Build Log - Simple Twin-Boom Pusher - Page 2 - RC Groups
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Apr 16, 2011, 09:21 AM
jclassic1
Depron doesn't have a skin so having to experiment a bit with the making of the booms.This is my first attempt which is not bad but there is room for improvement.The triangular section is very strong and light so should be well up to the job.This first example even came out reasonably straight so confident on making them right.

I can,t seem to get my head around using only one aileron, even though I would like to keep it to original spec I might just have to fit two.

John
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Apr 16, 2011, 12:29 PM
Trapped in California
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Tail Surfaces


Now let's make the tail surfaces. Cut a stabilizer out of FB, a piece that's fairly straight, measuring 13 inches by 4 inches. Then cut out the elevator (don't cut the hinge line all the way through), and bevel the bottom of the cut.

Apply tape to both top and bottom of the hinge line. You may also want to apply tape to the stabilizer's leading edge.

Notice the elevator has a span of 9 inches, which is shorter than the stabilizer. This allows the stabilizer to be glued to the tops of the tail booms without impeding the elevator movement.

Just like the aileron, cut about a 1/16-inch slot on both sides of the elevator to prevent binding.

The fins are easy to make too, and the shape is not critical. Make them whatever shape you want. You may also want to apply tape to the fin leading edges.

That's it! Tail surfaces complete!
Apr 16, 2011, 02:24 PM
Trapped in California
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Final Assembly


Now we're at final assembly.

Glue the booms to the bottom of the wing, each one 5 inches from the wing center (in line with the span of the stabilizer). Make sure they're square to the wing.

Glue the fuselage to the wing, and make sure it's square.

Glue the stabilizer to the tops of the booms.

Glue on the fins.

I like to strengthen all these final assembly joints with hot glue fillets.

Lastly, hold the plane up and sight down the middle. Is the wing warped? Is the stabilizer parallel with the wing? The straighter it is, the better it will fly.
Apr 18, 2011, 12:29 PM
Trapped in California
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Control and Power Systems Installation


Let's install the stuff to make this plane fly!

Cut a slot through both fuselage sides under the wing, big enough to put a servo wire through. This is for the elevator servo, which is on the opposite side of the fuselage from the receiver.
Apr 18, 2011, 12:35 PM
Trapped in California
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Then install your favorite elevator and aileron control horns. I've found it to be OK to just attach horns (screw kind with back plate) to the FB, no hardpoint required).
Apr 18, 2011, 12:37 PM
Trapped in California
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Mark the screw holes for the motor mount onto the firewall and drill. I'm using a Turnigy motor from HobbyKing for $6.
Apr 18, 2011, 01:46 PM
Trapped in California
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Mount the aileron and elevator servos.

I do this by wrapping the servo body with masking tape and hot-gluing them directly to the FB. I use the tape as to not get glue on the servo.

I also attach the ESC and receiver to the plane with sticky Velcro.

I used a black Sharpie pen to paint the tape black so that it blends with the fuselage a little more.

Secure the servo wires with clear packing tape.

A note on pushrods: For short aileron pushrods, I make them out of music wire with a Z-bend for the servo side, and a clevis soldered to the aileron side. For elevator pushrods I use 3/16-inch wood dowels, one end with a Z-bend wire, the other end with a threaded wire and clevis. For more on pushrods, see http://www.foamflyer.info/pushrods.html
Apr 18, 2011, 01:54 PM
Trapped in California
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The next step is to balance the plane. To make this easy, I use what I call "CG Feelers". These are simply small beads of hot glue attached to the bottom of the wing panels at the CG location. Once all electronics are installed, balance the plane by placing your fingertips on the hot glue beads, and set the battery on top of the fuselage such that the plane balances.

For the CG, it should be about 1.8 inches back from the leading edge of the wing. Why? Because a good CG is about 30% of the MAC (Mean Aerodynamic Chord). This plane has a constant chord wing of 6 inches, 30% of 6 is 1.8. Easy huh?
Apr 18, 2011, 02:01 PM
Trapped in California
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Once you know where the battery should go for the proper balance, cut a slot in the side of the fuselage (the side with the ESC). I draw around the battery onto the FB, then use a knife to cut the slot. Notice the battery will stick out of the fuselage a little, this is for easy removal and some cooling during flight.

There's many ways to secure the battery. What I do is I cut two slots on the fuselage side opposite the battery, and use a Velcro strap. I guess you could put tape or a rubber band around it, but in any case you really should secure the battery. An in-flight battery ejection is not pretty!
Apr 18, 2011, 02:03 PM
Trapped in California
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Lastly, secure the receiver antennas with a little tape.
Apr 20, 2011, 11:11 AM
Trapped in California
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I decided to apply some British markings to this plane, so I printed some with a color laser printer and attached them with yellow wood glue. Using a laser printer is better than inkjet, the color will not fade as quickly and is more immune to moisture. Notice how the large roundels on the top of the wing were cut to accomodate the steps in the KFm3 airfoil.
Apr 20, 2011, 11:06 PM
Trapped in California
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Finished RTF weight ended up at 16.5 ounces. Flight performance is excellent!

So41 (0 min 46 sec)
Apr 22, 2011, 11:20 AM
Registered User

Looks great


but I have one stupid question. It looks like you left the paper on the foam board on all parts of the airplane. Is that correct?
Apr 22, 2011, 12:31 PM
Always Ready!
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Love it. "The Flying Toblerone"

I'd think you could also taper the tail ends of the booms. And I had another thought... how about trying an inverted V-tail? -- seems like it would be easy to mate those up to the already angled booms. I bet this would really scoot as a delta wing as well. Might have to try my own.

hmmm .... got me thinkin'...
Last edited by warhead_71; Apr 22, 2011 at 02:00 PM.
Apr 22, 2011, 06:53 PM
Trapped in California
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Quote:
It looks like you left the paper on the foam board on all parts of the airplane. Is that correct?
Yes.


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