My Audio AOA

[bifft]

I've wanted an AOA in my plane since reading Aerodynamics for Naval Aviators back in the 90's. Tried to roll my own back then, wasn't enough of an electrical engineer. Built one based on a Sport Aviation article, it worked on the bench, and in the plane during testing but died shortly before first flight. Still have the hole in my panel, it is sitting here on my desk as I write this.

Vac's OnSpeed evangelism convinced me that an audio AOA has significant advantages over a panel gauge. I wanted to build one, but every time I looked some fairly significant parts were not available. Last year decided to roll my own. Going digital moved things into the software domain where I do know what I'm doing, so I succeeded where I had failed in the past.

Wrote it up here: My Audio AOA

Have about a half dozen flights with it so far. Might change the calibration a little bit, but am absolutely loving it. Doing landings using tone for speed and keeping eyes outside is so much easier than constantly switching attention back and forth between ASI and runway/traffic. My landings have become noticeably more precise. Stall warning works correctly for 1G stalls, 4G accelerated stalls or floating over the top of a loop well below "stall speed".

Thought I would start a new thread if anybody wanted to ask questions about it.

 

[johnpaul44]

I've wanted an AOA in my plane since reading Aerodynamics for Naval Aviators back in the 90's. Tried to roll my own back then, wasn't enough of an electrical engineer. Built one based on a Sport Aviation article, it worked on the bench, and in the plane during testing but died shortly before first flight. Still have the hole in my panel, it is sitting here on my desk as I write this.

Vac's OnSpeed evangelism convinced me that an audio AOA has significant advantages over a panel gauge. I wanted to build one, but every time I looked some fairly significant parts were not available. Last year decided to roll my own. Going digital moved things into the software domain where I do know what I'm doing, so I succeeded where I had failed in the past.

Wrote it up here: My Audio AOA

Have about a half dozen flights with it so far. Might change the calibration a little bit, but am absolutely loving it. Doing landings using tone for speed and keeping eyes outside is so much easier than constantly switching attention back and forth between ASI and runway/traffic. My landings have become noticeably more precise. Stall warning works correctly for 1G stalls, 4G accelerated stalls or floating over the top of a loop well below "stall speed".

Thought I would start a new thread if anybody wanted to ask questions about it.

thanks for doing this, I read through the write up very nice. How much do you think adding a flap sensor would change things as far as how you fly? even though on most RV's the difference between stall clean and stall full flaps is a few knots I'm wondering how much this would affect your end use of the device?

 

[Fffflats]

Floating over the top of a loop?

 

[Gino230]

Very Cool. I also want AOA, but I think I would like the visual indicator like the Fly on Speed one Vac has on his glareshield.

Do you think this would work with one of the commercially available Pitot tubes like Dynon or Garmin? As long as the angle of the opening is the same, shouldn't the result be the same? My D10A supports AOA, running a second pitot tube is on my project list.

Don't any of these commercial audio panels support audio inputs? Forgive my ignorance please.

Nice work!

 

[blaplante]

Don't any of these commercial audio panels support audio inputs? Forgive my ignorance please.

Yes most audio panels support "unswitched inputs". Currently installing one for a client.

 

[bifft]

thanks for doing this, I read through the write up very nice. How much do you think adding a flap sensor would change things as far as how you fly?

I would use it the same way, but have a more accurate "On-Speed" condition with the flaps down. Using the same audio cue with flaps down currently has me flying a little bit off. Not having the flap input means I'm not squeezing out the last 5% or so of possible performance.

 

[bifft]

Floating over the top of a loop?

Yes, over the top of the loop. Since gravity is pulling you the direction you want to turn you are usually well under 1G (I usually fly it close to 0). You can still pull to hard and stall. Did some in my testing to make sure it worked right in that case.

 

[bifft]

Do you think this would work with one of the commercially available Pitot tubes like Dynon or Garmin?

It should work, just need different calibration numbers.

 

[Fffflats]

Yes, over the top of the loop. Since gravity is pulling you the direction you want to turn you are usually well under 1G (I usually fly it close to 0). You can still pull to hard and stall. Did some in my testing to make sure it worked right in that case.

