Hope?
At least it made me think before posting. I now realize I had it wrong so what’s the point. I learned something and I find it funny to read all answers, right or wrong. It is after all a tricky question.
/Hugo 🙂
At least it made me think before posting. I now realize I had it wrong so what’s the point. I learned something and I find it funny to read all answers, right or wrong. It is after all a tricky question.
/Hugo 🙂
Everyone who thinks that the plane would still lift off should think whether the engines are actually pulling air THROUGH the wing.
Try wrapping your hand around a hair dryer when it is turned on. Feel the wind rushing past the back of oyur hand? Me neither 😎
Try wrapping your hand around a hair dryer when it is turned on. Feel the wind rushing past the back of oyur hand? Me neither 😎
That is one of the great things about this forum, indeed! You can actually get away, asking a question like this, and get your answer!!! I once asked about windmills, and got the answers too😀 😀 So Hugo, dont be too quick, sending questions to texas😀 😀 This is one of the more amusing kind of things😉
Steen😎
Good question the way it is posed. It makes you confuse yourself.
The plane merrily takes off without the wheels rotating. Excellent wear life on the tires and bearings.
The force of the engine has to be compensated for. It is, the plane moves forward. The belt system detects this and moves to stop the wheels from turning. A dot marked on the belt would be stationary with respect to the plane. The ground isn't.
-Chris
The plane merrily takes off without the wheels rotating. Excellent wear life on the tires and bearings.
The force of the engine has to be compensated for. It is, the plane moves forward. The belt system detects this and moves to stop the wheels from turning. A dot marked on the belt would be stationary with respect to the plane. The ground isn't.
-Chris
Texas? No way...till now. 😀 This is fun.
As I understand it, the wheels are just there to support the plane till it can be supported by the air. Because the wheels are not participating in pulling the plane forward, they can even turn in opposite direction. The motor is pulling (propeller) or pushing (jet engine) the plane forward anyway. The plane does not stand still and can therefore take off.
/Hugo
As I understand it, the wheels are just there to support the plane till it can be supported by the air. Because the wheels are not participating in pulling the plane forward, they can even turn in opposite direction. The motor is pulling (propeller) or pushing (jet engine) the plane forward anyway. The plane does not stand still and can therefore take off.
/Hugo
Dear eVITAERC,
please tell me you don't really mean what you say
If this wouldn't be a bit cruel, I would like to strap you right to the body of a REAL BIG hair dryer (lets say, a jet engine 😀 ) and watch you shoot forward, perhaps even take off... And fully without wheels...
Of course the engines don't "blow" air around the wings, but they accelerate air and hot exhaust gases backwards, giving these gas masses a certain momentum. And, as momentum needs to be conserved, the engine and with it the whole aircraft is given the same momentum in the opposite direction, thats FORWARD. So your plane WILL speed up until it reaches take-off velocity, it doesn't even NEED wheels for that...
btw, have you ever seen wheels mounted sideways on a space shuttle or rocket launch vehicle? Seems to be some kind of miracle, but they speed up WITHOUT wheels...😎
please tell me you don't really mean what you say
If this wouldn't be a bit cruel, I would like to strap you right to the body of a REAL BIG hair dryer (lets say, a jet engine 😀 ) and watch you shoot forward, perhaps even take off... And fully without wheels...
Of course the engines don't "blow" air around the wings, but they accelerate air and hot exhaust gases backwards, giving these gas masses a certain momentum. And, as momentum needs to be conserved, the engine and with it the whole aircraft is given the same momentum in the opposite direction, thats FORWARD. So your plane WILL speed up until it reaches take-off velocity, it doesn't even NEED wheels for that...
btw, have you ever seen wheels mounted sideways on a space shuttle or rocket launch vehicle? Seems to be some kind of miracle, but they speed up WITHOUT wheels...😎
Rundmaus said:Dear eVITAERC,
please tell me you don't really mean what you say
If this wouldn't be a bit cruel, I would like to strap you right to the body of a REAL BIG hair dryer (lets say, a jet engine 😀 ) and watch you shoot forward, perhaps even take off... And fully without wheels...
Of course the engines don't "blow" air around the wings, but they accelerate air and hot exhaust gases backwards, giving these gas masses a certain momentum. And, as momentum needs to be conserved, the engine and with it the whole aircraft is given the same momentum in the opposite direction, thats FORWARD. So your plane WILL speed up until it reaches take-off velocity, it doesn't even NEED wheels for that...
btw, have you ever seen wheels mounted sideways on a space shuttle or rocket launch vehicle? Seems to be some kind of miracle, but they speed up WITHOUT wheels...😎
Your whole argument about strapping me to gigantic hairdryers (which sounds strangely kinky... remind me to go see a counsoler) assumes that the hair dryer is a free-body...
...which the plane is not. Unlike the typical rocket propulsion system (which you described) it is coupled to the ground with the landing gear, which has wheels. As long as gravity is doing its job keeping normal force on the conveyer belt, and thereby inducing the rolling motion on the wheels which is coupled to the conveyer belt, and as long as the conveyer belt is designed in such a way that the tangential velocity of the belt is the same as the wheel's, the rolling motion of the wheel is annuled and there is no net force acting on the direction of propelling the plane forward. Instead it has all gone to keeping the conveyer belt going.
My point (which you seemingly missed) in the hair-dryer analogy is to show that without any relative motion of the wing with respect to the air, the air-drawing motion of the jet engines by itself does not pass air THROUGH the wings and therefore cannot produce lift.
Note that the conveyer belt would have to be some technical marvel in engineering. However if the constraints on the belt is as described then I believe the whole system would work in this way.
PS: The conveyer belt DOESN'T stop the wheel turning at all! Think of two gear cogs meshed together, with one driving the other.
I am surprised that no one has discussed rear fuselage engine mount. Would this not draw enough air over the foil to create lift?
Also, I really can't see the air, from friction, as being a huge factor. I would have thought the foil having air forced over it from the thrust of the engine to be the big factor and that to gain enough speed for lift off all you would have to do is compensate for the air friction normally associated with the runway takeoff. So if the plane is being held stationary by the conveyor belt then you have to make up the speed lost on the runway. So what I mean is that if the plane takes off at X amount of thrust and 250 km per hour then you run add the amount of thrust needed to compensate for the lack of speed along the runway and voila, you have created enough lift. So I say yes theoretically.
Now the question in my mind is how do you run an engine so hard that it compensates for loss takeoff speed? I not sure this is a realistic question.
Also, I really can't see the air, from friction, as being a huge factor. I would have thought the foil having air forced over it from the thrust of the engine to be the big factor and that to gain enough speed for lift off all you would have to do is compensate for the air friction normally associated with the runway takeoff. So if the plane is being held stationary by the conveyor belt then you have to make up the speed lost on the runway. So what I mean is that if the plane takes off at X amount of thrust and 250 km per hour then you run add the amount of thrust needed to compensate for the lack of speed along the runway and voila, you have created enough lift. So I say yes theoretically.
Now the question in my mind is how do you run an engine so hard that it compensates for loss takeoff speed? I not sure this is a realistic question.
Thats a totally different story as the question on hand, isnt it??😀
I am not sure at all, either! Its not possible! Ask the guy that jumped off the Eiffel tower, with wings attached😀
Steen🙂
I understand that there is no power transferred through the wheels, but the question was not stated in a way that implies that that is important. It should have stated that the conveyor moved at such a speed that the wheels did not rotate (i.e. the conveyor is moving forwards). If instead you take it to mean that the conveyor moves to cancel the linear speed of the wheels (i.e. conveyor moving backwards) then the plane will not take off, unless the wheels have no friction.
Cal Weldon said:
That is what I just thought of as well. However if we're taking all kinds of airplanes into consideration then why don't we just assume a VTOL plane and be done with it
Hi eVITAERC,
So you're saying a plane can't leave a skid mark? I see a definite problem with landings.
The error in logic is that the plane is not coupled to the ground via the landing gear. There is only a small energy loss due to rotational friction. This conveyer belt system reduces this friction to zero (or vary close to it, servo actuating force must be accounted for).
Now if the landing gear were encasted in cement in the ground, you would have an excellent point.
-Chris
So you're saying a plane can't leave a skid mark? I see a definite problem with landings.
