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

 

From: Lancair Mailing List [mailto:lml@lancaironline.net] On Behalf Of Terrence O'Neill
Sent: Sunday, March 30, 2014 2:18 PM
To: lml@lancaironline.net
Subject: [LML] Re: FW: Adding an AOA

 

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.

 

Terrence

L235/320

N211AL

 

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:

1.      On Ground

2.      Optimum Alpha Angle

3.      Cruise

 

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

control of the airplane.

 

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.

 

Advice?

 

D. Brunner

N241DB 750 hours