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Colyn,
Yes. We all like to think
that if we just decide we will avoid dangerous situations, that situation can
never happen to us. We should read the bumper sticker: Shit
Happens. We can all be distracted for a few seconds, and suddenly, There
you are. Now what?
The FAA made a fatal change in
aircraft Type Certification requirements right after WW II. They caved
into pressure from the suddenly-powerful and huge new wartime aviation industry,
by rescinding the requirement that all general aviation aircraft should
demonstrate recovery from a six turn spin. Because, they pleaded, it was
very risky and very expensive to demonstrate. non sequitur
argument. Instead they pressured the bureaucracy to require what's
called 'Placard Safety"... but it is really a cop-out, whereby we avoid
deliberate stalls and the resulting spins. Now it's just to
demonstrate recovery from an incipient spin... the first top turns, during which
a plane usually unstalls itself once or twice.
But, what about
unintentional stalls and spins? That could never happen to
me? Now, we die, because the marketing department and the unwise do not
design planes to be able to recover ... like the aerobatic pilots
demand.
I remember like yesterday when
my instructor had me make a steep climbing turn in the SNJ, and cross the
controls. We were instantly over the top and upside down and entering a
spin.
The SNJ, however, was DESIGNED
to recover from unusual attitudes and spins ... He even had me demonstrate I
could recover from an inverted spin. The SNJ could do it. Any plane
can have its surfaces and CG range designed to do it.
You may recall that GenAv
designs from before WW II, like the Howard DGA, had to
demonstrated that they could recover from a six turn spin, at aft CG, to
get their Aircraft Type Certificate, and so they can ... because the airplanes
were designed to be able to.
Now we put top priority on
speed, ignoring the possible surprise, and use the (several, not all) laminar
airfoils that stall like you said ... see the dashed-line in the Lift/AOA curves
in Abbott & Doenhoff ... that stall at say 16 degrees, but won't
unstall till they AOA is reduced to half that. We are not told, and do not
know, at what angle of attack these critical airfoils will unstall ...
and it's not at the same AOA at which they stall. We do not know whether
our planes will 'trim', or deep-stall, at some CG and AOA combination. A
wind tunnel test could reveal that.
Further, as noted in my last
comment a few days ago on tails, we don't know when the horizontal tails stall
and lose at least half their unstall power.
The designers of GenAv, like
Piper, Cessna, etc., for 50 years now, use thin airfoils there, and high aspect
ratios, both characteristics result in stalls at low tail-AOAs... only a few
degrees past the wing's stall AOA. They ignore the lessons of the old
days, with stubby tails of low ARs and lots of leading edge sweepback,
which kept the tails unstalled and powerful to high AOAs.
It would be nice, wouldn't it,
to have some University use it's wind tunnel to do a Cl and Cmac survey of the
Lancairs, from zero to 90 degrees, plus and minus, and then modify the
tails, horizontal and vertical, until they could enable the pilot to
recover from any -- any -- unusual attitude.
The drag penalty, I believe,
would be less than perhaps 5 knots, if any at all.
The builders and pilots like
yourself on this list are remarkably experienced and rational, and the
excellent airplane designs we appreciate outperforms nearly everything, except
at high AOAs. Good guys and their loved ones are suffering. How
could this be remedied?
Comments and other viewpoints
could add more perspective.
Terrence O'Neill
N211AL
L235/320 (modifying the
horizontal tail)
----- Original Message -----
Sent: Monday, June 05, 2006 08:43
AM
Subject: [LML] Re: David Hickman
Crash
Far as I can tell Martin did an awesome job on
the structure of the LIVP.
Notably, Martin said to me "No one should ever
stall a LIVP"
I'm afraid I can't credit the statement "The wing
tip is not designed to stall and as such the question of how it stalls is not
relevant" The lift vs. AOA curve on that airfoil I can only describe as
discontinuous. It goes from 100% CL to 50% in a small fraction of a
degree. (like less than .2). Washout doesn't make that go
away. If the root has stalled and the tips are all that is flying and
they are just a little bit different in incidence, guess what happens
next? Washout only gives you a little more time to notice
what is going on and get flying again before that happens.
There is no question in my mind that you don't
want to go there. I think most of the community agrees.
There is a huge question in my mind why
experienced Lancair pilots get there. I don't suppose I am
better than any of them. but I wonder what happens in your mind
that you let it happen, and how you can prepare for whatever THAT
is.
Colyn
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