Re: A brief commentary

From:         shevell@leland.stanford.edu (Richard Shevell)
Organization: Stanford University, Dept. of Aero/Astro
Date:         20 Jul 96 15:59:10 
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In article <airliners.1996.1334@ohare.Chicago.COM>, Tony Maddern
<tmaddern@cse.unsw.edu.au> wrote:

> With regard to the Chicago DC10 accident Glenn Carroll wrote:
> >
> >V2 is the speed one is supposed to fly with one engine out.  In
> >this case, with the outboard slats inappropriately retracted, V2 was
> >not sufficient to prevent a stall.  The aircraft could have been
> >flown and landed at a higher speed, so:  why is V2 so slow?
>
>      the Chicago DC10 did not stall but when the speed was reduced to
> V2 it came below Vmca for the aircraft with one engine failed and
> asymmetric leading edge flaps.

--
V2 is the speed at which an optimally flown airplane reaches a 35 ft.
height when an engine has failed during the takeoff run. The optimally
flown airplane is one that was lifted off at a speed at least 10% above the
Vmu speed, or 10% above the Vmc(minimum control speed with the critical
engine inoperative). The Vmu is the lowest speed at which the airplane can
be lifted off without exhibiting dangerous characteristics.  Being the
slowest permissible speed, it  generally gives the optimum flight path near
the ground, i.e. has the best obstacle clearance.  It does not necessarily
correspond to the best angle of climb but if one accelerates to a higher
speed, the climb angle is lowered during the acceleration.

There is another good rule.  If something is wrong with the airplane, and
one is flying near the lower end of the speed range, and IF ALL GROUND
OBSTACLES ARE CLEARED, there is no point in slowing down. The faster the
speed margin the better, so never give up speed!

I do not believe there was any indication that there was a Vmc problem in
the DC-10 Chicago accident. The airplane was well above Vmc. Furthermore at
V2, selected with slata extended, the DC-10 is above the stall speed even
with slats retracted although the speed margin is much reduced.  The stall
was due to the fact that when the rear support failed due to the crack
produced in replacing the pylon erroneously, the engine rotated about the
front support before pulling it through the leading edge and breaking up
thwe airfoil shape.  That is what caused the stall at V2.

Richard Shevell
Email: shevell@leland.stanford.edu