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Boslandew
10th Nov 2009, 17:48
Every time I see a big/fast aircraft land and see the smoke as the wheels are spun up by contact I wonder if any work has ever been done to see if wheels could be spun up to landing speeds prior to touchdown. Would a set of small fan blades mounted on the sides of each wheel have any effect?

DERG
10th Nov 2009, 18:12
Just adds to the workload the brakes have to do. All transfers into heat..a lot of airlines don't use reverse thrust these days.. they just stamp on the brakes hard..:ok:

MarkerInbound
10th Nov 2009, 18:26
Convair tried that idea on one of their aircraft (880/990?). Turns out it wasn't worth the weight.

DERG
10th Nov 2009, 18:29
Furthermore: on take off you will have more drag..not good!:ok:

Checkboard
10th Nov 2009, 19:22
It has been done, and is still done on some aircraft fitted with gravel landing kits. You can see the nose-wheel spin-up gear on this citation:

Photos: Cessna 550 Citation II Aircraft Pictures | Airliners.net (http://www.airliners.net/photo/NWI-Jet/Cessna-550-Citation/0867606/L/&tbl=&photo_nr=23&sok=&sort=&prev_id=0867607&next_id=0867605)

WindSheer
10th Nov 2009, 21:52
This has been discussed before.

The initial cost of the equipment, the space it occupy's, the fuel used carrying it, and the maintenance cost's towards running it......by far outway's the cost of the tread loss off the re-moulds!!

Although, with intense flying programmes surrounding e.g ryanair's 738's...maybe something like that would be viable.

Boffins...??

TURIN
10th Nov 2009, 22:47
Why not have a runway which is like a huge conveyor belt...............:}

SMOC
11th Nov 2009, 01:46
Why not have a runway which is like a huge conveyor belt...............

NOOOOOOOOOOOOOOOOOOOOO

Delete this thread before it starts!!!!! :eek:

Runaround Valve
11th Nov 2009, 05:46
Back in the mist of times in the 1950`s the company that I worked for had Lockheed L749 aircraft. On the outboard side of the nose wheel tyres were flaps that opened into the airstream to rotate the wheel before landing. However never saw a tyre as such as they were fitted with the flaps cut off. No idea of the reason why the flaps were removed.

Boslandew
11th Nov 2009, 16:03
Many thanks for the comments. I guess that if tire burn was a big enough or expensive enough problem, something would have been done about it and it obviously isn't.

grebllaw123d
11th Nov 2009, 16:48
I once had a senior Boeing engineer sitting in the cockpit on a flight to Seattle from Copenhagen (before 9/11). He had a fantastic knowledge of aviation, and he had an answer to the question in this thread.
He said that the main reason for not having such a system installed is, that the rotational speed of the wheels MUST match the actual ground speed closely in order to get any significant decrease in tire burn. This close match is very difficult to achieve for several reasons, so combined with the other negative factors (weight, costs etc...) makes an "anti tire burn" system a non starter.

Juliet Sierra Papa
11th Nov 2009, 20:21
Just adds to the workload the brakes have to do.

:confused:
JSP

Cough
11th Nov 2009, 22:24
JSP - I'm guessing that DERG is referring to the small amount of kinetic energy taken out of the landing aircraft when the wheels spin up (spin up wheels requires a force which comes from the velocity of the a/c), though I would think that it is less than a knot....

...Probably wrong tho'

ChristiaanJ
11th Nov 2009, 23:25
I'd never seen grebllaw123d's answer before, but it makes so much sense, that it settles the question for me.

CJ

DERG
12th Nov 2009, 10:15
Yes Cough I am. Every time I fly as a passenger on short haul jets these days I note the hard and short braking done on landing. The conclusion I came too: brake maintenance is cheaper than jet fuel and engine maintenance.

There are always jobs advertised for guys who maintain the brakes so I would guess the life of the brake components is short.:suspect:

sycamore
12th Nov 2009, 11:10
Check,are you sure that`s a spin-up device and not a brake on the nosewheel?

awblain
12th Nov 2009, 23:46
Cough - I've used this as a first-year physics example.

Spinning up the wheels should soak up about 0.6% of the kinetic energy when landing a 747 at M = 300 tons. This is equivalent to 0.3% of the speed, so less than a knot is right.

I assumed a moment of inertia of about I = 45 Kg-square-meter for a 747 tire, a mass of M_W = 200 Kg (guess) and a radius of R_W = 66cm.

The 0.6% number should be almost independent of R_W, but scales with the mass ratio M_W/M, and the moment of inertia to mass-radius-squared scaling value of I/(M_W * R_W * R_W), which I took to be 0.5. It's independent of landing speed. Landing light soaks up more of the total energy to spin the wheels.

fhegner
13th Nov 2009, 12:11
to DERG

A least one of the small regional jets - the BeA-146 - don't have trust reversers AFAIK..

DERG
13th Nov 2009, 12:40
Thanks for that advice..that is my fave aircraft to ride in too!:ok: