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AOA Calibration Question

L

lr172

Well Known Member
I am calibrating my G3X AOA and wondering the best recommendation for calibrating the On speed or green dot. I will use the recommended 1.3 X full flap stall speed. However, I am wonder what do do about power. I can either do it power off and a moderate decent rate or add some power and shallow out the decent. I am pretty sure this will result in different AOA angle results. I can also do it with or without flaps.

I know this is a good tool to have for approaches and landing phase, so want to be sure to set it up properly. It will be used in situations with both flaps (landing) and no flaps (approaches) and typically with a bit of power. However, not really sure if that means that I should be duplicating this in the setup.

A second question. Should it be 1.3 times the clean stall or full flap stall.

Hoping the experts can weigh in with guidance. My GrT computed this automatically and it works very well. The Garmin docs don't provide any significant guidance.

Larry
 
I don’t know the exact answer but I remember thinking about the same things. I suggest reading everything related to the ON SPEED project threads on this forum and here https://www.flyonspeed.org/. I’m sure you’ll find the information you’ll need to decide how to do it regarding the flaps and the power settings.
 
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Don?t overthink it. Remember, the airplane stalls at the same aoa, regardless of airspeed or power setting. I calibrated mine as described by the manual, and i get proper stall warning at all flap/power settings
 
Performance AOA Cues vs Progressive Stall Warning

Larry,

Short answer: IDLE. Steve is correct, the angle does not change.

Background: All AOA systems provide progressive stall warning. Some AOA systems, when properly calibrated, may provide performance cues. Examples of performance cues are best range, L/Dmax, and ONSPEED. In order to display these cues, the system has to accurately capture the "aircraft curve" and have proper "set points." Currently, all AOA systems require some sort of calibration, and if that's not done correctly, the "garbage in = garbage out" algorithm applies.

The OP is looking for an ONSPEED set point, so the answer is to calibrate IAW Garmin instructions (to set the aircraft curve) and then conduct some flight test. 1.3 Vs is where to look for ONSPEED, and if the Garmin system only captures one aircraft curve (i.e., you don't calibrate it for multiple flap settings), then multiply your normal landing flap configuration (Flaps 40 in the RV-6, and Flaps 30 in the RV-10) 1G stall speed by 1.3 and start there.

A single-curve calibration can actually work pretty well in an RV-3/4/6/7/8. The RV-9/10 and 14 require at least two curves because of the slotted flaps on those airplanes. Slotted flaps are more effective than plain flaps and have a bigger influence on AOA for the same size flap. For an RV-10, without a flap sensor or AOA that computes multiple curves, the answer is 1.3 x Flaps 30 stall speed (although you may want to tweak the final result + or - a bit based on your pitot/static accuracy). If the system has audio cues, there may be a setting that allows you to hear this parameter as well, which can be helpful. With flaps up, you'll still get AOA cues, but they won't be accurate for performance. Some progressive stall warning may be provided, but it may differ (i.e., how much in terms of airspeed) from what you see with flaps deployed. So calibrate for flaps down and then test a bit. Learn the difference between flaps down and flaps up during approach and landing, so that if you have to land flaps up for whatever reason, you learn whether or not you have to fly a different cue.

I don't want to highjack yet another AOA thread (or have this turn into a physics debate!), so recommend you take a look at our website at flyonspeed.org. Feel free to drop a line as well.

Cheers,

Vac
 
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Vac said:
Larry,

Short answer: IDLE. Steve is correct, the angle does not change.

Background: All AOA systems provide progressive stall warning. Some AOA systems, when properly calibrated, may provide performance cues. Examples of performance cues are best range, L/Dmax, and ONSPEED. In order to display these cues, the system has to accurately capture the "aircraft curve" and have proper "set points." Currently, all AOA systems require some sort of calibration, and if that's not done correctly, the "garbage in = garbage out" algorithm applies.

The OP is looking for an ONSPEED set point, so the answer is to calibrate IAW Garmin instructions (to set the aircraft curve) and then conduct some flight test. 1.3 Vs is where to look for ONSPEED, and if the Garmin system only captures one aircraft curve (i.e., you don't calibrate it for multiple flap settings), then multiply your normal landing flap configuration (Flaps 40 in the RV-6, and Flaps 30 in the RV-10) 1G stall speed by 1.3 and start there.

