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Old 05-05-2006, 04:46 PM
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Default RE: 1/2a speed plane wing design

The C/L speed guys have a vent tube facing the wind. They play with tank positioning and centrifical force to feed the engine. The more inboard the tank is in relation to the engine, the stronger the feed. Of course they are limited to the confines of the fuselage, so moving the tank is a very slight tuning technique. We don't have that C-force, and there are G forces that act on the fuel when the plane is accelerating, a bladder overcomes this and gives the engine a more constant supply. .049s that have this much of a fuel demand are pretty finicky about fuel feed pressure being constant. I'll take my chances with a bladder, but I have to admit that I have never tried my G&Z with a suction tank. Almost forgot, you can get fuel foaming with suction, you won't with a bladder.....score another one for bladders. Another bonus is that as the bladder empties, the walls get thicker and the pressure goes up at the end of the run to cool the engine off. Getting acclimated to using bladders takes some practice, some supplies and tools you might not normally use, go to kittingittogether and Larry Driskill can fix you up with all the necessities, bladders, Nelson plugs and some killer props. These planes are a challenge, there has been about as many moments of frustation, disappointment, rage, etc., as there has been excitement, joy, nirvana, etc. I went through many engine parts with the engine set on "kill" with too much compression and 50% nitro. The highest tach reading was 42,000 with the APC 4.2x4. I finally dropped the compression and nitro to 15% and the performance is still pretty good, [35,000 on the ground], and the parts are lasting at least 10 times longer. I would guess 5-10% less rpm with your .049, but that's a wild guess.