Would the plane take off?

[ScatterPlot]

Wow I felt like an idiot after the first about four posts. I thought no at first, then I was like, duh, yeah it will. For any people still needing an explanation, here's my go at it:

The wheels cannot produce any force other than straight up. Simple statics concept, if you try to push the ground under a cart then the cart won't move (assume frictionless wheels). The treadmill, therefore, cannot exert any force upon the airplane. The airplane in turn pushes against the air. Since there is a force pushing the plane to the left (say it's facing left) and nothing on the right (since the wheels can only push upwards, any other direction and they rotate) there is a net force to the left. What do imbalanced forces do? Induce motion. Hence, the plane will take off because it will start moving and behave EXACTLY like normal. There is a groundspeed, the plane does move sideways before taking off. The belt is irrelevant.

Example...
Say the belt is already moving at 100,000 miles an hour. With NO friction, will the plane move? No, so why would it not move when the plane is going 2 miles an hour in the opposite direction? 10 miles an hour? 300 miles an hour?

Nother example...
Say there was a hovercraft with wings. Put the hovercraft on a runway. Can it still move? Yes.

[Cow hunter]

looked it up/...... doesnt sound right but sayz the 747 has a takoff speed of 500mph...... maybe...... or not.......

[neppo1345]

Haha good for him. I'm a '98 BS Aeronautical Studies from the best flight school in the world University of North Dakota. I hold a Commercial, CFI, CFII certificate SEL. The example of taking off on an icy runway was a real-world example that I have done in my life.

I think this issue has already been answered enough. The airplane will fly.

Whats scary is that one day...you may be flying something that he him or myself have designed

Except I got the question right...

[benzy2]

At very first i was thinking that the thrust was dependent on wheel speed. Once the first guy said it would fly it made sence that it would move forward no matter how fast the ground under it was moving backwards. As long as the treadmill doesnt go so fast to bust something or cause so rediculously great amount of friction that the engines cant over come it the plane, as most have agreed on, will fly. The jets thrust air having nothing to do with the ground or its speed.

[anomoly40]

Haha good for him. I'm a '98 BS Aeronautical Studies from the best flight school in the world University of North Dakota.

Well he's just BS'in his way through it.

That joke never gets old.

[bjjb99]

Interesting puzzle.

From a purely physics standpoint, the wheels decouple the 747 from the conveyor belt runway, and the plane just takes off as it normally would. The wheels would just spin at twice their normal rate as the 747 rolls down the conveyor belt during takeoff.

Cow Hunter posted that the takeoff speed of a 747 was around 500 miles per hour. This seemed high to me, so I did a bit of digging. According to the following link:

http://www.airnewzealand.co.nz/aboutus/fleet/aircraft_statistics.htm

the takeoff speed is around 250 kilometers per hour, or about 155 miles per hour. This link:

http://www.aerospaceweb.org/question/performance/q0088.shtml

lists the takeoff speed to be 180 miles per hour. I think we can safely say that the takeoff speed for a 747 is at least 150 miles per hour, which will be important later in this post.

I also came across something interesting from Boeing's website. They have some PDF files listing various performance characteristics of aircraft for the purposes of airport planning. The section on a 747-400, the most common variant these days, lists a tire speed limit of 235 miles per hour.

If the plane is moving in one direction at some speed "V" and the conveyor belt is moving in the opposite direction at that same speed "V", the wheel speed will be 2V. Since 235 miles per hour is the tire speed limit, 2V = 235 mph. V = 117.5 mph. The 747 will exceed its tire speed limit by anywhere from 27 to 53 percent before it reaches its takeoff speed (of 150 or 180 mph). As to whether this will result in exploding tires or not is up for speculation, but if the tires do blow then the plane is no longer decoupled from the conveyor belt.

I'm not so sure the plane can take off from a conveyor belt runway under "real world" conditions, given the above tidbits of information... shame I already cast my vote in the poll.

BJJB

[bleachit]

if the tire speed limit is 235 mph, then my guess is after prolonged speeds of 235 you will see a failure. This failure will occur more rapidly as the speed increases. However, you may be able to get it up to 260 270 for short periods of time before seeing a failure, possible causing permanent tire damage making it unsafe to land.

well thats my speculation. safety is usually built into those numbers.

[beam]

If you want to analyze it to that degree, you would have to take in consideration that the amount of friction on the wheels is changing as the 747 is gaining speed. Once those wings start creating lift, which is long before takeoff, the amount of friction would start to decrease.

[benzy2]

If you want to analyze it to that degree, you would have to take in consideration that the amount of friction on the wheels is changing as the 747 is gaining speed. Once those wings start creating lift, which is long before takeoff, the amount of friction would start to decrease.