A single-curve calibration can actually work pretty well in an RV-3/4/6/7/8. The RV-9/10 and 14 require at least two curves because of the split flaps on those airplanes. Split flaps are more effective than plain flaps and have a bigger influence on AOA for the same size flap. For an RV-10, without a flap sensor or AOA that computes multiple curves, the answer is 1.3 x Flaps 30 stall speed (although you may want to tweak the final result + or - a bit based on your pitot/static accuracy). If the system has audio cues, there may be a setting that allows you to hear this parameter as well, which can be helpful. With flaps up, you'll still get AOA cues, but they won't be accurate for performance. Some progressive stall warning may be provided, but it may differ (i.e., how much in terms of airspeed) from what you see with flaps deployed. So calibrate for flaps down and then test a bit. Learn the difference between flaps down and flaps up during approach and landing, so that if you have to land flaps up for whatever reason, you learn whether or not you have to fly a different cue.

I don't want to highjack yet another AOA thread (or have this turn into a physics debate!), so recommend you take a look at our website at flyonspeed.org. Feel free to drop a line as well.

Cheers,

Vac
Click to expand...

Thank you Mike! Very helpful. A quick follow up question. Should I have the flaps 30 on the 10 when I do the 1.3 calibration? I did the stall and 1.1 calibrations with the flaps down. I am guessing that the 1.3 should be the same to give a proper curve. The garmin instructions do not specify whether to use them or not, though it offered the ability to use either for the full stall setup, based upon preference.

The garmin setup has you calibrate at 1.1 to set where the caution begins and when the tones start. Given that I stall at 50 and 61 (no flaps), should I consider setting the caution at 1.2 to get tones near the stall in no flap conditions? That will change the curve though.

Larry
 
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Larry,

Yes, use 1.3 Vs flaps 30 for your set point (keep all of your apples apples :)).

I'm not sure whether or not Garmin factors the 1.1 stall into their aircraft curve algorithm, so just use 1.1 Vs flaps 30 for now and then after your calibration is complete, experiment. Any single-curve calibration is going to be challenged in the -10. You want the most accurate performance in a normal landing configuration, so dial that in first and then see how things work at other flap settings and flaps up. Perhaps a Garmin expert can chime in on this.

Also, the 1.3 Vs is just a starting point. With the single-curve Dynon system, I ended up at 1.25 Vs flaps 40 (RV-4) for a final set-point.

Post or drop a line and I'll be happy to help or answer questions.

Good luck!

Vac
 
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Larry,

It doesn't matter what power setting or descent rate you use. What matters is that you are on a stabilized airspeed with wings level. The airspeed indicator is smoothed for readability and has a few seconds of delay. So trim to your desired airspeed, let it stabilize for a good few seconds and calibrate your Approach Target AOA (what G3x calls it) for that angle. Set it and then verify by flying it a couple of times.

Also make sure you recalculate your 51kts and 60kts stall speeds to current weight. Those numbers are for max gross weight. Here's the correction formula:

Vs-corrected = Vs-gross x the square root of (current weight / gross weight)

Or even better, just fly the stalls, record the numbers, and then fly the proper 1.3x approach speeds for calibration. No need for weight correction. Pitot tubes can have pretty big errors at those high angles of attack, so it's not a great idea to use book values.

It will take some getting used to flying such "slow" approaches when solo in the -10. :)

Lenny
 
Vac said:
Larry,

Yes, use 1.3 Vs flaps 30 for your set point (keep all of your apples apples :)).

I'm not sure whether or not Garmin factors the 1.1 stall into their aircraft curve algorithm, so just use 1.1 Vs flaps 30 for now and then after your calibration is complete, experiment. Any single-curve calibration is going to be challenged in the -10. You want the most accurate performance in a normal landing configuration, so dial that in first and then see how things work at other flap settings and flaps up. Perhaps a Garmin expert can chime in on this.

Also, the 1.3 Vs is just a starting point. With the single-curve Dynon system, I ended up at 1.25 Vs flaps 40 (RV-4) for a final set-point.

Post or drop a line and I'll be happy to help or answer questions.

Good luck!

Vac
Click to expand...

Thanks for the generous guidance on this.

Larry
 
Lenny Iszak said:
Larry,

It doesn't matter what power setting or descent rate you use. What matters is that you are on a stabilized airspeed with wings level. The airspeed indicator is smoothed for readability and has a few seconds of delay. So trim to your desired airspeed, let it stabilize for a good few seconds and calibrate your Approach Target AOA (what G3x calls it) for that angle. Set it and then verify by flying it a couple of times.

