Jerry-TS-MkII
Joined: 23 Aug 2017
Posts: 79
Location: Indiana
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 Posted: Tue Oct 05, 2021 1:54 pm Post subject: thrustline changes |
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Re: Thrust line comments
Put a tractor prop on the nose, and it has a fairly long arm. But
mounting 2X the HP above and behind (AND CLOSE to) the CG will be
different. Seeing all of these posts, reminds me of the following:
Prop thrust is greatest as slow speeds
Stab/Elevator effectiveness is least at slow speeds
Take off roll requires ground roll drag, also causing an additional
forward pitching moment.
Wing pitching moment is variable (on most airfoils, depending on AOA and
airspeed(?)
When considering thrust angle variables.. to what? CG, center of mass,
or center of drag?:
There is the CG measured with the AC level. Does anyone know the center
of mass on their Kolbs??
Or the center of drag which changes a lot with airspeed, loading, and
being on the ground, or in the air. I would assume induced drag is near
constant above stall speed, if level flight is maintained with trim.
But parasitic drag goes up with the cube of the speed, and drag on
take-off depends upon grass height, tire pressures, ground firmness and
TOW.
What doesn't change, is the number of questions asked when a perfectly
good airplane flies very differently with 2X the horse power initially
intended. A very small increase in opposing leverage could be
accomplished with only slightly larger Stab and Elevator! My Drifter is
very similar to my Kolb configuration, and yet the tail areas must be
twice as large! I never noticed ANY pitch issues flying the Drifter.
But I didn't bolt on 100 HP either!
If people are going to be arbitrary with a design which had minimal tail
area initially, why not improve THAT!?!? Oh, I forgot, you can't do
that with just a few washers! LOL There isn't hardly anything that can
be changed on an airplane, that doesn't affect a LOT of different
aspects.
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