I'm thinking this question had to been asked before, but I did a search and couldn't find anything on it. It's really bugging me, because I never could find out the right answer.

Suppose you have a jet airplane sitting on a runway. But this runway acts like a treadmill. The jet starts it's thrusters and for every mile an hour the Jet's wheels move forward, the treadmill moves a mile an hour in the opposite direction.

Will this jet eventually take off? Thanks.

Rob

No.

It's all about relative wind. If there is no wind flowing over the wings, there is no lift.

That's why carrier based aircraft do so well. First they generally have a good headwind and then they have the speed of the carrier added to this. They could be doing 60 knots before they even release brakes.

No.

It's all about relative wind. If there is no wind flowing over the wings, there is no lift.

That's why carrier based aircraft do so well. First they generally have a good headwind and then they have the speed of the carrier added to this. They could be doing 60 knots before they even release brakes.

Thanks Old_Fart, but...

We're talking about a jet which uses thrust. Theoretically, wouldn't the thrust propel the plane forward (even though the treadmill is moving in the opposite direction), and eventually take off?

No.

It's all about relative wind. If there is no wind flowing over the wings, there is no lift.

That's why carrier based aircraft do so well. First they generally have a good headwind and then they have the speed of the carrier added to this. They could be doing 60 knots before they even release brakes.
We're talking about how the plane gets up into the air. Not how it's propelled.
**edit** Forces on an Airplane (http://www.grc.nasa.gov/WWW/K-12/airplane/forces.html)

There was a very long thread here about that same subject a while ago. I'll try to dig it up.

Opps I was wrong, the conversation was on Digg. Plenty of discussion about this topic everywhere: plane treadmill take off - Google Search (http://www.google.com/search?hl=en&sa=X&oi=spell&resnum=0&ct=result&cd=1&q=plane+treadmill+take+off&spell=1)

I'm thinking this question had to been asked before, but I did a search and couldn't find anything on it. It's really bugging me, because I never could find out the right answer.

Suppose you have a jet airplane sitting on a runway. But this runway acts like a treadmill. The jet starts it's thrusters and for every mile an hour the Jet's wheels move forward, the treadmill moves a mile an hour in the opposite direction.

Will this jet eventually take off? Thanks.

Rob
As a pilot - the answer is no. Simple physics - there is no air passing under the wing to provide lift

Opps I was wrong, the convo was on Digg. Plenty of discussion about this topic everywhere: plane treadmill take off - Google Search (http://www.google.com/search?hl=en&sa=X&oi=spell&resnum=0&ct=result&cd=1&q=plane+treadmill+take+off&spell=1)

Thanks NeedKarma! That's what I was looking for! We had a HUGE debate at work about this awhile back that lasted for almost a month. I didn't know this was such a popular question.

On second thought, the tires would spin very fast but if the thrust was sufficient to move the craft against the still air, who cares how fast the tires have to turn?

Since there's no air flow over the wings, they are essentially useless in this scenario. So they may as well not be there. Now the question may be easier to comprehend - would a plane fuselage with jet engines but no wings ever lift off? Obvously not (unless it's a Harrier or some other VTOL design).

as a pilot - the answer is no. Simple physics - there is no air passing under the wing to provide lift

Are you sure? Jet planes are not axel driven. So why wouldn't the thrust propel the plane forward?

Btw- I don't know the answer. I'm just confused.

I've been thinking some more about this, and I want to revise my earlier answer. It's never too late to see the light! I had been thinking that the premise of the riddle was that the treadmill is designed to move at a speed that keeps the plane stationary. But what the riddle says "for every mile an hour the Jet's wheels move forward, the treadmill moves a mile an hour in the opposite direction" - thus if the plane (and its wheels) moves forward at 100 MPH, the treadmill moves the opposite direction at 100 MPH, which means the tires are spinning at the equivalent of 200 MPH. Hence the plane does move forward, and can take off. The tires will have had to spin at twice the rate as on a normal runway, but that's really the only difference.

ebaines, remember that the jet's engines are pushing against stationary air, irrespective of the tarmac, thereby producing thrust. The speed of the wheels on the landing gear don't enter into this equation.

ebaines, remember that the jet's engines are pushing against stationary air, irrespective of the tarmac, thereby producing thrust. The speed of the wheels on the landing gear don't enter into this equation.

Agreed. Previously I thought the premise of the riddle is that the treadmill moves fast enough to keep the plane stationary, and the only way that could be is if the friction between tires and treadmill would exactly counteract the thrust. Thus the treadmill would have to move at high enough speed to generate enough friction to counteract the jet's thrust. I now realize I had misinterpreted the wording of the riddle.

Would everyone agree that a car on the same treadmill/tarmac would never get above zero mph?

Depends...

What car are we testing and what is the top speed of the treadmill?

Fastest Cars - World's Fastest Production Cars (http://www.allfastcars.com/fastestcars.shtml)

Video Bugatti Veyron at top speed - bugatti, top, gear, 407, germany - Dailymotion Share Your Videos (http://www.dailymotion.com/video/x157l2_bugatti-veyron-at-top-speed)

I'm thinking this question had to been asked before, but I did a search and couldn't find anything on it. It's really bugging me, because I never could find out the right answer.

Suppose you have a jet airplane sitting on a runway. But this runway acts like a treadmill. The jet starts it's thrusters and for every mile an hour the Jet's wheels move forward, the treadmill moves a mile an hour in the opposite direction.

Will this jet eventually take off? Thanks.

Rob
If the aircraft isn't moving forward into the wind, the wings will not receive airflow and the plane will not take off. The only way this is theoretically possible is with a severe headwind equal to the takeoff speed of the aircraft. But in this case, I would not want to be in the aircraft.

A plane flys by a force called lift, lift is created by the air going past the wing at a specific angle ( this angle is adjusted by the flaps)

But the plan will have to have a forward motion to get lift, no lift no flying

Depends...

What car are we testing and what is the top speed of the treadmill?

Fastest Cars - World's Fastest Production Cars (http://www.allfastcars.com/fastestcars.shtml)

Video Bugatti Veyron at top speed - bugatti, top, gear, 407, germany - Dailymotion Share Your Videos (http://www.dailymotion.com/video/x157l2_bugatti-veyron-at-top-speed)

You're losing me. Any vehicle that is propelled by a drive train (i.e. it is driven by the wheels moving as opposed to thrust), theoretically, should remain stationary relative to someon standing next to the treadmill, correct?

This whole issue is one of thrust. Since a plane is not powered by it's wheels, they are in a sense, irrelevant. Technically, the plane should still move forward.

Picture a skateboard on the same treadmill with you at the opposite end (off the treadmill), holding a rope tied to the skateboard. Would you be able to pull the skateboard towards you?

Most treadmills are only capable of certain set speeds... does this version free-wheel?

Most treadmills are only capable of certain set speeds... does this version free-wheel?


I'm still getting to know you guys, so I'm not sure how to calibrate my sarcasm meter yet.

The treadmill will match any speed of the plane's wheels.

ROB :: I need to be in this also ,:: #1- when a plane starts moveing forward from the (THRUST OF THE JET ENGINE) THE wind going past the wings, causes a low pressure on top side and a high pressure on bottom side, as the plane goes faster and LIFT EQUALS WEIGHT THE plane reaches lift (KNOWN BY PILOTS AS ROTATION POINT)IF it's a prop it's the same except it pulls by the props. pulling air through the props. Now the engines ARE what pushes or pulls the air craft forward, they always take off into the wind, on a aircraft carrier, they turn the ship, HEADING INTO THE WIND ONCE THE AIRCRAFT REACHES THE POINT OF ( LIFT EQUALLS WEIGHT < WHEN YOU PULL BACK ON THE STICK {OR YOUK} IT IS GOING TO LEAVE THE GROUND WITH FULL POWER ON::::::" WITH engines running ,that plane is going to move forward. Back ,I BElieve it was late 80's or 90's they redesigned the race car to work on the same princeable as a plane , except in reverse, LOW ON BOTTOM <HIGH PRESSURE ON TOP , this was done so they could hold to the road better ,go faster and not lose control as they used to . I KNOW because iv'e been a pilot since back in50's I've flpwn jet and prop ,I still hold pilots license ,WITH AIRCRAFT SINGLE <MULTI ENG> INSTRUMENT> I was AIR FORCE ,for 12years F.B.E.

I'm still getting to know you guys, so I'm not sure how to calibrate my sarcasm meter yet.

The treadmill will match any speed of the plane's wheels.
Well, then if the treadmill matches the wheel's speed (like a dyno), the Veyron would sound damn good... sitting still!

And let the sarcasm flow freely! With me anyway!

