Will it take off?

[Rockets]

Plane or Shuttle, jet engine or rocket motor, wings or no wings

it really does not matter ( yes, I know a plane can't fly w/o

wings). The forward propulsion is the same. The wheels and conveyor

belt have no part in this equation. The conveyor belt could be

going a billion times faster in the opposite direction and the plane or

rocket will still fly. The thrust or drive is not against the belt.

It's not an automobile where the wheels are what's being powered or

driven against the ground or belt. In the case of the plane the wheels

are free rolling and totally independant of the propulsion.

What if the plane were already in flight and you were able to raise the

counter rotational conveyor belt up such that it contacted the

wheels. Would the plane suddenly stall out and be unable to take off

again??

I've probably restated whats previously already been stated several times already. My apologies to the original staters![]

[PhilMays]

I guess one other area that I am stuck at, and perhaps the "it will fly crowd" can explain is.

If it is on a conveyer belt, and that is the "Red Herron", are you saying you will still need the length of the runway for it to take off? Am I understanding that the thrust will still act like it does and that the wheels and conveyer belt is just a point to throw people?

[PhilMays]

Oh and Travis, thank you very much, you are far too kind. If not for me, I would post that picture on the Prettiest Woman thread. I my friend, am the proverbial beast.

That sunset picture was taken on our balcony during an Alaskan cruise in August. It was simply spectacular and I felt lucky to be at the right spot at the right time, with the right woman[]

[mas]

It will not fly, just as a car on a dyno with not reach any speed. The wing needs air to move over it's wings, and it is not getting any. Just like the car's tires need friction to move forward, it is not getting any on a dyno. If you are talking about propulsion (jet thrust) there could be enought, but then it is not longer an airplane, it is a rocket, and by definition it is not flying.

The Space Shuttle is perfectly stationery on the pad, but it sure can take off. However, when it takes off it is a rocket, when it lands it flying.

Travis

I should know better...

But I find myself stopping by just to gawk just like a rubber-necker who slows to gawk at an accident on the highway...and the carnage is - well, I am not sure if it is simply tragic or comedic! [] But then comedy is laughing at another's tragedy! ...Just ask Wiley.E.Coyote!

The first part of this is right on the money! The conveyor is analogous to a car on a dyno! And the velocity can theoretically become infinite while the total net displacement is equal to zero! And if the model is limited to this frame of reference, the plane does not fly![]

But then the analysis begins to very quickly go south.[]

So, let's see... An airplane is a plane, evidently by virtue that it is able to fly due to its forward force being delivered via the rotation of its wheels. [][:'(]

And if the forward force is delivered via jet thrust it is now a rocket and no longer an airplane and rockets do not fly. []

So close to understanding, yet so far!

Yes, if the forward force is delivered only via its wheels the plane will not have any forward displacement and as such no lift will be generated (precluding a VERY strong breeze flowing over the wing surface from the front!)

And I guess using our definitions of what constitutes a plane, this is a car! []

But force CAN be applied elsewhere in the model, and NOTHING in the problem precludes this. And the last time I "flew", just 9 days ago, it was on precisely one of those vehicles that I am now told cannot fly "by definition", as the non-airplane had jet engines and was acclerated due to jet propulsion acting directly upon the air and not by applying energy via 'drive' wheels.

So now the plane cannot fly as we have effectively redefined the meaning of what qualifies as an airplane and by what qualifies as flying. []

I can't help but be reminded of the comment that came out of the Watergate hearings that seems to apply here: If we were to bring an elephant into the room, we would be told that "no, its not an elephant... its a mouse with a glandular condition". []

Folks, its an airplane. And they do on occassion fly in exactly the manner alluded to above.

But lest some of you are out in the real world, Please remind me to avoid bridges in the future! But the analysis of this silly problem has certainly provided me with additional insight into why the world is in the shape it is in. And I will cry after I can stop laughing...or is that laugh after I stop crying...or well, it is such a dilemma! [] [] []

I think its time for some of you folks to stop 'thinking' and go watch football![]

Enjoy! [][]

[Ray Garrison]

PhilMays said

"I guess one other area that I am stuck at, and perhaps the "it will fly crowd" can explain is.

