No actually on modern jet and propeller aircraft it's a combination of drag, reverse thrust, and conventional wheel braking. Historically there are some light aircraft which use only wheel braking.

Ah, yeah. I was all the time thinking about propeller airplanes. More accurately fixed angle propeller ones (or whatever they are called). Must be due to the fact I've mostly used those in Flight Simulator...

Well, you learn something new every day.

On landing, depending on the geometry of the craft on landing gear, you might have concerns about how close its centre of mass is to the front wheels in which case the added friction arising from the speed of the conveyor belt could cause it to flip over and smash it's nose into the floor?

Ah, thought it was just drag and reverse thrust, didn't realize the wheels themselves have brakes.

actually the brakes on modern jets are *amazing*

Wow, you can almost smell the burning rubber.

spoilers = drag.

also, i said that the planes use wheel brakes in taxiing. my referances to speed should have made it obvious that i was refering to modern planes, especialy since the historical aircraft didnt have things like reverse thrust.

Spoilers mainly prevent lift. Many planes have actual air brakes for producing drag.

The Mythbusters have been pretty lacking lately. Their show isn't nearly as good as it was two or three seasons ago. This was probably the least scientific show I've seen yet.

"You drive this way real fast, and you fly that way real fast! Hurr!"

It wasn't super sciency because there wasn't much science they had to deal with. All they needed to show was pushing the car forward on the treadmill.

Usually, even with other limited-science subjects, they go through the effort of explaining the physics involved and using maths to determine various forces or whatnot. They also usually try to be accurate with their measurments, often inventing some sort of device to control speeds or weights or whatever. They didn't even do anything close to that this time, for any of their myths.

For anyone that missed it:



Thank you, Mythbusters, for making this thread not useless.

How do you pop a jet engine into reverse again?

(hint: you can't)

(no, airliners use wheel brakes to stop)

Uhm, yes, you can.

http://en.wikipedia.org/wiki/Thrust_reversal

It redirects the thrust of the jet forward, just as he said.

hey guys remember this thread

thrust diverters dont count

I thought the principle of flight was the Bernoulli Principle?

0 = ∆p + ρgh + (1/2)ρv[sup]2[/sup]

it was a series of diagrams. the later ones contained far fewer pictures and far more text calling alice retarded.

Thats how carburetors work!

Uhh, Jon, I think you need to read the Wiki page that Matty linked to:



It's the same thing dude, 'reverse thrust' covers the whole concept of using thrust from an engine to slow a plane down. On a jet the thrust is redirected forwards, on a prop plane the propellers dont actually reverse direction after landing, there's a mechanism that rotates the aspect of the blades so that the air is blown forward instead of backwards. Incidentally this is also how planes reverse.

alpha1, according to that Wiki page reverse thrust has been used as a braking aid on prop planes dating back to the 1930s. My original point was that all modern aircraft use a combination of drag (spoilers, airbrakes, whatever), reverse thrust, and wheel braking to slow down after landing.

thrust diverters dont count

Well, I didnt see MythBusters but from what I can see of that youtube clip- Im disappointed. It's tough to tell but judging by the orange cones it appears the plane is still accelerating faster than the 'conveyor' is moving in the oppisite direction.

*shrugs*

Jamie even specifically said when he saw the plane start to move forward he gunned it, meaning he was going faster than the plane's friggin takeoff velocity. If you need more proof you need to be shot.

Those of you that are saying:

The plane cannot take off because the plane is stationary and there is no air running over the wings

are completely correct. The plane requires air to be running over the wings for it to take off. The nuance in the problem is that even if the conveyor belt is travelling at the same speed as the plane, the plane will not be stationary.

The wheels are not powered. Imagine you are standing on a conveyor belt on rollerscates. The conveyor belt itself will turn the wheels below you, and you won't move even though the wheels below you are. Sure, you might need some initial force to overcome friction (like holding onto something) but when the conveyor belt accelerates you won't need more force (other than to keep stable).

It is the same with the plane. As the conveyor belt accelerates, it is the conveyor belt that moves the wheels below the plane. When the plane turns on its engines, it must travel forwards. It will require a tiny amount of energy to overcome the frictional force on the conveyor belt, but almost all of this energy will go towards forward motion exactly as it would without the conveyor belt. The wheels will be going crazy, they'll be going twice as fast as usual, but the plane will still be travelling forwards just as it would without the conveyor belt.

The point is that the conveyor belt doesn't make any difference. It just makes the little wheels spin much faster, but the plane will take off at the same speed with or without the conveyor belt. It doesn't need (much) extra energy to overcome to the motion of the conveyor belt.

Probably a better version of that analogy would be a person with rollarskates on a conveyor belt (exercise machine) while holding on a rope that is directly attached to the front of the machine. As he moves up the rope to the front, whatever happening under him is doing nothing when it comes to preventing him using the rope to move himself.

The RC car on the treadmill showed it perfectly. Adam was able to push the car forward with no resistance despite the treadmill moving in the opposite direction.

Yeah, that is a better analogy actually.

Also, on a more grammatical (and therefore more important) level, it's written aeroplane not 'airplane'.

No. Both are correct.

Heil Englishe!

Airplane is correct in the US.

the myth busters have it all wrong

Please tell me you're kidding.

Ok.. this question is stupid because, if the plane is moving in the opposite direction we have to assume it's using the power from it's engine to do that. The 'tarmac' is moving the opposite direction.

The only work at play here is the wheels on the plane are moving at 2x the speed. Because the wheels have no drive-train and are just 'hanging there'. The plane will still accelerate to the speed and lift off, the conveyor will not affect this ability.. so I think it's stupid and there is no myth to be busted.

That's right, there isn't. Unfortunately it takes something like this to convince some people.

It's ok to admit you are wrong sometimes, we wont think lesser of you for it.

Are you kidding? My entire beliefs system is founded on one basic principle; Jon`C is infallible.

I don't think you should lie. Its not very nice. Jon'C being wrong is like an airplane taking off from a conveyer belt on the moon.

impossible

Haven't you seen Firefly?