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mrspudandcompany(at)veriz
Guest

Posted: Fri Feb 11, 2011 8:44 am Post subject: AOA indicator

What effect does icing have on the accuracy of an AOA indicator?  Will it

give you an accurate indication of an impending stall if you have

accumulated ice on the wing leading edge?



Roger

nuckolls.bob(at)aeroelect
Guest

Posted: Fri Feb 11, 2011 9:24 am Post subject: AOA indicator

At 11:24 AM 2/11/2011, you wrote:

 	  Quote: 	
		  

<mrspudandcompany(at)verizon.net>



What effect does icing have on the accuracy of an AOA indicator?  Will it

give you an accurate indication of an impending stall if you have

accumulated ice on the wing leading edge?


	


    No . . . . Most AOA displays don't  give you

    an 'angle' display. They generally display bands

    of relative goodness/badness shaded in legacy red, yellow

    and green. The display will probably be fitted with a

    'sweet spot' . . . which represents an AOA value

    optimized by much flight testing.



    The problem is that the any sweet spot assumes that

    the wing is clean and stall breaks at xx.x degrees.

    Just lowering flaps can give you a new sweet spot at

    yy.y degrees. The more sophisticated AOA display

    systems will have inputs for flap position so that

    the sweet spot is automatically moved to a new value

    confirmed by careful flight testing.



    Once you add ice shapes on top of those super whippy,

    laminar flow, high efficiency, low drag, etc etc

    air foils, the stall break moves to zz.z degrees.



    Unless iced over, the AOA sensor will continue to

    give you an accurate AOA display. The problem is

    that any knowledge the AOA possesses with respect

    to airplane performance is now suspect.



    It's not a loss of display integrity that bites.

    It's a departure from performance conditions under which

    IAS or AOA sweet spots were deduced.

   Bob . . .

email(at)jaredyates.com
Guest

Posted: Fri Feb 11, 2011 9:27 am Post subject: AOA indicator

Generally, no, it will not give accurate information.  A wing that used to stall at 13 degrees might stall at 10 or 8 with ice (for instance, these aren't necessarily accurate numbers).  In fact, this has been a source of at least a few crashes of transport category airplanes that stalled on takeoff without activation of the stall protection systems.  Ice accumulation combined with an aggressive rotation rate and the ground effect were sufficient to push the stall AOA below the thresholds for the stick shaker and pusher, so in some cases the crews didn't even get any indication that the airplane was stalled, other than the sudden 90 degree bank angle.  An AOA indicator might or might not indicate degrees AOA correctly, but even if it does, it's information doesn't mean anything, since you don't know what the stall AOA is of your "new" experimental airfoil shape. 

On Fri, Feb 11, 2011 at 11:24 AM, ROGER &  JEAN CURTIS <mrspudandcompany(at)verizon.net (mrspudandcompany(at)verizon.net)> wrote:

 [quote]--> AeroElectric-List message posted by: "ROGER &  JEAN CURTIS" <mrspudandcompany(at)verizon.net (mrspudandcompany(at)verizon.net)>

  

 What effect does icing have on the accuracy of an AOA indicator?  Will it

 give you an accurate indication of an impending stall if you have

 accumulated ice on the wing leading edge?

 

 Roger

 

 

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 [b]

dee.whittington(at)gmail.
Guest

Posted: Sat Feb 12, 2011 5:55 am Post subject: AOA indicator

Even though what Bob says about the critical angle of attack changing with the accretion of ice is, of course, correct, it would be good to have an AOA indicator which was not killed by ice.  I just remembered that our new Grand Rapids HX (and in fact all new Grand Rapids EFIS units) now have a "AOA Indexer" built in. They display angle of attack on the left side of the screen derived from, I think, AHARS data, not from unheated pin holes in the wing. 



 Unfortunately, the GRT web site currently does not explain, or even mention this new feature. I've just brought this to the attention of Carlos Fernandez at GRT and he promised to update the web site.



