924Board.org

[xpernet]

If i had an R/C plane, i would do a simulation !!!!
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1977 Porsche 924
Sunroof Delete
Megasquirt II EFI & EDIS
Carrera GTS / 944 Body

"If one does not fail at times, then one has not challenged himself." Ferdinand Porsche

[Ozzie]

In which case the whole question is a contradiction in itself and is not worth this debate.
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Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

[Andrew NZ]

[Khal]

[D Hook]

[Kenodog]

Someone should send this to Mythbusters.Good excuse to somehow blow up a plane !
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1979 Euro 931, Olive
1981 931, Sabine
1991 Ford Ranger XLT 4x4, Ricky
1996 Ford E-350 ex-FedEx Van
2014 Mazda CX-5 (Kinderwagon)
2019 KTM 790 Adventure
2024 KLX300
2024 KLX140

[morghen]

hahah..Kenodog thats a good ideea...

if the runway turns as fast as it needs just to keep the plane motionless....then the ridle is pointless...and its kindergarden shit...no no but you cant take the toy even if its right infront of you...there is a forcefield that is blocking you !!

again...why not turn the plane around and fly the other way ?
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Supercharger and EFI kits
https://www.the924.com

[Kenodog]

If it were that simple to get the plane to fly then for practicality sake couldn't you just use a set of rollers - like from a dyno and use those to spin the wheels ? It would produce the same effect,burning the rubber off the wheels while providing NO lift or forward motion.
_________________
1979 Euro 931, Olive
1981 931, Sabine
1991 Ford Ranger XLT 4x4, Ricky
1996 Ford E-350 ex-FedEx Van
2014 Mazda CX-5 (Kinderwagon)
2019 KTM 790 Adventure
2024 KLX300
2024 KLX140

[macBdog]

[jamez]

Ignoring friction on the wheels the plane will take off just like normal. the plane will have forward motion because the jet engine is pushing against the air, not the runway. The wheels will however be spinning at an amazing rate.
If the treadmill kept on moving faster to try and stop the plane's forward motion, it would eventually be spinning so fast that the wheels would exceed their rmp limit and they would blow up.

If you don't ignore friction on the wheels and assuming the treadmill moves ever faster trying to stop the planes forward motion, then the treadmill will very quickly reach a speed that will cause wheel friction to be so high that the jet engines can't produce enough thrust to keep up, this is where it would reach equillibrium, and the plane would no longer have forward motion. Since the wheel friction is so low the speed of the treadmill would have to be enourmously high, and the wheels would definately have exceeded their rpm limit and have blown up.


Also, an airplane needs air over the wings to create lift. Despite what some of you have said, most jet aircraft do not use their engines like a rocket, and they do not control the direction of the applied thrust. that is called thrust vectoring and has only been used on a few ultra high tech military aircraft.

[Porsche924boy]

[Kenodog]

A jet DOES use it's thrust in the same way a rocket does.It's the ailerons,flaps,vertical and horizontal stabilizers that tell the plane where to go under power of that thrust.The sole reason a jet ever gets off the ground is because the engine's thrust pushes it to a speed where the wings create lift.This lift,coupled with it's forward motion,is controlled flight.
A stationary plane will not take off even if the thing has the afterburner cooking on high.This is why aircraft carriers have slingshots.
A moving plane will take off of course because the wings can do thier job and provide lift.
If a jet is sitting on the runway with the brakes applied and the engines running at takeoff power the jet does not instantly leap into the air just because the pilot takes his foot off the brakes.It still needs SOME time to roll down a runway to build up speed enough to lift off.
The plane needs forward motion to blow wind over the wings.
The riddle says it was an unusually calm day.No wind.The plane has an equal amount of force pushing against it for every pound of forward thrust that it produces.Therefore it's essentially just sitting there with it's engines screaming,wheels turning but is still STATIONARY in relation to the world around it.


No forward motion=no wind over the wings=no flight.
_________________
1979 Euro 931, Olive
1981 931, Sabine
1991 Ford Ranger XLT 4x4, Ricky
1996 Ford E-350 ex-FedEx Van
2014 Mazda CX-5 (Kinderwagon)
2019 KTM 790 Adventure
2024 KLX300
2024 KLX140

[Smoothie]

Absitively, if the plane, whether it be jet or prop, isn't moving and the air is still, it can't lift off. I'm pretty sure we'd all agree with that. The problem with the "riddle" is that it breaks some laws of physics in supposing that a treadmill acting on freewheeling wheels is going to prevent forward motion of the aircraft. Can't happen. The only way the treadmill could have an effect on and counteract the forward motion of the aircract is if wheel brakes were also applied. Myself and I'd assume most others that say it'll take off are basing their answer on the fact that a treadmill trying to counteract the forward motion simply wouldn't have any affect. We're not imagining that it could, so the plane just moves forward, attains the appropriate speed and lifts off.
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"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[Khal]

[Ozzie]

If the action of the treadmill is preventing the plane from having any air speed over the wings (ie motionless) it will not take off regardless of the relevent ground/treadmill speed.
However the question is unclear as to whether this is the case so- need more input, unable to make a determination at this time, insufficient data.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance