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Stratmando · Mar 27, 2008, 07:02 AM

If a car was on a "hypothetical" treadmill going 100 MPH, and treadmill was going 100 MPH, it would sit still.
If a jet was on a runway and treadmill was going 100 miles an hour, jet would move forward and take off, the wheel if hooked to wheel driven speedometer would show more than 100 MPH as Jet would move forward and take off. The wheels spin free.
I believe plane would take off.

BCDurbin · Mar 27, 2008, 07:39 AM

Originally Posted by Stratmando

If a car was on a "hypothetical" treadmill going 100 MPH, and treadmill was going 100 MPH, it would sit still.
If a jet was on a runway and treadmill was going 100 miles an hour, jet would move forward and take off, the wheel if hooked to wheel driven speedometer would show more than 100 MPH as Jet would move forward and take off. The wheels spin free.
I believe plane would take off.

I give up - this is not car vs aircraft situation - it is simple force vs. force - if they are equal nothing will move. If one force is greater ( i.e.. Lots of excessive force that everyone wants this hypothetical situation to have!) then the aircraft will move. And with enough excess force to overcome the force (friction) in the opposite direction, it will fly! So there I said it!
I still want to see you guys stand on the skateboard on the treadmill with a scale at the and of a rope!
You be good! - BCD

Stratmando · Mar 27, 2008, 07:49 AM

BCD, this is simple force versus force. Wheels spinning free versus Thrust against Air.

rodandy12 · Mar 27, 2008, 08:18 AM

Strat, you are reading things into the problem.

Jet moves. Treadmill counters. Zero velocity relative to a fixed point on the ground and the air mass. Where does the lift come from?

BCDurbin · Mar 27, 2008, 08:44 AM

Originally Posted by Stratmando

BCD, this is simple force versus force. Wheels spinning free versus Thrust against Air.

If wheels spun free I'd get much better gas mileage in my truck! Sorry nothing is free! Wheels are close to frictionless but not quite!

Friction --------------->>>>>> <<<<<<<-------------thrust

:D

Stratmando · Mar 27, 2008, 09:13 AM

Lift comes after Jet reaches it jumps off treadmill and reaches Vr.
I don't believe at this point we will convince each other.
Drag may equal thrust, however since wheels are freewheeling, you won't get the opposing force.

Flying Blue Eagle · Mar 27, 2008, 08:10 PM

Originally Posted by BCDurbin

easy on the keyboard there buddy! but after figuring out your question - to answer it in a word yes! you wouldn't believe me if I told you, but so far it's about 25 years! Next question! - BCD

BCD - IT was only a question, as so we all would know where some of your knowledge was comeing from. My knowledge comes from since 1955 in both prop and jet, also I have a a/c mech. License HAVE A GOOD DAY AND GOD BLESS:) :D

Flying Blue Eagle · Mar 27, 2008, 08:45 PM

OK Everyone . Lets all keep our cool, this is a conversation between us all trying to come up with an answer that really could make us all agree on ,SO LETS ALL KEEP IT FRENDILY AND REALLY ENJOYABLE <OK
Rodandy12 - The a/c generates its own wind flow over and under the wings in order to reach the point when ( LIFT = WEIGHT ) which I know you know ,YES a a/c takes off and lands into the wind as close as possible, IN order for this question we all have been discussing ,the a/c will be generating its own air flow RIGHT in order to take off . NOW look at it this way the tread mill starts moveing back ward ,so does the a/c ,but the pilot pushes the throttles full forward and then has full thrust and starts to move forward the faster he moves the lift process has already started and the friction on the treadmill becomes less ,because the more lift the a/c gets the less it is touching the treadmill and the less there is touching the treadmill and a/c keeps going faster and will reach rotation is this not right ;; Think of this , pick either one the B-%@ ot the C-!#) Loaded , youer at the enmd of the runway , checks are done ,all engines are full throttle you releas the brakes , it lounges forward,and the more you keep forward motion , the factor of lift starts from the first of forward movementand at ( X ) speed they reach the point of rotation, I know THE ( X ) speed will vary sometimes . BUT rereading the question I Think the a/c does not stand a chanch. Because the question say that they are both equal, There speed is equal. In a way I stand corrected, on part of it :: GOOD FLYING AND GOD BLESS;;; F.B.E.

