[Mrvile]

Quote:

Originally Posted by bhd812 /img/forum/go_quote.gif my paper plane was much better cause... A: I thought of it all my own.. B: everyone loves paper planes, unless you had your eye poked out when you were a child.. C: I thought of it all my own.. you see I being Me am always rite by default..

Well who didn't do stupid things regarding a rope and rollerskates as a kid??

 

[bhd812]

Quote:

Originally Posted by Mrvile /img/forum/go_quote.gif Well who didn't do stupid things regarding a rope and rollerskates as a kid??

true..Used one of those wheel boards mechanics use to slide under the car once..it did not work out to well though..oh well that was not my idea. my idea was to use a Chicago City garbage can with wheels but no one wanted to clean one first.

 

[Davesrose]

Quote:

Originally Posted by Febs /img/forum/go_quote.gif To use the same analogy, Daverose, how would you answer this question: Say you are wearing rollerskates. You are on a treadmill. The treadmill rolls back at the same speed you are moving forward. You have a rope in your hands attached to a stationary object (like a rock) a few feet in front of the treadmill. Suddenly, the front of the treadmill is lowered so that you are facing downward at a 45 degree angle. Will you roll forward? Suppose the speed of the treadmill increases. Will you still roll forward?

See, you're introducing more forces...with vector paths too!!

Why does everyone's "simple" example wind up getting more complex

So what acceleration is the treadmill in relation to?

When you're holding a rope, you're no longer connected with the treadmill....your rollerskate's wheels are going the same way as the treadmill, and your body is now pulling in the opposite direction. When you tilt the treadmill, that's introducing another vector (and so ends our analogy here). Gravity is now having a slighter force going forward. You can't hold the rope anymore because you've just mucked up your forward velocity vector and tumbled forward. Why did you do that Febs!!!

 

[Febs]

Quote:

Originally Posted by Davesrose /img/forum/go_quote.gif See, you're introducing more forces...with vector paths too!! Why does everyone's "simple" example wind up getting more complex So what acceleration is the treadmill in relation to? When you're holding a rope, you're no longer connected with the treadmill....your rollerskate's wheels are going the same way as the treadmill, and your body is now pulling in the opposite direction. When you tilt the treadmill, that's introducing another vector (and so ends our analogy here). Gravity is now having a slighter force going forward. You can't hold the rope anymore because you've just mucked up your forward velocity vector and tumbled forward. Why did you do that Febs!!!

I'm glad you understand the analogy. Vectors aside, the effect of the force of gravity in this analogy is precisely the same as the force of the thrust applied on the airplane by the engine.

 

[jules650]

I'm going to say no, with the assumption that there is zero forward movement of the plane relative to the ground. (not the conveyer belt)

 

[Lazarus Short]

Quote:

Originally Posted by Born2bwire /img/forum/go_quote.gif Oh no. NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO NO. For the Love of God close this thread before the beast awakens!

What beast? Don't you be doing a Patrick82 on us!

Laz

 

[ServinginEcuador]

No. The plane has 0 ground speed, and 0 airspeed (apart from the relative wind). Just the engines running at full blast don't generate enough air movement to sustain a plane in the air. Otherwise full throttle tests of jets sitting on the ground with their brakes engaged would simply lift off the ground. Which, BTW, doesn't happen.

Whether or not the plane is on a conveyor or not is irrelevant. No air speed = no go.

Hypothetically, if you did this while turned into hurricane or gale force winds the plane would lift off the ground like magic. We used to do this at Ft. Huachuca when the winds were really high. Point the nose into the wind, power up, and the plane would lift off the ground.

 

[ServinginEcuador]

BTW - it's air speed, not ground speed that matters to a plane. You can actually be going backwards in a plane, yet have more than enough air speed to generate the lift needed to sustain flight. The only thing ground speed matters about is figuring out how quickly you'll arrive at your destination.

 

[Febs]

For those of you who think the plane would not take off, what do you think would happen if the plane landed on the conveyor belt? Would it immediately come to a dead stop the second its wheels touch the conveyor?

 

[ServinginEcuador]

Quote:

Originally Posted by Febs /img/forum/go_quote.gif For those of you who think the plane would not take off, what do you think would happen if the plane landed on the conveyor belt? Would it immediately come to a dead stop the second its wheels touch the conveyor?

Relative to the conveyor - the plane isn't moving at all.

If you hit a moving conveyor the plane's breaks won't work, and other than thrust reversers and air resistance the plane would have a seriously long stopping distance.

 

[colonelkernel8]

Essentially everyone is restating my second answer in different ways. (Look at post 3)

Yes, the plane will take off.

 

[uzziah]

here's my question: so even if there is no air moving over the wings themselves, because the plane is pushing so hard against the STATIONARY air mass, it pulls itself up?

 

[Febs]

No one said the plane wasn't moving.

 

[Davesrose]

Quote:

Originally Posted by Febs /img/forum/go_quote.gif For those of you who think the plane would not take off, what do you think would happen if the plane landed on the conveyor belt? Would it immediately come to a dead stop the second its wheels touch the conveyor?

I explained that several pages ago....INERTIA. The plane's velocity is independent of the conveyor because it has a forward inertia...in that analogy. When it lands on a catapult that is going backwards, its forward inertia will go to zero when enough resistant is applied. Lets say the plane hits the conveyor belt with a forward acceleration. Assuming it's greater then the accelleration to the belt, it would continue to go forward. If it's less, or if it hits the breaks, it would stop like it would on a normal runway (on the belt). But if the belt is still going in reverse, it will follow the belt (because gravity is pulling down). It will be stationary to the belt if it rolls to a stop, but going in reverse to the observer on the ground.

Now if the plane is starting dead stop on this magic conveyor belt, it is not having any forward inertia, because it is not moving forward (the belt is matching its forward acceleration). It's exactly like a runner. A jet's thrust goes forward. If you want to tilt the catapult, then that changes things a bit....but in this example, the only acceleration is coming from forward thrust.

 

[Davesrose]

Quote:

Originally Posted by uzziah /img/forum/go_quote.gif here's my question: so even if there is no air moving over the wings themselves, because the plane is pushing so hard against the STATIONARY air mass, it pulls itself up?

I can see that for a VSTOL aircraft (is it changes thrust from forward to up), but not this example. Assuming this is a super landing gear that withstand anything with a super conveyor belt that follows the exact forward acceleration of the plane, then drag over the wings is the only thing that can lift the plane up. I was just thinking that if you have a special engine and propellers that provide enough lift by dragging air over the wings, entirely by themselves....then maybe.

I can see why no experiment like this has ever been done. This is one hypothetical that's a lot of money on futility