If it is on a conveyer belt, and that is the "Red Herron", are you

saying you will still need the length of the runway for it to take

off? Am I understanding that the thrust will still act like it does

and that the wheels and conveyer belt is just a point to throw people?"

Yes. It actually might need a slight bit more than the standard take off length, because there is some additional rolling friction due to the higher rotational speed of the wheels, but that should be pretty much diminimus.

When you said your were stuck at this point, what did you mean?

[mas]

I guess one other area that I am stuck at, and perhaps the "it will fly crowd" can explain is.

If it is on a conveyer belt, and that is the "Red Herron", are you saying you will still need the length of the runway for it to take off? Am I understanding that the thrust will still act like it does and that the wheels and conveyer belt is just a point to throw people?

An easy way to overcome this is via the use of a catapult, either complete (in that it is able to accelerate the vehicle without contact with a surface) or in a limited manner such as on an aircraft carrier! They are used specifically due to the limited availability of runways!

Runways are only necessary due to the fact that the instantaneous velocity does not begin at the velocity necessary to develop sufficient lift, not because flight requires wheels to turn! If you have a manner of thrust sufficient to accelerate the plane from rest to the velocity generating sufficient lift, no runway is necessary!

The entire conveyor 'part of the model' is a red herring relative to a plane's ability to fly! Just enlarge your frame of reference!

Stick a fork in me! I'm done here. []

[PhilMays]

Captains Log: 11/19/2006 2:15PM

I initially ran into a problem. The Rosanne Barr girdle was larger than I thought and could even comprehend. While I thought I could cut it down to a 300 x 60 foot piece, I could only manage to cut it down to 378 x 84 as our local land fill could not take any more scraps.

I have had to make do. I ordered several 100 more Mexican jumping Chinchilla's to make up for the extra length of the conveyer belt.

I placed the MIG on the belt and 300 pounds of raisins in the front. As the Mexican jumping Chinchilla's ran for the raisins, I slowly increased the speed of the MIG, THEN IT HAPPENED! The very fabric in the seam of the Space /Time continuation opened up. I saw bright colors and was propelled down a tunnel of light! Time itself started to reverse, I saw my Grandparents, Einstein, Lincoln, King George, Moses, Adam, and indeed...Dinasours, Even the very first Moss and Lichens. I eventially ended up in a holocoustic world of volcanic activity and storms beyond your wildest imagination.

It then hit me, I think my time expired on the parking meter and I'll be damned if I'm going to get another parking ticket, so I went back and put another quarter in the meter. Now the Chinchilla's are on strike, the MIG has been seized by the government, and Rosanne Barr is looking for me, so BACK TO THE CAVE!

[PhilMays]

I was stuck at the converyer belt and the concept of maintaining the axact coordinates. However, I can see now where it will travel forward and that the Conveyer belt was set-up to throw one off. OK I'm like a politician....I'm changing sides, IT CAN FLY!!!

[dtel's wife]

Phil,

Entertaining, as always.

[PhilMays]

Phil,

Entertaining, as always.

Why thank you! MY wife thinks I'm a nerd!

[sputnik]

I was stuck at the converyer belt and the concept of maintaining the axact coordinates. However, I can see now where it will travel forward and that the Conveyer belt was set-up to throw one off. OK I'm like a politician....I'm changing sides, IT CAN FLY!!!

Good job Phil.

[PhilMays]

Thank You Sputnik

Now, I am going to get a LOT of wood and a woodchuck and we will solve this very important age old problem!

[bodcaw boy]

will it take off?

yes.

4....3....2....

boy!!

[klipschaholik]

Hmm, maybe looking at the problem from another perspective will help the non believers. Watch this video clip of a glider being towed into the air with a rope attached to a winch. The rope provides the forward force to accelerate the plane to a speed that enables to wings to support lift and it takes off. Now consider the ground underneath the glider as moving in the opposite direction and speed as the glider moves forward. Just as the winch rope is not connected to the ground, the air forced out the back of the engine or propeller is not connected to the ground either. Therefore the glider moves forward, accelerates and is able to fly off. The aircraft sitting on the rolling surface will with the thrust generated accerates forward across the surface and takes off as well. Does everbody follow what I say?

=

[Travis In Austin]

I finially had the nerve to ask my wife last night. She thinks I'm wierd anyway for going to this sight and "chatting".

Let me "set the table". Last night we went to Circuit City and Best Buy as I wanted to buy a SACD or DVD-A. A line had formed at both places for the new Nintendo game thingy. I got in the car a caughed "nerd" several times just watching these people in the cold.

Anyway when we got home and I read this thread and decided to pose this question to her. Keep in mind she has a graduate degree and works in the medical field in an operating room on very delicate cases giving anesthesia. Certainly no dumb cookie and I contend, almost as smart as I [].

Phil,

In my opinion you have the best Avatar on the forum.

It will not fly, just as a car on a dyno with not reach any speed. The wing needs air to move over it's wings, and it is not getting any. Just like the car's tires need friction to move forward, it is not getting any on a dyno. If you are talking about propulsion (jet thrust) there could be enought, but then it is not longer an airplane, it is a rocket, and by definition it is not flying.

The Space Shuttle is perfectly stationery on the pad, but it sure can take off. However, when it takes off it is a rocket, when it lands it flying.

Travis

I am really having a problem understanding why there's so much misunderstanding here. A car moves by using it's tires to push against the road. Put a car on a dyno, or conveyor belt or whatever, and it won't move, because the surface the tires are pushing against is going in the other direction at the same speed, so the car's body doesn't move.

A plane moves by pushing against the air, not the ground. [That is the whole point, under the problem given, if I understand it correctly, the plane remains in a fixed position reletive to the ground. Assuming no wind, no air is moving over the wings and thus no lift. The plane has to move forward in order to get air over its wings. I am picturing the plane like a rat on a treadmill, if speeds are matched and it does not move forward relative to the ground, it can run until his little hears explodes, put he does not move forward. If the converyer belt system is such that the plane does not more forward it does not fly. Put chocks around all the tires on a plane, put it at full throttle, it does not fly.] What the ground beneath the plane is doing has no impact on what the air the plane is sitting in is doing. [That is true, but wings are not moving through the air, or if there is not a head wind stronger then the stall speed of the plane, it will not "fly." ] If the air is stationary, and the plane is pushing against the air, [it is not pusihing against the air, it is stationery because the belt keeps it from creeping forward]. The wheels are not driven, remember, they just rotate as the plane moves relative to the ground. [that's exactly right, but because of this no air flows over the air foil/wing, thus no lift is created and it will not fly.]

Try this. You're flying above this conveyor belt. Your landing speed is, say, 100 mph. The belt is moving in the opposite direction at 100 mph. Could you do a touch and go? Well, sure. When the wheels touch the belt, they will begin rotating at a speed of 200 mph (you're going forward at 100 mph, [not under the problem given, as soon as it touchs the belt it is stopped, not moving forward at all] , belt is going backwards at 100 mph) but you could touch down, run down the belt at an airspeed of 100 mph, and take off again. Now go around, touch down, throttle back a bit to, say, an airspeed of 50 mph, then accelerate and take off. We can do that, right? Okay, do another go around. Touch down, throttle almost all the way back until you have an indicated airspeed of 0 mph, and the only thing the prop is doing is resisting the rearward force the belt is imparting through the friction of the rotating wheels. this is exactly the starting point of the question, except that the belt is moving faster in this scenario. Now accelerate and take off. [The problem assumes that the plane cannot accelerate, the belt matches the speed of the plane as trys to move forward, you have changed the hypo so that the plane already has enough lift to fly.] Still with me? The belt could be moving at any arbitrary speed, it doesn't matter. The plane's thrust comes from pushing against the air, not the belt. As long as the air is not moving in the same direction and the same speed as the belt is moving, the plane will propel itself through the air and take off.

[Travis In Austin]

I guess one other area that I am stuck at, and perhaps the "it will fly crowd" can explain is.

If it is on a conveyer belt, and that is the "Red Herron", are you saying you will still need the length of the runway for it to take off? Am I understanding that the thrust will still act like it does and that the wheels and conveyer belt is just a point to throw people?

An easy way to overcome this is via the use of a catapult, either complete (in that it is able to accelerate the vehicle without contact with a surface) or in a limited manner such as on an aircraft carrier! They are used specifically due to the limited availability of runways!

