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Old Feb 02, 2014, 10:35 AM
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Pitch effects of flaps

Think you know how flaps affect pitch trim on a Cessna? How about a B2 bomber? Or better yet, a swept wing glider. Here's your chance to show your stuff.

I've got a prototype swept wing glider with massive flaps and tomorrow it will see air for the first time. What will happen when flaps are deployed?

Here's the last post in the build thread.


Click here to go to the poll

Kent
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Last edited by Knoll53; Feb 02, 2014 at 10:41 AM.
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Old Feb 02, 2014, 01:04 PM
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When you deploy the flaps -- something -or nothing much will happen-
why?
the airspeed at which you deploy them is going to change the response.
a lot.
IF you had the trims all set for hands off flying - then simply deployed the flaps - at cruise speed - the model will zoom- unless something is wrong.
IF you have slowed the model to minimum speeds for controlled flight -deploying the flaps will likely cause the model to slow down and may fall under controllable speed.
IF you couple in a little down elevator (to offset lift) and deploy the flaps at low airspeed - and have set the deployment to happen at a reduced rate say 2 seconds - you will likely just get a slowing of the model -
That is how I setup my flapped models .
at full (second stage deployment) - the model should settle a little more
IF you finally add in more drag (crow) - it should finally settle faster .
the fact that the wings are swept - means little.
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Old Feb 02, 2014, 02:46 PM
Herk
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Sounds like a vote to choose "All of the Above."
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Old Feb 02, 2014, 03:01 PM
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Now I'm catching on.....

So the idea of the poll is to attempt to smoothly and slowly apply flaps from a minimum sink rate (that is slow). Of course any change in flap position will cause a temporary change, but I'll attempt to lessen that effect slowly deflecting flaps about 45 degrees.

Kent
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Old Feb 02, 2014, 04:24 PM
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The pitch response to flaps depends on the static margin. The more nose heavy she is the more negative her pitch response to flaps will be.
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Old Feb 02, 2014, 05:00 PM
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Originally Posted by nmasters View Post
The pitch response to flaps depends on the static margin. The more nose heavy she is the more negative her pitch response to flaps will be.
But, remember Norm - on a swept flying wing the flap deflection has the effect of increasing twist -- The equation has a lot of variables.
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Old Feb 02, 2014, 05:18 PM
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The equation has a lot of variables.
Yep, but most of them are frozen. All I'm saying is that if he flys it nose heavy and observes one pitch response it'll be more positive when he moves the CG aft.
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Old Feb 02, 2014, 05:20 PM
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from a practical standpoint : who flies a glider with flaps in a nose heavy configuration.
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Old Feb 02, 2014, 05:28 PM
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Flaps on a swept flying wing??

I'd hazard a guess the nose down pitching will need to be offset with some nose up pitching with the control surfaces out near the tip.

End result would probably similiar to employing crow braking on a conventional 4-servo wing glider with verly little net gain in lift but a large gain in drag..
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Old Feb 02, 2014, 06:14 PM
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Well, if you believe the science you can do the math - Kent did -- H
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Old Feb 02, 2014, 09:44 PM
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Flaps on a swept flying wing??
This question gets to the primary purpose of the poll. Because it is a swept wing, the flap placement along that sweep will affect whether a nose up or nose down pitch is induced. The wing sweep make flap placement much more critical. It is certainly possible to have a strong nose up from a forward short flap, which, to say the least, is "counter intuitive".

So ignoring all other factors as much as possible, just based on the placement and length of the flap shown in the drawing,what will the effect be?

It is difficult to predict, so you guys can just guess or do the math with your vote. There is a lot to be said for the That Looks About Right method. I used the TLAR method to modify the answer from the math.

Maybe someone has fast and dirty method for determining the pitch effect from flaps on a swept wing?...............I'm hoping.

The first flight will have a static margin of about 11% then if that goes well the remaining flights will be around 6%, which is good enough for the first day. There will be no elevator (elevon) mixing to the flaps for this test. The very forward CG provides positive pitch control for the initial flights. After initial testing, I'll move the CG back until the pitch response become twitchy. Probably end up around 4% static margin.


Kent
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Old Feb 02, 2014, 10:21 PM
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Old Feb 02, 2014, 10:33 PM
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If you're focusing on the fact that the wing is swept, you're over thinking it.
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Old Feb 02, 2014, 11:47 PM
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If you're focusing on the fact that the wing is swept, you're over thinking it.
Really? Pleas explain how to use camber flaps on a non-swept wing without an on-board computer
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Old Feb 03, 2014, 12:08 AM
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Norm your question is unexpected, I agree with everything you said. These forums have already seen an interesting discussion of the stability of a hershey bar flying wing, in which case flaps are indistinguishable from elevators.

Which brings me to my next point. Kent, I expect your flaps will behave a lot like your elevators, but with a little more lift and a little less pitching moment per degree of deflection.

With what methods are you calculating your wing aerodynamic center? A vortex lattice method would answer your question with great accuracy.

-David
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