Build the Finch from Depron Foam and Balsa
Construct your Finch RC plane from a variety of materials
Finch micro RC plane made from balsa and ply
The three channel Finch micro RC model airplane is made from a free full size CAD plan you can down load here. Simply print out the plans using Microsoft Word and tape the paper tiles together. The plans are drawn with TurboCAD and contain all the information needed to complete the model. Read on and discover how Evert, based in the Netherlands, converted his Finch into a combination balsa and foam RC model plane.
The Hague, Netherlands
As an aside, if you ever visit Europe, spend some time in the Netherlands. It is a wonderful country with great people. The Hague is my favorite stop. The Hague is the Netherlands seat of government, and is an historic, scenic city located on the Dutch North Sea coast.
The Finch is designed for the ParkZone line of micro radio control gear used in their popular P-51 Mustang ARF foam radio control model plane. The Finch’s electronics can be purchased from Horizon Hobby. Just search for PKZ3351 (a single unit with a receiver, electronic speed control and two servos, just an incredible value); PKZ3624 (motor and gearbox); PKZ3601 (130mm x 70 mm prop) and PKZ1035 (120 mAh lipo battery) on the Horizon Hobby website.
Front view of foam Finch
Finch dimensions
The Finch has a wingspan of 20”, a length of 15.3” and weighs around 1.1 ounces. I designed my Finch to be constructed from balsa and some plywood. There is certainly no reason why portions of the Finch could not be constructed from foam and other building materials, so long as the weight is kept within reasonable limits.
This is just the approach that Evert took with his rendition of the Finch. The Finch uses an open structure design with easy access to the radio control gear, wing installation and tail controls. Evert elected to use balsa for much of the fuselage structure, but incorporated depron foam for the wing ribs and tail structure.
Bottom view of Evert's foam Finch RC plane
Evert employed lightweight carbon rods for the wing’s main spar and leading and trailing edges. Note also the use of carbon rods to support the wing with struts on either side. This is a good idea as you do not have the strength from the 1/32”plywood wing dihedral brace in the wing’s center section that you have with the balsa ribs and spar.
Evert used Acrocover for a covering material. Note that there is no need to tightly shrink the covering on these smaller RC model planes. You should try and get the covering as smooth as possible. There is not enough structural strength to support a drum tight finish to your covering job. As with my version of the Finch, Evert covered just the top surface of the wing to save weight.
Detail of Evert's control set up and servo brick
Evert obtained his RC gear from a local Netherlands supplier. He employed a GP 6 motor, two super micro servos, and a 2.4 GHz orange R415 DSM 2 receiver. There are a wide variety of control systems available for micro RC models. The critical item is to ensure the finished model weight is as low as possible.
Foam tail construction
A Finch foam RC model plane technique that I find especially innovative is Evert’s use of foam for the tail structure. One of the things you quickly discover when designing and building micro electric RC planes is the fact you do not need the same amount of internal structure as is required with the larger gas powered aircraft.
Top view of foam Finch
For example, I used one 3/32” square balsa interior frame section in the stabilizer. At the slow speeds the Finch flies at, Evert simply used foam to outline the entire tail section and dispensed with the interior brace. This approach saved aft tail weight and will help locate the correct center of gravity in the proper range, yet not detract from good flight characteristics.
Wheels are often a challenge with very small RC model aircraft. If you are not careful, wheels can add a lot of weight. For my version of the Finch, I used the tiny foam wheels from the ParkZone Cessna 210. The Finch spends a short moment on the ground during takeoff, so these small and lightweight wheels work fine.
Top view of balsa Finch
Dubro makes a set of ultra-light weight plastic spoke wheels for micro RC models. Note that these wheels were used on the Pietenpol with balsa covers, a visually appealing technique. You could try and make a pair of spoke wheels using thread and the lost jig process described here. Evert used depron foam for his Finch wheels.
Foam is used for the vast majority of almost and ready to fly micro RC airplanes. As Evert capably demonstrates, foam can be easily adapted to the more traditional balsa structure for a micro RC plane. Evert, thanks once again for sharing the results of your modeling work.