Chickadee Prototype Model Plane Design

Front view of the completed Chickadee park flyer

Front view of the completed Chickadee park flyer

The Chickadee is one of my early electric radio control model airplane designs. The Chickadee was published in the Sept 2009 issue of Quiet and Electric Flight International magazine. Construction plans for the Chickadee are included with my Blackburn plan set and can be purchased here.

The Chickadee is an easy aircraft to build and would make a great choice for an initial plans built model. Most of the balsa and plywood required is likely in your scrap wood bin.

The Chickadee was an interesting step in my learning process regarding designing model aircraft. In the case of the Chickadee, I was new to the world of indoor and park flyer RC aircraft. I had just completed the Sig Demoiselle kit and was very impressed with the construction techniques employed for this unique RC flyer.

I thought that the Demoiselle’s use of balsa wing dowels that plugged into metal mounting tubes was a neat innovation. I also liked the idea of the wing’s leading and trailing edges in effect becoming fore and aft structural spars for the completed wing, using the ribs to provide the airfoil shape.

In the early days of RC electric modeling, before the widespread use of lipo batteries and powerful brushless motors, keeping a model at a light weight was critical for successful flight characteristics. Thus to deal with the weight issue the Demoiselle designer used a geared brushed electric motor and nicad batteries (both standard for the time) and employed covering on just the top surface of the wing and horizontal tail.

Detail of the Chickadee nose section and control system layout

Detail of the Chickadee nose section and control system layout

My idea was to emulate these construction methods for the Chickadee. I kept the wings pretty much dimensioned to the same area as was used on the Demoiselle. I liked the metal tube wing mounts and installed these as well, permitting a removable wing. The metal tubes also established the correct dihedral setting. I used TLAR (that looks about right) for sizing of the tail control surfaces.

Detail of the wing balsa dowel attachment tubes and control servo for the Chickadee

Detail of the wing balsa dowel attachment tubes and control servo for the Chickadee

As the Chickadee would be set up for three channels (throttle, rudder and elevator) I made the elevator and rudder a bit oversize to ensure full control authority at the slower airspeeds used for indoor flight. I knew from experience that my outrunner electric motor would provide plenty of thrust.

My strategy was to validate these area and layout considerations in the Chickadee and use as a basis for future model design. I deliberately kept the Chickadee prototype simple with a flat fuselage arrangement and a standard braced mounting for the firewall and electric motor. Once this was proven in test flights it would be a modest effort to add various visual finishing details such as a cowling and cockpit side panels.

Quiet and Electric Flight International magazine published the Chickadee plan in their Sept 2009 issue

Quiet and Electric Flight International magazine published the Chickadee plan in their Sept 2009 issue

This turned out to be a sound approach. The first Chickadee went together quickly. But the prototype could not fly. Initial taxi tests showed that the design did not have sufficient positive wing incidence, as the model had plenty of thrust for a high speed taxi but did not readily lift off.

As the design was open and easy to modify it was a straightforward task to change the length of the two forward wing mount posts to raise the wing leading edge and increase the wing’s incidence. The result was a Chickadee that smoothly lifted off the ground during takeoff and flew well at slower airspeeds. I now had a plane design that worked.

Wing attachment scheme for the Chickadee

Wing attachment scheme for the Chickadee

As I mentioned earlier the idea behind getting the Chickadee’s overall setup established was to use this as a template for future RC model planes. This is exactly what I did for my design of the Blackburn. From the Chickadee I had the correct wing span, area and incidence proven. The proper center of gravity location and correct tail moments and all areas and throws were properly arranged.

To create a Blackburn design it was a simple matter to retain the incidence established for the Chickadee and “lower” the Chickadee’s high mounted wing onto the top of the Blackburn fuselage. This was easy to do with TurboCAD. I then via CAD “filled in” the structure and shape of the Blackburn to more or less fit within the Chickadee’s outline.

One clever innovation I introduced with the Blackburn was the use of a lightweight plywood plate on the fuselage top that allowed for the electric motor mount, the servo/battery/receiver installation and a strong landing gear attachment area. This proved to be a useful approach to provide the necessary strength to counter the inherently flimsy structure of the original Blackburn design, characteristic of all wire-braced aircraft produced in the first decade of flight.

The key learning point is that I used a quick-build approach for the Chickadee to establish the design parameters and allow for rapid modification as needed for items like the wing incidence. Now that I have these constraints and sizes established, future successful models can be produced from the Chickadee design parameters.

 

 

Chickadee CAD plans

Chickadee CAD plans

Author: Gordon McKay