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Chris,
Since Advanced Flight Systems bought the AOA system from Jim Franz, I
assume (dangerous) they kept the setting logic - two points clean and two points
with the flaps beyond 1/3 along with a sensor to detect the flap
position. Stall AOA changes slightly as a relative wind angle from
the wing chord line which may change somewhat with some flap extension
(usually used in landing config) The beyond 1/3 flap setting was
conservative as the original (circa 1998) was to be set up for beyond
the 2/3 flap position.
I have no idea what other systems use as the critical AOA sense
logic if they are not using upper/lower wing pressure.
The only problem with the wing pressure sensing system is that it is
set up on one wing - what about what the other one is doing???? Huh????
Huh????
Scott
In a message dated 3/31/2014 3:02:24 P.M. Central Daylight Time,
chris_zavatson@yahoo.com writes:
"[Don't forget that you can stall an airplane at almost any
airspeed, but the critical angle of attack at which the wing stalls will
always be the same. While 80-90 knots might be a "safe" airspeed flying
straight & level & lightly loaded, if you increase the wing loading
with a 60 degree bank (or simply load up with full tanks & baggage), your
80-90 knots might just not be so safe anymore. If you go to http://www.advanced-flight-systems.com/Support/AOAsupport/AOA%20Manual%20rev4.pdf and scroll down to page 17 (The
"How it works" chapter) you'll have a better understanding of the "gotchas"
that conventional flight training has always danced around concerning AOA.
Just my $0.02. <marv> ]"
It seems two alarm set points would be
beneficial. One, more narrowly focused once on final, and another with a
greater margin for everything else.
Chris Zavatson
N91CZ
360std
On Monday, March 31, 2014 10:42 AM,
"Sky2high@aol.com" <Sky2high@aol.com> wrote:
Doug,
There is always room for refinement.
A fighter pilot is not a Lancair pilot. Did he land your
plane? Perhaps your question would be best answered by an experienced
Lancair Instructor.
In certificated type airplanes that are built to the same
specs and on jigs, Vso is test flight determined - perhaps for
max gross weight, rearward CG loading, etc. Perhaps not. But,
usually these aircraft go through thorough stall tests at various flaps
setting, weights and CGs with the stuff out. Then Vso is determined in
reality or is computed and verified from design specs.
Notice that V speeds are IASs. This can work because the
IAS indication is calibrated via flight test and the correction data for
position, instrument and system error is noted in the
POH. Of course, one wonders if the correction data was obtained at all
attitudes (AOA) and speeds.
I believe your aircraft is unique as denoted in the manufacturer's field
on the registration form. So, has your ASI been calibrated? Was
Vso determined through exhaustive tests at differing parameters?
I don't know if you can get creative with your AOA
system settings as I am not familiar with it. I did use the
forerunner to the Advance Systems system that uses upper and lower wing
pressures along with pitot-static data to determine AOA. The slope of
the straight line function was established by flight-setting two
points on that line.
Vso x 1.3 (if a useful Vso is known) may not provide enough
safety margin for high performance Lancairs in differing configurations
and weather conditions - like turbulence on final or trying to fly close in
square patterns.
There are techniques to overcome slowness or dangerous flat approaches
such as a steeper approach angle to retain enough kinetic energy for flight
path corrections, although this requires care to stop the descent high
enough above the runway.
Good luck,
Scott Krueger.
In a message dated 3/31/2014 6:35:55 A.M. Central Daylight Time,
douglasbrunner@earthlink.net writes:
Scott,
I
understand that the AOA takes into account atmospheric conditions, g
loading, weight of the plane, etc. That is why I am interested in it
rather than just using airspeed. My problem is that one of the points
to be used for calibration is, in my opinion, a subjective
point.
You
say that 1.3 Vso is dangerous with a high performance wing. What
number is a better one?
I
was taught to fly final at 110 and to slow to 90 over the numbers – which is
what I normally do. Recently, I flew with a retired fighter pilot who
told me I was too fast on final. I told him that it was better to be
too fast and land long than be too slow and stall. But it started me
thinking about a more optimal speed given how much runway I frequently
use.
From: Lancair
Mailing List [mailto:lml@lancaironline.net] On Behalf Of
Sky2high@aol.com
Sent: Sunday, March 30, 2014 5:24
PM
To: lml@lancaironline.net
Subject: [LML] Re: FW:
Adding an AOA
Sophisticated
AOA indications take into account atmospheric conditions and G-loading along
with IAS. In theory, there are straight line functions between
interesting points on the relevant AOA such as best glide, stall, etc.
The old fashioned 1.3 Vso is dangerous in aircraft with high performance
wings - because the stall speed does vary with G-load and, uh, the
air. In Lancairs, 1.3 Vso does not provide proper margins in all
cases.
The
sophisticated AOA systems need only 2 points on the straight line to
calibrate the function (uh. the parallel straight line moves because of
the other parameters. Some system calibrations do not require the
stall point as one measure (see Advanced Systems). Some require
the zero G (zero lift) point as one. Be careful.
Simpler
system rely merely on AOA to the relative wind. This is useful because
exceeding the stall AOA results in a stall. The sophisticated
systems yield other useful information (best glide, etc).
Do
further study to educate yourself about AOA.
Terrence,
There
is no “angle” to mark. Both instruments use an array of colored
lights - in both, the top colored light is a red arrow pointing down
– presumably this is to indicate a stall.
The
way that both are made to be used is to define a safe speed (roughly 1.3
Vso) that can be used during landing (and other maneuvers)
My
question was whether to set it to 1.3 Vso or to do the maneuver described
in the setup.
D.
Brunner
D.,
IMHO the
prime purpose of an AOA is:
To make
the wing's STALL ANGLE visible to the pilot. You do that by
flying the plane and stalling it as you watch the AOA... then mark that
angle.
The next most
useful AOA info is the best L/D or best R/C... done the same way... fly
the plane while watching the best R/C for a given power setting, and make
that angle.
On Mar 30,
2014, at 9:23 AM, Douglas Brunner wrote:
My question has
to do with the calibration. Both systems require a calibration at 3
points:
The “on ground”
and “cruise” are self explanatory, however the definition of “Optimum
Alpha Angle” seems a little “loosey-goosey” to me. Here are the
definitions:
Alpha Systems
“Optimum Alpha Angle”
· Able to hold
altitude – as close to 0 VSI as possible, zero sink
· Full aileron,
elevator and rudder control – no buffet or loss of control surface
stability
Bendix King
“Optimum Alpha Angle”
· Able to hold
altitude, 0 Vertical Speed, zero sink (5 to 10 fpm climb OK)
· Full aileron,
elevator and rudder control, not in a buffet, pilot to identify the set
point by
pitching back
slowly to a pitch no longer able to climb but able to hold altitude with
full
First of all,
since this is a system meant to be used in landing (or at least that is
how I will mostly use it), I intend to calibrate the “Optimum Alpha Angle”
in landing configuration (gear down, full flaps). However,
determining when I have “full aileron, elevator and rudder control” isn’t
all that clear to me. I am sure that I can tell when I have aileron,
elevator and rudder control – but the “full” part is less clear.
Does that mean a full control deflection? Not something I am anxious
to try that close to stall.
Alternatively,
I could just do a stall in landing configuration and set the “Optimum
Alpha Angle” to 1.3 x stall.
D.
Brunner
N241DB 750
hours
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