AOA INDICATOR

What kind of experience? A couple folks here have different types installed.
 
Specifically interested in the classic USN green/red chevron with center ball.
Very useful tool. Difficult or expensive installation? Where to find?
Thanks
 
With a couple thousand hours using the classic USN system, I came to the conclusion that the KLR-10 was the answer for a certified airplane. I never bought it though, went the experimental route. In any case, you want audible output, so you dont have to look at the indicator from base to final. JMHO.
 
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catmandu said:
With a couple thousand hours using the classic USN system, I came to the conclusion that the KLR-10 was the answer for a certified airplane. I never bought it though, went the experimental route. In any case, you want audible output, so you dont have to look at the indicator from base to final. JMHO.
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NordicDave said:
Not exactly wha the OP was asking for, but this system looks interesting.


Write-up: https://www.mountainflying.com/Pages/articles/alpha_systems_aoa.html
Unit at Spruce: https://www.aircraftspruce.com/cata...eSBmNoqIaDXhLJGbSB1H-KqOM8C5AiScaAtmwEALw_wcB

Company website: http://lift-mgt.com

I'm looking at this analog system over a digital version. I'm also not a big fan of the prob-less AOA systems. I'd like to know when left actually starts the leave the wings than a calculation there of.
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Many thanks,
Looks like $2,000 ish parts and install.
Agree completely with analog over digital.
Another “project”.
Merry Christmas, Prosperous New Year!
 
catmandu said:
With a couple thousand hours using the classic USN system, I came to the conclusion that the KLR-10 was the answer for a certified airplane. I never bought it though, went the experimental route. In any case, you want audible output, so you dont have to look at the indicator from base to final. JMHO.
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One of our club 172s has an AoA gauge very much like the standard Navy one we had in the Prowler. It's where they belong up on the glare shield and in your scan in the pattern. I flew the on-speed doughnut right to touchdown the first time.... Whoops. :eek:

I do like having it and suspect I will when it comes to my forever airplane.
 
I have one, I use it, I just don’t trust my life with it... I have trust issues but that’s for a different post
 
Flew on for a while, I do like them especially in ice and odd conditions, but for a light weight plane not sure I’d really bother, now I wouldn’t take one off the plane if it was already there
 
WannFly said:
I have one, I use it, I just don’t trust my life with it... I have trust issues but that’s for a different post
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Must make things difficult in IMC, trusting those instruments and all...o_O
 
WannFly said:
I have one, I use it, I just don’t trust my life with it... I have trust issues but that’s for a different post
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This video pretty much sums it up: https://www.ispot.tv/ad/oieq/xfinity-app-the-slowskys-directions

xfinity-app-the-slowskys-directions-large-2.jpg
 
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Isn't the alpha systems a good enough match?
 
Does the accuracy on some of these indexers/indicators vary and or degrade with increasing degree of bank angle? As in steep bank base to final slow airspeed config. Seems that would be a very practical condition to have reliable lift reserve information.
 
n2230b said:
Does the accuracy on some of these indexers/indicators vary and or degrade with increasing degree of bank angle? As in steep bank base to final slow airspeed config. Seems that would be a very practical condition to have reliable lift reserve information.
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The typical differential pressure or rotating vane/probe systems will still indicate within the normal accuracy of the system* assuming coordinated flight, i.e. no sideslip/ball-centered/no slip or skid, however you choose to refer to it.

The 'lift reserve' system is very similar to a differential probe AOA system without the calculation/calibration to convert differential pressure to angle of attack. I speak only for myself, but I'm not a fan of them.


* Hard to say they'll be accurate without knowing how accurate a particular system is in wings-level flight. If it's accurate at some AOA wings-level it will be accurate at that same AOA in a bank - again, assuming coordinated flight.

Nauga,
at the chevron station
 
nauga said:
The typical differential pressure or rotating vane/probe systems will still indicate within the normal accuracy of the system* assuming coordinated flight, i.e. no sideslip/ball-centered/no slip or skid, however you choose to refer to it.

The 'lift reserve' system is very similar to a differential probe AOA system without the calculation/calibration to convert differential pressure to angle of attack. I speak only for myself, but I'm not a fan of them.


* Hard to say they'll be accurate without knowing how accurate a particular system is in wings-level flight. If it's accurate at some AOA wings-level it will be accurate at that same AOA in a bank - again, assuming coordinated flight.