Would everyone agree that a car on the same treadmill/tarmac would never get above zero mph?

No. Read the question more carefully.

Imagine a car moving at 40 MPH relative to the speed of the treadmill (i.e. the car's speedometer would read 40 MPH). But imagine also that the treadmill is only going at 20 MPH relative to the ground in the opposite direction. This means the car will move at 20 MPH relative to the ground, correct? Under these conditions the car is satisfying the condition of the question as originally posed, that is: "for every mile an hour the [car's] wheels move forward, the treadmill moves a mile an hour in the opposite direction." If we assume that these speeds are measured in a consistent way relative to the ground, then the car does indeed move forward.

Hehe, this keeps me thinking. I hate that!

The vehicle's speedometer may indicate a mechanical interpretation, but the key here is MPH, miles per hour, and if it's sitting still on the treadmill/dyno, it isn't covering any miles.

Going back to thte aircraft analogy... speed over ground (SOG) would be zero. Substitute the speedometer with GPS. I think your car is not moving.

lobroster, next time we want all of the variable, as much of the given info, upfront. OK, buddy?

The treadmill will match any speed of the plane's wheels.

The problem here is that this phrase is open to different interpretations, and the answer depends on how you think of "the speed of the plane's wheels." If this phrase means that the treadmill matches the forward horizontal velocity of the axle of the wheel, (i.e, the point of its average velocity relative to the ground) then the plane does move forward as I've shown before, and could take off. However, if the phrase means that the treadmill matches the speed of the contact point of the tire relative to the axle (i.e. its spinning velocity relative to the axle), then the plane stands still and it can't take off. By the way, the only way for this to physically work is for the frictional forces between tire and treadmill to exactly counter-balance the thrust of the engine, and if you ignore this rolling friction then it's easy to show that the treadmill must move infinitely fast. But that's another discussion.

There are too many variables to say whether the plane would take off or not. However, if you say there was NO wind at all and the platform on which the treadmill moves is stationary then the plane would defiantly NOT take off. As people have said, a plane takes off due to the lift under it's wings, it generates this lift by traveling at high velocity. The plane on the treadmill would have high speed, but no velocity. Velocity is movement in a direction. The plane would still be stationary.

If you imagine yourself running on an exercise treadmill, you can run very fast, but you will not feel a strong wind in your face. The same applies to the plane.

Since the wheels spin free. Jet would move forward. As thrust increases, it will push jet forward, wheels would spin. Jet would jump off treadmill and at rotation speed, it would lift off.

Hello lob:

The plane would take off. Unlike a car which pushes against the road, a plane pushes against the air.

Let's say the entire runway was a treadmill geared to the parameters discussed. The plane begins pushing the air and it moves against the ground at 1 mph. The treadmill goes at 1 mph but the plane is pushing against the air at 1 mph and IS moving over the ground. The thrust of the engines against the air isn't going to stop moving the airplane because of its wheels.

Ergo. If the plane is moving against the air at 1 mph, and the treadmill is moving at 1 mph, the treadmill is STILL 1 mph slower than the plane is moving over the ground, so the plane would begin its take off run normally.

As the speed of the plane against the air reaches say, 120 mph, the wheels would ordinarily be going 120 also, but because the treadmill is moving to match the wheels, the treadmill is still 120 mph slower than the air that is pushing the airplane - and the airplane would take off.

What do I win?

excon

excon:

There is NO AIR PUSHING AGAINST THE PLANE.
Unless I've interpreted the question wrongly, the plane would not take off. If the plane was going 1000000mph on a completely flat, and infinitely long, surface in a vacuum the plan would still not take off. It would just keep going straight. SPEED makes no difference in this conundrum, it's the VELOCITY of the aircraft. Of course, like I said in my previous answer, there are too many variables which would change the output of this question, however we must say (for arguments sake) that 100% of the thrust generated by the engines is converted into kinetic energy in the wheels, and the forces active on the wheels and treadmill are balanced. If this is so then for each 1mph the planes wheels move forward, the treadmill reverses the effect my matching the speed in the reverse direction. Therefore, even when the plane is at max speed it is still standing stationary and there are no forces allowing the plane to take off.

