TakeOff Thrust Setting on the B-747

Date:         31 Mar 2000 22:25:32 
From:         sharat@playful.com
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Here's a couple of questions I'd like to submit to the readers of
sci.aeronautics.airliners:

Consider a Boeing 747-400 at MTOW just about to start the T/O roll with
Flaps 20 degrees.

Q1) What fraction of the Maximum Engine Thrust is the TakeOff Thrust at
the start of the roll. Is this thrust setting held fixed through V1 and
VR?

Now, at rotation and possibly the earliest stages of climbout (prior to
rolling in the flaps), the angle of attack (angle of incidence in the
U.K) is +ve, therby increasing the lift, but also increasing the drag.

Q2) If the engine thrust remains the same during rotation and initial
climbout, wouldnt the increased drag result in a decrease in airspeed?

Q3) If the supposition in Q2 above is correct, does the autothrottle (if
at all engaged during T/O) adjust the engine thrust to maintain the
speed/accelerate the aircraft to V2 (safe climb-out speed)?

Finally,

Q4) If the engine thrust actually increases during rotation and climbout
to overcome the increased drag, doesnt it follow that the Engine Thrust
at the commencement of the Ground Roll cannot possibly be the maximum
engine thrust?

-Sharat Chandrasekhar

Airliner Enthusiast

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