Message-ID: <000e01c004d8$b5a1c9e0$bc080b3f@computername>
From: "Skip Slater" <skipslater@earthlink.net>
To: <lancair.list@olsusa.com>
Subject: Re: Computed AOA
Date: Sat, 12 Aug 2000 20:43:55 -0700
Reply-To: lancair.list@olsusa.com
Mime-Version: 1.0

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John,
   I seem to have struck a nerve.  My point wasn't to criticize the SFS
system per se (which I've seen but haven't flown) but to question the
accuracy of a computed AOA which is susceptible to user input errors and
assumptions about weight's effect on lift versus a display derived simply
from a sensor like Proprietary Software System's (PSS).  I agree it isn't
going to be accurate in all flight regimes where you may be at partial flaps
or gear, but then it isn't designed to be as capable as what you see in
jets.  As Jim pointed out, a vane or sensor the type of which we flew in the
Navy can't be put on a propellor powered plane like a Lancair.  As for how
accurate his system is, only Jim can answer that.
   I'm sure the PSS AOA system gives a stall warning with a few knots to
spare; it should.  But beyond a simple stall warning, you can visually see
on the display where your AOA is.  While that may not be of much use in
cruise, it sure could be in establishing a best angle glide in the event of
an engine failure, which would be accurate for any weight.  An example of
when you could really use an accurate L/D max display is in an extremis
situation such as a wake turbulance, mountain wave or windshear type episode
where you want to be squeezing all the Bernoullis of lift possible from your
wing.  In a case like that, you need to know how far beyond a stall warning
you can take your plane before it starts falling.  I don't know of a better
system available to us to determine that than the type Jim makes.  Granted,
we may only be talking about a few knots difference between the two systems,
but that's significant to me.
     I concur with you that the SFS system is impressive in it's
sophistification and complexity and I'm sure you'll be happy with it's AOA
display.  Heck, I'd like to have a SFS system myself if I could afford one.
But even if I could, I'd still be installing a PSS AOA as well.
   Cheers,
   Skip


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