WILL IT FLY?
- Thread starter Jotaru
- Start date
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I see what you're all trying to say. It's like putting a jet powered drag car on the treadmill. There is no force acting on the wheels, so there is no force acting on the treadmill. It will remain stationary while the drag car flies right off the front of the treadmill. Now accelerate the treadmill to 340 mph at the same time the line-lock is removed from the afterburning drag car and the drag car will go nowhere. Unless there is a force acting directly on the treadmill, the tread will not move. It's like throwing a cat onto a treadmill moving at 5 mph. The cat is going to fly right off it. The only factor here is runway distance. It's way too short. Plane will do this:
Right over the front of the treadmill. Even if you accelerate the wheel to 155 mph, generate the thrust to maintain that speed, and stop the treadmill suddenly, the plane will still be accelerating from 0, and again will faceplant right off the front of the treadmill.
Zeri
Retainer of the House of Ultimague
I'm with Furax on this one. So you say the engines generate the air flow required, and given the design of the shape of the wing, it will create some drag, but I don't think it'll be enough to lift the roughly 150,000 lbs your standard Boeing 737 weighs at take off (considerably less without fuel and cargo etc). I think you need to have that additional drag from the atmosphere for lift.
I mean, it seems counter to this exercise, but remove the treadmill for a minute, and instead shove the plane in a giant vacuum sealed runway tunnel (ignoring issues of pressurization here). Even without air, the plane will move forward because of the engines and newton's law of equal opposite reaction (this is how space shuttles move in the vacuum of space). But without molecules of air flowing over and under the wing, that plane can drive around forever as fast as it likes, but it'll never lift.
The treadmill, while not a vacuum, doesn't provide sufficient airflow over the wing. On the other hand, put it on a treadmill with a giant fan at the front, and you'll see it lift off like a kite.
I've got a treadmill at home. Anyone got a model plane? ^_^
This is true... if the plane doesn't move. No matter how damned fast the wheels / treadmill / anything are going, if there's no wind going over the wings, it won't takeoff, period. The debate basically boils down to, will the plane move (accelerate) with respect to the general frame of reference, i.e. air, non-moving earth (not the treadmill) etc.
Varying frames of reference make for exciting questions. Think on this: You have an escalator, but not a stair type, a ramp type, and it is going upstairs. You start at the top, get on a skateboard, and start to roll down. Sure, the treadmill doesn't accelerate in this problem, but it doesnt matter, as it is actually moving FASTER upwards than you are moving downwards at the very onset of the question. Would you argue that you won't roll down the ramp due to gravity?
The main factors in a plane taking off are distance, thrust, drag, lift, land speed and weight. They all have to be balanced for take off, fuck with any of them, and you'll crash. In this case, we don't have enough distance, we have more than enough thrust, low enough weight, no drag at all, no lift at all, and no land speed.
I can say for a fact the plane will not take off if it has no wind for drag over the wings. The thrust from the engines only provides forward motion. The flaps then force the wind going over and under the wing to push the plane in whatever direction it wants to go. Up for take off or down for landing. Perfect example of this is when I am skydiving. If I am in your standard arch body position and I want to do a 360 barrel roll. All I have to do is pull one arm into my chest. Because at that point the drag is on the arm that is still out it cause me to turn in that direction. To stabilize that back out I just need to put my arm back. If there is no wind going over the planes wing the flaps will be unable to make the plane go somewhat upright to take off. Now if the engines were pointed downward some then it would be causing downward thrust instead just horizontal. But then It would just crash in front of the treadmill.<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com
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This is true... if the plane doesn't move. No matter how damned fast the wheels / treadmill / anything are going, if there's no wind going over the wings, it won't takeoff, period. The debate basically boils down to, will the plane move (accelerate) with respect to the general frame of reference, i.e. air, non-moving earth (not the treadmill) etc.
