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Fourier Analysis of in-flight RPM---Brodak 40

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phil c:
Might be "quicker" to incorporate a sensor on the bellcrank to detect when and how fast the bellcrank moves away from neutral.  The best servo I've seen has a 9 millisecond response time, you can probably figure about the same time to read a sensor and output a response to an motor controller.  It's probably useless to try it with an IC engine.  It takes much longer than the servo for the motor to start responding to a throttle change.  An electric motor might just respond before the plane got past the midpoint of a square corner.  Even then, there is a lag between when the motor applies more torque to the prop and the prop actually starts spinning faster and the air actually starts moving faster to apply sufficient force to accelerate the plane.  Just going from RC experience and watching carrier planes, the total loop with an IC engine takes about 2 seconds from the pilot moving the throttle until the plane starts to respond.

Alan Hahn:

--- Quote from: phil c on October 13, 2009, 03:59:14 PM ---Might be "quicker" to incorporate a sensor on the bellcrank to detect when and how fast the bellcrank moves away from neutral.  The best servo I've seen has a 9 millisecond response time, you can probably figure about the same time to read a sensor and output a response to an motor controller.  It's probably useless to try it with an IC engine.  It takes much longer than the servo for the motor to start responding to a throttle change.  An electric motor might just respond before the plane got past the midpoint of a square corner.  Even then, there is a lag between when the motor applies more torque to the prop and the prop actually starts spinning faster and the air actually starts moving faster to apply sufficient force to accelerate the plane.  Just going from RC experience and watching carrier planes, the total loop with an IC engine takes about 2 seconds from the pilot moving the throttle until the plane starts to respond.

--- End quote ---
Electrics can be pretty darn fast since as soon as the current flows, the torque jumps up. Since the prop is so light, the acceleration is pretty fast. I have actually slowed down the throttle response of my electric setup--because I takeoff at 7600 rpm and transition to 8000 just before the wingover. I didn't want the rpm to jump too fast.

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