Nauga,
at the chevron station[/QUO

Your observation regarding coordinated flight is crucial and goes to the heart of my question. Also agree with analog v indirect-derived indications. I tend to lean towards the vane system......and likely it is the most fragile, difficult to calibrate as well as most expensive. You think this would be a job for an avionics shop or is it something an A & P might do?
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n2230b said:
Your observation regarding coordinated flight is crucial and goes to the heart of my question. Also agree with analog v indirect-derived indications. I tend to lean towards the vane system......and likely it is the most fragile, difficult to calibrate as well as most expensive. You think this would be a job for an avionics shop or is it something an A & P might do?
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No AOA sensor on only one side will be accurate in uncoordinated flight. It *might* be an accurate measure of AOA for the wing/side it is installed, but tells you nothing about the other side, which is almost certainly 'seeing' a different AOA when uncoordinated.

Note I didn't say anything about analog vs. digital - it's entirely possible to have analog AOA indicators based on differential pressure or with airflow direction detectors ('vanes'), but most anything that reads 'degrees' on a linear scale will have some kind of digital signal processing. Many older indicators read in 'units' - uncalibrated, but still consistent in that stall for a given configuration would always occur at xx units, and L/D max at yy units - elegant simplicity. If you aren't trying to match aerodynamic predictions or other analysis this can be perfectly adequate, but is often overlooked these days because it's so easy to get calibrated degrees in the cockpit. Differential pressure systems can be analog in this way just like vanes, but neither are likely to be found these days.

As far as my preference goes, if I need accurate AOA for some kind of engineering analysis I prefer a vane (with digital signal processing and calibration, not analog), but that's also going to be mounted on a boom and out in relatively clean airflow (like, say, a wingtip) to get the best chance of accuracy. For everyday ops I like the differential pressure systems (again with digital signal processing and calibration) because I already have two of the pressures needed (total and static) and the third comes from the same fairly robust probe.

I'm entirely in the experimental/developmental world so I honestly don't know what A&P involvement is required in a part 23 airplane, but diff pressure calibrations are usually done in-flight so that part is probably on you. A probe cal can (should, AFAIC) be done on the ground but I don't know who would have to do yours.

Nauga,
boomin'
 
My exp Cub has a G3X Touch so adding AOA is simple. Install a GAP26 probe and connect a few wires. I’m curious about the usefulness in a Cub with a modified high lift wing. It wouldn’t be a big investment at $199 for the probe and a couple of hours to install. I may try it just for fun.

Nauga, how do you think it would it work on a Cub wing with slats?
 
Stewartb said:
Nauga, how do you think it would it work on a Cub wing with slats?
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Do the slats extend and retract or are they fixed like slots or droop? Where is the probe (or will the probe be) in relation to the slat and if it's the same as your current probe what kind of position error correction (indicated to calibrated) do you have for airspeed at low speeds with and without the slats extended (see first question)?

Nauga,
with curved air
 
Mackey slats pivot. The leading edge drops very little as the trailing edges lift. Clearly they allow higher AOA but on my wings the split flaps rotate the nose down. Garmin specs say probe at or forward of 25% chord with the forward limit 2" ahead of the leading edge. I'd favor closer to 15-20% chord. What I don't know is whether a typical probe can handle the wider range of AOA that slats provide. How these very effective flaps fit into it is also unknown.

Ground effect assisted landing speeds with flaps are in the low 20s. And its rock solid at that so slower is possible.

Thanks for your thoughts.
 
Stewartb said:
Garmin specs say probe at or forward of 25% chord with the forward limit 2" ahead of the leading edge. I'd favor closer to 15-20% chord. What I don't know is whether a typical probe can handle the wider range of AOA that slats provide. How these very effective flaps fit into it is also unknown.

Ground effect landing speeds with flaps are in the low 20s.
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Good info, thanks. Without knowing the geometry of the slats but knowing a little about the probe I'd say that the slats are almost certainly going to change the calibration of the probe - not just changing the physical AOA the wing is at for a given speed but also the calibration from sensed pressures to real AOA in degrees. That isn't necessarily bad, just something to know. For steady flow at some fixed slat position the wing would still stall at the same *indicated* AOA regardless of weight, etc, just like if it were reading the true AOA. If the slats have multiple deflection options or can change with no pilot input that only compounds the calibration problem.

I can't really say if the probe will see 'clean' air, which is what it needs to provide consistent indications. Behind a slat it may see unsteady flow which will show up as noisy or inconsistent AOA indications. But then again, it might not.

