I have the same equipment in my IV-P as Fred, but am pressurized
and have winglets. I agree with Fred’s assessment below, and add the
following.
My Chelton gets “confused” on the ground, and
generates an audible stall warning during windy/gusty conditions…I
suspect it’s when the pitot senses enough wind to generate a speed input
below flying speed, but have not confirmed this. In any case, the warning can
be silenced, but reoccurs each time the Chelton thinks stall conditions are met…on
the ground—very annoying. I wound up disabling it using the internal software
setting. I have never had it generate an audible stall warning in the air, even
when calibrating the Jim Frantz AOA system, so suspect I’ve never gotten the
Chelton’s required airspeed, etc settings properly set.
The Advanced Flight Systems (bought from Jim Frantz) AOA has
worked very well, as Fred describes below. In-flight calibration was necessary,
and Bill Harrelson and I flew a couple of calibration flights, including
un-accelerated stalls, to set it up. Once calibrated, I could fly the airplane
at both ends of the weight limit and ease it onto the runway using the AOA. It
annunciates into my audio system, and I can pretty consistently get the words, “angle,
angle” just at touchdown…quitting before the rest of the phrase, “push,
push.” I really like it; probably works better than the similar
mechanical systems we used on the F-4 and F-111.
I must confess that the AOA system developed a problem a few
months ago that’s still bugging me. It seems to go into the test mode
randomly when powered up. AFS has checked the computer module, and I now
suspect a wiring harness problem, and am saving it for winter work. Guess this sounds
like I don’t practice what I preach…install and use an AOA…but
having been exposed to AOA systems for all of my AF flying, I am a believer…and
really like my system…when it’s working.
The Chelton is truly a magic EFIS, but it’s not an AOA;
too many limitations/assumptions to make it a useful tool for me/my specific
airplane.
Bob
From: Lancair Mailing
List [mailto:lml@lancaironline.net] On Behalf Of Frederick Moreno
Sent: Tuesday, October 06, 2009 1:23 PM
To: lml@lancaironline.net
Subject: [LML] FW: InFO 09015: Benefits of AOA Instrument in Lancairs
“Does anyone have the Chelton system
AND one of the AOA insturments installed, and has operational experience comparing
the Chelton's depiction of impending stall with the AOA's sequential indication
of impending stall?”
I
have the early Jim Frantz AOA unit (now called AOA Pro) and the early Chelton
IDU-1 with Pinpoint GADAHRS. I fly AOA for approach, with the
modification that when it gets bumpy, the AOA is very sensitive and quick, too
fast to be truly useful, so I cross check between AOA and airspeed which is
much slower to respond, and then fly airspeed once I have conformed the AOA
that I want at a particular landing weight.
The
Chelton is set up to speak in the head set along with the engine
monitor. Since my intercom has only two unswitched inputs, my AOA does
not verbally annunciate. However, my AOA is directly in my field of view
(see photo) since I use it as the primary indicator on final approach.
The
Chelton does a good job, particularly in the pattern when relatively slow and
you bank the airplane. It presents the visual stall warning descending
half circle in yellow if you tighten the base to final turn too much.
However,
the Chelton is not weight compensated when you are straight and level, one
G. For my airplane which is non-pressurized, the difference between light
(pilot only 20 gallons of fuel, about 2300 pounds) and heavy (four porkers,
some baggage and full fuel, about 3300 pounds) is substantial (43%), and
substantial adjustments in speed (like 20%) are required. I have no
winglets or wing span increases, just the bare 30 foot wing.
When
light I slow enough on final (maybe 90 knots) that the Chelton starts to
display warnings since it is calibrated to a heavier condition and thinks the
airplane is going too slow, but the airplane will still float on flare.
When really heavy, approaching maybe 105 or more on short final, the AOA shows
the lift reserve is getting smaller and smaller, but even through flare the
Chelton never squawks. Therefore the margin with the Chelton is fine when
heavy, but excessive when light the way I have it set up.
Conversely,
if you set your Chelton stall speeds based on flying at midweight, the Chelton
may not provide enough margin when heavy.
The
AOA always delivers a good result. Line up the bars at the right point
and it flies onto the runway with no float and stays planted, regardless of
weight. However, the amount of braking difference between heavy and light
is substantial as you might surmise.
Fred