right Ive done a quick google & there is a fairly good explanation here:

http://mouser.org/log/archives/2006/02/001003.html

no it doesnt as its moving relative to the stationary ground surrounding the treadmill.

Thunderbirds once did a rescue mission like that though.

involved 3 cars and them matching the speed of the plane, and the plane landing, on their roofs, and the cars slowing down. :|

Shakey:

QuoteThe engines pull the plan forwards with lots of force, causing it to speed up (forget about flying for now). Engines=lots of power=lots of acceleration = lots of speed. Once the plane, from this acceleration, is moving at 200mph RELATIVE TO THE AIR (the wings dont care about the ground) the air is passing over them at 200mph, so lift is generated.

aye which is what I was getting at.

Lots of power to pull it forwards along a nice runway to generate that 200mph airspeed, but the treadmill in my mind had lots of power to let it pull itself forward on the runway/treadmill, which pulled it "backward" by the same amount (doesnt happen on a real runway of course). Which meant it was in fact a stationary airplane, having never actually moved. so.. full power with brakes on so to speak. Soooo couldnt see how it could take off.

Quote from: Daveright Ive done a quick google & there is a fairly good explanation here:

http://mouser.org/log/archives/2006/02/001003.html

Good find

Quote from: M3ta7h3adLots of power to pull it forwards along a nice runway to generate that 200mph airspeed, but the treadmill in my mind had lots of power to let it pull itself forward on the runway/treadmill, which pulled it "backward" by the same amount (doesnt happen on a real runway of course). Which meant it was in fact a stationary airplane, having never actually moved. so.. full power with brakes on so to speak. Soooo couldnt see how it could take off.

because it can still move forwards at 200mph while the runway moves back at at 200mph

wheels simply move along at 400mph

the treadmill can move backwards at 1000 miles per hour in theory (wed have to assume very strong wheels here) & it wouldnt matter.

imagine if you tied a rope to the plane & didnt turn the engines on but spun the treadmill - the plane would stay still - it doesnt matter how fast you spin th treadmill the plane will stay still and the wheels move faster to compensate - now imagine if you apply a big force to it - i.e. from the jet engines - it will move forwards - the wheels are free moving so the fact that the ground is moving has relativly little effect.

The main force a plane has to overcome on takeoff is the air resistance.

lol dave. I get it.

Was missing the vital part that your link gave me

Read as far as "2m/s in total" and went ahhhhh yea..

sorry dude - was writing that previous post before I saw your reply  

So would the conveyor belt have to be the same length as a normal runway? Im guessing itd be the same length, but it would be better for crash landings cos its bouncy.


edit: dinny question, but hey..

Quote from: M3ta7h3adlol dave. I get it.

Was missing the vital part that your link gave me

Read as far as "2m/s in total" and went ahhhhh yea..

The penny drops.  You assumed the plane stayed stationary, when clearly it doesnt.  That was your stumbling block; anything you dreamed up beyond that point was consequently irrelevent.

i was pretty certain it was going to take off, but wasnt gonna but in cause i cannot resolve forces to save my life

So basically:

IF the belt could actually manage to hold the plane stationary, it would never take off. No lift would occur (lift is due to lower pressure over the aerofoil wings made by air rushing over the top faster than the bottom).

BUT the belt simply couldnt do that, as the plane is pushing on air, not on the ground, and so will reach desired take-off speed anyway, belt or no belt, wheels or no wheels.

Here ya go, morans:

Quote from: ask a pilotJan. 5, 2007 | Last month, New York Times technology columnist David Pogue set the Web abuzz by rekindling an old brainteaser about whether a theoretical airplane would be able to take off from a theoretical treadmill. The puzzle was "ripping around the Internet" (Pogues words), and appeals for clarification quickly reached Ask the Pilots in box. Will it or wont it fly, people wanted to know, imploring me to weigh in.

Belatedly, and grudgingly, I will now do so. Such topics tend to induce the rapid closure of my eyelids, and while Id like to tell you this is the kind of shop talk that keeps aviators engaged and alert in those quiet midnight hours high above the ocean, nothing could be further from the truth. (Mostly theyre just bemoaning the loss of their pensions and talking about movies.) Nevertheless, here goes ...

"Imagine a plane is sitting on a massive conveyor belt," poses Pogues Dec. 11 Times blog, "as wide and as long as a runway. The conveyer belt is designed to exactly match the speed of the wheels, moving in the opposite direction. Can the plane take off?"

When I last checked, more than 860 people had posted their opinions, split about 50/50 between those who say the airplane will fly and those who insist it cant. If you look carefully you can locate my own contribution, flatly declaring that no, absolutely not, the aircraft will not get off the ground. "If this is truly ripping around the Internet," I snarked, "then heaven help us. The plane will not fly. Of course it wont fly."

And why should it? How can it fly if its not moving? For an aircraft to get and stay aloft, it needs lift; it needs air passing above and below its wings. And for that it needs to move. For a cursory lesson on how this works, simply shove your arm out the window of a speeding car. Shape your hand into an approximation of a wing, angle it slightly into the oncoming wind, and voilà, its flying.

Now, imagine you are in that same car, on a treadmill. The cars wheels are spinning -- be it at 60 mph or 600 mph -- but when you put your hand out the window, does it rise up? Of course not. Your hand wont fly, and the plane wont fly either for exactly the same reason: because for all its efforts, the vehicle isnt moving. You have zero relative speed and zero lift.

This seemed so obvious that it needed a caveat: "On the other hand, if you were able to generate a tremendous enough amount of thrust," I noted in a follow-up post, "and redirect the vector of that thrust downward, you could, conceivably, lift the plane off like a rocket. Heck, you can make anything fly if you stick enough power under it. But that isnt fair to the spirit of the premise."

Except, wait a minute, what is the premise?

Go back and read it. "Imagine a plane is sitting on a massive conveyor belt," it says, "as wide and as long as a runway." Id glanced right over those key words, "as long as a runway." I was so caught up in the image of a motionless plane on a regular old treadmill -- like the kind you might see at the gym -- that I missed the whole question. Looking back, that does seem a dull and senseless riddle: Can a plane fly if it cant move? Obviously not. There has to be more to it.

And there is. At heart, this has nothing to do with the principles of lift but, rather, with those of friction and acceleration. The gist of the question is better understood as follows: Will an airplane, under its own power, remain motionless on a 10,000-foot-long treadmill, or will it roll forward? Will it accelerate and fly?

Turns out the answer is yes. A distinctly theoretical yes, for reasons well get to shortly, but for all intents and purposes of the puzzle, thats yes enough.

A car wont accelerate on a treadmill; the belt will always match the rotation of the tires. You will not accelerate on a treadmill; the belt always runs in sync with your footfalls. But an airplane is different. An airplanes wheels are not powered by gears or a drive train. They hang inertly below, and are free-spinning. The thrust force that moves the plane along couldnt care less about the ground. The engines are not fighting against the surface, they are fighting against the air.

Confusing, I know, and in the interest of full disclosure, physics was the one class in high school that I outright failed and had to take twice (you try ciphering out equations while listening to Minor Threat on a pair of clandestinely strung ear buds). And some of you might remember what happened the last time I combined things aeronautical and mathematical. So lets get somebody else to explain.

According to Paul J. Camp, a professor in the department of physics at Spelman College, its all pretty simple. "At first, the conveyor will hold the plane still. But only to a certain point, after which, driven by thrust from its engines, the craft will accelerate."

But the problem clearly states: The conveyer belt is designed to exactly match the speed of the wheels, moving in the opposite direction.

"The key is in the behavior of friction," Camp says. "Friction is a peculiar force in that it has an upper limit. For instance, push an object on your desk, but not hard enough to move it. Why doesnt it move? Because the friction force exactly balances the force of your push. At some point you push hard enough to set the object in motion. This is the point where friction has topped out and is not capable of growing any larger."

With the airplane and treadmill, there is, at the outset, friction force capable of rotating the tires at the proper speed to keep the plane stationary. However, as the thrust is increased, that force eventually maxes out. (Two separate frictions are at play here, actually, one between the tires and belt, the other between the planes axles/bearings and its wheels. The first will max out before the second.)

"And at that point the wheels no longer roll, they slide," says Camp. "Or rather, they roll and slide at the same time. Tire motion is now decoupled from the belt motion. No matter how much you whiz up the treadmill, you wont add any more rotational velocity to the wheels because friction is already doing everything it is capable of. The plane skids toward takeoff -- likely accompanied by much smoke and a powerful rubbery stink."

And there you have it, at least on paper. Bear in mind that for a plane to reach that point of decoupling would require two things above and beyond the pale of normal engineering. First, a remarkable amount of power -- far more than any jetliner, and probably any military plane, is capable of developing. The illustration on Pogues blog is of an Airbus A320; some sort of rocket plane would be more appropriate. Second, no existing aircraft tires could take such abuse. The rotational velocity required before reaching the friction limit would have them bursting within seconds, causing the plane to be flung backward. Believe it or not, landing gear isnt engineered with giant treadmills in mind, and pilots need to adhere to maximum groundspeed limits, lest their tires wind up like this. These limits occasionally present problems during tailwind operations or in the case of flap and slat malfunctions -- scenarios dictating the need for unusually high takeoff or landing speeds.

For good measure, the treadmill itself, as described, could never be built. It cant "exactly match the speed of the wheels," because the wheels will turn at the speed of the treadmill plus the speed of the plane relative to the ground. When the speed of the plane is greater than zero (which it is the moment its wheels start to spin; otherwise they would never move), then the problem becomes impossible. By definition, the wheels have to be turning faster than the treadmill.

Whose idea was this crazy problem?

Meanwhile I cant decide if this is good or bad news for the conveyor belt industry and treadmill enthusiasts worldwide. Though, as they say, any publicity is good publicity.

And just to repeat: gosh what a pointless question.

Quote from: maximusotterHere ya go, morans:

Morons

youre a bit late max - the problem has already been debated and explained over 4 pages