quote Originally posted by Cliff Pennock: Maybe this will clear things up a bit for those that still think the plane will not fly.

I wondered if Cliff would eventually have to comment. This is just TOO funny.

------------------
Ron

It's the Soldier, not the reporter
Who has given us the freedom of the press.
It's the Soldier, not the poet,
Who has given us the freedom of speech.
It's the Soldier, not the politicians
That ensures our right to Life, Liberty and the Pursuit of Happiness.
It's the Soldier who salutes the flag,
Who serves beneath the flag,
And whose coffin is draped by the flag.

LOL nvm... not even gettin involoved in this...

[This message has been edited by BLK 86 FSTBAK GT (edited 12-24-2007).]

quote Originally posted by Patrick: Nowhere, absolutely nowhere, does the scenario as stated proclaim that the forward motion is "countered" (or prevented or eliminated). Nowhere in the scenario has it been stated that the plane remains stationary. YOU are the one imagining and stating these things, and you are simply wrong, wrong, wrong...

quote A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction).

Isn't plane speed forward motion?

The talk of friction in the bearings is just clouding the issue.
If the aircraft has a V1 of 85 knots, the conveyer will only be running 85 knots (track the speed of the air craft). Combined, only 170 knots is not enough to cause large amounts of friction.

Next,
If the plane is not moving, the treadmill is not moving either. The plane has to move forward for the treadmill to move backwards. The plane stops moving forward and the treadmill stops moving backwards.

Repeat after me
IT WILL FLY
IT WILL FLY
IT WILL FLY


Gene

Banned from the local Mall!! Hahahah!!! Not really..but I DID upset the security guard I was Christmas shopping, and I passed a toy store Isaw one of these:

Cheap!! yep!! 45 euros!! 3 channel R/C.Bought it, I took it out into the Mall, and plugged in the battery (they are charged enough to work for 2-3 minutes). 2 minutes to assemble it.There is a moving pavement, about 100 yards long,outside the store which moves when somebody steps on it. I waited until it was empty, put the plane on it, and broke the beam which starts the pavement. It carried the plane away from me, but facing towards me. When it was about 25 yards away from me, I started the motors, opened the throttle..and it EASILY overcame the rearward motion of the moving pavement, moved forward VERY quickly ON ITS WHEELS, and TOOK OFF... Although the pavement is either moving at a constant speed, or stopped, it proved to ME it would fly.
Of course, my activities drew the attention of a 'Jobsworth' Security Guard, who insisted I stop 'playing' on a public walkway..I took the plane back to the shop, got my money back (15 days 'trial' and return ), and came home. I want to try to do it again, with a friend to film it. Couldn´t do it on my own..need 3 hands at least to fly and film Will have to try it when there is a different Guard on duty.
Should have charged the Toy Shop a commission..several people stopped to watch, and a couple asked where I got it. Bet they sell some extra models now

Nick

What was the difference in the speed of the walkway and the takeoff speed of the plane?

The walkway travels at about 3 ft a second. The plane took about 20 ft of GROUND DISTANCE, say 30ft of the moving walkway, to take off..say 6 seconds.I then put it on the floor beside the walkway, and it took about 3 seconds to take off, in about 12 ft. of ground distance. These are just guestimates..I didn´t have a tape measure with me The walkway seems to be made of a rubber type surface, on an interlocking belt. Of course, a full-sized plane would require a lot longer taxi to reach flying speed, but it proved to me that it will take off and fly.
Nick

quote Originally posted by rogergarrison: Ya bear and I flew F4s too. Im reading this hypothetical problem too literally I guess. Im seeing that they are saying that the treadmill CAN run fast enough to counter or match the forward thrust thereby keeping it stationary relative to the air. Let me try a little description of the way Im seeing it. we have a plane that can take off on a standard runway with no wind at 40mph. Now that plane could take off on its own with a 40mph headwind just setting there if not tied down. If its put on a carrier going say 30 mph forward, the plane only has to gain 10 mph to take off right. Now put the plane on the same carrier that is steaming backward at 40 mph as the plane is trying to take off going the other way (now with a 40mph tailwind).The plane with the same ground roll speed as before now is remaining stationary relative to the surrounding air...right..as its moving down the deck. It wont fly, but simply would fall off the end of the deck when it got there wouldnt it.

