Yes, it would fly if you had a hell of a hair dryer.

SpaceGazelle wrote:

Yes, it would fly if you had a hell of a hair dryer.

Also yes, which is why wind tunnels are a thing.

No I mean I told you what to write with my big science galaxy brain genius

I don't care how it takes off, I want to know how it moves!

GurtTractor wrote:

Eating dinner right now, but after I will explain to you how

Spoiler:

it will actually take off.

Is it by hot air?

It must be a problem with the conveyor belt.

Just watched the Mythbusters stuff.

The plane is going nowhere unless the air moving over the wings if moving sufficiently fast.  This is silly, you're all silly, and I'm going to play more Superhot now.

The Mythbusters answer is a cop out surely; what if the conveyor could match the jet’s speed? You’re then into the realms of how jet engines work, and it still wouldn’t go the way they say if I’m understanding it right.

Jet engines work in a manner where acceleration builds as speed builds, sort of the other way around from a typical combustion engine. It’s to do with the compressibility of air and the fact the airflow through the turbine helps to compress the incoming air, by turning the powered compressor.

If you take off at 200mph, and the conveyor’s set to max out at 200mph, there’s almost no chance your jet will actually even get to much about 200mph (or even to it) without airflow through the engines to help with acceleration. You’re certainly not getting to 400mph, on the assumption that the conveyor’s effectively a runway’s length.

Yossarian wrote:

Just watched the Mythbusters stuff.

Spoiler:

It’s kind of a bit of a trick question, IMO, because the answer is that the conveyor belt can’t match the speed of the plane, the plane can always go faster. The wheels can just spin freely against the conveyor belt, the plane can then get additional forward momentum from the propeller (or jets). The phrasing of the question makes it sound like the plane will stay in one place, but it moves forward and takes off.

Elmlea wrote:

Its wings are still stationary relative to the air in that scenario though, even if the wheels are turning at the rate they’d need to at 400mph. Also the tyres would have burst.

The belt is moving at 200mph. The plane is moving at 200mph the other way. The wheels are also moving at 200mph.

The plane is just providing sufficient thrust to move forwards and counter the belt. On a normal runway the same level of thrust would have the plane move at 400mph and the tyres would burst.

Instead of a conveyor belt think of it as headwind.

Its just a tricky worded question that encourages the reader to jump to the conclusion that one speed counters the other which of course it does but the plane can apply more power to overcome it.

Edit: Mythbusters used a propeller plane. It really is a wording thing more than practical.

So the answer is that it will take off because planes work by applying thrust to the air, not through the wheels like on a car. The wheels are free spinning and provide relatively very little resistance to prevent the plane from moving forward. Conceivably if the conveyor was moving fast enough the bearings would seize up or the tires would burst, but I did specify (after a clarifying edit, oops) that -

think of it as an engineering experiment, as the plane starts to move forward the conveyor moves backwards at the same rate of acceleration the plane would have were it on solid stationary ground.

That bit is important because if it was set to match the exact forward relative speed of the plane it could cause a feedback loop to infinity. So just imagine it as the conveyor has been programmed to match the typical acceleration of that specific plane.

The conveyor could be moving at a much much faster rate than the ground speed of the plane and the plane could still likely take off, because all the wheels are doing is keeping the plane off of the ground.

Here is the practical demonstration from the lads -



The dislike ratio is wonderful.

Unlikely wrote:

Jesus wept.

Was he not allowed to fly it then

Keep in mind that I never said the plane was being held stationary by anything, that was an assumption most of you lept to.