Absolute AoA System – Accurate AoA for Every Flight Phase

[HolyMicro]

Say goodbye to limitations and hello to precision. In response to the FAA's Special Airworthiness Information Bulletin (SAIB: 2024-07), Holy Micro! LLC presents the Absolute AoA System, a next-generation solution designed to provide accurate Angle of Attack (AoA) data for all phases of flight.

Why Absolute AoA?

Unlike traditional single-sensor differential pressure systems that are limited to near-stall warnings, the Absolute AoA System provides reliable AoA information throughout your entire flight—from climb to cruise to landing, unaffected by density altitude, weight, or loading. Fly Absolute AoA for all your V speeds including BestGlide/Best Range (L/Dmax) &VEC.

The Holy Micro! Difference

This innovative & fully independent system utilizes many sensors to calculate and calibrate normalized pressure ratio, an accurate method proven through extensive studies & flight tests to maintain precision across all phases of flight.

Additionally, our cutting-edge LiDAR technology automatically detects & adjusts for flap position & landing configuration. Whether you’re flying at high or low altitudes or speeds or loading, the Absolute AoA System delivers consistent, reliable AoA data-regardless of conditions.

Fly with Confidence, Fly Absolute AoA

Enhance your safety and performance with an Angle of Attack system you can trust. Say goodbye to guesswork and limitations— Absolute AoA system ensures you have the critical data you need, when you need it.

Easy Installation, Advanced Features

Installs in just 1 hour – no long tubes, no hassle

      Multiple digital displays to fit your cockpit including HUD

      Many AoA presentation options

Independent Air-Data System

NORSEE approval in progress

Patent Pending

Upgrade your aircraft with the most advanced AoA system available. Take advantage of Limited-Time Offer: Pre-Register and Save 40%

 

Meet Us at Upcoming Events!

·         Sun 'n Fun – April 1-6, Bldg B, Booth B27-28

·         EAA AirVenture Oshkosh – July 21-27, Bldg C, Booth 3149-50

Download the FAA Special Airworthiness Information Bulletin (SAIB: 2024-07) to learn more about AoA advancements and why the Absolute AoA System is the future of flight safety.

 

Fly Smarter; Fly Safer; Fly Absolute AoA.

 

[takair]

Do you have pictures or info on the display and the sensor install?  Does it require a mast for pressure sensing?

[A64Pilot]

52 minutes ago, takair said:

Do you have pictures or info on the display and the sensor install?  Does it require a mast for pressure sensing?

My guess is your going to have to call, last week at the Umatilla FBO they were giving away neat little fans advertising their landing height altimeters.

I can find out no real data on the things by going to their website ref installation etc, just marketing videos. I could find data on how they will place systems into an A&P’s business and only expect payment upon installation etc, but no data on installation.

I did some flight testing years ago on AOA systems for Crop Dusters as they constantly maneuver on the ragged edge of stall, most Ag pilots defeat stall warnings by pulling the CB or merely bending the vane down because it’s a nuisance, it goes off in most every turn when heavy when properly adjusted, they maneuver that close to stall.

Anyway I came away unimpressed, none were as good as training and while I’m sure some have, but I never saw one in an Ag plane. Stall speeds are VERY high in an Ag plane because as the Hopper can be dumped very quickly the FAA only requires stall speeds to be met with the hopper empty, so you can image what happens in a 5,000 lb airplane’s stall speed wise when you put 5,000 lbs in the hopper doubling it’s weight.

Stall angle of attack does not change with weight but speed sure does. Especially when you add in the G loading from sharp turns.

I’m not against them if you want one by all means install one, just in my opinion don’t rely on it and I think that money is better spent on training personally. Nothing trumps experience and the safest way to get that is from training. My opinion of course.

Edited February 13 by A64Pilot

[dkkim73]

It would certainly be a good thing to get some actual info on how the thing works and what it looks like. The Eagle AOA sensor is well-reputed but the install is more involved. It seems Holy Micro takes more of a wireless approach with their other stuff. If they can do a good job with AOA, easier install and lower price, it might have some legs. 

I agree the collateral is more marketing-heavy. Maybe it's all just early, who knows. 

As to ag planes, I've always thought the bravery of those pilots was underrated. And those low patterns are very meditative to watch, too. 

