Plane on conveyor, would it take off ? — HELP!!

I’ve never got the discussion, it’s obvious it wouldn’t take off

I agree. Quite pointless, unless it’s a Harrier :diablo:

Ryan

I’ve never got the discussion, it’s obvious it wouldn’t take off

To be fair, I wasn’t arguing that it was definate proof, just that…..that’s what they did and that’s what happened?

The fact that the “conveyor” of faberic had no (none, zip, zero, nada) effect on the takeoff roll dispite any concern that the conveyor’s speed may have been a bit too slow, fast or whatever makes your counterpoint inconsequential.

The thought/point that the material my have not matched the exact initial speed of the aircraft and THAT is why the aircraft tookoff is comical. Rather than pick apart visual clues perhaps some folks should spend more time learning basic physics.

I think on the next mythbusters they should prove that the only reason that the space shuttle takes off is because the launch pad matches the rotational velocity of the Earth EXACTLY. We all know if the launch pad didn’t rotate with the Earth the space shuttle would sit helplessly on the pad with engines blasting. Oh the humanity!!! Earth = largest moving conveyor ever!!

Really sorry to bring this back up! But there is a good reason for it (close it back down if it is inappropriate mods).

There was just an episode of Mythbusters on, on Discovery (5-6pm, 29th Aug 08), where they allowed a single seater, light aircraft to take off ON a large piece of material acting as a moving runway, that was pulled in the opposite direction of the plane as it took off – and matched the speed. The plane took off easily. Their conclusion that a plane cannot take off if on a moving runway……busted.

Sy 🙂

There was one problem with the Mythbusters episode…they gave no evidence of matching initial speed with the moving material.

The original puzzle was an aircraft at take off thrust releases its brakes as it starts to move the conveyer somehow matches that speed to counteract the impetous of the thrust through the airframe rotating the wheels.

This isn’t what the Mythbusters did.

Thanks GA. I knew it was pushing it, but a little lightbulb apeared over my head when I watched it, as I knew it may provide something worthwile to this 🙂

Moderator Message

We’ll allow it this time, as the new posting is relevant and answers the question originally posed in the thread.

However, this does not stand as a general precedent for others to resurrect aged threads at will.

GA

Really sorry to bring this back up! But there is a good reason for it (close it back down if it is inappropriate mods).

There was just an episode of Mythbusters on, on Discovery (5-6pm, 29th Aug 08), where they allowed a single seater, light aircraft to take off ON a large piece of material acting as a moving runway, that was pulled in the opposite direction of the plane as it took off – and matched the speed. The plane took off easily. Their conclusion that a plane cannot take off if on a moving runway……busted.

Sy 🙂

Ooooh noes!!!

Another of these 😉

Did this on Hexus forums and we got to about 20 pages before everyone was arguing and it got locked.

on no… what have i started…

Great posts though guys… its taking some reading but theres a general feel…

RickT

Ooooh noes!!!

Another of these 😉

Did this on Hexus forums and we got to about 20 pages before everyone was arguing and it got locked.

But, someone tried a test and videoed it, put a skateboard with a fan on it and a big sheet of paper…and moved the paper as a conveyor belt. And the skateboard still moved…dunno what that proves though, I’ll have a look for it later 🙂

Here is my 2 cents. I’m no scientist or engineer, but lets see if I can understand what you are all on about:

Picture a running manchine at a gym. You ‘run’ one way, as the belt that you are running on goes the other way. To stay on the machine, you have to match, do you not, the speed of the belt.

To run off the end of the machine, i.e. go forward, you have ‘run’ faster than the belt.

So, to keep the aircraft stationary the thrust provided by the engines would have to be such as to keep the aircraft on the belt, without moving forward. To move forward, and get the aircraft to a speed at which it can rotate, and take off, the thrust would have to be double what the engines would provide on a normal take off on a normal runway.

As long as the thrust is such that it allows the aircraft to ‘beat’ the speed of the belt, and push the aircraft forward, it would eventually, be moving fast enough to fly.

hhmmm. but then again…

that’s assuming the idea of the running machine i.e. forward motion provided by the legs.

however, with an aircraft, the forward motion isn’t created by an engine turning wheels. the engines on an aircraft arent linked to the wheels. so the speed of the rotation of the wheels is surely, until they shred, irrelevant.

the engines are stuck on wings, which take in air, and push the aircraft forward by compressing and speeding up the velocity of the air and then throwing it out as thrust.

put jet engines on your arms or shoulders, and wheels on your feet stand on the running machine, turn the treadmill on, don’t move your legs, you will go forward. ok, so you won’t fly because you’re not an aircraft, but you’ll move forward, faster and faster.

a plane on the conveyor belt, would take off. the aircraft would move forward, there would be airflow over the wings, and, at the right speed, it will take off.

now either that is a load of rubbish and i’ve missed the whole point of the question, or thats just repeating what others have said.