The AOA range of differential pressure systems is typically really good, even if the calibration over that range may not be. Where you might run into problems is because of the resolution of the pressure transducers and your low approach speed. You may be operating down at the low end of the transducer range where differential pressure for a given AOA is very low and also highly susceptible to disturbances. Of course the same holds true for your airspeed indicator, so you're either already experiencing this or the system has enough resolution that it's not a problem.

Notice I've used a lot of 'mights, maybes, and coulds.' I can't (or won't) say with any certainty that it will or won't work in your application. Personally I wouldn't put a wing-mounted AOA sensor behind any variable-camber device, and I would treat very-low-speed pneumatic sensors with suspicion - or at the very least I'd go in with pretty limited expectations. That doesn't mean you can't or shouldn't.

Nauga,
under pressure
 
The G3X airspeed tape doesn't light up until 20 mph. How the ADHRS computer would handle AOA at 20 would be interesting but in reality that speed isn't practical out of ground effect.

I do appreciate the comments. At $199 it could be a fun experiment to play with. I'll sleep on it for a few nights and see if it gains traction.
 
The AoA from GAP26 does require an AoA pressure line. It will have 3 ports that are plumbed (one additional on top of your existing static and pitot lines). For me, it wasn’t a straight forward replacement because of this, which is why I am mentioning it.

Also, it may not be clear from the G3x manuals, but you actually do configure the AoA for different flight modes. They recommend configuring AoA at flight modes like stall, high cruise, and approach configuration, etc. It seems straightforward but you are mapping these pressure points and then the G3x interpolates between these points. You can set and reset any of these points while in flight if you think the settings need modification. You also do set when you wish the AoA indicator to display on the G3x (Example: don’t display AoA below 20 Kts).

I have not flown enough with the AoA system to transition to AoA flying quite yet. I imagine it’d take a bit of practice to learn to “trust” it. Theoretically, it makes sense that it is a better indicator of lift but I am far from ready to divert from airspeed.

Stewartb said:
The G3X airspeed tape doesn't light up until 20 mph. How the ADHRS computer would handle AOA at 20 would be interesting but in reality that speed isn't practical out of ground effect.

I do appreciate the comments. At $199 it could be a fun experiment to play with. I'll sleep on it for a few nights and see if it gains traction.
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The GAP26 probe includes pitot and AOA pressure lines. I get that. The GSU25 adhrs is already there and has a port for the AOA line so for me the install is simple. I'll retain my original static port since the GAP doesn't have one. In my proposed installation the question is whether the GAP26 will effectively sense high AOAs that my modified wing can sustain. I've asked Garmin to see what they say about my application. If a go I'll initially use the display on the GDU and if I see merit? I'll add the remote indicator on top of the glare screen.
 
Stewartb said:
The GAP26 probe includes pitot and AOA pressure lines. I get that. The GSU25 adhrs is already there and has a port for the AOA line so for me the install is simple. I'll retain my original static port since the GAP doesn't have one. In my proposed installation the question is whether the GAP26 will effectively sense high AOAs that my modified wing can sustain. I've asked Garmin to see what they say about my application. If a go I'll initially use the display on the GDU and if I see merit? I'll add the remote indicator on top of the glare screen.
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Interesting question for sure. Given that the AoA essentially reads from 0 to X pressure, I'd assume any configuration can be flown assuming that the position of the pitot is per guidance. They give a range in their installation guide of something like no further back than 1/3 of the chord line length from the leading edge, something like that. I can't remember off the top of my head. I did this install last year. Good luck with the installation! It is a neat toy for me at the moment. Will see if I can trust it enough to fly on it.
 
I read up quite a bit on these and came to the conclusion that there really isn't a reliable AOA indicator. To start with, a modern wing has different airfoil sections and there is no one AOA. This also changes as soon as you put the flaps down. There was a study done I can't immediately find and the compared three different systems (I think the Garmin unit, the Aspen probeless one, and another one), and they were all hugely different depending on the phase of flight to the point I would consider them practically useless. It also greatly depended on where you installed the probe and Garmin changed their installation instructions based on the study, which says a lot about how well they tested the thing in the first place.

I was at a talk in Oshkosh about these and it was mentioned that during a time you'd commonly need them, base to final, you're looking out the window anyways. I am sure the F-22 and 787, etc. have these tested and certified with the airframe for many many dollars and I'd imagine are quite accurate. I don't think the ones we get in a box from spruce are worth 10 cents.
 
I couldn't care less what my AOA is in cruise or with a clean wing. Dirty wing? Given a stall speed near 20mph there isn't much margin for error. I think an AOA setup for that might be helpful. I'm fixin to find out.
 
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