Also you would have to account for which direction the wind was blowing. You would also need to take into consideration altitude of the takeoff and many other things. If we really go by real world situations you would need to take into consideration all real workd factors and not just the capability of the tires.

[epterry]

Interesting puzzle.

From a purely physics standpoint, the wheels decouple the 747 from the conveyor belt runway, and the plane just takes off as it normally would. The wheels would just spin at twice their normal rate as the 747 rolls down the conveyor belt during takeoff.

Cow Hunter posted that the takeoff speed of a 747 was around 500 miles per hour. This seemed high to me, so I did a bit of digging. According to the following link:

http://www.airnewzealand.co.nz/aboutus/fleet/aircraft_statistics.htm

the takeoff speed is around 250 kilometers per hour, or about 155 miles per hour. This link:

http://www.aerospaceweb.org/question/performance/q0088.shtml

lists the takeoff speed to be 180 miles per hour. I think we can safely say that the takeoff speed for a 747 is at least 150 miles per hour, which will be important later in this post.

I also came across something interesting from Boeing's website. They have some PDF files listing various performance characteristics of aircraft for the purposes of airport planning. The section on a 747-400, the most common variant these days, lists a tire speed limit of 235 miles per hour.

If the plane is moving in one direction at some speed "V" and the conveyor belt is moving in the opposite direction at that same speed "V", the wheel speed will be 2V. Since 235 miles per hour is the tire speed limit, 2V = 235 mph. V = 117.5 mph. The 747 will exceed its tire speed limit by anywhere from 27 to 53 percent before it reaches its takeoff speed (of 150 or 180 mph). As to whether this will result in exploding tires or not is up for speculation, but if the tires do blow then the plane is no longer decoupled from the conveyor belt.

I'm not so sure the plane can take off from a conveyor belt runway under "real world" conditions, given the above tidbits of information... shame I already cast my vote in the poll.

BJJB

I was about to say something like that. I would say that the answer could be yes or no and it would depend on several things. This is a very short list and even then it is just about the tires:

1 At what speed/load combination do the tires blow?
2 If the tires do not go then at what speed do the bearings go?
3 Is the conveyer moving in a -1 to 1 ratio or does it just speed up as the planes actual ground speed (not the conveyer) increases? In this case the wheels would definitely go.
4 Would it take the jets more time to spool up?
5 Would that mean that it spent more time on the ground, changing tire rating?
6 Would the conveyer cause a different tire rating then concrete?
7 would the tires and the conveyer create increased rotational friction?
8 What about temp(if it was really really really cold say -100C then what of the tires)?
9 What elevation (by increasing takeoff speed then the tires may go)
That is as many as I can think of off the top of my head, but that is all I need to say that this question needs a lot more details. Oh and if it had the necessary details, I would not be qualified to answer anyway.

Heh I just thought of a good way to demonstrate a little thing about tires. Put a hot-weels car on a grinder... heh
epterry oh sorry about the nasty grammar I am a little sick and therefore not all here today.

[billybob_81067]

I think I'd worry more about a ginormous conveyor runway blowing up at over 100mph than the tires on the plane blowing up at 235 mph.

That's just me though.

[Army]

Heh I just thought of a good way to demonstrate a little thing about tires. Put a hot-weels car on a grinder... heh
epterry oh sorry about the nasty grammar I am a little sick and therefore not all here today.

Yes, very good way!
But notice that you must hold the car onto the grinder (your hand/jet engines). Now, simply roll the car around the grinder...easy, right? Nothing stopping you from doing that, as the wheels easily match whatever speed the grinder is doing, AND what YOU induce. Now, here's the tricky part....


....take the car off the grinder while making the "PTPTPTPTPTPTPT" noise to simulate a take off using the propulsion from your hand/jet engine. Hey look, the car is flying!

Guys, it was a trick question that had NOTHING to do with physics, calculus, wind shear, Toby Kieth, or godzilla spit. The belt and wheels mean NOTHING.

[jdev]

I think eveyone is overengineering this.

the statement only says that the plane goes with the conveyor belt. it mentions nothing of the planes jet engines actually engaging. so, as far as the plane taking off, I dont believe it would take off in the sense it would fly. It would probably eventually get out of control and crash off the conveyor belt if it is not secured down say for example a car on a dyno.

[Army]

Amazing....

J, the plane IS moving (re-read the original post). The ONLY way the plane can possibly move, is by its engines. The ONLY way the plane can actually fly, is for the engines to push it to take off speed.

There is NO way the wheels or belt will have anything to do with that.

Forward motion is NOT dependant on the belt or wheels. Heck, you could have snow-skis on each strut, the plane will still fly.

[Army]

THIS JUST IN!!!!

I have no idea why it didn't dawn on me before!!!

Float planes, lacking wheels, quite often land on MOVING RIVERS. The plane...WITHOUT WHEELS AND AGAINST THE CURRENT....still flies.