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Myth Busters/Can a plane take off on a conveyor belt
Posted on 10/24/07 at 5:42 pm
Posted on 10/24/07 at 5:42 pm
LINK
Airplane Hour
(Weds., December 12 at 9 PM ET/PT)
Adam and Jamie find out if either of them can safely land a Boeing 747-400 on a runway in varying weather conditions. Meanwhile, Kari, Tory and Grant risk life and limb to investigate skydiving myths regularly featured in Hollywood action films. Is it possible to catch up with someone in freefall if that person jumps out a plane before you do? Can you really hold a conversation during freefall? And would you survive if you opened your parachute only a few feet off the ground? Finally, Adam and Jamie carefully navigate their way through a myth that has baffled everyone from web bloggers to pilots. If a plane is traveling at takeoff speed on a conveyor belt, and the belt is matching that speed in the opposite direction, can the plane take off? Extensive small-scale testing with a super treadmill and a nearly uncontrollable model airplane don't completely resolve the myth, so our flight cadets supersize the myth with help from a willing pilot and his Ultralight flying machine.
That should be a good episode.
eta: For the record, if (and that is a BIG if), the experiment is run properly, the plane should take off.
Airplane Hour
(Weds., December 12 at 9 PM ET/PT)
Adam and Jamie find out if either of them can safely land a Boeing 747-400 on a runway in varying weather conditions. Meanwhile, Kari, Tory and Grant risk life and limb to investigate skydiving myths regularly featured in Hollywood action films. Is it possible to catch up with someone in freefall if that person jumps out a plane before you do? Can you really hold a conversation during freefall? And would you survive if you opened your parachute only a few feet off the ground? Finally, Adam and Jamie carefully navigate their way through a myth that has baffled everyone from web bloggers to pilots. If a plane is traveling at takeoff speed on a conveyor belt, and the belt is matching that speed in the opposite direction, can the plane take off? Extensive small-scale testing with a super treadmill and a nearly uncontrollable model airplane don't completely resolve the myth, so our flight cadets supersize the myth with help from a willing pilot and his Ultralight flying machine.
That should be a good episode.
eta: For the record, if (and that is a BIG if), the experiment is run properly, the plane should take off.
This post was edited on 10/25/07 at 6:04 pm
Posted on 10/24/07 at 5:45 pm to ags01
Great show!
Posted on 10/24/07 at 5:56 pm to ags01
quote:
f a plane is traveling at takeoff speed on a conveyor belt, and the belt is matching that speed in the opposite direction, can the plane take off?
um, yes?
if the plane's at takeoff speed, it's at take off speed...it has enough forward speed and lift to take off.
the fact that the conveyor belt is "matching" the plane's ground speed doesn't mean that the plane is traveling slower, it just means that the wheels are spinning faster.
Posted on 10/24/07 at 5:58 pm to Putty
quote:
if the plane's at takeoff speed, it's at take off speed...it has enough forward speed and lift to take off.
the fact that the conveyor belt is "matching" the plane's ground speed doesn't mean that the plane is traveling slower, it just means that the wheels are spinning faster.
Hey, everyone...
LOOK AT THE NERD!!!
Posted on 10/24/07 at 6:00 pm to Putty
So Putty you're saying that it just means the plane will have to exert twice the effort to reach that forward speed?
This post was edited on 10/24/07 at 6:02 pm
Posted on 10/24/07 at 6:02 pm to Thomas Hudson
quote:
But the fact that it's on a conveyor belt moving the opposite direction at the same speed should mean that it's actual foward speed is zero, right? So there's no actual air flowing over the wings to creat lift.
In theory, it would take off, but I've always had my doubts. Should be a good show.
Posted on 10/24/07 at 6:04 pm to Putty
quote:
quote:
f a plane is traveling at takeoff speed on a conveyor belt, and the belt is matching that speed in the opposite direction, can the plane take off?
um, yes?
if the plane's at takeoff speed, it's at take off speed...it has enough forward speed and lift to take off.
the fact that the conveyor belt is "matching" the plane's ground speed doesn't mean that the plane is traveling slower, it just means that the wheels are spinning faster.
I took it to mean that the plane is stationary relative to the surrounding air. - no flight.
The speed of the wheels has nothing to do with flight. The lift comes from the air over the wings.
I know you know that Putty, but, unless I'm missing something here, this myth is dumb and not worth testing.
Posted on 10/24/07 at 6:04 pm to Thomas Hudson
nope....the plane doesn't rely on its wheels for propulsion.
if the plane's "takeoff speed" is 100 mph, then the plane will be traveling forward at 100mph, the belt will be traveling backwards at 100 mph, and the wheels will be turning at whatever rpms are necessary to theoretically hit 200 mph.
if the plane's "takeoff speed" is 100 mph, then the plane will be traveling forward at 100mph, the belt will be traveling backwards at 100 mph, and the wheels will be turning at whatever rpms are necessary to theoretically hit 200 mph.