[A64Pilot]

Ag wise I think maybe back in the day when you bought a cheap surplus Stearman, paid cash and modded it and went to work bravery if you will was a thing.

Nowdays if you use new new prices you can’t get an Ag plane for less than a Million bucks which is actually cheap once you consider it’s a 750 HP turbine, but especially once you get into multiple millions your getting insurance involved most likely as most can’t pay cash, so it’s become much more professional if you will, an accident prone pilot quickly becomes an unemployed one.

In truth it’s sort of boring believe it or not, it’s hard work with very long hours, and usually seasonal. When there is work daylight to Sundown isn’t uncommon, and you usually get behind with weather and higher wind days factored in.

This is an old Garrett Thrush, likely 80’s 

This is a GE powered Thrush which I Certified a couple of years before Retirement, unfortunately I believe GE has orphaned this engine.

Both of these are small one man operations is South Ga. The small one man operators are more common than you might think.

 

[Pinecone]

T-38A and B and the A-10A had AoA. 

In both, we have a gauge that gave AoA from a vane, all the time.  Then there was the Indexer on the left canopy bow that was only active with the gear down.  The ONLY use for the gauge was to fly a max range or max endurance profile.  You would fly to a mark on the AoA guage.  And set power for level flight.  Normal cruise was to set a MACH or IAS and fly.

The A-10 also had AoA tones in the headset.  But this was due to a quirk where the wing stalled about 1 AoA unit before the buffet.  And max performance was 1 AoA before the stall.   So there was a max performance tone and a stall tone.  I think a setup like this would be great for ag planes.

But overall, having flown with it, I see no real use for full range AoA.

I like the Alpha Eagle display.  Most like the ones I flew in the USAF and gives me the info I need without anything extra cluttering things up.

[HolyMicro]

22 hours ago, dkkim73 said:

It would certainly be a good thing to get some actual info on how the thing works and what it looks like. The Eagle AOA sensor is well-reputed but the install is more involved. It seems Holy Micro takes more of a wireless approach with their other stuff. If they can do a good job with AOA, easier install and lower price, it might have some legs. 

I agree the collateral is more marketing-heavy. Maybe it's all just early, who knows. 

As to ag planes, I've always thought the bravery of those pilots was underrated. And those low patterns are very meditative to watch, too. 

The normal retail price for our entire Absolute AoA system is under $2000. It includes a mast/probe that can be installed on any inspection plate located under the wing, in front of the flap. The tubes from the probe connect to sensor electronics mounted directly above the inspection plate. Additionally, there is a processor unit that can be installed behind the instrument panel. The connection between the sensor electronics and the processor can be either wired or wireless, and the display is linked to the processor.

For setup and calibration, the Absolute AoA system comes with a digital HMI (Human-Machine Interface), similar in size to a 6.5-inch phone. This device is used to connect to the system and perform calibration.

The Absolute AoA system offers a variety of display size options, ranging from 3.5 inches to 2.4 inches, including bar-style displays. These digital displays feature touch functionality, allowing you to adjust settings and choose your preferred AoA presentation style.

The most important  feature of our Absolute AoA system is its normalized pressure system, which ensures highly accurate and consistent readings across all phases of flight. Unlike traditional pressure differential systems, ours is a ratio-based system that uses multiple sensors. Pressure differential systems are only reliable near the stall speed they were calibrated for. Outside of that range, especially under varying loading, density altitude conditions and flap, they become non-linear and inaccurate. While the FAA only requires that an AoA system's stall warning activate before the aircraft's built-in stall warning, our system goes far beyond that. It allows you to accurately fly all your V speeds (Vx, Vy, Va, Best Glide, etc.) regardless of density altitude or loading conditions.

When flaps are deployed, the wing's chord length, area, and camber change, increasing lift, altering pitch, shifting the center of pressure, and reducing stall speed. If these factors are not accounted for, AoA readings become inaccurate. Our Absolute AoA system automatically detects flap position without requiring any physical connection to the flap system or internal wiring. This is achieved through LiDAR technology integrated into the probe, which monitors and detects flap position. This ensures accurate AoA readings during approach, even with flaps and gear extended. Again, this is a normalized pressure ratio system, not a pressure differential system. Pressure differential systems are essentially limited to stall warnings and are not linear across the entire flight envelope.

