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EMAproducts(at)aol.com
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 Posted: Sun Feb 13, 2011 6:06 pm Post subject: AOA |
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My comment on icing and AOA systems ~~If you encounter any type of icing turn the AOA OFF unless you have full de-icing vane & aircraft. We haven't even done R&D on a heated vane because of liability. Even Boeing can't give you hard numbers with icing on wings. Heated vane and icing on wings is NOT a good deal!
Elbie Mendenhall, EM Aviation, LLC www.riteangle.com
Is it your understanding that Elbie
| Quote: | claims that the "sweet spot" on his or any other
AOA display is golden under all challenges that
a pilot might face for comfortable arrival with
the earth?
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[quote][b]
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nuckolls.bob(at)aeroelect
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| Posted: Mon Feb 14, 2011 7:12 am Post subject: AOA |
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At 08:03 PM 2/13/2011, you wrote:
| Quote: | My comment on icing and AOA systems ~~If you encounter any type of icing turn the AOA OFF unless you have full de-icing vane & aircraft. We haven't even done R&D on a heated vane because of liability. Even Boeing can't give you hard numbers with icing on wings. Heated vane and icing on wings is NOT a good deal!
Elbie Mendenhall, EM Aviation, LLC www.riteangle.com |
Exactly. The fleet of bizjets at HBC were all
qualified for flight into known ice. Everything
was heated or hammered.
I'll have to call some of my jet-jockey friends
at HBC and inquire as to words in the POH concerning
usefulness and cautions about AOA displays
on the production fleet.
I worked a REALLY strange problem on the Beechjet
some years back were pilots experienced loss of
IAS on BOTH sides of the airplane. Displays always
recovered at lower, warmer altitudes.
This often occurred in relatively clear air.
There was a LOT of brainstorming by a LOT
of grey beards as to the physics behind this
rare but disturbing event.
My task involved cutting a pitot tube open,
peppering it with thermocouples and putting
it back together again so that we could study
not only temperatures at the surfaces to be
de-iced but internally. There was some question
of ice crystals bouncing through the labyrinth
of pressure channels only to melt and re-freeze
inside the pitot tube.
During the fire drill for sniffing out root cause,
somebody asked the question: "How does the existence
of a working AOA display help the pilot who is
temporarily deprived of IAS?" Good question.
The Beechjet had been fitted with AOA indication
since its birth as the Mitusbishi Diamondjet.
But nobody had ever researched and written the
approve procedure for using AOA as an aid to
maneuvering without IAS.
That amendment was quickly added to the POH.
I'm not sure we ever deduced how pitot pressure
was being obstructed. I'll have to ask how that
problem resolved too. But it was interesting
that a perfectly useful display had existed
for so long but was never fully developed as a
component of plan-b, plan-c, etc. Shucks, with
DUAL air data systems, what are the odds?
Bob . . . [quote][b]
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dvanwinkle(at)royell.org
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| Posted: Tue Feb 15, 2011 11:14 pm Post subject: AOA |
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Bob
I just noticed your comments about loss of IAS on both sides of the Beechjet. l attended 2 of your Seminars and I know we talked about both having worked for Cessna. When I left Cessna as a Flight Test Engineer in 1968, I went to work for the Army Aviation Systems Cmd in St Louis as a Dept of Army Civilian Senior Aeronautical Engineer and was there for 28+ years. Most of my time there was spent with the Army's Fixed Wing Electronic Intelligence Gathering Aircraft. In the later years I was the Army Technical Manager for 7 different versions of the RC-12 (Super Kingair 200), the last 4 versions comprised of 36 aircraft with 1200 SHP engines and Gross Weights in the 16,000 to 16,500 lb range. In the early '90s, we took the RC-12N configuration which had the largest antenna array to Duluth, Mn in January for natural icing tests. The Army test crew from EAFB had a specially instrumented U-21 to search for icing conditions and would then call out the RC-12N. I rode with the Army test crew on flights 2 and 3 as a FTE/ Observer. On flight 2, we were in a low stratus layer around 3000 ft MSL, 140 KTS, about 45% cruise power. At 50 minutes we has collected 5 1/2 inches of ice with all of the deice going, at 90% cruise power for the same air speed and had just lost the right pitot airspeed. About 3 minutes later we lost the left pitot airspeed. About 2 minutes later, we climbed out of the low stratus layer so the U-21 could get photos of the ice buildups. Fortunately the U-21 was able to get a picture of the right pitot which showed that ice had grown forward on the unheated pitot mast and then curved downward to block the pitot inlet, at no time actually touching the pitot tube itself. Before the U-21 could move to the left side, the left mast had lost enough ice that the left airspeed had come back and a few minutes later the right airspeed was back. Beech attempted to get some heat in the mast , but abbreviated tests the following winter showed that it was insufficient. Bob, I don't know whether the Beechjet used the same pitot units or a similar design, but that was our findings on the Model 200.
Alden Van Winkle
Slo Build RV-9A
dvanwinkle(at)royell.org (dvanwinkle(at)royell.org)
[quote] ---
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