What use is V(f)?

Discussion in 'Pilot Training' started by Lindberg, Jan 1, 2019.

  1. Lindberg

    Lindberg En-Route

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    If my understanding is correct, and maybe it isn't, V(F), "design flap speed," is what the designers intended V(FE) to be. 1) Is that correct? 2) If so, why would I care? Don't I just need to know the actual V(FE)?
     
  2. nauga

    nauga Pattern Altitude PoA Supporter

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    VF is the speed the manufacturer used when analyzing aerodynamic load cases with flaps extended and designing structure for same, and VFE is the max speed "allowed" with flaps extended. Ideally they would be the same speed, as VFE cannot be greater than VF (per CFR14 part 23.1511) and if VF is much larger than VFE the airplane is designed for loads it doesn't experience in flight.

    ETA: VF is a speed used in design and analysis and VFE is an operating limitation.

    Nauga,
    flappin'
     
    Last edited: Jan 1, 2019
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  3. Let'sgoflying!

    Let'sgoflying! Touchdown! Greaser! PoA Supporter

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    aircraft designer thing vs operational (pilot) thing
     
  4. Clip4

    Clip4 En-Route

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    Think of the speeds this way, Vf is the speed you will not exceed the design and damage the fully extended flap. Vfe is the speed that provides for less stress fatigue and wear on the flap and flap mechanisms with the flap fully extended. Vlo is the speed where moving the flap does not cause damage.
     
  5. TK211X

    TK211X Pre-takeoff checklist

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  6. Lindberg

    Lindberg En-Route

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    So why do I need to know what Vf means for the commercial written? Seems they'd ask about Vfe instead.
     
  7. Unit74

    Unit74 Final Approach

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    Cuz it's the gubment...... Just memorize it and move on. You using Sheppard? I just bought the CAX test prep last week.
     
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  8. Lachlan

    Lachlan En-Route

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    F that. Just slip.
     
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  9. Lindberg

    Lindberg En-Route

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    ASA Prepware
     
  10. nauga

    nauga Pattern Altitude PoA Supporter

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    I can see the FAA testing to see if you know the difference between a real operating limitation and a design limit, but this seems like a strange way to do it. Do the exam prep companies rely on reported questions or is there a government source for the Vf question? IOW could it be a mistake in the material you have? ISTR the FAA stopped publishing the question bank a long time ago. I'd be curious to know if you see it when you take your written.

    Nauga,
    and a target of opportunity
     
  11. Lindberg

    Lindberg En-Route

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    I'll let you know after I take the test. I've got the book and online (from the same source) and both have had Vf as well as Vfe.
     
  12. Fearless Tower

    Fearless Tower Touchdown! Greaser!

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    Vlo is Landing Gear Operating Speed. Has nothing to do with flaps.
     
  13. Jim_CAK

    Jim_CAK Pre-takeoff checklist PoA Supporter

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    I am using multiple sources for the Commercial written and they all distinguish between Vf and Vfe.
    @write-stuff - Any insights into how prep software test questions are determined?
     
  14. Lindberg

    Lindberg En-Route

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    Many of the questions on the actual test were either very close or exactly what I got from ASA. Unfortunately I didn't get a question on either Vf or Vfe, so I'll never know where that came from.