Re: Rudder control & front gear

From:         geohull@ditell.com (George Hull)
Organization: DirecTell L.C. - Park City, UT. - 1.801.647.0214
Date:         12 May 95 03:22:49 
References:   1 2 3
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In article <airliners.1995.531@ohare.Chicago.COM>,
robert_leong@earthlink.net (Robert Leong) wrote:

> rdd@netcom.com (Robert Dorsett) wrote:
>
> >The 747 is a bit different: it's controlled by the tiller on the ground, by
> >the rudder when aerodynamically active.  It has a further option of steering
> >using the center gear bogies to further assist the nose gear.
>
> What is a 'center gear bogies'?

The center bogies are the "training wheels" under the fuselage . . usually
found on long-range heavy airliners to supplement the load-carrying
ability of the normal main gear.  Some aircraft have the option of leaving
the center gear retracted if the aircraft is operating below a limiting
weight.

> Do large jets have differential breaking of the left or right main
> landing gears and if yes, are they used to assist in turning as do
> light plans?

Yes, they have control of the brakes on the individual main gear using the
respective brake pedal (depressing the top of the rudder pedal activates
the brakes on that side).  Typically the nose wheel steering is sufficient
to control turning in normal operations.  Differential braking and
selective use of thrust reverse may be necessary on slippery surfaces . .
but not normally.  Differential braking is not used on transports like it
is in light planes.

> I once asked a MD80 pilot while sitting on the ground on a quick stop
> over if he can tell me what the climb rate during initial takeoff was,
> he told me he didn't know!  So I said oh and returned to my seat.  Can
> this be for real?  Do they just go by the airspeed during climb and
> don't really care what the VSI is as long as it is climbing?

The vertical speed will depend on lots of variables . . he wasn't wrong to
tell you that he didn't know what it would be.  He could have told you his
takeoff weight and the speed schedule for departure and climb, but lots of
variables, including the need to trade airspeed for climb performance,
would affect the climb rate at any given time.  A typical vertical speed
for a B-757 departure from a sea level airport might be in the range from
2000 to 3000 fpm during a normal climb at low altitudes.  As that airliner
approaches 41,000 feet in the climb it might only be climbing at 300 fpm.
It would have been easy for your captain to just give you a number, but he
told you the truth.

George