A lot of RC airplane enthusiasts have a dream of seeing the full size replica of their favorite plane flying. However, it isn’t easy to copy the precise dimensions of the full size version and make it into what you want. Even if you know how to use CAD software to draw and design the airplane, in order to make it stable, you have to also know the aerodynamic principles. That is always the first step for flying any model airplane. Before ever attempting to build and fly your very own model, you need to have your skill set up to at least intermediate. You will need to then chose a trainer full scale type of airplane.
The trainer airplane has built in stability in the design. The wings are rectangular and have a constant chord. The wings are also located above the fuselage, helping it to have pendulum stability. Generally, the landing gear is also a tricycle type. This does not mean that the stability will be the same when the airplane is scaled down, though. Those sort of airplanes do not fly well at all when you copy the same dimensions on your scaled down model. Like stated before, the aerodynamic designed has to be considered. This is known at the “Scale Effect” on the plane. You are not able to scale down the viscosity of the air of the air molecules. This will create a different behavior. Many factors, such as the wing are and location, the location of the horizontal and vertical stabilizer, and the design of the airfoil all play a huge role on the stability of the airplane.
It is essential to completely redesign the airplane. In order to achieve stability on the miniature dimensions, you have to redesign it based on the Reynolds number as well as the lift and drag coefficients. This is the reason that many of the kits have specifications that are for 30% to 40%. This number is the percentage copied from the original, full sized airplane. Many times, things like the stabilizer was changed on the model. Other times, it is the wing are or the airfoil type to help with the stability. The larger the model, the easier it is to copy the behavior and the exact dimensions of the full size airplane. Because of this, 1/4 scale model airplanes tend to be quite popular with people that are serious about their RC airplane models. Unfortunately, because of the cost and set up and the inherent dangers of the larger plane, only those with a lot of money can have these. They require a large field to fly in and a lot of fuel. They are only for the most serious RC airplane collectors.