About this Plan
DFH-23. Radio control mini-pattern plane, for Cox TD .020 engine.
Quote: "The combination of the very powerful Cox TD .020 and modern lightweight radio gear makes it possible to fly all maneuvers in the FAI program except start (no wheels), spin, inverted spin (no throttle), and landing (no wheels). Perhaps a rule cheater would argue that it is 'scalelike performance' to catapult (hand launch) and land on a belly sled like the Me-163?
It is more difficult to do the maneuvers with a small plane. A 5-second slow roll feels like 15 seconds, and it is hard to keep it in stable knife-edge flight. The 'full size' .60 engine is 30 times as big as the TO .020, but the big planes' weight is only 15 times that of the small plane. That makes all climbing maneuvers more difficult, as the power-to-weight ratio is only half that of the .60's.
But think back 10-15 years and remember that the .60 engines of that time had only half the power of the modern OPS and similar .60's. That is the same power-to-weight relation as with this .020 model (if we forget about propeller efficiencies). We had. world championships in the 60's with old Vecos and Super Tigres of that time, and all were impressed by the performance. Nowadays people grumble about too high speed, safety, cost, noise, field shortage, transportation problems, and so on and so forth.
Then why not fly Pattern .020, which we can do today? It is not suitable for beginners or old fumble fingers. And we can let Grandpa play with his ridiculous mammoth planes. He needs the size and slow movements because of slightly dimmy eyes, fumbly fingers and not-so-quick reactions. Let's all other go .020 (is anyone left?).
BUILDING THE MODEL You must be a real weight watcher when you build it. First, always use lightweight balsa, then as little epoxy or white glue as possible. Use old-fashioned model glue or modern cyanoacrylate glue (Zap, Hot Stuff, etc.). Finish it with dope and only use an epoxy fuel-proof coating at the tank area back to the wing. The foam rubber around the R/C gear weighs a lot; use strips of Ace 'Sticky Foam' instead. The R/C gear connecting wires can be shortened and even the servo connectors can be taken away.
THE WING: The rear part of the airfoil is flat, and as there is no dihedral, the whole rear part of the wing is flat. Therefore, if you have a flat building board, you just pin down the rear sheets and the wing will be straight and warp-free. A) Make one wing rib pack as shown in the photo and use every second rib to the right and to the left (you won't feel the different thickness in flight). Mark where the flat part starts. B) Cut one sheet covering the flat area. C) Pin it to the building board with the ribs on it. Fit the front spar and the short connecting center spars. Put on the top sheeting starting from the leading edge. Note that the wing is open in the front center except for the short center spars. D) Turn the wing over and put on the front sheeting. E) Mount the aileron torque rods and tubing.
THE TANK: The standard Cox tank is only used as a spacer because it is too small and won't work during inverted flying. The standard clunk tank won't work in this size. Therefore, a special homemade tank is needed.
First step in building the fuselage is to glue the firewall and main bulkhead in place, and glue the sides together at the tail. A) Start by soldering an open cylinder. B) Solder the front end. C) Make the plumbing and solder it to the open tank. The moving part must rotate easily. D) When satisfied, put on the back end. E) Leak test under water.
THE FUSELAGE: A) Make the fuselage sides and bulkheads. Glue the sides to the big wing bulkhead and the front bulkhead and at the tail. B) Put in the tank and all bulkheads. C) Push in the wing and mount all details. D) Mount the stabilizer and fin. E) Put on the top angled sides and then the top sheet..."
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Supplementary file notes
Article pages, thanks to RFJ.
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