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I have always enjoyed designing and building my own model airplanes. The process to design a conventional airplane is not that difficult. Aircraft design today is still much like it was in the days of Orville and Wilbur Wright. Sure materials and powerplants have changed but aerodynamics are the same as they have been since the dawn of time. On this page, I will take you through some design criteria. I will show you how to make sure the wings are big enough and not too big and the same with the tail surfaces of your airplane. I will stick with a conventional, tractor type aircraft and not get into canard winged aircraft or other designs and I will try to keep everything in laymen's terms.
There are two main things you need to keep in mind when designing your own plane, wing loading and power loading.
Wing loading - the loaded weight of the airplane divided by the area of the wing. In other words, how much weight does the "ready to fly" airplane put on each square inch, square centimeter or square foot (any unit of measure can be used here) of the wing. One of the thngs you want to strive for is the lowest wing loading you can achieve.
Some people marvel that a plane as large as a jumbo jet can fly. The same aerodynamics that allow a small rubber band powered airplane to fly are the same aerodynamics that keep a jumbo jet in the air.
Power loading - the ratio of the power of the engine in an airplane to its loaded weight. If you have a 1,000 pound airplane powered by a 100 horsepower engine, the power loading is 10:1.
Many modern 3D model aircraft can defy gravity and hover, much like a helicopter. This is because their power is greater than the weight of the aircraft. I don't know of any full sized aircraft that can perform this maneuver yet but as building materials get lighter and lighter, the day will probably come that a full sized aircraft can do all the same maneuvers a model can.
A Harrier can take off and land vertically because the amount of thrust coming out of the jet nozzles is as great or greater than the weight of an aircraft.
Power vs. Drag
Pretty much anything can fly, given enough power. In designing an airplane we want to use a minimum amount of power for our goals. The larger engine requires more fuel and more expense. In your design, I encourage you to keep things aerodynamic and light. If you have a model airplane with a 5 horsepower engine and the plane will fly 80 miles per hour, you can't put a 10 horsepower engine in the same plane and expect to double your speed. I just can't stress the importance of a clean, aerodynamic airplane.
Square fuselages are more aerodynamically dirty than round ones. A radial engine will create more drag than a plane with a streamlined cowl. Surprisingly, a wider fuselage can cause less drag than a very thin one. There is thing called the "fineness ratio". This ratio shows the perfect length to width of a surface for the best aerodynamics. The best ratio is about 3 to 1. If you look at the drop tanks on a P-51 Mustang in World War II, that is about the perfect aerodynamic shape for a fuselge. Ideally, the fuselage should be three units long and one unit wide. So don't worry about making a fuselage that is barely wide enough to hold your radio gear!
The Lanceair IV is an incredible airplane and one of very few airplanes that can fly over five times it's stall speed. The reason it can is because it has a very "clean" aerodynamic shape and a large engine but the shape of the plane is the biggest factor!
Determining What Your Deisgn Will Look Like
This is the first big question you have to ask yourself and if you are reading this, you probably already have a design in your head. It is just a matter of getting it out of your head and turned into a flying machine.
Since the inception of flying machines, they have actually changed very little. Powerplants have changed, the size of airplanes have changed but most airplanes still have ailerons, a rudder, an elevator, and a powerplant.
When you know what you want your plane to look like, take a look at other planes that may look similar. Determine what size of an airplane you want and what size and kind of engine you want to use to power your plane. What kind of building materials do you want to use to build your plane?
A scale plane is easy to design. All you have to do is scale down the plane from the real one or scale it up from drawings. A plane that is not scale will take a little more work but by following some rules of thumb can be easy.
These are the basic types of radio controlled airplanes today:
Trainers - Usually are lightly built with low wing loading. Typically have high wing with flat bottom airfoil.
Sport - Usually have medium wing loading, smaller wing area than a trainer and typically use semi-symmetrical or fully symmetrical airfoils.
Pattern - Have light to medium wing loading and long tail moments, making aerobatic meneuvers more smooth. Almost always have a fully symmetrical airfoil so they can perform inverted aerobatics as easly as those that are perforned right side up.
Pylon - Typically have smaller wings with higher wing loadings. Tend to have very low drag to increase speed.