Lumenier RB2205C-12 2400KV SKITZO Ceramic Bearing Motor
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Old Mar 13, 2010, 02:39 AM
Lamborghini12345 is offline
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Discussion

The Effect of tape on LE an TE


Well today I put some reinforcing tape with single direction fibers on the LE and TE of my Glider in a length wise direction. On both they wrapped over about 20mm.

Now I was thinking that this would improve Glide because there would be less resistance between the air being broken at the front and leaving the back instead of the bare EPP.

So I took her out for a spin with the tape adding 4g to the wing and she sank in the wind and couldn't penetrate or Glide well at all. I thought this was due to the windy conditions and went home.

To get rid of weight I removed the TE tape and later went for another spin at the School up the road. It was still sinking at not penetrating well. So I removed the tape on the Polyhedral sections of the wing. Noticeable improvement in Glide, launch and turn. I then removed the middle sections tape and an instant improvement everywhere!

Now I would have though the tape would reduce drag but maybe the bumps from the reinforcing tape messed with the flow of air over the top of the airfoil? Or maybe the difference in surface texture caused uneven flow and drag or downforce?

Can anyone explain it? Is there a simple explanation?
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Old Mar 13, 2010, 03:47 AM
JetPlaneFlyer is offline
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Models often benefit from some 'roughness' on the upper wing surface. Contest gliders often have 'turbulators' which are usually in the form of a zagged edged strip running spanwise along the upper wing surface. http://www.mh-aerotools.de/airfoils/turbulat.htm

These turbulators help prevent or delay the formation of laminar seperation bubbles. Laminar seperation bubbles cause drag: http://www.mh-aerotools.de/airfoils/bubbles.htm.

On your model it's possible that the rough surface finish of the foam was acting as a turbulator and the packing tape spoiled the effect..

Steve
Old Mar 13, 2010, 05:25 AM
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Any model using tape on the exposed surface of the wing will not be aerodynamically clean enough to gain anthing significant from any quasi streamlining you'd get from the smooth surface of the tape. Not to mention that most EPP foams used for non-skinned model structures are rough enough that even when taped the multiple high points stick up and affect the lay of the smooth tape to the extent that the tape is rough enough that there isn't any significant extension of the laminar flow segment. And without that there's no significant improvement.
Old Mar 13, 2010, 02:31 PM
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Thanks for explaining that guys, I have sanded the EPP very smooth but it still is EPP. Do you think it would have the same effect if I used one piece of laminating film to cover the whole wing in one go?
Old Mar 14, 2010, 04:53 PM
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I laminated my EPP flying wing with 3 mil laminate.. It supposedly glides better and has a higher top speed. I haven't flown one without the laminate though.. This is just from what Lee at crashtesthobby.com said about it.
Old Mar 14, 2010, 10:06 PM
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If it's stiff enough to bridge the points and produce a nice smooth shape it SHOULD aid the top speed.
Old Mar 27, 2010, 11:42 PM
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I think the size of the airfoil and thickness of the tape amplified the effect on it causing the loss in performance as well.
Old Mar 28, 2010, 05:24 AM
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As per my first post.. On a lifting airfoil smooth is not necassarilly good. Laminar airflow is desirable in full size applications but at low Re numbers (small/medium relativly low speed models) it can and does lead to laminar seperation bubbles which create much more drag than a turbulent boundy layer would.. So on low Re airfoils it's often desirable to have some roughness to intentionally create a turbulent boundy layer.

My assumption in the smooth tape (or at least smoother than foam) is causing seperation bubbles.

The best solution may be smooth tape of the rear 2/3rd of the chord and 'rough' foam on the front 1/3rd?

Steve


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