The flying monkeys got me...

Helis and fixed wing

AMA 957918
IRCHA 4345
AMA Intro Pilot Instructor

Wednesday, July 27, 2016

Big Stik Build Update

The CG was waaay off forward, as I expected. I moved the Ignition and Receiver packs as far aft as I can, and they are now underneath the wing hard-point aft of the elevator and rudder servos.

Even then she took 3 oz (88 grams) of weight to balance. I opened the underside just forward of the Vert Stab and inserted this weight, epoxied it in, and closed the opening, coted it and voila, nice and balanced. The fuel tank is mostly forward of CG so there will be some nose heaviness.

In trying to tune the engine the other day I learned a few things and burned out the throttle servo.

The plane dry weight is 7.2 lbs. The Master Airscrew 13x8x3 triple blade runs at 8000-8200 rpm and develops 6 lbs of static thrust. The Master Airscrew 14x8 twin blade runs at the same rpm and develops 6.6 lbs of static thrust. I went with the twin blade, and a thrust to weight ratio of 0.91.

The small amount of resistance in the throttle control arm, from the slight bend as it exits the firewall to the plastic pipe that covers it as it moves aft was creating enough resistance that the throttle servo burned out. I lubed it up with some silicone, but will need to put a small bend in the control linkage as it attaches to the throttle to alleviate any side bending force increasing the resistance. It seems to move okay... maybe it was just a bad servo? We'll see.

I have debated adding some additional hard point attachment to the fron of the wing. The solid single hard point seems more than adequate.

The ignition works fine. But tuning this engine reliably is troublesome.

Lastly, the Spektrum AR7610 7-ch receiver that was in the ill fated Spitfire won't bind... I suspect it did take some water damage.

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