Pitch vs. power - causes of excessive sink and hard landings

Discussion in 'Pilot Training' started by DaveInPA, Jul 5, 2020.

  1. Stewartb

    Stewartb Final Approach

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    Seriously? Your flight instruction didn’t include flying behind the power curve? Go find a better instructor and learn about it.
     
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  2. Silvaire

    Silvaire En-Route

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    Yup. Forget the “but” and go with your first thought there. You’re on the right track.
     
  3. JonH

    JonH Pre-takeoff checklist

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    You go fly with him lol.
     
  4. RoscoeT

    RoscoeT Pattern Altitude

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    ASI, fine - VSI, utterly pointless, forget it, it doesn't matter. VSI is one of the most useless instruments in the airplane anyway and shouldn't be referenced during the landing process. For any given airspeed, it'll change with load, power setting, and flap setting, slipping, not slipping, etc. The feel and responsiveness of the elevator will tell you everything you need to know about your energy state as you break the glide...if you learn it and pay attention to it.

    Learn backside of the power curve, but I can't imagine you were actually approaching this slow in this region. You're not even close at 1.3Vso. 65KTS in a 172 is more than 1.3Vso. You were probably pulling power off at the same time you started to round out and are confusing the change in descent rate from pulling power with something you did with the elevator. Do some power off approaches to landings. This is a Cessna 172. It is basically a glider.
     
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  5. kgruber

    kgruber En-Route

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    In a "perfect" landing the pitch is moving logarithmically in one continuous motion. From slow to fast.

    If you EVER have to pull and then stop for a second, it is poor form.
     
  6. Salty

    Salty Touchdown! Greaser!

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    Sure. If there are no gusts or direction changes in the wind.
     
  7. kgruber

    kgruber En-Route

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    You have keen insight into the obvious
     
  8. Salty

    Salty Touchdown! Greaser!

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    How often do you land with no gusts or changes in the wind?
     
  9. RoscoeT

    RoscoeT Pattern Altitude

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    Calm conditions happen plenty. Can we move on?
     
  10. Salty

    Salty Touchdown! Greaser!

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    Sure, you can move on. I didn't want a student to think they were doing something wrong because they couldn't land with one continuous motion every time. In Florida it's pretty rare you can do that.
     
  11. RoscoeT

    RoscoeT Pattern Altitude

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    If you read how it was written, I really don't think that was gonna happen. There is such a thing as in-person flight instructors and common sense that exist outside of the internet forum world.
     
  12. tspear

    tspear En-Route

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    I am by no means an expert, but I have never moved the yoke in a logarithmic fashion. That seems like a recipe for disaster and a good way to jam the controls.
    That also seems like a good way to get POI with a low wing that lands rather flat. My time is mostly Cirrus, with a little Diamond, Mooney and Piper with the occasional Cessna.
    Not one of the low wing planes do you "accelerate" or change the rate you pull the yoke back in the flaire. It was always a steady motion. For Cessna, I do not recall (not enough time in them).

    Tim
     
  13. RoscoeT

    RoscoeT Pattern Altitude

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    "Perfect" was in quotes. Assuming you land as slowly as possible, with the nose as high as your airplane will allow, the airplane is constantly slowing as you increase your pitch attitude. This means in order to keep holding the tires off the runway, you must accelerate the rate at which you move the elevator aft due to the constantly decreasing elevator authority. That is all. This is nothing to get hung up on.
     
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  14. FlySince9

    FlySince9 En-Route

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    BULL! that's about the stupidest thing I've ever read on this board... And that takes some doing...
     
  15. Dan Thomas

    Dan Thomas Final Approach

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    Were you ever an instructor in 172s and other airplanes, seeing students doing that very thing in soft-field landings and getting too slow, which means a high pitch attitude? And were you ever a mechanic that had to look for a cracked rear fuselage bulkhead (tail tiedown ring punching up into it), or a kinked stabilizer rear spar, caused by the lead weights on the elevator horns yanking down on the stab? Or cracked rudder hinges, cracked when that big lead weight on the rudder horn kept moving down, loading the rudder hinge brackets vertically and bending them and cracking them? Just what is your experience?
     
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  16. tspear

    tspear En-Route

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    Could be the fact I am in IT; so I am exposed to logarithmic functions and performance calculations often enough to know there is no way this applies. So his statement came across as basically BS.
    I do not believe I have "accelerated" the speed of pulling back the yoke in the flair or after the wheels touch (for aerodynamic braking ever in my life); if I have it has never been enough of a delta to notice.

