A plane on a runway, how smart is r3vlimited?

[bwanac]

OK.

The idea that the wheels just spin faster and the plane can still take off is correct. Another simulation I thought of.

Place a toy car on a treadmill. Move the belt and the car moves backward. Now with a plane the jets are applying a force to make it move forward. While this toy car is on the treadmill, put you finger behind it and push. You'll notice that you can push the car forward, and the wheels are not preventing you in any manner, just spinning faster. Now if it were a plane, the air would be moving under its wings, and would eventually take off granted the conveyor belt is long enough.

[Reynard38]

Wheel speed means nothing. Thrust mean nothing (gliders still fly with no thrust). Lift is what makes a plane fly. This requires air moving over the wings, and angle of attack between the wing and that wind.
We we use airpseed indicators in airplanes, not speedometers. If the plane on the treadmill has sufficient airspeed it will fly, otherwise no.

[RobertK]

Yes it will. The wheel speed has nothing to do with it. The plane's speed is matched by the conveyor, NOT the wheels' speed. So if the plane is moving at 200mph, then enough lift will be generated to fly.

That's only assuming that the plane's wheels produce no friction. I'm not arguing the wheel speed at all. We've got that one out of the way.

Here's an example of what I'm talking about.




By the way.. the conveyor cannot simply accelerate and not increase it's force (thrust). An increase in speed of the converyor requires an increase in acceleration which requires addtional force.

The plane requires the engines to pull it across the ground (moving or not) to get up to the proper speed required for take off. The plane can take off only if it can produce enough thrust to overcome the friction being made at the wheels and allow it to accelerate against them.

[redhatpat]

And so this problem makes it to r3vlimited...

Some people really need to think this through before posting.

Of course the plane will take off. Airplanes create forward motion by moving air via props or jets, not by moving its wheels. A planes wheels freewheel. The conveyor belt is irrelevant to the plane's motion.

[RCWells]

Yes it will. The wheel speed has nothing to do with it. The plane's speed is matched by the conveyor, NOT the wheels' speed. So if the plane is moving at 200mph, then enough lift will be generated to fly.

[RobertK]

I think of it like this.

First stand on a treadmill and turn it on.. oops! You fell off!

Next, put some rollerskates on, stand on the treadmill and turn it on. You will eventually fall off but not as fast (because the wheels reduce friction).

Last, now attach a rope to a the wall in front of you and at the end attach a vegtable basket scale, get back on the treadmill one more time with the rollerskates on, and hold yourself in place. The scale will give you a good idea of the amount of forward thrust need to keep you in place on the treadmill. Increase the speed of the treadmill and let me know if the scale does not increase the weight reading.

[blunttech]

if this plane ever takes off will someone let me know as i need cheap airfare to get my mom down to puerto vallarta in feb

[Mike325]

Think of it this way maybe. You are on a treadmill. You turn it on and you don't move. You will fall off because the belt is moving. When you match the speed of the belt, you don't go forward or backwards. You are moving your legs, but covering no distance. So now, the plane's wheels are moving at the same speed as the conveyor belt. A plane gets it drive from the engines moving air, not from drive at the wheels. This means that the plane's engine have to be on and creating enough push to push the plane as fast as the conveyor belt. If the wheels are moving at the same speed as the belt, the plane will go nowhere, it is in one spot, not covering any distance. No distance = no movement. No movement = no wind. No wind = no fly.

You can give me my metal now kthnx.

[RobertK]

You forget that significant drag is being created at the wheels and the force of the coveyer moving against the wheels is transfered to the plane.

Put the plane on the conveyer going 0mph eventually the plane will roll off the end. So it is relevent unless you are implying that the plane is already at a specific speed before hitting the conveyer.

If you are setting the plane on the conveyer at 0mph and then start both at the same time then you would need the coefficients above to calculate the amount of thrust and speed needed to overcome the friction and drag create at the wheels & conveyer belt.

[joshh]

Rock paper scissors anyone???

[1991 318is]

The question is clear. "The plane moves..." - implies speed. Speed is time to distance. The plane is moving in relation to point(s) in space - not the conveyer. The speed matching part of the conveyer belt is simply for distraction. It has no bearing on the speed of the plane in relation to time and distance traveled.
Again - "The plane moves..."

[Axxe]

The conveyor DOES NOT MATCH THRUST!! IT ONLY MATCHES SPEED!!

[RobertK]

Ok damnit.

This question bugged the shit out of me all night to the point that I actually went to one of the head professor's in the department I work for at UT and asked him.

Here is the response.

In simple realistic case.. No.. the plane will not take off. Through the wheels are free flowing they are not frictionless and do create drag at more than one point in the equation.

Otherwise there is not enough information to create a formula. Assuming that the conveyer system is able to perfectly match the acceleration and thrust of the plane. - Here is what I was told is relevent to this equation that is not mentioned

[1] Max thrust of the plane
[2] Max acceleration of the plane
[3] Weight of the aircraft
[4] Weight of the wheel
[5] Number of Wheels on the plane
[6] Coefficient of rolling friction @ wheel and conveyer belt
[7] Coefficient of rolling friction @ wheel and axel link

[joshh]

I can firmly say with these examples, I do not know WTF I'm talking about, but at least I can admit it.....

I did another test last night. I filled a glass up with ice, filled it up with water till the ice was actually floating....EXACTLY the same as if I had just filled it without ice once melted. Intresting...

[Axxe]

There's a big difference between knowing what you're talking about and thinking you know what you're talking about.

Yes, and judging by your post, you fall under the latter :D