"Peter Dohm" wrote in
:


"Bertie the Bunyip" wrote in message
...
Tina wrote in
news:3de72bf8-4626-4420-8b38-9b7248d4a236
@p25g2000hsf.googlegroups.com
:

On Jun 11, 1:13 am, Bertie the Bunyip wrote:


Well, the airpane doesn't pitch so much largely because the slats
and flaps come out together, unlike airplanes with flaps only. If
you fly smoothly power changes should be minimal. We don't really
flare in the same way you would in most. just a quick tug at abou
t15 feet to reduce the rate of descent, but we're not supposed to
grease it on for a few reasons. One, float and wasted runway. two,
it gets all the spoilers and othe squat switch things going as well
as the immediate availability of brakes. three, it breaks the
surface tension of any water if it's a wet runway and four it gets
the wheels spinning straight away. you can scuff tires badly in a
greaser..

Bertie

I can understand everything you said about firm landings, except the
tire scuffing comment. It would seem to me landing firm would smoke
the tires since they have to accelerate to the correct speed right
now, where a gentle touch down would let them accelerate more
slowly. A more gentle acceleration means less shear forces on the
tire, so I'm missing something important. Are there any insights you
can offer?


Yeah. They're pretty heavy and take a bit to get spinning, so if you
grease it on, you just scuff rubber off of one spot until they start
rotating. It's even worse on a wet runway, where water can slice
through rubber very quickly. Sounds crazy, i know. If you're at an
airport where you can see the tires, it's not uncommon to see parts
of tires with oval wear patches where they've worn through to the
first layer of cord. That's allowed, btw.


Bertie

This may be mostly a function of speed. I never heard of it at the
entry level, such as 150s and 172s, but the issue has been discussed
from time to time in the aviation magazines--especially is there is
any drag on the brakes.



Yeah, speed and the mass of the things. At a guess, I'd say 737 wheels
weigh in the region of 200 lbs and larger aircraft even more of course.
Takes a moment ot get them going. Nothing to do with brakes, of course




Bertie