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Old Nov 30, 2002, 06:22 AM
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Another gap seal efficiency question

I was thinking of putting gap seal on the ailerons and elevator of my Mini Floh HLG. On both the ailerons and elevator the gap is just a frogs hair less than 3mm wide and the ailerons are fairly long--over half the length of the wing. So, with such a seemingly small gap, will there be a gain in airfoil efficiency that makes using gap seal worth it? Thanks!

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Old Dec 11, 2002, 12:05 PM
Pierre Audette is offline
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Does it whistle? That would be due to a pressure differential between two surfaces, with air going through an opening. In the case or ailerons, the airflow would be disrupted at the trailing edge, and I would think it will affect lift & drag.

For a quick solution, try some 3M Blenderm tape. It's stretchy and removable. Apply it to one side, by applying full deflection to the ailerons and taping the gap. Go fly and see. Actually, you could do the taping a the field, so you could test back to back the effect with and w/o the tape.
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Old Nov 06, 2015, 10:24 AM
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I was thinking about that this morning because I have 54" full span aileron plane with about a 1/8 inch gap. It is very responsive so I didn't bother for 5 years or so. Today I will try some of my usual Monokote seals, especially considering that in level flight my 4 lb electric will have 4 lbs of air pressure difference between the top and bottom of the wing.
Every place the air finds it's way back together other than the TE probably means one more thing in an accumulation of inefficient factors.

Get in a 3 G maneuver and now the wing will develop 12 lbs of pressure between the top and bottom. Right ?
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Old Nov 06, 2015, 11:13 AM
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[QUOTE=Chophop;33127756especially considering that in level flight my 4 lb electric will have 4 lbs of air pressure difference between the top and bottom of the wing.

Get in a 3 G maneuver and now the wing will develop 12 lbs of pressure between the top and bottom. Right ?[/QUOTE]


Pressure is measured in force per unit area, so the average pressure difference would be 4lb (or 12lb at 3g) divided by the wing area to give lbs/in^2 or similar pressure unit. With 500 in^2 of wing area, the average pressure difference would be 0.008lb/in^2 (0.024lb/in^2 at 3g). The pressure difference is distributed over the whole wing, but concentrated at the LE. There is a large upper surface suction peak and lower surface pressure peak near the LE. Most of the lift occurs in the forward 30% of the wing.

The pressure difference as far back as the hinge gap is quite small, but still significant. Stopping flow through hinge gap can improve efficiency.

Kevin
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Old Nov 06, 2015, 11:20 AM
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I have been thinking undesired turbs can increase the effective thickness of the wing and that means more drag. The turbs at the TE might make the TE taper useless unless the air comes back together in a tidy way ?

Look at the huge bubble the air brake makes and watch near the TE where the water is actually lifting up vertically ! Exciting news to me.

Mooney Speed Brake Air Flow Separation (0 min 33 sec)
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Old Nov 07, 2015, 07:49 AM
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Got the gap seals on, but you know what they say, never mod or buy a new airplane or you will cause 3 weeks bad weather. True again. I tried to test it but the turbulence was nearly unmanageable. Came back in, two tries to land, got in on the 2nd one.

Checked the weather map, I went through a 180° wind change and a frontal line right over me.

Anyhow, the roll rate skyrocketed. It is wild, must be more than 500°/ second. I have to wait for the weather to s s s s set t t tle to try again.
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Old Nov 08, 2015, 11:12 AM
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Ok now the weather settled enough to test it. The roll rate is now so fast I was worried it would fly apart or something. I had to reduce the travel to 70% and the roll rate is still insane.

The trim vs speed and/or motor speed changed dramatically. It needs some serious down thrust because the nose now drops quite a bit on slow down and power off and mainly some intolerable nose up with full power now.

Glide and "inertia" has noticeably improved. Unfortunately the landing float has increased, the thing has 540 sq in wing area and weighs 4 lbs, nearly a glider. I already set up spoilerons that allow for a nice high alpha landing and makes the airplane actually have a level descent rate when activated.
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Old Nov 08, 2015, 10:26 PM
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A pleasant surprise And a lesson learned... both good.
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