Mythbusters to take on - PLANE ON A TREADMILL!!...

Originally posted by flyUnity
http://community.discovery.com/eve/f...5321919039/p/1

[quote]Originally Posted by Discovery Channel Press Release
"MYTHBUSTERS" CONTINUES TO MAKE SCIENCE COOL WITH SEVEN ALL-NEW EPISODES BEGINNING OCTOBER 31...

...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 ...[text shortened]... Plane WILL take off.

Many of you all said that it WONT take off,

I guess we will see

Is it just me or did they completely fail to address the airplane on conveyor belt question? In the new episode I just finished watching, the mythbusters addressed the other airplane related myths mentioned (except for the parachute opening a few feet from ground thing) -- but not the one that prompted this thread.

Originally posted by LemonJello
Is it just me or did they completely fail to address the airplane on conveyor belt question? In the new episode I just finished watching, the mythbusters addressed the other airplane related myths mentioned (except for the parachute opening a few feet from ground thing) -- but not the one that prompted this thread.

http://forums.jetcareers.com/general-topics/56705-official-mythbusters-plane-treadmill-thread.html

Seems the missing Plane on A Treadmill (PoaT) has sparked internet fervor. Turns out many other internet forum communities were dying to see this argument settled once and for all as well.
There is an 80 post thread with over 12,000 views in less than an hour at the MythDoods website.



From the Mythbusters forum:


Quote:
I have just received an email from Dan Tapster, executive producer of MythBusters.

Thanks to all the activity, he can't log in and asked me to post this for him.


quote:
"Adam? Jamie? Dan? Someone step up and tell us what happened tonight."
Dear all,
As wbarnhill called out, I thought I should step in to what is rapidly becoming a hornet's nest. I will try to calm things down but I don't hold out much hope!
First up, for those concerned that this story has been cancelled, don't worry, planes on a conveyer belt has been filmed, is spectacular, and will be part of what us Mythbusters refer to as 'episode 97'. Currently that is due to air on January 30th.
Secondly, for those very aggrieved fans feeling "duped" into watching tonight's show, I can only apologise. I'm not sure why the listings / internet advertised that tonight's show contained POCB. I will endeavour to find out an answer but for those conspiracy theorists amongst you, I can assure you that it will have just been an honest mistake. At one point
several months ago, POCB was going to be part of Airplane Hour. Somewhere, someone has mistakenly posted the wrong listing. It will have been a genuine mistake but nonetheless it was a mistake which is unacceptable. As said I will try to find out what went wrong and hope that you will see fit to forgive the team at Discovery.
Thanks in advance,
Dan
And with that, the entire board is going "READ ONLY" until I can clean up the mess.

MythMod

Originally posted by flyUnity
http://forums.jetcareers.com/general-topics/56705-official-mythbusters-plane-treadmill-thread.html

Seems the missing Plane on A Treadmill (PoaT) has sparked internet fervor. Turns out many other internet forum communities were dying to see this argument settled once and for all as well.
There is an 80 post thread with over 12,000 views in less than an h ...[text shortened]... , the entire board is going "READ ONLY" until I can clean up the mess.

MythMod

Thanks for that info.

Prior to watching the episode, I looked at the listings on tvguide.com. The listing caption did explicitly state that POCB was going to be part of the episode. So I was a little confused when that failed to obtain. I'm glad to hear it is still due to air and that they didn't scrap the idea altogether.

Originally posted by flyUnity
http://community.discovery.com/eve/f...5321919039/p/1

[quote]Originally Posted by Discovery Channel Press Release
"MYTHBUSTERS" CONTINUES TO MAKE SCIENCE COOL WITH SEVEN ALL-NEW EPISODES BEGINNING OCTOBER 31...

...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 ...[text shortened]... Plane WILL take off.

Many of you all said that it WONT take off,

I guess we will see

u need lift to make it take off it will not unless it is a harrier jump jet or some kind of nossel to move the air being pushed to make the plane get off of the ground

Originally posted by youwillfall
u need lift to make it take off it will not unless it is a harrier jump jet or some kind of nossel to move the air being pushed to make the plane get off of the ground

Read the first 4 pages of this thread.

