Thread: Thrust ???
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Old 11-21-2005, 05:20 PM
  #5  
britbrat
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Default RE: Thrust ???

ORIGINAL: JohnW

Since everything a plane does reacts about the center of mass, if the thrust line is above the CM, you will have a natural down pitch when hovering due to thrust, i.e. you will need up elevator.
Cheers.

It isn't that simple. In the vertical, perturbing effects due to the center of mass location are much less significant than they are in more level flight attitudes.

The location of the centers of lift & drag (they frequently don't coincide) must be considered along with the center of mass. Even in a true hover, there are still substantial lift & drag effects due to the powerfull propwash over the flying surfaces & other airframe components in the propwash (landing gear for example). In some circumstances, they can have more impact than the center of mass.

Trim you model for hands-off level flight at full speed, or at least a high cruise speed, then pull into the vertical at speed and observe the direction in which the plane deviates from the vertical line as it decelerates. Repeat the test, but kill the throttle after entering the climb & observe the result.

Repeat the test again, but enter with closed throttle from a high speed dive, then open the throttle in the vertical climb & observe the result.

From those three evolutions you should be able to clearly see the effects of thrust line.
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