Probably has to do with the velocity at the end of the hose. The long hose lowers the pressure drop at the end enough to get you into a resonant region. Slowing down the motor, or partly blocking the flow in some way might get a similar effect with a shorter hose.
Probably means you have a lot less effective suction too. Probably want something larger in diameter for that long a run. Just for experimentation, you might try putting a tapered end on the hose, something with not more than about 7 degrees per side of taper. (That is what I read produces low drag on the afterbody of an airplane fuselage.) It might smooth the intake flow to the hose enough to stop the shreik. Mark Holm [EMAIL PROTECTED] RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED] Please note that subscribe and unsubscribe messages must be sent in text only format with MIME turned off.
