I gave up after the last post... it's like going back in time trying to convince the 1300th century folks that the world is round and not flat.
CallMeJoe
Diamond Member
- Jul 30, 2004
- 6,938
- 5
- 81
Aerodynamics must not be your forte. Recip, turbo prop or jet, engine wash over the wing is a negligible part of wing lift. The fraction of the wing affected by the engine wash is not sufficient to provide any significant lift. Look at a Piaggio P180 Avanti or a Beechcraft Starship. Both turboprops, both pusher props (no significant prop wash over the wings) and they both fly very nicely.
The plane can move forward on solid ground because solid ground is NOT moving backwards. The world is rotating and it's taking everything with it along for the ride. If you're out in space, the world is one big conveyor belt. If you accelerate a plane on this huge conveyor belt, the plane moves forward on the conveyor belt, and if it's capable of moving fast enough it will be stationary to the observer in their little space ship. In order for the plane to appear moving forward to the observer, it would have to move twice as fast as the world's rotation, which would require a hell of a lot more energy. And yes I'm aware it's a terrible explanation, but I'm running short on analogies.
I'd love to take you up on that wager if we can agree as to the precise definition of driving in this context, which ofcourse I'm sure we'll be incapable of doing.
DrPizza
Administrator Elite Member Goat Whisperer
Wow, I can see why this thread has gotten so long!
And, it's all the fault of the OP who thought he was wording his post cleverly enough to remove any ambiguities.
1. Those who say the plane can't move forward are, in a sense, correct. For if the plane was to move forward, we'd have a paradox. The conveyor *cannot match the speed* of the wheels on a forward moving plane, unless the wheels are skidding. People keep pointing to "if the plane is going 100mph, then the conveyor will be going 100mph in the opposite direction and the wheels will simply be spinning at 200mph." No, the OP said the conveyor matches the speed of the wheels, not the speed of the plane. 100mph doesn't equal 200mph, except in those trick proofs that require division by zero.
In other words, the speed of the wheels = the speed of the conveyor + the speed of the plane. Since conveyor speed = wheel speed, then logically, plane speed = 0. Anyone using that sentence as the basis of claiming the plane doesn't move is correct. You can't ignore this important fact. But, unfortunately, most of the people who have come to this realization don't quite realize the meaning of it. It's not a matter of the conveyor keeping the plane in place... it results from an impossible constraints on the problem.
2. If the conveyor matched the speed of the plane, rather than the speed of the wheels (which is impossible), then the plane would indeed take off, with the speed of the wheels always double the speed of the airplane as it accelerated down the runway. (assuming no slippage of the wheels)
--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
Now, for those who are saying that a spinning conveyor can keep a jet from moving forward (I've already established that the constraints given by the OP are impossible), try this at home:
Turn on a treadmill... set its speed to 10mph, but keep it level. Put on a pair of rollerblades. Skate across the room at 6 or 7 mph. Hop onto the treadmill while moving forward. Note that the treadmill does *NOT* stop you from moving forward, even though it's moving in the opposite direction at a speed greater than you're moving forward.
And, it's all the fault of the OP who thought he was wording his post cleverly enough to remove any ambiguities.
1. Those who say the plane can't move forward are, in a sense, correct. For if the plane was to move forward, we'd have a paradox. The conveyor *cannot match the speed* of the wheels on a forward moving plane, unless the wheels are skidding. People keep pointing to "if the plane is going 100mph, then the conveyor will be going 100mph in the opposite direction and the wheels will simply be spinning at 200mph." No, the OP said the conveyor matches the speed of the wheels, not the speed of the plane. 100mph doesn't equal 200mph, except in those trick proofs that require division by zero.
In other words, the speed of the wheels = the speed of the conveyor + the speed of the plane. Since conveyor speed = wheel speed, then logically, plane speed = 0. Anyone using that sentence as the basis of claiming the plane doesn't move is correct. You can't ignore this important fact. But, unfortunately, most of the people who have come to this realization don't quite realize the meaning of it. It's not a matter of the conveyor keeping the plane in place... it results from an impossible constraints on the problem.
