Re: Acceleration of a 747

Date:         26 Apr 98 03:44:22 
From:         Carl Peters <cpeters@i1.net>
Organization: Internet 1st, Inc
References:   1 2
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JWizardC wrote:
> .. but the simple
> answer is this: All commercial aircraft are certified to be able to
> accelerate to takeoff speed -> and decelerate to a stop <- within the
> confines of the runway.

This is not true. 'Take off speed' (actually rotation speed, Vr, with
actual takeoff occurring a little faster) depends on variables such
aircraft weight, winds, temp, etc. It is V1 that is the speed at
which point thereafter the aircraft is committed to takeoff,
as insufficient runway would be left to abort. In many flights,
except when the a/c is light and/or there is a great field
length, V1 occurs before Vr. Regards to certification, this
is not tested - you don't have abort attempts practiced at all
different airports, with all the different variables arranged -
this would take years. Instead, acceleration and braking are
measured, then these abilities are used in tables and calculations
published by the manufacturer (with variables such as wind, temp,
included), with which V1 can be calculated for a given flight.

Next time you're at an airport, watch the traffic. I routinely
see 747's, L-1011's, and 727's use 6-8000 feet of a 10,000+ foot
runway - I assure you, an abort at Vr would guarantee a bad
day for pilots and passengers. Another case to show this point
is the location where new aircraft are sometimes taken for
rejected takeoffs during testing and certification. These
are done at max takeoff weight - Boeing took the 777 to
Edwards AFB's 15,000 foot runway to ensure they would have
the distance to stop.

Carl Peters