AOA vs Stall Horn

Discussion in 'Flight Following' started by TimRF79, Apr 29, 2021.

  1. Stewartb

    Stewartb Final Approach

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    Funny how guys with experience with AOA (or lots of other mods) get told they’re wrong by guys with no experience?

    Why do guys land in gusty winds with less than normal flaps and higher than normal speeds? Because they can’t feel the wing and they can’t trust the stall indicator.
     
  2. 455 Bravo Uniform

    455 Bravo Uniform En-Route

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    Are shoulder harnesses necessary? No.

    An AOA indicator is not vital. But it’s there if/when you need to hit trees or cars at the minimum possible speed without falling out of the sky first.

    To say it’s not necessary is true. It doesn’t mean it’s not useful and perhaps even well advised. Put those stupid seatbelts on.
     
  3. luvflyin

    luvflyin Touchdown! Greaser!

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    Good example. The ability to crash at a slower speed. Once the Stall Horn goes off, how much slower are you going to get? Yeah, there are some pilots with the experience and talent to confidently keep getting slower while it's blaring and get to the edge before wing stall. And there are those who don't.
     
  4. Daleandee

    Daleandee Pattern Altitude

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    Well ... if you don't want one, don't need one, & don't care to have one the answer is easy ... don't have one! :crazy:

    But I want one, don't need one, do like having one and it's my plane, my choice!

    Yulp I have one ... :happydance:
     
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  5. PaulS

    PaulS Touchdown! Greaser!

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    Wait a minute, what are we talking about here??
     
  6. Tarheelpilot

    Tarheelpilot Final Approach

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    Have you ever used an AOA?
     
  7. Salty

    Salty Final Approach

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    Hang on, not seeing how an AOA is going to give me best glide. What am I missing?
     
  8. Flocker

    Flocker Pre-takeoff checklist

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    Does anyone know where I can get a good AOA indicator? LMAO.
     
  9. Daleandee

    Daleandee Pattern Altitude

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    Freedom of choice ...
     
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  10. DoubleD

    DoubleD Pre-takeoff checklist

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    Don't know about you guys, but I can't hear the stall warning horn over engine noise and headset unless I'm specifically listening for it. Totally useless IMO.
     
  11. Chip Sylverne

    Chip Sylverne Final Approach

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    Quit with the negative waves, man.
    Get in your airplane. Get to a safe altitude and fly the POH book numbers for L/D max at your weight with engine at idle. Make note of the AOA, or even on the AOA.. That will be your best glide AOA, no matter your weight or altitude. If the fan stops in the future, just immediately pitch to that attitude.
     
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  12. luvflyin

    luvflyin Touchdown! Greaser!

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    Yes. An Alpha Systems.
     
  13. Salty

    Salty Final Approach

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    How is that easier than pitching for airspeed?
     
  14. nauga

    nauga Administrator Management Council Member PoA Supporter

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    Airspeed for best L/D changes with weight. AOA for best L/D does not.

    Nauga,
    now in units
     
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  15. luvflyin

    luvflyin Touchdown! Greaser!

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    Not from them. The Lift Management Accessories Organization does not sell them
     
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  16. Salty

    Salty Final Approach

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    Yeah, I thought about that after I posted.
     
  17. Tarheelpilot

    Tarheelpilot Final Approach

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    Ok. Just curious.
     
  18. Cogito

    Cogito Pre-takeoff checklist

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    An AOA can push the stick forward, (on Garmin G3X, at least) and keep you from getting slow if you're saturated. Just have to turn this off if you're practicing stalls.
     
  19. SoCal RV Flyer

    SoCal RV Flyer En-Route

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    Yes...know your speeds. 76 KIAS in my plane for just me and half tanks; 82 KIAS at max gross.
     
  20. nauga

    nauga Administrator Management Council Member PoA Supporter

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    Or your AOA. 15 units at zero fuel weight. At max gross...let's see.........15 units. ;)

    Nauga,
    constantly
     
  21. MBDiagMan

    MBDiagMan En-Route

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    Cessna didn’t put a stall warning on the 140 in 1948. It’s not necessary on it anyway.
     