As for the carrier scenario, the plane would take off if it had enough ground roll distance. A tailwind *extends* your takeoff run, it doesn't necessarily double it or make it impossible to lift off. That's just like taking off from a (land) runway with a tailwind. You can do it, but it will take more distance. You just might run out of aircraft carrier before you get enough lift.

I looked at the performance charts for my airplane - 1976 Cessna Turbo 210. The Takeoff Distance chart in the POH says:

"Decrease distances 10% for each 10 knots headwind. For operation with tailwinds up to 10 knots, increase distances by 10% for each 2.5 knots." It doesn't say what happens after 10 kts.

It is interesting that a headwind and tailwind don't have the same effect. Anyway, a tailwind isn't helpful, but the only way it will keep you from lifting off is if you run out of runway.

[This message has been edited by fierobear (edited 12-24-2007).]

quote Originally posted by fierofetish: The walkway travels at about 3 ft a second. The plane took about 20 ft of GROUND DISTANCE, say 30ft of the moving walkway, to take off..say 6 seconds.I then put it on the floor beside the walkway, and it took about 3 seconds to take off, in about 12 ft. of ground distance. These are just guestimates..I didn´t have a tape measure with me The walkway seems to be made of a rubber type surface, on an interlocking belt. Of course, a full-sized plane would require a lot longer taxi to reach flying speed, but it proved to me that it will take off and fly. Nick

The plane is moving faster than the walkway, so lets increase the speed of the walkway until it equals the speed the plane took off.

quote Originally posted by Gokart Mozart: The plane is moving faster than the walkway, so lets increase the speed of the walkway until it equals the speed the plane took off.

But...you forgot to ask WHY it is moving faster than the walkway. It's because the propeller PULLED it through the air. The wheels don't care what is happening below them.

quote Originally posted by Gokart Mozart: Ground friction vs air thrust. Car will move, plane won't.

Nope. both are an example of a single entity working on two different mediums. One is ground vs rollers, the other is air vs conveyor belt.

But I agree with others: I give up.

quote Originally posted by fierobear: Uh, gokart...you've got that exactly opposite. Folks who think the plane won't move, let's try this one more time. The airplane's wheels DO NOT DRIVE the airplane. They spin freely. It is the PROPELLER that moves the airplane forward. That's why the call it a *propeller*, because it...drumroll please...propells. The airplanes wheels couldn't care less what is happening below them, as long as they can rotate freely. If you duct tape the wheels to the treadmill, the plane will do in the direction of the treadmill. If the engine is off (propeller not turning), the plane will probably move in the direction of the treadmill. Start the engine, rev to takeoff power, and the plane is *outta there*. As for the Fiero, Cliff said that the FRONT wheels are on a treadmill (rollers). If you start the Fiero engine, put it in gear and gun it, the car will *scream* off that treadmill. Same thing with a plane. Why? Because the treadmill is acting on wheels that DO NOT control the motion of the car. Same as the plane.

You contradicted yourself in the first sentence and last paragraph.

Once again, the treadmill the plane is on is opposite of the plane speed. It doesn't matter what propulsion is used. solid rockets on skids, 1000 balloons taped to the back, the issue is plane speed. What do forward motion and plane speed have in common?

Ok, I take back that I give up - this is just too much fun to discuss.

quote Originally posted by Gokart Mozart: Once again, the treadmill the plane is on is opposite of the plane speed.

Exactly. So here we have a Cessna with a forward speed of 80 knots. Which means the backward speed of the belt this plane is on is 80 knots. Equal but in opposite direction.

Tell me how the plane does NOT take off with a forward speed of 80 knots.

Forward speed is indicated 80 kts but actual is 0. The plane is not moving forward.

[This message has been edited by Gokart Mozart (edited 12-24-2007).]

quote Originally posted by Gokart Mozart: Forward speed is indicated 80 kts but actual is 0. The plane is not moving forward.

But...HOW DOES the treadmill exert the force on the plane? How does it counterract the plane's forward speed. How CAN it?

I think I see where the " the wont plane fly " folks are missing it.

Ground is earth = 0 mph
Conveyer speed = - 80mph
Plane speed = + 80mph
Wheel speed in relation to the conveyer is 160 mph.

Follow Me?

