Generate Your Own Model Airplane Design
Initial steps preparing parameters for an original model airplane design
Creating a personal model airplane design is a challenging and rewarding aspect of the RC airplane hobby. Drafting a model aircraft plan is really not difficult, and employs a series of steps and skills that can be easily acquired. Following are some initial thoughts that anyone planning a model airplane design needs to consider. These are by no means final statements, but rather starting points from which you can evolve and mature your particular model airplane design and RC plan.
Determine plane type
The first step in laying out a model airplane design is to determine the aerodynamic considerations and what type of airplane you wish to build. Will it be a trainer, a sport flyer or some sort of scale project? Will your subject be a high, mid or low wing aircraft? Airfoil selection is important, with the Clark Y being a great first choice.
Once you know what type of plane you wish to design, the next step is figuring out the size of the model. I usually start with determining the wingspan of the model airplane design, as the wingspan will be used as the basis for further model dimensions.
The Finch micro RC free model airplane plan can be easily downloaded and viewed. The Finch is a clear and easy to read example of a model airplane design.
Prototype Yard Ace wingspan was too short
The wingspan can also give you an initial idea of the size of the motor for your finished project. For gas powered model airplane designs, the size of the engine is important, as you will have to design and build in the necessary fuselage support configuration. For electric powered models, there are lesser requirements for the motor structure due to the smoother operation of electric power as compared to a gas engine.
Second Yard Ace with longer wingspan
Once you have determined the model airplane wingspan, there are several rules of thumb for fuselage and tail surface model airplane design dimensions. You next need to determine the wing chord, or distance between the wing leading and trailing edge. For normal sport flying aircraft, the aspect ratio (wingspan squared divided by the wing area) should be no less than 5:1. The aspect ratio for a constant chord wing is simply the wingspan divided by the chord. I always subscribe to the theory of keeping things simple when starting out on new projects of this nature. Thus for your first model aircraft design project, use a constant chord wing. A constant chord wing, using a single rib size, is easier to design and build as compared to a tapered wing.
Clark Y airfoil
Select the proper airfoil
You will have to choose an airfoil for your model airplane design. There are a wide variety of airfoils you can select from, and they vary with the type of aircraft being contemplated. An aerobatic model would use a symmetrical airfoil shape, while an antique airplane plan would use a higher camber rib shape to account for the slow flight speeds characteristic of these aircraft. My airfoil preference is a standard Clark Y, designed in the 1930s for full scale aircraft. The Clark Y works well with everyday sport RC model airplanes, and I have used the Clark Y on all my RC aircraft design plans.
Rules of thumb for determining the parameters for a model airplane
You will next determine the length of the fuselage. A good rule of thumb is for the fuselage length to be around 75% of the wingspan. The nose length (distance from wing leading edge to the prop) should be around 20% of the fuselage length. The distance from the wing trailing edge to the leading edge of the horizontal stabilizer should be around 40% of the fuselage length. The horizontal tail surface area should be around 25-30% of the wing area, and the vertical tail around 35% of the stabilizer area.
TLAR = That Looks About Right
Follow how parameters for the Robin are figured out
My design of the Robin and its CAD plan is a great review from start to finish of an RC model airplane design. Note that all these model airplane design planning parameters are just starting points for your final model airplane plan. I am a firm believer in the benefits of the TLAR (That Looks About Right) approach to model aircraft design and layout. If in doubt as to your initial aircraft dimensions, consider adding a bit to the nose or tail length, or increasing the wing span. You can quickly get into trouble on your first flight if the tail or wing surfaces are too small. However, you will almost always be alright if these surface areas are a bit too large or the moments too long. For example, my first version of the Yard Ace had a wing span that was too short. The model flew much faster than anticipated to maintain flight. On the updated version of the Yard Ace, I simply lengthened the wing span - very easy to do when drawing a model plan with TurboCAD - and the airplane flew much better with the increase in wing area.
Gliders have high aspect ratio wings, over 7:1
The center of gravity should be located a third of the wing chord back from the wing’s leading edge. I always add a bit of positive wing incidence to my model airplane designs.
Keep your design light
As a final note, make every effort to design your model airplane as light as possible. One of the huge advantages of electric model airplane flight is the ability to keep motor mount and overall airframe structure to an absolute minimum, due to the lack of vibration as compared with a conventional gas engine. Model aircraft that are built at a minimum weight always fly better than the same model airplane design completed with a heavier weight.