Will it take off?

[Kevin - Blown 95 TA]

The plane will take off & fly because the thrust from the engines is pushing against the still air, not the moving runway (conveyor).

The moving runway will cause some more wheel friction and it might have a negative effect from the gradient of air movement as the air is pulled along by the conveyor surface, but the engines are up high enough that that shouldn't matter. If the plane started moving backward before it tried to move forward, then it would have to overcome more of it's own inertia to get going. But disregarding these factors, it would take off and fly.

[blackthunder50]

Ahh, i get it haha, it will take off, right?

[thomas]

I just got home from the Dave Mathews Band concert. It was a great time!!!

If somebody were to replace the entire stage with a giant treadmill, and the band members all had motion sensors on their ankles, what would happen if Dave Mathews farted?

nice....

[fastTa]

Some of you are VASTLY, VASTLY underestimating the amount of friction between the conveyor and the tires of the commercial aircraft. Go tie a cable to a 747 and let me know how much force is required to even move it one centimeter. I'll help you out....it is a huge amount! The converyor has the exact same capacity to inversely apply the same amount of force to the aircraft given the conveyor motors are strong enough. If you never fired the jets and let the conveyor run up to a certain speed the plane would go backwards at an equal rate to the conveyor after a very little amount of elapsed time. Yes, with the brakes comletely disengaged.

[Jeff_in_Atl]

Some of you are VASTLY, VASTLY underestimating the amount of friction between the conveyor and the tires of the commercial aircraft. Go tie a cable to a 747 and let me know how much force is required to even move it one centimeter. I'll help you out....it is a huge amount! The converyor has the exact same capacity to inversely apply the same amount of force to the aircraft given the conveyor motors are strong enough. If you never fired the jets and let the conveyor run up to a certain speed the plane would go backwards at an equal rate to the conveyor after a very little amount of elapsed time. Yes, with the brakes comletely disengaged.

Some of you are VASTLY, VASTLY overestimating the amount of friction between the conveyor and the tires of the commercial aircraft.

Actually the question does not state that the plane in question is commercial, private, jet, propeller, RC, paper or anything. You are adding a condition that is not stated in the question just to make it harder. What if it were a F22 in full afterburner at 70,000 pounds of thrust. You could tie the plane to the conveyer and the F22 would rip it out of the ground and drag it down the runway then take off and carry it to 50,000 feet.

[TraceZ]

Some of you are VASTLY, VASTLY overestimating the amount of friction between the conveyor and the tires of the commercial aircraft.

Actually the question does not state that the plane in question is commercial, private, jet, propeller, RC, paper or anything. You are adding a condition that is not stated in the question just to make it harder. What if it were a F22 in full afterburner at 70,000 pounds of thrust. You could tie the plane to the conveyer and the F22 would rip it out of the ground and drag it down the runway then take off and carry it to 50,000 feet.

This is the whole concept of scale.
As the scale increases, all the forces increase, pretty much proportianally. As the weight of the craft increases, friction in the wheels increases, amount of thrust produced increases... It all increases.

It changes nothing.

[fastTa]

Some of you are VASTLY, VASTLY overestimating the amount of friction between the conveyor and the tires of the commercial aircraft.

If it makes you feel better.

Actually the question does not state that the plane in question is commercial, private, jet, propeller, RC, paper or anything. You are adding a condition that is not stated in the question just to make it harder. What if it were a F22 in full afterburner at 70,000 pounds of thrust. You could tie the plane to the conveyer and the F22 would rip it out of the ground and drag it down the runway then take off and carry it to 50,000 feet.

I was stationed aboard the USS Abraham Lincoln CVN 72 for 1 1/2 years. You make friends with most everyone on the ship very quickly...even the pilots. We had F-14's and 18's on board. On the non flight OP days tht pilots were allowed to just "play around". One day I and a few of my buddies were up on the island and the airmen and pilots were horsing around with the arresting cables and the 14's. There are 4 arresting cables spaced evenly across the flightdeck. They "stop" the aircraft when they land. There are huge brakes, much like a drum brake on a car, down below that are used once the aircraft arresting hook catches the cable. Obviously there is not much power needed to retract the cable once the cable is pulled out. They use a 1.75 HP electric motor with high ratio reduction gearing to retract the cables.

On this day the pilots were messing around and the 14 we were watching had just landed and he still had the cable hooked. When aircraft land on an aircraft carrier they land at 100% throttle, afterburners and all, just in case they miss one of the 4 cables they can safely take back off and make another landing. When they planes are at FULL throttle that little 1.75 HP electric motor pulls the aircraft back about 20-30 feet to relieve the tention on the cable.

Your perception of thrust derived from a jet engine when the plane is at a relatively slow speed or at rest is WAY, WAY off.

[Jeff_in_Atl]

They use a 1.75 HP electric motor with high ratio reduction gearing to retract the cables.

