Airplane physics question

You just couldn't resist...could ya?

 

So are people still convinced the plane won't fly?

 

Only 50%

 

.
Image Unavailable, Please Login

 

The airflow over the wings cause it to create lift so, airspeed decides lift/flight not ground speed or moving ground-belt.

I am surprised so many people think a moving ground will cancel the planes ability to create lift? So, people would believe that if you fly a small airplane over water the is rushing past at over 100 mph the plane will crash down?

 

I've just built a huge conveyer. Rob is going to fly his plane to my property and we are going to try this out. We'll let you know what we find out when he takes off.



GT

 

A big YES. The conveyor belt will always match the speed of the tire provided the tires aren't slipping. Just becoz the
Conveyor belt matches the exact speed of tire rotation doesn't mean the plane has to be stationary. All it means
Is that the tire is not skidding or slipping. The plane can move forward becoz of thrust, ( prop blast or jet thrust ) being the
Driving force. The wheels will spin faster than normal becoz of conveyor belt effect but will not achieve sufficient
speed to make the air speed zero. Airplane wheels will just roll freely to minimize point of contact resistance ( ground ).
I'll even give you a negative wind, meaning wind coming from behind. As soon as that pitot tube or IAS ( indicated air
Speed ) and wing senses enough wind for lift, that plane will take off.

It is the air rushing past the wings that makes the plane fly, not the ground speed. Planes can take off with wind
coming from behind. The plane will need longer runway, that's all. Your conveyor belt speed will ALWAYS match
the exact speed of the tire until lift off when the tire looses contact with the conveyor belt. The plane will move forward becoz of thrust generated. The plane makes is own wind by moving thru the air. You can speed up the conveyor
belt as fast as you want but since it cannot control the air above it the plane will fly.

 

If i understood the question right, it is asking if the plane could take off ONLY by the conveyor belt moving? If that's correct then the plne would be hovering, which they don't do.

 

Just make sure the back end of your conveyor belt is perched over the now opened missle site.

 

Geez this has gone on a long time and frankly the 50% no fly votes concern me.
You guys ever heard of a seaplane?

 

In order for me to draw a conclusion, I need to know one more key piece of information.......

How drunk is the pilot???

 

Won't fly in a a vacuum.

 

I got fooled. I voted no, but the answer is yes, they plane will fly.

The thrust from the engines will push the plane forward, the wheels will just be spinning twice as fast as normal when it takes off.

 

Image Unavailable, Please Login
Image Unavailable, Please Login

 

Yes, indeed. As long as the plane has positive thrust, attitude stability, and sufficient aerodynamic pressure (to generate "lift")........ it CAN achieve take off.

....sorry about breathing life into this old thread, but I just now came across it

 

I have not read all 50 pages but surely someone posted the Mythbusters Episode


[ame]http://www.youtube.com/watch?v=YORCk1BN7QY[/ame]

 

Badly flawed. Didn't stick to premise of thread which reads thusly;

 

The Mythbusters conclusion clearly shows that the conveyor is not keeping up with the wheel speed (you can see the plane passing several cones showing the wheels turning faster than the conveyor is moving). If it were, there would be no relative airspeed, and thus, no lift. I say the plane does not fly.

If a plane somehow gets enough relative airspeed from the prop pushing air over the general area to create lift, then I say the plane could fly, but that would not happen with a typical plane propulsion system. It would need something like a rocket to create enough general air movement.


BT

 

Good point BT. I see what you are saying. The statement does say the conveyor belt is designed to exactly match the speed of the wheels in an opposite direction.
If this condition is met as stated, the plane will never move forward. If the wheel speed is met in an opposite direction with the conveyor belt moving at exactly the same speed, there will be no ground roll and no air speed, no lift.
After 51 pages, I am sure this has been pointed out several times by gentleman much brighter than me, just an interesting thread.
Ok, now the dead horse can go back to sleep.

 

This is the best summary. If the premise of the question is followed the plane will not take off. If the premise is broken, then the reality is that the plane will take off, as shown on the Mythbusters clip. so again, if the question is to be answered following the premise of the question, the plane will not take off as there would be no relative airspeed.

BT

 

Sorry i'm late to the party, and i also apologize in advance for not having read the whole thread

I'd like to offer the board a well-reasoned answer to the original question ... but it's in 5 parts

I used to be an engineer, and let's just say i'm no stranger to physics We'll start with a brief introduction to friction, and develop the story from there.

Are you guys game, to indulge me through a 5-part answer, developed in 5 posts? Thanks in advance. Maybe we'll just start with Part I, straight away ... you guys let me know if what i might offer is worthy of continuation

 

Whatever it is.....we've already heard it.

 

PART I : Basics of Friction

Let's start basic, by imagining a slab of rubber on your table. Nothing is touching it, except your table

What forces are acting on this rubber slab? Just two : the vertical force of gravity, pulling it down, and the force of the table, balancing the gravitational force by pushing up against the slab.

Now, let's exert a horizontal, or lateral, force on the slab ... by trying to push it across the table. At first, the slab/table interface will "resist" this lateral force, through the force of friction. You exert a lateral force with your finger, but this finger-force is balanced in the horizontal dimension by the friction force acting on the slab in the other direction ... so the slab refuses to move. It's worth noting that the while the friction force is acting against your push on the slab, the slab must also then be exerting an equal & opposite friction force to the table. But the table's legs are stuck to the floor ... so it's not moving

But alas, you keep increasing the horizontal force on the slab, and at some point the slab starts to move. You have exceeded the maximum friction force that the table/slab interface can produce. This maximum friction force is established by a simple, well known relationship : Fmax = u*N, where Fmax is the maximum friction force, u is the coefficient of friction, and N is the normal, or vertical force exerted by the table on the slab (that's the vertical force balancing the gravitational force).

What do we learn from this quick intro to friction, as it might relate to the original question? One key point, i think it may be the most relevant : you can't "tell" how much lateral friction force is acting between the rubber slab and the table, just by me telling you that the slab isn't moving The friction force, balancing the finger-push, may be close to zero (if you're pushing very lightly), or may be close to the Fmax limit (if you're pushing hard, but not hard enough to move the slab) ... but in all cases, the slab isn't moving (until your finger-push exceeds Fmax).

And so it is with a rolling tire A rolling tire, that is not ... i repeat, NOT ... sliding on the surface of a road, is very much like our rubber slab on the table. The point on the tire, right where it's touching the road, is NOT moving relative to the road ... IF the tire isn't sliding. (That contact point on the tire isn't moving horizontally, if the tire isn't sliding, and it's vertical velocity is also zero, as it reaches the bottom of its movement. This well-known principle of kinematics allows the contact point of the tire to be considered an "instantaneous center", but we won't need to develop that any further here). There may very well be a horizontal or lateral friction force present, between the rolling tire and the road, but we can't tell without examining the situation further. Which is exactly what we'll do in Part II, when we examine both the front & rear tires of a 4 wheel car, with rear wheel drive, driving down the road

 

well , surely no need to listen again.

But i've got some spare time tonight, so i'll just proceed anyway. Feel free to ignore, of course

 

Looking forward to your insights!