To calibrate our system, you must fly at the correct speeds for the current density altitude and loading conditions. Before the calibration flight, you will need to calculate the appropriate speeds for each AoA you intend to fly (e.g., Vx, Vy, Va, Best Glide). Once calibrated, the system provides precise AoA indications tailored to the present loading and density conditions. This is the key difference that sets our system apart.

 

[exM20K]

@HolyMicro Have you made provisions for heating the probe/mast?

-dan

[A64Pilot]

A problem with trying to use AOA for Ag planes is they are Manuvering pretty aggressively when they are most vulnerable, plus your looking out avoiding trees etc

The way an aircraft turns is of course by modifying the lift between the two wings, for this reason the high wing, that is the wing your turning away from will stall first assuming your maintaining trim, if your AOA is on the left wing it won’t accurately reflect the right wings proximity to stall and if your turning left the right wing is closest to stall. Then add in that often when turning they are most often also pulling up and it aggravates the situation. To really be most useful you would need an AOA sensor on both wings.

Airfoil on a Thrush is from memory a NACA 4412, that airfoil is a high lift one that is very leading edge damage tolerant and has very gentle stall behavior, it has a very pronounced pre stall buffet, that buffet is what many use in a turn to know how close they are, plus we have a 1.5 degree washout twist in the wing that unless pretty deeply stalled ensure the tips keep flying, this usually prevents a dropped wing in a stall, if the stall isn’t aggressively approached. It’s downsides is it’s relatively high drag and flaps are less effective with it, so it’s less efficient. TANSTAAFL.

An Ag plane Thrush anyway maneuvers regularly so close to stall, right at the beginning actually or arguably actually in a stall that an AOA sensor would indicate a stall very often, it would be a nuisance just as the factory vane is.

The saving grace if you will is two fold, the stall is very gentle and the washout means it’s progressive, from the wing root outboard, so a wing shouldn’t drop if your in trim until very deep in the stall.

Other aircraft in trying to push efficiency aren’t as forgiving and have a reputation for being accident prone in the turn, those aircraft as their wings aren’t washed out you have to drop the flaps to turn to wash out the wing or it may tip stall, and go over on its back, which at 50 or 100 ft isn’t of course recoverable.

Some Thrush drivers who came from those other aircraft also drop flaps in a turn as they learned that way, but it’s usually just added drag on a Thrush.

So in my opinion an aircraft with a very benign stall, like say a Cherokee 140 for instance an AOA just isn’t really very useful for stall warning anyway, but an aircraft who’s stall isn’t benign maybe it is. Any aircraft in my opinion with stall strips does not have a benign stall by definition as the purpose of stall strips is to tame the stall behavior or sometimes if in front of the ailerons they are to provide pre stall warning, but either way they are there because they need to be there, not for looks

 

Edited February 14 by A64Pilot

[Pinecone]

On 2/14/2025 at 9:50 AM, A64Pilot said:

A problem with trying to use AOA for Ag planes is they are Manuvering pretty aggressively when they are most vulnerable, plus your looking out avoiding trees etc

Just like we did in the A-10.  A bit higher, as we only went down to 100 AGL, but we pulled more G there.

That is why the headset tone was so useful, not looking inside or at anything, looking out and hearing the max performance tone told you that the plane was doing the best it could do.

[A64Pilot]

On 2/15/2025 at 10:31 AM, Pinecone said:

Just like we did in the A-10.  A bit higher, as we only went down to 100 AGL, but we pulled more G there.

That is why the headset tone was so useful, not looking inside or at anything, looking out and hearing the max performance tone told you that the plane was doing the best it could do.

Having never flown an A-10 I’m going to assume it’s stall wasn’t nearly as progressive as the Thrush and frankly you guys didn’t push so deep into a stall in each turn, just because it’s stall wasn’t as forgiving?

If for example if flying like a Thrush does and you saw something that needed to be avoided or your RAW gear went off, all you could do would be to ease or roll out of the turn or just grimace and hope it doesn’t hurt too much, cause there is no maneuverability left, you can’t tighten the turn at all

Ag planes don’t usually pull much G, they can’t they are too heavily loaded, the FAA’s position was the pilots got G tolerant and over G’d the aircraft. So I put a G meter in the MVP aircraft with alerts in the MVP-50 equipped ones to alert them, but I found out in testing to increase our wing spar life limit that you cant really over stress a new Thrush wing without exceeding VNE, the wing stalls right about the time you hit the G limit at max gross weight and actual wing stress is both G and weight dependent, so lightweight you can exceed G limits, but it’s not over stressing the wing. We hired an Engineering firm that put strain gauges all over the wing spar upper caps and I had to go out and fly flight profiles. On an aircraft that has huge changes in its weight, G alone isn’t a very good way to determine wing stress, but in simple aircraft it’s all we have.

