Re: Design Philosophy -Reply

John Bent (jbent_at_glink.net.hk)
Sun, 30 Mar 1997 07:57:12 +0800

Airliners don't like 9G. Let's put this to bed. A recent study, to which
I have previously referred, shows very clearly (from Flight Safety
Foundation CFIT data) that airline pilots can't fly "edge of envelope"
optimal avoidance manoevres as well as fly-by-wire envelope protection
programmes, [especially at the end of a long flight, when arousal levels
may be reduced]. This study shows manual attempts to do this cause the
aircraft to "cycle" in and out of max alpha, in some actual cases exceeding
max alpha by 4+ degrees. Is this the way to go? Demonstrated results from
a sample of "envelope protected" aircraft, commencing avoidance at the same
parameter-set, show an average gain of 5 seconds of survival time, 1200
feet horizontally, and 100feet vertically. Let's see the data which
supports the argument that airliners "have been saved" by exceedence of
envelope limits! Lets have the details of such cases, if there really ever
was such an event. I know of no aerodynamic argument which would support
envelope exceedance as a optimal flight path.

There is a flight safety argument which makes "envelope protection" a
design responsibility, rather than an option for further discussion.


John Bent

At 04:35 29/03/97 -0800, you wrote:
>At 02:26 PM 3/25/97 -0500, you wrote:
>>I do have a serious thought on this: there can be no doubt that
>>differences in levels of automation, and differences in tasks
>>automated exist among manufacturers and airlines. More important, ....
>
>
>====Not that it matters Geff, but I 100% agree with your stand. There have
>been numerous incidents of 9+ G saves during the F-4 era...which can no
>longer take place with the F-16. I assume the one F-16 loss you mentioned
>was the Red Flag low level incident where the airplane ran out of airspeed
>and simply nosed into the ground?
>
>
>Another area of concern that I have is the availability of overboosting the
>engines to get short duration added thrust which might save an airplane and
>a lot of people...try that in an Airbus or other EEC equipped engine.
>
>However, while we can't get the extra when we need it we also will not be
>allowed to get it when we screw up. But then, that is what they pay pilots
>big bucks for...not to screw up too often.
>
>Reid
>
>
>