See a lot of people reading this seem to get the idea that there's going to be "exponential acceleration" or "infinite speed" or silly things like that. Remember, all the question said is that the conveyor belt moves backwards at the same speed the plane moves forward. Nothing about the landing gear or how fast they're spinning. So if the plane is moving forward at 150 mph, the belt is only going backwards at 150 mph. So the plane takes off and the wheels are only spinning at a leisurely 300 mph. (Which, who knows if they can handle it, but landing gear that can't handle twice the speed of takeoff are pretty poorly designed if you ask me)

Oh... dammit. I picked no before I thought about it thouroughly.

Well.... Covering all bases.

Who knows, how speed is measured in this particular case?

Well, since I posited the question in the original post, I'll define how we're measuring speed.

The airplane is measuring airspeed, like usual. We'll assume there's no wind and thus airspeed = groundspeed. The airplane's computer is sending the airspeed information to the conveyor belt, which then moves backwards at that same speed. The important point is that both objects are measuring speed relative to the ground, not to each other.

In this case, chassis will put up with twice the usual speed, and plane will take off. Maybe, with some difficulty, due to increased drag on chassis, but not much.

How would the plane take off?

If the net speed is 0 there is no air moving over and under the wing. Wings deflect moving air so it moves at an angle causing pressure changes which creates lift.

Without speed there is no air moving over the wing so the plane cannot take off.

Why is the net speed zero? Talk me through your reasoning.

Net speed would be zero, if plane would gather speed by rotating it`s wheels, like a car.

It, however, gathers it with the help of jet engines, which have nothing to do with chassis, and chassis will be just dragged against rotating belt.

Because the plane is not actually moving, the wheels are just spinning.

Why is the plane not actually moving though? Remember, if the plane isn't moving then neither is the conveyor belt, so why would the wheels be spinning?

Yeah the plane would be moving at a normal rate of speed minus the amount of drag created by the wheels.

it's like a person on a treadmill. The person is running forward at whatever speed and the treadmill is moving backwards. Is the person moving forwards? No. They're staying in the same place.

The wheels do not control the forward motion of the plane. The thrust of the engines is what pushes the plane forward.

As I said in the thread that I linked to, you could substitute hover-pads for the landing gear wheels and the plane would still be able to take off.

Ok, now imagine this same scenario with a person wearing some wile e coyote style rocket skates. The thrust created by the rockets would make them literally move foreward. The wheels don't mean anything.

You're not listening to what the question is asking. the treadmill goes backwards at the same speed the plane goes forwards. Your person on a treadmill is not moving forwards, so why is the treadmill moving backwards.

The engine moves the air.

The vector of the backward spinning wheels is 90 degrees from the vector of the plane's flight. It will have no "drag" effect on the plane.

I mean friction drag from rolling the wheels over the belt. Twice the speed would stress the chassis, and probably jerk it here and there more then a fair bit.

On a side note, I have troubles imaging conveyor, which could keep up with plane`s speed at takeoff without some hardcore iron.

is it indoors? it couldnt take of if the roof is right there.

no it wouldn't because engineers are not stupid people

the size and length would be much, much more impressive than the speed. Either the belt would be under an astronomical amount of tension or you'd have serious problems with the belt stretching just by the force of the conveyor. That's without a plane sitting on it.

The airplane will likely have to use slightly more thrust than usual to attain takeoff speeds.

That`s what I meant about belt. Noone requires it to be whole, though, as far as I see. It can consist of short segments.

As for engineers not being stupid, there is a limit to everything. Even for military stuff, which is hardy as hell, and redundant at least twice, going twice as fast as normal operational mode will put a stress. Not to mention, that moving belt introduces a significant additional force on the chassis.

Why are you talking about the practicality of such a conveyor belt? It's totally irrelevant.

Sorry. Tangents are quite... Often, at such questions.

Exceptionally, since now everyone is informed, that consensus is towards plane taking off, with good reasons for it.

uh... no it doesn't? That's sorta why landing gear exists you know.

Landing gear is designed to take a hellish beating. You can touch down, hard, at a 747's cruising speed and it won't destroy the landing gear. There is absolutely no way you can reach that level of stress on the gear prior to takeoff.

A 747, by the way, is designed to take off at a measly 250 kph. I would be greatly concerned if aircraft companies could only barely manage to build a wheel that could spin that fast.

In addition to that, the landing gear is designed shear off before it "introduces significant additional force on the chassis", so really no part of your assertation makes any sense at all.

500 kph is quite a significant speed, no?

You might ask Formula fanats. They will explain, that every extra kph is taking a toll on wheels.

250 kph could be tolerated by usual car. 500 kph - not really.

But I meant different force - conveyor itself. No matter, how one will tune it up, belt will have random backwards-forwards little accelerations based on how stretched belt is, what part of belt it is, shape of rollers, and such.