If you’re floating through the loop, you’re really falling through it. You should have positive g through the entire loop. Flying the loop, you’re using positive pitch rate. If you’re “floating” you’re really falling and letting longitudinal stability bring your nose back down. By “floating” you are what we call ballistic. You are out of energy and have no capacity to alter anything till you let gravity pull you down regaining some kinetic. Technically you’re out of control in that moment.

 

[FlyNow]

I've wanted an AOA in my plane since reading Aerodynamics for Naval Aviators back in the 90's. Tried to roll my own back then, wasn't enough of an electrical engineer. Built one based on a Sport Aviation article, it worked on the bench, and in the plane during testing but died shortly before first flight. Still have the hole in my panel, it is sitting here on my desk as I write this.

Vac's OnSpeed evangelism convinced me that an audio AOA has significant advantages over a panel gauge. I wanted to build one, but every time I looked some fairly significant parts were not available. Last year decided to roll my own. Going digital moved things into the software domain where I do know what I'm doing, so I succeeded where I had failed in the past.

Wrote it up here: My Audio AOA

Have about a half dozen flights with it so far. Might change the calibration a little bit, but am absolutely loving it. Doing landings using tone for speed and keeping eyes outside is so much easier than constantly switching attention back and forth between ASI and runway/traffic. My landings have become noticeably more precise. Stall warning works correctly for 1G stalls, 4G accelerated stalls or floating over the top of a loop well below "stall speed".

Thought I would start a new thread if anybody wanted to ask questions about it.

bifft, thank you for this. Writing up and releasing your initial hardware and software design is in the true spirit of open source collaboration. I also have been wanting to build the OnSpeed AOA and have been waiting years for the team to publish the latest design that they have been working on.

Your project is a good starting point and the Pico is a great choice. I don't have a flap position sensor, but adding one and adding support to your code should be pretty easy. Audio indication is all I've really been wanting, but for those that want a visual indicator, this project could probably be adapted: https://vansairforce.net/threads/microefis-v1-0.240907/post-1906171

The Pi Pico is well supported so I was able to install a few packages on my Linux workstation and build your software within a few minutes (I'm also a software guy). I'll be buying some parts and giving this a try. Thanks again.

Russell

 

[bifft]

If you’re floating through the loop, you’re really falling through it.

Yes, falling as much as flying. My aerobatics instructor says he goes a bit negative to round out the top in some airplanes. I usually keep it slightly positive, but as I have airspeed, I am in control, just with very low kinetic energy (with lots of potential energy as I am at the top of a loop above my 3000 AGL aerobatic floor). Flew some very slowly on purpose to test low speed stall warning with the AOA.

 

[bifft]

Your project is a good starting point and the Pico is a great choice. I don't have a flap position sensor, but adding one and adding support to your code should be pretty easy. Audio indication is all I've really been wanting, but for those that want a visual indicator, this project could probably be adapted: https://vansairforce.net/threads/microefis-v1-0.240907/post-1906171

Yes, with modern computers even something as low end as a Pi Pico is sleeping 75% of the time on this project. It would be easy to add a visual indicator, I thought of just using a simple 8 segment LED block with green-yellow-red lights. Would be easy to add to the code, have plenty of GPIO pins left over to drive the lights. Decided against it as it is "scope drift". Just get the audio working.

 

[Fffflats]

Yes, falling as much as flying. My aerobatics instructor says he goes a bit negative to round out the top in some airplanes. I usually keep it slightly positive, but as I have airspeed, I am in control, just with very low kinetic energy (with lots of potential energy as I am at the top of a loop above my 3000 AGL aerobatic floor). Flew some very slowly on purpose to test low speed stall warning with the AOA.

The difference between minimum vertical vs tactical vertical.