The error in logic is that the plane is not coupled to the ground via the landing gear. There is only a small energy loss due to rotational friction. This conveyer belt system reduces this friction to zero (or vary close to it, servo actuating force must be accounted for).
Now if the landing gear were encasted in cement in the ground, you would have an excellent point.
-Chris
eVITAERC said:
We were typing at the same time. Even the ehaust from an underwing mount would add some draw over the top. There's simply too much air coming out for it not to.
If it were easy to build we'd already see it on aircraft carriers, for both take off and landing.
And it matters not whether you speak of linear or circular movement of the wheel/belt, opposite is still opposite.
I would have thought every plane that lands or takes off parallel to the equator would put an end this before it started.
anatech said:
Of course the plane can leave skid marks. That's friction at work. Rolling motion also depends on friction 100% you know
😉
The whole marvel of rolling motions is that there is continually a point on the wheel fixed to the ground via static friction. The wheel moves in such a way that friction never does any work, and therefore theoretically NO energy is lost in the rolling motion due to friction! (At least no in the tire rubbers anyways).
So in fact the gear IS coupled to the ground statically 100% all the time. It's the relative motion of other parts (pivoting of the wheel relative to the ground) that produces the forward motion of "rolling". However the conveyer belt in question exactly annuls that, so we nave no forward motion, no matter how hard the plane engine pushes.
Note that a cemented landing gear actually works less ideally, since at some point the engine would break the plane off the landing gear coupling to the fuselage, and it'll belliy-slide its way to a takeoff 😉
Ya, using the Earth's rotation to create lift is just too easy.
We also haven't touched on the air flow created by the conveyor belt itself.
Damn, I hate these threads, I'm supposed to be modding.🙂
We also haven't touched on the air flow created by the conveyor belt itself.
Damn, I hate these threads, I'm supposed to be modding.🙂
Cal Weldon said:
Well...
Technically that would be true, some air does get drawn along with the jetstream, but the engine would have to be pushing REALLY REALLY hard to produce any significant lift.
Also I took the conveyer belt thing to be: Wheel moves forward, so the surface of the conveyer belt moves backward. Simple.
rfbrw said:
Cal Weldon said:
Hehe nice try, but there's no wind 😎
Oh guys...
that simply can't be true... I must be dreaming...
Can you believe that a plane (assume a takeoff speed of 200km/h) can lift off on top of a conveyor belt that moves BACKWARDS at 200 km/h...?
YES, it WILL take off, as long as you have sufficient engine power, your wheel bearings create not too much friction heat and your whole landing gear is designed to operate at 400km/h...
The only thing important for taking off ist sufficient relative velocity between the plane's wings and the surrounding air. Assume no wind so you can say sufficient relative velocity between plane and ground. And this velocity is reached by the thrust of the planes engines, no need for the landing gear to do this... Back to the question, the only situation in which the plane would NOT lift of is when you fix its landing gear to the ground, mechanically.. as long as the plane is free to move relative to ground, it will lift off..
Andreas
that simply can't be true... I must be dreaming...
Can you believe that a plane (assume a takeoff speed of 200km/h) can lift off on top of a conveyor belt that moves BACKWARDS at 200 km/h...?
YES, it WILL take off, as long as you have sufficient engine power, your wheel bearings create not too much friction heat and your whole landing gear is designed to operate at 400km/h...
The only thing important for taking off ist sufficient relative velocity between the plane's wings and the surrounding air. Assume no wind so you can say sufficient relative velocity between plane and ground. And this velocity is reached by the thrust of the planes engines, no need for the landing gear to do this... Back to the question, the only situation in which the plane would NOT lift of is when you fix its landing gear to the ground, mechanically.. as long as the plane is free to move relative to ground, it will lift off..
Andreas
Andreas,
You and I are on the same page. I wonder if there is someone who actually knows the relation or ratio between the air flow over the wing as created by the engine thrust versus the amount of lift created by the plane through the air (on the runway). Maybe it's you. If we have that, we have our answer.
You and I are on the same page. I wonder if there is someone who actually knows the relation or ratio between the air flow over the wing as created by the engine thrust versus the amount of lift created by the plane through the air (on the runway). Maybe it's you. If we have that, we have our answer.
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