Now, consider additional jerking, friction and vibration those accelerations will introduce? Might I remind, that runway for same 747 is a very smooth concrete stretch about two miles long?

I think, that about a minute or so of HARD jerking of chassis from side to side might be not so good for them, y`kbow.


_______________________________________


Of course, it`s another tangent, since original question had nothing to do with technical details. ^_^

so if planes do take off from conveyor belts, why don't airports use those instead of long airstrips?

I'm not sure what a Formula fanat is, but I don't think you quite comprehend exactly what a landing gear is.

They are not connected to an engine. They are not connected to a transmission or a gearbox or what-have-you. It's a freely spinning wheel. It is not a car tire - besides being much thicker, they're inflated with nitrogen gas.

No you didn't, you have no idea how planes work at all and now you're backpedaling.

From side to side? Do you know what a conveyor belt even is?

Regardless, that statement is blithely ignorant of the fact that airplanes are indeed designed to handle lateral shearing stresses on the landing gear. They are actually designed to spin out without killing the passengers, which should tell you a lot about how strong those oversized Formula 1 racecar tires are. :downs:

because the conveyor belt would have to be just as long as the airstrip and you couldn't land on it

Hahah, landfish, you crazy!

I support this idea, all planes should take off from conveyor belts so that they will be like helicopters!!!!!!!

Sigh.

Alright, that is IT. I`m sick of people putting words in my mouth.

1) Operating wheel at twice the speed it was designed for, WILL put strain on it. No buts about it. It might take it once, might take it twice. Or might not. A game of chance.
On a side note, there is NO such thing as free spinning. Wheels are spinning in roller-bearings, usually - which have own limits of tolerable speed and vibration.

2) I don`t know, WHAT did anyone assumed (I have no command over fantasies.), but I meant, that conveyer, simply by moving, will add an extra helping of shaking and friction to the chassis. Shaking from side to side (Or, back and forth, if that`s more understandable.) might be quite nasty on the chassis themselves, not just wheels.
And that omitting, that everyone on the plane will get bumpy ride.

except, as I already said, the wheel is in fact designed to spin at that speed.

english, movie reference I cannot make here because it is bannable, do you speak it?

clearly not your own at least


giant nitrogen-injected flying Formula 1 tires have shocks too FYI

Brilliant observation, Captain Obvious.

Now, for the golden medal, what is more prone to be disrupted from vibration - several inches of spring and cylinder of gas, or chassis rod, which is easily over a meter long?

As far as I know, noone disproved the levers, yet.

several inches? a meter?

We are still talking about planes here, right?

Inches - that`s about Formula shocks.

Meter - that`s front staunchion on the civilian passenger plane.

Right. Okay, anyway. According to internet,

"On September 21, 2005, JetBlue Airways Flight 292 successfully landed with its nose gear turned 90 degrees sideways, resulting in a shower of sparks and flame after touchdown. Passengers aboard the aircraft witnessed the landing via satellite television receivers installed in their seatbacks. This type of incident is very uncommon as the nose oleo struts are designed with centering cams to hold the nosewheels straight until the weight of the aircraft compresses it."

Gearless landings are also the most common type of 'accident' (where the pilot simply forgets to lower them) but they are very rarely fatal. Generally speaking the plane is still serviceable but usually needs new engines because it sorta slides to a stop on them.

Just an FYI in case you still think airplanes are built like cars (hint: they aren't)

Uh. I`m sorry, but are you pretending to be silly on a reason?

I don`t argue, that plane will just fall apart, if chassis will give away.

I`m saying, that if one of the struts will collapse, or lose enough of wheels to be wrenched sideways, then there`s no talking about take-off - only about crash-landing.

the internet makes you stupid

No it won't. No, it goddamn won't. Listen to me. LISTEN TO ME.

Airplanes are all designed to slide to a stop without landing gear. It damages the plane severely but they are all capable of doing this. Every single one, from the A380 to the F-22. This does not compromise the chassis. If there is enough force on the landing gear to compromise the chassis, the landing gear breaks away.

You do not understand how airplanes work, you do not understand how they are designed, you do not understand anything and the fact that you continue to refer to the construction of a racecar when you're talking about planes is evidence of how ignorant you are. Please stop posting about this, you very obviously don't have a clue.

That airplane that landed with the front gear turned 90 degrees sideways? The 'struts' didn't collapse. They're really really strong.

You can't even read what I'm posting. I try not to say this to new people because it's asinine and elitist, but seriously get out. Get out and go back to wherever you came from.

...Alright, one MORE time.

I`m NOT claiming, that plane will be destroyed, if chassis gives away. Repeating for third time - especially for those in tank.

I am saying, that IF it does (for which there is a risk on conveyer, for reasons I stated above), then taking off with lame strut won`t be possible.

If THIS will not get through, I don`t know, what will... Jackhammer, maybe?