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Old Nov 01, 2012, 06:58 AM
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USA, GA, Jesup
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Adverse Yaw

Aeajr

I'm trying to get my head around your comments about adverse yaw.

Using the flap to help avoid adverse yaw instead of the aileron doesn't make sense to me. The flap works just like an aileron, it goes down, increases the wing's camber, creates lift (and drag) and consequently adverse yaw.

It appears to me that the difference between flaps and ailerons is a somewhat arbitrary line drawn on the monokote of the trailing edge, unless you are talking about sophisticated flaps such as Fowler.

The flaps are usually inboard of the ailerons, so the "leverage" of the adverse yaw would be lower than that of the ailerons but that would seem to be offset by the lower leverage of the roll vector. (The further out the ailerons are, the faster the roll rate will be, all else being equal).

I understand that using the flap will increase the roll rate (In the case of the Ultra Stick series= quite considerably) but I just don't see the lowered adverse yaw. I'm somewhat new to sailplanes, so I'm trying to learn.

Bob
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Old Nov 01, 2012, 11:31 AM
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Bob, we use differential, more up deflection vs down aileron throw takes care of adverse yaw with proper use of rudder (not just straight Ail-Rud mixing).

Marc
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Old Nov 01, 2012, 12:08 PM
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Quote:
Originally Posted by bobinjesup View Post
Aeajr

I'm trying to get my head around your comments about adverse yaw.

Using the flap to help avoid adverse yaw instead of the aileron doesn't make sense to me. The flap works just like an aileron, it goes down, increases the wing's camber, creates lift (and drag) and consequently adverse yaw.

It appears to me that the difference between flaps and ailerons is a somewhat arbitrary line drawn on the monokote of the trailing edge, unless you are talking about sophisticated flaps such as Fowler.

The flaps are usually inboard of the ailerons, so the "leverage" of the adverse yaw would be lower than that of the ailerons but that would seem to be offset by the lower leverage of the roll vector. (The further out the ailerons are, the faster the roll rate will be, all else being equal).

I understand that using the flap will increase the roll rate (In the case of the Ultra Stick series= quite considerably) but I just don't see the lowered adverse yaw. I'm somewhat new to sailplanes, so I'm trying to learn.

Bob
I am not aeronatuical engineer so what I report is based on what I have read from those who are actually designers and engineers. Let me illustrate with some numbers. Again this is my understading.

Let's say you want to roll right. Using some arbitrarly numbers:

Right aileron goes up 20 mm
Left aileron goes down 10 mm

You roll.

Now if you make the same roll but with Right flap up 2 mm, right aileron up15 mm
left aileron down 7 mm and left flap down 3 mm you will get about the same roll but will affect less drag as all surfaces are deflected less. In addition, the left aileron, which is the greater contributors to adverse yaw is down 30% less.

You may also need less rudder to combat the adverse yaw, reducing the drag prodcued by the rudder too.

Now, one could argue that it all adds up to the same thing. I could not argue the point, but this is my understanding of how it works.

But the point of my original post is more focused on the travel of the flaps. The poster I was trying to help was concerned that the flaps would only move up about 1 mm. He seemed disturbed that he could not match the movement of the ailerons in the up position. I was trying to illustrate why it was not necessary to have them match for a TD glider. This is not an aerobat. We are trying to effect roll with the least surface movement and the least drag and the least adverse yaw.

I could be wrong about the whole thing, but that is how I understand it.
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Old Nov 01, 2012, 02:24 PM
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Is it just me or does it not very closely resemble the 70's era Aquila I have hanging in my hobby room. Same full elevator, same dihedral break in the main wing, same canopy, It's a few inches longer, my Aquila is 103" I THINK...

Anyone else have an Aquila to compare?
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Old Nov 01, 2012, 02:51 PM
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The Mystique is bigger, much newer airfoil, different planform, no counter-balanced rudder, full house control, electric power, and on and on. They are the same since they have two wings, a fuse, full flying stab, a poly break, and vertical surface.

If there is any resemblance, is they are both sailplanes and that is it. I flew an Aquila for a while, and I promise that the Mystique is a major step forward.

Marc
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Old Nov 01, 2012, 03:38 PM
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I agree with Marc. The Mystique isn't really much like the Aquilla. Of course, the last time I saw my Aquilla, it was heading for the Atlantic, from Minnesota, at around 5,000 feet. She was so well trimmed that she didn't even need the radio turned on for a perfect hi-start launch into a gentle right turn!
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Old Nov 01, 2012, 08:17 PM
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Originally Posted by OVSS Boss View Post
Rick/XIA-Mixing ail-flp is the norm on unlimited ships world wide except when you are in landing mode. Mixing the ail-flp has nothing to with the speed of the ship in any mode, full span camber changing has more control of that and you still have ail-flp mixing turned on in cruise, thermal and reflex modes.