TO ALL- EXCON & Stratmando , Both of you are getting close to what really makes &causes it to take off and fly. > The wheels on a aircraftARE free spining, it has nothing to do wiyh making the aircraft. The Thrust of the jet engines is all that makes the aircraft,Move forward, ( UNLESS IT HAS JATO ON THE TAIL END BEHIND THE AFT WHEEL, 32bottles, 1000 lbs thrust per bottle,the rack held 32bottles, on the b-47 jet bomber) I'm not giving out any secret stuff::: Each of the 6 engines gave 6700lbs thrust (DRY) WET is over 7000 per eng. . The hot air comeing out the tail cone ,is the thrust, Which CAUSES THE AIRCRAFT TO MOVE FORWARD ::: NOW , FROM THE AIRCRAFT moveing forward, the air moveing under and over the wings starts things in motion for the completion of flight. As the aircraft, picks up speed, IT WILL MEET THE POINT OF LIFT<WHICH WE CALLED THE (ROTATION POINT) - takeoff, The hot air gasses comeing out the tail cone contuious the push that moves it through the air,witch in turn keeps the needed air flow over and under the wings to give the a/c the needed lift to fly .( AS TO AIR FLOWTO THE WINGS< AIR GOING OVER THE TOP<HAS Further TO TRAVEL <WHICH IN TURN CAUSES THE (LOW PRESSURE ON TOP OF WINGS), (THE AIR PASSING UNDER THE WINGS <TRAVELS FASTER < WHICH IN TURN CAUSES THE HIGH PRESSURE NEEDED TO GIVE LIFT TO THE A/C::: For the A/C ,or any a/c to fly (the LAW KNOWNAS - when lift = Weight It WILL FLY) The only difference of a prop POWERED A/c is, ( IT PULLES THE AIR Through THE BLADES AND Expels IT AT MUCH Higher SPEED AND POWER) Durning flight the prope OR props. Keep the a/c FLYING forward giving the needed lift to stay flying, allso the prop,OR props pulls the a/c forward. I could really blow some if I tried to explane the reversing the engines on prop or jets durning landings. Will that's another issiue to discuse later YOU-All have a good day, nice flying F.B.E.

The more I think about this question the more my answer changes...
I was thinking about how a normal jet plane on a normal tarmac runway would move, and I believe that, relative to the plane, the ground is moving in the reverse direction to the direction of force anyway.

So, I thought, when a plane on a normal runway is moving at 50mph, the ground is moving 50mph in the reverse direction relative to the plane. So, this would be similar the treadmill in question. However on a normal runway the push of the jet engines against the air behind it pushes the plane forward and therefore air flows around it allowing the plane to get the amount of lift needed for a take off.

In reality of course the runway is not moving an inch, but the treadmill IS.

Imagine a whole runway replaced by the treadmill, and the plane starts its run at the END of the runway. Now, switch the treadmill on so it's moving backwards at 50mph. The plane would travel along the treadmill backwards at 50mph, and with wind rushing into it from the back. Now slowly accelerate the plane until it is no longer moving backwards, obviously the wheels of the plane would have to have a high enough RPM to keep the plane at 50mph. Now, the speed and velocity of the plane are non-existent, (it's not covering any distance so it is moving at 0mph, and it's not moving in a direction so it has no velocity).
However... the plane is using the thrust of it's engines to push itself forward, not the wheels . So, the wheels would be moving twice as fast, the combined speed of the wheels and treadmill, but the pane would, as long as the thrust is great enough, still be moving forwards and therefore would have the wind speed etc to take off.


I correct my previous answers.

SHempAM- YOU are getting very close to the answer to all this. Remember that the wheels on any aircraft have nothing to do with the power of the aircraft takeing off. they are (FREE SPINNING). The engines provide all the power to take off and to fly;;; think of this ( A plane takeing off on snow or ice or even water,) t's only way to move is from the engines, and as it moves it has wind passing ,over and under the wings. which in turn starts in motion WHEN LIFT = WEIGHT <ROTATION POINT IS MEANT AND IT TAKES OFF AND FLYS) THE WHEELS BEING FREE SPINNING < WILL NOT KEEP IT FROM MOVEING FORWARD;; IT was mentioned about VACUMN, What about the space shuttle. It fly in the vacumn of space. Don't IT?? F.B.E. I SURE WISH SOME other PILOTS OR AIRCRAFT ENGINEERS WOULD GET INVOLVED IN THIS . HAVE A GOOD DAY & GOD BLESS good flying

Especially my post # 13 on page two.


...the jet's engines are pushing against stationary air, irrespective of the tarmac, thereby producing thrust. The speed of the wheels on the landing gear don't enter into this equation.

