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Author Topic: Flap sizes  (Read 1205 times)

Offline Allan Perret

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Flap sizes
« on: August 17, 2010, 11:53:15 AM »
Seems like most of the current designs use ~.75" longer span on left wing panel (and flap) and ~1/8" extral chord on the tip of the right flap.
I understand the longer left panel, but what about the right flap's area vs the left's ? 
Is the intent of the extra chord to make the right flap equal in area to the left flap,  or is it to make it larger (and by how much) in area than the left flap ?
If the latter, what is the reason for that ?
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Allan Perret
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Offline Randy Powell

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Re: Flap sizes
« Reply #1 on: August 17, 2010, 12:00:00 PM »
Allen,

The idea, generally, is to balance the flap area. If you use equal panel wings, then it's easy. The flaps are the same. If you use any asymmetry then it can get more complicated. If you have full span flaps, then the outboard flaps has to have a larger tip chord to balance the area with the inboard flap; the idea being that both flaps have the same area.

Some designers give the outboard flap a bit more area than the inboard flap. Not a lot, but maybe 2 or 3% bigger. This allows you to carry more tip weight.
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Offline Allan Perret

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Re: Flap sizes
« Reply #2 on: August 17, 2010, 01:34:50 PM »
OK,  I know this is where it can get really complicated,  but.. 
If your tip weight is such that you think you need more right flap area to carry it,  wouldnt that be too much weight ?? 
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Allan Perret
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Offline Randy Powell

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Re: Flap sizes
« Reply #3 on: August 17, 2010, 03:57:15 PM »
Allan,

Well, that's what I always thought, but if you check out Paul Walker's Impact plans, that's what you'll see. Paul is known as a very, very good windy weather pilot. I suspect that the additional tip weight helps in turbulent or just windy conditions. And the extra flap allows you to carry it.
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Offline Igor Burger

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Re: Flap sizes
« Reply #4 on: August 18, 2010, 10:12:41 AM »
Quote from: Allan Perret on August 17, 2010, 11:53:15 AM
Is the intent of the extra chord to make the right flap equal in area to the left flap,  or is it to make it larger (and by how much) in area than the left flap ?

None of that and also not "carrying more weight" in absolute meaning. The important property is not the size of the flap, but RATIO of flap chord to wing chord. Assume that you have symmetrical wing with equivalent flaps. And now try to extent the outer flap by 10%. If the flap is in neutral, then the outer wing will be little larger. Not 10%, but if the flap is say 20% of the wing, then only 10% of 20% = 2%. So it will need little more tip weight to fly level. But if the flap is at 30degrees, those 10% will have greater effect. Means if you want keep level position in corners, you need to add more tip weight. So larger outboard flap is a trimming tool that allows keeping wing in level (or better without roll) in corners, as well in rounds and also in level flight.

And why we need more relative tip weight in rounds and level? Just because lines are soft, and they do not act as a tip weight (inner) immediately in tight corner, but they are effective in rounds.
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Offline Allan Perret

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Re: Flap sizes
« Reply #5 on: August 18, 2010, 05:32:59 PM »
Quote from: Igor Burger on August 18, 2010, 10:12:41 AM
None of that and also not "carrying more weight" in absolute meaning. The important property is not the size of the flap, but RATIO of flap chord to wing chord. Assume that you have symmetrical wing with equivalent flaps. And now try to extent the outer flap by 10%. If the flap is in neutral, then the outer wing will be little larger. Not 10%, but if the flap is say 20% of the wing, then only 10% of 20% = 2%. So it will need little more tip weight to fly level. But if the flap is at 30degrees, those 10% will have greater effect. Means if you want keep level position in corners, you need to add more tip weight. So larger outboard flap is a trimming tool that allows keeping wing in level (or better without roll) in corners, as well in rounds and also in level flight.

And why we need more relative tip weight in rounds and level? Just because lines are soft, and they do not act as a tip weight (inner) immediately in tight corner, but they are effective in rounds.

Not understanding what you are saying. 
"Assume that you have symmetrical wing with equivalent flaps"  Symmetrical in airfoil or planform (equal panel spans) ?
"And now try to extent the outer flap by 10%."   I'm not sure if you mean increase flap area by 10% or deflect flap 10 degrees...
"If the flap is in neutral, then the outer wing will be little larger."    Whats the connection between flap position and wing size ?

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Allan Perret
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Offline Igor Burger

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Re: Flap sizes
« Reply #6 on: August 18, 2010, 11:10:29 PM »

"Assume that you have symmetrical wing with equivalent flaps"  Symmetrical in airfoil or planform (equal panel spans) ?
Both


"And now try to extent the outer flap by 10%."   I'm not sure if you mean increase flap area by 10% or deflect flap 10 degrees...
to increase the CHORD of the flap by 10%

"If the flap is in neutral, then the outer wing will be little larger."    Whats the connection between flap position and wing size ?
If the flap is at 0 degrees deflection and flap chard is 10% longer then wing chord is 2% longer (in that my example)
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