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5 Answers

Floating during landing

Asked by: 8378 views
Aerodynamics

When landing, flare will take longer (floating) if you have a higher than landing speed; going faster reduces induced drag, and, ground effect is produced by induced drag. Why airplanes float? 

 

Sorry maybe i am misunderstanding something.

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5 Answers



  1. Bob Watson on May 14, 2013

    I think the more important point is that lift increases with speed. If you have too much lift, the airplane will want to keep flying (or floating, if you’re close to the ground).

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  2. Chris Carlson on May 14, 2013

    Induced drag does not creat ground effect, ground effect destroys so e of the airflow that causes induced drag, and makes lift more effective at given airspeed. When near the ground, lift will then be greater in ground effect at a given airspeed.

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  3. Mark Kolber on May 14, 2013

    …in the simplest terms, because, if you are above stall speed, the airplane is flying.

    You can, of course, =force= the airplane to land at the higher speed, but then you end up like this: http://youtu.be/C1fFrEuuMF8

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  4. Sam Dawson on May 14, 2013

    As Mark and the others pointed out you float because you have too much energy (speed), and as Mark’s video shows while floating is not great forcing an airplane to land is worse.

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  5. Brian on May 15, 2013

    Ground effect isn’t produced by induced drag, it’s produced by being within wing span proximity of the ground. It’s effects increase exponentially, meaning if you’re an inch off the ground you are experiencing a far greater impact than a wing span height. To give you an idea, look at the decrease in induced drag when compared with three different heights:

    Wing span ——— 1.4% decrease in induced drag
    1/4 Wing span —- 23.5% decrease in induced drag
    1/10 Wing span — 47.6% decrease in induced drag

    So why do we float and, more importantly in my opinion, why does ground effect make floating much worse? I need not rehash what’s already been discussed as the answer to the first half of this: we float because of excess forward energy. What about ground effects role though?

    To answer this we must know how the aircraft dissipates it’s forward energy. The answer is through drag. Since ground effect reduces our drag it slows this dissipation of forward energy. In other words, if you’re fast stay out of ground effect to bleed off your energy.

    —

    For a fun experiment take your typical trainer to a long runway: 4-5k will suffice. Approach in a normal landing configuration (full flaps, or 30 degrees, in the rare case you have a barn door type aircraft w/40+) at roughly 5 knots below Vfe.

    On the first pass round out over the numbers and stay as close to the ground as you can. Bleed off your speed till you land or reach a pre determined go around point. I use a point 2/3rds down the runway for this demo as a go around point. Do it a second time, but level off at least a wing span height. Note the tremendously different result.

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