You can go to zero falling through but not negative. If you go negative, you’re fighting against the looping. Though really you don’t want to go less than one. Positive g throughout means you’re flying not falling throughout. More importantly, positive g means no physiological push-pull effects. An aerobatics instructor might be used to significantly inclined seats so as to reduce if not cancel push-pull. Remember while the airplane considers anything less than zero negative, the body considers such with anything less than one. Try pulling to your no-flap onspeed AOA and holding this through your loop till any g builds back up. (With an RV, your loop is quick so won’t really get back to g.) Don’t be afraid of the egg shape loop. They might deliberately push to round the top out, but why.

Speaking of AOA testing, have you looked at accelerated stall as well as onset rate of g to stall? There is a pressure diff vulnerability in these that vanes don’t have. But this same vulnerability enables you to use the AOA for takeoff. While preserving means to takeoff, if you haven’t, you can compensate for accelerated and onset rate in the press diff system.

 

[Fffflats]

Yes, with modern computers even something as low end as a Pi Pico is sleeping 75% of the time on this project. It would be easy to add a visual indicator

Bringing the thought from that thread,

Thoughts for yaw indication at high AOA and negative AOA of high magnitude? The old school turn needle is the only way to reliably see yaw in a spin. You wouldn’t need a TN per se but something that is yaw only and does not include roll rate in any fashion.

 

[DennisRhodes]

The idea of an audio AOA seems like an good idea. ie. new twist to the old stall warning horn.
Your idea and test success could well be a marketable experimental product. Items that could make that happen would be.... 1. A probe that would fit underside the RV wing in say one of the inspection holes.. 2. Electronic components in a small enclosure that could mount inside that same wing inspection hole and then. 3. A signal wire routed to the cockpit for plugging into the audio music port on your Headset. or 4. maybe a very small 2 1/4 or smaller panel cut out with a power switch and audio port jack.

 

[BobTurner]

The idea of an audio AOA seems like an good idea. ie. new twist to the old stall warning horn.
Your idea and test success could well be a marketable experimental product. Items that could make that happen would be.... 1. A probe that would fit underside the RV wing in say one of the inspection holes.. 2. Electronic components in a small enclosure that could mount inside that same wing inspection hole and then. 3. A signal wire routed to the cockpit for plugging into the audio music port on your Headset. or 4. maybe a very small 2 1/4 or smaller panel cut out with a power switch and audio port jack.

Not sure how marketable it really is, given that virtually all new EFIS units come with AOA built in…it really is an idea whose time has come.

 

[Ironflight]

Not sure how marketable it really is, given that virtually all new EFIS units come with AOA built in…it really is an idea whose time has come.

We have that discussion a lot on the EAA Safety Committee AoA group - and one of the “old-timers” (RVG) keeps reminding us that there are still thousands of simple Homebuilt aircraft that don;’t (and never will) have an EFIS - and we’d love to have an answer for those guys as well. I’m talking about guys with tube and fabric single-eaters that use a handheld radio because they don’t have an electrical system. Something simple like the OP’s system would be awesome for that market!

 

[Pilot135pd]

Not sure how marketable it really is, given that virtually all new EFIS units come with AOA built in…it really is an idea whose time has come.

You'd be surprised how many people still don't like AOA, and I'm sure they know how it works because these people are airline pilots and others who've been pilots all of their lives. I've already told a couple of them about installing an AOA pitot tube on my next plane, and people have very bad reactions against it. It's a crazy attitude, but of course it's getting installed no matter what anyone says.

 

[bifft]

Don’t be afraid of the egg shape loop. They might deliberately push to round the top out, but why.

I'm not afraid of them, but a round top is needed if you want to score high in competition. I don't compete, so usually aim for a constant angular rate, which will be fairly egg-shaped.

Speaking of AOA testing, have you looked at accelerated stall as well as onset rate of g to stall? There is a pressure diff vulnerability in these that vanes don’t have. But this same vulnerability enables you to use the AOA for takeoff. While preserving means to takeoff, if you haven’t, you can compensate for accelerated and onset rate in the press diff system.

Did test accelerated stalls up to 4g. Haven't tried a high onset rate. Might give it a try next flight.