EDIT: yes, Ive contradicted myself, but did so to try and explain it, and showed my ‘thought processes’ if you like. I also had help from an aero engineer. whether it’s correct or not, I don’t know.

As you say, it must have made life interesting for those on the flight-deck trying to do their “day jobs” and stay on their feet in the face of a constant 40Kt gale 😮

Heh! Heh! Much more fun at night and in the wet stuff, freezing or otherwise and trying to keep clear of prop’s, intakes and exhausts.

With that latter I recall an incident on Vic’ where I was burned by the exhaust of port engine of a Sea Vixen whilst, as ‘plane captain’, on walk around removing blanks, U/C locks etc (normal practice was to duck under port tail boom and then past the pen-nib fairing so it was at very close range) when the aircraft on which it was my job to signal pilot to start port engine but an orficer intervened – not his place to do so.

I proceded removing starboard U/C lock and climbed up onto starboard wing to remove wing jury strut. This was attached to the outer wing through a lug screwed into the wing with the strut end having a mating fork end on a screw thread with a locking collar. I had my left thumb pressing against the pip-pin, connecting fork to lug, sensing when the pressure came off to ease the pin as I turned the locking collar.

Things were well under control when the same orficer, unnoticed by myself, had climbed up on the mainplane via the starboard flap shroud, removed the large hex Alan key (used for drop tank caps) and proceeded to whack the split pin with it. Of course it met my thumb first. So now I had a sore face and a throbbing thumb.

My Sea Vixen was at the front of Fly 2, immediately aft of the starboard JBD (jet blast deflector) and I had been aware of the Bucc’ being ranged on the starboard cat’ and had judged I would be finished and back on the deck before it went to full power for launch.

But with this orficer’s intervention, unnecessary, I was still up there as the Bucc’ went to full power. The jet efflux was directed up the JBD directly onto the Vixen’s folded starboard wing leading edge, the aircraft being ranged in Fly 2 en-echelon, which neatly deflected it straight at myself.

There followed an interesting couple of minutes where, as I held on to the still in place jury strut, the hot avcat fumes further agravated my sore face, my goggles stretched away on their elastic straps and my tool pouch webbing belt slowly slipped through the buckle.

Fortunately the jury strut saved me from further injury.

There was a sequel to this when the following day during the early morning details this same orficer came unstuck when he tried to intervene again. But that, as the say, is another story.

Hope you don’t mind me sharing that with you.

And the speeds you quoted are conservative on both wind speed and carrier speed.

Not being sure of the detail I was inclined to be cautious – total over the deck windspeed of up to 40Kts – 45Kts closer to the truth perhaps? As you say, it must have made life interesting for those on the flight-deck trying to do their “day jobs” and stay on their feet in the face of a constant 40Kt gale 😮

Quote (CSheppardholedi):”I would think that the whole argument does boil down to whether the wheels can stand twice takeoff speed. The engines will act normally, less the drag of the axle friction being doubled, the wings will produce just as much lift. If it can reach rotation before the tires fail, it will lift off. IMHO” Unquote

No, take off is purely related to airspeed over the wings, ground speed relative to the moving conveyor belt is totally irrelevant. If the aircraft remains stationary relative to the surrounding ground (i.e not the moving belt surface), then, unless ambient wind speed equals take off speed, the ‘plane will NOT take off.

Paul F

The lift for an aircraft is provided by the flow of air around the wing as it moves forward down the runway. If it is standing still, albeit with it’s wheels spinning on a conveyer type runway, there is no forward movement, hence no lift, hence no take off..

1L.

My opinion too. Like a hamster on a treadmill. I knew there were a coiple of reasons why planes came with wheels an this is probably one of them.:D

I would think that the whole argument does boil down to whether the wheels can stand twice takeoff speed. The engines will act normally, less the drag of the axle friction being doubled, the wings will produce just as much lift. If it can reach rotation before the tires fail, it will lift off. IMHO:D

And an aircraft carrier has the ability to be turned to face directly into the prevailing wind, … assuming wind speed is 15kts, and the carrier can also steam at 15kts, this gives a cumulative windspeed/airspeed down the flight deck of 30kts – a not insignificant benefit on take off. It’s 30kts less you need to gain/achieve when accelerating your ‘plane from a standing start.

Paul F

Thanks for that Paul 🙂 I didn’t include all that because I thought it was stating the obvious. But then I guess I was wrong and its isn’t obvious to many who haven’t been there and done it and know what it is like bracing oneself against the wind over the deck during launch, and during recovery for that matter.

In my time on Ark we used to stay put in Phantoms down in Fly 4 (far aft port side) whilst recoveries were under way once having started engine test runs.

Quite an interesting view of every deck arrival. I was thinking of taking a camera with me on one such occasion but by then somebody had decided that the practice of sitting in Phantoms in Fly 4 with aircraft screaming in across ones nose was a tad dangerous.:D

And the speeds you quoted are conservative on both wind speed and carrier speed.

