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kccustom

Can the plane take off?

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Guest navinjohnson
[quote name='n_w95482;746727']An example of the above post would be watching birds flying into a strong wind. Sometimes you can see them staying aloft like normal but in relation to the ground, they're not moving forward, and sometimes they go backwards.[/quote]

If we are talking about a jet aircraft, there is no air movement across the wing because the thrust of the engine is negated by the moving runway. Jet air craft will not take-off in this scenario.

Even if it is a prop, or turbo-prop, their may possible be enough air movement across the wing. I think this would only be possible on a twin engine though, as a single would only create air movement around the fuselage and only a small portion of the wing. An airplane with a propeller might be able to take off.

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[quote name='krazypoloc;746729']So you are saying that argument states that the airspeed is concurrent with the ground speed? Sorry, but I didn't take that from the initial question. If that were the case then yes the plane would in fact fly, and would be more like a kite than any other object I would imagine.

And I am not a pilot, I was a crew chief, and FE in the USAF for a number of years.

And actually I have a complete understanding of fluid dynamics. But I'll disregard that as you thought I was referring to you as not knowledgeable in this area. I was in fact referring to the link I have posted previously. :)[/quote]

Yeah; the wording is somewhat ambiguous; but in essence states that the conveyor is moving at the same speed as the aircraft (viewed from a stationary point not on the conveyor; i.e. beside the runway, such as a control tower); resulting in the wheels spinning twice as fast as they would on a regular runway.

Yep, being a Flight Engineer you'd be expected to understand the principles of flight and how an airplane works.

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[quote name='navinjohnson;746742']If we are talking about a jet aircraft, there is no air movement across the wing because the thrust of the engine is negated by the moving runway. Jet air craft will not take-off in this scenario.

Even if it is a prop, or turbo-prop, their may possible be enough air movement across the wing. I think this would only be possible on a twin engine though, as a single would only create air movement around the fuselage and only a small portion of the wing. An airplane with a propeller might be able to take off.[/quote]

The type of propulsion system is irrelevant. The jets/props are thrusters that push (or pull in most propeller configurations) the aircraft through the air.

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Guest navinjohnson
they aren't pushing the aircraft through the air though. they are pushing it against the moving runway. The aircraft remains stationary to the ground, there is no air movement over the wings and the aircraft does not take off.

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Guest LookBackX2
As long as the airplane's propulsion system (whatever it is) can provide force capable of overcoming the extra rolling resistance created by the conveyor belt it should be able to lift off. As soon as it lifts off, the equation returns to normal since the plane is no longer in contact with the belt.

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[quote name='navinjohnson;746745']they aren't pushing the aircraft through the air though. they are pushing it against the moving runway. The aircraft remains stationary to the ground, there is no air movement over the wings and the aircraft does not take off.[/quote]

The thrusters actually push the plane through the air and are by no means linked to the runway; the wheels are not powered at all. Propellers pull (or push in the case of a rear prop) against the ambient air (much like the propeller on an outboard boat engine); while jets push against the ambient air to propel the aircraft (like the jet on a wave-runner).

A similar question (following the same principles) would be:
If a boat is in a river where the riverbed is a giant conveyor that moves at the same speed but opposite direction as the boat, would the boat move?

Please take the time to read my previous posts; hopefully it'll be more obvious then.

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[quote name='LookBackX2;746748']As long as the airplane's propulsion system (whatever it is) can provide force capable of overcoming the extra rolling resistance created by the conveyor belt it should be able to lift off. As soon as it lifts off, the equation returns to normal since the plane is no longer in contact with the belt.[/quote]

Multi-engine aircraft are designed with enough thrust that if an engine fails the plane can still take off and the rolling resistance is small compared to the drag; so this isn't an issue.

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Guest Neezer
ok...I wanted to keep my mouth shut, but radodrill....for having "passed the FE exam, and having 2 BS degrees in engineering," you don't have a firm grasp of physics.

