Re: can someone please help me...

Date:         23 Aug 98 14:34:09 
From:         cowboy@ram.net.au
Organization: Deja News - The Leader in Internet Discussion
References:   1
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In article <airliners.1998.1232@ohare.Chicago.COM>, "Paul Rotzler" <protzler@microconnect.net> wrote:
>     This isn't a technical question at all, I am just curious on what the
> climbrate is for the 747 from takeoff, to cruising altitude. Also, what do
> they usually descend at?

cowboy's comment: we have covered this with the question about the concord.

The climb rate is not constant and is influenced throughout the climb by the
power to weight ratio. the heavier the aeroplane , the lower the initial
cruise altitude. The rate at take off must be a minimum depending on how many
engines the aeroplane has so that it can clear obstacles if a critical engine
fails. In the b747 it is a gross of 3%. At max auw and hot ambients the roc
is not impressive.

The normal climb schedule for jet airliners is to fly, climb at a fixed IAS
until around 24-25000ft to lock onto a fixed mach number and continue on that
until cruise is reached. In all likelihood this is the cruise mach also. At
the start climbing at constant ias the aeroplane is in the accelerating phase
of the climb and the roc , initially high (relatively) decreases as altitude
is gained. At the IAS/ mach cross over point is neared the roc would be
relatively quite poor.	As the aeroplane starts to climb at the fixed mach
number it is in the decelerating portion of the climb schedule and so
initially the roc increases again ( not as much as at take off but more than
that experienced just prior to the speed change over altitude). This new
increased roc does not last for long and evenually as the aeroplane
approaches its cruise altitude is down to just over a 200fpm if the aeroplane
is climbing to optium for the weight.

There are speeds, dependent on aircraft weight , for high gradient or max rate
climb's that are flown if ATC demands.

At cruise altitude the aeroplane is always initially too heavy and suffering a
fuel penalty and it remains there until it is suffering a fuel penalty by
becoming too light, when it climbs to where it is too heavy, etcetera ,
etcetera,etcetera.

The reverse procedure is followed in the descent.(some other poster have a go)
The rates can vary depending on what is trying to be achieved. For instance an
emergency descent with the pax standing on the back of the seat in front of
them can go higher than 14000fpm. That is, as I said , an emergency descent
following loss of cabin pressure.

Optimising the performance of heavy jets on a long sector such as syd-lax,
Bkk - Lon so the max payload is carried and the sector is completed depite
the wx is what makes this type of flying so fascinating. The climb and the
descent are aminor part of the entire sector. cowboy@ram.net.au

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