The AH-64D’s computer took speed, air density and gross weight and computed G limit as G limit in a helicopter is often more of an aerodynamic limit than a structural one, but most aircraft don’t have Air Data computers et all to do that.

The old Thrush wing has a 5400 hour lower spar cap life limit, the new wing had a very conservative 29,000 hour limit that we extended to 54,000 hours mostly for marketing as there really aren’t any 29,000 hour Ag planes much less 54,000 hour ones.

A few died in years past when the main spar cap failed on a Thrush and it lost a wing, wing failure isn’t uncommon on Ag aircraft, we chose to deal with it by designing a new wing that was simply stronger and pushed the wing life to be in excess to the aircraft expected life, our competitor chose to new redesign but stick with spar cap replacements.

Not to try to bore too many, but the reason the wings were failing was the original aircraft was a 6,000 lb aircraft that had a realistic speed of about 120 mph, the aircraft was STC’d originally, then later manufactured with a turbine engine and actual flying weight exceeded 10,000 lbs and operating speeds were up to 160ish, it wasn’t a poorly designed wing it just that weight and speed simply overloaded the design and it failed.

Brazilian Ipanema, and it’s wings are externally braced.

https://youtu.be/NbHGzPVpsgo?si=KcxoCwn6VfyfZntb

Edited February 16 by A64Pilot

[A64Pilot]

To give a comparison, in Test Flights of captured BF-109’s the Allies found that it probably due to its leading edge slats could out turn a Spit, but in dogfights that was almost never the case, why?

It seems that a BF-109 had almost no warning of impending stall, when it did it went over on its back and trying to recover from a spin you lose a lot of energy and apparently your in a very vulnerable position, so German pilots were very reticent to pull as hard in a turn as the Spit drivers, the Spit apparently had a very progressive stall and a pronounced pre stall buffet so they became comfortable pushing the envelope.

Although you will find flight tests that say the opposite. I have a friend that flew Merlin powered BF-109’s in I believe the Czech Air Force, he apparently defected to the US long ago in apparently unusual circumstances, he won’t talk about how he got here, but on his office wall he has a picture of him standing in front of a US F-86 dressed for flight and holding a helmet.

Some of us believe he defected in a Mig. We speculate that under the assumption that it’s unusual for a former Communist pilot to get a ride in what was then a front line US Fighter.

I guess the BF-109 needed an AOA sensor?

Edited February 16 by A64Pilot

[HolyMicro]

On 2/14/2025 at 8:12 PM, exM20K said:

@HolyMicro Have you made provisions for heating the probe/mast?

-dan

Yes.

[Pinecone]

On 2/16/2025 at 10:34 AM, A64Pilot said:

Having never flown an A-10 I’m going to assume it’s stall wasn’t nearly as progressive as the Thrush and frankly you guys didn’t push so deep into a stall in each turn, just because it’s stall wasn’t as forgiving?

When the A-10 wing stalls, the flight path stops turning.  See the video of the Paris Air Show crash.  The nose is up, but the flight path is still steep into the ground.

And there is NO warning of the stall.  The buffet happens at a higher AOA than the stall.  Also no nose drop at the stall point.

So, normally in a straight wing airplane, for max performance, you pull to the buffet, then slightly release the backpressure to the point of no buffet.  If you do that in an A-10, you are still stalled and will hit the ground.

So we got headset tones for Max Performance and for Stall.  I would think a headset tone for max performance AOA for an ag plane would be perfect.  You can fly every turn at max performance for the GW and conditions.

[A64Pilot]

Tones would be obnoxious as you would be listening to them for half the time you were spraying, depending on length of the field your turning about half the time.

[Pinecone]

I found them to not be annoying.  And we would be at the tone for long periods. Especially when air to air training.

Just checked, and I misremembered (or they changed after I flew it).  Now the steady tone is 2 AOA units before stall and chopped tone is 1 AOA unit before stall.  Steady tone is max performance.