Re: Power for Take-Off

Date:         17 Sep 97 02:49:23 
From: (Mary Shafer)
Organization: NASA Dryden Flight Research Center, Edwards CA
References:   1 2 3
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On 11 Sep 97 03:35:31 , (PAUL G MAYER) said:

Chris Dahler ( wrote:

: All multiengine aircraft, from light piston twins to the B-747, have
: to be able to accelerate to takeoff speed, lose an engine, and still
: be able to meet certain climb criteria before the FAA will certify
: the aircraft as airworthy.  <snip>

P> Not quite.  It's true that FAR 25 aircraft must meet minimum
P> one-engine out climb criteria in order to be certified.  However,
P> "light piston twins" are certified under FAR 23 which has no such
P> requirement.  In hot and high conditions (such as here in Las
P> Vegas, NV) it is quite common to takeoff in a light twin that WILL
P> NOT FLY if one engine decides to take the rest of the day off.

Not that this has anything at all to do with certified aircraft (GA or
airline) but the SR-71 is pretty marginal on one engine with the gear
down, in or out of ground effect.  Looking at the charts in the Dash 1
Appendix I, it's pretty obvious that it's possible to take off below
single-engine minimum control speed, as well as not being able to fly
level, let alone climb, depending on weight, wind and so on, and where
you are in the climb.  The emergency procedures section on takeoff
makes this pretty explicit, with aborting, with a warning about
single-engine directional control speed, as the first possibility and
ejecting as the only possibility if the plane won't accelerate or
climb.  (I've just checked the Dash 1 and NATOPS manual for two other
planes and this latter doesn't seem to be likely enough to mention,
except for the general discussion at the beginning of the section.)

When this issue came up in the safety reviews for the SR-71 with the
LASRE experiment mounted on the back, the question was resolved by
reference to our having already regarded the possibility of losing an
engine when still below minimum single-engine control speed as an
accepted risk, as it was part of the operational envelope of the
aircraft.  Adding the experiment didn't change this risk enough to
change our assessment of it.  The same was true, by the way, of the
question of how much the added drag increased the takeoff distance, as
the concern was whether we'd have enough of the 15,000 ft runway left
to abort in.  Simulation and calculation determined that the increase
was only about 75 ft, mostly since drag isn't very high at the lower
speeds, so we crossed this one of the list of serious concerns, too.
We are, however, going to do some very careful analysis of the data
from the taxi tests and envelope-expansion flights.

Mary Shafer               NASA Dryden Flight Research Center, Edwards, CA
SR-71 Flying Qualities Lead Engineer     Of course I don't speak for NASA                               DoD #362 KotFR
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