    Tim
     
  17. RoscoeT

    RoscoeT Pattern Altitude

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    Doesn't matter whether or not you've done it, the statement made conforms to the reality of physics. Doesn't mean it's REQUIRED by you other or other pilots to do. And we're talking before the wheels touch, not after.
     
  18. brcase

    brcase Pattern Altitude

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    And if you don't have quite enough power you will do a great soft field landing.
    Brian
    CFIIG/ASEL
     
  19. brcase

    brcase Pattern Altitude

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    Great Idea but 65kts is ok to approach at, but way to fast to fly down the runway. I would guess if you touch at 65kts you will touch nose wheel 1st, at a minimum very flat.

    don't watch there airspeed, flying down the runway is an entirely visual maneuver, hold it off the runway and set the power so you slow until the nose is about our takeoff attitude, probably cowling just about on the horizon. then fly down the runway at 2 feet as far as you can or want to.

    Brian
    CFIIG/ASEL
     
  20. brcase

    brcase Pattern Altitude

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    in 7000 hours of flying I don't recall ever once looking at the VSI during an approach to landing. I probably have but it wasn't memorable.

    Glancing at the Airspeed during the approach is a very good idea, as this is the time you can easily be deceived by the illusions of being close to the ground and wind effects as to how fast you are going. Trimming for the correct speed and letting the plane fly the approach helps a lot, but still good to double check frequently. If it feels like you are going fast you will likely slow down even if you really are slow. Being consistent on your approach speeds will really help you be consistent in your landings. As you start doing short field approaches it becomes critical to maintain the correct speed. In most performance speeds the penalty for being 5kts fast is usually about 1/2 the penalty of being 5kts slow.

    Once Below 50-100 feet AGL landing is an entirely visual maneuver and you shouldn't be looking in the cockpit at all.

    As to your aerodynamics question, it has sort of been answered in that as you slow down you enter the back side of the drag curve and the plane slows down much faster as you raise the nose. In order to maintain altitude you must pull back a bit faster as the Angle of attack and drag increase. In reality this really isn't noticeable and should be more just a continuous pull because you don't want ti maintain altitude but just slow the descent as the plane descends to the runway. If you try to pull to just maintain altitude the increase in drag increases your descent is usually just enough for a nice touchdown if you are reasonable distance above the runway. I often use the phrase "when you feel the plane sinking 'that sinking feeling' you need to pull"

    My guess as to what you are doing is rounding out to high for the speed/configuration you are at approaching at. (The less excess energy you have the close and faster you will need to round out above the runway.) Then you slow down to high above the runway and the plane starts dropping and you don't have the energy to stop the descent before you touch down, or you are not pulling fast enough to stop the descent. The faster you are dropping the faster you need to pull to stop the descent. Adding more energy (power or speed) or less drag (less flaps) will give you more time to ease it down to the runway. You might have to aim a bit closer to the end of the runway to land at your designated spot, as you might float a bit more than you are used to. If you don't over do the power or speed,you will find you will not float very far.

    Brian
    CFIIG/ASEL
     
    Last edited: Jul 9, 2020
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  21. brcase

    brcase Pattern Altitude

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    Bit of Trivia, the only required instrument in a Schweitzer 2-33 is an Airspeed Indicator. Pretty obvious what they think is important.
    Brian
    CFIIG/ASEL
     
  22. brcase

    brcase Pattern Altitude

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    someone can probably prove me wrong. I know better than to say you "can't". But in my experience it is very difficult to touch the tail of a 172 on the ground without significant power (like a soft field landing or takeoff). Touching the tail with 30 degree flaps or more is pretty challenging even with power, probably not impossible.

    Brian
    CFIIG/ASEL
     
  23. FlySince9

    FlySince9 En-Route

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    The OP is not a student. This is a guy working on his commercial. To arbitrarily state that doing this is dangerous is ridiculous. If you can’t keep your tail from smashing into the runway, you’ve got a serious problem.
    I have over 500 hours in Skyhawks and have done this exercise many times. You don’t have to be a CFI or a mechanic to keep your tail from smashing into the runway. Keeping an airspeed just above stall and enough power to stay airborne does not involve an attitude any more aggressive than a normal flare.
     
  24. dmspilot

    dmspilot Final Approach

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    Dude nobody said that they can't keep from striking the tail on the runway. But if someone wanted to strike the tail on the runway, you perfectly described how one could do it.
     
  25. Stewartb

    Stewartb Final Approach

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    In a 172 I'd say hitting the tail is from going too fast. Too slow and you hit the nose gear first. And yes, I used to own one.
     
