Baby Robin on a conveyor belt?

Tried that one. It just falls out of the sky when it reaches the end of the conveyor belt……

speedo drive goes the centre of the hub.

Oh is the scene where they repair the speedo only in the directors cut?

shame tho, the flying has wrecked it.

That bloody Doc Emmett Brown; being all good at inventing stuff

So if the conveyor belt is moving at 25mph in this case, what speed would the plane be moving backward in your estimation with the engine turned off?

Next question. Are you agreed that the plane would have to apply some thrust to prevent it from going backwards in relation to a fixed point on the ground whilst on the conveyor belt (but not necessarily to actually move forwards in relation to a fixed point on the ground)?

So if the conveyor belt is moving at 25mph in this case, what speed would the plane be moving backward in your estimation with the engine turned off?

I dunno – lets say 24mph for arguments sake?

Are you agreed that the plane would have to apply some thrust to prevent it from going backwards in relation to a fixed point on the ground whilst on the conveyor belt

Yep.

For the aircraft the fly it needs to achieve (in this case) 25mph of forward airspeed over the wings. This could be achieved by tethering it to the ground at a fixed point in relation to the ground and blowing (either through wind or a big **** off turbine) air over the wings or on a still day moving the wings forward in relation to a fixed point on the ground at 25mph. Agreed?

If the aircraft is to apply EXACTLY THE SAME AMOUNT OF THRUST it required to JUST make this speed on a normal runway, how when impeded by the drag you acknowledged above will it reach the same 25mph?

well…it just needs a little more thrust to overcome the small amount of extra rolling resistance.

well…it just needs a little more thrust to overcome the small amount of extra rolling resistance.

And that is where the experiment was compromised. Obviously if the plane tanked it with huge amount of thrust it could easily take off, especially if you use an aircraft with such a low take off speed so the margins for error are so small. The true test is that the aircraft can take off without using any more thrust than the bare minimum required in normal conditions.

This is brilliant, when this thread is done can we ask it again?

If the aircraft is to apply EXACTLY THE SAME AMOUNT OF THRUST it required to JUST make this speed on a normal runway, how when impeded by the drag you acknowledged above will it reach the same 25mph?

Who said anything about “EXACTLY THE SAME AMOUNT OF THRUST”?

The question is simply “can it take off?”

It will need exactly the same thrust PLUS a tiny bit more to overcome the extra rolling resistance / wheelbearing drag (or it will require a slightly longer runway)

Who said anything about “EXACTLY THE SAME AMOUNT OF THRUST”?

The question is simply “can it take off?”

It will need exactly the same thrust PLUS a tiny bit more to overcome the extra rolling resistance / wheelbearing drag.

Sorry, but you entirely missed the point of the conundrum. Of course an aircraft can take off from a rolling runway if it uses more thrust – only a proper thicky could not work that out- think aircraft carier. It’s if it required extra thrust which is the crux of the issue.

Of course an aircraft can take off from a rolling runway if it uses more thrust

If you thought that was the actual question you must have thought the rest of the world was proper stupid 🙂

Sorry, but you entirely missed the point of the conundrum

No, you have. Thrust is nothing to do with the argument. People imagine that the plane simply will not move – hence comments about “why don’t we just replace runways with small conveyor belts”. They picture a plane gaining ‘speed’ (ie groundspeed) on the conveyor, then magically taking off. Of course this won’t happen, but the plane will just accelerate and take off as normal. People don’t get it because they’re idiots.

Now I know you’re just trolling, convert. 😆

Mythbusters state the myth as:

“An airplane cannot take off from a runway which is moving backwards (like a treadmill) at a speed equal to its normal ground speed during takeoff.”

In one of those earlier threads I stated it as:

“If you put a plane on a very powerful, very long, very wide treadmill and fired up the engines, then would the treadmill operator be able to prevent the plane taking off by running the treadmill in the opposite direction?”

http://www.airplaneonatreadmill.com/ states it as:

“A plane is standing on a large treadmill or conveyor belt. The plane moves in one direction, while the conveyor moves in the opposite direction. This conveyor has a control system that tracks the plane speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction). Can the plane take off?”

No mention of “EXACTLY THE SAME AMOUNT OF THRUST” in any of that.

“If you put a plane on a very powerful, very long, very wide treadmill and fired up the engines, then would the treadmill operator be able to prevent the plane taking off by running the treadmill in the opposite direction?”

Yes.

scuzz – Member
“If you put a plane on a very powerful, very long, very wide treadmill and fired up the engines, then would the treadmill operator be able to prevent the plane taking off by running the treadmill in the opposite direction?”

Yes.

Umm no.

“If you put a plane on a very powerful, very long, very wide treadmill and fired up the engines, then would the treadmill operator be able to prevent the plane taking off by running the treadmill in the opposite direction?”
Yes.

dear god

My theory: these threads are entirely populated by people who understand the question perfectly, but half of them are pretending they don’t to wind up the other half.

Wheels are attached to planes. If you park a plane by putting the brakes on, and then throttle the engine up, the plane will not move.

The rolling resistance of a wheel varies with the square of the wheels’ rotational velocity (consult any introductory dynamics text). As this velocity can be anything (the treadmill is very powerful), there will be a velocity with a rolling resistance which is greater than the thrust of the engines, just like the maximum friction from the tyre is greater than the thrust of the engines for the parked case.

Yes, everything will explode, and the rolling resistance coefficient is tiny (around 0.01), but since you asked…

Areoplanes take off because they have wings, right?

Just checking.

Oh Scuzz, please…..

I really don’t know what to say.

ha ha ha

Wheels are attached to planes. If you park a plane by putting the brakes on, and then throttle the engine up, the plane will not move.

The rolling resistance of a wheel varies with the square of the wheels’ rotational velocity (consult any introductory dynamics text). As this velocity can be anything (the treadmill is very powerful), there will be a velocity with a rolling resistance which is greater than the thrust of the engines, just like the maximum friction from the tyre is greater than the thrust of the engines for the parked case.

Yes, everything will explode, and the rolling resistance coefficient is tiny (around 0.01), but since you asked…

I don’t know whether to laugh or cry

dont cry al. the dynamic coefficient of friction will tear the skin right off your face. it’s in literally the most basic textbooks mate.

scuzz: yeah okay 🙄 I suspect that’s why the other versions simply say the treadmill speed matches that of the plane.

If we’re allowing the treadmill to be driven close to light speed without anything exploding/melting then it might generate enough force from rolling resistance to hold back a plane at maximum thrust – though the treadmill would probably be displacing enough air backwards at that point that it would actually generate lift and of course a sonic boom at ground level might well launch the plane into the air anyway 😀

😆

What if we put superglue on the treadmill track?

miketually – Member
My theory: these threads are entirely populated by people who understand the question perfectly, but half of them are pretending they don’t to wind up the other half.

*applauds* \o/

the dynamic coefficient of friction will tear the skin right off your face. it’s in literally the most basic textbooks mate.

Yes but what about the affect that wind resistance will have on those tear rolling down my face? will that be enough to stop the skin tearing action?

(either through wind or a big **** off turbine) air over the wings or on a still day moving the wings forward in relation to a fixed point on the ground at 25mph. Agreed?

If the aircraft is to apply EXACTLY THE SAME AMOUNT OF THRUST it required to JUST make this speed

Profanity, caps and bold text – engaged.

Move this thread to Rage Speed 4, Scotty.

Everyone is right. Yeh hey!

Normal conditions – Plane applies a smidgen more thrust and takes off. Whoop.

Magic superpowerful speed matching treadmill – shakes plane to pieces

Ignoring rules of reality but obeying certain rules of physics – friction in the wheels matches the max thrust of the plane and it doesn’t take off.

End of thread!

Wheels are attached to planes. If you park a plane by putting the brakes on, and then throttle the engine up, the plane will not move.

Yes but on a conveyor belt putting the brakes on will allow the thrust from the engine to act on the conveyor belt, driving it forwards and allowing air to move over the wings, so allowing the plane to take off.

If you want to take off on a conveyor belt put your wheel brakes on…didn’t we do this 240,000,000 posts ago?

Methinks you may have “direction of travel” or “troll” issues there gwaelod,

Methinks you may have “direction of travel” or “troll” issues there gwaelod

No mun…not if the conveyor belt is freewheeling and so isn’t being driven by some sort of force outside of the Plane/Conveyor/Atmosphere system

Why would the conveyor belt / treadmill be freewheeling??

It’s driven. By a motor. In the opposite direction to the plane.

Is it???

I think I have had a fundamental misunderstanding of this all the way through..I always assumed the conveyor belt was freewheeling

Hence the “trolling” post.

doh

I think I have had a fundamental misunderstanding of this all the way through..I always assumed the conveyor belt was freewheeling

🙄

Not another one 😀

Not that it matters, but it would also take off just fine from a freewheeling belt (without needing to use the brakes) for pretty much exactly the same reasons.