The high ratio gear reduction has the effect of multiplying the torque and if it is a worm gear a million horsepower isn't going to rotate that 1.75 hp motor. Just like the power window motor on a car. Well I'm not sure about a GM but Ford uses a worm gear and you can not move the motor through the worm gear. That's one reason that design is used. Try connecting that 1.75 hp motor directly to the jet and see how fast it unwinds when the jet hits the throttle.

[fastTa]

The high ratio gear reduction has the effect of multiplying the torque and if it is a worm gear a million horsepower isn't going to rotate that 1.75 hp motor. Just like the power window motor on a car. Well I'm not sure about a GM but Ford uses a worm gear and you can not move the motor through the worm gear. That's one reason that design is used. Try connecting that 1.75 hp motor directly to the jet and see how fast it unwinds when the jet hits the throttle.

A "million" horsepower? LOL! The cables are only about 1.75" thick. It is not geared that much. Just enough to have enough power to drag the cable across the flightdeck back into place.

That is also the reason aircraft carriers have catapults. The jets simply do not have anywhere NEAR enough thrust to obtain the 150+ neccesary launch airspeed....even with the 1000+ ft flightdeck.

[Jeff_in_Atl]

A "million" horsepower? LOL! The cables are only about 1.75" thick. It is not geared that much. Just enough to have enough power to drag the cable across the flightdeck back into place.

That is also the reason aircraft carriers have catapults. The jets simply do not have anywhere NEAR enough thrust to obtain the 150+ neccesary launch airspeed....even with the 1000+ ft flightdeck.

Yea in 200 feet. LOL The deck may be 1000 feet but they don't use all of it for taking off.

[fastTa]

Yea in 200 feet. LOL The deck may be 1000 feet but they don't use all of it for taking off.

That is precisely my point! LOL. Even if they were to start from the very back of the flightdeck, the 1000+ feet would still not be anywhere near enough distance. Trust me, I watched my fair share of carrier pilot traing at NAS Alameda, CA. They mark off the distance of flightdecks on the ground runway. Even 2000+ feet isn't anywhere near enough for them to build 150+ MPH. This is why carriers need catapults.

[Jeff_in_Atl]

That is precisely my point! LOL. Even if they were to start from the very back of the flightdeck, the 1000+ feet would still not be anywhere near enough distance. Trust me, I watched my fair share of carrier pilot traing at NAS Alameda, CA. They mark off the distance of flightdecks on the ground runway. Even 2000+ feet isn't anywhere near enough for them to build 150+ MPH. This is why carriers need catapults.

How about this. A harrier weights about 12,500 pounds and puts out 23,800 pounds of thrust. They can take off without a runway. With a thrust to weight ratio of 2:1 they have no problem picking their own weight up off the deck. Marine carriers don't have a catipult.

Is there a thrust to horsepower conversion?

[TraceZ]

Here is an interesting thought.

1) We know an airplane has enough power to overcome the friction in its landing wheels and bearings. If it did not, no airplane would ever be able to move itself.

2) the friction in the wheel and bearing would not be substantially changed at speed X versus speed 2(X).

Therefore, the conveyor would make the wheels spin faster, but would not substantially impact the ability of the aircraft to move forward and gain airspeed.

One thing I do see is that the wheels have rotational mass, and the airplane will need to acceterate those wheels to twice the RPMs they normally have to get up to before liftoff. This will require a little more energy than normal, but not a considerable percentage of the amount of energy spend during an average takeoff. I doubt the pilots would even notice it.

[Jeff_in_Atl]

2) the friction in the wheel and bearing would not be substantially changed at speed X versus speed 2(X).

Yea I look at it like can a plane that can take off at 100 mph do 200 mph on the ground. They took a F104 Star fighter out to Bonneville for speed test and went like 400 mphs then they redesigned the landing gear and broke the speed of sound on the ground.

[fastTa]

Here is an interesting thought.

1) We know an airplane has enough power to overcome the friction in its landing wheels and bearings. If it did not, no airplane would ever be able to move itself.

2) the friction in the wheel and bearing would not be substantially changed at speed X versus speed 2(X).

Therefore, the conveyor would make the wheels spin faster, but would not substantially impact the ability of the aircraft to move forward and gain airspeed.

One thing I do see is that the wheels have rotational mass, and the airplane will need to acceterate those wheels to twice the RPMs they normally have to get up to before liftoff. This will require a little more energy than normal, but not a considerable percentage of the amount of energy spend during an average takeoff. I doubt the pilots would even notice it.

Oh boy. It's not the rotating mass of the tires...it's not the friction produced by the bearings. Again, your completely missing the amount of drag between the tire and the runway surface. Distribute the weight of the plane respectively amongst the tires and you have an enormous amount of force being pushed down upon each tire. Enormous. I suspect that the bearings and tires could likely handle the doubled rotating velocity, but the friction would be the decisively limiting factor.