Doug.
...What Scott said.
Terrence
Sent from my iPad
Doug,
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.
Scott Krueger
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:
I am thinking of adding an AOA to
my plane. The two models that I am looking at are the Bendix King KLR 10
(http://www.bendixking.com/Products/Flight-Controls-Indicators/Indicators/KLR-10)
and one of the Alpha Systems units (http://www.alphasystemsaoa.com/)
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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