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Old Sep 24, 2012, 11:17 AM
There's Something in the Air
Ne-Aero's Avatar
United States, NH, Hillsborough
Joined Jul 2005
265 Posts
Discussion
Flaps vs Spoilers for XC Sailplanes

Hi all,

I'm wondering why the use of spoilers on XC sailplanes is so low compared to flaps.

As I see it, Flaps:
  • Have the added benefit of enabling you to vary the Camber of the wing's trailing edge (at the center panels) for thermalling
  • Are simpler to build into a wing

But are these the only reasons for the widespread use of flaps over spoilers?



Take Care,
John
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Old Sep 24, 2012, 12:20 PM
LSF303 / AMA Life Member
tkallev's Avatar
USA, IL, Wheeling
Joined Jan 2003
3,126 Posts
Flaps are easier to build without compromising the top surface of the wing like a poorly fitted spoiler might.
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Old Sep 24, 2012, 01:20 PM
There's Something in the Air
Ne-Aero's Avatar
United States, NH, Hillsborough
Joined Jul 2005
265 Posts
OK, so a poorly fitted spoiler is less performant because of the disruption to the wing's upper surface than a well fitted flap and it is easier to make a well fitted flap than a well fitted spoiler.

But what about the case of a well fitted spoiler against a well fitted flap?
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Old Sep 24, 2012, 04:20 PM
Master of the Wind
G Norsworthy's Avatar
United States, CA, San Jose
Joined Sep 2008
1,168 Posts
My analysis shows a pretty big penalty for not having camber change. So you need the flaps to win. Also installing spoilers in a composite wing means cutting a hole right where you are most likely to fold the wing. Like servo cutouts, it can be dealt with in the design but it is another thing to worry about. Plus the attention to detail required to make a nice fitting spoiler is in my experience a level above cutting a flap out.

If you need to drop the plane in a tight spot, which happens frequently in some areas, flaps are much easier than spoilers.
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Old Sep 24, 2012, 04:26 PM
Nathan Miller
thermal145's Avatar
Peachtree City GA
Joined Apr 2007
135 Posts
Spoilers are of almost no use to a dedicated XC glider -spoilers will only reduce lift and add drag, while flaps allow you to increase lift with little drag penalty at lower deflections for thermalling, and of course larger flap deflections will provide a large increase in both lift and drag. At high flap settings, stall speed is reduced which helps with a slower, steeper landing approach which is helpful in an off field landing situation.
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Old Oct 01, 2012, 10:26 PM
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dbaya's Avatar
United States, CA, Union City
Joined Mar 2004
403 Posts
I could sure use some flap or spoilers on XC#8. Last 2 contest I have damaged my plane during landing. At Davis a couple months ago I had great race and completed the course. We stopped our truck in the corner between some trees and power lines. The other side was a huge clear plowed field. Circled and Circled several times. 15 to 20 feet off the deck. Changed directions and ended up hitting a lower power line then the power pole itself. Cal Valley I hit a fence during landing. Tired to keep the plane on the downwind side only to misjudge and find myself about to run into a fence.

We don't get points for landing, but it sure not cool damaging on a perfect XC flying day.
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