[This message has been edited by Wolfhound (edited 12-24-2007).]

quote Originally posted by Gokart Mozart: Forward speed is indicated 80 kts but actual is 0. The plane is not moving forward.

Wrong!! The airplane is travelling at 80 knots relative to the fixed ground, but is actually flying at 160 knots relative to the conveyor belt!!!
Nick
Bah!!! Wolfhound beat me to it
Nick

[This message has been edited by fierofetish (edited 12-24-2007).]

Step away from the plane!

Let's look at the wings in realtion to a fixed point. On the treadmill, going 80 kts, the plane is sitting still. If you had a headwind of 5 kts, does the plane speed indicator show 85? The plane is not going 80 kts against the atmosphere, all it has is the 5 kt headwind. It ain't movin.

Watch THIS:
http://video.google.com/vid...ype=search&plindex=3
Inertia explained!! ..and the flowerpot doesn´t even have WHEELS!!!
Nick

[This message has been edited by fierofetish (edited 12-24-2007).]

quote Originally posted by Gokart Mozart: Step away from the plane! Let's look at the wings in realtion to a fixed point. On the treadmill, going 80 kts, the plane is sitting still. If you had a headwind of 5 kts, does the plane speed indicator show 85? The plane is not going 80 kts against the atmosphere, all it has is the 5 kt headwind. It ain't movin.

- On a treadmill, with the engine running and prop pulling, the airplane does it's normal speed.

- The planes' *indicated* airspeed with a 5 knot headwind is still 80kts. It's *groundspeed* would be 75kts once airborne (at an indicated airspeed of 80kts).

quote Originally posted by Gokart Mozart: Forward speed in indicated 80 kts but actual is 0. The plane is not moving forward.

If the plane is not moving forward, then indicated speed is zero. Unless you think speed is measured at the wheels like in a car. Even so, what makes the conveyor belt move? The plane's forward motion. How does a plane move forward? Not by its wheels but by its propellor. So if and only if the plane has an actual forward motion using the same frame of reference as the conveyor belt, will the conveyor belt move. Meaning the plane will move forward no matter what, and the conveyor belt can not counteract this motion. And as soon as the plane has enough airspeed, it will take off. And for all the plane cares, the conveyor belt could move in the opposite direction 2x, 3x or 4x as fast as the planes forward motion. It would not matter.

If the plane is not moving forward, what makes the conveyer move rearward, since in the original problem, forward movement of the plane determines rearward movement speed of the belt.

Nick, We were thinking the samething at the same time weird.

I wish I could have video'd what happened with the plane and walkway...but having read some posts here, I don´t think MYTHBUSTERS WILL PROVE A G'D*MNED THING EITHER, EVEN IF IT HAS THE SAME RESULTS!! AAAAAGGHHHHH!! Oh...and it WILL!!!!)
Nick

[This message has been edited by fierofetish (edited 12-24-2007).]

Maybe if we understood why some don't think the plane will fly, we could approach it from that perspective. I honestly don't know how to explain it any other way than has already been presented here. I guess some folks just simply don't understand or they're are just trying to push our buttons.

------------------
Ron

It's the Soldier, not the reporter
Who has given us the freedom of the press.
It's the Soldier, not the poet,
Who has given us the freedom of speech.
It's the Soldier, not the politicians
That ensures our right to Life, Liberty and the Pursuit of Happiness.
It's the Soldier who salutes the flag,
Who serves beneath the flag,
And whose coffin is draped by the flag.

OK, I'll back up.
The pitot tube is how planes determine airspeed. It will show no speed, no matter how much thrust is used.

Here is a video of an experiment that helps illustrate how this works.

quote Originally posted by Gokart Mozart: Why won't it fly? There's no airflow over the wings.

OK, so why isn't there any airflow?

The only difference between this aircraft and one on a normal airstrip is the proverbial conveyor. I've tried to explain why the plane can fly, please explain why it can't.

------------------
Ron

It's the Soldier, not the reporter
Who has given us the freedom of the press.
It's the Soldier, not the poet,
Who has given us the freedom of speech.
It's the Soldier, not the politicians
That ensures our right to Life, Liberty and the Pursuit of Happiness.
It's the Soldier who salutes the flag,
Who serves beneath the flag,
And whose coffin is draped by the flag.