lobrobster · Mar 27, 2008, 09:03 PM

Originally Posted by BCDurbin

The rope is an outside force - very much different than thrust. Without that rope the skateboard would move backwards at exactly the same pace as the treadmill. The rope is a force that would keep it in place. Your holding the rope and walking is an ADDITIONAL force that would propel the skateboard! I agree that if you tow the aircraft off it will fly eventually but that is not the premise of the original question - it said that all forces (thrust and treadmill travel) are equal. It would take more thrust than treadmill travel for the aircraft to fly - equally, more treadmill travel than thrust - and the aircraft would move backwards!!

Ok, let's try a different scenario...

You know those conveyor belts they use at the checkout line at the grocery store (the ones you put your groceries on and the cashier moves them up by pressing a button)? Now imagine putting a roller skate on it and the cashier turning it on. Even if the conveyor belt was moving 50mph. do you think you could hold the roller skate in place? Of course. You could do it with one finger. Now how about pushing it in the opposite direction? Do you think you could walk the skate to the opposite end of the conveyor belt? Of course you could. In fact, you could put a super powerful fan behind the skate and have it blow the skate forward too. That's how thrust works.

The thrust 'pushes' the plane (in a prop plane it would be 'pulled') along the runway (or treadmill). Again, it is completely independent of its wheels. Get rid of this notion that it's the same principle as a car or bicycle. Jets are powered by thrust and do not have drive trains. I've run out of ways to explain or describe it.

rodandy12 · Mar 28, 2008, 05:52 AM

FBE,

Right. The problem says, "for every mile an hour the Jet's wheels move forward, the treadmill moves a mile an hour in the opposite direction." The treadmill perfectly matches whatever forward velocity the jet produces. That means the speed of the jet relative to a point on the ground just off the treadmill is always zero. The thrust generated by the jet is exactly compensated for by the treadmill.

Technically it is the air over that spot on the ground that matters. The jet isn't moving in it. No relative movement, no velocity, no lift.

All the other stuff you said was correct, but it involved relative movement. Gotta' push that air foil through the air to get off the ground.

Lobro,

Technically, the term thrust applies to jet engines, power is the term for prop aircraft.

Stratmando · Mar 28, 2008, 06:35 AM

I come back hoping we all understand, the faster the treadmill goes, it still has no effect on freewheeling wheels, whether jet or prop, Aircraft will move forward, jump off treadmill, or if hypothetically speaking, a 10 mile long treadmill, craft will move forward and take off.

lobrobster · Mar 28, 2008, 09:27 AM

Originally Posted by rodandy12

The treadmill perfectly matches whatever forward velocity the jet produces.

I believe this is incorrect and it's the key to the question. The treadmill doesn't match the velocity of the jet, it matches the velocity of its wheels. All the difference in the world.

lobro,

Technically, the term thrust applies to jet engines, power is the term for prop aircraft.

Right, I understand that. The scenario would work with either a jet or a powerful enough propeller driven plane. A jet plane is 'pushed', a propeller driven plane is 'pulled'.

Stratmando · Mar 28, 2008, 03:34 PM

Here's another way,
Any plane will take off the treadmill, the movement of the treadmill is to spin the wheels, spins only the wheels, Prop or jet will push against the Air, and take off.
I'll try not to respond a couple of times.
I used to think the World was Round, Now I know It is Square.

Flying Blue Eagle · Mar 28, 2008, 09:00 PM

Originally Posted by Stratmando

Heres another way,
Any plane will take off of the treadmill, the movement of the treadmill is to spin the wheels, spins only the wheels, Prop or jet will push against the Air, and take off.
I'll try not to respond a couple of times.
I used to think the World was Round, Now I know It is Square.

