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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:
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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