2. If the conveyor matched the speed of the plane, rather than the speed of the wheels (which is impossible), then the plane would indeed take off, with the speed of the wheels always double the speed of the airplane as it accelerated down the runway. (assuming no slippage of the wheels)
--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
Now, for those who are saying that a spinning conveyor can keep a jet from moving forward (I've already established that the constraints given by the OP are impossible), try this at home:
Turn on a treadmill... set its speed to 10mph, but keep it level. Put on a pair of rollerblades. Skate across the room at 6 or 7 mph. Hop onto the treadmill while moving forward. Note that the treadmill does *NOT* stop you from moving forward, even though it's moving in the opposite direction at a speed greater than you're moving forward.
That seems to work, however there's really no way to settle the dispute as we both apparently have a different understanding of the situation. Damned if anyone can convince one or the other of the 'truth' whatever one may believe it to be.
I was gonna clear up the angular/forward momentum complication of the wheels, but I noticed the problem well into the thread, I figured editing it at that point would create more confusion than was already present. Not necessarily a bad thing though, now we have two problems to work with, even so we still can't agree on a conclusion even with the same interpretation.
If the plane has no wheels it cannot possibly depend on them to move
A plane with floaties will take off because it does not hold traction with the water, so the speed of the water underneath the plane; whatever it may be, could not be directly proportional to the speed of the plane.
mugs
Lifer
- Apr 29, 2003
- 48,920
- 46
- 91
Originally posted by: NanoStuff
The plane can move forward on solid ground because solid ground is NOT moving backwards. The world is rotating and it's taking everything with it along for the ride. If you're out in space, the world is one big conveyor belt. If you accelerate a plane on this huge conveyor belt, the plane moves forward on the conveyor belt, and if it's capable of moving fast enough it will be stationary to the observer in their little space ship. In order for the plane to appear moving forward to the observer, it would have to move twice as fast as the world's rotation, which would require a hell of a lot more energy. And yes I'm aware it's a terrible explanation, but I'm running short on analogies.
I don't even know what you were trying to trying to explain.
Let me repeat this fact... as long as the wheels of the plane are intact, there is no speed at which the conveyor belt can move that will prevent the plane from moving and taking off.
Look at the friction formula I posted before. It does not depend on the speed of the wheels. The only things holding the plane back are friction in the wheels and air resitance. Neither of those differ between when the plane is on the treadmill and when it is on solid ground.
Those who are saying wheels are not important or negligible to a plane's acceleration need to visit your local municipal airport. Every once in a blue moon, a pilot will forget to remove the blocks from in front of the tires. Needless to say, the plane goes nowhere even with the prop at high rev's.. and this is a piston engine prop plane which does get some airflow over its wings at a standstill.
Another thing you will notice at the municipal airport is airplanes taxiing down the runway and steering, making turns and such. This is only possible by force applied against the plane by wheels in a non-slippage condition. Prop planes do not vector thrust. So obviously there is a force applied against the plane in order for it to make a left turn to get out on the runway. The wheels are not slipping, they are moving, and there is friction, else the plane would not be able to turn.
Another thing you will notice at the municipal airport is airplanes taxiing down the runway and steering, making turns and such. This is only possible by force applied against the plane by wheels in a non-slippage condition. Prop planes do not vector thrust. So obviously there is a force applied against the plane in order for it to make a left turn to get out on the runway. The wheels are not slipping, they are moving, and there is friction, else the plane would not be able to turn.
In the given scenario, I KNOW it acts like a car. My challenge is to try and get you to see this.
TRENDING THREADS
-
Discussion Zen 5 Speculation (EPYC Turin and Strix Point/Granite Ridge - Ryzen 9000)- Started by DisEnchantment
- Replies: 25K
-
Discussion Intel Meteor, Arrow, Lunar & Panther Lakes + WCL Discussion Threads
- Started by Tigerick
- Replies: 23K
-
Discussion Intel current and future Lakes & Rapids thread- Started by TheF34RChannel
- Replies: 23K
-
-
Facebook
Twitter