Is AOA Real?

[jnmeade]

Is the AOA depicted by Dynon a real AOA, as one would expect from a vane input instrument, or is it a inferred or referred AOA based on differences in pitot and static (correction - should read "port") pressure?

My bottom line question is can one fly the AOA? In a previous existence, I flew a Citation that had AOA and we made all approaches and landings by reference to the AOA and ignored air speed. Can I do the same thing with my airplane using the Dynon system?

(Don't get me started about the lack of an HUD for the AOA)

 

[Carl_Froehlich]

To the first question - yes. AOA is a function of pitot and AOA port pressure difference (not static). The Dynon pitot has both a pitot and AOA port.

To the second question - perhaps yes. Assuming you calibrated the AOA for the same plane configuration (e.g. flaps and such) you can ride the AOA. I note however this, in my opinion, is not as practical as say an F-18. I had my son-in-law (F-18 jockey) fly and approach in my old RV-10. He was dead on the approach when he applied power and pulled the nose up. After I took the plane back I asked why he did that. “I’m just setting up my AOA”. In other words I rely on the AOA tones (not visual indication) for the clues that I’m doing a normal approach. The tones coming in right before the wheel touch.

Carl

 

[RV14_TD]

The AOA future that we use in HDX is at best half cooked. No awareness of flap position, no "on the speed" indication whatsoever.
Advanced displays use a much sophisticated AOA algorithm and I very much wonder why Dynon would not implement it in HDX.

 

[Rhino]

The approach to a stall is accompanied by a pressure differential. That differential doesn't usually change with flap position, and rarely very much when it does. The difference in pressure differential with or without flaps is miniscule at best in most aircraft, and most customers report they see little to no difference from AOA systems that change with flap position. While I can appreciate the personal preference for certain types of displays, the purpose of the AOA is to show you your changing potential for a stall. Indicators that use algorithms to change with flap or gear position aren't truly showing you how close you are to a stall. They're showing you how close they estimate you might be. They can sometimes be inaccurate in turns or other 'non-standard' conditions, because lift and flap effects change in those circumstances, and because they're, to at least some extent, dependent on calculations rather than actual conditions. By using pressure differential alone, the Dynon indicator is more accurately showing you how close you actually are to a stall, regardless of control surface positions or attitude. Everybody has their preferences. There are pros and cons on both sides. I'll choose the Dynon method.

 

[RV14_TD]

The approach to a stall is accompanied by a pressure differential. That differential doesn't usually change with flap position, and rarely very much when it does. The difference in pressure differential with or without flaps is miniscule at best in most aircraft, and most customers report they see little to no difference from AOA systems that change with flap position. While I can appreciate the personal preference for certain types of displays, the purpose of the AOA is to show you your changing potential for a stall. Indicators that use algorithms to change with flap or gear position aren't truly showing you how close you are to a stall. They're showing you how close they estimate you might be. They can sometimes be inaccurate in turns or other 'non-standard' conditions, because lift and flap effects change in those circumstances, and because they're, to at least some extent, dependent on calculations rather than actual conditions. By using pressure differential alone, the Dynon indicator is more accurately showing you how close you actually are to a stall, regardless of control surface positions or attitude. Everybody has their preferences. There are pros and cons on both sides. I'll choose the Dynon method.

I would challenge you on the assumption that flap deflection doesn't significantly change the critical AOA
Look here: https://www.n91cz.net/AOA/AoA_Article_Web.pdf

 

[jnmeade]

We're getting AOA as stall warning getting conflated with AOA as speed-to-fly (not in the glider term but in the sense of seeking efficiency).

 

[RV14_TD]

Those folks https://www.flyonspeed.org/ put together a nice solution, but it requires a free COM port, a luxury I can't afford
That's why I'm complaining about the lack of a comprehensive AOA functionality in HDX here

 

[Rhino]

I would challenge you on the assumption that flap deflection doesn't significantly change the critical AOA
Look here: https://www.n91cz.net/AOA/AoA_Article_Web.pdf

I would challenge you to read my post and your link more carefully. I never said anything about changing critical AOA. I referenced pressure differential indicating stall approach, which rarely changes to a significant degree, even with changes to critical AOA. Your link speaks only of the change in angle, not measured pressure differential. I can pitch up significantly and never get near a stall, as long as I increase power sufficiently. The same applies in a descent. My change in critical angle of attack, by itself, does not in any way indicate an approach to stall condition, no matter if it's caused by attitude or flap settings. It changes the possibility, but it's not a finite indication. Pressure differential is a far more reliable indication. But like I said, to each his own. Choose whatever you want. Using pressure differential alone is an arguably simplistic approach, and can have drawbacks as well. Just be aware of what you're actually getting with your choice, and don’t discount other possibilities based on a false premise.