Varying frames of reference make for exciting questions. Think on this: You have an escalator, but not a stair type, a ramp type, and it is going upstairs. You start at the top, get on a skateboard, and start to roll down. Sure, the treadmill doesn't accelerate in this problem, but it doesnt matter, as it is actually moving FASTER upwards than you are moving downwards at the very onset of the question. Would you argue that you won't roll down the ramp due to gravity?
Of course you would, The gravitational pull, 32 ft/s², is greater than the upward speed of the treadmill. Friction and opposite ramp speed won't be much of a factor if the guy has good bearings in his skateboard and has enough mass. He'll roll down the ramp.
Relate that to the airplane example. Replace gravitational pull with thrust from engines from example A, replace upward speed of treadmill with the backward speed of the treadmill from example A. Again, although the treadmill in example A accelerates, it is safe to dismiss this, as in example B, the treadmill is already rolling faster against you than you are rolling against it at time=0.
No, it's NOT deeper than that. The question is, will it fly? The short answer is: no. Don't make it more complicated than it is. If you want to make it deeper, then ask, "given a runway moving at x m/s, would a plane take off from sea level, if held stationary until it achieves y kN of thrust, on a runway n meters long, with the wind having a speed of 0?"
joff
Its deeper than that because the question isn't 'can a plane fly without air moving over its wings'... disregarding VTOL technology, it can't. The question is more 'will the plane move', so its just kinda depressing when someone just answers 'no airspeed = flight'. In your example you are assuming that the plane is held stationary; however, that was never stated, and it is where many people get hung up. The wording of this problem may be tricky because some people read it as "The plane will not accelerate, period. Can it fly", however, this is not meant to be the case. Leaving it vague like that simply leaves more room for thought from people, another explanation as to why it 'wouldn't' fly, etc. As a given, no, the plane won't take off if it is unable to gain any speed in relation to the air around it. Moreover, however, can the plane accelerate? If it can accelerate in this system at even 1m/s^2, it will eventually fly.
You're not trying to launch the skateboarder into the air. You're only trying to roll him down a moving ramp. In this, you're trying to launch a 80,000 kg plane into the air on a ramp way too short and no lift on the wings, it will not take off.
What's the title of this thread again?
Anyway, if you're now asking if it will move. Yes, it will move. Depending on the speed of the treadmill/runway and the thrust of the engines, it will move either backwards or forwards, depending on which is greater.
You aren't trying to 'launch' anything, just accelerate it to the point where the air pressure over the wings sucks it off the runway. If it will accelerate, it will be at 10mph one second... 20mph the next.. so on and so forth. Eventually it will just 'fly', there is no real 'launching' involved. If it doesn't accelerate, it just sits there at 0mph and looks retarded.
Edit: Throwing this in, just in case / before things get too heated.. I meant this as a simple discussion piece, I'm bored as hell, had to wake up at 2am this morning and nothing to do til later, so sitting here chattin about something that makes no real difference in life is a good time buster. I don't mean to get anyone wound up or pissed off, as with all 'its hard to tell **** emotion via text', its just me wantin' to BS around about something, and that's it.
Edit: Throwing this in, just in case / before things get too heated.. I meant this as a simple discussion piece, I'm bored as hell, had to wake up at 2am this morning and nothing to do til later, so sitting here chattin about something that makes no real difference in life is a good time buster. I don't mean to get anyone wound up or pissed off, as with all 'its hard to tell **** emotion via text', its just me wantin' to BS around about something, and that's it.
the plane is stationary to the air around it being on a treadmill. unless there is some downward thrust if there is no air moving around the plane it can not get up in the air. It can go as fast as it wants but if the treadmill is going to stay at the exsact same speed there is no airflow to create drag. There for it won't take off.
If we totally disregard any physics whatsoever, then stick a rocket in my ass and put me on a fucking treadmill with my arms extended out like wings, and I'll eventually take off too. I hated this discussion on 4chan and I hate it here.