The landing gear, as you mentioned, could be ski's on snow or ice, or pontoon's on water, which in the case of landing on a river, the effective surface could be moving with the aircraft or could be moving against the aircraft. The aircraft carrier is a poor analogy here because it represents a "treadmill" moving forward.

Yeah, I get the gist of this now. But I still think that a small variation in the question, or the interpretation of the question, could change the answer (that's how I got confused). I hadn't read the question properly, I thought it said:

"For every mile an hour the PLANE moves forward, the treadmill moves backward one mile an hour."

Of course now I see that the question said the WHEELS would be moving backward for each mph, not the whole plane.


Satisfaction at last..

Hello again:

That's what I was saying. Actually at the time of rotation, the wheels would be going backwards at twice the speed of R. Half the speed would be taken up by the airplane moving down the runway, and the other half of the speed would be the treadmill moving backwards at that same speed.

And, the plane takes off. I didn't splain it good, but I knew what I meant.

excon

CapyainRich- I kind of figuered that you were ,but I didn't realluy catch it on the first page, sorry . Iv'e been trying hard to explain it in what is called (LAYMANS TERMS ) like I tell MY doctor ,when he snows me in. You know that on landing and take off , no matter what kind of water snow ice a/c carrier ground , the airplane always lands& takes Into the wind as stright as possible, although there are times known as cross wind. I was taught in the USAF instead of slide slipping (nose into cross Wind) to use what is called cross control , I liked it a lot better, that's what I always use. HAVE A GOOD DAY< NICE FLYING F.B.E.

I like Cross control, Accelerated Stalls, and Critically Slow Flight(at the edge of stall)
EAA+AOPA

Hey stratmando- Do you ever let it go to the horn ? Let the right wing stall and go into deliberet stall and following spin? Totsal of 1 1/2 turns for recovery? IT'S FUn HAVE a good DAY Happy Flying. F.B.E.

I love Stalls/Spins, Unusual Attitude and Recovery(DUH). I used to smile when flying "Under the Hood", Eyes Closed, Instructor would fly random turns/climbs, and I then recover from where ever he left me. Nose high, rapidly declining airspeed, or in the middle of spins. Those were good times.
Take Care Blue Eagle.

Sttratmando & CaptainRich ;;; Tell me how you like what is called ( ACCURACY LANDINGS?? ) Most so at night . I really loved doing them . Good day GOD bless, And Good Flying ;;;; F.B.E.

According to the parameters of the question, the energy of the jet engine is used to keep pace with the treadmill. No energy remains to accelerate it to take-off speed.

According to the parameters of the question, the energy of the jet engine is used to keep pace with the treadmill. No energy remains to accelerate it to take-off speed.
The treadmill is static. The thrust is against the air, not the tarmac/treadmill.
The jet will take off, despite any or no contact with terra firma. Reread some of the earlier responses...

I have to agree with Captain Rich - The thrust is not turning the wheels, but pushing the aircraft. It will not make a difference how fast the wheels are spinning at the start of takeoff, they will just spin faster as the aircraft thrust propels it forward.

Sttratmando & CaptainRich ;;; Tell me how you like what is called ( ACCURACY LANDINGS????) Most so at night . I really loved doing them . Good day GOD bless, And Good Flying ;;;; F.B.E.
Night crosswinds touch and goes are fun. Accuracy always, Love short field landing also,
Chandells, Unusual Attitude, Critically slow flight. I just remembered I like it all, except straight flying, When I would get bored I would tune to a AM station on the ADF for company. Take Care FBE

Night crosswinds touch and goes are fun. Accuracy always, Love short field landing also,
Chandells, Unusual Attitude, Critically slow flight. I just remembered I like it all, except straight flying, When I would get bored I would tune to a AM station on the ADF for company. Take Care FBE
... and my mom would tell me to straighten up and fly right! Hehe
Having learned to fly small planes in Alaska, I was a licensed Private Pilot before I bothered to get my driver's license. Short take-offs and landings on crooked, sloping beaches with no control other than knowing nobody else was servicing that village was the standard.
AM stations? If you were aloft, you could pick up a few on a clear day!! Hahaha Just you rarely had time to enjoy them. Boink! Next village!

Captain, That would be so cool. Wish I had a chance to be a Bush Pilot. Plus I love Prospecting, Great combination.