  26. dmspilot

    dmspilot Final Approach

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    Are you talking airspeed or how fast you pull the elevator back? :confused:
     
  27. FlySince9

    FlySince9 En-Route

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    Dude... I say again... BULL!
     
  28. flyingron

    flyingron Touchdown! Greaser! PoA Supporter

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    It's all about ENERGY. You have a certain amount of energy that is going to get you to the touchdown point. You can change all the pitch you want and it won't help substantially (there will be slight variation due to drag changes as you depart from the best glide speed). You have a few things that can decrease energy (less power, adding drag from flaps or slips), and but one to add energy (more power).

    Once you've mastered energy management, it's just a matter of getting the wheels down nicely: straight (unless you're flying an Ercoupe or crosswind gear) and the mains first.

    You have to understand which one you're having problems with. A lot of people think it's the latter, but if you come in with too much energy you're going to float or balloon (or in the worst case slam it down to force it), too little and you're going to come up short or drop it in.
     
  29. Dan Thomas

    Dan Thomas Final Approach

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    If you try to hold it off the runway with some power, and the airplane starts to sink, the tendency is to raise the nose instead of adding power. That slows the airplane further and eventually it sinks suddenly, possibly with the wing roots beginning to stall, and it comes down nose-high and can strike the tail. The 172 has minimal tail clearance in the normal touchdown attitude and it's easy to strike it. Now, the older 172s had a higher ground stance and better clearance, but in the late '60s Cessna lowered the airplane and created this problem.

    And I had Commercial students--some of them MY students---make this mistake.

    If one pushes the tail down to the surface and measures the wing's chordline angle, you see that it's at around 12 degrees to the surface. It's impossible to stall the airplane in a normal nose-high three-point landing, since stall angle is around 17 degrees, and when you are moving parallel to the surface the AoA will be about that. But if you're two or three feet up you can get that nose much higher without stalling, and when sink develops at that angle the stall is right behind it as the flight path turns downward.

    I replaced countless tiedown rings on 172s due to this. I've seen the ring broken off and the skin at the bulkhead worn away. I'be had to replace cracked rudder hinge brackets and once had to do a bunch of work to a 150's rudder when some student banged the tail hard on the runway and the rudder horn---that tab that carries the lead weight at the top of the rudder---got bent downward and buckled the sheet metal. I've seen the elevator horns pulled loose on the elevator due to the same thing. Always looking for kinked stab aft spars and buckled sheet metal skin. The stab front spar is already easily broken, so that's an automatic check. People pushing down on the stab to turn the airplane on the ground can crack it.

    As a Director of Maintenance I was constantly receiving information such as SAIBs and SBs and SLs and service manual updates based on stuff other mechanics were finding, and often found it myself if I went looking for it. The average pilot/owner has no idea what all is involved with aircraft maintenance and sometiomes doesn't believe it until he sees it. I'm still waiting for FlySince9's qualifications and experience details.

    Landing fast results in a nose-low landing and possibly touching nosewheel first, which can have some nasty outcomes. It's basic aerodynamics: higher speed requires less angle of attack to support the airplane's weight, and lower speed requires a higher angle of attack to support that same weight.
     
  30. flyingron

    flyingron Touchdown! Greaser! PoA Supporter

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    In a 172, no part of the wing (roots or otherwise) is going to stall. Even if it did, it won't make the tail hit. The tail hits because someone pulls back too hard close to the ground, usually because they fear they are going to hit early (every stail strike I've seen has been that, or overrotation on soft field takeoffs).
     
  31. FlySince9

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    For all you tail strikers... Flying a 172 down the runway a foot or two off the runway, just above stall, and using power to keep it there is no more dangerous than a normal landing where power is added just before touchdown to soften the landing. The only difference is putting in enough power so the airplane does not land. The archaic, analytical math done above is how these conversations digress from a very simple concept. Fly the dam plane and DON'T STRIKE THE TAIL! As the pilot, you do what needs to be done to get a desired result. If you are dumb enough to be 10 feet off the runway and stall the thing... you might definitely bend something. That is just an example of going for the ride and not being in control of the outcome. If you're doing the exercise correctly there is virtually no chance that will happen. If you are 10 feet above the runway and getting too slow... GO AROUND!
     
  32. eman1200

    eman1200 Touchdown! Greaser! PoA Supporter

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    Bro do you even lift
    You’re a tail striker.
     
  33. FlySince9

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    I'm talking airplane tail...Not the 2 legged kind...
     
  34. Salty

    Salty Touchdown! Greaser!

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    [​IMG]
     
  35. FlySince9

    FlySince9 En-Route

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    That's a wet Striker....