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4 Answers

Greatest altitude shortest distance

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After takeoff, flying at Vx, will a flaps or no flaps configuration achieve the highest altitude in the shortest distance?

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4 Answers

  1. Wes Beard on Feb 22, 2014

    It depends on the aircraft. What you want to do is minimize the drag and maximize the power available from the engine. Remember, the aircraft climbs due to excess thrust.

    I would imagine that if the flaps are below around 20° or lower it might be better to have flaps. Any flaps in excess of around 20° will cause too much drag.

    The C-172N POH states Vx is with flaps up and the short field takeoff technique is with flaps up.

    A C-172S G-1000 shows Vx for both flaps 10° and flaps up. The short field technique is to climb with flaps 10° till obstacles are cleared and then accelerate and slowly retract flaps.

    A Piper Arrow states Vx is also with flaps up and the short field takeoff technique is with flaps 25° and slowly retract flaps once Vx is achieved.

    A C-182RG POH states VX is with flaps 20° but also gives Vx with flaps up. The short field technique is with flaps 20° and gear down till obstacles are cleared then pitch down and accelerate and reduce flaps.

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  2. Brian on Feb 22, 2014

    “and maximize the power available from the engine.”

    Thrust, not power for climb angle.

    OP, flaps add drag that you need to minimize. On the other hand they allow you to fly at a slower speed and thrust is inversely proportional to speed. In other words, flying slower means having more thrust. (In a propeller aircraft)

    So it is conceivable that the thrust provide by allowing you to fly slower is overcoming the drag the flaps have added. However, as a general rule this will not be the case. You will usually get a better Vx climb clean than with flaps.

    Though, as Wes points out, this is airplane specific. Some STOL aircraft achieve their best climb angle with full flaps due to the tremendously slow speed it allows them to fly. Or so I’m told, I don’t personally have flight experience in a plane that has such a capability!

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  3. Brian on Feb 22, 2014

    Here Mark: http://www.askacfi.com/5494/how-to-explain-flaps-to-a-student-pilot.htm

    From someone you might know 😉 Read Nathan’s response to this thread. Namely, “I’d generally limit the discussion to ensuring that they understand….snip… 3) they increase drag.”

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  4. John D Collins on Feb 25, 2014

    Also, Vx is configuration dependent. Vx with flaps down is different than with flaps up. Now a days, the POH often doesn’t provide information on Vx or Vy in any configuration other than with flaps and for a retractable gear with the gear up (IOW in the clean configuration). For example, the book speed for my Bonanza for Vy is 96 Kts, but that is clean configuration. With the gear and flaps down, Vy is 71 Kts. Big difference based on configuration in my aircraft. BTW, the 71 Kts is not published as a Vy in the POH, but is provided in an earlier manual called the Owner’s Manual. It is sort of provided in the POH in an obscure way in that there is a “Balked Landing Speed” used to climb out if you decide to go around, strangely it is 71 Kts, I wonder why.

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