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jb92563
Joined: 23 Mar 2007
Posts: 314
Location: Southern California
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 Posted: Thu Mar 06, 2008 1:10 pm Post subject: Re: Firestar Videos and VG's |
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VG's placement along the chord of the wing is unique to each airfoil type.
How far back have people been placing their VG's of FS or UltraStar?
I'm inclined to just place a couple bays worth and then do an oil test.
The way I believe VG's work, and please correct me if you think I am wrong, is as follows:
At a moderate angle of attack the Air flows (probably turbulent flow) over the leading edge till it reaches a point of separation past the max thickness point on the wing.
The vortex generators are ahead of the Max thickness point and serve to additionally energize the flow by means of a vortex that keeps the flow attached to the wing further back than normal allowing more lift to be generated and hence lowers the stall speed.
With that reasoning I would think the optimum place to put the VG's is just before the separation point but not to far ahead as further ahead will increase drag.
Did landshorter test a Kolb airfoil in the Tunnel or do field testing on a Kolb to determine the best placement point?
I think oil tests on a test section might be my best option.
Mispositioned VG's would either add more drag at higher speed or not work at all if placed to far aft.
If your VG's are not working then they need to come forward on the wing.
So how far back are Kolbs getting their VG's?
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JetPilot
Joined: 10 Jan 2006
Posts: 1246
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| Posted: Sun Mar 09, 2008 10:21 am Post subject: Re: Firestar Videos and VG's |
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Most of that testing has already been done for you. Landshorter recommends that VG's be placed 11 % of the chord back from the leading edge of the wing.
Just as important as the distance from the leading edge is the angle of the VG into the wind so that it creates effective vorticies without stalling and creating to much drag, which is 15 degrees into the wind. These numbers are not Kolb specific, but they work well in most of our class airplanes. A lot of people have used landshorter VG's at the recommended positions on Kolbs with great results. My results were so good, and my plane flys so well that its not worth my time moving the the VG's around to different positions.
Mike
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apilot(at)surewest.net
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| Posted: Sun Mar 09, 2008 7:44 pm Post subject: Firestar Videos and VG's |
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Is the angle of 15 degrees into the relative air up or down? And is the relative air the air that comes up the airfoil or the direct air from the path of the aircraft? Thanks, Vic
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mdnanwelch7(at)hotmail.co
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| Posted: Sun Mar 09, 2008 9:40 pm Post subject: Firestar Videos and VG's |
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| Quote: | Is the angle of 15 degrees into the relative air up or down? And is the relative air the air that comes up the
airfoil or the direct air from the path of the aircraft? Thanks, Vic
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Vic,
The relative air Mike was referring to is the "sideways" air, not up or down. Here's what he meant.....assuming no wind, calm air, level flight. Okay? Now, pretend you have a long piece of yarn taped to the leading edge of the wing, on top, blowing in the wind. In our situation, it is straight back. Now, swing that yarn to the left 15 degrees, that's a VG angle. Swing it to the right 15 degrees, that's the other VG angle.
If it were me that was placing VG's on a wing, I would imagine making a template, for absolutely gnat's hiney perfect placement, would be a good idea.
Mike W
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