Re: Acceleration of a 747

Date:         29 May 98 02:44:02 
From:         "Donald Mc Lean" <>
Organization: Mittagong Mania -
References:   1
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Acceleration is about power to weight ratio so as has been suggested by
some writers , it depends on the BRW of the aeroplane, the heavier , the
slower acceleration.  If you are watching departures at the terminal
note the service destination, thats an indication of the t/o weight not
the number of passengers.
Vr can never be less than V1 and only at very light weights would be
theoretically the same.  In this case pilots make Vr 2kts faster so
there is a definite call at the decision speed V1. These V speeds are
all a function of the BRW and the BRW is a function of the r/w length
and temp and pressure but mainly temp, these of course being the
variables that effect the engine thrust. The heavier the BRW the higher
the V1, Vr and V2. Certification states that Vr is 1.1Vs and V2 can
never be less than 1.2Vs but could be much more depending on the
obstacles in the second segment off the end of the runway.
For landing the same rules apply. Approach speed (Vref) is set at
certification as  1.3Vs so will be a function of the aeroplanes landing
weight. Vs covers any flap selection but in all cases less flap means
more runway and higher speeds.