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Old 05-10-2002, 06:19 PM
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Default Balancing and Control Throws

If you have access to RealFlight or other simulator, I would pick an appropriate bipe model and fly it on the simulator, fool around with the control throws and have all the virtual crashes you want until you are happy with the throws (which will be in degrees, not inches). Then translate those throws to your Pitts, and go conservative for the trimming out flights. Add to the throws as you like when you find the conservative throws too limiting.

For test flights I would skip the dual rates, just fly on conservative "low" rate. Add the high rates later, as you determine how much more you want.

A little expo is always nice, but you don't need much if any for conservative throws. As you set up high rates later, then expo becomes more desirable.

As to CG, if you are still framing or at least not covered, my favorite method for setting CG is to locate the plan-recommended CG on the top wing (for a bipe or high-wing model). Normally at that point the structure will have at least a double center wing rib, and perhaps the main spar will intersect at that point also. Whatever structure is there, beef it up a little bit through the thickness of the wing with small pieces of balsa block or triangle stock, and drill a vertical hole 1/4" or 5/16" through that spot. Take a dowel of the appropriate diameter and drill a vertical pilot hole down its center, to receive an appropriate sized screw eye from your local hardware store. Epoxy the dowel into the wing. When the model is covered and you are ready to position the battery, hang the bugger by the screw eye with a line from the ceiling, light fixture, whatever, and hang just a few inches above whatever surface (floor, bench, table) you're working with. With a little luck, you will be pretty close to balance both front to back and side to side, and you can fine tune the balance just by putting the battery to one side or another of the fuselage, a little forward or aft of receiver. I like to take my first flight with the nose down just a degree or two, then adjust later on after flight testing.

If CG is off by more than what the battery placement can correct, you can add weight to nose by going from wooden to APC prop, or lighten the nose by going from APC to wooden prop. (My preference is for wood, because I like a light prop for the engine to turn, but I will use an APC if I need more noseweight.)

If battery placement plus prop selection still leaves you off, then the next thing I would do is add a redundant battery. (Ask Red Scholefield about how to set this up.) I'd a lot rather have another few ounces of battery on standby than a useless piece of lead somewhere.

If two batteries won't solve your CG problem, then radical measures are called for. Now you may have to swap engines for something a bit lighter or heavier, or remount the engine a little further in or out, maybe move servos to tail, etc. All this is of course best done with framed up but not covered fuselage.

Other measures: for less tailweight, take off your sheet balsa tailfeathers and build up sticks; for added tailweight, balsa sheet your tailfeathers, cover with fiberglass and epoxy.. If you're going to have to add weight, you might as well get some benefit from it.

By the way, I am often the only one at the field when I fly, so it is helpful for me to be able to pick up my plane in one hand and transmitter in the other. If your plane is not too big (less than 1/4 scale) you can handle it easily if you make up something like a little stevedore's hook to keep in your pocket, then slip it through the screw-eye. By picking it up at CG you can walk with it easily in one hand, lift it over fence or barrier, etc. If I am going to leave my CG jig in permanently, I normally run a piece of 8-32 threaded rod all the way through the thickness of the wing, fasten it on the bottom with fender washer & nylon locking nut, another washer and locking bolt on top, then thread on a drawer pull knob selected for low drag finish. This doesn't look very scale like, but I like the convenience of it.