Regarding yaw indication, for a pressure system would need two additional probe tubes and lines, and at least one pressure diff. sensor. Or a gyro (which I see could be pretty cheap) but then need some kind of output. Make the sound stereo? Something on the panel? Either would add quite a bit of complexity to what I hoped to be a simple project. For spins I'll just look along the cowl, see which rudder I'm pushing.

 

[Pilot135pd]

Regarding yaw indication, for a pressure system would need two additional probe tubes and lines, and at least one pressure diff. sensor. Or a gyro (which I see could be pretty cheap) but then need some kind of output. Make the sound stereo? Something on the panel? Either would add quite a bit of complexity to what I hoped to be a simple project. For spins I'll just look along the cowl, see which rudder I'm pushing.

OnSpeed has stereo audio depicting yaw: If you're out of trim where you would normally have to "step on the RIGHT ball", you'll here a louder AOA tone in your RIGHT ear, and that tells you to step on the right rudder pedal, and vice-versa.

 

[justa6ereh]

I’m just programming my iPad and autopilots to do loops for me….then I can stay home and watch on my other iPad.

 

[Fffflats]

You'd be surprised how many people still don't like AOA, and I'm sure they know how it works because these people are airline pilots and others who've been pilots all of their lives. I've already told a couple of them about installing an AOA pitot tube on my next plane, and people have very bad reactions against it. It's a crazy attitude, but of course it's getting installed no matter what anyone says.

I’d argue most airline pilots don’t know how it works. As for not liking it, this is because they grew up on speed and far as they can tell, speed has been adequate for them. Classic human problem. They don’t know the history of AOA and why we went to speed either, I call this being “the thirteenth monkey.” You might otherwise know it as “cutting the ends off your roast.”

 

[Fffflats]

OnSpeed has stereo audio depicting yaw: If you're out of trim where you would normally have to "step on the RIGHT ball", you'll here a louder AOA tone in your RIGHT ear, and that tells you to step on the right rudder pedal, and vice-versa.

I like this idea but I also want to be able to turn such a feature off, beneficial for others, but some of us have asymmetric hearing loss.

 

[Fffflats]

For spins I'll just look along the cowl, see which rudder I'm pushing.

You can do this, however, such is fallible. You can reduce the fallibility of it by taking your free hand, the one that pulled the power, and putting it over your brow so as to block site of much of the roll component.

I'm not afraid of them, but a round top is needed if you want to score high in competition. I don't compete, so usually aim for a constant angular rate, which will be fairly egg-shaped.

A difference in precision aerobatics vs “relative aerobatics.” Rounding it out slows your angular rate down hence you may lose a shot opportunity… though it is possible if you see them at an energy deficit such that they won’t be able to get back up to you to float it so as to more easily move to control. Alternately, might want to float to prevent a high-to-low steep merge possibly even making such a non-merge. If you’re the low guy and you have the energy, you might want to be starting that over the top early and really tighten that top “corner” of the egg in a steep low-to-high.

 

[dmattmul]

You'd be surprised how many people still don't like AOA, and I'm sure they know how it works because these people are airline pilots and others who've been pilots all of their lives. I've already told a couple of them about installing an AOA pitot tube on my next plane, and people have very bad reactions against it. It's a crazy attitude, but of course it's getting installed no matter what anyone says.

I'm a huge believer in audible AOA. Yes, I have the green/yellow/red chevrons on my G3X but honestly don't watch them when landing. If I don't hear the beep-beep when I'm low and slowing it down, I'm still too fast. Slowing it down probably has saved me a lot of $$$ on tires and brakes over the years. If the beep is to slow, I smell rubber and that's a waste. (faster the beep the slower I am going) I flew into OSH 2022 first time and being asked to maneuver in the pattern at altitudes not use to and turn to final heard the beep-beep, added power and lowered the nose, landing uneventful.

 

[Pilot135pd]

I like this idea but I also want to be able to turn such a feature off, beneficial for others, but some of us have asymmetric hearing loss.

Just switch your headset to MONO and you'll still get AOA tones but you'll get the one side audio in both ears.