord of the airfoil you are plotting times percent of the station/ordinate pairs in percent. In other words, if the number given is 1.25 then multiply times 1.25%. If your calculator does not have a percent key, then multiply times 1.25 and then divide by 100. Ordinates of this type are presented in two sets of ordinate pairs - one for the upper portion of the airfoil and one for the lower. 2. Stations from 0 to 1. In this case it is straight multiplication of the chord times each of the station/ordinate pairs. This standard also differentiates between the top and the bottom of the airfoil. 3. The last example is the style used for computer programs. This is listing of ordinate pairs with no differentiation between the top and bottom of the airfoil. Numbers are from 0 to 1. The listing starts at the trailing edge of the airfoil and moves forward defining the underside of the airfoil and then the leading edge, the top of the wing and back to the trailing edge again. It sounds more complicated than it is - again, it is simple multiplication.

  Calculating the Ordinates to be Plotted  For this example I will be plotting a NACA 2412 airfoil. The NACA 2412 is a semi-symmetrical airfoil (cambered) that is stable and somewhat fast although it would not be the best choice for

an extreme speed aircraft. It would be a good choice for a onedesign club racer because it has no bad habits and will not get to speeds that the average pilot can't handle. The first table below is the set of ordinates for the NACA 2412. The listing uses standard (1) above. I will be calculating ordinates for and plotting an airfoil having a 9" chord. Multiply all stations and ordinates by the chord. Again, the numbers given in the ordinate listing are percentages. That means you multiply the chord by the station or ordinate in percent. To find the second station for example, multiply 9" x 1.25%. The leading edge (L.E.) radius is also multiplied by the chord to get the actual radius. This is also a percentage. The second table contains the resulting numbers after multiplying them by the wing chord. All numbers are in inches for this example. Calculating and plotting works the same regardless of your number system.

NACA 2412 Ordinates  Upper surface

NACA 2412 (9" Chord) 

Lower surface

Station Ordinate

Station Ordinate

Upper surface

Lower surface

Station Ordinate

Station Ordinate

0 

0 

0 

0

0.000

0.000

0.000 

0.000

1.25 

2.15 

1.25 

1.65

0.113

0.194

0.113 

‐0.149

2.5 

2.99 

2.5 

‐ 2.27

0.225

0.269

0.225 

‐0.204

5.0 

4.13 

5.0 

‐ 3.01

0.450

0.372

0.450 

‐0.271

7.5 

4.96 

7.5 

‐ 3.46

0.675

0.446

0.675 

‐0.311

10 

5.63 

10 

‐ 3.75

0.900

0.507

0.900 

‐0.338

15 

6.61 

15 

‐ 4.10

1.350

0.595

1.350 

‐0.369

20 

7.26 

20 

‐ 4.23

1.800

0.653

1.800 

‐0.381

25 

7.67 

25 

‐ 4.22

2.250

0.690

2.250 

‐0.380

30 

7.88 

30 

‐ 4.12

2.700

0.709

2.700 

‐0.371

40 

7.80 

40 

‐ 3.80

3.600

0.702

3.600 

‐0.342

50 

7.24 

50 

‐ 3.34

4.500

0.652

4.500 

‐0.301

60 

6.36 

60 

‐ 2.76

5.400

0.570

5.400 

‐0.248

70 

5.18 

70 

‐ 2.14

6.300

0.466

6.300 

‐0.193

80 

3.75 

80 

‐ 1.50

7.200

0.338

7.200 

‐0.135

90 

2.08 

90 

‐ 0.82

8.100

0.187

8.100 

‐0.074

95 

1.14 

95 

‐ 0.48

8.550

0.103

8.550 

‐0.043

100 

0 

100 

0

9.000

0.000

9.000 

0.000

L.E. Radius = 0.142 

L.E. radius: 1.58 Slope of radius through L.E.: 0.10  

 

This particular airfoil has stations that are identical for both the upper and lower surfaces but that is not always true. Be sure to pay attention to what you are doing. I have made the mistake of assuming the stations were the same when they weren't which resulted in some strange airfoil plots. Now that you have the numbers they need to be plotted on paper. The ordinate/station pairs are simply (x, y) coordinates. The Station is X and the Ordinate is Y.

    Now that we have know the way how to calculate the co‐ ordinates of an aerofoil we will be using this information and  other requirements to finalize our wing design.    An airfoil can be drawn with a minimum of drafting instruments. You will need a sharp pencil, accurate scale (ruler), and a good curve. I use ship curves because they better match the shape of an airfoil. French curves are more common, but tend to have curves that are too sharp. If you do not want to buy ship curves then an adjustable curve might work. I've tried few different types of adjustable curves and none of them were satisfactory to me. Your results may vary. If you must use French Curves, try to find one that is at least twice the length of the airfoil you are drawing. You can also bend a stick of wood which is surprisingly accurate. I use a piece of 1/8" x 1/4" spruce to draw long curves, such as fuselages, when I draw plans.

The ca alculator only nee eds to be e able to o multip ply, so an ny calcula ator will work.

Draw a center rline slig ghtly longer than n the airfoil cho ord. Draw lines to represen r nt the fro ont of the e leadin ng edge and the ailing ed dge. rear of the tra hord of this airfoiil is 9" so o that is the dista ance the e lines arre The ch spaced d.

t marks alon ng the ce enterline to indica ate the station s Make tick locations. on of the e leading edge an nd centerline is point p (0, 0) The intersectio for this ordinatte standard. e standarrds have e the trailing edge as poin nt (0, 0). Some ordinate If you aren't sure whatt standard you're e using, just plott the

points. If you are usin ng the sa ame stan ndard as I am he ere, the nt to the left. airfoil will poin If you plot the e points backward b ds, the airfoil a will point to o the right. Either way you u end up p with the e same airfoil. a

v station n lines th hrough the t ticks you mad de in the e Draw vertical previo ous step. If the stations are diffe erent forr the upp per and lower porrtions off n you sho ould probably ma ake ticks s for one e side. the airrfoil then Then draw d the e lines. Repeat R fo or the un nderside of the airfoil. a

rdinate location l ns at eac ch station n. Tick offf the or The trailing ed dge of this airfoil tapers to t 0" thic ckness. Howeverr, I heet this wing witth 1/16" balsa. That T means I willl have to o will sh fudge the airfo oil somew what to a s . for the sheeting.

The ne ext imag ge actually repres sents two steps combine c d into on ne. I negle ected to scan the e drawing between steps s. t slop pe of rad dius thro ough the e leading edge. Draw the Slope = Rise over o Ru un = y diivided by y x. In this t case the Slop pe is 0.1. aw the slope line,, start att point (0 0, 0). Measure M b back 1" (x) ( To dra along the airfo oil cente erline and from there measure m u .1 inc up ch D a line throu ugh pointt (0, 0) and a the point p you u just (y). Draw marke ed. The ce enter of the t circle e represe enting th he leadin ng edge is i found on the slo ope line e by mea asuring from f poin nt (0, 0) to a disttance eq qual to the radius of o the lea ading edge. For ex xample, if i the dia ameter of the le eading ed dge is 1", then measu ure back 1/2" (ra adius) alo ong the slope line. That is the centerr of the circle c tha at repres sents the e leading edge. Draw D the e circle. Using curves that t matc ch the po oint bestt, draw the t airfoiil outline e. Norma ally I use e severall differen nt curves s by selecting the e curve that t best matches m the t airfo oil in any given se ection. The airfoil is ta angent to the le eading ed dge.