Stratmando & capt. Rich- If I hadn't been married and 3 kids at the time I got out of air force I would have gone far North,it crossed my mind more then once.Or even in upper canada, around those moutain lakes, that high country is the most beautiful country on earth. Like you said stratmando be a bush pilot. IM talking about on up above cilivitation just before NO MANS LAND!! Good Day and GOD BLESS AND good flying;;;; Oh ,no matter how fast it goes in the oppsit direction ,THE JETS OR THE PROPS OF THE ENGINES WILL MAKE THE A/C GO FORWARD FAST ENOUGH THE A/C WILL MEAT ROTATION POINT( TAKEOFF) :: F.B.E.

Now what if the treadmill went it the opposite direction? At twice the speed? Would the aircraft use less thrust to takoff?

NO - it will not take off in the original question - the friction of the static air and the travel of the treadmill cancel each other out. If the treadmill travel went faster - the aircraft would move backwards!

now what if the treadmill went it the opposite direction? at twice the speed? would the aircraft use less thrust to takoff?

NO - it will not take off in the original question - the friction of the static air and the travel of the treadmill cancel each other out. If the treadmill travel went faster - the aircraft would move backwards!!

NO BC you are wrong - because the wheels will be spinning and the engines would develop enough thrust to make the a/c to roll forward and reach its takeoff speed, the weels are not what makes a a/c to move forward, the engines are not in any way connected to the wheels as it is in a car, or truck etc. etc. the tires will start to skid over the tredmillas thrust is incresed and the faster the a/c roll forward the lighter it becomes on the treadmill which starts from the time the a/c starts moveing , andf before it reaches the point of rotation,( LIFTOFF OR TAKE OFF ) All a/c have a point in speed for rotation , every a/c is different speeds, but there has been times that I was not at rotation point and was able to take off with the use of fllaps, ( Once lift = weight you have lift off ) HAVE A GOOD DAY & GOD BLESS:::: F.B.E.:) :D

NO BC you are wrong - because the wheels will be spinning and the engines would develope enough thrust to make the a/c to roll forward and reach its takeoff speed, the weels are not what makes a a/c to move forward, the engines are not in any way connected to the wheels as it is in a car, or truck ect. ect. the tires will start to skid over the tredmillas thrust is incresed and the faster the a/c roll forward the lighter it becomes on the treadmill which starts from the time the a/c starts moveing , andf befor it reaches the point of rotation,( LIFTOFF OR TAKE OFF ) All a/c have a point in speed for rotation , every a/c is different speeds, but there has been times that i was not at rotation point and was able to take off with the use of fllaps, ( Once lift = weight you have lift off ) HAVE A GOOD DAY & GOD BLESS:::: F.B.E.:) :D

A treadmill is not a frictionless platform! The wheels are not frictionless! The motion of the treadmill will push backwards on the wheels of the aircraft.
If there is no thrust - the aircraft would move backwards! The thrust must overcome that friction just to make the aircraft stay in one position.

A treadmill is not a frictionless platform! The wheels are not frictionless! The motion of the treadmill will push backwards on the wheels of the aircraft. :eek: :eek:
If there is no thrust - the aircraft would move backwards! The thrust must overcome that friction just to make the aircraft stay in one position.
BCDurbin - I do not believe that you know the princibles of flight< One thing there is no tread mill made that could hold back a a/c with engines at full thurst GOOD DAY & GOD BLESS :: F.B.E. :) :D

A treadmill is not a frictionless platform! The wheels are not frictionless! The motion of the treadmill will push backwards on the wheels of the aircraft.
If there is no thrust - the aircraft would move backwards! The thrust must overcome that friction just to make the aircraft stay in one position.

Put it this way...

Imagine a skateboard on a treadmill. Tie a rope to the skateboard and stand along side of the treadmill. Now turn the treadmill on. The skateboard will start moving backward, but you can easily run along side the treadmill pulling the skateboard forward. The reason you can do this is because you yourself are not on the treadmill. In other words, the forward force is completely independent of the treadmill AND the skateboard's wheels

The above example is also the principle of thrust. The thrust 'pushes' the jet forward independent of the aircraft's (wheels). If you're still having trouble, imagine another plane flying overhead with a tow rope attached to the plane on the treadmill. Regardless of how fast the treadmill is going in the reverse direction, the flying plane would not only be able to pull the plane on the treadmill forward, but would pull it forward at the speed in which it was flying. Again, thrust works the same way. Since it is independent of the aircraft's wheels it would eventually reach rotation.