I do use some minor ail-rud mixing, but learn to use that left hand and the rudder stick cause just using the mix can bite you in the arse when you need the ship to maintain a coordinated turn in a thermal.

Marc
Yes. With this ship, the flaps do not move up more than a millimeter or two. Given that you will only have flap movement when the aileron moves down, you will create additional drag on the outside of the turn. Therefore, in addition to the extra drag, you need rudder to help the ship turn.

I do it on my modified Radian Pro - the flaps do move in concert with the ailerons in certain modes. Not on this ship, tho.

Rick N
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Old Nov 02, 2012, 07:56 AM
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Red Bluff CA
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Originally Posted by xiaoyu80305 View Post
I probably use different motor and spinner. I like the spinner from Multiplex. What is the axle nut that you are talking about? Are you talking about the nut that holds the axle, which is a part of spinner?
The motor shaft needs to be 19 to 20 mm
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Old Nov 02, 2012, 01:03 PM
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Boulder, CO USA
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Quote:
Originally Posted by aeajr View Post
On a thermal glider, the goal of A to F mixing is not so much to get a faster roll but to get the roll you need with less aileron movement on the down stroke. By mixing in about 50% down flap to the down aileron movement you will need less down ailerom movement to achieve the same roll. This produces less adverse yaw and less drag.

1 mm of flap on the up aileron side is enough if that is all you can get. I get maybe 2 mm on my high end molded ships. That is plenty for reflex. And for a to f mixing.

Everything is a compromise. Servos have a limited range of travel. Priority for flap is max down travel for landing. Roll is a secondary use. To get more up you would have to give up some down travel. That would not be the best use of that surface.
Your answer is very clear and making a lot sense. I have this question for a while, but never got answered until now! Thanks,
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Old Nov 02, 2012, 01:06 PM
Joined Jan 2007
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Quote:
Originally Posted by aeajr View Post
On a thermal glider, the goal of A to F mixing is not so much to get a faster roll but to get the roll you need with less aileron movement on the down stroke. By mixing in about 50% down flap to the down aileron movement you will need less down ailerom movement to achieve the same roll. This produces less adverse yaw and less drag.

1 mm of flap on the up aileron side is enough if that is all you can get. I get maybe 2 mm on my high end molded ships. That is plenty for reflex. And for a to f mixing.

Everything is a compromise. Servos have a limited range of travel. Priority for flap is max down travel for landing. Roll is a secondary use. To get more up you would have to give up some down travel. That would not be the best use of that surface.
Guys, Flaperons were not used when testing the Mystique. You can achieve 1.5mm of up travel which is plenty for camber changing and what the hinge gap was designed for.
Modifying the Flap gap may induce flutter so please be careful when making changes to the standard kit setup..
Pete
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Old Nov 02, 2012, 01:13 PM
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Originally Posted by TeamHorizon View Post
Guys, Flaperons were not used when testing the Mystique. You can achieve 1.5mm of up travel which is plenty for camber changing and what the hinge gap was designed for.
Modifying the Flap gap may induce flutter so please be careful when making changes to the standard kit setup..
Pete
That is a very good point!
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Old Nov 02, 2012, 02:01 PM
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Originally Posted by OVSS Boss View Post
The Mystique is bigger, much newer airfoil, different planform, no counter-balanced rudder, full house control, electric power, and on and on. They are the same since they have two wings, a fuse, full flying stab, a poly break, and vertical surface.

If there is any resemblance, is they are both sailplanes and that is it. I flew an Aquila for a while, and I promise that the Mystique is a major step forward.

Marc
Thanks...
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Old Nov 02, 2012, 04:39 PM
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Originally Posted by RTaylor View Post
The motor shaft needs to be 19 to 20 mm
Thank you for your measurement! Is 19 to 20 mm from the motor mount surface or from the firewall of the fuselage?
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Old Nov 02, 2012, 07:58 PM
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Red Bluff CA
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Originally Posted by xiaoyu80305 View Post
Thank you for your measurement! Is 19 to 20 mm from the motor mount surface or from the firewall of the fuselage?
From motor.
Randy
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Old Nov 03, 2012, 06:10 AM
Electric
Joined Oct 2009
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Made a CF windshield since I had the materials.

My stock windshield seemed heavy at 2.00 ozs. Curiosity took over

Before stock= 2.00oz
New carbon fiber one= 0.72oz

Why did I make one?.... because I could, and 1.28oz less weight, is less weight
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