  22. Clip4

    Clip4 Final Approach

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    If you are flying a typical production airplane in and out of a typical public airport, there is no need for an AOA.
     
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  23. Chip Sylverne

    Chip Sylverne Final Approach

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    Quit with the negative waves, man.
    I see that many of the new electronic instrument are including AOA's that compute aoa from air data. Anyone have any experience with how accurate they are? seems like a great value added, if they work.
     
  24. nauga

    nauga Administrator Management Council Member PoA Supporter

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    TLDR: the big-name systems tend to be accurate enough to be used as a performance instrument. There are some outliers that have some issues (and some that advertise these issues as 'features') but by and large they're decent.

    Long-form answer: Define "accurate." They are as accurate as their calibration, which can be airplane dependent. That being said, how you use them may not require explicit 'accuracy'. Most AOA flying doesn't need a super tight calibration from raw air data to degrees (or radians if you're a glutton for punishment), all you (or I) care about is that the indications are consistent, i.e. it always reads the same value at the same true angle of attack and that the indicated value has the same trend as the true angle of attack - it increases as angle of attack increases and decreases when angle of attack decreases. I don't care if it reads 22 'units' when I'm really at 12 degrees AOA, so long as it *always* reads 22 at 12. Pneumatic AOA systems can do this pretty well as long as there's a little signal processing to account for total pressure in addition to the differential.

    Nauga,
    under pressure
     
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  25. luvflyin

    luvflyin Touchdown! Greaser!

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    There was thread quite awhile back about that. After reading about them and how they worked, I thought that I would trust them only so far and thought that they shouldn't be using the term AOA.
     
  26. nauga

    nauga Administrator Management Council Member PoA Supporter

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    Had to dig out the link but here's a paper by the same guy that did the 'impossible turn' paper that everyone likes to reference. They *can* be pretty accurate, but there are no absolutes. The normalization with dynamic pressure he shows makes the results consistent and unique is what I was alluding to when I said "as long as there's a little signal processing to account for total pressure in addition to the differential."

    As for not calling it AOA, I'm not sure

    Nauga,
    abnormalized
     
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  27. Stewartb

    Stewartb Final Approach

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    My G3X’s GSU-25 is the system’s air data computer. It’s equipped with an AOA port but lots of guys tee it into the static line to not utilize it. I added Garmin’s AOA probe and connected the new Pitot and AOA lines (re-plumbing an installed GSU is not fun). A separate static line is still required. The primary G3X screen supports AOA without adding the separate box on the windscreen but it can be added easily. The pilot determines the airspeeds for the green and yellow ranges. You run a stall series in setup mode and the G3X sets the red range. Its a very interesting instrument. Garmin calls it a true AOA indicator, not a lift reserve indicator. That’s an interesting topic on its own, AOA vs LRI.
     
  28. luvflyin

    luvflyin Touchdown! Greaser!

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    Yeah on the AOA vs LRI thing. Is a vane type the only true AOA? I dunno. Comparing both of them to these 'air data computer' things, the one I remember reading about had no external, additional probelike thingies. It was just crunching the numbers from the things that were already in the plane. The pilots guide had warnings about it's short comings. I still don't like them calling it an AOA.
     
  29. nauga

    nauga Administrator Management Council Member PoA Supporter

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    Yours really is an AOA indicator. A 'lift reserve indicator' is essentially the same plumbing without the normalization with dynamic pressure, and as such doesn't require any additional signal processing. I'm not a big fan of them, but some people love 'em.

    Nauga,
    ported
     
  30. nauga

    nauga Administrator Management Council Member PoA Supporter

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    No. Differential pressure can easily be as 'accurate' as a typical vane if it's implemented correctly. They just have different sources of error and ways to manage them.