Now thaat we havee An aerofooil we will be using this t aerofoiil in our model m airplaane. I know you will be thinking why the hell h I dint used u the claark y aeroffoil as stateed above, well w in thiss example you saw thhen NACA A 2412 airffoil Charactteristic of the t airfoil which w I meentioned beefore was “The NAC CA 2412 is a semi-symmetrical airrfoil (cambered) that is stable and somewhat fast” f

Our reqquirement is i to have an a aircraft which is sttable and predictable p e, that meanns no extreeme stall ch haracteristtics , also I wanted thhat the persson or the man m flyingg this trainer should d be a little more futuure proof , that t meanss after he finishes fi thee learningg phase he can learn simple s aerobatic manneuvers tooo, deng this typee of aerofoill is a add aid for the instructor i w which will be comforrtable for him h to takee out the air craft c out off some veryy tight andd scary situuations.

Let’s reeview the th hings we have h figureed out till now. n

• • • •

A high win A ng style airplane  D Dihedral o of 5* initially (can be changged latter)  A An engine e of .25 cu u in  T Total weig ght of 700 0gms to 1 1kgs 

• A stable and d fitting too applicatioon aerofoil design.(N NACA 24122) Next wee will be sttarting the design of the wing,

   

 

AEROFOIL SECTIONS AND LIFT  COEFFICIENTS      The efficiency of a wing is influenced greatly by its aerofoil section  or profile, which has some degree and type of chamber and some  thickness form. Fuselages and other similar‐shaped components  of a model also produce some lift force, depending again on their   shape and angle of attack. Re‐entry vehicles for space flight have  been designed as "LIFTING BODIES " without wings, but for all  practical purposes in Aero‐modeling, the lift contribution of a  fuselage may be ignored. A poorly designed and constructed  fuselage interferes with the vertical and horizontal stability of an  airplane. For Convenience, aerodynamicists adopt a convenction  which allows all very complex factors of wing trim and shape to be  summed up in one figure, THE COEFFICIENT OF LIFT. This tells how  the model as a whole, or any part taken separately, is working as  a lift producer. A lift coefficient or Cl of 1.3 indicates more lifting  than cl=1.0 or 0.6 cl has no dimentions, since it is an abstract  figure for comparison purpose and calculations.    For level flight, the total lift force generated by a model must be  equal to its weight so it is correct to right   TOTAL LIFT = TOTAL WEIGHT, OR L=W ( ACTION = REACTION)   

This will not apply exactly if the model is descending or climbing.  figure bellow shows, the factors affecting lift force at model size  or area, speed of flight, air mass density and the aerofoil‐plus‐trim  factor, Cl in every case, an increase in one of these factors,greater    

 

  area, more speed, increased density or higher lift coefficient, will  produce a larger lift force.   mathematicaly    L = 1/2(p x V^2 x S x CL)         

Deg: Wing  Now that we have the aerofoil with us we can calculate the other  wing dimensions.    Calculating the Aspect Ratio of a Wing or Flying Surface  The Aspect Ratio is the ratio of wingspan to average wing chord. Average wing chord for a tapered wing is the root chord plus the tip chord divided by two. For a constant chord wing, the average chord is the chord anywhere along the wing . Why Aspect Ratio is Important •

The Aspect Ratio of a wing is an indicator of the aircraft's roll response. All else being equal, high aspect ratio wings (narrow chord to span) will have a slower roll response than a low aspect ratio wing.

•

The Aspect Ratio of a flying surface largely determines the lift to drag ratio of the surface. High aspect ratio wings, such as on sailplanes, are more efficient and have a higher lift to drag ratio.

•

High aspect ratio wings are more easily broken and are less tolerant of poor engineering, poor building and flight outside design parameters.

A wing area of 600 sq in , with an aspect ratio of 5:1 will will have a span of 55 inches and having a 9 inch chord   The aspect ratio of a sailplane lies between 6 and above  The aspect ratio of a good trainer lies between 4:1‐6:1  Aspect ratio of a good sport flyer lies between 4:1‐3:1  Aspect ratio of a 3d and fun fly models lies b/w  less than 3  Calculating the Wing Area for Constant Chord, Tapered and  Delta Wings  In order to determine the wing loading, you must know the wing area. Wing area for model aircraft is always given in square inches(in2) w Why Wing Area is Important •

Taken on its own, wing area is not important. However, the wing area must be calculated to determine wing loading which is very important.

Calculating Wing Area of Multi-Wing Aircraft •

Calculate the wing area for each wing individually. Add these areas together to find the total wing area.  

The area of a simple rectangular, constant chord wing is found by multiplying the width x the height. In aircraft that is: Wing Area = Wing Span x Wing Chord

    To find the area of a tapered wing, use the formula for a Trapezoid. Find the average chord and multiply it times the wing span: Average Chord = ( Root Chord + Tip Chord ) ÷ 2 Wing Area = Wing Span x Average Chord

  Note: It does not matter if a wing sweeps or not. The formula for a tapered wing is used with no regard for the sweep.

         

  The wing loading of an aircraft is the measure of weight carried by each given unit of area. For model aircraft, wing loading is expressed as ounces per square foot (oz./ft2). Experience with different models will make this figure more meaningful to you. Why Wing Loading is Important •

Wing loading is the only indicator of how "heavy" an aircraft is. The actual weight of an aircraft is meaningless. A 50 lb model having as many square feet of wing area is a lightweight. A 6 lb model having 2 square feet of wing is very heavy and will fly like a sledgehammer (or maybe not quite that well).

•

•

The lighter the wing loading, the slower the aircraft can take-off, fly and land. It will also have a better climb. A larger model can have a higher wing loading and fly comparably to a smaller aircraft having a lower wing loading due to differences in the aerodynamics of different size aircraft. For example, let's say we have two aircraft that are absolutely identical except for physical size. The smaller model has a 36" wing span while the larger aircraft has a 108" wing span. The smaller model may have a wing loading of 8 oz./ft2 and the larger aircraft may have a wing loading of 35 oz./ft2. Both of these aircraft may

perform nearly identically at substantially different wing loadings due to the difference in size. Note that these figures are off the top of my head and not meant to be taken literally. It is a good idea to inform the person who is test flying your model as to the wing loading so they have an idea of how long of a take off run it will need to build air speed. This is something that comes with experience because there are no stall warning indicators in model aircraft as there are in full-scale aircraft.