Posted on 10/24/07 at 6:24 pm to Putty
there is motion between the wheels and the belt. however, there is no motion between the wings and air. the plane itself, not counting the rotating wheels, is stationary. if there is no air flowing over the wings at takeoff speed, i don't think the plane can take off.
that's my 2 cents.
that's my 2 cents.
Posted on 10/24/07 at 6:25 pm to Jimbeaux
quote:
The speed of the wheels has nothing to do with flight. The lift comes from the air over the wings.
Yep, I'm taking Jimbeaux's side rather than Putty's. The plane is stationary in reality, sure the wheels are churning at "take off speed" but the plane - and the air around its wings - is not moving. The ground speed is irrelevant.
shite, they could make air-craft carriers a hellova lot smaller by just making plane-sized treadmills...
Posted on 10/24/07 at 6:27 pm to GaryMyMan
quote:
and the air around its wings - is not moving.
If those jet engines are firing away at takeoff speed, the air around them (and as a result around the wings) isn't going to be moving? Seems like it would be similar to trying to take a plane off in a windtunnel without using the engines or wheels. If the air is going fast enough, it'll lift straight up.
Posted on 10/24/07 at 6:29 pm to Putty
Yep, Putty.. I think you're wrong on this...
Posted on 10/24/07 at 6:31 pm to LSUBoo
quote:
If those jet engines are firing away at takeoff speed, the air around them (and as a result around the wings) isn't going to be moving? Seems like it would be similar to trying to take a plane off in a windtunnel without using the engines or wheels. If the air is going fast enough, it'll lift straight up.
Nope. The air is pulled into the engines, but there is no air flow over the wings. No air flow - no lift.
A wind tunnel pushes air over the wings. Airflow over the wings - lift.
Posted on 10/24/07 at 6:32 pm to LSUBoo
quote:
If those jet engines are firing away at takeoff speed, the air around them (and as a result around the wings) isn't going to be moving? Seems like it would be similar to trying to take a plane off in a windtunnel without using the engines or wheels. If the air is going fast enough, it'll lift straight up.
O.K. fine. Just forget about the wheels and the treadmill they are sitting on.
If the jet engines are creating the thrust (they are), then the plane will move forward relative to the air around it. If the jet were in a vacuum (the jet would have to provide it's own oxygen supply), it would still move forward, but would not achieve flight because there is no air moving over the wings to create lift.
This post was edited on 10/24/07 at 6:36 pm
Posted on 10/24/07 at 6:32 pm to TigersRuleTheEarth
quote:
Nope. The air is pulled into the engines, but there is no air flow over the wings. No air flow - no lift.
I would agree with you... but look this one up online, many proofs that the plane will take off. I've always doubted that it actually would, we'll see I guess.
Posted on 10/24/07 at 6:46 pm to LSUBoo
From your first link:
That argument they are refuting is flawed. The ground is not the propulsion medium, the air is. The treadmill (ground) does not exert an exact oposite force on the plane at take off. If this was the case no plane would ever take off on a regular runway.
ETA: we'll see tonight, but I'd bet my degree on it.
quote:
But the ground the aircraft is sitting on in this case is NOT stationary, its providing an exactly CANCELLING force pushing the aircraft back.
That argument they are refuting is flawed. The ground is not the propulsion medium, the air is. The treadmill (ground) does not exert an exact oposite force on the plane at take off. If this was the case no plane would ever take off on a regular runway.
ETA: we'll see tonight, but I'd bet my degree on it.
This post was edited on 10/24/07 at 6:54 pm
Posted on 10/24/07 at 6:50 pm to TigersRuleTheEarth
Their wording is poor... the ground isn't pushing back, it's just preventing the wheels from rolling forward along the ground. The treadmill isn't providing any force on the airspeed of the plane, which is the point of the problem.
If by tonight, you mean, sometime in December, then cool.
Hope you don't lose your degree, because in theory, you should.... but in theory, communism is a good thing.
quote:
ETA: we'll see tonight, but I'd bet my degree on it.
If by tonight, you mean, sometime in December, then cool.
Hope you don't lose your degree, because in theory, you should.... but in theory, communism is a good thing.Posted on 10/24/07 at 6:53 pm to LSUBoo
quote:
sometime in December,
Damn, didn't read that the show was in December.
Come look for me on the board in December to see if I trade my degree in.
Posted on 10/24/07 at 6:55 pm to TigersRuleTheEarth
quote:
Come look for me on the board in December to see if I trade my degree in.
Will do. Will be bumping this thread like crazy.
ETA: But like I've said... just in theory it works, I really have doubts about a full-scale test. I'm not even sure those guys could pull off a full-scale test.
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