A demo on an Ace RC (Ralph Cooney designed) throttle needle for the Babe-Bee or “tank mount” reed valve .049″ engine(s). My apologies for the video’s quality… Fuel is Sig Champion “25″. I am testing this arrangement for a sm. RC trainer that I am building from scratch. The needle is simply a pc. of .0625″ o.d. music wire, with a taper of approx. .375″ in length, ground on one end to a “blunt” needle profile. The engine’s venturi i.d. is .0635″, so the needle is a nice fit and will stop the engine when inserted past the taper. The homemade muffler is more of a “baffle” than a muffler. It simply “pushes on” over the cylinder and is made from 2-2″ dia. bicycle inner-tube rubber discs with 1/2″ hole in center and stapled around the edges. Al. tubing large enough to fit over the glow head is cut to approx. 1/2″ L. with 1/4″ hole(s) drilled in it for breathing. This is sandwiched between the 2 rubber discs, and I used 3/4″ L. pcs. of 1/4″ brass tubing with a flare on one end as a header pipe(s). Some high-end r.p.m. is lost, but the added back pressure helps the throttle transition and a lower idle ability. Note that the glow plug “driver” is on throughout the test, which also aids in low idle. Ext. tank is a Sullivan 2 oz. with a feedline through a hole/grommet drilled in the Cox tank and attached to the back-plate nipple. Test yielded avg. r.p.m.’s from 2800-11,500 with a 6″ x 3″ Cox grey prop., a “mylar” reed and std. Cox glow head w/1 copper gasket. There are LOTS of variables which will determine r.p.m. range. ie: prop. (size/pitch/weight), primary (fuel) needle setting, exhaust restriction, fuel type, glow plug type/compression ratio, phase of the moon… Anyone familiar with running these engines knows what I mean. I like this throttle design because it actually meters the “mixture” of fuel/air from the primary needle, and one can experiment with different needle-taper profiles, for varying performance curves. Your comments are welcome.
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