Hi,
Why propeller thrust line is always a little higher than CG at the vertical direction? The link below gives good discussion.
ASK DJ Aerotech Question
But i don't understand why he says
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How the moment arms for aerodynamic drag changes when CG is moving upward?
Why, exactly, can't we let the thrust line go through the CG? And what if it is below CG?
I tried to look for the answer in some books. But, typically, textbook only gives the moment analysis without telling what will happen if I change the design. If someone's sure about which books tell that, let me know. I'm quite interested in reading about them.
Why propeller thrust line is always a little higher than CG at the vertical direction? The link below gives good discussion.
ASK DJ Aerotech Question
But i don't understand why he says
'
| Why can't we just put a post on top of the motor pylon with a large counterweight the top of it (maybe the battery?), and move the C/G upward enough to get it on the thrust line? Great idea, except that in the process the moment arm for the drag vector of the water on the hull, and the moment arms for aerodynamic drag on the wing, fuselage, and just about everything else on the model is now further below relative to the C/G than before. The nose-down effect of the thrust will be eliminated, but the other nose-down effects will be increased enough to completely cancel out the benefit. Some days you just can't win! |
How the moment arms for aerodynamic drag changes when CG is moving upward?
Why, exactly, can't we let the thrust line go through the CG? And what if it is below CG?
I tried to look for the answer in some books. But, typically, textbook only gives the moment analysis without telling what will happen if I change the design. If someone's sure about which books tell that, let me know. I'm quite interested in reading about them.
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