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Aileron design

Old 01-18-2011, 05:29 PM
  #1  
JackM
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Default Aileron design

I am in the process of redesigning a rubber powered Sperry monoplane into a 38" wingspan electric plane.

The ailerons are out at the wingtips and I plan to use pull pull controls linked to a single servo arm.

I need to determine the best hinge arrangement. IE hinge at center, hinge at top surface.

Any thoughts or suggestions as to best way to hinge and most importantly why? I plan on using CA hinges.

This is intended to be a gentle flyer!

Thanks,

Jack
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Old 01-19-2011, 01:39 AM
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tobydogs
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hello Brian,your question is a little vague,but if i understand it...i may have the answer.

if the pull /pull is piano wire and buried into the trailing edge till it reaches the ailerons then you should hing center of the Te with your ca hings.

if you ailerons are at the wing tips and the wing span is 38inch,use 3 ca hings per aileron.

the only time I'd off center the hing is if i were doing flaps,and those are located at the bottom edge of the Te.

hope this was what your looking for ,but if not...post a picture for us to see.
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Old 01-19-2011, 01:47 AM
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quorneng
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JackM
This is what I do for my gentle flyers.
Top hinge with a full length tape.
This "seals" the aileron preventing air leaking through the hinge so improves effectiveness. It also provides a smooth surface for the faster moving air.
Of course this requires a clearance gap on the underside so I use a differential action (more up than down) to keep the gap as small as possible.
One further advantage is that this gap gets smaller as the aileron moves down reducing the drag a bit where as the gap get much bigger on the up aileron producing more drag which actually aids the differential effect.
With such a set up even quite steep turns have little or no adverse yaw so no rudder is required.
This shows the top and under side.
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Note the top tape hinge (actually just Sellotape!) and the servo arm angled forward to give a mechanical differential action.
I have use this system on quite a few planes.
I hope this helps
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Old 01-19-2011, 09:39 AM
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If you really want to use CA hinges then they more or less MUST be centre-hinged. They're just not intended to be glued on top or bottom of a surface.

And if you really mean pull/pull controls (wires to the top and bottom of the aileron with a two-sided control horn) then your bigger problem is going to be getting the control runs clean and organising the necessary pulleys etc. For a setup like that I don't think I'd use CA hinges because they're generally rather stiff.

Steve
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Old 01-19-2011, 02:19 PM
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JackM
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Originally Posted by stuart View Post
post a picture for us to see.




Here are the two choices I see. If there are others please advise! Choice B seems obvious but maybe A has some advantages. I'm not concerned with the pull pull mechanism since that was dealt with in another thread. I am wondering how much movement to allow for though.

Any insite appreciated.

Jack
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Old 01-19-2011, 03:07 PM
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As has been said above, A has some advantages especially for a slow flyer. The design has a greater effect up than down which gives some built in differential that reduces adverse yaw.
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Old 01-19-2011, 03:12 PM
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JackM
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Originally Posted by Turner View Post
As has been said above, A has some advantages especially for a slow flyer. The design has a greater effect up than down which gives some built in differential that reduces adverse yaw.
Is that due to the surface area?

Jack
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Old 01-19-2011, 03:22 PM
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I hadn't looked at it that way but yes, that's right. The mechanics of it reduce the size of the surface when down.
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Old 01-19-2011, 03:54 PM
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JackM
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Originally Posted by Turner View Post
reduces adverse yaw.

I've been reading about aerodynamics and flight but am still a beginner so please be patient.

What do you mean by adverse yaw?

Jack
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Old 01-19-2011, 04:09 PM
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With no differential the down aileron produces more drag than the up aileron. There are probably many factors but I think the main one is greater pressure under the wing than over. The higher drag on the down aileron causes the plane to yaw to that side which is opposite of what is desired. Increasing up deflection while decreasing down deflection decreases this effect.
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Old 01-19-2011, 04:29 PM
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JackM
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Turner,

OK, I understand that. Does the larger gap in the bottom surface of the wing/aileron have any effect on the way the wing functions in straight flight?

Jack
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Old 01-19-2011, 04:37 PM
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I would guess that it probably does have some effect but many use this design with good results. The smaller the gap, that will still allow full deflection, the better.
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Old 01-19-2011, 04:51 PM
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Turner,

Thanks! Guess A aileron is the way I will go unless I run into some other issue. I'll have to do some cad models to work out the gap.

It seems that a gap would produce turbulance which seems to me to be more acceptable on the top of the wing than on the bottom. That being said, I don't see a problem.

I'm waiting for a book on aerodynamics and model airplane design to arrive.

Back to work.....

Jack
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Old 01-19-2011, 06:51 PM
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Originally Posted by JackM View Post
...It seems that a gap would produce turbulance which seems to me to be more acceptable on the top of the wing than on the bottom....
I thought the same thing and was planning a wing with them hinged at the bottom for that reason. But then I realized that the built in differential would cause more adverse yaw.

Someday I would like to try and use a thin piece of mylar attached to the wing that would fill the gap but flex enough to allow full movement. In the end the benefits would probably be small.
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Old 01-19-2011, 07:32 PM
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Mylar surface would seem to work but I think you are right about benefits being minimal.

I had Andy Lennen (sp?) book out of the library and a lot of what he tried to explain was a bit too complex for me to digest in a short time. So much to learn!