Here is a situation that might make it a bit easier to understand:
Can a plane take off if it is just sitting on the ground and a headwind starts up? Suppose the plane needs to be going 100 Kph to take off normally, and all of a sudden the plane is just sitting on the runway ready to start his engine and a 100 Kph headwind (trying to push the airplane backwards) starts up. Now you have relative movement of air across the wing, top and bottom. Will the aircraft take off? Will it be able to STAY off the ground?
Suppose you now change things so there is a long thin cable strong enough to do the job, this cable is tied to the plane in the middle so it will not skew the plane around, and the other end tied to a tree a klick or so in front of the plane. Do you see the differance? Now the plane will take off, and stay off the ground, it is now a kite.
Now substitute the running engine for the string. It is providing the same countering force as the cable. In the case of the plane sitting still and a big headwind happens, the plane may get off the ground but friction with the air will ensure at some point that the air will not be moving fast enough and there will be not enough lift to keep it in the air and it will settle back down to the ground or more probably flip over first. Suppose the pilot is able to control the decent enough to just touch the ground again, then the original friction on the ground will cause the relative velocity of the air to make enough lift to get it off the ground again in a never ending cycle. Suppose we take the case of a glider. A glider can never just take off in a headwind unless it can also fall some distance at an angle forward, such as being on a downward facing slope. In that case gravity will cause a forward movement that will counter the wind just moving the plane backwards which, without the downward motion, will just flip it over. The downward motion is what gives the glider the equivalent of the thrust provided by an engine, jet or propeller. Unless those conditions are met, the plane cannot get very far other than just flipping over or flopping back down to the ground.
So now you take a look at the case of the plane in a head wind but now the engine starts up the instant the wind lifts the plane off the ground. Now the engine acts exactly like the cable strung to the tree which makes it a kite. But the engine replaces the cable and so it can take off in the headwind at zero forward motion relative to the ground and presumable could either continue rising or maybe even staying just a few feet off the ground but in a controlled manner just apparently levitating in place. That can only happen if the wind keeps up at the same velocity. Now put a treadmill under the plane. It doesn't much matter how fast the treadmill runs, the plane won't take off, assuming the plane has wheels. If it is going in the direction causing forward movement of the plane so to increase the lift effect on the wings, it can only do that up to the point that the wheel friction is overcome by the drag of the plane, after that, the wheels just spin and the plane may be moving forward but without some countering force like an engine, it can't go fast enough to get off the ground. Now suppose you don't have wheels. Suppose the plane now has a locking mechanism like wheel chocks and now the treadmill starts up pushing the plane into the wind forward, at some point, assuming the velocity is high enough, like the 100 Kph point in the example given, or just applying the planes brakes, same effect, then at some point the plane can get off the ground. Which is not the same thing as saying the plane can 'take off'. "Taking off" implies to me at least, that the plane is now flying. There is a big difference in the plane just leaving the ground and the plane 'taking off'. In order for the plane to be considered "taking off" you need either of the three conditions I mentioned earlier, a cable tied to a tree and a fast wind, an engine and a fast wind, or a downward slope to accomplish the same thing that the engine or the cable does. So a forward moving treadmill of sufficient length can get a plane to leave the surface of the treadmill but that alone is not the same thing as flying.

That the whole explanation makes sense and seems convincing. I always thought that this was a trivial question. Now I just don't know any more.

Here is another question: What is 'flying'?
Suppose you take a glider and you have this super physics where the top surface of the wings can expand like a balloon and you have a large supply of helium in a tank that you can fill the balloons up enough to make the whole thing levitate to some useful altitude, say 10 Km. Then at that altitude you have a pump that can recompress the helium back into a tank and the wings become wings again.
Just at that point in time a headwind starts up. Is the glider 'flying' at that point? What allows the glider to 'fly'? What happens to the glider at that point in time where it is just suspended in midair and you have just completed the transition back to normal wings and the headwind starts blowing, starting to push the plane backwards?
We are of course assuming for our thought experiment that there is a pilot aboard.
Also, remember those movies of fighter jets taking off from an aircraft carrier? Those steam powered catapults accelerate the jet with an incredible force, enough to get the jet up to its takeoff speed in a few seconds, must be going 5 or more G's. At the same time the jet engine is going like a banshee and the combination of the two gets the plane flying. But notice when the jet starts to leave the front of the carrier, the plane falls a bit first, so why doesn't it just go up at an angle the moment the plane reaches takeoff speed, something like 240 Kph in the case of a fully loaded combat jet.
So how long would the jet stay in the air if the super sling is the only thing accelerating the jet? The sling can get it up to the required 240 Kph just by itself so what happens to the jet in that case, engines off?

Originally posted by sonhouse
Here is another question: What is 'flying'?
Suppose you take a glider and you have this super physics where the top surface of the wings can expand like a balloon and you have a large supply of helium in a tank that you can fill the balloons up enough to make the whole thing levitate to some useful altitude, say 10 Km. Then at that altitude you have a pump ...[text shortened]... he required 240 Kph just by itself so what happens to the jet in that case, engines off?

there is a difference between takeoff speed, and climb speed, 240 may be the takeoff speed, (the slowest the plane can fly) but it will accelerate in the air just above the ground until it reaches climb speed which is the speed that the jet climbs the fastest at.. say 290. the jet pilots probaly pitch down to acellerate the jet faster to climb speed.

