|
09-02-2006, 01:25 PM,
|
|
|
|
A conundrum to mull over.
came across this on another site. I've not seen it here although no doubt it has been discussed elsewhere by members here. An intersting conundrum.
A plane is standing on a runway that can move (some sort of giant conveyer belt).
The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane's speed and tunes the speed of the conveyer to be exactly the same as that of the plane, but in the opposite direction.
Can the plane take off?
|
|
|
|
09-02-2006, 01:51 PM,
|
|
|
Nigel
Senior Member
|
Posts: 669
Threads: 157
Joined: Feb 2003
|
|
|
A conundrum to mull over.
Nope. Lift from the wings is dependent upon airspeed, not groundspeed (or even relative groundspeed). In this case, if I've understood the configuration correctly, the plane has an airspeed of zero, and it isn't going anywhere.
Now, if the plane and belt were all located in a windtunnel, with a 200mph headwind directed towards the plane - in that case, the airflow over the wings would generate sufficient lift for the plane to take off, even though its effective groundspeed was still zero.
|
|
|
|
09-02-2006, 04:03 PM,
|
|
|
Sweder
Twittenista
|
Posts: 6,577
Threads: 420
Joined: Nov 2004
|
|
A conundrum to mull over.
Yes . . . just take the cheese away from the mice, they'll stop running on their little treadmills, the runway will grind to a halt and the plane will whizz off down the runway and launch into the skies.
Oh, sorry . . . were you being serious?
I'll get me aviators' jacket . . . 
The harder the conflict, the more glorious the triumph
|
|
|
|
09-02-2006, 04:04 PM,
|
|
|
|
A conundrum to mull over.
But I'm not sure why :o
You appear to be saying that if a plane requires (say) ground speed of 80mph to generate enough airspeed to lift, then it could not take off with an 80mph tailwind because airspeed would be zero.
|
|
|
|
10-02-2006, 05:46 AM,
|
|
|
|
A conundrum to mull over.
...while you guys are busy arguing over giant conveyor belts and cheese-wielding mice, the pilot has taken himself off to the bar and is too pissed to fly the bloody thing anyway.
Serves you right for flying EasyJet.
|
|
|
|
10-02-2006, 07:19 AM,
|
|
|
marathondan
Back on the road
|
Posts: 2,335
Threads: 89
Joined: Oct 2005
|
|
A conundrum to mull over.
Not sure if this was ever meant to be taken seriously.
But if so, then to my mind, SP's proposition: Seafront Plodder Wrote:You appear to be saying that if a plane requires (say) ground speed of 80mph to generate enough airspeed to lift, then it could not take off with an 80mph tailwind because airspeed would be zero. seems to be correct. Lift is generated by the relative motion of wings to air.
Is this some sort of allusion to the futility of running on a treadmill?
|
|
|
|
10-02-2006, 12:15 PM,
|
|
|
marathondan
Back on the road
|
Posts: 2,335
Threads: 89
Joined: Oct 2005
|
|
A conundrum to mull over.
Sweder, I heartily agree with your proposal, but it seems we're all wrong. See here. When the pilot starts the engines, the plane moves as normal, no matter how fast the wheels are spinning on the treadmill. Or to put it another way, no matter how fast the treadmill turns, it won't be able to stop the plane moving and taking off (unless it moves so fast as to melt the bearings in the wheels...)
NB I particularly like the explanation "imagine you're standing on a health-club treadmill in rollerblades while holding a rope attached to the wall in front of you" - something I do all the time of course.
SP, did you know the answer when you first posted this?
|
|
|
|
10-02-2006, 12:51 PM,
|
|
|
A conundrum to mull over.
Nope. Still being discussed elsewhere, although as here, some posters are hell bent on taking things waay off topic.
|
|
|
|