“NOTE: the weight of a model, neglecting small changes caused by fuel consumption, is constant during one flight. The speed at a given trim (angle of attack) will depend entirely on the wing loading

W/S = L/S = 1/2 X P x V^2 x Cl With above formula we can have the required value of cl and then we can select a corresponding airfoil with that value” How to Calculate Wing Loading  In this example, we will use an aircraft weighing 5-1/2 lbs (5 lbs 8 oz.) with 600 square inches of wing area. Calculating the wing loading requires that the wing area be converted to square feet (ft2) and pounds to ounces.

1) Convert the area to square feet. There are 144 (12 x 12) square inches in a square foot. 600 in2 ÷ 144 = 4.17 ft2

2) Convert the total empty weight (ready-to-fly with no fuel) to ounces. There are 16 ounces in a pound. 5.5 lbs x 16 = 88 oz. 3) Divide the weight by the area: 88 oz. ÷ 4.17 ft2 = 21.1 oz./ft2 Using round numbers, this gives the aircraft a wingloading of 21 oz./ft2 or You can perform the entire calculation in one shot using simple substitution: (Weight x 2304) ÷ Wing Area Where weight is in pounds and wing area is in square inches Plugging the numbers from this example into the above formula gives us this: ( 5.5 x 2304 ) ÷ 600 = 21.1 oz./ft2 That means .6kg/ft2 For multi-wing aircraft, divide the overall weight of the aircraft by the total wing area for all wings.

At this point the we have following wing specifications • Wing area : 600 sq in • Chord : 9 in • Span: 55 in   We are not deg a forward swept wing or a some other fancy  styles, cause being a trainer model we should keep in mind that  latter when model is in final stage and some other person wants  to make a model who is a absolute beginner , making a forward  swept wing or tapered wing will be a hectic task, also constant  chord or rectangular wing adds to easeness with which the wing  can be completed, also when a crash occurs , making separate ribs  or airfoils of a tapered or other style wing is a hectic task. So to  avoid all these difficulties we used the rectangle style wing.    Now after deg the wing we can move on to deg a  fuselage which is not a tough task.    CONCLUSION: Above text gives an idea on how to select an airfoil  and how to design a simple wing, laying out the foundation for  more advanced models if we wish to design in near future.    ## for person seeking formulas behind these calculations  Mean chords   A  useful  parameter,  the  standard mean  chord  or  the   geometric mean  chord,  is   denoted by E,  defined by E  =  SG/b or SNIb. It should be stated  whether SG or SN  is used. This definition may also be written as 

 where y is distance measured from the centre‐

line  towards the starboard (right‐hand   to the pilot) tip. This standard mean chord is often abbreviated  to  SMC.   Another mean chord is the aerodynamic mean chord (AMC),  denoted by EA  or E;   and is defined by 

  WHERE The plan‐area of the wing including the continuation  within the fuselage is the gross   wing area, SG. The unqualified term wing area S  is usually  intended to mean this   gross wing area. The plan‐area of the exposed wing, i.e. excluding   the continuation within the fuselage, is the net wing area, SN.    Chords   The two lengths CT and co are the  tip and root chords  respectively; with  the alter‐   native convention, the root chord is the distance between the  intersections with the  

fuselage centre‐line  of  the leading and trailing edges produced.  The ratio ct/c0  is the   taper  ratio A.  Sometimes the  reciprocal of  this, namely co/ct,  is  taken as the  taper   ratio. For most wings CT/C0  < 1.  For square wing the tapering ratio is       The non‐dimensional quantity F/(pV2S) where Fis an aerodynamic  force and S  is an area is  similar to  the  type often developed and  used  in aerody‐namics. It is not, however, used in precisely this  form. In place of pV2 it is conven‐tional for incompressible flow to  use ipVz,  the dynamic pressure of the free‐stream flow. The  actual physical area of the body, such as the planform area of the  wing, or the maximum cross‐sectional area  of  a  fuselage is  usually used  for  S. Thus  aero‐dynamic force coefficient  is usually  defined as follows: 

  The two most important force coefficients are the lift and drag  coefficients, defined by: 

  The impression is sometimes formed that lift and drag coefficients  cannot exceed unity.  This  is  not  true; with modern   developments some wings  can  produce  lift coefficients based on  their plan‐area of  10 or more. Aerodynamic moments  also  can  

be  expressed  in  the  form  of  non‐dimensional coefficients.  Since a moment is the product of a force and a length it follows  that a non‐dimensional  form  for  a  moment  is  Q/pV2Sl,  where   Q  is  any  aerodynamic moment and 1 is a  reference length. Here  again it is conventional to replace pV2 by .5pV2.  In the case of the  pitching moment of a wing the area is  the plan‐area S and the  length  is  the wing  chord C or c'A(c bar)  (see  Section  1.3.1).  Then  the  pitching moment coefficient Cm  is defined by 

  These are the few parameters which are used in more complex  formulae to calculate various characteristic values to design an  aircraft.   But still the fact remains still the same, like most thing in  aerodynamic world, values depends. Depends on what we want  and how we want.  Taking discussion on other wing styles and formulas are beyond  the scope of this report.                     

                                                       

Deg a fuselage.    Fuselage in general does not have any real significance in lifting  and there is no rule to design a fuselage in aero‐modeling, except  in few cases where the shape of fuselage also acts as a lifting in  some models like gee‐bee, 

    In general the fuselage is shaped as stream lined possible to  reduce the overall drag of an airplane. It should be spacious which  can accommodate hands of every size , when setting up and  fitting up the servo, repairing the model in the event of a crash.    Like when we are deg a model for high speed we want that  the drag created by the whole model to be minimal, and also by  the fuse to be minimum hence the structure of the fuselage  should be as close to streamlined symmetrical airfoil as possible   

but the fuselage specification which will be enough for our trainer  airplane will be common to most of the airplanes, the fuse should  be sturdy enough to resist the vibrations produced by the engine  few minor crashes, it should be stream linned in order to reduce  overall drag. It should be having good tensile strength and must  me built light.  A thumb rule for fuselage construction is that longer the fuse  more stable the airplane is , for general sports flyer and trainer  the  fuselage will be 75% of the wingspan of the model and our formula will be 75% of 55” or .75 X 55=41.2”

  Now that we have a fuselage length we have to have other details  of tail plane, ailerons, fin, rudder and elevator.    For keeping things easy I will give out following formulas using  which I will be calculating the above mentioned dimentions,  1.ailerons = 10% of wing area= (10/100)x 600= 60 sq inch.  2. Horizontal Stabilizer to be in a range from 20% to 30% of the area of the wing. I generally use 22 to 23% in my designs. Please note that Deltas and flying wings are different designs and require different considerations So horizontal stabilizer = 22% of wing area= 132 sq in we will assume it to be a span of 3 times the cord or 3C.We’ll round these numbers off and use just a little math, thus our cord will be 132/3=44 and the square rootof 44 equals our cord of 6.633”. The span of the stabilize will be 3C or 6.633” X C =18.99”. Our Stabilizer now has the dimentions of 18.99” X 6.633”. 4. Vertical fin to be in a range of about 1/3 the the area of the horizontal Stab. I generally assume this to be from the top of the horizontal stab to the top of the vertical fin. So, again with just a little math we can arrive at some basic designs so fin area = (1/3) x 132= 44 sq inch

5. 6.

