Airspeeds for calibrating GAP26 AOA indicator on a Bravo

[rbp]

As part of the new panel installation, I had the GAP26 AOA probe installed.

I am picking it up tomorrow, and the AOA system needs to be calibrated in the air by flying 4 different airspeeds and pressing some buttons on the G3X, as per the following diagram. The PDF file for the calibration procedure is attached. 

I'm looking for feedback on the airspeeds I'm intending to program in:

Stall Warning:   65 -- 1.1*59 (Vs0)
Caution Alert:   69 -- one kt less than 70KIAS -- Short field approach Flaps 33, P 4-4 AFM
Approach target: 75 -- Normal approach speed Flaps 33, AFM 4-4
Minimum Visible: 90 -- target speed on downwind

 

AOA Calibration.pdf

[adverseyaw]

75 KIAS and "just above stall" are the two airspeeds I used. Be sure to fly at the noted gross weight.

I'm curious to see if you can program it through the GTN -- the instructions you've sent are for the G3X (which I don't have) and my avionics guy gave me the simplified two-airspeed setup via the AoA display. I didn't even realize it could be configured through the displays.

[rbp]

Sorry, yes, I meant G3X. thans

You have the GAP26 on your Bravo?

I don't have the HUD annunciator, just the display on the G3X
 

75KIAS is the target (circle) airspeed? when does the first green segment show up? 

[rbp]

I created a spreadsheet that lays out the calibration procedure, including airspeeds and configuration 

[adverseyaw]

Yep, I've got the GAP 26 on my Bravo. I've got a G500TXi but have the GAP running through the HUD mounted just to the right of the roll cage center post.

The green circle shows up at your approach AoA, which will be 75 when at gross landing weight but typically less.

I haven't taken note of the airspeed where the first green bar comes on, maybe ten or fifteen knots above approach speed. In the HUD-only setup, this isn't an airspeed I choose directly, the system picks it based on Vs0 and 1.3Vs0.

[rbp]

did you do the calibration yourself? can you share the calibration data? 

[carusoam]

Note for @adverseyaw above…

-a-

[adverseyaw]

I did, but I only have the HUD so I'm not sure if I can get the calibration data out.

I'm curious to see how the numbers differ across different airplanes, but I have doubts about whether you could meaningfully use or compare the values. Every probe installation will differ in position and angle, and even Bravo airfoils differ with/without TKS sleeves.

[rbp]

6 hours ago, adverseyaw said:

I did, but I only have the HUD so I'm not sure if I can get the calibration data out.

I'm curious to see how the numbers differ across different airplanes, but I have doubts about whether you could meaningfully use or compare the values. Every probe installation will differ in position and angle, and even Bravo airfoils differ with/without TKS sleeves.

It’s in the configuration page

 

I’m not trying to steal the numbers. You can’t merely type them in I’m just curious about the comparison

[adverseyaw]

I think you're referring to the configuration page on the G3X but I don't have a G3X.

[rbp]

 

6 hours ago, adverseyaw said:

I did, but I only have the HUD so I'm not sure if I can get the calibration data out.

 

how did you perform the calibration? can you share the instructions? 

[exM20K]

6 hours ago, adverseyaw said:

I did, but I only have the HUD so I'm not sure if I can get the calibration data out.

I'm curious to see how the numbers differ across different airplanes, but I have doubts about whether you could meaningfully use or compare the values. Every probe installation will differ in position and angle, and even Bravo airfoils differ with/without TKS sleeves.

I don’t see an actual stall anywhere in this procedure.  It is worthwhile to put the plane in landing configuration and take it to a stall or incipient stall to see what *your* plane’s IAS is.  @K.Kammer told me once the weight/CG that the test pilots use is, 3000 and 46” IIRC.  Mine, with TKS, was right on the book number, but I’ve owned planes with airspeed indicators that were significantly off.

-dan

[adverseyaw]

It doesn't look like I have the printout of the installation manual my avionics shop gave me. Going from memory, it was: 1. Hold the Set button down in straight and level flight, 2. Get to 1.3Vs0 and press the set button, 3. Get to just above stall and press the set button. The instructions were about two pages long with diagrams but that was the gist of it. It took about ten minutes once on station to fly the profile as it takes time to fully stabilize on a specified airspeed. It was similar to creating a glide polar, just abbreviated to only two airspeeds.

Finding the actual stall speed is a prerequisite, I agree. Mine was within a knot of the published speed. In my view, the Garmin procedures are correct, they just require a test pilot mindset.

Edited April 30, 2022 by adverseyaw

[rbp]

regarding airspeeds, I created a worksheet that calculates the various airspeeds based on weight: https://docs.google.com/spreadsheets/d/1LO5Z3rV3T97boM30R7PXCXU____-gLr291xOL_Ks4-I/edit?usp=sharing

i took 59 (Vso), 70 (shortfield), and 75 (normal) based on the speeds in the M20M AFM, to yield 65, 69, and 75 as the target airspeeds for Stall, Caution, Target at MGTOW, which is then adjusted for actual weight based on the Lift Equasion (https://www.grc.nasa.gov/WWW/K-12/airplane/lifteq.html) 

and i want the indicator to come on below 90KIAS (Min Visible)

Edited April 30, 2022 by rbp