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Thread: Aoa

  1. #11
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    Default Re: Aoa

    Exactly what av8rps says here.

    Quote Originally Posted by av8rps View Post
    Yeah, I agree. But when you calibrate it you are primarily identifying at what speed and angle the wing begins losing lift, right?...

  2. #12
    Senior Member jiott's Avatar
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    Default Re: Aoa

    There are many places on the internet where you can read really good explanations of AOA and measuring systems. In a nutshell what I have gathered is that stall has very little to do with airspeed but everything to do with wing chord angle to the relative wind direction. If all conditions remain the same as is true in many landing approaches, then yes airspeed can be a good indicator. But if things change such as bank angle, flap configuration, control coordination, and some other things I can't remember now, then airspeed is no longer an accurate measure; however AOA instrumentation is still accurate. You and only one other guy I know has the balls to actually fly a short field approach with the wing starting to shudder. Since all AOA instrumentation is progressive rather than singular, you can fly a short field approach as close to or as far away from stall as you feel comfortable. I like my Dynon system that starts a slow beep in my headphones and progressively gets faster until the beep becomes a steady tone immediately before stall buffet. This progression is programmable during the setup and calibration. It also allows you to keep your eyes outside where they belong.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  3. #13
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    Default Re: Aoa

    AOA in a KF is a waste of $$.

  4. #14
    Senior Member Esser's Avatar
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    Default Re: Aoa

    I like the idea of an audible alert so your eyes are outside.
    ------------------
    Josh Esser
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  5. #15
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    Default Re: Aoa

    Good point. I just rely on seat of the pants and sink rate. Below 45-50 mph sink rate increases proportionally. When you're falling like a rock, you're probably stalled....

  6. #16
    Super Moderator Av8r3400's Avatar
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    Default Re: Aoa

    Quote Originally Posted by Esser View Post
    I like the idea of an audible alert so your eyes are outside.
    I do too. Having the Dynon in the panel, it wasn't a big leap to get e dual pitot tube and hook it up.

    Many people don't understand this isn't just a speed warning, it is a differential pressure measurement by two differently angled pitot tubes giving the angle of the relative wind to the wing chord.
    Av8r3400
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  7. #17
    Senior Member jiott's Avatar
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    Default Re: Aoa

    Floog you are one of the guys I mentioned who flys landing approaches in an early stall condition. Not for everyone, including me.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  8. #18
    Senior Member aviator79's Avatar
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    Default Re: Aoa

    Quote Originally Posted by jiott View Post
    There are many places on the internet where you can read really good explanations of AOA and measuring systems. In a nutshell what I have gathered is that stall has very little to do with airspeed but everything to do with wing chord angle to the relative wind direction...
    This.
    To placard your panel in lieu of an AOA indicator, you'd have to have a multi-dimensional lookup table with at least bank angle, weight, CG location, and you'd have to cross-reference several instruments with that table to know at what speed your plane will stall. A common stall/spin LOC scenario is pulling too hard of a bank to compensate for overshooting final. I very much doubt you'll take the time to figure out your stall speed in that scenario, but an AOA indicator can let you know how much margin you have at a glance.

    You may or may not find that AOA information is necessary or useful the way you fly your airplane, but making a table is definitely not the same thing as having a calibrated AOA indicator.

  9. #19
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    Default Re: Aoa

    Jott, How did you know I was 'one of those guys???

    1.3Vso is not an 'early stall' or even an 'imminent stall'. That's a normal safe stabilized approach airspeed for many aircraft including Kitfoxes. 45-50 mph is in that range and it's a safe margin above the stall in smooth air. As I mentioned, a slower approach speed gives a greater sink rate (steeper angle) that allows me better short field landing performance. "Slow down to go down."

    I'll admit that in 'feeling out' the slowest possible approach speed, I have, on two occasions, unintentionally stalled less than a hundred feet from the ground! In one instance, I thought I was too high to make the intended touchdown spot: the leading edge of the numbers on an 8,000 ft runway. I slowed even more, stalled, then recovered with a blast of power and made one of my finest landings and on that spot! In the other instance, a headwind to tailwind shear on short final sent me down like a falling elevator (stalled). It was again a full power recovery. In both cases, I had to change out my underwear.... But I did land SHORT. Ha, ha! Love the Kitfox!

  10. #20
    Senior Member av8rps's Avatar
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    Default Re: Aoa

    Ok, I'm learning more about why some of you like an AOA. And hey, in aviation the more tools you have the better off you are. So please understand that I'm not dissing anyone for having one.

    Part of my reason for questioning an AOA was based on an experience I had helping a friend calibrate one on his Highlander. By the time we were done I felt it was as if we just installed a stall warning horn (which I also did on another friends homebuilt previous). Of course, while I truly felt both had over-killed their simple and super docile airplanes, they both felt better having their new gadgets. And what the heck, if it improves safety for them, more power to them. I just never felt the need as I find Kitfoxes, Highlanders, and Avids just so easy to fly. It's almost as if they talk to you when they get close to stalling.

    But to further improve my understanding of an AOA I'm going to take the advice given earlier and cruise the internet on AOA's to see what I can learn. I'm actually still curious about what I might be missing? I'll report back if I have an epiphany.

    And for the record, I don't fly approaches with the airframe buffeting in a stall. But I am confident I could if needed to. I generally don't even use the standard 1.3 x stall speed for landing approaches as I learned back in my early Avid Flyer ownership days that while my 360 lb Avid stalled at only 22 mph, the sink rate was incredible under 30 mph due to the super high lift but draggy airfoil, so a 45 mph (or more) approach worked much better. It would interesting to see how an AOA would suggest landing that Avid?

    With all that said, I feel our Kitfoxes are just so docile and predictable that an average pilot should easily be able to understand what the plane is telling you as it approaches a stall, regardless of all the variables like weight, speed, bank angle etc, etc.

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