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Old Dec 07, 2012, 12:15 PM
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I'm curious as to why some think that the dynamic stability theory, math, etc., developed for full-scale aviation are not applicable to our aircraft?

Are we waving our hands and using the excuse of Reynolds number? Or is it something else?
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Old Dec 07, 2012, 12:23 PM
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Quote:
Originally Posted by Cap_n_Dave View Post
I'm curious as to why some think that the dynamic stability theory, math, etc., developed for full-scale aviation are not applicable to our aircraft?

Are we waving our hands and using the excuse of Reynolds number? Or is it something else?
They are, AFAIK. Dynamic modal analysis has been around, for models, for a fair amount of time, first with AVL then with XFLR5.
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Old Dec 07, 2012, 12:34 PM
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So then why is there any controversy about the dive test and CG position?
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Old Dec 07, 2012, 01:46 PM
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umm...perhaps because some of us (like me) are completely ignorant of anything except what we can visually experience.
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Old Dec 07, 2012, 02:06 PM
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Here's a little diagram I found somewhere to help muddy the water a little . Actually a good visual.....
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Old Dec 07, 2012, 04:02 PM
MrE
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Originally Posted by Cap_n_Dave View Post
So then why is there any controversy about the dive test and CG position?
Im not sure which controversy your talking about and Im also not familiar with the math of dynamic stability. Could you explain what you mean?
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Old Dec 07, 2012, 05:11 PM
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Im not sure which controversy your talking about and Im also not familiar with the math of dynamic stability. Could you explain what you mean?
The controversy ... some people think the dive test is not useful. I haven't read the other threads, but the phrase 'downwind turn' was invoked and that subject is controversial because some insist it is a ' problem' and other insist it isn't. I am assuming there are charge opinions about the dive test.

The math ... I can' t tell you how to derive the equations from first principles (that leaked out of my ears many years ago), but I can give you the equations (I have to find my notes...will post later tonight or tomorrow). I am thinking that things won't be any clearer after it's all said an done.
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Old Dec 08, 2012, 10:56 AM
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Mmm, I prefer the inverted downwind low altitude in sink dive test myself.

Jared
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Old Dec 08, 2012, 12:17 PM
Herk
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Ok model has now been retrimmed for very high speed

What is the aerodynamic decalage now

Rhetorical question - long winded responses not required.
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Old Dec 08, 2012, 09:58 PM
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It's lower. You changed the zero lift angle of the horizontal stabilizer by pushing forward on the stick. The zero lift line drawn along the fuselage should be redrawn closer to the wing.
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Old Dec 08, 2012, 10:29 PM
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can I be silly and further muddle things and change it to, say, an Alula-style flying wing?
Well, not really, unless someone really really wants to

I applied all y'all's wonderful info to the maiden flights of my new Alula on the slopes today. I almost didn't even build it after flying my buddy's and not liking it's flight responses at all. After getting mine dialed in, we focused attention on his, and not long after, we both had nice flying planes!!!
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Old Dec 09, 2012, 06:39 AM
Herk
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Originally Posted by AMBeck View Post
It's lower. You changed the zero lift angle of the horizontal stabilizer by pushing forward on the stick. The zero lift line drawn along the fuselage should be redrawn closer to the wing.
Correct - Decalage changes every time you change the trim.

In fact it changes every time you move the elevator control.
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Old Dec 09, 2012, 07:42 PM
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I've been reading your articles for years!
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Old Dec 09, 2012, 08:43 PM
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ooo...I was unaware I had any articles to be read

Seriously, thank you all for being kind with answers. For you guys, it's like someone asking a mechanic "how do I change my oil?" and i've seen lots of threads dive-bomb regarding replies, but you folks have stepped up, given many many different perspectives, and in the end, my oil got changed, thank you!
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Old Dec 09, 2012, 08:55 PM
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I am glad to hear of your success and your friends.

I wonder how many gliders have been retired due to improper setup/tuning.

Happy Holidays
Curtis
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