In which part of the flight does a plane reach maximum lift? My logic: I think a plane reach maximum lift in a horizontal flight, when a plane start rolling on a runway, landing gear produce more friction and when landing, flaps and landing gear generate more fricition with the air. In conclusion i think the maximum lift is like this: Horizontal flight > Takeoff > Landing
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$\begingroup$ You seem to be confusing max lift to minimum drag. If you haven't heard the term L/D Max before, (best lift to drag ratio) I suggest you research that. It may be what you are looking for... $\endgroup$– Michael HallApr 9, 2021 at 14:30
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$\begingroup$ If it's still on the runway, it seems obvious that it's not generating as much lift as if it were climbing, no? $\endgroup$– jamesqfApr 9, 2021 at 16:25
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$\begingroup$ Do you understand the difference between lift as a force in pounds or Newtons, and lift as a coefficient? $\endgroup$– quiet flyerApr 11, 2021 at 13:31
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$\begingroup$ Part of this question seems redundant with-- aviation.stackexchange.com/a/56476/34686 -- key sentence "Clearly, Lift is less than Weight in a powered climb" $\endgroup$– quiet flyerApr 11, 2021 at 13:33
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$\begingroup$ The above was for a linear climb. But think about what happens whenever the flight path is curving ("bending") upwards. A curvature requires a "centripetal force", which means an excess force above and beyond what is required to oppose gravity. If the flight path is initially near horizontal and then curves upward, lift will be > weight until the upward curving stops (or until the flight path has curved well above horizontal). Isn't this a good description of what happens the instant the wheels leave the ground, and for a second or two thereafter? ) $\endgroup$– quiet flyerApr 11, 2021 at 14:33
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3 Answers
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In a steep turn, at high speed.
In addition to the lift needed to compensate weight, a turn requires the wing to produce additional lift to accelerate the aircraft sideways. Speed is required so enough dynamic pressure is available to produce all that lift.
The same happens at the bottom of a tight loop when weight and the lift needed to compensate centrifugal forces add up.
A third high-lift scenario happens when the airplane flies at high speed through a strong vertical updraft. In order to not overstress the structure, maximum speed is limited in gusty weather.
answered Apr 9, 2021 at 14:11
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1$\begingroup$ Would it be correct to say that the lift is proportional to whatever the G meter (if equipped) is reading? $\endgroup$ Apr 9, 2021 at 16:45
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1$\begingroup$ @FredLarson in addition it is proportional to the airplane mass (as lift is force, not acceleration) too, which can be also variable even in flight (fuel consumption). $\endgroup$– MartinApr 10, 2021 at 11:45
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In level flight the lift must equal the weight of the aircraft (which will typically reduce as it burns fuel). If lift exceeds weight then the aircraft will accelerate upwards; thus is something that we typically see at takeoff, and hopefully just before landing when the aircraft‘s rate of descent drops to almost zero. The maximum lift would be generated when the aircraft pulls out of a steep dive, converting kinetic energy into lift which would allow more lift than could be generated by the power of the engines alone.
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Technically speaking any airplane generates maximum lift just before the wings come off. Whether that is interesting to obtain or not, depends on your need for adrenaline.
During a normal flight in a one engine GA airplane, the moment at which most lift is created is during the first few seconds after rotation.
In more agile airplanes like military jets, maximum airlift is created well beyond bed time, which is not desirable at all.
The most common situation for any airplane to get closest to its maximum airlift is when it hits turbulent updraft immediately after turbulent downdraft, which occasionally is known to make the wings come off.
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$\begingroup$ Re: "During a normal flight in a one engine GA airplane" -- I wonder why you specified "one engine", tends to give the impression that on a typical flight in a Pitts Special or even a Cessna 152 the max lift (at least per unit weight) is less than in a typical flight in a King Air or 747. Not true, at least the way I fly-- $\endgroup$ Apr 27, 2021 at 15:29
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$\begingroup$ @quietflyer You don't fly 747s or King Airs, do you? Whatever, Its not the point I'm trying to make. And I don't fly that way either, but that doesn't mean anything. $\endgroup$– user55607Apr 27, 2021 at 16:03