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I had a CFI recently tell me that all landings, especially crosswind landings, should end up with the full use of flaps when available.  He went on to say that if an aircraft has 40 degrees of flaps available that is what should be used.  I had read recently that in order to maintain greater control of the aircraft during a strong crosswind landing it is better to use no more than 20 degrees of flaps as this way a pilot can maintain greater control of the aircraft upon touchdown as a slightly higher speed would be required creating more air across the control surfaces for a longer period of time.

Which is considered to be the best recommended practice for crosswind landings:  More flaps or less flaps?

 

Thanks

8 Answers



  1. Wes Beard on Mar 01, 2013

    I once had a chief pilot tell me the same thing for the airplanes we were flying. I pulled out the POH and showed him where he was incorrect. The POH for a C-172 states that minimum flaps (20°) should be used in a crosswind landing though using more is recommended if the field length warrants the shorter landing distance.

    The chief pilots philosophy was that we should always touchdown at the slowest possible airspeed in case there is a crash. If we find ourselves needing to land without flaps due to a crosswind, we should just divert and go somewhere else.

    The best practice is to follow what the POH states. At least there, you can prove that you were following the guidance from the manufacturer.

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  2. Sam Dawson on Mar 02, 2013

    Some POHs say something about flap use in cross winds… some don’t.

    In transport category airplanes (at least the ones I have flown), ALL landings are full flap landings unless it is an EP (emergency procedure) that requires a 0 flap landing.

    There are advantages and disadvantages to both techniques. Personally I’ve noticed little difference between being able to land in a cross wind with/without flaps and prefer to use the maximum flaps possible to minimize energy.
    It’s a debate that will probably not be answered here.

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  3. Mark Kolber on Mar 02, 2013

    As Sam said, there are advantages and disadvantages to both.

    I think the primary advantage of full flaps is what the CFI in the question referred to – slowest touchdown speed means less opportunity for a problem, more ability to control if there is one, and less damage and injury if there’s a mishap.

    Although more effective flight controls due to a higher airspeed is probably the most often cited rationale for use of less flaps, there are others.

    Two common ones have to do with the crosswind slip. For example, the C172 has the famous recommendation against slips with full flaps due to the potential for aerodynamic cloaking of the rudder. Another is the recommendation in a number of airplanes to avoid extended slips with full flaps for fuel flow reasons. In both of those cases, the longer the slip phase of the crosswind landing, the more problematic in theory.

    But like Sam, I haven’t seen that much difference in practice. IMO it’s more a technique issue than anything else.

    BTW, one side-story: When I was trained, I learned reduced flaps for the aerodynamic plus and managed to pick up the idea that full flap landings were downright dangerous. That fear was not dispelled until I was working on my CFI. I commented to my instructor that I would never use full flaps in a crosswind landing. The next lesson took place with 15-20 KT direct crosswinds. My instructor said, “OK, I want to see full flaps crosswind landings.” It was a complete non-event.

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  4. Best Answer


    Brian on Mar 02, 2013

    “For example, the C172 has the famous recommendation against slips with full flaps due to the potential for aerodynamic cloaking of the rudder.”

    I’d like to clear this up, please don’t take offense. I myself spewed what some unkowning CFI told me before reading this book as well. :) The quote that follows is from a book written by the Cessna’s chief test pilot:

    —Quote: Cessna Wings for the World, p41—With the advent of the large slotted flaps in the C-170, C-180, and C-172 we encountered a nose down pitch in forward slips with the wing flaps deflected. In some cases it was sever enough to lift the pilot against his seat belt if he was slow in checking the motion. For this reason a caution note was placed in most of the owner’s manuals under “Landings” reading “Slips should be avoided with flap setting greater than 30 degrees due to a downward pitch encountered under certain combinations of airspeed, side-slip angle, and center of gravity loading.” Since wing-low drift correction in cross-wind landings is normally performed with a minimum flap setting (for better rudder control) this limitation did not apply to that maneuver. The cause of the pitching motion is the transition of a strong wing downwash over the tail in straight flight to a lessened downwash angle over part of the horizontal tail caused by the influence of a relative “upwash increment” from the upturned aileron in slipping flight. Although not stated in the owner’s manuals, we privately encouraged flight instructors to explore these effects at high altitude, and to pass on the information to their students. This phenomenon was elusive and sometimes hard to duplicate, but it was thought that a pilot should be aware of its existence and know how to counteract it if it occurs close to the ground.

    When the larger dorsal fin was adopted in the 1972 C-172L, this side-slip pitch phenomenon was eliminated, but the cautionary placard was retained. In the higher-powered C-172P and C-R172 the placard was applicable to a mild pitching “pumping” motion resulting from the flap outboard-end vortex impingement on the horizontal tail at some combination of side-slip angle, power, and airspeed. —End Quote—

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  5. Brian on Mar 02, 2013

    I personally choose to always use full flaps. If I need to salvage a bad landing with a massive slip I’ll just go around. Especially if it’s truly a challenging cross wind day. No sense in saving stupid in my opinion.

    True there are issues with control being effected with flaps. Namely the nose down pitching moment and subsequently reduced control in pitch. Yaw is not one of them, though the slower speed achievable with full flaps does reduce control effectiveness across all surfaces.

    That said, if you look at landing accidents, nine times out of ten it will go something like this: The pilot successfully put the aircraft on the ground, rolled for a short distance, and then suddenly lost control… Point is, most landing accident are because the pilot had too much speed (energy) and failed to maintain control after being on the ground.

    So keep it under control, land slow, and statistically you’ll be better off. That’s what I do anyway.


    On an ending note, here is one of my scary stupid pilot stories. Maybe someone can get something out of it, I know I did:

    I once got stuck up in the air (pushy boss) with a student in a 152. Let’s leave it at the winds were well into the 30s, directly across the runway, but thankfully not too gusty. I full flap landed, diagonally across the runway, and touched down with the stall horn blaring still in a crabbed flight. It didn’t feel nice, I’m sure my landing gear didn’t like it, and I will never let another person push me to fly stupid again. That being said, I am confident that the only reason I didn’t fill out an accident/incident report on this day was because the airplane simply didn’t have enough energy left for me to even worry about losing control. (Perhaps full aileron into the wind immediately on touchdown helped.)

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  6. Mark Kolber on Mar 03, 2013

    Brian, you’re correct. In the case of the Cessna it was blanketing of the horizontal tail, not the rudder. I was thinking of another aircraft.

    I’m not sure why I would take offense to the correction and extended explanation.

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  7. Brian on Mar 05, 2013

    Oh wow. Mark, it just clicked as to who you are. Great to have you on board! I wouldn’t expect you to take offense, but it’s hard sometimes to read/convey tone in through text. So I added that as a precautionary measure.

    By the way, this is shdw. :)

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  8. Mark Kolber on Mar 05, 2013

    Thanks Brian. But you never know… I was once posting on a forum without my real name and I was in the habit of changing third-party personal pronouns (I still do from time to time). In one post, I would refer to “he,” in another to “she.” There was one person who was convinced I had to be a woman.

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