 

[Rhino]

Those folks https://www.flyonspeed.org/ put together a nice solution, but it requires a free COM port, a luxury I can't afford
That's why I'm complaining about the lack of a comprehensive AOA functionality in HDX here

vlittle, of VX Aviation and a user here, used to have a panel indicator, but I don't think it's offered anymore. But Vern might be able to offer some helpful insights.

 

[RV14_TD]

I would challenge you to read my post and your link more carefully. I never said anything about changing critical AOA. I referenced pressure differential indicating stall approach, which rarely changes to a significant degree, even with changes to critical AOA. Your link speaks only of the change in angle, not measured pressure differential. I can pitch up significantly and never get near a stall, as long as I increase power sufficiently. The same applies in a descent. My change in critical angle of attack, by itself, does not in any way indicate an approach to stall condition, no matter if it's caused by attitude or flap settings. It changes the possibility, but it's not a finite indication. Pressure differential is a far more reliable indication. But like I said, to each his own. Choose whatever you want. Using pressure differential alone is an arguably simplistic approach, and can have drawbacks as well. Just be aware of what you're actually getting with your choice, and don’t discount other possibilities based on a false premise.

I stand corrected,
having said that, I believe it would be more or less trivial for Dynon to implement the "fly on speed" version of AOA indicator, as I understand it was adopted by Advanced

 

[RV14_TD]

vlittle, of VX Aviation and a user here, used to have a panel indicator, but I don't think it's offered anymore. But Vern might be able to offer some helpful insights.

Thanks! What I'm really looking for is a tone in my headset which would allow me to fly an approach with my eyes outside of the cockpit

 

[hoyden]

I started flying AOA a few months ago in my HDX equipped RV-6. I set up the tone to start upon entering the yellow zone and the tone goes continuous right about stall. Most of my attention is directed outside now with reference to the display to ensure my sink rate is about 600 fpm and to note the IAS. This technique has shortened the time I spend in ground effect. I haven't yet flown in gusting conditions but I imagine I will want to add a few kts to my speed.

 

[skysailor]

As mentioned by Hoyden, the initial onset of tone is fully adjustable so you could indeed set it to give a pulsing tone when on speed for approach and retain the different continuous sound for stall leaving you to fly eyes out. Works great!

 

[RV14_TD]

This is what we need. Image grabbed from here

 

[Rhino]

Thanks! What I'm really looking for is a tone in my headset which would allow me to fly an approach with my eyes outside of the cockpit

Vern may have worked on a HUD too. I know someone did, but I don't remember who. I bet Vern would remember though.

 

[airguy]

Thanks! What I'm really looking for is a tone in my headset which would allow me to fly an approach with my eyes outside of the cockpit

I hope you are referring to a VFR approach here - flying a true "approach" should have your eyes inside only, until you break out or hit minimums.

 

[RV14_TD]

I hope you are referring to a VFR approach here - flying a true "approach" should have your eyes inside only, until you break out or hit minimums.

Thank you, I was not specific enough.

 

[Rhino]

I doubt you'll see that from Dynon anytime soon. That's a robust feature that just isn't in great demand in their primary customer base, especially when customers see the cost involved. I'm sure there are all sorts of features Dynon would like to have, but the customer demand doesn't support the costs to upgrade the hardware and software necessary to achieve those goals. You have to remember that they're a relatively small operation, catering to a customer base that is largely 'grass roots'. The customers like features, like anyone else, but many can't afford the cost of a system with those added features. Dynon has to consider that. If they cater to the higher end, they risk losing customers on the lower end, and vice versa. They're trying to strike the best balance they can, and that means they can't put everything into their systems. I suspect they lean more toward the lower end because their customers have other choices on the higher end, but not so much down low. Catering to that market garners them a level of brand loyalty that isn't matched on the high end. Considering the state of the current system, we aren't likely to see any significant upgrades until the next full redesign. Among other things, there's a serious software space limitation that they keep running up against. That's just my personal take though. I could be completely wrong.

 

[RV14_TD]

While I agree with everything you said I believe that Dynon can't stand still, because the competition keeps on adding new features to their products. Dynon need to innovate and stay ahead to survive.

 

[Rhino]

They're not standing still by any means. They're just being very selective on what they add. I think it's going to be interesting to see whay system comes next, and when. They're obviously bumping up against space limitations with this one. Maybe they can simply expand within this design, or come up with an entirely new concept.