Runways are only necessary due to the fact that the instantaneous velocity does not begin at the velocity necessary to develop sufficient lift, not because flight requires wheels to turn! If you have a manner of thrust sufficient to accelerate the plane from rest to the velocity generating sufficient lift, no runway is necessary!

The entire conveyor 'part of the model' is a red herring relative to a plane's ability to fly! Just enlarge your frame of reference!

Stick a fork in me! I'm done here. []

Thank you,

That is exactly why it will not fly. Aircraft carriers would have belts, and not catapults if this worked. It is much easier to make a belt that moves ahead at 115 knots then it is to maintain and use those catapults. If it would fly by being put on a belt you could launch a plane off almost any size ship. We could cut the cost of a carrier in half and have twice the fleet, unfortunately it won't work.

The reason it won't fly is the very reason we have multi-billion dollar aircraft carriers and 300 million dollar wind tunnels. Because putting a plane on a belt so as to have it remain stopped, relative to the ground will not get it in the air, unless it is a Harrier.

Travis

[sputnik]

I'll just repeat my question for dwilawyer:

How does the conveyor impart any horizontal force to the body of the plane that opposes the plane's thrust?

You're under the misconception that the plane remains stationary.

[Travis In Austin]

Thrust has nothing to do with it. If I understand the original problem, the plane does not move forward. Tie a plane to an anchor, if it can't move forward it can't fly. If the belt is rigged in such a way that the plane does not move forward relative to the ground, all of the thrust in the world is not going to get it in the air unless that thrust is directed downward as in the case of a Harrier. Thrust does not make a plane fly, it is the means by which it moves the plane through the air, which causes air to move over the wing, which causes lift.

Here is a much better example. Everyone has held there hand out a moving car with your palm flat and parralel to the ground. You can make your tilt your hand back and forth to cause your arm to go up and down. Your hand becomes a wing in effect, with air moving over it.

It the WILL FLY's are correct, you can put a car on a dyno, get in it and the same thing is going to happen with your hand. We all know that it won't because your hand is not moving through the air.

[klipschaholik]

That's your problem, there is nothing in the original problem that says the airplane doesn't move. The whole basis of this hypothetical scenario is that the ground below the airplane moves. What you can't seem to grasp is that the ground below the plane is moving but not with respect to the earth, therefore the plane can and does move forward with respect to earth. Read the problem again.

a plane is standing on a movable runway( something like a conveyor).as the plane moves the conveyor moves

[Travis In Austin]

I'll just repeat my question for dwilawyer:

How does the conveyor impart any horizontal force to the body of the plane that opposes the plane's thrust?

You're under the misconception that the plane remains stationary.

I guess the real question is under these facts does the plane remain stationary on the belt or not: a plane is standing on a movable runway( something like a conveyor).as the plane moves the conveyor moves but in the opposite direction.the conveyor has a system that tracks the speed of the plane and matches it exactly in the opposite direction.

If the plane moves forward (relative to the ground, not the belt, assuming no head-wind) to the point it can get to stall speed (assume 100 mph) then it flys. If in cannot reach that speed, relative to the ground, because the belt moves in the opposite direction, then it does not fly.

The way I read the problem, there is no way for the planes wings to move through the air at 100 mph, but if they do, it will fly.

I guess i am just reading it wrong, planes don't care about ground speed, as has been point out on here, what is important is airspeed. So if there is a 50 mph headwind, the planes AIR SPEED indicator (ASI) would read 50 mph even while it was sitting perfectly still on the runway. The plane would start accelerting down the runway and when it reached 100 mph could fly, which in the case of a 50mph headwind would be a ground speed of 50 mps. If it took off downwind, or with the wind, it would have to get up to a ground speed of 150 mph in order to fly. So I guess the big question is what does the problem mean by "Speed."

I read the problem as meaning when the plane just started to creep forward on the belt the belt would move in reverse meaning that the plane did not actually increase its ground speed at all.

The problem works the exact same way with a car, instead the question is not "will it fly" the question is can the car ever reach a speed of 100 mph relative to the ground, not the belt. If it can, the plane will fly, if it can't it won't. It is as simple as that.

Travis