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Thread: Angle of attack

  1. #11

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    Bob, I really don't look forward to cutting or even just drilliing into the wings, they are old! And I don't have a glare sheild, must less space on top of it. But thanks for the info and advice. If you have any photos of the AFS device or its installation maybe you could post them here. I'll also try to look it up online.

    And as for as a stall warning, that may be good also, but the feel of the controls and buffet of the airframe, (tailplane) are good ones that don't require looking at an instrument.

  2. #12
    Sam Buchanan's Avatar
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    Quote Originally Posted by Bill Greenwood View Post

    The biggest reason that I have not installed the AOA is having to cut into the wing, and also shortage of panel space for the indicator. I don't have any EFIS in my plane and don't want one, but if I did have an AOA, I would like to have it stand out and not be buried in another display if I was going to be using for a critical moment like landing.
    My LRI probe is mounted to an inspection cover. Other probes have been mounted to a wing strut. Cutting into a wing should not be necessary in order to install an AOA sensor.

    My guess, and nothing much to base this on , is that once you start using an AOA you probably find that is and the airspeed indicator are pretty much in agreement. By that I mean that if you do a short field slow landing and come in on the margin at the bottom of the color arc on the AOA, then you will be at the speed that you would use anyway on the airpseed indicator for such a landing. Thus one comfirms the other.
    Only if flying weight and density altitude never change.

    But when weight or DA changes, the plane will stall at a different indicated airspeed. If you intend to land at a short grass strip on a hot day and you have a bubba passenger, what will be the indicated stall speed? Some mental gymnastics may get you close, but the AOA won't lie, it will accurately indicate how close you are to stall regardless of conditions.

    And that is the beauty and true safety value of AOA. I had a bug try to fly up the pitot tube and the EFIS went goofy. But the mechanical LRI was untouched and provided the same values I always use for every landing. Sometimes I get asked what landing speed I use in the RV-6. My reply is "not sure, I'm watching the AOA".
    Sam Buchanan
    The RV Journal RV-6 build log
    Fokker D.VII semi-replica build log

  3. #13

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    Sam, next time you are doing landings maybe try a few with a glance at both the airspeed indicator and the AOA indicator, so that you can see if the AOA is telling you anything different than the airspeed. I would think that anyone would do that when they first installed the AOA and did the first flights afterward, unless it is a new plane.

    For some large planes like an airliner or transport or bomber, where weight will vary a lot, an AOA may be usefull. I don't have much direct experience with these types.
    Of course stall speed varies with weight,and usually in the operators manual stall speeds are given at gross weigth, both clean and as VSO, so they are at the top edge and give you a little margin of safe airspeed if you are heavy.


    But does stall speed vary with a change in density altitude and which way?
    It has been my experience that stall speed, with the same weight and same configuration ,and same g load is at the same INDICATED airspeed, even if the true airspeed is different.
    My Cub for instance stalls at 38mph indicated , power off, and it is the same summer or winter.

    As for installation , the plane I'd use it on does not have struts, and no inspection covers on the leading edge, but I may take a look again at more specifics of that. I don't see much point in putting one on a Cub that lands in a few hundred feet anyway.
    Last edited by Bill Greenwood; 12-18-2012 at 11:03 PM.

  4. #14
    Sam Buchanan's Avatar
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    Quote Originally Posted by Bill Greenwood View Post
    Sam, next time you are doing landings maybe try a few with a glance at both the airspeed indicator and the AOA indicator, so that you can see if the AOA is telling you anything different than the airspeed. I would think that anyone would do that when they first installed the AOA and did the first flights afterward, unless it is a new plane.
    In my article I explained how I tested the LRI with two different loadings of the RV-6. Stall speed changed but AOA indication at stall didn't.

    And I didn't mean to imply I never look at the airspeed. I usually cross check a couple of times just to make sure nothing weird is happening but when doing a high performance landing (or takeoff) on a short strip the LRI is the primary instrument.

    As for installation , the plane I'd use it on does not have struts, and no inspection covers on the leading edge, but I may take a look again at more specifics of that. I don't see much point in putting one on a Cub that lands in a few hundred feet anyway.
    Is AOA essential for flight? Of course not, but I guarantee that once accustomed to having it available its value will be appreciated. I really like knowing precisely how close I am to having the wing stall. I even put one on my Legal Eagle for test flights because its stall speed is so low the airspeed indicator falls off the scale.
    Last edited by Sam Buchanan; 12-19-2012 at 08:05 AM.
    Sam Buchanan
    The RV Journal RV-6 build log
    Fokker D.VII semi-replica build log

  5. #15

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    Quote Originally Posted by Bill Greenwood View Post
    Bob, I really don't look forward to cutting or even just drilliing into the wings, they are old! And I don't have a glare sheild, must less space on top of it. But thanks for the info and advice. If you have any photos of the AFS device or its installation maybe you could post them here. I'll also try to look it up online.

    And as for as a stall warning, that may be good also, but the feel of the controls and buffet of the airframe, (tailplane) are good ones that don't require looking at an instrument.

    All the AFS AOA support and installation docs can be found at: http://www.advanced-flight-systems.c...oasupport.html

    Marketing/Sales data at: http://www.advanced-flight-systems.c...s/AOA/aoa.html
    --
    Bob Leffler
    RV-10 Flying
    www.mykitlog.com/rleffler

  6. #16

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    Sam, you wrote that when density altitude changes,"the plane will stall at a different indicated airspeed".