Regards,

Jack
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Old 01-19-2011, 08:05 PM
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Andy Lennon was a brilliant designer. I have his book, RC Model Aircraft Design. It has a number of aileron variants that are hinged at the top for proper differential but avoid the gap at the bottom. Much of the book is over my head but there is much to be learned from it. I'd love to build his Robin someday.
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Old 01-19-2011, 09:36 PM
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Robin IS interesting!!! The part of Andy's book that caught my attention the most was the STOL stuff and the NASA droop. I really want to play with no droop and droop on an airframe to see the difference. I also like float planes and want to play with stol stuff.

Back to work.....

Jack
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Old 01-20-2011, 04:55 PM
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JackM
It is more important to maintain a smooth airflow on the top of the wing than underneath.
A wing works by speeding up the airflow over the top and reducing it underneath. Speeding it up locally reduces its pressure and vice versa. This difference in the pressure between the upper and lower wing surface gives the lift.
Speeding up an airflow is a fairly delicate business. It is quite easy to disturb the flow so it slows down by itself so smooth gentle specially shaped curves are required.
The upshot of all this is that a big long aileron 'slot' across this delicate airflow stream is not ideal.
The only saving grace is that the aileron 'slot' is fairly near the trailing edge of the wing where any airflow disturbance will not have too much effect on the wing as a whole.

Well that the theory and applying it has certainly worked for me.
I hope this helps.
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Old 01-20-2011, 04:57 PM
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JackM
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Simon.

Thanks! Yup, faster air less dense.

Jack


Originally Posted by quorneng View Post
JackM
It is more important to maintain a smooth airflow on the top of the wing than underneath.
A wing works by speeding up the airflow over the top and reducing it underneath. Speeding it up locally reduces its pressure and vice versa. This difference in the pressure between the upper and lower wing surface gives the lift.
Speeding up an airflow is a fairly delicate business. It is quite easy to disturb the flow so it slows down by itself so smooth gentle specially shaped curves are required.
The upshot of all this is that a big long aileron 'slot' across this delicate airflow stream is not ideal.
The only saving grace is that the aileron 'slot' is fairly near the trailing edge of the wing where any airflow disturbance will not have too much effect on the wing as a whole.

Well that the theory and applying it has certainly worked for me.
I hope this helps.
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Old 01-20-2011, 05:11 PM
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Plus.. Having a nice tight joint on the upper surface of the wing, where you see it most, looks nicer
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Old 01-20-2011, 05:22 PM
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JackM
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Originally Posted by JetPlaneFlyer View Post
Plus.. Having a nice tight joint on the upper surface of the wing, where you see it most, looks nicer
Definitely agree there! I have no idea of what the prototype wing/aileron looked like since it is just a line on the drawing.

Have to figure out what type of hinge to use. I have some CA hinges but maybe something different would be better. The wing will be covered with tissue/dope and painted.

Jack
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Old 01-20-2011, 05:38 PM
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I have another approach I've used on one foam plane.

I created the aileron with a carbon fiber tube as the leading edge, glued full-length to the aileron. On the outboard end I made a pin of strong nylon that just fit inside the tube and allowed the tube to rotate easily around the pin. The trailing edge of the aileron area of the wing was sanded to conform to the tube. Finally a music wire torque rod, with the end hammered to a flat was epoxied into the inboard end of the aileron carbon tube. A close-fitting but not snug plastic sleeve was slipped over the torque rod and the assembly was glued into the wing by putting glue on the outboard support pin and the sleeve over the torque rod. A slot had been cut in the bottom of the wing for the pin and the torque rod to allow the aileron to have proper alignment with the wing. The slot can be filled after aileron installation to preserve the smoothness of the bottom surface. The result was an aileron with no visible control horns that merged with the wing with only a minor gap on both the top and the bottom. The close fit of the tube to the wing trailing edge and the long (nearly 1/2 the circumference of the tube) narrow (just enough gap to allow free movement) path from the bottom to the top of the wing through the gap ensured minimal leakage, though not completely sealed.

This arrangement supports the aileron at only the two ends. But the carbon tube is VERY resistant to both flexing and twisting. I never had the slightest problem with flutter, even at 100 Mph.
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Old 01-20-2011, 05:58 PM
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JackM
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Sounds like a very sound way to attach an aileron but this plane shows the aileron running right to the wing tip so can't have a pivot on the outboard end easily. Good idea though and worth saving in the gray matter!

Jack

Originally Posted by MustangMan View Post
I have another approach I've used on one foam plane.

I created the aileron with a carbon fiber tube as the leading edge, glued full-length to the aileron. On the outboard end I made a pin of strong nylon that just fit inside the tube and allowed the tube to rotate easily around the pin. The trailing edge of the aileron area of the wing was sanded to conform to the tube. Finally a music wire torque rod, with the end hammered to a flat was epoxied into the inboard end of the aileron carbon tube. A close-fitting but not snug plastic sleeve was slipped over the torque rod and the assembly was glued into the wing by putting glue on the outboard support pin and the sleeve over the torque rod. A slot had been cut in the bottom of the wing for the pin and the torque rod to allow the aileron to have proper alignment with the wing. The slot can be filled after aileron installation to preserve the smoothness of the bottom surface. The result was an aileron with no visible control horns that merged with the wing with only a minor gap on both the top and the bottom. The close fit of the tube to the wing trailing edge and the long (nearly 1/2 the circumference of the tube) narrow (just enough gap to allow free movement) path from the bottom to the top of the wing through the gap ensured minimal leakage, though not completely sealed.

This arrangement supports the aileron at only the two ends. But the carbon tube is VERY resistant to both flexing and twisting. I never had the slightest problem with flutter, even at 100 Mph.
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