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Keeping the flow attached where it is coming down the window should reduce drag but increase the lift. On the Evo I would expect the improved quality of airflow to the rear wing to end up with a net reduction of lift though.

In the late 80s I saw an airflow device that was kind of like reverse of a NACA duct but turned backwards. The front edge was the wide part and it protruded higher up into the airflow the farther back you went. The rear of it was an abrupt vertical cut off with an outline like the front of a NACA duct. These shapes were then placed in a row. It was patented and the guy who made it said it would keep the airflow attached around very aggressive corners. One way he was pushing to sell them was as strips to put on the front edge of semi trailers to keep the air attached from the front face to the top and sides of the trailer. They were very active at highway speed but they are quite a bit more aggressive in the airflow then a conventional vortex generator.

Those were about an inch high and spaced about out every couple inches. We were playing with the idea of putting the same shaped bumps in the floor of an intake runner to try and get the flow to turn towards the valve more efficiently. We couldn’t find a way to fab them and then get them to stay in place so we scrapped the idea.

Wayne

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Old 12-10-2004, 12:10 PM
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Reminds me of Riblets
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Old 12-10-2004, 01:02 PM
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Quote:
Originally posted by Bill Verburg
Reminds me of Riblets
That is a great website, I bookedmarked in in my "Aircraft" folder.

Perhaps I will find out if the Ford Tr-Motor's corrigated skin helped or hurt it's performance afterall.
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Old 12-10-2004, 01:18 PM
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Perhaps I will find out if the Ford Tr-Motor's corrigated skin helped or hurt it's performance afterall
I doubt it but stranger things have proven to be true
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Old 12-10-2004, 01:20 PM
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From the Riblets site....................

Also check out the "compliant" wall /skin section, very interesting.
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Old 12-10-2004, 01:21 PM
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As mentioned above, VG's are in fact for flow separation prevention. The small vorticees produced by VG's help reattach airflow and better the L/D ratio (drag reduction). They are more effective near stall speed.

Chris
Old 12-10-2004, 04:49 PM
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re "compliant" wall /skin

Check out:

Kramer, M. O. 1960. Boundary layer stabilization by distributed damping. J. Amer. Soc. Naval Eng. 72: 25-33.

- very interesting article on dolphin blubber -- never heard from the guy again after he got those US Navy grants....
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Old 12-10-2004, 04:59 PM
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Interesting stuff about vortex generators. Here's a bit more.

Shortly after the F/A-18 was introduced into the fleet, a serious flaw was discovered in the spars that supported the vertical stabilizers.

While troubleshooting a fuel leak, one of our airframes mechanics was removed a few of the skin panels at the base of one of the verticals. What he discovered was quite scary! I'm just estimating, but there are something like 10 or 12 (maybe a few more) spars that make up the framework for the vertical. The leading spar was cracked all the way through, and the following 3 or 4 had working cracks. This thing was headed for a definite failure.

Had these spars failed, the results could/would have been loss of controlled flight. After performing fleetwide inspections of these spars, Navy and Marine Corps wide, several more similar cracks were discovered. It seems the force of impact of the airstream was just too much for these things.

The fix? You can see in this picture. We called it a LEX Fence. The leading part of the wing that came forward along the fuselage was the LEX (Leading Edge Extension) This modification was applied to all F/A-18 Hornets in the fleet, the cracked/broken spars were repared or replaced and they never returned. Apparently these fences broke the airstream up enough to relieve the stress without causing a loss of control.

Just a little FYI...


Randy
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Old 02-28-2005, 06:01 AM
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Is the LEX fence the modern form/version of the dorsal extension vertical stablizer spine of the B-17?

Production:


Prototype:
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Old 02-28-2005, 06:27 AM
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No, it is called a "tail root extension" and serves only to enhance yaw stability.

We designed one longer on the 737-300/400/500 for that purpose -
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Old 02-28-2005, 06:29 AM
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Fabbing some micro VG's out of aluminum stock wouldn't be difficult, nor would slicing the paint with a razor and adhering them above the rear window.

There's probably some airflow separation that results back there, as the tufts moving forward indicate-- there's a "burble" over the rear window. This is, I suppose, why the GT guys run aluminum plates to raise the wing up out of this turbulent layer.

At the end of the day, though, it's all a question of segment times.

Only place I can think this would be helpful would be in stock class racing, and you might get away with it by calling them "spoilers," but the "spoiler height" rule might get you.

Rather than slicing the paint I would prefer to make one fewer mistake per lap . . .
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Old 02-28-2005, 07:05 AM
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hmmm .. looks more like tripping the boundary layer (like golf-ball Dimples) than what would be called a Vortex-Generator.

Thou' I suppose sales will be better when associated to a jet, rather than a little white game-ball.

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Old 02-28-2005, 07:42 AM
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Quote:
Originally posted by Craig911
No, it is called a "tail root extension"
Right, I knew they were different - still a "fix" is a "fix".

Cool F-18 links talking about LEX fences.

http://www.nas.nasa.gov/Pubs/TechSums/9394/014_nas.html

This one is more general, yet better - same source though.

http://www.aerospaceweb.org/question/planes/q0176.shtml


They reinforced the vertical stablizers while they were at it.
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Old 02-28-2005, 07:58 AM
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Quote:
Originally posted by island911
[B]hmmm .. looks more like tripping the boundary layer (like golf-ball Dimples) than what would be called a Vortex-Generator.

Thou' I suppose sales will be better when associated to a jet, rather than a little white game-ball.
Here is an article which talks about both - some very good diagrams and pictures too.

http://www.aerospaceweb.org/question/aerodynamics/q0215.shtml

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Old 02-28-2005, 08:17 AM
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Quote:
Originally posted by kach22i
Here is an article which talks about both - some very good diagrams and pictures too.

http://www.aerospaceweb.org/question/aerodynamics/q0215.shtml

. . . kach, good find; that's an excellent web page, on the subject.

key pharagraph:
"However, there do exist other types of devices commonly used on wings that create a similar effect to the dimples used on golf balls. Though these wing devices also create turbulence in order to delay flow separation, the purpose is not to decrease drag but to increase lift. One of the most popular of these devices is the vortex generator."
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Old 02-28-2005, 08:31 AM
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I can't imagine that the vortex generator increases lift in and of itself, but rather by enabling better airflow over the wing.
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Old 02-28-2005, 08:35 AM
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We actually expirimented with these on our model airplanes. They were referred to as "turbulator strips" in my conversations. Did help stall characteristics on the small planes, esepcially on stall-prone ones like the Extra 300.. ...but not very much...

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Old 02-28-2005, 08:48 AM
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