    I don't think I am misquoting you, but I don't think that is true.

    I think a plane will stall at the same INDICATED AIRSPEED even at different density altitudes, If not, then if we flew from sea level in Tex or Wis to Leadville, Colo which is 10,000 feet airport; we would need to fly our landing approach (normally 1.3 VSO ) at a different indicated airspeed, since the density altitude will be vastly different, by perhaps 10,000 feet not counting temperature changes. If we went from winter in Denver to summer in Scottsdale the temp would be vastly different , but I think the stall would stiil be at the same indicated airspeed( if g load and configuration is the same). Of course the true airspeed will be higher, maybe 15 knots higher at high density altitude ,but we are talking about INDICATED , not true.

    That is not the way that I learned to fly and not the way that I do fly. Of course , I may be wrong.
    I may have been doing it the wrong way for 30 years, using the same indicated airspeed for each approach, if the weight and wind are not a factor.

    What say you? Not on weight change affect on INDICATED STALL SPEED, which we know , but on density alititude affects.

    Bob, thanks for the info on installation.
    One thing I noticed is that the factory has specific installation locations, even to the 1/4 inch for the planes listed. But what happens if you want to put in a AOA and your plane is not one that they have tested? You don't want to try trial and error locations and and end up with mulitple holes drilled in the wing or even in inspection covers?

    That is not how I learned to fly and not how I fly an approach.
    Last edited by Bill Greenwood; 12-19-2012 at 11:14 AM.

  7. #17

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    Quote Originally Posted by Bill Greenwood View Post
    Bob, thanks for the info on installation.
    One thing I noticed is that the factory has specific installation locations, even to the 1/4 inch for the planes listed. But what happens if you want to put in a AOA and your plane is not one that they have tested? You don't want to try trial and error locations and and end up with mulitple holes drilled in the wing or even in inspection covers?
    I can't help you there. That would be a good question to give Rob Hickman at AFS. They do have an online support forum if you are truly curious. I was fortunate in the I have the same a/c (RV-10) that Rob has. I can copy his parameters and get 99% dialed in, then conduct testing to validate the settings.

    bob
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    Bob Leffler
    RV-10 Flying
    www.mykitlog.com/rleffler

  8. #18

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    Stall speed will be at the same indicated airspeed given the same weight, CG, and G load, independent of density altitude. The indicated airspeed stall speed changes with aircraft weight and G loading. Remember indicated airspeed is NOT true airspeed.

    For your typical light aircraft, you can use indicated airspeed and do not need something with colored lights to tell you that you are not at the appropriate approach airspeed. On your average Piper, or even an RV, an AOA indicator has some cool factor, but adds weight and duplicates the information that you already have. I will observe that far too many pilots do not do a good enough job of identifying and flying the appropriate airspeed on approach for the airplane configuration and weight. If your indicated airspeed is going up and down 15kts on final, adding an AOA indicator will just add the entertainment and distraction of its display moving up and down and changing color in sync with the airspeed indicator's needle. In the end, you will likely get greater benefit from spending the money on avgas and flying patterns to build your stick and rudder skills.

    On the topic of where you locate the ports in a wing for a differential pressure based AOA calculation, the location of the ports is dependent on the wing and the shape of its leading edge. If you can find an airplane that has the same wing section that yours has, and the AOA port locations have already been figured out for that wing, then you have a good starting point. But if your flying skills are good enough to calibrate that type of AOA system, you likely do not need that gizmo anyway.

    An AOA display is a great help when you launch at a weight of 750,000 lbs and your landing weight is 450,000 lbs. For a Piper Cub, not so much.

    Gadgets are fun, but if you are in this for the flying, buy gas.

    Best of luck,

    Wes
    N78PS

  9. #19

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    A homemade AOA probe can be made for $10 for use with an EFIS. See post #14 of this thread:
    http://www.vansairforce.com/communit...ad.php?t=34040
    I installed it on my RV-12 with Dynon D-180 and the AOA works great.
    Although I have not tried it, the homemade probe should work with a differential pressure gauge (0 to 5" water) with the second port connected to the pitot tube.
    Joe Gores

  10. #20

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    Sport Aviation AOA articles

    I did a search of past EAA articles and found the following pertaining to AOA:
    Better Way to Fly - May 1998 http://www.oshkosh365.org/saarchive/...1998_05_06.pdf
    Carrier Pilots' Secret - July 1999 http://www.oshkosh365.org/saarchive/...1999_07_31.pdf
    Test Pilot: Angle of Attack - April 2001 http://www.oshkosh365.org/saarchive/...2001_04_20.pdf
    Test Pilot: Angle of attack and lift/drag - May 2001 http://www.oshkosh365.org/saarchive/...2001_05_19.pdf
    Test Pilot: Angle of Attack - November 2003
    REPRINT of Apr 2001 article http://www.oshkosh365.org/saarchive/...2003_11_20.pdf
    Shop Talk: Angle of Attack Indicator - December 2008
    http://www.oshkosh365.org/saarchive/...2008_12_21.pdf
    The December 2008 article by Dave Barker describes how to build the AOA sensor using a hall effect transducer and LED bar graph display.
    Below are links to the author's website. Dave Barker's pdf gives more detailed construction details than the EAA magazine article.
    http://www.barkeraircraft.com/files/AOA_rDisplay.pdf
    http://www.barkeraircraft.com/AOA_kit.html
    Although Dave Barker no longer sells AOA kits, he still has some circuit boards available. There is a link to his email address on his website.
    Joe Gores

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