Elevator area= 25% of stab area = .25 x 132= 33 sq inch from above the length of tail plane is 18.99 so is the elevator length now chord of the elevator is 33/18.99= 1.7 inches 

Rudder area=25% of vert stab .25 of 132 “=33 now the length of the rudder is 6” then the chord will be of 5.5  

7. This means a rectangle of 6.63 will be the vertical stabilizer , it will be  ugly looking and aerodynamically less efficient so to over come both  of them we can add a dorsal fin and reduce the size of the stabilizer.  Calculating cg is a tiresome job, it is based on hit and trial method so  but still we can approximate in following way  The following formula determines the "CG" location expressed in percent of the Mean Aerodynamic Chord as measured from the M.A.C.’s leading edge: CG = [0.17 + 0.3 x ((TMA) x (SH) x HTE))] x 100 CG = [0.17 + 0.3 x ((MAC) x (SW Definitions: • • • •

CG: Aft most center of gravity with adequate stability margin. T.M.A.: The Mean Aerodynamic Chord S.H.: The area of the horizonal stabilizer. S.W.: Wing area including the portion of the wing under or over the fuselage. H.T.E.: Horizontal Tail Efficiency. Value ranges from 0.5 for a flat tail located in its normal position in the down wash of the wing to 0.9 for a "T-Tail" at the top of the vertical stabilizer. Before we start banging numbers into the calculator, we need to determine 2 critical factors in the formula. They are the M.A.C. and the T.M.A. We will start with the M.A.C. because we need it to determine the T.M.A. There are two ways I know to find the M.A.C. The first is mathmatical, the second is graphic. The graphic method has the advantage of not only determining the M.A.C., but also indicates its location on the wing. If you have a straight rectangular wing, the M.A.C. is the actual wing chord.

Let’s go over the mathmatical method first. To use the following formula, you need to know only two things: the wing’s chord at the root (Cr) and the tip (Ct). Plug these numbers into the formula below. M.A.C.= 2/3 [Cr + (Ct -((Cr x Ct) M.A.C.= 2/3 [Cr + (Ct -(((Cr + CT)))] Using the example of a wing with a 15" root chord (Cr) and a tip chord (Ct) of 10", the formula cranks out a M.A.C. of 12.7". This is very close to being the average chord of the wing. Now. let’s take a look at a graphic method. If you have either full size or scale drawing of your wing, the hard part is already done as the first step is to make a scale drawing of "your" wing. Figure 1 is a scale computer drawing of the wing in the above example. On your drawing, draw two lines; the first extends forward (perpendicular to the wing span) from the leading edge at the tip and it’s length is equal to the length of the root chord (Cr) on your drawing. Next, draw a line extending back (again perpendicular to the wingspan) from the trailing edge at the root that is as long as the tip chord (Cr) on your drawing.

Actually, you can reverse the direction of these lines and the results will be the same but one must go forward and the other back. From the forward end of the line at the tip, draw a line that connects to the aft end of the line at the root. This line will cut diagonally across the wing. The next step is to draw a line that connects the midpoint of the root chord (Cr) to the midpoint of the tip chord (Ct). The location of the M.A.C. is at the intersection of the lines drawn in these two steps. The length of the M.A.C. is the chord of the wing at that point. Measure your scale or full size drawing. Now, that we know what the M.A.C. is, we can determine the T.M.A. To do this, measure the distance from a point at the root that is 25% of the M.A.C. to the midpoint of the horizonal stab root chord. You can do this either on the model itself, the full size plans or your scale drawing.

At this point, we now know the M.A.C. (12.7") and the T.M.A. (33"). Now, we need to know the areas of the wing and the horizonal stabilizer. For non-rectangular surfaces, the easiest way to calculate the area is to divide the wing into rectangles and triangles. The area of a triangle is equal to 1/2 the length times the width. For example, the wing area is 875 sq." (SW) and the horizontal stab area (SH) is 165 sq.".

HTE (Horizontal Tail Efficiency) For the horizontal tail efficiency, let’s pick a number...we’ll assume that the tail is in the normal location, so we’ll use 0.5 in our formula. Here’s what our formula will look like. Formula : CG = [ 0.17 + (0.30 x (( TMA ) x ( SH ) x HTE ))] x 100 CG = [ 0.17 + (0.30 x (( MAC SW Formula with example values : CG = [ 0.17 + (0.30 x (( 33 ) x ( 165 ) x 0.5 ))] x 100 CG = [ 0.17 + (0.30 x (( 12 ) x ( 875 Formula results : CG = 24.35% of the M.A.C. or 3.09" It is important to that this is measured from the leading edge at the M.A.C., not at the wing root...or event worse, at the wing tip. For those incline to utilize "T" tail designs, let’s look at what happens when you change to that configuration HTE will now be 0.9 instead of 0.5. All the variables appear below. We have changed the desired location of the CG by almost 1" just by making changes to the tail feathers. , this formula FACTOR

Old Value

New Value

Old CG

New CG

H.T.E.

0.5

0.9

24.3% (3.1")

30.2% (3.8")

SH

165. sq."

200.sq. "

24.3% (3.1")

25.9% (3.3")

T.M.A.

33"

25"

24.3% (3.1")

22.6% (2.9")

We will be using the 25% for our cg calculation of wing chord i.e 25% of 9” = 2.25 inch Nose length is 8.82 in tail length is 23.10 Name

span

Wing span Ailerons Tail plane rudder Elevator Fuse nose Tail

55 inch 55 inch 18inch 6 18 8.82inch 23.10inch

chord 9 inch 1 inch 6 inch 5inch 2 inch

3.21  8.02 

                          Final vertical stab design                         

 

9.22 

MODEL CONSTRUCTION AND PLAN LAY  OUT    

Before we can start with the construction of the model , we will be  laying out the plan for our model which will form the most basic  foundation for our model airplane construction. It will be our guide in  most of the building process and should be handled with care.    But before hand we will be having a look on the tools and stuffs  necessary for model airplane building.  1. 2. 3. 4. 5. 6. 7.

Paper pins: to hold delicate parts while ing.  CA: commonly known as fevi quick.  Cello tape: for holding some parts temporarily.  Rubber bands: same as cellotape.  Sand paper: for sanding woods in order to give shape to them  Saw: for cutting woods and other stiff things  Nose pliers: for holding and tightening screws and cutting spoke  wire  8. Wood Screws.  9. Metallic scale and measuring tape  10. Etc  11. Plywoods  12. Drill and drillbitts   13. Screw driver set 

There are basically 4 types of construction techniques available. 

1. 2. 3. 4.

Using BALSA. (Traditional)  Using plastics. (Traditional)  Using fiber glass clothing(new)  Using carbon fiber. 

 

In this construction we will be using Balsa construction method for  making our model, since this is a trainer model the person making this  model should have room for correcting errors, since balsa is a soft  wood and is easy to work upon it, we decided that we will be using  balsa . Beside balsa plastics is also a good option but major  disadvantage of this material is that it is hard to work on and have no  room for errors, also it gives less accurate output.   Use of fiber glass clothing and carbon fiber both require high degree of  precession and craftsmanship , although the output model is rugged  and tough it is not suggested to start airplane construction with this  materials .  One more thing the glues used in this construction and other tools are:  1. 2. 3. 4. 5.

Epoxy  CA  Dendrite  Balsa cement  Balsa knife (tool) 

  Before we can start with construction we should lay out the basic plan  of the model airplane which will serve as a guide in future builds. 

• To start with take white sheet of 30” and draw  a rectangle of  27.5” x 9” to form one half of the wing.   • Then draw another rectangle of 40” x 5”   • The nose length is of 8.82” X 5” inches mark it  • Next take the airfoil diagram we made early and place it over the  fuselage , with the leading edge of the airfoil at the marked place  • Now draw an outline of the airfoil, (The chord of the airfoil will be  9”)  • Next draw another rectangle continuing from the trailing edge of  the airfoil whose length is  23.10”  • Now with free hand connect the gapps and give fuse a nice shape.  • Now erase the left over area. Here is the side view of the fuselage,  with top and side view of the wing. 

Here is a depiction     

 

   

• Take the projections of the side view of the fuselage and draw a  straight line.  • This is the center line where the tapering of the fuselage happens  Here we will be drawing bottom view  • Then draw a straight line 2.5” above and below the line, this is the  max thickness of the fuselage  • At the rear most end of the projection mark .5” above and below  the center line.  • Now draw the projection of the wing on the bottom view of the  fuselage. These will act as basic former section template for the  overall design.    • Now  the lines as shown by the figure.

   

Now we have a side view and a top view of the fuselage, the next thing  we have to find out the number of airfoils sections (Ribs) to be used in  order to give wing a uniform and strong structure, so by approximation  we will be requiring a total of 22 ribs at 2.5” distance to each other for  the whole wing meaning 11 ribs at one side of the wing.  We have enough info right now to start deg our fuselage, I will be  showing you the fusion of two styles, the sheet construction and truss  construction style,       Cut a sheet of 3mm balsa wood as shown, from f1 to f2   Lightly sand the sheet to remove fuzz. If doublers (a half copy of the fuselage side stick together with the fuselage inside to make fuselage stronger ) need to be added before the sides are built go ahead and add them. the fuselage sides using double-stick Scotch tape. Sand the sides to an exact match. Take your time aligning the sides so that you don't remove any more material than necessary. Note that the right side may be shorter than the left side due to right thrust. If this is the case with your model then take that into when sanding. As always, to build a left and a right side. I find that placing them next to each other as a mirror image helps prevent building two of the same side.

    There is normally a longeron that runs the full length of the fuselage from nose to tail. There is also one that will start behind the wing saddle. Glue these longerons in place while clamping the assemblies against a good straightedge. In this image you can see two strong magnets at the rear of the wing saddle that are applying clamping pressure to the lower longeron. The magnets are set up to attract to each other. I jumped the gun and glued the small plywood gussets you can see in this photo. I chiseled them back off because they would have impeded construction later.

Place waxed paper over the plan to prevent the plan from becoming a permanent part of the structure. Align straightedges over the plan outlines to guarantee that the outlines of the structure are straight. I set up the fuselage so that the outside is down. That ensures that the longerons, uprights and diagonals will be flush. If either the top or bottom longeron is curved then you will have to bend it to match the plan and pin it in place

“A truss based model is fairly good in strength and very light in weight” This model uses both sheet and truss making concept. 

The most difficult part of building a truss is cutting proper angles on the ends of the braces while ending up at the correct length. In fact this is one aspect of construction that I found extremely frustrating until I found a nearly foolproof method. Attempting to cut angles on sticks using a razor, hobby knife or razor saw will often lead to unsatisfactory results. Attempting to hold the part in hand while sanding isn't any better. The diagonal bracing is even more difficult because it has two double-bevels that not only must be the correct angle, but that angle must be at the correct angle to the centerline of the brace.

Making the Braces  Note: Always make the longest braces first and work your way to the shortest. There are two very good reasons for this: 1. If you make the short braces first you may end up with a bunch of short scraps that aren't long enough for the longer braces. 2. If you have to reject a brace because it ended up too short, you can use it for a shorter brace. I skipped another step. You may think that you see uprights in this photo but you actually don't. You're either imagining things or maybe you can see into the future. What you should see is a plywood sanding template. Cut a piece of scrap plywood that aligns perfectly on all sides. Take measurements from the plan to ensure the angles are correct. Take care making the template because it will determine how well the ts of the uprights and diagonal bracing will fit.

  Make a sanding block having faces that are all square to each other. I used 3/4" square pine.Use spray glue or dendrite to attach medium (220) sandpaper to one side and fine (400) paper to the other.  Note: This sanding block will come in handy for all kinds of purposes, so don't think of it as a limited use item.Place the upright brace against the side of the template and gently sand the one end.Balsa sands away at a much faster rate than plywood so the template should easily last through the project. If you happen to sand too much of the template away, correct it before sanding any more braces.

Fit the sanded end of the upright to ensure the angle is correct. Lightly mark the other end with asingle-edge razor blade. Use the template to sand the end of the brace to fit.Be conservative and leave the brace over-length at first. Sand a little away at a

time. Fit often.The bracing should be a good fit — not too snug and definitely not loose.

    Here you can see several upright braces glued into place.

The template you made will make short work of this task and for a change, the diagonal braces will actually fit properly.Cut the piece over-length as shown. Lay the brace over the fuselage side

aligning it with the plan.I normally ignore the plan and instead align the brace so that it centers on the corners made by the

upright and longeron. Carefully align the razor over the longeron and existing upright and use it to lightly mark the bevels.You do not have to mark directly above the t. In fact, it's best to mark slightly oversize.It is important that the angle of the cut lines exactly match the corner in relation to the centerline of the diagonal piece. Read that a few times until it makes sense Place the diagonal brace over the correct corner of the template ensuring that the marked lines are aligned properly with the template and that the end of the brace is centered over the template corner..

Sand the end to shape. Although I didn't do it, a piece of sandpaper spray glued to the template would have helped prevent the diagonals from sliding around while I was sanding.

At this point only one end is sanded to shape but look at both ends. The opposite end should be too long but should center over the existing t.If the other end isn't centered properly then note which way the diagonal must rotate. Take the diagonal back to the template to correct it.When you are satisfied with the first end, mark it with pencil so that you know which side is up and which end is which. It's easy to flip the part around when adding glue or whatever. Once glue is on the ends, it is more difficult to tell which end is which.

