Fairchild A10 Tank Buster, 74 inch WS

by Mick Hirst last updated 13 February 2003     page 1 of  5

After the relative success of my A10 Prototype I decided to attempt a larger version, more to scale and a target wing span of about 72 inch. I would have liked to try using a couple of ducted fans but apart from the cost the overall weight would have made it very difficult to get airborne from our grass strip so conventional tractor units were again selected. Since the power developed from the pair of SC32 used on the prototype was more than adequate it made sense to use the same format. The benefits being minimising the weight and using a small 3 bladed prop (8*6) allowed the engine nacelles to be correctly positioned close to the fus' (I just hope the nacelles don't smother the power output).

I developed the plans using AutoCAD, by pulling in a scanned 3 view technical image. Then plot  around all the components required and scale the whole up to the required size (having removed the layer containing the scanned images first). The only real deviation from scale is the engine nacelles, increasing the diameter by 8% simply to allow total enclosure of the engine exhaust systems. To upsize the whole plan to accommodate the desired nacelle size would have meant a wing span of approx. 80 inches which I thought might have been just too big for the engines hence the compromise.

The detail of the plan took quite a long time to develop as I was trying to design a system with totally hidden control drives, snakes, levers, horns etc. This also made the kit a little more difficult to build, as the drives needed to be built in as construction was taking place i.e. snakes and torque rods had to be positioned as the formers were installed rather than construct the basic frame then install snakes.

The system uses 9 servos, 2 for the engine throttles, 2 for ailerons, 1 each for flaps, rudders, elevator, retracts and steering. Three servos are mounted in the wing and undercarriage pods, the other six below the cockpit canopy. The engines have Intelligent Glow Systems (IGS) on board to minimise in-flight engine failure and improve throttling.

The wing panels, foam cores cut with the able assistance of Frank (or should I say I assisted Frank). Note slots cut in foam to house torque rods, cables and tubing.

The first dry fit of all the major parts to check the overall looks. When you're building the individual components it always throws doubts in your mind about the final outcome. As they say "if it looks right, it probably is", and so far I'm pleased although there's still a lot more fitting to be done.

After spending several hours fitting the retract system I decided to abort utilising them and reverted to the usual fixed undercarriage. Fitting the retractable nose wheel with steering and sprung OLEO was achieved, although a bit tricky, but on testing I found a problem. Application of a speed restrictor to slow the action highlighted fallibility in the "up position" locking device, similarly when inducing an air leak the "down position" lock also failed to engage. Although the failure rate was in the order of less than 10% Murphy's law has a habit of proving its theory just when you least expect. When actioned at full speed the retracts worked fine but who can predict an air leak.

The "Engine management" installed below the canopy. I deviated from the installation instructions by using a change-over switch on the IGS output to select either on-board glow start (auto) or portable clip-on glow unit (start). Because I'm using a common battery source for both engines I wanted total independent control over either engine for safety reasons, where the recommended method would not provide for this situation. For more details on the IGS click

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