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Thread: No Do Overs! Defined Minimum Maneuvering Speed or D.M.M.S.

  1. #21
    Senior Member jiott's Avatar
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    Default Re: No Do Overs! Defined Minimum Maneuvering Speed or D.M.M.S.

    I believe that the DMMS can be defined for any configuration you want; it makes the most sense to me to define it in my normal landing configuration (1/2 flaps).

    You never want to pull flaps on an engine out situation if you want to maximize your glide distance. Best glide is speed is always set with clean configuration. Only after the landing spot is assured would you pull flaps to add drag and steepen your approach.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  2. #22
    Senior Member PapuaPilot's Avatar
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    Default Re: No Do Overs! Defined Minimum Maneuvering Speed or D.M.M.S.

    In the video the instructor said that DMMS is 1.3 Vs plus 8% or (1.3 * 1.08 = 1.404). He said the 8% is the increase in stall speed in a 30 degree bank which has to do with the increased load factor in a bank. I believe his rational is that if you keep your plane above DMMS you can safely maneuver and bank up to 30 degrees with out risk of LOC or stalling.

    Using Vs (your clean stall speed) is the most conservative choice. If you add flaps or are flying at a lower GW your stall speed will be even lower, giving you more margin from stall at DMMS.
    Phil Nelson
    A&P-IA, Maintenance Instructor
    KF 5 Outback, Cont. IO-240
    Flying since 2016

  3. #23
    Senior Member aviator79's Avatar
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    Default Re: No Do Overs! Defined Minimum Maneuvering Speed or D.M.M.S.

    Quote Originally Posted by jiott View Post
    You never want to pull flaps on an engine out situation if you want to maximize your glide distance.
    Thanks for saying this Jim. I hear other flight instructors tell students things like "The first 15 degrees of flaps give you more lift than drag, after that, they give you more drag than lift." Unless your airplane is of a very stupid design, this is a false statement that leads people to do dumb things like try to add flaps to extend their glide.
    --Brian
    Flying - S7SS

  4. #24
    Senior Member 109JB's Avatar
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    Default Re: No Do Overs! Defined Minimum Maneuvering Speed or D.M.M.S.

    Quote Originally Posted by aviator79 View Post
    Thanks for saying this Jim...
    Not entirely true. You should always use what the POH/AFM says to use and not rules of thumb one way or another.

    In the case of at least one airplane that I know of, the DA20-A1 Katana, the best glide is accomplished with T/O flaps and not full up. This is likely because the "0 degree" flap setting is a reflexed position for increased cruise performance. Now later versions of the Katana aren't the same and use flaps up (Cruise position) for best glide angle.

    In the case of the Kitfox, at least my KF IV, the flaps have an infinitely variable range and are also used as the pitch trim. In the takeoff position there is a fair amount of up flap still available. So is glide in a Kitfox better with flaps fully up, at takeoff position, or somewhere else???

  5. #25
    Senior Member aviator79's Avatar
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    Default Re: No Do Overs! Defined Minimum Maneuvering Speed or D.M.M.S.

    Okay, there are some designs that aren't "stupid" that have some combination of flap setting and airspeed that yields a higher L/D than the flaps up position at any speed. And I very strongly agree that the POH/AFM is the authority on what do do when your engine quits.

    I still maintain that instructors who categorically state that the first notch of flaps gives more lift than drag very much misunderstand what flaps do and are propagating information that could lead their students to do something dumb if applied in the wrong context.
    --Brian
    Flying - S7SS

  6. #26

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    Default Re: No Do Overs! Defined Minimum Maneuvering Speed or D.M.M.S.

    I’ve been sitting in PANC enjoying the reserve life of the celebrated international airline variety and just came across this thread.

    What this instructor is teaching is spot on and should be taught to all students, regardless of their experience level. Traditionally what has been taught and ingrained is to pitch for best glide, look for a spot to land, and commit. In the airline industry this is taught completely different and we’ve moved away from the “don’t lose altitude” mindset into the “don’t lose control and hit cumulus granite mindset.”

    The training after the Colgan crash in Buffalo has further pushed this training to include EET (extended envelope training), or in layman’s terms extreme upset recovery. Pilots have been taught forever when in an upset condition to level the wings and then lower the nose; modern and advanced practices (including aerobatic/military training) are now focusing on unloading the wing. The ONLY way to unload when in an upset recovery (extreme nose high and extreme bank scenario) is to push, regardless of bank angle. The same applies to engine failure after takeoff, you push to ensure no loss of AOA which leads to a decrease in speed at a very critical phase of flight.

    The concept of a DMMS is knowing the slowest you can go at EVERY configuration setting so that you have both stall AND bank protection. As long as you do not allow yourself to get slower than DMMS at XYZ configuration you have maneuvering capability. Once you get slower than that speed you have two options, lower the nose or add more lift (extend the flaps).

    By experimenting with each flap setting and applying the DMMS formula you can set a safe DMMS speed for each flap setting. This would best be recreated at the worst case scenario, i.e. max gross weight/cg limit. That often times isn’t feasible, but it gets you closer than you were before without this knowledge; it also helps prevent the student from initially pitching for Vg and trying to “extend” the glide or try to make the impossible 180° turn. If they can unload and stay in control being forced to choose options in front of them, their survival rates increase tremendously. The simple act of immediately lowering the nose in a takeoff may reveal potential landing options that they may not have seen before, and likely would miss as they continue to pitch back and end up in an uncoordinated state of flight.

    This is especially important in mountain flying as the “off-field” options and maneuvering room are severely limited. Your only option with an engine failure after takeoff from a mountain airstrip may require at least a 30° bank to make an acceptable landing area. Knowing the DMMS for different configurations is literally the difference between life and death.

  7. #27

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    Default Re: No Do Overs! Defined Minimum Maneuvering Speed or D.M.M.S.

    Here is another of his videos with some very good info,

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