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Old May 15, 2012, 02:27 PM
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I too think that what is being described is a dart. The only configuration I could think about is an odd one with more than one horizontal surface, set up so that it is stable at a slight angle either way up by playing with a wing with a thick trailing edge and a noticeable wake. Essentially using the same effect that causes sometimes control surface hysteresis. And even that sounds very unlikely to work.
[edit] another possible option: flat plate canard, proper "thick" wing section, CG set far back and the canard partially stalled. It might end up being stable only at a set speed, but could be stable either way. Again, not sure it would work.
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Old May 15, 2012, 02:35 PM
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Old May 15, 2012, 02:47 PM
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Quote:
Originally Posted by Steve Anderson View Post
In the interest of learning my error, how do you explain this plane with symmetric sections. He claims no trim change from upright to inverted.

http://www.rcgroups.com/forums/showp...7&postcount=35
Again - glider powered by gravity.
IF your claim worked for level constant speed - there would be no need for a motor .
Gliders move due to gravity and or updraft. One moves it down -the other moves it up
Neither creates a steady speed at constant altitude.


The condition - -level constant speed - plane simply rolled from inverted to upright requires something to restabilize the required wing angle in either case The amount of trim required for either case may/may not be the same amount but not the same setting
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Old May 15, 2012, 02:57 PM
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Old May 15, 2012, 03:03 PM
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Quote:
Originally Posted by Steve Anderson View Post
In the interest of learning my error, how do you explain this plane with symmetric sections. He claims no trim change from upright to inverted.

http://www.rcgroups.com/forums/showp...7&postcount=35
.
Didn't hear any claims about anything, just the usual inappropriate pirated music.
There's no demonstration of anything relative to the setup of the plane.
Constantly moving the control sticks isn't a way to show stable flight with no trim changes due to how the sticks are being held.
There is that pesky gravity and the wind to help it fly.
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Old May 15, 2012, 03:56 PM
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Old May 15, 2012, 04:25 PM
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A section cut through the flight path of the projectile tossed from the cliff.
It's a "projectile" because by definition, a zero-zero setup has no lift.
There's only gravity... always, and drag.. depends on the shape.
There's simple physics equations that can relate the distance the projectile impacts from the point of toss, and the time of plummet.
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Old May 15, 2012, 05:26 PM
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Old May 16, 2012, 01:28 AM
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Come on guys

This thread is degenerating away from common sense

Say the downwash angle hitting the horizontal stab is only 2 or 3 degrees

It will still have a significant effect on pitch trim and pitch stability dynamics

Who would deny that?

Steve

Quote:
Originally Posted by richard hanson View Post
THIS ONE-- I gotta see- using a glider ??
Have you ever flown a model or full sized craft ?
The slope glider relies on upwards air currents and gravity to generate movement
In order to demonstrate your "idea" - you would need a constant ,calm air environment
Oh yes - and power .
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Old May 16, 2012, 01:36 AM
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Btw I was filming the downwash angle behind my wing the last 2 days. It is definitely more than 2 or 3 degrees! Steve
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Old May 16, 2012, 01:56 AM
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Old May 16, 2012, 01:57 AM
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Btw I'm still on the fence re the original thesis of this thread. I certainly concede that that the momentum involved with the downwash associated with x pounds of lift depends on many variables. Yet it seems to me that once the downwash is created, it must perpetuate until it is absorbed by the ground. The shear forces between air molecules simply propagate/ disperse the momentum of the downwash out to a larger volume of air, right?
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Old May 16, 2012, 02:02 AM
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And btw I'm still 100% convinced that the ground feels a downforce equal to the weight of the plane, no matter what fraction of that downforce is due to the downward momentum of the downwash and what fraction is due to some sort of downpressure not associated with momentum... steve
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Old May 16, 2012, 02:05 AM
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Quote:
Originally Posted by Steve Anderson View Post
I agree the zero-zero setup would be a projectile. I made an error when I missed that an example airplane in a book I was using had everything falling on the same reference line and symmetrical but the wing is mount with 3 angle of attack. So, I am sorry guys.

Sparky Paul, thank you for the post with the drawing.

I think 0 0 need not be a projectile. The zero angle horizontal stab meets the airflow at a negative a-o-a, because it is in the wing's downwash. So the configuration can be positively pitch-stable. I will check the rc slope glider thread tomorrow to see if they have chimed in... steve
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Old May 16, 2012, 02:09 AM
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The glider I described back in post 141 shows an interesting behavior. If I release it with a slight downward flight path at the right speed, it will establish a climb. If I turn it upside down it does the same thing. This does not sound like a projectile to me. Perhaps those who are so certain a 0-0 setup will be a projectile ought to actually try it.
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