Repeat the above steps for the other end.Note that if the fuselage has straight outlines, but also tapers, then the angle on the ends will always be the same on braces that are aligned in the same direction.However, the diagonal braces are not parallel to each other and therefore the angle on the end will not be at the same angle to the centerline of the brace. I know that sounds confusing, but once you start making these pieces you'll understand what I mean. My point is that you can't stack up all the diagonals and cut them at once. They won't fit if you do that.

If the diagonal is still too long then you can make adjustments while sanding away the excess. Always use the template. If the length of the diagonal is correct, but one end or the other doesn't fit properly then there's not much you can do. Your choices are to live with it or try again with a new part. This was my first time using a template and I only had to discard two parts. I have a higher reject ratio using a disk sander and a much higher reject ratio making braces when cutting and sanding by hand.

This is how the diagonal should fit. The diagonal slips in place easily but is not too loose and not too snug. Do not force a tight brace into position. It will create undesirable internal stresses and may weaken the longeron by crushing the wood fibers. It will also be forcing the glue t apart of the upright braces.

Double-glue the ends of the braces using carpenter's glue. Put some glue on each end and set the part aside for a minute. Put some glue in the existing t as well.

After giving the glue some time to soak into the end grain, add a little more glue and put the part in place. Ensure everything is flat on the board while the glue dries. Make a scooper from a toothpick or bamboo skewer by cutting a long bevel on the end. Use it to scoop up all the glue that oozes out. Your work will look especially neat now that you have made perfect fitting ts using nicely sanded pieces and there is no visible glue.

The aft end of the fuselage is usually filled with balsa wood rather than diagonal pieces. The fill reinforces the tail and it allows you to cut pushrod exits.If you didn't have sheet wood surrounding the exits, you would have to cut holes in uned covering. The covering would eventually begin to tear away.You can use thinner wood here if you arrange the grain vertically to act as a web. A lot of planes turn out tail heavy. Do everything you can to make the tail strong while using as little material as possible.

Most of the hard work is done. When this assembly is dry, remove it from the board and build the other side.It is best if you can build the second side directly over the first. Put a piece of wax paper between the two sides and line the parts of the second side up carefully.You can pin directly through both sides into your building surface or set up straightedges that are higher so that they enclose the outlines of both sides.Be sure to place the outsides of  the fuselage sides together!If you put an inside against an outside you will build two left or two right sides which will not make you happy when you realize you have to throw a lot of work away and build a new side.

Block sand the inside of the fuselage sides now. Keep sanding until all ts are flush. Go ahead and finish sand because this is your last opportunity to do it. This step is very important! Remove the sanding dust and then apply strategically placed double-stick tape to one fuselage side.Carefully align the other side directly over the first. Check to ensure the sides are aligned as well as they can be — particularly the wing saddles, firewall and tail. Pull the fuselage sides apart and stick them back together until they're right.Using a long sanding block, sand the sides to an exact match to include the wing saddles if needed.Check your work carefully because this step will save you from all kinds of alignment problems later.

Take measurements from the plans and use landmarks in the construction to draw the locations of all the formers and other items inside one fuselage side while the sides are still taped together.Use a good square to transfer the lines to the outside edge. Use these lines to locate and draw former locations inside the other fuselage side. If the firewall has right thrust be sure to locate the lines properly on each fuselage side because they will be in different locations.

Separate the two sides and then block sand the outside to remove excess glue and to bring everything flush.The outsides can be rough sanded because they will need additional sanding as you progress with building the fuselage.

Many designs and kits leave out gussets. However, I strongly urge you to use them. They weigh practically nothing but greatly increase the strength of the brace ts.If you choose not to use gussets then the only thing preventing the braces from popping loose in a hard jolt is tension from the covering.Note that gussets are glued to the inside of the fuselage sides. The notch will capture the cross-braces.I make gussets from 1/64" plywood which can be easily cut with scissors.Be sure to clean glue ooze from around the gusset and especially from inside the notch where the cross-braces go. Blobs of glue will interfere with the fit of cross-braces installed later.

Clamp the gussets while the glue dries to ensure the strongest possible glue t.

When the glue has dried place both sides on the board as a mirror image. Take care aligning them.I put a stop at the front and the tail post to keep the sides from moving.

Glue the gussets on the second side aligning them with the gussets on the first side. This will ensure that the cross-braces are exactly perpendicular to the fuselage centerline in top view.

Flip the sides around and repeat the above steps. Do not leave the sides together while the glue dries. The sides will end up glued together by the glue that oozed out.Don't forget to clamp the gussets while they dry.

This ends up with preparation of fuselage sides. Now for making the whole fuselage, use the plans top or bottom view and cut braces of different length and glue them perpendicular to the sides of the fuselage

“above model is design of nitin you can see the complete former bracing on the model along with the plan prepared” 

  “Another view of a example plan “   

If you have followed all steps correctly the fuselage is ready.                   

Wing construction    Construction of wing is similar to as that of construction of a truss  fuselage,   A wing comprises of L.E (leading edge), ribs, trailing edge,spars and  ailerons, in this section we will be making a wing and then using hinges  we will be attaching the ailerons to the wings.    We Know that the estimated cg of our model which we calculated  earlier was at 25‐30% of the chord, suppose 25% is the cg location then  add spars to the wings at 25% of the main chord, that means for a 9”  chord spar will be located at 2.25  inch    

  Technicaly saying spar is a stick which runs span wise in a wing to  provide strength and hold the wind structures and ribs,  Rib is nothing but the airfoil with gaps cut such that spar, leading edge  and trailing edge can fit them self in slots so that they can form the  skeleton of the wing.  Now you take the rib which we ploted and cut a 8mm from the leading  edge of that airfoil next cut .5 inch from the trailing edge of the aerofoil  , cut two square of 6mm on top and bottom of the airfoil at 2.5 inch  from the leading edge. 

 

You will get something similar to this  Cut 22 ribs while cutting make sure to sand the ribs to exact size with  no roughness and oddness existing , 11 for one side and 11 for other ,  now that you have ribs cut 4 spar of 6mmx6mmx27.5” ,  2 for each side. Place a spar on the table and mark lines at a distance of  2.5”, after that carefully place the rib over it, such that the bottom spar  slot gets fixed with the spar, after making sure the the rib is placed  straight quickly apply CA, similarly fix other ribs to the spar, after this  carefully place the top spar over the top spar slot, and apply CA, repeat  this with the other wing too, now that your two wing half’s is ready , its  time to make wing brace or the dihedral brace.  Now cut the leading edge (spar of 8mmx8mmx27.5”) and trailing  edge(sheeting of 4mm x .5”x.27.5”), two in number and glue them in  there places and sand them to match the airfoil pattern.  Cut two plywood of length of 5” and height of the rib at the point  where the two spar’s are located.  We agreed with the dihedral angle of 5* so , cut the dihedral brace such  that one of the tips of the dihedral brace makes 5* with the table, now  place the dihedral brace in one wing by cutting just behind the location  of the spar, put the dihedral brace in other wing but this time at just  opposite side. Cut’s are made in both wing such that the dihedral  braces are adjusted between the wing and there is no gap between the  two wing halves. Now apply epoxy to every  in the wing to be  double sure. 

