If the airflow over the wing...?

Question

is strong enough to maintain lift, is it possible for an aircraft (ex. a 747) to hover in one place?

Just crossed my mind.

Answer 1

Yes.

The wing does not care whether it is moving or stationary what matters is the relative speed of the wind over the wing.

Answer 2

Well, yes and of course no!

The effect of air flowing over over the wing produces lift (let's steer clear of all the aerofoil sections, angles of attack and all the other jargon that only serves to confuse the argument. And don't let people blind you with stuff a bout Newtonian mechanics because the physics of lift is fiendish complicated and the mathematics - equations to do with circulation and so on - is even worse: technically lift is a first order effect caused by third order forces).

The thing to concentrate on is that the air doesn't know it's moving nor does the wing but providing one is moving relative to the other lift is produced and, if you produce enough of it, the wing will fly. Small aeroplanes and small scale models of big aeroplanes are frequently 'flown' in wind tunnels. But they are tethered, which is another way of saying they're flown like kites.

I've done it myself in a 'grasshopper' glider - OK a lot smaller than a 747 - but the principle is the same. However, the practical problems of doing it in a large aircraft would make it virtually impossible (never say never, because sooner or later some maniac will try!).  

The most obvious problem is that, if a 747 was pointing into a 200 mph wind, with its brakes on as soon as it got airborne the wind would blow it backwards which means the the speed of the air over the wing would drop, lift would be lost and you'd end up with a very expensive ball of scrap metal! To make it hover you'd have to tether it, in effect, fly it like a kite and since a Jumbo produces 400-odd tons of lift you'd need a pretty big string!

So, in theory it's possible, but in practice it's not.

Hope this helps.

Answer 3

Whats all this hovering a cub stuff? I have backed up a 172 and a Britten Norman Islander ( a 6200 lb twin ), but the last is not to hard to do, if you know your planes youll know what I mean...... Its actually easier than a skyhawk. You can hover or back up anything if the relative wind is strong enough. Had an Aztec pretty slow once too.

Answer 4

airflow over a wing isnt even strong enough to keep a light plane in the air. an airplane flies by accelerating air down, thus creating lift(newtons law for every action there is an equal and opposite reaction). that said, there are aircraft with stall speeds so low that if they are facing into the wind, and the wind is strong enough to over come the stall speed of the aircraft, you can actually get the aircraft to hover. the german observation plane of WW ll named the storch was one such aircraft. it had a stall speed of just 12 knots, thus if it was facing into a 12 knot headwind, you could actually get the aircraft to "hover".

Answer 5

Sorta.  The airflow over the wing is required to provide the lift, so it would be very windy.  This is known as relative wind and is basic to all flight; it's why airplanes takeoff and land into the wind, why the Navy turns carriers into the wind and accelerates to launch aircraft, etc.

In the example in your question, assuming the wing was in a takeoff configuration for the weight of the 747, the wind would be blowing about 150 knots to allow it to lift off.  So you can see this is pretty hypothetical.

Answer 6

yes, the "airspeed" might be 150 knots, with a 150 knot headwind, the GROUNDSPEED would be 0, in essence, hovering over the ground.

I have actually flown backwards (over the ground)in the piper cub with a very stiff wind doing ground reference maneuvers

Answer 7

Lol.  Yes, there are aircraft that maintain airflow over the wing so they can hover.  They call them helicopters.  Why would you want a 747 to hover?  It's purpose is to move people over long distances at high speeds.  You probably know that you could make anything fly if you put enough power behind it, or enough wind under it.  Look at what happened with all the tornadoes today!  

Please be sure to save some of these questions for when you become a pro-pilot, so you can be patient with young people when they want to ask you something while you are at work.  Just don't forget where you came from.

Answer 8

No because you would need to counter the force exerted across the forward surfaces of the fuselage, wings, etc.  

If your aircraft was sitting on the ramp with the wind across the wings, while it may (and does) produce lift, it will also be producing a rearward thrust against the front surfaces.

So the aircraft would have to be tethered or producing a forward thrust equal to that being exerted against its surfaces.

Even a very light aircraft wont hover, it will lift and go backwards.

Answer 9

I have seen small airplanes like the Piper Cub "hover " in one place, and even fly backwards in relation to the ground below when facing into a strong enough headwind.  I suppose it would be possile for a larger aircraft to do the same, but it would have to be one heck of a headwind!

Answer 10

Yes, it can happen.  For the 747, you would need a headwind of about 180-200 MPH, but that is not unheard of.  Expect the stick shaker to go off.

We practice slow flight in the big tin angels, same as in the Cessna 150.  In the 150 you can "hover" or back up in about a 45 MPH headwind.  Expect the kazoo (stall warning horn) to squeal at you a lot.

Answer 11

No, because of the FLOW. For an aircraft to hover in one place, there must be no FLOW. An aircraft in flight always displaces air, and so creates air flow. For a flight craft to hover, it must cause the air to cease flowing. In helicopters and Vertical Lift jets, there are mechanisms in the design (propellers/jets/flaps/etc.) that enable the pilot to artificially arrest the flow of air and to build up a "cushion" by causing a stationary air situation in which the craft is suspended.

A craft as big as a 747 will need adjusters so large and so many, that the adjusters themselves will need adjusters. In other words, in theory, the engineering is possible, but practically, it would be too costly. The cost could end up being more than the cost of the 747.