iamcal.com Since May 2000

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• Hello!

You know stuff about aeroplanes.

On top gear, they've wound a jumbo jet up to full power, and driven cars behind it, and they got blown down the runway.

The question I have is - how the hell did they stop the plane from moving forward at full throttle?

brakes

sounds silly, but true
even a much higher power-to-weight ratio biplane can hold itself still at full throttle on the brakes. delightfully, the old-style undercarriage planes (ie, non-tricycle, little tailwheel) can be held stationary in place dead horizontal, with the tail wheel in the air and the fuselage blown sideways and the wheels locked.

memory: dad driving perpendicularly off the grass apron onto the grass runway, and, on reaching the halfway-point across the runway, opening the throttle over slight brakes, part elevators, and full right rudder. plane popped from facing away from us and tilted back down towards us, to square on facing to our right and horizontal in one smooth curve, before insanely teetering on only two front wheels for a long second, then tearing off down the runway.

And most people's perception is that the reverse thrust that passenger jets do is most of the decceleration. This is shite. It does next to fuck all (probably about 10-15% absolute max) and they only do it to try and increase the life on the brakes that the jets use. Brakes are about £1K per disk, and at least one disk per wheel. You do the maths...

The brakes (carbon - that's where F1 got the idea from) are amazingly efficient when combined with the right tyre, and do most of the stopping by some margin.

Yeah, we've discussed braking before.
But there was a danger of it tearing up bits of the runway if it ran for more than 20 seconds - how does it have so much traction?

It doesn't have traction, it has thrust. It is much harder to overcome initial friction than to increase friction until it stops something - momentum is a very powerful element. It would rip up the runway because it would just pull the locked wheels along and the (very soft) tyres would drag up the tarmac. Don't forget, a car is trying to turn the wheels, a plane isn't - it's trying to push the aircraft forward.

The tyres are really soft as well, for reference. They are very sticky and grippy compounds and last relatively miniscule mileage compared to even an F1 tyre. They probably only do 160 landings (and then a further 160 after re-treading) ever in their life, although new compounds may increase that.

$knowledge ++;

Thanks, boys.

Can you tell me how the guy from F1 is avoiding paying all his household bills by using tyre warmers? I read it but can't quite get my head into the right font to take advantage

What?

Just answer the Doc, Brock.

Lord - look at this: answers.google.com/answers/...

A plane is standing on a runway that can move (like a giant conveyor
belt). This conveyor has a control system that tracks the plane's
speed and tunes the speed of the conveyor to be exactly the same (but
in the opposite direction).

Will the plane be able to take off?

The debate this question has caused amazes me.

/my answer
Of course it would. It's not a car, it moves via jet engines, not it's wheels.
But so many people seem unable to grasp this that I'm beginning to think that I must be wrong.

/my answer
Of course it wouldn't.
The flames pouring out of the conveyor belt from its belt+insulated wheels overheating at 250mph under a couple of hundred tons of weight, not to mention the heat from the plane's wheels+tyres now doing TWICE the speed of the plane, would ignite the fuel in the wings and the jet would briefly but brightly lift off the runway on the billowing ball of incandescent explosion.

Oh, wait. I guess that technically IS a take-off.

I feel such a fool.

Well I dont know alot about these things but this is how it sits in my head:

The plane may be moving via jets and not wheels but it needs the air resistance (or whatever it is) against the wings to lift off. Which wont be there as the plane wouldnt actually be moving. Unless its a jump jet or something.

true re air resistance etc.
BUT, the wheels for a plane only offer resistance, not drive.
that is, they are essentially lubrication between the plane and the ground.

if they were wholly frictionless, the conveyor belt could do a squillion miles an hour and the plane would just sit there- not taking off, not doin nuttin. example: hovercraft. if the plane then opened the throttles, it would start to move forwards.
add friction (and even in this context of a hypothetical "active" conveyor belt impedance-matching the plane speed): it won't move forwards as fast as it would otherwise have done.

so the enginespeed will be higher for takeoff speed than it would be in a frictionless/etc. environment.

and then of course, you get that great explosion -- whee!!!

not many people know that wheel-arch fires on takeoff are not that uncommon in commercial "heavy aviation" jets -- braking the spinning wheels to a stop after takeoff heats them via the disks quite dramatically. if you've ever wondered why military jets suck their little wheels up straight away on demo flights but leave them down longer routinely, or why commercial jets always straggle along with their undercarriage down oddly longly, now you know. much less expensive.

also, putting wind-vanes on the wheels sharply increases tyre life. they spin up on landing, so there's far less friction on touchdown. heavys' tyres frequently blow out on landing.

The conveyor belt would just make the wheels spin faster, and the plane would still speed up at roughly the same rate as it usually did. The wheels would just go ballistic and spin at twice their usual speed. Air speed is the key. It is the source of forward motion (the engines only push air) and the source of the ability to take off. As long as the drag effect of the moving runway is minimal (only affected by the wheel bearing drag, effectively) then the plane will be largely unaffected.

Ground speed is pretty arbritary, and only matters in respect to V1. This is the 'point of no return' speed at which the decision to take off or not must be made, as to go any faster will mean they will be unable to stop in the available runway space.

Salt: I'd like to see evidence of that, to be honest. The wheels would naturally return to the same speed as that dictated by the vanes just after they left the ground, so would decellerate anyway. The inertia in the wheels alone is tiny compared to when it is on the ground so the braking force is massively reduced, so I fail to see where enough heat for spontaneous combustion would come from.

I imagine the carbon disk would still get pretty hot in this use anyway (as they do, but not all that hot stopping an unloaded wheel being blown around by air) but nowhere near as much as under braking. Unless the wheels are braked to a stop when they are actually inside the undercarriage box, there would be more than enough airflow to dissipate the heat.

Undercarriage fires are usually caused by getting the grease in the axle assembly too hot. If this doesn't happen on landing, it sure as shit ain't hotter in this circumstance. Maybe it's because it touches the soundproofing in the undercarriage box?

brock: *affable handwaving* dude, you GOTTA take a less black&white view of things. remember your previous (protracted) assertions that "reducing weight on the wheels can not change how the suspension sits nor the tendency for wheelspin!" and "if they thought it was military, it must have been doing high-G aerobatics!". you gotta look at the actual mundane day-to-day-isms which are really driving these things, rather than extrapolating extreme cases based on one or another theory-in-isolation.
</overreacting>


yes, if you hang around forever with your wheels down, the wheels' speed will approach/become the speed "dictated" by vanes attached to them. or rather, the axle friction will slow them until their speed matches any further driving force, which for traditional undercarriage wheels is 0, but for newer heavy commercial aviation is non-0 courtesy of attached vanes.

this is why you see jumbo jets heading off to japan with the wheels down.

oh wait. you don't see that.
maybe there are other factors to consider...

in real life, airlines have to trade-off various costs.
and make no mistake -- cost is the Overwhelmingly OVERRIDING consideration for airlines and has been for at least 2 decades. (nb: NOT quality, NOR safety.)
the cost (fuel) of driving to spain with the wheels down is horrific relative to the cost (materials degradation, extinguishers) of braking hard then slamming the wheels up as fast as possible.

ever wondered why the front wheel on a tricycle carriage plane doesn't fold up as soon as they're off the ground? they're past V2 at that point- why not just fold it away? it's not difficult to do: they have separate controls for each wheel-arch.

you can see military-budget planes do this. i've seen an airshow RAF plane and film of a navy plane squat as the guys folded the undercarriage while they were still driving on it (!)

no, the total amount of heat is not as much as when landing. but when landing, does the plane then fold its undercarriage up into the wheelarches and settle peacefully to the ground for a nice overnight kip, while the passengers scramble out onto the tarmac?
no.
the wheels sit at the end of a long robust metal pole a long way away from the plane body. for at least an hour under normal circumstances, including taxiing in and out, un- and re-loading, and refuelling.

further indication of things being more complex in context than in isolation: if wheel grease heat was the be-all and end-all of wheel fires, you would expect the bulk of wheel fires to occur while on the runway, the remainder on the taxiway, and a subset while parking/docking. but in fact, the bulk of wheel fires occur after takeoff.

milspec self-extinguishing fire-retardant retarded undercarriage

Suspension: Yeah it was protracted, but you were wrong. Being obtuse a couple of times and misunderstanding me, but essentially wrong. /me shrugs

I asked for some proof, not further asssertions. All you've done is state obesrvations that could potentially support your theory/POV. No proof. The (admittedly brief) little search I did produced plenty of reports of fires on landing due to undercarriage grease catching fire, but none on take off. That was why I asked you for some proof. Still want to see it, as I don't understand/get it, and want to. That's what arguments are mostly about. Spreading knowledge.

Cost: Yup. I know that. Goes without saying.

One of the main reasons that undercarriage is left down so long after take off is safety, actually. Should the plane have a problem, then the pilots will have enough to do without having to put the wheels down. They put them up after a 'safe' altitude where a 'go-around' would be theoretically easier or perhaps unlikely to happen. Also, there is less chance of a critical undercarriage failure if they are already left down. Most engine faults (by far) occur on take off, and this is the most dangerous time of a flight as the plane is usually at it's most stressed and with less margin for error.

Wheels: "if you hang around forever"? Just how good do you think the bearings are? The wheels will decellerate to their air-driven speed in, at the most, a minute after leaving the ground on their own. Commercial jets leave their wheels down longer than that anyway, because they don't have enough height to risk raising them. And the effect of wheels at those speeds actually helps the aircraft create lift anyway, by increasing drag under the body relative to above it - that is why the stall speed is lower with the wheels down. It is inefficient, both aerodynamically and interms of fuel, but any lift is useful at that stage of maximum risk. Once the extra lift is not needed (when the plane has accelerated into the efficient airspeed range of it's aerodynamic surfaces) then the cost of it (drag/fuel) is not palatable.

This is not about "extrapolating extreme cases based on one or another theory-in-isolation", none of my disagreements on this sort of thing are. They are about failing (with my engineering brain, which can overlook the obvious sometimes. Although rarely when it is a vehicular application) to see where the causal element is. Particularly in this case. Wheels with no ground contact are piss easy to stop. They don't weigh very much (comparatively) and would stop in less than ten seconds, I estimate. Probably a lot less.

Stop a car from 100mph and put your hand on the disc. You'll burn your fingers. Jack the car up and spin the wheel up to 100 mph, disengage drive and jump on the brakes. The wheel will stop inside of 2 seconds. Probably within 1. There will be a big 'boing' from the suspension and the car will leap about a little, but you could put your hand straight on the disc and not even know you'd just done it. It just doesn't generate enough heat (and yes, before you ask, I have done this, not that I needed to to prove it).

Stopping the wheels in the air just doesn't generate a fraction of the heat that they will on the ground. So if the wheel assembly can cope with this massively higher heat and soak from stopping the plane, why can't it cope with the heat soak from a much smaller heat input? That's what I don't understand. I haven't said you're wrong, I've said I don't understand how that can happen/it doesn't make sense to me, so show me something that explains it.

All very interesting but does the plane take off?

and what about the bunny rabbits?

Yes. The plane takes off.

Forgive me if I'm wrong. So the plane creates the resistance from its own jets sucking the air over/under its wings. Is that it?

No, the plane creates thrust by sucking/pushing air through it's engines. This moves the plane forward, totally independantly to whatever you do to it's wheels. The wheels will just spin at twice their usual speed (once for the speed of the plane relative to the ground, and once for the reverse speed of the conveyor belt).

Once the planes forward speed through the air is fast enough, the plane will take off as the speed of the air over the wings is high enough to produce lift.

Ooh I get it. Ta. It took a stretch to realise the double-speed wheels thing but it seems fairly obvious now.

yeah, the wheels are essentially just lubrication between the plane and the ground

and brock, re-read that suspension thread. i was right, as your belated realisation's implications underlined.

Nope. I have read it again (not in the last week or two, in case things have changed). Your basic understanding of the physics of the bike is wrong. I just got a definition wrong during the discussion. The error I posted about the ballistic arc makes no difference at all to the bike example, merely to the plane/zero-g one.

Clever men are so sexy.

*sigh*

Fuck off - so you'd let Einstein come on your face?
Or maybe you'd like to lick up Dr. Hawking's dribble?
Or maybe you're being sarcastic?

sorry brock, your basic understanding of physics is wrong.

Grim, for a 'clever' guy you can be a real arsehole at times. A lot of women find clever men sexy.

Just look at Marilyn Munroe and Arthur Miller.

Grim...I don't appreciate your tone.

Of course you'd let Einstein come on your face.

At least, I would, anyway...

I hate to be the one to break this to you, Doc, but Einstein is dead.

It might make quite a nice mask, actually. Any donors?

Y'know, I never understood how Dexy's Midnight Runners 'Come on Eileen' got past the BBC censors.

bwahahahahahaha!

(that song takes me back)

Just look at Marilyn Munroe and Arthur Miller.
Grim...I don't appreciate your tone.

So that's one woman there then (who also married the highly intelligent Joe DiMaggio, unless this 'Munroe' woman is someone totally different).

It's bullshit. Clever can be sexy, but only as a small after-thought to the visual side of things.
Because, in fairness, you wouldn't want to bump uglies with someone who looked like Big Old Albert.

And 'tone'?
You've been here before, right? This is ihaveanopinionandiamstickingtoityoucansuckmyballsifyouthinkotherwise.com =]

WH: Seriously, how about Greased Lightning? That song contained filth, but was never edited for radio play.

ihaveanopinionandiamstickingtoityoucansuckmyballsifyouthinkotherwise.com =]

fair enough. but you know how sensitive I am. ;)

Sorry, but clever men are sexy. Just my opinion. Look at Cal. He's no oil painting, but damn.

Yeah, you can tell from the three people you listed in the 'babe/babemagnet' thread.

So if Jeffy boy here was stupid you'd kick him out of bed, I suppose?

WH: Seriously, how about Greased Lightning? That song contained filth, but was never edited for radio play.

To save you a Google :

"Greased Lightnin'"

Why this car is automatic
It's systematic
It's hydromatic
Why it's grease lightning (Grease lightning)

We'll get some overhead lifters and some four barrel quads
oh yeah
(Keep talking whoa keep talking)
A fuel injection cutoff and chrome plated rods oh yeah
(I'll get the money I'll kill to get the money)
With a four speed on the floor they'll be waiting at the door
You know that ain't no shit we'll be getting lots of tit
In Grease Lightning
Go, go, go, go, go, go, go, go, go, go

Go grease lightning you're burning up the quarter mile
(Grease lightning go grease lightning)
Go grease lightning you're coasting through the heat lap trial
You are supreme the chicks'll cream for grease lightning
Go, go, go, go, go, go, go, go, go, go

Purple french tail lights and thirty inch fins
oh yeah
A Palomino dashboard and duel muffler twins
oh yeah
With new pistons, plugs, and shocks I can get off my rocks
You know that I ain't bragging she's a real pussy wagon
Grease lightning

Go grease lightning you're burning up the quarter mile
(Grease lightning go grease lightning)
Go grease lighting you're coasting through the heat lap trial
You are supreme the chicks'll cream for grease lightning
Go grease lightning you're burning up the quarter mile
(Grease lightning go grease lightning)
Go grease lighting you're coasting through the hit lap trial
You are supreme the chicks'll cream for grease lightning
Lightning, lightning, lightning
Lightning, lightning, lightning
Lightning

Yeah, you can tell from the three people you listed in the 'babe/babemagnet' thread.

So if Jeffy boy here was stupid you'd kick him out of bed, I suppose?

I didn't say that only clever men are sexy. Those guys are sexy for other reasons; usually charisma, which is intelligence.

I can't see Jeff? (red x)?

Fuck!
Greased Lightnin(')g is more filthy that I thought!

And men in positions of power also have a high pulling ability, regardless of their physical attractiveness. That's why pug-ugly cabinet ministers are always getting into scandalous situations. Women can't resists a jump with a high flyer.

Look at Cal. He's no oil painting, but damn.

Ha, ha, ha, ha, haaaaaaa, up yours, geek boy.

No, wait.. ......

Grim ..... did you miss that little joke-ette? I wasn't referring to the lyrics of DMR's song but the title, which is actually innocuous. It was a play on words, wannit? You know, 'come' on Eileen.

Greased Lightening probably got through because the lazy buggers at the Beeb weren't on the ball. Or Mike Reid had moved on to pastures new.

WH: Yeah, I got that. Stupid internet. Stupid words.

Oh good.


Stupid boy.

So that's one woman there then (who also married the highly intelligent Joe DiMaggio, unless this 'Munroe' woman is someone totally different).

Ah, but she was a gold digger.


The Washington Post has a view on this.

that's a scarily apposite article, wh -- thanks! i've been chewing on some articles re a similar framework for a while now, but having trouble finding non-inflammatory wordings, let alone any useful third-party studies.

in essence: men primarily select for reproductive fitness, women primarily select for social dominance. (both sexes socially reward intelligence, e.g. the popularity of crime novels, suggesting this could be a prime driver in the evolution of our freakishly big brains relative to all other animals.)

this paper you've linked to demonstrates the eventual results of those "marginal propensities to breed" (economist joke).

and can i say that this is one of the more gloriously coy ways of saying "gold-diggers" that i have EVER come across:

One longitudinal study of people in Oakland, Calif. , found that attractiveness among women was the "strongest determinant of their husband's occupational status."

Ah, it's nature then. Not my fault I like big, handsome, sexy, intelligent, powerful men.

EDIT : rich

Don't you think it's interesting that women are given the label 'Gold Digger' when it's men that grab all the money/power for themselves? How else is she supposed to get access to it in a man's world? Hm?

So men are Gold Grabbers!

nothing to stop women grabbing too. choosing not to do something is not the same as being excluded.

i'm a leg man, myself

(How'd they do that?)^^^

But you must admit, for the large part, in the past especially, women were deliberately excluded?

"sorry brock, your basic understanding of physics is wrong."

You can be as sorry as you like, but it fucking isn't. Your blinkered viewpoint doesn't allow you to be wrong, though, it would appear. Do some background reading, and you will find that I paid attention at school and university as well as whilst using this 'basic understanding of physics' every day for the last 10 years since I left.

I tried to explain it to you, but you insist that I am wrong, even though I checked with some of my text books when you tried to call me out (despite my confidence). Or are they flawed in their thinking too?

Y'know, I never understood how Dexy's Midnight Runners 'Come on Eileen' got past the BBC censors.

Come.
Together.
Right now.
Over me.

Sounds like you and John Lennon are having some boy fun, doc. Good point, though. The Beeb blue-pencil department should have blown a fuse over that one.

doc: oh is THAT how they did it?

brock: sorry mate: no. you'll note you repeated your primary error on that thread even here: assuming effective weight is either 100% or 0% and nothing else. black&white, shortcut rules of thumb; like i said before. trouble is: your shortcuts there contradict newton's third law (and observed behaviour) -- a bit of a reach even for the most prestigious of textbooks.

syl: hmm. i see your point. but bear in mind also that women who were determined to compete equally in commerce/business (NOT the same as simply demanding high status) were a smaller and smaller proportion the further and further back you go, but appear to have been individually equally successful.
even in politics -- which piece is the most powerful on the traditional chess board? (1,000+ years old) do you think that's accidental or satirical? food for thought.

"assuming effective weight is either 100% or 0% and nothing else"

Utter fantasy, both in this thread and the other. Where the fuck have I said that in either thread? This, from the same bloke that doesn't believe that it is easier to move a small mass (in the direction of gravitational effect) than a large one (against it)? Clearly, you fundamentally fail to understand what I am trying to explain to you. This is something that I think you have some sort of mental block about, but I am not wrong about the things I have posted.

Salti, you are wrong. I have tried over some considerable time to explain it to you, but you refuse to believe things that I tell you that are represented as fact in Physics and Engineering text books. THIS is why you think I am wrong, because you refuse to believe the basics. I have no fucking idea why, the only thing I can think is that you refuse to allow anyone to know better than you.

There is no fucking way I would be this indignant if I hadn't checked 5 times that what I was saying wasn't right. You clearly don't have any respect for my knowledge, education or experience, but at least take note of my detesting being wrong. I would either have admitted it by now, or dropped the damn thing.

Incidentally, where is that "the bulk of wheel fires occur after takeoff" proof, or even some suggestion of its occurence? I searched for about 20 minutes last night (including the CAA accident report logs) and didn't find one instance, or even mention, of wheel fires on take-off. But you seem to have made a seemingly authorative declaration, and then gone quiet when someone called you on it. Show proof.

I suspect that is why you refused to carry on the suspension thread. You had no theoretical basis for your assumptions, and too much pride to be corrected.

i DO understand, and i explained your error at length in the suspension thread, then formally signed off on about iteration 10 when you refused to actually read what i wrote but simply repeated the error back at me in increasingly high dudgeon.
it took about 5 go-rounds just to get you to think about what i said re bike rear suspension stretching under high acceleration, not compressing, but it didn't stop the same high dudgeon then, either.

but here's a clue: read newton's third law, think about it, then consider that while i repeatedly stressed that resulting equilibrium points are the balance of forces for both bodies and that if the forces change then the equilibrium point changes, you have read this as "the same bloke that doesn't believe that it is easier to move a small mass (in the direction of gravitational effect) than a large one (against it)". you simply can't get to your representation of what i said from what i actually said -- only by keywording and extrapolating in a fixed frame of reference.

and, as i said before, if you're not going to listen, there's no point me talking. it literally is just wasted time, for both of us.

Not entirely a waste of time since readers would have learned a thing or two. (Apart from the stuff that flew way, way over my head)

Doc:you are going to have fantastic hair with all that stuff in it. Apparently it makes hair shiny and full of body. (B3ta lady tried it)

I want to start a Jizz-Shampoo company. Why do we waste all those litres every year?

Litres?

Wow, do you think it's actually a litre a year?

/researches

Okay. The average male, through his adult life (16 years +), ejaculates, on average, three times a week until he is 60. The 'usual' amount ejaculated is 2.75ml (down from 3.5ml fifty years ago - pah).

So (3 * 2.75) * 52 = 429ml, less that half a litre.
Boo.

However, cosider 'harvesting' the Southern Right Whale's 'output' - 5 gallons a hit! That's a bucketful, baby!

My history's going to make for some interesting web-log reading...

after months and months of begging and pleading i finally got my girlfriend to let me have butt sex with her. try as i could she just couldnt take my dick up her butt. i was pissed off . i slipped her some sleeping pills in her drink and fucked her ass anyway. i dont care because she did promise it to me. she woke up thinking that her ass hurt from our trying the night before. ill never tell her the truth.

Fair play, man! She promised!

/waaargh!
/dies

AND whales have prehensile penises

Hmmm, well, not everyone is going to want Jizz Shampoo (TM) so I imagine that enough could be harvested in an average sized country to meet the demand. But wouldn't it be more economical to market it as a facial cream? You'd be able to sell little pots of the stuff at a much higher mark-up than big bottles of shampoo. It could be called ... oh, I don't know .... 'Cum On My Face'?

I have my own special dispenser for that already!
Form an orderly queue, ladies!

=]

Hehe. A clip from The Daily Show a few days ago saw Sharon Stone in Israel claiming "I came in my faith". Jon Stewart hoped she didn't have a lisp.

Salt/Brock - I certainly couldn't settle your argument but perhaps you should lay them out in lighter terms. You both have a penchant for explaining at length. Maybe this is why you're getting wires crossed. I'd like to know the answer. Of course, I've forgotten the question, but still... I need closure.

429ml X =/- 3 billion males? (12870 000 000 000 L)
We need to set up harvesting stations everywhere. *tick *tick*

We need something like this at the harvesting stations

hahahaha!

Alfie, can you design a sign for us?