Also make sure you recalculate your 51kts and 60kts stall speeds to current weight. Those numbers are for max gross weight. Here's the correction formula:

Vs-corrected = Vs-gross x the square root of (current weight / gross weight)

Or even better, just fly the stalls, record the numbers, and then fly the proper 1.3x approach speeds for calibration. No need for weight correction. Pitot tubes can have pretty big errors at those high angles of attack, so it's not a great idea to use book values.

It will take some getting used to flying such "slow" approaches when solo in the -10. :)

Lenny
Click to expand...

Thanks Lenny. My 50/61 were observed stall speeds while solo. I haven't done any testing with additional weight yet. If I do all the different calibrations solo, I am assuming they will still work well when at gross. Is that correct?

I have noticed interesting low speed approaches solo. Looks like I am diving to the airport if I am a tad high and dropping some altitude, like I am used to doing in the 6. They are some powerfull flaps. Starting to get used to it. I have noticed that if do a std. FAA approach it is much better, but I am just so used to the steep approaches in my 6 that I will need a bit of retraining or get used the the big pull in the flare.

For those that may be following this, I used a simple rivet in the wing for AOA and not a combo pitot. My kit had a gretz heated pitot and thought I would try this before dropping the coin on a garmin or dynon pitot. Seems to have worked well. I stole the idea from the 12 kits and Scott was very helpfull in sharing what was learned through the 12 aoa port testing.

Larry
 
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Energy on Final

Larry,

A few points to ponder in no particular order:

1. Nothing wrong with a 3 degree final, it just may require that you carry some power. Any power-off final is going to coincide with glide angle for the configuration you're flying. Totally fine to "fall" down (i.e., descend at glide angle) to a 3 degree wire, make a pitch and power adjustment and catch it. I do that as a matter of course in a visual pattern and like to be stable 10-12" prior to touchdown. Having a solid ONSPEED AOA cue, really helps with pitch and power adjustments.

2. The slotted flaps in the -9/-10 and -14 are more powerful than the plain flaps in the -3/4/6/7/8 and have a greater impact on performance.

3. After calibration, the proper way to use AOA to land is to apply a "trust, but verify first" matrix. As you develop experience, you will have known 1 G IAS "check points" for different weights. So, each approach, you initially cross-check for nominal airspeed, and can then transition to alpha.

4. An "alpha" approach may seem slow until you gain experience with the technique. Because you know AOA, you know what your aerodynamic margin is (i.e., how far from the stall you are) and you also know what your energy is (i.e., the 1.2-1.4 Vs you used to calibrate your system). The best thing about carrying proper energy into the flare is that you'll find your aim point and touchdown to be much more consistent.

5. I use the basic USN landing technique: slow to ONSPEED, maintain ONSPEED using fine pitch corrections and control glideslope using throttle. Works equally well in a visual pattern or on the gauges. I just flare at the end ;)

BTW, excellent idea to pull one of your pressures from a wing rivet. That's some solid EAB thinking!

v/r,

Vac
 
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Vac said:
Larry,

A few points to ponder in no particular order:

1. Nothing wrong with a 3 degree final, it just may require that you carry some power. Any power-off final is going to coincide with glide angle for the configuration you're flying. Totally fine to "fall" down (i.e., descend at glide angle) to a 3 degree wire, make a pitch and power adjustment and catch it. I do that as a matter of course in a visual pattern and like to be stable 10-12" prior to touchdown. Having a solid ONSPEED AOA cue, really helps with pitch and power adjustments.

2. The slotted flaps in the -9/-10 and -14 are more powerful than the plain flaps in the -3/4/6/7/8 and have a greater impact on performance.

3. After calibration, the proper way to use AOA to land is to apply a "trust, but verify first" matrix. As you develop experience, you will have known 1 G IAS "check points" for different weights. So, each approach, you initially cross-check for nominal airspeed, and can then transition to alpha.

4. An "alpha" approach may seem slow until you gain experience with the technique. Because you know AOA, you know what your aerodynamic margin is (i.e., how far from the stall you are) and you also know what your energy is (i.e., the 1.2-1.4 Vs you used to calibrate your system). The best thing about carrying proper energy into the flare is that you'll find your aim point and touchdown to be much more consistent.

5. I use the basic USN landing technique: slow to ONSPEED, maintain ONSPEED using fine pitch corrections and control glideslope using throttle. Works equally well in a visual pattern or on the gauges. I just flare at the end ;)

BTW, excellent idea to pull one of your pressures from a wing rivet. That's some solid EAB thinking!

v/r,

Vac
Click to expand...

Thanks! Very helpfull.
 
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