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6 Answers

Flaps to the climb angle.

Asked by: 3463 views Aerodynamics

If you keep airspeed V2. Why is the climb angle higher if you use 5 degree flaps instead of 30 degree when taking off?


If the flaps is 30 degree and airspeed is the same (V2) I think both of the lift and drag should be higher. The climb angle should be higher.

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6 Answers

  1. Bill Trussell on Mar 08, 2013

    To properly answer this question you would need to know the aircraft type or the flap type under consideration.

    In transport category aircraft the first increment of flaps usually results in an increase in the wing area (fowler or some variation on that type of flap). There is also the possibility of some other lift augmentation being provided at various stages of flap application.

    For most aircraft I have found that the first applications of flaps is more lift than drag. With higher increments it is the opposite, with more drag being applied than lifting capability.

    In the generic example you cited above I would say the cause of the condition is more drag at 30 degrees vs more lift at 5 degrees for the same speed.

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  2. Wes Beard on Mar 08, 2013

    The aircraft climbs due to excess thrust. Another way to think about it excess thrust equals excess energy. Energy that is being converted to potential energy. Flaps at 30 degrees sap up a lot of that energy in the form of drag.

    As a result, the plane will not climb as quickly with flaps 30 than at flaps 10. Bill is correct in the type of flaps determines how some of that excess energy is converted, either to potential energy (lift) or drag.

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  3. Brian on Mar 09, 2013

    All flaps, regardless of type, add drag. Sure they add lift, but we don’t climb because of lift so the addition of lift means nothing if we keep airspeed the same. Now, on the other hand, if you fly at a lower speed climb angle may increase with the use of flaps.

    Rate of climb will never increase from any use of flap as it is purely a thrust available minus drag equation. And the flaps only added to the drag side of that equation.

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  4. Nathan Parker on Mar 09, 2013

    The climb angle is determined by the quantity of thrust in relation to the quantity of drag. Less drag, higher climb angle.

    This idea of “more lift” is meaningless; the lift on an airplane in unaccelerated flight is pretty much equal to the weight of the airplane. If you have more lift than that, the airplane will perform a loop. πŸ˜‰

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  5. Brian on Mar 09, 2013

    “The climb angle is determined by the quantity of thrust in relation to the quantity of drag. Less drag, higher climb angle.”

    This isn’t applicable to the OP as speed is constant in his two cases. However, we’ve talked about this in the past: Since thrust increases when you reduce speed and flaps allow you to fly slower it is conceivable that the thrust gained may out weigh the drag penalty.

    And I don’t know what you’re talking about, lift makes you climb and weight makes you fall. It’s clear as day in the 4 forces picture! πŸ˜‰ *sarcasm*

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  6. Nathan Parker on Mar 09, 2013

    “This isn’t applicable to the OP…”

    Au contraire….it’s always applicable. And the idea that thrust increases with low airspeed is a propeller thing, not a turbojet thing, but, of course, today’s turbofans behave more like props at low airspeed…. Not really important for this question, though.

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