Min. drag speed vs flaps on a swept wing?
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Min. drag speed vs flaps on a swept wing?
Hi!
Can anyone tell me how extending the flaps/slats affects the shape of the the drag curve and whether the V min drag moves significantly from the clean config speed?
Can anyone tell me how extending the flaps/slats affects the shape of the the drag curve and whether the V min drag moves significantly from the clean config speed?
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From: France - mostly
At the minimum drag speed the drag due to lift (induced drag) equals the parasitic drag (drag at zero lift). Extending slats & flaps increases primarily the parasitic drag. Hence the minimum drag speed reduces. Same when extending the gear.
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Thanks for excellent reply Hazelnuts! 
Now, a follow up question (a bit general one, I am afraid). At (roughly) what point during deceleration and configuring for landing on a modern medium/heavy swept wing transport jet does one enter the back side of the drag curve?
P.S. Induced drag is proportional to Cl^2. Doesn't it increase sigificantly when extending flaps/slats?
Now, a follow up question (a bit general one, I am afraid). At (roughly) what point during deceleration and configuring for landing on a modern medium/heavy swept wing transport jet does one enter the back side of the drag curve?
P.S. Induced drag is proportional to Cl^2. Doesn't it increase sigificantly when extending flaps/slats?
Last edited by Stuck_in_an_ATR; 26th October 2012 at 12:02.
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From: by the seaside
Half an answer as retired
Land flaps on the Trident made only a slight difference in stall speed reduction from take off settings. Their main use was to increase drag to enable the Speys to operate in a rpm regime that gave a fast throttle response.
Min drag clean was around 225knots and we normally only got well onto the back side of the curve when reducing to Va.
I believe that with modern design although Va may be on the backside of the curve it should be relatively flat whereas on the Trident it certainly wasn't - hence Cyprus airways broke one during training in Nicosia in1972.
The only other time that I flew noticeably behind the curve was a MD80 after severe wind shear coupled with a large temperature inversion when pitch power didn't work and I was forced to overpower the skipper and drop the nose.
Concorde min drag around 400 knots.
So The answer to one of your questions is only when you reduce to approach speed.
Land flaps on the Trident made only a slight difference in stall speed reduction from take off settings. Their main use was to increase drag to enable the Speys to operate in a rpm regime that gave a fast throttle response.
Min drag clean was around 225knots and we normally only got well onto the back side of the curve when reducing to Va.
I believe that with modern design although Va may be on the backside of the curve it should be relatively flat whereas on the Trident it certainly wasn't - hence Cyprus airways broke one during training in Nicosia in1972.
The only other time that I flew noticeably behind the curve was a MD80 after severe wind shear coupled with a large temperature inversion when pitch power didn't work and I was forced to overpower the skipper and drop the nose.
Concorde min drag around 400 knots.
So The answer to one of your questions is only when you reduce to approach speed.