    Nauga,
    who knows 'implemented correctly' is not always applicable, but that applies to vanes as well
     
  31. luvflyin

    luvflyin Touchdown! Greaser!

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    ??? Aren't these Lift Reserve Indicators. It has it's own external probe. I am probably misunderstanding what you are saying.
    https://www.alphasystemsaoa.com/
     
  32. luvflyin

    luvflyin Touchdown! Greaser!

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    Yeah, I get that. But getting that 'pressure differential' from something that is not specifically designed for that purpose, AOA, seems inaccurate to me. The Garmin thing without 'probes' being a true AOA while the LRI with probes designed for that purpose not being, is not passing the logic check with me.
     
  33. dmspilot

    dmspilot En-Route

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    What I want to know is how many pages before someone says what's in my avatar?
     
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  34. PaulS

    PaulS Touchdown! Greaser!

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    It's a blue donut. The AOA in the FIKI perspective + doesn't have one.
     
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  35. luvflyin

    luvflyin Touchdown! Greaser!

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    Two. 73 posts to be exact. You just did. Speaking of which, is that guy from Hawaii still around here. The one who was hawking AOA's. He changed the go to punchline here from Cirrus Chutes to Blue Donuts for awhile:goofy:
     
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  36. nauga

    nauga Administrator Management Council Member PoA Supporter

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    A 'lift reserve indicator' works by differential pressure, and it's indication will change if angle of attack is constant but dynamic pressure (i.e. airspeed) varies, so it is not a true indication of angle of attack. If that differential pressure is normalized (read: divided by) with dynamic pressure it will not vary with dynamic pressure but will show the same quantity at the same angle of attack even if dynamic pressure varies, so can be calibrated to indicate the angle of attack.

    I'm just not getting the distinction, sorry. Pressure at different points can be used to calculate airspeed, altitude, angle of attack, and so on. A vane can be used as a means of sensing airflow direction at some location, and pressure at different points can be used as a means of sensing airflow direction at some location. Either can be a valid way of calculating and displaying angle of attack. The Dynon 'thing' I have is just a second port on my pitot tube, as I believe the Garmin unit is. Just because some sensors use a separate probe does not invalidate what they measure - and a vane is, in fact, a separate probe.

    Nauga,
    and curved air
     
    Last edited: May 1, 2021
  37. luvflyin

    luvflyin Touchdown! Greaser!

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    Does your Dynon thing use the Pitot Tube that was on the plane before you installed the Dynon. Or does it come with a Pitot to replace the one already there? What I'm getting at is the 'accuracy' of the Ram/Static difference. The accuracy of the difference needed it seems to me would be more to give accurate AOA indications than would be needed to give just airspeed. Giving airspeed is what Pitot Tubes do. Piper vane style Pitots look a lot like the sensors supplied with LRI's. Don't some 'tube type' pitots not even have a static port? The static port is over yonder on the fuselage somewhere? Not arguing, just trying to understand all this.
     
  38. Stewartb

    Stewartb Final Approach

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    The Garmin probe. Instructions require the static come from a different source not under the wing. Two different size holes in the nose, three little holes on the bottom.
     

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  39. nauga

    nauga Administrator Management Council Member PoA Supporter

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    The pneumatic AOA systems don't use the difference between ram and static to calculate AOA, it's the difference between total (ram) and a different port that measures something not fully aligned with the flow and not completely static. Pitot tubes don't 'give airspeed', they give pressures which are used to calculate airspeed or any number of other parameters. Your airspeed indicator is 'calculating' indicated airspeed mechanically using the known relationship between a pressure differential and speed. My pitot tube has a port in the tip (total) and a not-quite-aligned port, the static port is not on the tube. The static input is only used in the dynamic pressure used to normalize the measurement. The pressure differential for AOA (but not the full calculation) is the difference between the total and the not-quite-aligned ports.

    Nauga,
    whose curves collapse
     
  40. Chip Sylverne

    Chip Sylverne Final Approach

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    Quit with the negative waves, man.
    Display name?