[This message has been edited by blackrams (edited 12-24-2007).]

Of course it cannot. That is the hook for these guys. The treadmill or conveyer without splitting hairs simply cannot effect the planes forward motion.

The conveyor's control system is stopping the airplane from moving forward, like chocks. Full throttle, the plane still can't takeoff. Look at the opposite effect: a catapult. The plane needs 1/4 the distance to takeoff.

Here is an analogy for you. Because this is exactly what this argument sounds like.

Forget the fact that a rooster can't lay an egg! which side of the roof will it fall down?

quote Originally posted by Gokart Mozart: The conveyor's control system is stopping the airplane from moving forward, like chocks. Full throttle, the plane still can't takeoff. Look at the opposite effect: a catapult. The plane needs 1/4 the distance to takeoff.

No. It isn't.

We all agree the plane has to move to take off. But you're saying the movement of the conveyor counteracts the propulsion of the plane, therefore keeping the plane stationary. That is wrong.

We know the plane's engine pushes against the air - that propels the plane, right?

When the conveyor starts going backwards - how does it stop the plane? The only point of contact between the plane and the conveyor is the landing gear. The wheels are free to turn - so the conveyor cannot affect the speed of the plane.

Nowhere in the original question does it say the plane is stationary.
Nowhere in the original question does it say the conveyor counteracts the plane's speed.

You're saying if the plane is being propelled forward at 100 mph, and the conveyor is going backwards at 100 mph, the plane itself is stationary.

Well consider a real aircraft fllying over the ground at 100 mph, then. The ground isn't moving. Does the plane come to a complete stop the instant the wheels touch the ground? Or do the wheels just spin? Why isn't the stationary ground stopping the movement of the plane?

quote Originally posted by Gokart Mozart: The conveyor's control system is stopping the airplane from moving forward, like chocks. Full throttle, the plane still can't takeoff. Look at the opposite effect: a catapult. The plane needs 1/4 the distance to takeoff.

The conveyor is matching the wheel speed, not preventing the plane from moving forward. A catapult is used to get the aircraft up to sufficient airspeed before it runs out of carrier. I still don't see (from your perspective) what's stopping the aircraft from moving forward. It's got thrust from the propellor what's stopping it?

------------------
Ron

It's the Soldier, not the reporter
Who has given us the freedom of the press.
It's the Soldier, not the poet,
Who has given us the freedom of speech.
It's the Soldier, not the politicians
That ensures our right to Life, Liberty and the Pursuit of Happiness.
It's the Soldier who salutes the flag,
Who serves beneath the flag,
And whose coffin is draped by the flag.

quote Originally posted by blackrams: The conveyor is matching the wheel speed, not preventing the plane from moving forward. A catapult is used to get the aircraft up to sufficient airspeed before it runs out of carrier. I still don't see (from your perspective) what's stopping the aircraft from moving forward. It's got thrust from the propellor what's stopping it?

Actually, wheel speed isn't mentioned. Here's the original question:

"A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction)."


Notice there is no mention of the plane being stationary.
No mention of the conveyor having any impact on anything - it just says the conveyor's speed is equal and opposite to the plane's speed.

Any effect, if there is any, of the conveyor's speed is the conclusion of the reader. It is not stated in the question.

quote Originally posted by Formula88: Actually, wheel speed isn't mentioned. Here's the original question: "A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction)." Notice there is no mention of the plane being stationary. No mention of the conveyor having any impact on anything - it just says the conveyor's speed is equal and opposite to the plane's speed. Any effect, if there is any, of the conveyor's speed is the conclusion of the reader. It is not stated in the question.

You are correct which even further enhances the point.

From a physics perspective, the guys who think the conveyor can stop the airplane are confusing speed with force. Force creates speed, not the other way around. They're also failing to understand that since an airplane's wheels are free-spinning, they can spin independently of the plane's forward motion. It takes a lot less force to spin the wheels than it does to push the airplane. Therefore, the treadmill (which is spinning the wheels) is exerting a lot less force on the airplane than the airplane's engine.

Repeat after me: THE NET FORCE IS IN THE FORWARD DIRECTION

If you still cannot understand how this works, I suggest you borrow or purchase a basic physics textbook. Either that, or do a Google search for things like "Newton's Second Law of Motion" and "vector math". Educate yourself!