Why does an aircraft take off?
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Ya well there you go, if you have 150kt wind then you've achieved enough airflow over the wing to produce lift. The only thing left to do is to achieve the right angle of attack. That's why even with 150kt winds you still need to PULL BACK ON THE CONTROLS to get the right angle of attack before the plane lifts off.
If you happen to live on the east coast of the US right now go to any flight school or GA airport and you'll see them tying down all their airplanes due to the impending hurricane. Thats because with the high winds there can be enough speed over the wings to have the planes lift off, no thrust required.
If you happen to live on the east coast of the US right now go to any flight school or GA airport and you'll see them tying down all their airplanes due to the impending hurricane. Thats because with the high winds there can be enough speed over the wings to have the planes lift off, no thrust required.
The query was "During what phase of flight is lift the greatest?" and the answer was "In general, the takeoff".
All thrust does is provide speed/airflow over the wing to create the lift.
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Don't forget aircraft use high lift devices at take off / landing too - flaps and slats to increase the lift available at lower speeds. Consequently, the greatest lift is available during approach, when all the high lift devices are deployed to their maximum settings.
If you think of it this way:
An L1011 can weigh about 225tons at take off.
The engines can only produce about 70 tons of thrust.
To make the 225 tons go upwards, the aircraft structure would have to generate 155 tons of lift even if the engines pointed straight down as they couldn't overcome the weight of the aircraft.
If you think of it this way:
An L1011 can weigh about 225tons at take off.
The engines can only produce about 70 tons of thrust.
To make the 225 tons go upwards, the aircraft structure would have to generate 155 tons of lift even if the engines pointed straight down as they couldn't overcome the weight of the aircraft.
Last edited by glum; 29th Oct 2012 at 23:37. Reason: Number stoopidity...
Originally Posted by AirGek
I came across this yesterday when reading "Ace The Techincal Pilot Interview". The query was "During what phase of flight is lift the greatest?" and the answer was "In general, the takeoff".
I wonder why in the world people keep insisting on reading this faulty book?
Why does aircraft take off?
As weight reduces (fuel burn off), so does the lift required to hold the thing up in the air.
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Once there was a very large a/c and someone filled it full of freight to try and make a big profit on 1 flight. They found a very long runway (perhaps that's why the USAF go to the Nevada desert. You can have a rwy as long as you want in any direction.) They then nitro'ed the engines and blasted off, very slowly. I think curvature of the earth came to their rescue.
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How is the 100 tons (say) needed by your aircraft on approach "More" than the 225 tons needed to get it off the ground? The wing may be producing lift more efficiently (Lbs per Sq ft of wing area) but it is isn't producing more lift, mathematically speakng
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Originally Posted by Clandestino
In general? Not a chance. Generally lift is greatest in rapid pull-ups or very steep turns.
And the reason because I read this book is to have a quick summary of the various subjects.
Last edited by AirGek; 29th Oct 2012 at 15:46.
As long as I know the phases are take off, climb, cruise, descent, approach and landing.
And the reason because I read this book is to have a quick summary of the various subjects.
I can see this thread getting very silly.
Anyway, to discount the turns: lift produced by the wings of typical airliner doing V2+10 climbout is lesser, both in total terms and as a fraction of weight, than the lift produced by the same aeroplane during low level-off (say 5000ft as the inbound traffic to LHR jumps over you) a few minutes later. So statement "lift is generally highest at takeoff" is quite silly and most of the time false.
People struggling and failing to comprehend Newtonian mechanics shouldn't be allowed to write flying handbooks. Too bad this ban would interfere with the free market or some PC let's-respect-everyone crap.
To answer the OP in as neutral a manner as possible:
Differential pressure applied over an area results in differential force. When forces are unequal, an object tends to accelerate in the direction of the lesser of two forces. The airfoil can been as the boundary/contact point/contact plane, of two different forces.
In the case of the airplane .. when the force acting in the "up" direction exceeds the force acting in the "down" direction, aircraft (anything else for that matter) will tend to go up unless otherwise constrained (in otherwords, being acted upon by yet another force).
Depending upon how much runway you have, and how much thrust, and what the shape of your airfoil is, it is conceivable that you could start rolling down the runway and eventually, with no further manipulation of the controls, achieve liftoff due to the differential described above as your speed increased above an airspeed that procuded a differential large enough to do so. (also depends upon the shape and location and neutral position of the horizontal stab ... )
Differential pressure applied over an area results in differential force. When forces are unequal, an object tends to accelerate in the direction of the lesser of two forces. The airfoil can been as the boundary/contact point/contact plane, of two different forces.
In the case of the airplane .. when the force acting in the "up" direction exceeds the force acting in the "down" direction, aircraft (anything else for that matter) will tend to go up unless otherwise constrained (in otherwords, being acted upon by yet another force).
Depending upon how much runway you have, and how much thrust, and what the shape of your airfoil is, it is conceivable that you could start rolling down the runway and eventually, with no further manipulation of the controls, achieve liftoff due to the differential described above as your speed increased above an airspeed that procuded a differential large enough to do so. (also depends upon the shape and location and neutral position of the horizontal stab ... )
No. Highest Cl is at alpha crit and we definitively don't want that at take-off.
EDIT: Well, taken in the contest of flight phases, could be, but is as relevant to general discussion about flying as is the difference between airspeeds of common and African swallow.
EDIT: Well, taken in the contest of flight phases, could be, but is as relevant to general discussion about flying as is the difference between airspeeds of common and African swallow.
Last edited by Clandestino; 29th Oct 2012 at 17:04.
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Originally Posted by Clandestino
You don't mind the summary being wrong as long as it's quick?
) this is wrong.It's not the only thing I think it's wrong. I saw also that best lift/drag ratio is obtained at Vmd which according to what I belive to know it's obtained at 1.32 Vmd for a jet, the tangent at the drag curve not the lower part, equal to best endurance...
Avoid imitations
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If take off is not achieved because lift overcomes weight, due to airfoil angle of attack, then how do helicopters take off?