Originally posted by flyUnity
there is a difference between takeoff speed, and climb speed, 240 may be the takeoff speed, (the slowest the plane can fly) but it will accelerate in the air just above the ground until it reaches climb speed which is the speed that the jet climbs the fastest at.. say 290. the jet pilots probaly pitch down to acellerate the jet faster to climb speed.

Exactly correct of course but I think there is not a jet on any carrier unless the jet is a VTOL that doesn't dip some after the catapult. It is not going at climb speed at the end of the catapult run, so it gets that speed a second or so after the cat reaches the end of its run by the huge thrust of the jet engine, otherwise its in the drink for the pilot.
BTW, I just saw a video of a new navy jet called the F-35 Lightning II, another VTOL like the Harrier, looks like two down thrusters. There was a lot of problems with VTOL's where the downwards thrust interfered with the intake and the engine would sputter or go out and end the takeoff or maybe crash. It looks like they got that one under control though.

my brain hurts..

Did the stinkin' plane take off or not already!

Originally posted by ih8sens
my brain hurts..

Did the stinkin' plane take off or not already!

That depends on how we define our thought experiment. One treadmill has the wheels unlocked and its just sitting on the surface just like it would be if it were taking off for real from a runway. So now the engine is turned off. The treadmill starts up, the fact that the plane has drag keeps the plane from going fast enough to achieve takeoff velocity so the wheels just spin with the plane going a bit forward maybe. No takeoff.
The second experiment has the wheels chocked or brakes on and the engine is turned off. Now the lock on the wheel counteracts the drag on the plane, it can now get up to takeoff velocity and may rise a bit but now the drag of the atmosphere overwhelms the forward velocity and it just lands again or flips over. No takeoff.
The third has the plane on a traedmill as in example 1, but the engine is going. This time the engine produces enough thrust to counter the drag and it takes off when it gets to takeoff velocity.
The fourth experiment has the brakes locked and the engine running, the plane takes off but a bit faster because as opposed to experiment three in which the engine is running, it has to make up for the fact that the wheels are free running. In #4, the wheels are locked and the engine can devote all its effort to increasing the forward velocity and the two forces work together and takeoff happens but faster and with less forward movement than #3. It is exactly like a jet taking off from an aircraft carrier using a catapult, but in that case the wheels are free to rotate and the whole plane is hooked to the catapult cable accelerating the plane at a tremendous G force rate. So the jet takes off as does the plane with engine running and wheels locked on a treadmill. Does that explain it or did I use too many words again?

Originally posted by sonhouse
That depends on how we define our thought experiment. One treadmill has the wheels unlocked and its just sitting on the surface just like it would be if it were taking off for real from a runway. So now the engine is turned off. The treadmill starts up, the fact that the plane has drag keeps the plane from going fast enough to achieve takeoff velocity so th ...[text shortened]... unning and wheels locked on a treadmill. Does that explain it or did I use too many words again?

umm.. I think your reading the question wrong,, the treadmill is going BACKWARDS. not forward like it appears you seem to believe

Originally posted by flyUnity
umm.. I think your reading the question wrong,, the treadmill is going BACKWARDS. not forward like it appears you seem to believe

I considered that direction also but it seems to be trivial, the plane would be at least partially forced to go tail first, no way anything like takeoff could happen unless the plane was somehow turned around and that was not in the question so it is a no-brainer to see nothing would happen. If a jet catapult on an aircraft carrier happened to grab the fighter jet in such a way as to sling it around, it for sure would not take off, just be flung over the front of the carrier into the drink. Plus, any engine thrust would be slowing the plane down even more. I guess it would depend on how fast the treadmill ran. If it was going slow enough, and the engine was running full bore, and the wheels were not locked and there was room for the plane to move, then it could conceivably get off the ground but only because it has a strong engine. So I considered the other direction as being more conducive to an actual liftoff.

Originally posted by sonhouse
That depends on how we define our thought experiment. One treadmill has the wheels unlocked and its just sitting on the surface just like it would be if it were taking off for real from a runway. So now the engine is turned off. The treadmill starts up, the fact that the plane has drag keeps the plane from going fast enough to achieve takeoff velocity so th ...[text shortened]... unning and wheels locked on a treadmill. Does that explain it or did I use too many words again?

I'm really a big fan of words under 6 letters... but yah I think i got it.. it works exactly the way i expected it to work .