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Old Jan 19, 2014, 09:23 PM
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United States, NC, Chapel Hill
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Question
Airbrakes to control Yaw?

I am working on my first flying wing. It is a swept wing with fins at the wing tips, sort of like a Zagi on steroid.
I have working split airbrakes and I was wondering if they can be used to
control yaw in flight. The idea would be to deploy the airbrake on one wing to increase the drag on the wing and induce yaw. I have already set up the radio for that, but before I give it an actual try I'd like to hear from people with more experience.
Thank you
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Old Jan 20, 2014, 11:06 AM
'tis nothing
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United States, CA, Napa
Joined Dec 2011
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I don't see it. The air brake will cause similar forces to the wing as does an aileron, in the case of a flying wing, elevons. The braked wing will simply stop flying compared to the other and it will turn just as if you used a single aileron.

Try it and let us know what happens.

BTW, why do you want to induce yaw?
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Old Jan 20, 2014, 11:22 AM
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I remember this concept being used in one of the early full-size ultralights. Push right pedal, the right side winglet turns out, causing drag on right wingtip and right yaw. Push left pedal, the left side winglet turns out, causing drag on left wingtip and left yaw. Push both pedals, both winglets turn out causing increased sink rate and no yaw. Worked just as intended without any issues.
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Old Jan 20, 2014, 11:55 AM
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Split surface airbrakes work well to control yaw. However, they are extremely high drag when compared to a conventional rudder.

With a computer stabilized airplane that uses them for active yaw stabilization without vertical surfaces, like the B2, it makes perfect sense.However, in a model airplane with a a vertical stab, the utility is reduced.

One thing to watch out for when testing is coupling between air brake deployment and the pitch axis.
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Old Jan 20, 2014, 06:28 PM
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To what purpose, if I may ask? Unless the wing is a dihedral all yaw will do is make the plane, well, yaw. The big wing bombers made by Northrup had them, but you're not using it as a bomber.

Are you?
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Old Jan 20, 2014, 06:40 PM
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Correct me if I'm wrong, but isn't that how the B-2 controls yaw? By opening the split airbrakes?
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Old Jan 20, 2014, 06:57 PM
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Quote:
Originally Posted by Fly Wheel View Post
To what purpose, if I may ask? Unless the wing is a dihedral all yaw will do is make the plane, well, yaw. The big wing bombers used by Northrup had them, but you're not using it as a bomber.

Are you?
Well, aside from "because I can do it" reason, and the fact that involves only some programming on the radio side, one thing with this plane is that once the
front wheel is up, there is no way to control yaw. So I am thinking about landing in crosswind and/or yaw corrections at take off when the front wheel is up...
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Old Jan 22, 2014, 12:10 PM
'tis nothing
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Any reason is a good reason. Do it and let us know how it works.
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Old Jan 22, 2014, 07:00 PM
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http://www.rcgroups.com/forums/showthread.php?t=1699318
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Old Jan 22, 2014, 07:46 PM
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One of the best links I have seen is some time, Thanks!
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Old Jan 23, 2014, 09:09 AM
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Originally Posted by nmasters View Post
Looks very interesting. One main difference, which may prove essential, is that
in my case the split airbrakes are close to the wing root, so they may not
be nearly as effective in terms of induced moment about the vertical axis
as when they are close to the tips...
Once I get comfortable flying it I will try some experiments....
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Old Jan 23, 2014, 10:51 AM
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Think of your drag rudder as applying torque to the center of gravity. Torque is the length of the lever times the force. If a force (in this case drag) is applied right up close to the thing you're trying to twist it will take a lot of force to get the job done. However if you double the distance that you apply the force you also double the torque that it makes so it makes sense to put the drag rudders on the wing tips to keep the drag that they produce to a minimum. If building a linkage for horizontal drag rudders in the wing is too difficult drag rudders on the fins is a simpler option. You can activate vertical rudders with one pull wire and close them with a rubber band.

--Norm
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Old Jan 23, 2014, 10:51 AM
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They won't do much near the root as far as yaw, they need some moment arm.
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Old Jan 23, 2014, 09:25 PM
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Quote:
Originally Posted by nmasters View Post
Think of your drag rudder as applying torque to the center of gravity. Torque is the length of the lever times the force. If a force (in this case drag) is applied right up close to the thing you're trying to twist it will take a lot of force to get the job done. However if you double the distance that you apply the force you also double the torque that it makes so it makes sense to put the drag rudders on the wing tips to keep the drag that they produce to a minimum. If building a linkage for horizontal drag rudders in the wing is too difficult drag rudders on the fins is a simpler option. You can activate vertical rudders with one pull wire and close them with a rubber band.

--Norm
That makes sense. Adding rudders to the fins may be a more effective solution.
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Old Jan 24, 2014, 06:13 AM
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Also, the greater the wing sweep, the more the rudder is behind the CG, and that will give you more moment arm.
So for a "plank" style wing (very little sweep, if any at all), rudders on wing tips are very weak - which is why planks typically have the rudder on a fin that is placed as far back as possible on the fuselage pod.
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