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Saturday, November 19, 2011

Z8RC P-38 Mini

I picked up a 27 MHz Toughfoam P-38 for $39. It was a terrible deal!  The thing doesn't fly at all, let alone fly right.  It is actually a 2-channel "design" - throttle plus differential throttle. It has no control surfaces.  Great idea? Maybe. But it doesn't work at all, at least not in this plane--it rolls over and crashes after takeoff every time.
But there is good news.  It doesn't break.  The "toughfoam" is larger-scale type EPO foam, so the thing is pretty indestructible at the expense of a more toyish look.   More great news is that it is so easy to retro fit with actual radio control.

Enter my spare parts bin.  I can't even remember what the guts once were, but they sure went into this liitle EPO bird in a hurry.  Total conversion time was about an hour.
Wingspan = 19.1"
Motors = Brushed, gear-reduced, counter-rotating
Airfoil cross section = Molded, thick camber with flat bottom
Flying weight with 250 mAh 1-cell battery = 3.4 oz

First I scored the bottom hinge line of the each control surface with a hot soldering iron, guided against a metal straight edge.  Then I snipped the sides of each control surface with kitchen scissors.  Hey, that went faster than I thought!

I stuck to installing only ailerons and elevator, since the rudders look difficult to cut in a way they could move freely.

The aileron servos popped on with heavy duty 3M double-sided tape.  I used a long, thin Phillips screwdriver to poke holes through the three fuselages so I could neatly pass the aileron servo wires through, and then taped them to the underside of the wing with Scotch. Zing... done!

The only other control surface to figure out is elevator.  The elevator servo is part of the main PCB, so the thin piano wire push rod was super easy to install with the same kind of screwdriver hole, poked through the rear of the center fuselage.

I glued-in ultra micro type control horns by stabbing them into the foam with a dot of foam-safe CA.  New control surfaces were functional after about 15 minutes work.

Almost finished.......

When I pulled the old electronics out, there were two sets of motor wires, I snipped them off their original circuit boad.  Next I soldered the left/right motors' white wires together.  To that solder joint I added a thin, solid core copper wire pin from a 1/2 inch snip of copper wire from inside a piece of telephone cord.  I did the same with the left/right motors' black and blue wires.  I plugged each pin into the Ultra Micro circuit board' motor output.  Test for polarity. Swap pin orientation if required.  Bend away from each other and tack in place with a piece of electrical tape.

Done!

A 250 mAH 1-cell squeezes into the plastic opening tightly; a perfect fit as a battery holder.  Presto, the airplane is ready to fly and grade.
The red/blue wires squished under the control board 
are left over from the embedded LEDs.  I didn't hook 
them up, but still might.  The rudder servo (top one 
in photo) could be used to fashion a steerable nose wheel.
In the Air:

Confucius once said, "Make an airplane fast and wind blow faster."  He was right.

More to come...
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