I have a scratchbuilt project (FW-190) whose mechanical retracts would make me much happier if I could drive them with linear motion - - push/pull. An air conversion would do that. But I don't want to spend any more weight and install any more equipment than necesary to get that done. So...how small (aka 'light') an air tank and air cylinders can I get away with if I will tolerate two up/down cycles between charges? Any benefit to parallel use of two small tanks?

Alternately, could I use a pair of S-148 servos converted to linear motion, one servo per gear leg (retracts are .40-size Thunder Tiger with 3.5" Dave Brown foamie wheels) to drive the retracts, assuming that the linear travel is long enough?

How about a pair of HiTec HS-77BBs, slowed down to 4 sec cycle time by one of these:
http://www.dionysusdesign.com/produc...products_id=41

This is what I plan on using in my Master Scale (Jemco) Dauntless

I have a p-47 with mechanical retracts being actuated by an old set of Sonic Tronics cylinders. I don't know if they are still available but would fit your need perfectly. Weight wise, I am quessing less than the weight of two retract servos, power wise much more effective.
If you can find any, the cylinders bolt to a mount in the center of the wing like the servos and use standard wire linkages with threaded ends like normal pushrod wire. A small robart air tank and valve are used, giving many cycles at 100 psi. I am sure that the small robart cylinders from their 60 size retracts could be hooked up the same way if you can't find any of the old SonicTronics cylinders.


Larry