Lobrobster - Boy did you say the RIGHT THINGS, I hope maybe he will understand now that the a/c will move forward as the pilot advances the throttle and increases the thrust of the engines,and will increase the speed of the a/c and reach the ROTATION POINT AND TAKE OFF> ALso as he increses the speed ,he starts to have lift and will start losing contact with the treadmill,;: thanks Lobrobster you earned a greenie for your answer ;;; Have a good day and GOD BLESS :: F.B.E.

Put it this way...

Imagine a skateboard on a treadmill. Tie a rope to the skateboard and stand along side of the treadmill. Now turn the treadmill on. The skateboard will start moving backward, but you can easily run along side the treadmill pulling the skateboard forward. The reason you can do this is because you yourself are not on the treadmill. In other words, the forward force is completely independent of the treadmill AND the skateboard's wheels

no - turn the treadmill on first then see how much force it takes to hold the skateboard in place - there is friction there! the original question did not say this was frictionless.

The above example is also the principle of thrust. The thrust 'pushes' the jet forward independent of the aircraft's (wheels). If you're still having trouble, imagine another plane flying overhead with a tow rope attached to the plane on the treadmill. Regardless of how fast the treadmill is going in the reverse direction, the flying plane would not only be able to pull the plane on the treadmill forward, but would pull it forward at the speed in which it was flying. Again, thrust works the same way. Since it is independent of the aircraft's wheels it would eventually reach rotation.

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!

BCDurbin - I do not believe that you know the princibles of flight< One thing there is no tread mill made that could hold back a a/c with engines at full thurst GOOD DAY & GOD BLESS :: F.B.E. :) :D

You are talking reality - the original question was just theoretical. I have no doubt that a jet could outthrust a REAL treadmill - the question stated if the 'treadmill travel' and the aircraft speed (thrust) were equal! And in the opposite direction! Am I right? Any additional force by the aircraft (rope or thrust!) would propel the aircraft forward - just as any additional force would move the aircraft backwards! But if all forces are equal there will be no movement. :)

BCDurdin - I have one question to ask you first?? DO YOU HAVE ANY EXPER> ON A?C OR AS SA PILOT< IN ANY WAY?? F.B.E.

BCDurdin - I have one question to ask you first???? DO YOU HAVE ANY EXPER> ON A?C OR AS SA PILOT< IN ANY WAY?????? F.B.E.

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

Put it this way...

...... Tie a rope to the skateboard and stand along side of the treadmill. Now turn the treadmill on. The skateboard will start moving backward, but you can easily run along side the treadmill pulling the skateboard forward. ........

Put a scale/g-force meter on the end of that rope and see how much force it takes to hold the skateboard in place. Now stand on the skateboard and see if takes more force. I have no doubt you could pull it off the treadmill but it will take excess force in the forward direction to do it. Especially after you stand on it. Try two people - it's more fun that way when you fall down! - BCD

The jet starts it's thrusters and for every mile an hour the Jet's wheels move forward, the treadmill moves a mile an hour in the opposite direction.

The question has to do with a hypothetical situation. A body with lift that ordinarily could fly is in a situation where it cannot achieve any velocity relative to the wind. If the jet accelerates to 100 kts, the treadmill accelerates to 100 kts in the opposite direction. Relative to the surface of the earth, the jet is not moving. Relative to the wind, it is not moving. No movement through the wind... no lift.

No liftee. No flyee.

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.

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

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

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?

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

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.

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

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.

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.

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.

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.

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'.

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.

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: :)

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.

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.

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

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.

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.

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.

It will fly surely cause run way & landing gear have supporting role, actually role of air. And it cause of Newton’s 3rd law when engine do action in reaction of the action plane go forward. Weather its on runway or floating on air. Even if you heard about air tunnel which is used to check plane model in that they use opposite thing plane is stationary and air is passing through the wings. And on that basis it will float on air.
Second thing is that plane is not using land or runway as surface resistance to go forward like car. So finally in plane case if its on treadmill, it could fly but in car case car couldn't go forward.

Good

Exact point.

Didn't they try this on mythbusters? Not with a jet aircraft though

Rebel-2 - The answer to your question is ( YES 0 GO TO
MythBusters Episode 97: "Airplane on a Conveyor Belt" (http://mythbustersresults.com/episode97)
Have a good day and keep her between the cloudsa and GOD BLESS ;;F.B.E.