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Imagine a piston engine airplane (let's say a DC-3) flying at cruise speed and altitude over a calm sea, trying to reach an unreachable airstrip straight ahead, just above sea level. Fuel is very low and ditching may occur at some point even if highest lift to drag to consumption ratio is achieved.

Would a ground effect low horizontal flight increase the range? That could mean ditching closer to the shore, and getting help sooner (or even landing safely).

If yes, is it also the case for a modern jet airliner usually cruising faster and in a much thinner air, and are there some emergency procedures or regulations about that?

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    $\begingroup$ I can't speak for the physics of that, but attempting cruise speed on a DC-3 in ground effect sounds like a rapid way to smash your aircraft into the sea at full speed. While physically this might have some benefits (Though I doubt it - altitude is energy / cash in the bank) the risks would almost certainly outweigh any rewards. $\endgroup$
    – Dan
    Aug 18, 2017 at 11:54
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    $\begingroup$ @Dan I suppose the comparison is idle descent to sea level, cruise there and ditch, vs stay at cruise level, then idle descent and ditch. Either way, you're using the altitude energy at some point, and the plan is ditching after all (let's assume a highly skilled pilot and a mysteriously calm sea) $\endgroup$
    – Sanchises
    Aug 18, 2017 at 12:45
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    $\begingroup$ @Sanchises you suppose right, excellent summary, thanks! $\endgroup$
    – user721108
    Aug 18, 2017 at 13:07
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    $\begingroup$ Not too high nor too low... are you trying to rewrite the Icarus Legend? $\endgroup$
    – jean
    Aug 18, 2017 at 19:26
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    $\begingroup$ @Dan: Well, you can do it with a Cherokee over a dry lake bed. (Don't ask me how I know :-)) $\endgroup$
    – jamesqf
    Aug 19, 2017 at 6:15

3 Answers 3

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When flying close to the ground, there is an important reduction of induced drag, the larger the closer to the ground one flies, so the airplane needs less engine thrust to keep a given airspeed. Anyone who has made a low pass over a long runway may attest this...

Flying in ground effect is a nice way to save fuel and extend the range. I remember reading that it was often used by carrier planes returning from a mission low in fuel...

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  • $\begingroup$ Interesting. I'm guessing there's little to no testing done to find fuel usage / range in ground effect, to compare it with a higher max range / lean altitude. Maybe military or crop dusters might have more info... $\endgroup$
    – Xen2050
    Dec 27, 2017 at 22:44
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During glider training, I was taught to use ground effect to my advantage if I was going to come up short on final. It's been a long time, but my recollection is that I was taught to get to ground effect efficiently (no drag devices out, appropriate airspeed), and then ride in it as close the ground as is safe until (hopefully) reaching the runway. A glider in a clean configuration can go a long, long ways in ground effect.

I was also taught to maintain some excess energy on final, to speed up through significant sink, etc. Riding in ground effect was a "when all else has failed" measure.

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    $\begingroup$ While I can't speak for glider training in the past, but I was taught (2015-2016) to always have some spoiler deployed on final. Some instructors teach half, some 2/3rds, but both with the idea of having options both if you are low and slow or high and fast. $\endgroup$ Aug 18, 2017 at 18:50
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    $\begingroup$ I believe I was taught the same. So "maintain a clean configuration" isn't quite right. I'll edit that, and thanks for pointing it out. $\endgroup$ Aug 18, 2017 at 19:48
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There has been an incident with a propeller machine where one engine failed.

Cause the other engine would run hot while keeping the altitude, the pilot decided to descend till he reach ground effect to reduce the stress of the one last engine. Also the pilot asked the passengers to throw out their luggage to reduce the ballast. Finally they flew over one hour in ground effect and reached land.

A modern airliner would most likely glide cause of the much higher cruise height. See Gimli Glider and Air Transat Flight 236

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    $\begingroup$ Do you have a source where we could find more about this "incident" ? $\endgroup$
    – Jimy
    Aug 18, 2017 at 13:38
  • $\begingroup$ I'm going to look for it. If I remember right, it was mentioned in the "Mayday" series. $\endgroup$
    – merspieler
    Aug 21, 2017 at 9:10

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