Gaz6002 Posted February 6, 2008 Share Posted February 6, 2008 So the plane's ground speed is zero??? If it is then the plane will not take off as it is the airspeed that it requires to produce lift. If the conveyor runway was moving in the same direction as the plane, therefore doubling its ground speed, it would take off quicker.....much like a plane on an aircraft carrier, hence why they have to take off into wind from the read to front of the ship. *Ducks* This was my thinking... until I unleashed the onslaught on Mr C... Quote Link to comment Share on other sites More sharing options...
Ric Posted February 6, 2008 Share Posted February 6, 2008 um, nothing? Quote Link to comment Share on other sites More sharing options...
Thorin Posted February 6, 2008 Share Posted February 6, 2008 I wasn't making any inflamatory comments The gravity thing was a terrible pun though, I admit to that. Not as good as your "steps" one, but made me chuckle Right, sorted then. Next up - the perennial non-question "what happens if I drive at the speed of light and turn on my headlights..." What do you plan on using to power the treadmill to get it up to that speed? Quote Link to comment Share on other sites More sharing options...
Alex Posted February 6, 2008 Share Posted February 6, 2008 What do you plan on using to power the treadmill to get it up to that speed? The fighter jet that can't take off from it Quote Link to comment Share on other sites More sharing options...
Kranz Posted February 6, 2008 Share Posted February 6, 2008 I wasn't making any inflamatory comments The gravity thing was a terrible pun though, I admit to that. Right, sorted then. Next up - the perennial non-question "what happens if I drive at the speed of light and turn on my headlights..." The photons build up in the headlight and cause it to burst Quote Link to comment Share on other sites More sharing options...
Gaz6002 Posted February 6, 2008 Share Posted February 6, 2008 I wasn't making any inflamatory comments The gravity thing was a terrible pun though, I admit to that. Right, sorted then. Next up - the perennial non-question "what happens if I drive at the speed of light and turn on my headlights..." The comments about the intelligence of people not agreeing with you were the inflamatory ones - hence me seeing red and not sense. That's my excuse and i'm sticking to it. Quote Link to comment Share on other sites More sharing options...
rpslaughter1982 Posted February 6, 2008 Share Posted February 6, 2008 So the plane's ground speed is zero??? If it is then the plane will not take off as it is the airspeed that it requires to produce lift. If the conveyor runway was moving in the same direction as the plane, therefore doubling its ground speed, it would take off quicker.....much like a plane on an aircraft carrier, hence why they have to take off into wind from the read to front of the ship. The ground speed wouldn't be zero unless the belt was travelling in the same direction as the plane. The ground speed would be greater but this wouldn't effect the plane taking off. most planes try to take off into wind on land or sea as it increases the air speed which is what effects take off speed. If a plane flies into a 70 mph head wind it's air speed may be 150mph but the ground speed would be 80 mph. Likewise with a tail wind of 30 mph you may have an air speed of 180 mph and a ground speed of 210mph. Quote Link to comment Share on other sites More sharing options...
Kranz Posted February 6, 2008 Share Posted February 6, 2008 The ground speed wouldn't be zero unless the belt was travelling in the same direction as the plane. If the belt was travelling in the same direction as the plane, and matching its speed, then the ground speed would be double. Much the same as walking on a travelator at the airport (one of those flat escalator things). Quote Link to comment Share on other sites More sharing options...
tbourner Posted February 6, 2008 Share Posted February 6, 2008 Quote Link to comment Share on other sites More sharing options...
Soop Dogg Posted February 6, 2008 Share Posted February 6, 2008 Think of the conveyor belt runway thing like this to show that the speed of the conveyor (and hence wheel speed) has absolutely no effect on the take-off speed of the aircraft: If the take-off speed of your plane is 180mph, then make the runway move at a steady 180mph FORWARDS, but hang on to the plane so that it's stationary. This will make the wheels of the plane move in reverse - right? Ok, now wind up the engines so they start to develop thrust. (Then stop hanging on to it so that it can move) Obviously the air around the plane is still stationary. Will the engines have to move the aircraft forwards at 2x180mph for it to take off? (As that's when the wheels will be doing 180mph relative to the conveyor) Of course not - the aircraft will still take off at 180mph relative to the air around it. In fact, in this case, the aircraft will take off when the wheels have just stopped moving. So, you can see that the wheel speed has absolutely no effect on when the aircraft will take off as it can still take off even if the wheels are not moving at all. Quote Link to comment Share on other sites More sharing options...
rpslaughter1982 Posted February 6, 2008 Share Posted February 6, 2008 If the belt was travelling in the same direction as the plane, and matching its speed, then the ground speed would be double. Much the same as walking on a travelator at the airport (one of those flat escalator things). Sorry I was talking about ground speed in relation to the speed of the belt not what the belt is on. The speed of the belt is irrelevant to the take off, if there was zero friction in the hubs of the plane wheels then the plane would not move even if it was not creating thrust. Same is if you had zero friction on your feet you would not move on the ‘travelator’. Quote Link to comment Share on other sites More sharing options...
tbourner Posted February 6, 2008 Share Posted February 6, 2008 Much the same as walking on a travelator at the airport (one of those flat escalator things). If you did that and the travelator was set to move at the same speed you were walking at, surely it'd speed up to an infinite speed as quickly as the feedback circuit would allow!! Quote Link to comment Share on other sites More sharing options...
Kranz Posted February 6, 2008 Share Posted February 6, 2008 Sorry I was talking about ground speed in relation to the speed of the belt not what the belt is on. The speed of the belt is irrelevant to the take off, if there was zero friction in the plane wheels then the plane would not move even if it was not creating thrust. Same is if you had zero friction on your feet you would not move on the ‘travelator’. Oh bu**er it. I wrote a long, well thought out post but then decided I can't decide if I have considered all the factors so I say Who cares?? I've got to take the nipper to the park Quote Link to comment Share on other sites More sharing options...
rpslaughter1982 Posted February 6, 2008 Share Posted February 6, 2008 Oh bu**er it. I wrote a long, well thought out post but then decided I can't decide if I have considered all the factors so I say Who cares?? I've got to take the nipper to the park very true. (although I just thought of the example of a car wheel spinning, the wheels could be doing any speed but without the friction it will not be transfered into forward motion) Quote Link to comment Share on other sites More sharing options...
Kranz Posted February 6, 2008 Share Posted February 6, 2008 Ok, I had a think about this at the park. The plane is effectively uncoupled from the conveyor due to the freewheeling nature of the wheels, and negating any drag from bearings and tyres then the wheels can be doing what they like.... its the thrust from the engine(s) that will gain forward velocity and airspeed. So it will damn well take off It'll just need a bit more power to overcome tyre & wheel bearing drag. What a ball ache of a question LOL Edit: To use my travelator example, its like a bike on a travelator being held in one place by a glamorous assistant pushing on the back of the saddle. To hold it steady will require a force equal to that of the drag caused by the tyres & bearings. To accelerate it will require a bit more force, but it can easily accelerate forwards as long as there is sufficient push from behind. The push is the same as the thrust from the plane's engine(s). Quote Link to comment Share on other sites More sharing options...
Gaz6002 Posted February 6, 2008 Share Posted February 6, 2008 Quote Link to comment Share on other sites More sharing options...
Mike B Posted February 6, 2008 Share Posted February 6, 2008 what happens if it's a harrier? Quote Link to comment Share on other sites More sharing options...
Matt H Posted February 6, 2008 Share Posted February 6, 2008 what happens if it's a harrier? It arches its thurst to 45 degrees (as they always do for take offs) and then take off just like a harrier does normally, no difference Quote Link to comment Share on other sites More sharing options...
RobSheffield Posted February 6, 2008 Share Posted February 6, 2008 Bless you all for arguing this out so far, 144 posts Quote Link to comment Share on other sites More sharing options...
JustGav Posted February 6, 2008 Share Posted February 6, 2008 I wasn't making any inflamatory comments The gravity thing was a terrible pun though, I admit to that. Right, sorted then. Next up - the perennial non-question "what happens if I drive at the speed of light and turn on my headlights..." All depends, since you can't actually attain the speed of light as your mass would be 0. However lets extend it and say you get near the speed of light... Which then means it is all down to of view in relation to relativity. Lorenz contractions would mean that inside the car the headlights would appear to be on and the world would seem much smaller due to lorenz contractions. However outside the vehicle it will be contracted and the light would be appear to be travelling at normal speed Quote Link to comment Share on other sites More sharing options...
RiceRocket Posted February 6, 2008 Share Posted February 6, 2008 Talk about storm in a teacup....! http://mythbusters-wiki.discovery.com/page/Plane+on+a+Conveyor+Belt Quote Link to comment Share on other sites More sharing options...
TonyP Posted February 6, 2008 Share Posted February 6, 2008 Talk about storm in a teacup....! http://mythbusters-wiki.discovery.com/page/Plane+on+a+Conveyor+Belt Oh. Now I get it. Why didn't someone explain it that simply before?:d Quote Link to comment Share on other sites More sharing options...
MrRalphMan Posted February 6, 2008 Author Share Posted February 6, 2008 Oh. Now I get it. Why didn't someone explain it that simply before?:d Where would be the fun in that? Quote Link to comment Share on other sites More sharing options...
OhGod Posted February 6, 2008 Share Posted February 6, 2008 The only problem I have with the "will take off" logic is it seems to assume completely free-spinning, frictionless wheels. Is bringing friction into this over complicating the question? Plane turns on engines to produce thrust for 10mph, wheels turn at 10mph. Treadmill turns on, in opposite direction, going 10mph - wheels now freely turn at 20mph? Plane turns engine off, thereby cancelling it's 10mph worth of thrust (yes, mph isn't a unit of thrust, but it was producing thrust to achieve 10mph, etc etc..) - does the plane now remain stationary, with wheels freely turning, or does it now get dragged backwards at 10mph by the treadmill? How, by cancelling the force that was producing a 10mph forward speed, did we go from +10mph to -10mph? Or, the plane is sat on the treadmill/runway thingy. Treadmill starts up at -10mph, does the plane start moving backwards at 10mph, or remain stationary with the wheels spinning at 10mph? Engines come on to produce thrust that would, on a static runway, give the plane a 5mph speed. Does the plane now start going forward at 5mph, with the wheels at 15mph, or is it still travelling backwards but at a reduced rate of -5mph? Something just seems to be missing - and I think it's friction/rolling resistance/whatever - but maybe that's getting too involved. Quote Link to comment Share on other sites More sharing options...
MrRalphMan Posted February 6, 2008 Author Share Posted February 6, 2008 But the treadmill keeps pace with the plane, so no worries there. Quote Link to comment Share on other sites More sharing options...
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