BASIL
<<<disagree with the suggestion that up elevator has
any significant value. Very little of the aircraft weight is supported
by the nosewheel therefore up elevator will transfer little weight
before the nose lifts and, as IAS reduces, the elevator will, in any
case, become less effective.>>>
....That's why the
"progressive" backstick is being advocated. You can still fly the
sight-picture out the front window and temper the degree of backstick -
but I've never found "nosegear rising" to be an issue. It's an imaginary issue only. Surely you aren't claiming that
with spoilers up and under max reverse and braking, that there isn't a
strong cumulative nose-down pitching moment? That's why the term
"effective" weight-shift towards the nose is being used. The fact that a
747 (and other widebody aircraft) might have both body and wing-gear
doesn't change that "towards" directionality. Or maybe just think of it
as the elevator (and hoz stabilizer of course)
levering the maingear into the ground by using the nose-gear as a fulcrum. You are "effectively" increasing the weight on the main-gear wheels courtesy of your up elevator input at speed (if used early enough you will stop the anti-skid cycling and help the autobrake achieve its programmed retardation schedule). Maybe it's just too difficult a concept for some to wrap their mind around.
.
<<<For those who have never turned e.g., a 747-400,
over wet piano keys, the sideskid even at low speed would come as a
surprising indication of how little weight is supported by the
nosewheels.>>>
.... This has not a lot to do with the
dynamics of landing. Any airplane's nosewheels will slip when turning on
wet piano keys.....whatever its C of G (and both pre-takeoff or
post-landing). It's less a function of weight and more to do with a loss
of traction due to a nosewheels' tread being hamfistedly cocked off from
the direction of a/c travel inertia, whilst on a slippery painted surface.
.
<<<On the landing roll I certainly do not wish to
remove weight from the nose wheel and reduce non-aerodynamic
directional control.>>>
You obviously don't subscribe to
the theory of wheelbarrowing then...but perhaps just consider it to be a
more equitable distribution of weight. Wheelbarrowing could be thought
of as "pushing a length of thread" or perhaps what happens when you
inadvertently use front wheel brakes (only) on a bicycle at speed (vice
both F & R hand-brakes). Those who advocate stick forward have obviously
not tried that. I wouldn't recommend it in a fighter, that's for sure. Be reassured that the progressive backstick technique considerably enhances directional control
.
<<<Auto spoiler deployment on landing can cause a
pronounced nose up pitching moment and a habit of applying nose up
elevator too soon after landing could cause a
tailscrape.>>>
Nobody is advocating any motor moronic
whipping into automatic "loadsa backstick". Please stop diminishing the
overall argument by escalating into gross handling nonsensicalities. The
advocated technique is to introduce progressive backstick as or AFTER the
reverse has cut in, spoilers are up and auto-braking (or toe-braking) is
underway. You can control what happens to the nose by observing through
the front window.
.
It's
almost amusing, but actually quite tragic, that the
progressive backstick stopping technique has been allowed to fade into
obscurity. The plaintive cries of the now retired old and bold actually
seem to read as: "why wasn't I told?" Sorry about that.
Perhaps someone should start a thread on other "lost arts".
.
In Reply to Conan the Barber's Query
Effectiveness of the Technique?
In my secondary duty as a maint Test Pilot at an Advanced Jet Training
School I used to torment the Hell out of other instructors by planting
the jet on the numbers and turning off impossibly early and thereby
getting the really short taxi to parking - wet or dry runway and no
maxarets/anti-skid. I'd normally only do that on back-to-back functional
check-flights and be relatively heavy with fuel normally, because of
that. Additionally, but quite non-critical, I used to run the electric
elevator trim all the way forward once the main-gear was on, just to
have the trim-tab working for me as an elevator extension -rather than
against me => more power to the elbow. Those who tried to
emulate the feat, even at light weights at the end of an instructional
sortie, usually missed the turn-off (and had a long slowspeed taxi to
the next) and/or blew a tire. The Chief Flying Instructor eventually
blew up at a staff meeting, regaled everybody about all the blown tires
and demanded to know how I did it. In four engine aircraft I rarely used
it in anger, just for training and demo purposes.
My guess is that a figure of the order of 20% better than book figures
on dry runways and similar on wet runways, with maybe slightly less on
really nasty rubbery and slushy surfaces. But runway surfaces vary so much over their length, particularly because of the rubber buildups in that
critical last 2000 feet. Braking achieved early on, in the "clean"
second third of the runway, is what it's all about.