oldtimer Posted November 19, 2006 Share Posted November 19, 2006 I'll just repeat my question for dwilawyer: How does the conveyor impart any horizontal force to the body of the plane that opposes the plane's thrust? You're under the misconception that the plane remains stationary. The real question here is does the plane remain stationary? Lets take the example of thrust regarding a rocket. The rocket's thrust overcomes gravity to propel it into the atmosphere. The thrust on the plane likewise propels the plane fast enough to create airflow over the wings creating lift. It overcomes the friction on the ground caused by the weight of the plane to propel it forward. Once the thrust is enough to counteract the friction of weight (gravity) it will move forward. It does not matter if the plane has wheels or skids or is on a rail. It moves forward, creating lift, and takes off. With enough thrust the plane does not remain stationary because it overcomes the friction of its own weight (yes gravity). The car on the dyno does not move forward because the thrust of the car is sent through the wheels. If you can spin wheels on your car you know this intrinsically. The car will not move if the wheels have no traction. A plane does not rely on traction. That's why it can take off on ice as long as it goes straight enough for proper airflow over the wings. Does this make sense? Quote Link to comment Share on other sites More sharing options...
Moderators Travis In Austin Posted November 19, 2006 Moderators Share Posted November 19, 2006 That's your problem, there is nothing in the original problem that says the airplane doesn't move. The whole basis of this hypothetical scenario is that the ground below the airplane moves. What you can't seem to grasp is that the ground below the plane is moving but not with respect to the earth, therefore the plane can and does move forward with respect to earth. Read the problem again. a plane is standing on a movable runway( something like a conveyor).as the plane moves the conveyor moves So the belt thing is just a big trick. The belt has nothing to do with it then? Let's say the top speed of the plane, in still air, is 50 mph, and the belt can go many times that speed in reverse. The plane speeds up to one mile per hour, the belt, and the very same instant move in reverse at 1 mph, the plane has free spining wheels so it just keeps proceeding down the belt. From above, it would appear as though it was taking off a normal runway THIS WILL ANSWER THE ENTIRE PROBLEM: If the planes propeller/jet (it does not matter what it is) produces enough thrust for the plane on a normal surface like a real runway to reach 1 mph, and the belt is moving 1 mph in reverse, what is the speed of the plane relative to the ground. If is is -1 it won't fly, if if is 0 it will not fly, and if it is 1 mph it will eventualy fly when it reachs Vx. If the belt has no friction and wheels have no friction and allows the plane to move forward it will fly. So the hypo assumes that if the belt started to move in reverse at 1mph without any thrust from the plane the plane would still remain stationairy because no friction (body a rest tends to stay at rest, etc.) If that is the case, the plane will fly. Quote Link to comment Share on other sites More sharing options...
klipschaholik Posted November 19, 2006 Share Posted November 19, 2006 In short the wheels will turn at two times the speed of the aircraft with respect to earth (not the mat) and yes under ideal frictionless conditions the plane would stay still if the conveyor moved underneath and the aircraft had no power applied. Quote Link to comment Share on other sites More sharing options...
sputnik Posted November 19, 2006 Share Posted November 19, 2006 Another beer goes out to dwilawyer. Would a dwilawyer drink a beer? My hat's off to the non-engineers/scientists that are getting this. Quote Link to comment Share on other sites More sharing options...
PhilMays Posted November 19, 2006 Share Posted November 19, 2006 Captains Log: 11/19/02 7:00PM I have a very large pile of wood and a woodchuck. The woodchuck started chucking wood, and then went on break. Apparently I have hired a union woodchuck. The woodchuck has produced his contract and while he can chuck wood very well and better than any other species of woodchuck, he won't. The woodchuck is now insisting that if I do not give him 7 breaks a day and guarantee his job over the next 143 years, he will go on strike tomorrow. Quote Link to comment Share on other sites More sharing options...
customsteve01 Posted November 19, 2006 Share Posted November 19, 2006 Phil, Let him go on strike and go buy a chainsaw.................................. you'll save a bundle of money and alot of headaches. [] Travis, I don't think we can explain it to you where you will understand it. But, it will fly. Steve Quote Link to comment Share on other sites More sharing options...
PhilMays Posted November 19, 2006 Share Posted November 19, 2006 I had a very hard time getting my mind out of the box from the wheels/conveyor belt distraction. On the aircraft, the wheels never have or ever will provide thrust. They are simply the mechanical piece to allow the plane to interact with the surface (support weight) for the thrust mechanics (jet/prop) to do it's job until the weight can be transfered from the wheels to the wings. It will fly and it will roll down this huge conveyor belt just like it was a runway and the wheels will be spinning like a frat boys head the next day after a good mixer! It takes a bit for us that do not work in an engineering field, but once you get it, you get it! Quote Link to comment Share on other sites More sharing options...
Moderators Travis In Austin Posted November 19, 2006 Moderators Share Posted November 19, 2006 Phil, Let him go on strike and go buy a chainsaw.................................. you'll save a bundle of money and alot of headaches. [] Travis, I don't think we can explain it to you where you will understand it. But, it will fly. Steve Steve, I agree it will fly, as long as the ground speed reaches the stall speed, it will also take at least as many feet of moving runway as it would regular runway for it to fly. Travis Quote Link to comment Share on other sites More sharing options...
customsteve01 Posted November 19, 2006 Share Posted November 19, 2006 Travis, Ground speed has nothing to do with when a plane takes off. Its is all about airspeed. Steve Quote Link to comment Share on other sites More sharing options...
Moderators Travis In Austin Posted November 19, 2006 Moderators Share Posted November 19, 2006 Travis, Ground speed has nothing to do with when a plane takes off. Its is all about airspeed. Steve Steve, I am well aware of that, I have been a pilot 30 years. I said assuming no wind, thus ground speed will equal air speed in my example. See my posts above re: IAS vs. Ground Speed. Travis Quote Link to comment Share on other sites More sharing options...
mas Posted November 20, 2006 Share Posted November 20, 2006 Hey kids, you can all yell at me, but this is one of those discussions that reinforces the notion that 100 monkeys placed in a room with typewriters will never recreate Shakespeare! ...But it does seem more reminicent of letting an inflated balloon loose and trying to guess precisely which direction it will fly! [] [] [] Quote Link to comment Share on other sites More sharing options...
PhilMays Posted November 20, 2006 Share Posted November 20, 2006 Hey kids, you can all yell at me, but this is one of those discussions that reinforces the notion that 100 monkeys placed in a room with typewriters will never recreate Shakespeare! ...But it does seem more reminicent of letting an inflated balloon loose and trying to guess precisely which direction it will fly! [] [] [] Time for your meds...nighty night... Quote Link to comment Share on other sites More sharing options...
Moderators Travis In Austin Posted November 20, 2006 Moderators Share Posted November 20, 2006 Hey kids, you can all yell at me, but this is one of those discussions that reinforces the notion that 100 monkeys placed in a room with typewriters will never recreate Shakespeare! ...But it does seem more reminicent of letting an inflated balloon loose and trying to guess precisely which direction it will fly! [] [] [] Time for your meds...nighty night... I liked this discussion/reasoning/debate a whole lot better then the SS vs. PP vs. SET debate or the vinyl vs. CD "discussion." So here is another one, but a lot easier. Two planes take off from the same airport heading due East (90 degree headingforget the magnetic heading and all of that stuff). There is a 10 mph direct cross-wind (from the South at 180 degrees). One plane is a Piper Cub and cruises at 85 mph and the other is a Gulfstream G-V that cruises at 500mph. How far will each plane be off course one hour after take off? Travis Quote Link to comment Share on other sites More sharing options...
sputnik Posted November 20, 2006 Share Posted November 20, 2006 If the pilots are any good, why would they be off couse at all? Quote Link to comment Share on other sites More sharing options...
D-MAN Posted November 20, 2006 Share Posted November 20, 2006 Airflow over the wings is what makes it fly, and with zero air speed over the wings, zero flight. DM Why do you assume there is "zero air speed"? What force is exerted by the conveyor on the plane to impede the plane's forward motion? I have to go out for a while. So you have time to think. Are you NUTS?! the jet engines exhausting one way and the conveyor going the opposite direction at exactly the same compensating speed? Try ZERO air speed... To think otherwise is shockingly stupid, but I see you've already signed up for that one. I'm going out for awhile so you have time to not be as ... DM Quote Link to comment Share on other sites More sharing options...
Moderators Travis In Austin Posted November 20, 2006 Moderators Share Posted November 20, 2006 Oh they are great pilots, but they both belong to the Klipsch forum and just decided to fly due East without taking into consideration any cross-wind to settle a bet. In other words they line the compass up with E/90 and fly for one hour. Quote Link to comment Share on other sites More sharing options...
customsteve01 Posted November 20, 2006 Share Posted November 20, 2006 D-MAN, All that will happen is the wheels will be turning at twice the speed. The forward movement thru the air will be the same. Steve Quote Link to comment Share on other sites More sharing options...
sputnik Posted November 20, 2006 Share Posted November 20, 2006 dwilawyer, OK, I'll bite - I just wanted to make sure it wasn't some sort of lawyer trick. In one hour, both planes should be 10 miles north of the intended flight path. The Gulf Stream will have travelled 500 miles east and 10 miles north and will be off course by ATAN(10/500) or 1.46 degrees. The Piper will have travelled 85 miles east and will also be 10 miles north of the intended flight path and will be off course by ATAN(10/85) or 6.71 degrees. D-MAN will still be stuck on the conveyor. Quote Link to comment Share on other sites More sharing options...
klipschaholik Posted November 20, 2006 Share Posted November 20, 2006 Shouldn't it be 1.146 degrees and 6.71 degrees? 10/500 arcTan = 1.146 10/85 arcTan = 6.71 Quote Link to comment Share on other sites More sharing options...
sputnik Posted November 20, 2006 Share Posted November 20, 2006 Shouldn't it be 1.146 degrees and 6.71 degrees? 10/500 arcTan = 1.146 10/85 arcTan = 6.71 Right, I should have used a calculator instead of counting on my fingers. [:$] Quote Link to comment Share on other sites More sharing options...
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