…. besides by design a carrier shoots aircraft off at near sea level so altitude can be another limiting factor for many airfield take offs.

And an aircraft carrier has the ability to be turned to face directly into the prevailing wind, whatever direction it is blowing from, unlike a fixed runway, so maximum “into wind” benefit can be gained at all times. In theory land-based runways are usually alligned into the “average” or “most common” prevailing wind, but once built any deviation from this wind direction must result in an element of crosswind, and thus less of a useful headwind component, unless the wind swings through a full 180 degrees whereupon you can simply use the runway from the other direction.

Also, a ‘carrier can steam into the wind, thus in effect increasing any “natural” windspeed over it’s deck, and thus over the wing of any aircraft sitting on the deck.

So, assuming wind speed is 15kts, and the carrier can also steam at 15kts, this gives a cumulative windspeed/airspeed down the flight deck of 30kts – a not insignificant benefit on take off. It’s 30kts less you need to gain/achieve when accelerating your ‘plane from a standing start.

Paul F

sorry, If you apply the brakes on an aircraft and run the engines at 100% most aircraft won’t move. I do it all the time, you can see aircraft do it when they do a “rated takeoff”

The operative word there being ‘most’. The aircraft you do it on all the time are probably quite different from those of my experience.

…the F4 Phantom proved the theory that with enough thrust you could fly a housebrick. But he is correct in the general assumption that with no wing an aircraft will not fly.

And it was one of these I have in mind, an F4K to be specific. One did not even have to engage afterburner (re-heat) on one of these to overcome brakes and chocks. This is the very reason why we when doing full power-runs and re-heat runs were required to used the arrestor hook hold back whilst on Ark and alameda (not sure of spelling) chocks whilst ashore. These latter consisted of a pair web re-inforced steel angle plates bolted into concrete with the aircraft being pulled forward so that main wheel tyres were firmly abutting the steel angle. Then another pair of steel re-inforced angles would be bolted down aft of the wheels.

To be sure most aircraft did a power run up against brakes at runway threshold prior to take off and I watched many a Vixen, Hunter, Buc’, Scimitar or Phantom do this.

As to the original question I agree with those that state that without airflow over an aircraft mainplane then no lift will be generated for take off.

Driving the aircraft forward at twice the speed of the conveyer going in the opposite will achieve little other than making the wheels rotate at twice the rate normal for take off and thus likely reach their rotation speed limit sooner and disintigrate.

This ground speed limiting factor is one of the reasons behind the fact that aircraft are capabable of being shot off of carrier cat’s at higher weights than mostly possible from an airfield runway. Particularly at high ambient temperatures, besides by design a carrier shoots aircraft off at near sea level so altitude can be another limiting factor for many airfield take offs.

This latter is a little broadcast fact the the air force would rather politicians not know about.:diablo:

Once again I have been logged out before completing a post and thus the New Posts facility is once again meaningless.:mad:

Don’t forget, it’s the “airspeed” (i.e. speed of the wing relative to the air it is passing through) of a plane on it’s takeoff run that generates lift, not it’s ground speed (speed relative to a fixed point on the ground).

So, as has been said earlier, a plane is not propelled by it’s wheels, but by the thrust of it’s engines, thus if the wing remains stationary then airsped is zero, so no lift is generated, and no take off can happen.

Conversely of course, if the plane is stationary (i.e. parked), but the wind speed is sufficient (say 200mph) and blowing stright on the nose, then even a fully loaded A380 could theoretically take off vertically, as despite experincing zero ground speed, the wings would be experiencing a 200mph airspeed, and thus generating sufficient lift (subject to suitable flap/slat settings) to lift the beast off the ground. Now theres a worrying thought!

If in any doubt, try it out on MS Flight sim, using a small Cessna 172 – set ground level wind speed to a steady 80 -90kts, and you should be able to take off and land near-vertically simply by setting the flaps and working the control column – though if you haven’t got the plane pointed dead into wind then it’ll probably be turned over pdq!

Ask pilots of light aircraft with good STOL characteristics, such as Austers – a strong gust of wind (say 15 – 20mph) immediately after touch down and can easily get the aircraft airborne again as the wing starts to generate lift again as a result of the increased airspeed. It’s unlikely to happen to quite the same extent on an airliner, because spoilers tend to be activated very quickly so as to ensure lift is destroyed, as much as to slow the aircraft down, but from experience I know that a gusty 40Kt wind down the runway at Guernsey can lead to an interesting final approach/landing/roll out for something like a BAe146 😎 , as the wing sees sudden increases and decreases in apparent airspeed, even though ground speed is fairly constant.

Paul F

The lift for an aircraft is provided by the flow of air around the wing as it moves forward down the runway. If it is standing still, albeit with it’s wheels spinning on a conveyer type runway, there is no forward movement, hence no lift, hence no take off..

1L.

Exactly.. it’s common sense!!