will it take off?

[gizmo]

The conveyor is doing nothing but spinning the wheels. The prop will still pull the plane through the air regardess of how fast or even what direction the conveyor moves and the plane will fly.

Nothing complicated about this. Don't read too much into it and it makes sense.

I am a pilot and an engineer and I have argued this scenario about a dozen times now.

In the interest of keeping this thing going senselessly, I will add another two cents.

I spent 3 years on the aircraft carrier Enterprise and I now design conveyor systems.

The plane will fly as if the conveyor was not even there, but the prop needs to be installed backwards to counter it...really...its true.

 

[silverdollar6]

And the pilot needs to be upside down.

 

[turnkey4099]

And the pilot needs to be upside down.

Well that's stupid! It only applies in the Northern Hemisphere!

Harry K

 

[Steve_Miller]

I spent 3 years on the aircraft carrier Enterprise and I now design conveyor systems.

Seems with this statement your never going to get any design jobs for this type conveyor.

Steve

 

[patrick_g]

I have carefully noted the posts with bogus ideas so I can qualify future advice given by those authors.

Listen to everyone but qualify your sources.

I didn't see what the dificulty is. The original post clearly stated the givens and the outcome should be obvious to the most casual observer.

Since the conveyer belt runs as fast as is required to keep the plane standing still with respect to "the world" there is no wind over the wings except as provided by local weather and I suggest there isn't enough wind to equal or exceed the speed needed to let the craft lift off. Actually, unless the person stating the problem allows for wind, there isn't any.

The air is standing still with respect to the world, i.e. no wind. The aircraft is standing still with respect to the world due to the clever control of the conveyor belt. So the aircraft is standing still with respect to the air. No air flow over trhe wings eguals no lift.

If we temporarily lift restrictions of maximum thrust of the aircraft and make it super powerful, eventually, at enourmous speeds (hypersonic), the drag of the surface of the conveyor belt will propel enough air down the "runway" to provide enough lift such that the aircraft will lift of the runway with no apparent forward motion with respect to the world.

Once free of the conveyor belt and airborn the aircraft will be propelled forward but if the conveyor belt/runway does not extend forward of the aircraft a sufficient distance or if the conveyor belt is slowed to a stop the plane will return to the ground (landing or crash? can't say, not enough information)

If the aircraft doesn't develop enough forward speed with respect to the world and its zero wind before leaving the region of conveyor developed wind the pland will lose lift and fall out of the air. Not enough information is given to know if the aircraft will developp flying speed before abruptly leaving the region of conveyor accelerated air.

Ignoring the super powerful propulsion idea for the plane and a hyperfast conveyor belt, the problem is quite trivial. Aircraft like sailboats are governed by relative wind. The only relative wind (above zero knots) in the original problem statement is that blown over the wings by the prop if there is one. Jets would have much less. Developing enough lift to take off using the prop blast is possible but not achievable to the vast majority of aircraft.

If we can use an F-35 or a Harrier jump jet or an Osprey then the problem as stated is meaningless so it must be assumed these special aircraft were not to be used.

A practical concern would be overheating a piston engine. You would be at max throttle for an extended period and only have the limited airflow created by the prop with no cooling assist from "ram air" due to motion through the air.

Oh by the way, the pitostatic system would indicate zero or near zero airspeed and that is what counts for wings generating lift.

Pat

 

[Paddy]

Patrick G,

You of all people, with physics background, miss read the problem.

Your statement;
"Since the conveyer belt runs as fast as is required to keep the plane standing still with respect to "the world" there is no wind over the wings..."

The problem stated the convayor could match the speed of the airplane. No mention of stationary any where. If the plane is stationary, so is the convayor! Also a common but incorrect assumption here has been folks assuming wheel speed is matched. Agian, the problem states nothing about matching wheel speed but does state matches the plane's speed.

If this problem had been modified to state it was a person running on a tredmill and asked if the runner would ever get to the finish line 100' away. The answer would be the same, yes. You see airplanes and wheels are not relevent. It's the trick part of this trick question, objects moving in equal speeds but in oposite directions. Same would be true for a car in this same situation. The speed-o-meter would record twice the actual velicity of the the car, but none the less the car is moving.

Draw a vector diagram based on each sentance of the problem and you will see one of your first staements is correct:

"I didn't see what the dificulty is. The original post clearly stated the givens and the outcome should be obvious to the most casual observer."

 

[Tom_Veatch]

I have carefully noted the posts with bogus ideas so I can qualify future advice given by those authors.
...

Well, Pat, I didn't see a "smiley" after that statement, so on the off-chance you might have been serious, please allow me to point out that an author's conclusion in this imaginary, nonsense scenario really has no bearing on what valuable expertise that same author might bring to a discussion of real-world, tractor oriented problems. No offense intended.

As I mentioned before, depending on the assumptions made as to the meanings and definitions not explicitly stated, one can come to valid, self-consistent, and totally opposite answers to the stated problem.

The problem doesn't state what the airplane speed/movement is relative to. If it's assumed to be relative to the conveyor, and the conveyor's movement/speed is assumed to be relative to the "world", then it's a no-fly situation. If the airplane movement/speed and the conveyor movement/speed are both assumed to be relative to the "world", then it's an obvious "fly" situation. As you said, simple and obvious. Just depends on the assumptions made.

 

[Egon]

Ahh -- Folks don't worry. Pete's been supplying Pat & Egon with some Greenmountain again.

If it's a Tiger Moth facing into a Good Southern Alberta Chinook the pilot may well be facing to Vancouver but end up in Regina and be able to land going backwards !

 

[Tom_Veatch]

...
If it's a Tiger Moth facing into a Good Southern Alberta Chinook the pilot may well be facing to Vancouver but end up in Regina and be able to land going backwards !

That's not an unusual situation with our Kansas breezes - probably the same with Oklahoma and Nebraska. More than once flying IFR (I Follow Roads) in a Cessna 150 I've watched cars on the Interstate passing me. "Time to Spare, Go by Air"

 

[Paddy]

Tom,

That's a generous statement. But... I feel the problem solver can safely assume the reference for speed is the same for both the plane and convayor. It would be very odd for two objects speed referenced from diff ref points with out coment.

The most vaild point the "it won't fly" group can make is in the wording of the last statment of the question, "will it fly?". Since no speed is given any one could answer the plane goes down the convayor at 10 mph...no fly. If the last staement was "CAN it fly?" Then lift off speed could be obtained.