The boat example that you just gave is completely different than the airplane example. the water in a riverbed is naturally flowing downhill. the air doesn't naturally "flow" at speeds that will allow a plane to take off. (don't even start with hurricanes and tornadoes cause that is just being stupid.) In the question stated above, the situation is this:

immagine the there is a flagpole right next to the planes wingtip on the side of the conveyor belt. this flagpole is on solid ground....it doesn't move. the conveyor provides enough friction into the system to keep the plane stationary with respect to our flagpole. To possibly think that an engine mounted anywhere on a plane can move enough air across the wing, while the plane's groundspeed is zero, to cause the plane to lift off is crazy.

I also have a BS in aerospace engineering and mechanics, the only difference between our degrees is that mine came from an accredited university not the shopping mall.

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[quote name='radodrill;746721']If the discussion were about a car you'd be correct about no absolute velocity; since the car is propelled by the engine turning the wheels.

However, in the case of an aircraft, the airspeed is the defining factor (ground speed is irrelevant). The thrusters (be it propeller or jet) push/pull the aircraft through the air; the rotation of the wheels is a result of the plane's movement with respect to the ground. If the airspeed is high enough (even if the ground speed is 0) the plane will still take off.

This is the reason why small (private) aircraft are tied down when they're parked on the tarmac; gust winds have been known to pick up small planes.[/quote]

Haha, yeah I was stationed at Hurlburt Field for a few years(Fort Walton Beach, FL) and I've seen some aircraft "float" when hurricane force winds are present. Although we would usually relocate them to a safer area those topical storms sneak up on us some times. Pretty crazy seeing a 160K Lbs. aircraft leave the ground momentarily.

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[quote name='Neezer;746758']ok...I wanted to keep my mouth shut, but radodrill....for having "passed the FE exam, and having 2 BS degrees in engineering," you don't have a firm grasp of physics.

The boat example that you just gave is completely different than the airplane example. the water in a riverbed is naturally flowing downhill. the air doesn't naturally "flow" at speeds that will allow a plane to take off. (don't even start with hurricanes and tornadoes cause that is just being stupid.) In the question stated above, the situation is this:

immagine the there is a flagpole right next to the planes wingtip on the side of the conveyor belt. this flagpole is on solid ground....it doesn't move. the conveyor provides enough friction into the system to keep the plane stationary with respect to our flagpole. To possibly think that an engine mounted anywhere on a plane can move enough air across the wing, while the plane's groundspeed is zero, to cause the plane to lift off is crazy.

I also have a BS in aerospace engineering and mechanics, the only difference between our degrees is that mine came from an accredited university not the shopping mall.[/quote]

Radodrill is speaking under the assumption that the airspeed is concurrent with speed of the conveyor belt. So if this is true then the plane would in fact fly. If the airspeed is just the speed of the ground, or 0Mph, the the plane would not fly, even a turboprop, which would have the highest possible lift impact due to the majority of the thrust passing over the wings. But Because it passes air over and under the wing (in most cases) it would thereby negate any perceivable lift.

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Guest Neezer
[quote name='krazypoloc;746762']Radodrill is speaking under the assumption that the airspeed is concurrent with speed of the conveyor belt. So if this is true then the plane would in fact fly. If the airspeed is just the speed of the ground, or 0Mph, the the plane would not fly, even a turboprop, which would have the highest possible lift impact due to the majority of the thrust passing over the wings. Because it passes air over and under the wing (in most cases) thereby negating any perceivable lift.[/quote]


exactly...but there is no way that the air is going to be moving at the speed of the conveyor. I would like it explained to me how and why that might happen...if you can explain how all that air is going to get moving uniformly like in a wind tunnel, then I might change my mind, but I can think of nothing that would do this. (don't even think of bringing up the boundary layer near the surface of the conveyor cause it would be much to thin to even remotely effect the wings of even a small plane that is only a few feet off the ground).

Faulty assumptions cause planes to not fly....

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Yes, but as previously stated it is a very vague and "ambiguous" question. Probably designed by a physics professor to stimulate the thought process or something....I don't know. Thats why I gave two different opinions. One opinion for one "variable", one for the other.

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