Aircraft Prototype Design Methods for RC Flight
Prototypes are a crucial step in RC model airplane design
Creating an original RC model airplane design is easy if you follow a few basic steps. A foundation requirement for flying an original design is the ability to construct a model airplane from a kit or set of plans. With the proliferation of almost and ready to fly RC models, building skills cannot be assumed for all modelers. But they can certainly be learned. If you can build a model from a kit or set of plans, you can prepare an original aircraft prototype design.
View the evolution of the Robin's prototype RC model airplane design
What is the importance of an aircraft prototype design? In this day and age of the internet and advanced Computer Aided Design programs, cannot a well flying RC model airplane simply be conceived, designed and then flown in its final form?
Prototype design and full scale aircraft
Interestingly enough, the answer to the above question is “no”. For example, the Boeing Company, when designing a full size airliner, needs to do computer work on simulators and extensively fly a prototype before going to the final production configuration. This was demonstrated during the B-787 Dreamliner's much delayed flight test program. The same approach applies to RC modelers. Computers can certainly aid in the model airplane design process. But the chief advantage of a CAD program is speeding up the plan drafting process. With a program like TurboCAD, a simple model airplane plan can be drawn quickly in under an hour by an experienced designer. Take a look at replicas built by the EAA for further ideas on RC plane designs.
Rules of thumbs for model airplane design dimensions
Probably the most important aspect for a successful model plane designer is practical experience. After you create your first two or three model aircraft, you intuitively anticipate various design challenges and meet them in the construction of the prototype model airplane version. Design parameter rules of thumb are also very helpful in getting your design proportioned correctly for its first attempt at flight.
The Sig Demoiselle employs a unique design
Even while using all the design skills available - experience, CAD programs and parameter rules of thumb - there is still the need to construct and fly an aircraft prototype design. This approach can be done in several ways.
Prototype and follow on design
For example, you can build an entire aircraft that is essentially a prototype for a follow on design. I did this with the Chickadee. I was inspired by the unique construction method Sig employed for their Demoiselle electric powered RC model plane. The Demoiselle employed a wing balsa dowel mounting scheme that I had never seen before. I replicated this approach with the Chickadee and achieved satisfactory results. One of the key insights gained from the Demoiselle and applied to the Chickadee was the need for a large positive wing incidence to handle the slow flight characteristics for this type of aircraft.
Chickadee adapts Demoiselle wing construction
I then evolved the Chickadee aircraft prototype design parameters as a starting point for my Blackburn RC model airplane layout. The Blackburn has very similar wing area, incidence and tail moments when compared to the Chickadee. There was no need for a prototype of the Blackburn, as the first version had “already flown” in the form of the Chickadee.
Finch micro RC model airplane
The experience gained from designing the Chickadee and Blackburn flowed into the Finch RC model plane design. You can see the heritage of the Chickadee design as applied to the Finch, to include the foam version of the Finch. The key aircraft prototype design element that I needed to consider for the Finch was a low flight weight. I was not too concerned with weight on the Chickadee, as I knew the electric motor and battery combination provided ample thrust.
LiddleRod is designed for ParkZone electronics
The “aircraft prototype” experience for the Finch was actually gained with my build of the LiddleRod aircraft kit. I was intrigued by the LiddleRod, as the plane was designed expressly for the ParkZone line of geared electric motor and electronic controls. The LiddleRod provided good insights to the power of this tiny motor and the required target aircraft weight. I added a bit of extra wing area to the Finch and designed a light structure. The Pietenpol Air Camper is useful for determining micro aircraft dimensions. The only real way to verify these design assumptions was to fly the prototype, and see it the model would get airborne. This worked out well.
Classic prototype design
I employed a more classic approach to aircraft prototype design with the Robin. I had never designed a balsa profile RC model airplane before, and I needed to verify my proposed construction method and aircraft parameter layout. I did this with the Robin prototype. As you can see, I simply attached the motor to the nose for the prototype without much elegant design. There was no special shape to the wing or fuselage outline, just more or less a rectangle. The idea was to obtain the proper airplane layout, see if the target weight could be achieved, and then ensure the model had enough power to successfully fly.
Robin prototype RC model airplane
There were a few tweaks learned from the prototype that needed to be applied to the Robin’s final design, such as moving as much of the electronic equipment forward to achieve the proper center of gravity. I even added half an inch to the nose to aid with CG location. Once these design elements were confirmed with the prototype, I then prepared the final set of TurboCAD plans and constructed the final version of the Robin.
Prototype development
All RC aircraft designers benefit from a prototype of a model aircraft design. The prototype builds on your modeling experience, previous kits or plans, as well as any new aircraft layout or construction methods. An aircraft prototype design saves valuable time by allowing an initial version to highlight any design shortfalls. This allows you to focus on building and flying a mature final RC airplane design with minimum worries.