This is the final step , after the epoxy has cured, cover the first tree ribs  of the skeleton with 2mm or 1mm balsa and sand it at leading edge and  trailing edge. We are done now.  After this use dendrite and monokote to cover the wing, 1st cover the  bottom and then cover the top, you will notice many wrinkle’s and  spots on the wing , which looks ugly and doesn’t  gives good flow of air,  so to make it tight strong and more aerodynamically usable use Iron  and iron the wing, heat gun can also be used, as the plastic will shrink  the wing will become stronger and  more efficient.  Now that the wing is finished we will add ailerons to the wing’s ,  previously we calculated the area for aileron to be 60sq in making it 55”  wide and 1”. Use a 4mm light weight balsa sheet for this and sand it to  a perfect triange in shape, after that use pins and ca to place hinge in  place . the figure illustratrates it 

  This is what a finished wing will look like 

   

  An example of wing construction.  Now that we have constructed the wing , we should jump back to  fuselage , use the same covering method to cover the fuselage, but  before we will be installing a servo tray inside the fuselage and will be  installing firewall and control linkages before we can finish up with  fuselage.  Take two spoke wire and insert it in the fuselage make sure the  threaded part of the spoke is outside and the non‐threaded part is  inside and is visible and accessible from the place where the wing hold  down will be located i.e from the place where wing is located. Now add  the firewall (a type of very hard former used for making the foundation  for engine mount) (use 4mm plywood) at the front of the airplane and 

use epoxy to fix it, after the epoxy has dried and the firewall is in place ,  drill holes according to the engine mount and drill holes in the mount  according to the engine. With that, drill holes in the middle of the  firewall for the fule tubings coming from the fule tank located just  behind the firewall.  When this is done, purchase a .25 size nose leg and attach it to the  engine mount and add collect to secure it. When this is done add a  nose arm and add it to the nose leg, now insert a spoke wire connecting  the nose arm into the fuselage such that it does not block the fuel tank  placement schem.  When done add a plywood of 4mm with the width of the former on the  lower most part of the wing bay of the fuselage and use epoxy to glue  it. Buy a under carriage and screw it on the plywood such that the  wheel line of the undercarriage lies just below the cg of the  airplane.Now cover whole body of the airplane with monocote and do  same as done with the wing i.e iron it This finishes with the fuselage.  Now we will be making tail plane and vertical stabilizers, as we have  seen and calculated the area 

s   

 

  Elevator parameters are:  Chord ‐1.7” or 2” running span wise of the tail plane  Rudder parameters are  tip‐ 2"  root‐ 5.18”  area= 32 sq inches  after making elevator and rudder and the main plane hinge elevator  with the tail plane and hinge rudder with the fin. After that glue the tail  plane and fin arrangement in the fuselage such that the tailplane is  parallel to ground and the fin and tail plan are perfectly perpendicular  to each other , Now we have a fuselage ready and wing ready.  We are all set for flying in just few more steps.         

 

    Finished airplane.           

         

      SETUP: servo and onboard electronics    The model we designed has four controls, to successfully fly this model we have  to use a 4channel (transmitter and receiver with 4 servos) , each channel for each  control. like channel one for ailerons, two for throttle, 3 for elevator, 4 for rudder.  Add control horns to the control surfaces , and attach them to the spokes next ,  add two balsa sticks in the fuselage just below the wing compartment such that  the separation between the sticks is just large enough to accommodate 3 servo in  it, next attach the servo horn with the spoke (called push rods)  One servo with elevator push rod, one servo with throttle push rod , and one  servo for both rudder and nose leg.  After this is done , connect each servo to their respective channel, the fourth  servo goes on the wing top , drill a hole on the top of the wing at the center of the  wing such that it can accommodate a balsa knife and cut the top layer balsa to  accommodate the servo , make a hole in the bottom of the wing just bellow the  servo located in the wing and guide the servo wire through that hole and connect  it to its channel. We are all set for flying once the engine is mounted.  Before we mount the engine we have to check wethere there is any bend in the  fuselage  or not, if there is a bent and it is significant enough then we have to  change the engine thrust line for it , but for now we assume the fuse is just right ,  then mount the engine and connect the pipe from the fueltank to its fuel feed  and another pipe from fuel tank to pressure feed.  

“ A typical fuel tank of an airplane contains two pipes on for sucking fuel and  pouring fuel and the other for pressure feed , which enable the constant flow of  fuel in the engine in loops and rolls”  Now take out a 9x6 propeller  and a spinner, and tighten all of these to the engine  such that , the dead center of the engine makes 7:35 when seen from the front of  the engine with a propeller screwed.    Before you can fly, you should have these tools with you all the time  1. Plier set  2. Screwdriver set  3. 4‐way‐wrench  4. Celotape and ca  5. Electric starter or a chicken stick  6. Hot shot or glow igniter if using a glow engine  7. Fuel pump  8. 12v battery for the starter  9. Spare propellers and spare spinners  10.30 min epoxy if available   11.And lots of patience  After accuiring these stuffs , there are few precautions people should take while  flying.  1. Never fly alone.  2. If you are in‐experienced or novice or a beginner NEVER FLY with without a  trainer or experienced flyer.  3. Never fly into the crowd as model hits 80‐70 mph which can be fatal if it  hits someone.  4. Never fly in closed area.  5. Never fly near high power line.   Radio installation 

•

Always check your radio installation against the plans before building anything. If you need to plug precut holes or cut new holes, it is a lot easier to do before the component is built. Make sure you write notes and good measurements on the plans so you what you were doing later.

•

Most R/C models have a removable wing that covers the radio compartment. The fuselage has a "U" shape through this compartment and is inherently weaker and more flexible than the rest of the fuselage. This arrangement has been proven to work satisfactorily. However there is no reason not to improve it.

  cut a former that splits the radio compartment into two parts. The aft section is the servo compartment and the forward section is thereceiver/battery compartment. Measure the length of the battery and receiver. Add 1" to the longer measurement and that is how far back from the LE the new former should go. You want enough room to surround the receiver and battery pack with foam without it being able to shift around. Mount the switch and the charge jack in the servo compartment so the wires coming from them do not have the receiver or battery pushed up against them. Be sure to cut a 1/2" or larger hole in the former to the servo leads to the receiver and also drill a hole for the throttlepushrod housing. In the above image, the charge jack is mounted in the wrong compartment due to poor planning on my part. It is in the way and I have to be careful not to stress the wires too much when

working around it. A wire can break causing intermittent and result in bad things happening to my model. Unfortunately in this case there wasn't a lot of room in the servo compartment to mount the jack. In retrospect, the former could have been moved slightly forward to make the servo compartment larger. •

Please use foam rubber to wrap your receiver in. I have seen several planes at the field that were simply stuck inside the airframe using sticky-back Velcro. When you are holding your plane and you can feel the vibration coursing through it, the receiver is feeling the same thing and it is not good for it at all. The electronics we put in our models are delicate and should be treated as such. Some people seem to think these things were designed to withstand anything, but they are wrong.

