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From: G-S on 8 Sep 2007 22:28 Aeek wrote: > On Sat, 08 Sep 2007 11:56:05 GMT, "Boxer" <someone(a)nowhere.com> wrote: > >> When I was flying a Cessna 182 I could never find the reverse thrust button >> so I just used the brakes on the wheels. > > Did think about light planes after posting. Q. How much speed to you > shed by maximising drag vs by using the brakes? Well... I could touch down and stop in as little as 50 mts using the brakes hard (not good for the tyres but a useful emergency technique to learn), without any brakes the plane would roll for several hundred metres. That's a fair difference in my book. Of course different planes will have different results... G-S
From: Bernie Dwyer on 9 Sep 2007 21:00 GB wrote: > > Aeek <aeeeeeek(a)tpg.com.au> wrote in > news:qvv4e3d8273c51ug269dh09mb386d16fk5(a)4ax.com: > > Aircraft brakes are reverse thrust, the force doesn't go through the > > tires. Same as when taking off. The tyres just have to survive the > > incidental accelerations and hitting the ground, they are not part of > > the drive train. Traction isn't what an aircraft tyre is about. > <snip useful info> That "hitting the ground" thing has always bothered me - when an aircraft lands, the wheels go from stationary to the rotational equivalent of the landing speed in a very short space of time. That's got to put put a hell of a stress on the rubber, shortening its life, and I'll bet that tyres for a 747 aren't cheap ("just re-tread them, Mario, we're selling it to Garuda next week"). Has anyone ever thought of pre-spinning the wheels (with small electric motors or maybe compressed air) just before touchdown, to save on wear and tear? -- Bernie Dwyer There are no 'z' in my address
From: JohnO on 9 Sep 2007 21:46 On Mon, 10 Sep 2007 11:00:20 +1000, Bernie Dwyer <b_duibhirz(a)yahooz.comz.auz> wrote: >GB wrote: >> >> Aeek <aeeeeeek(a)tpg.com.au> wrote in >> news:qvv4e3d8273c51ug269dh09mb386d16fk5(a)4ax.com: >> > Aircraft brakes are reverse thrust, the force doesn't go through the >> > tires. Same as when taking off. The tyres just have to survive the >> > incidental accelerations and hitting the ground, they are not part of >> > the drive train. Traction isn't what an aircraft tyre is about. >> ><snip useful info> > >That "hitting the ground" thing has always bothered me - when an >aircraft lands, the wheels go from stationary to the rotational >equivalent of the landing speed in a very short space of time. That's >got to put put a hell of a stress on the rubber, shortening its life, >and I'll bet that tyres for a 747 aren't cheap ("just re-tread them, >Mario, we're selling it to Garuda next week"). Has anyone ever thought >of pre-spinning the wheels (with small electric motors or maybe >compressed air) just before touchdown, to save on wear and tear? I read somewhere (the net?) [1] - that the F16 fighter has its wheels spinning before it touches the deck. Johno Beer mate? [1] if it was the net, it has to be true
From: BT Humble on 10 Sep 2007 23:10 Boxer wrote: > "Jordan" <jwprin...(a)otpusnet.com.au> wrote in message > > Knobdoodle wrote: > > >> I don't think it was a Mosquito either. > >> It was a Merlin but it was from something unglamorous from what I recall > >> of the original story. > > > Could have been the unsupercharged version that was used as a tank engine? > > I used to drive one in a Centurion. What was your best 400m drag time? Come on, don't pretend that you never tried it! ;-) BTH (By the way, any word on that tent pole?)
From: Yeebok on 11 Sep 2007 22:39
Logic (or physics) dictates that the friction created by the wheels would scrub some speed. Like GB said it's not something I'd have considered as an impact on decelerating a plane whilst on the ground, but I would be very surprised if there was no energy moved from 'plane speed' to 'tyre speed', e=mc^2 etc. Mr_Hankey(a)qnr.com.au wrote: > GB wrote: > >> Mr_Hankey(a)qnr.com.au wrote in news:vs0de3lje86dcfcfjtqr76609cp0pfvgrn@ >> 4ax.com: >>> Yah, I guess it all looks a bit definitive, sorry about that. >>> Sources are my own study material, small knowledge of fluid dynamics >>> (applied to unloaded turbines or air driven rotors), conversations >>> with experienced pilots and instructors, some commonsense... >>> If you want Internet sources, google has plenty... I used "landing >>> gear wheel spin", but you can roll your own as you wish... >>> And I'm certain you will find plenty that contradict what I say :) >> More than likely! That's the whole point of the intarweb, isn't it?! >> >> It seems logically valid, I'd just never heard the claim made >> before (and I've made something of a study of things aviation >> over the years). -2 to -5 knots does seem like a lot... > > Have a look at your ASI next time you touch down. Even though it's > generally low off the scale, the needle still drops - significantly on > bitumen, less so on grass. > Qualitatively, the figures look OK by me. > |