"No. The plane's wheel bearings have infinitely less frictions than my fat butt sitting on a treadmill belt.

The only force the engines have to overcome is the rolling friction in the wheel bearings. That force doesn't add up to a rounding error compared to the tens of thousands of pounds of thrust the engines will develop."

i am not getting on how the plane will not have airflow going opposite over its wings if the ground the plane is sitting on is moving. on a carrier, the carrier generates air speed moving, so would the treadmill. what ever the plane is sitting on and moving will generate air speed.

if the plane has a top air speed of 100mph and the treadmill is making a 150mph wind across the planes wings in the opposite direction the plane needs for lift, i do not see how the plane will ever take off.

 

That's just it. the treadmill is not making anything across the wings. It cannot move the plane because the wheel bearings + the engines take the treadmill right out of the picture.

I'd explain it better, but I'm too darn drunk right now.

 

*SIGH*
The only thing that matters is how fast the air is flowing over the surface of the airfoil. (the wing)
Now whether the plane is moving forward or the wind is blowing that day is irrelevent to whether the plane will get airborn or not.
It's in how much lift is generated over the airfoil and that is only possible with movement of air over the wing in relation to the position of the wing.
Without that the plane will not leave the ground.
Irrelevent whether the plane is moving forward, backward, whatever. The air must be moving from the front leading edge of the wing toward the rear at a minimum speed in order for the necessary lift to be generated.

 

yes, thats what i been saying, thats why i said if there is more wind coming from behind than the plane can compensate for, it will not lift off.

it doesn't matter if the plane is moving backwards in relation to the ground, it maters in relation to the air.

 

I'm slow but finally catching on to the question. The answer is yes. The plane is not a ground drive vehicle. The engine thrust will propel the plane regardless of wheel contact with a treadmill. A hydroplane will take off without the use of any wheels at all. It's all relative to ground speed and the lift created by moving through the air.

Maybe I should start watching the videos in the beginning of these things.

 

I think the big problem is the question gets worded wrong a lot.

The question should be stated like this.

There is an airplane sitting on a runway that acts like a large conveyor belt. As the airplane accelerates for take-off, the conveyor belt accelerates in the opposite direction to match the speed of the airplane. Will the airplane take off?

Now that we have the question worded right, lets look into the solution more.

As the plane accelerates the engines create thrust by pushing against the surrounding air. Since the friction in the wheels is negligible the plane will start to move forward. Once the plane starts moving forward the treadmill starts to move in the opposite direction, but because the friction in the wheels is negligible the conveyor belt exerts no force on the plane, it simply causes the wheels to spin twice as fast as the plane's forward speed.

For example when the plane reaces a speed of 100mph, the treadmill will also be moving at 100mph in the opposite direction, the wheels will have to spin at 200mph when compared to the treadmill surface.

Your aircraft carrier example is a completely different situation because the while the plane is creating no thrust and is sitting still on the deck it is still acutally in motion when compared to the earth as a whole. Also you are dealing with wind. Neither of these are facotrs in the original question. The reason aircraft carriers turn into the wind when launching planes is to make it easier to launch. It is the same reasoning they launch toward the front of the carrier instead of the rear. If the carrier was sitting still and there was no wind lets say that a plane had to travel X piles per hour in order to launch. Now lets say the carrier is moving 10mph, but there is no wind. The plane would only have to accelerate to (X-10)mph in order to launch because the airflow over the wings was already equivalent to the plane moving at 10mph. Now if you point the carrier into a 20mph wind, with the carrier moving at 10mph, the plane only has to accelerate to (X-10-20) or (X-30)mph to launch. Because when sitting still the surrounding air is already flowing over the wings at 30mph.

Now lets say you launch off the back of the carrier. If the carrier is moving 10mph you would have to accelerate to (X+10)mph in order to launch, because at 10mph there would be no airflow over the wings because the plane and air would both be sitting still relative to the earth, while the carrier simply drove out from under it. Now lets say your heading downwind with a 20mph wind. The plane would have to accelerate to (X+30)mph because it would have to travel 30mph just to overcome the relative motion of the boat and the wind.

Wow, my brain hurts now. I'm going to bed

 

I thought the aircraft analogy was answered quite nicely in another thread by this brilliant poster.....

https://www.ford-trucks.com/forums/6...12-12-a-5.html

Or, if you don't want to follow the link.....

And by the way, WWII aircraft carriers needed to go at a much higher speed because the flight decks were much shorter and their catapults didn't have near the power (or length) as modern day carriers have. Also, flank speed for them was much less than modern carriers. The CVE (so-called Jeep carriers) had a flank speed of well under 20 knots compared to today's carriers being into the upper 30's or even faster it has been rumored .

But anyway, back on topic, you can't compare a treadmill to a carrier - you are just confusing the issue.

 

That's what I was referring to. The catapult system. I guess that just slipped by some. Turn the plane around and use our 100 mph super treadmill as a catapult system and the plane takes off pretty quick.

I guess unless you've seen it people just assume planes take off & land on carriers with no assistance.

 

bf250...you're to be commended for giving this scenario so much thought and explaining your rationale...you are definitely sticking to your guns and that's an admirable trait.

But when all the pieces of this debate finally fit together, and the light goes off in your head...let me know so I can shut down my PC. Because that light will be so bright it'll fry my LCD monitor!

J/K !!!! It's a good debate!

 

Ok, for those who 1) cannot follow the logic and/or 2) refuse to believe their own eyes after watching the video proof posted in post#3 and still think the jet will not fly away normally.

Here is the math.

A 747 weighs 393,000 lbs (empty) and has four engines that produce 63,000lbs of thrust each.

The coefficient of rolling friction for properly maintained air-filled tires on a smooth surface is between 0.01 and 0.015
The standard friction equation used to determine the value of rolling resistance is:
FR = ìRW
where:
• FR is the resistive force of rolling friction
• ìR is the coefficient of rolling friction for the two surfaces
• W is the total weight of the 747 jet
• ìRW is ìR times W

So resistive rolling friction caused by the wheels contacting the backwards moving treadmill = 5895 lbs=0.015*393,000 lbs

Gee, that only leaves 246,105lbs of thrust available for forward movement! Do you really believe the jet is not going to move forward if it only takes 2% of its power to overcome the backwards force?

 

Great post. And worth mentioning is that like any friction situation that I know of, you get the highest friction in the static (stopped) condition. If you have ever flown a plane, or paid attention to the sound of an airplane engines, you notice that the engines rev or spool up to get the plane rolling, then throttle way back to keep it rolling.

Thanks for injecting some science into this thread, Sigma. You trying to ruin it or something?

 

it's a Poll. i blame it on Beast. everything will crash.

 

Sigma...you're data is faulty. The friction coefficient is off.










They us "properly maintained nitrogen-filled tires"...


So wouldn't that result in an even less friction coefficient and MO' POWER to allow the jet to take off??

Just kidding. After 6 pages of posts on this, a person gets loopy.

 

No, Nitrogen INCREASES rolling friction. HELIUM!!! will decrease friction significantly.

 

Stop the insanity.....Please....The AARAM will take the plane out....