•

I used to install the radio after the basic structure was complete. What usually ended up happening was I had a lot of binding to take care of and it was hard to get everything lined up properly. It also took a lot of time for a less than satisfactory result.

Now I do the servo installation before I even begin framing up the fuselage. It seems tedious, but the actual fact is I save a lot of time by doing it in the beginning. There are a couple measurements you need to have. First, I put the grommets and eyelets in the servos and then I measure from the bottom of the grommet to the center of servo arm (servo in side view). This tells me where the servo rails need to be from the pushrods. Now it is an easy task to glue rails into the fuselage sides before I them and also cut the pushrod exits. The only other measurement I need is how from the tail the pushrod exit should be. Just draw a line on the plan from where the servo will be mounted (you will need to know what servo arm

you are going to use) to the control horn. The hole goes where the line intersects the fuselage side. When installing servos, one of the biggest mistakes I see made is to crank down the screws until they squeeze the life out of the rubber grommets. Those grommets are there to absorb vibration which they will not do if they are too tight. The idea here is to tighten the screws only to the point where the grommets start to bulge and then stop. After all the screws are in, try to wiggle the servo. If it is solid, then the job is done.   FINAL check.  Before you takeoff you should check your tx/rx for glitches and interferences, if it  exists double check and make sure the wires inside the fuselage is not touching  any metallic parts, check for cuts on the receiver wire and check whether the  antenna of the receiver if fully extended or not.   If there is no glitch you can proceed with your flying.         

Extras : formula and concepts  “These topics should be utilized by people having keen interest in field of aviation and thinks beyond  Aero‐modeling and at large scale , for Aero‐modeling the report preceding above this topic is more than  sufficient” 

Calculating Theoretical Speed  Theoretical speed means that the propeller is 100% efficient and that there is no  loss due to aerodynamic drag, etc.  A perfect airplane flying in a perfect world.   That's not going to happen here on earth, but this still gives you a starting point. 

For this example we'll use an engine turning a 7" pitch propeller at 15,000 RPM.  Convert Revolutions Per Minute (RPM) to Revolutions Per Hour (RPH):  RPM x 60 = RPH  15,000 x 60 = 900,000 RPH  Find Inches Per Hour assuming 100% efficiency:  RPH x Propeller Pitch = Inches per Hour  900,000 x 7 = 6300000 inches per hour  Convert to Miles Per Hour (12" x 5280' = inches in a mile):  6300000 ÷  (12 x 5280) = 99.4 MPH  The bottom line (assuming 100% propeller efficiency and zero airframe drag):  Speed = ( RPM x Pitch ) ÷ 1056  In reality the average sport model with this combination might do 75‐80 MPH on  a good day.    Calculating Propeller Efficiency    Going a little farther, we can actually set up a speed trial to determine how fast  an aircraft is going and then determine propeller efficiency using those numbers  (time over distance).  So let's say you time your aircraft on a 100 yard (300 feet) course (upwind and  downwind to make it even).  The average time is 2.7 seconds.  Convert the distance covered to miles by dividing distance covered in feet by  number of feet in a mile.  There are 5,280 feet in a mile. 

300 ÷ 5280 = .0568 miles  Convert elapsed time to hours by dividing time in seconds by seconds in an hour.   There are 3600 seconds in an hour.  2.7 ÷ 3600 = .00075 hours  Find Miles Per Hour:  .0568 ÷ .00075 = 75.7 mph  If our timer was accurate and the distance is accurate then that speed will be  accurate.  An easier way is to use a radar gun, but then you don't get to do all this  fun math.  Going back to the previous example, let's determine the overall loss of efficiency  and then, for convenience, blame it all on the propeller.  Divide actual speed by the theoretical speed using a 100% efficient propeller and  an aircraft having zero drag:  75.7 ÷ 99.4 = 76.16% efficiency  Unless we have an onboard tachometer, we do not really know what the RPM of  the engine is.  Also, the lack of efficiency could very easily be attributed to the  airframe design ‐ not necessarily the fault of the propeller.  Still, it is something to  play around with if you are so inclined.       

Working out the lift coefficient    

TO calculate the lift coefficient of a model in a given trim condition , it is necessary to know the  speed at which it is flying, its wing area, and flying weight. The speed is easy to determine if the  model can be flown several times over a mearsured distance and timed with a stop watch. 

  The stamdard lift formula may be re‐arranged to give cl in  of model weight, if it scales  1kg. This indiacates a mass of 1 kg. it needs a lift force of 1x 9.81 newtons to  it 

  NOTES  The aerodynamic center of an airfoil is usually close to 25% of the chord behind the leading  edge of the airfoil. When making tests on a model airfoil, such as in a wind‐tunnel, if the force  sensor is not aligned with the quarter‐chord of the airfoil, but offset by a distance x, the  pitching moment about the quarter‐chord point, Mc / 4 is given by    where the indicated values of D and L are the drag and lift on the model, as measured by the  force sensor.        ___________  horizontal stabilizer:    As for EQUILIBRIUM, an aeroplane must be in balance longitudinally in order to fly. This means  the This means that the net effect of all the forces acting on the aeroplane produces no overall  pitching moment about the centre of gravity. Without a tailplane there would be only one  combination of speed and center of gravity position for which this requirement was met. The 

tailplane provides a balancing force to maintain equilibrium for different speeds and center of  gravity positions. Because the tailplane is located some distance from the center of gravity,  even the small amount of lift it produces can generate a large pitching moment at the centre of  gravity.  The issue of stability:  An aeroplane with a wing only is normally unstable in pitch (longitudinal stability). This means  that any disturbance (such as a gust) which raises the nose produces a nose‐up pitching  moment which tends to raise the nose further. With the same disturbance, the presence of a  tailplane produces a restoring nose‐down pitching moment which counteracts the natural  instability of the wing and makes the aircraft longitudinally stable.  _______________    pitching moment coefficient is important in the study of the longitudinal static stability of  aircraft  The pitching moment coefficient Cm is defined as follows     where M is the pitching moment, q is the dynamic pressure, S is the planform area, and c is the  length of the chord of the airfoil. Cm is a dimensionless coefficient so consistent units must be  used for M, q, S and c.  Pitching moment coefficient is fundamental to the definition of aerodynamic center of an  airfoil. The aerodynamic center is defined to be the point on the chord line of the airfoil at  which the pitching moment coefficient does not vary with angle of attack, or at least does not  vary significantly over the operating range of angle of attack of the airfoil.  In the case of a symmetric airfoil, the lift force acts through one point for all angles of attack,  and the center of pressure does not move as it does in a cambered airfoil. Consequently  thepitching moment coefficient for a symmetric airfoil is zero.  Pitching moment is, by convention, considered to be positive when it acts to pitch the airfoil in  the nose‐up direction. Conventional cambered airfoils ed at the aerodynamic center  pitch nose‐down so the pitching moment coefficient of these airfoils is negative