HAY SYRATMANDO - IF this old world is square, then what happens when we go over the edge and start down hill will we be able to make the next turn? And if we do will gravety hold us up while we are upside down.? I think IM in trouble BYBYBYhbhbh;;

IM still IN yhe same thinking as you are on the way we read and understood the question at first< AND ON THOSE TERMS IT WOULD BE THE WAY THAT YOU AND I STILL THINK< THE WAY THEY ARE SAYING THE PORE A?C WOULD NOT STAND A CHANCH <SINCE HE CAN't GIVE THE A/C FULL THROTTLE IN ORDER TO MOVE IN THE OPPSIT DIRECTION. HAY TAT TAINT FAIR!! F.B.E. GODBLESS:eek: :confused: :confused: :)

Sitkadiver · Apr 6, 2008, 08:16 PM

Thank You "MYTHUSTERS", from he Discovery Channel. They tested this myth and found that the treadmill speed had no effect on the ability of an aircraft to take off. Since the thrust produced by the prop is independent of the wheel speed, the plane still takes off like normal.

lobrobster · Apr 7, 2008, 07:01 AM

Originally Posted by Sitkadiver

Thank You "MYTHUSTERS", from he Discovery Channel. They tested this myth and found that the treadmill speed had no effect on the ability of an aircraft to take off. Since the thrust produced by the prop is independent of the wheel speed, the plane still takes off like normal.

Are you serious? I would have loved to have seen that! When did that show air? I wonder if there's any way to get a copy of it.

Stratmando · Apr 7, 2008, 07:11 AM

I missed the episode too, but here it is:
http://mythbustersresults.com/episode97

Flying Blue Eagle · Apr 8, 2008, 09:07 PM

Lobrobster - Boy ,I have heard a really good one on how to describe something, and I think you have done a very Good job of describing the problem, Good going . I just wish that I could take a ( B-47 jet bomber and try this problem, Just to find out wjhat would happen. O f corse I want to use water alcacol , for wet thurst and put 32 bottles of ( ATO 0 on the rear behind the aft wheel well, A 1000 lbs. of thrust per bottle, ha ha ,good by conveyr belt , If I couldn't take off from it ,THen good by belt ( BECAUSE I WOULD MELT IT AND TAKE OFF, _ NOTICE THE WORD ( HEAT & MELT )

I DO NOT SEE how the belt could move as fast as the a/c would move forward, I says that for every mile an hour the a/c moves forward, the belt moves BACKWARD< causeing the a/c to go no where. ( THE wheels are free weeling ,there is little friction , that will cause the a/c to just sit there. The power of the thrust from the engines has nothing to do with the wheels of the a/c, they have not one thing to do with the power of the a/c , moveing forward, IT IS THE THRUST OF THE ENGINES THAT IS AND WILL MOVE THE A?C FORWARD< AND TO REACH ROTATION POINT ) I can see that IF it was a car , truck , or any type of vehicle, that has a drive train from the engine to the drive wheels that this would happen, the more gas you give the engine the faster the wheels are going to turn and then the belt is going to counter react and travel in the oppsite direction, WHICH MEANS YOU HAVE THE QUESTION IN VIEW.

THE HEAT FROM THE JET ENGINES WOULD MELT THE BELT REAL QUICK ANY WAY< AND YOU COULD THEN WAVE GOODD BY TO THE A/C. YOU al have a good day and safe flying, keep her between the clouds, GOD BLESS ::: F.B.E.

561packrat · Sep 7, 2008, 05:45 PM

this thread might be dead, but I'm bored. Brakes-off, Jet engine produces thrust, action= reaction, jet will move forward, accelerating, wings pass through air, creates lift. Factor in the following for nit-pickers to ponder: ground effect ( consider up to altitude equal to 1/2 wingspan), thrust-to-weight ratio, thrust-drag-lift -gravity, pilot's shoe size, add pinch a' salt, cook for one hour at 350 F.

Flying Blue Eagle · Sep 11, 2008, 08:23 PM

Originally Posted by BCDurbin

easy on the keyboard there buddy! but after figuring out your question - to answer it in a word yes! you wouldn't believe me if I told you, but so far it's about 25 years! Next question! - BCD

BCDURDEN - Well I hate to burst your bubble because I have since back in the early 50's.So I guess that is double on your time . I have flown as PIC in several different types and single threw multi engione,Prop and jet > By the way I was not getting smart I was wondering if you had any exper. In actually flying anm a?c, Thec reasion was because of the asnswers you were giving. Sorry I ruffled your tail feathers . Good day and GOD BLESS F.B.E.