 Dee



 At 11:19 AM 2/11/2011, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckolls.bob(at)aeroelectric.com>



 At 11:24 AM 2/11/2011, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: "ROGER &  JEAN CURTIS" <mrspudandcompany(at)verizon.net>



 What effect does icing have on the accuracy of an AOA indicator?  Will it

 give you an accurate indication of an impending stall if you have

 accumulated ice on the wing leading edge? 	


    No . . . . Most AOA displays don't  give you

    an 'angle' display. They generally display bands

    of relative goodness/badness shaded in legacy red, yellow

    and green. The display will probably be fitted with a

    'sweet spot' . . . which represents an AOA value

    optimized by much flight testing.



    The problem is that the any sweet spot assumes that

    the wing is clean and stall breaks at xx.x degrees.

    Just lowering flaps can give you a new sweet spot at

    yy.y degrees. The more sophisticated AOA display

    systems will have inputs for flap position so that

    the sweet spot is automatically moved to a new value

    confirmed by careful flight testing.



    Once you add ice shapes on top of those super whippy,

    laminar flow, high efficiency, low drag, etc etc

    air foils, the stall break moves to zz.z degrees.



    Unless iced over, the AOA sensor will continue to

    give you an accurate AOA display. The problem is

    that any knowledge the AOA possesses with respect

    to airplane performance is now suspect.



    It's not a loss of display integrity that bites.

    It's a departure from performance conditions under which

    IAS or AOA sweet spots were deduced.



 

   Bob . . . 



 AeroElectric-List Email Forum -

  http://www.matronics.com/Navigator?AeroElectric-List

 - MATRONICS WEB FORUMS -

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 - List Contribution Web Site -

 -Matt Dralle, List Admin.

  http://www.matronics.com/contribution

 

 	
 

 DeWitt (Dee) Whittington

 406 N Mulberry St

 Richmond, VA 23220-3320

 (804) 358-4333 phone and fax

 SKYPE: hilltopkid

 dee.whittington(at)gmail.com     [quote][b]

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Feb 12, 2011 7:59 am Post subject: AOA indicator

 	  Quote: 	
		  They display angle of attack on the left side of the screen derived 

from, I think, AHARS data, not from unheated pin holes in the wing.



Unfortunately, the GRT web site currently does not explain, or even 

mention this new feature. I've just brought this to the attention of 

Carlos Fernandez at GRT and he promised to update the web site.


	


    How does it matter where and how some AOA value is

    measured or synthesized once the wing is iced?



    I was once enamored of the delta-p AOA sensor

    designs. There have been a number of articles

    published on the technique. I've posted a collection

    of my archived articles at:



http://www.aeroelectric.com/articles/Angle_of_Attack/



    There was an article in a Sport Aviation issue in

    2005 for a DIY AOA sensor/display package. Anyone

    got a copy in their library? I'd sure like to

    read a copy.



    The common thread that runs through these articles

    is an absence of discussion as to when the readings

    so carefully calibrated and displayed are not

    to be trusted.



   Bob . . .

pwmac(at)sisna.com
Guest

Posted: Sat Feb 12, 2011 9:08 am Post subject: AOA indicator

Interestinb, but production units are out there.

Lets not ignore what Elbie said about the AOA in icing contitions.

For sure he is the guru on these devices for all kinds of airplanes

http://www.riteangle.com/

PaulW

=========



At 06:55 AM 2/12/2011, you wrote:

 	  Quote: 	
		  

<nuckolls.bob(at)aeroelectric.com>

>They display angle of attack on the left side of the screen derived 

>from, I think, AHARS data, not from unheated pin holes in the wing.

>

>Unfortunately, the GRT web site currently does not explain, or even 

>mention this new feature. I've just brought this to the attention 

>of Carlos Fernandez at GRT and he promised to update the web site.



    How does it matter where and how some AOA value is

    measured or synthesized once the wing is iced?



    I was once enamored of the delta-p AOA sensor

    designs. There have been a number of articles

    published on the technique. I've posted a collection

    of my archived articles at:



http://www.aeroelectric.com/articles/Angle_of_Attack/



    There was an article in a Sport Aviation issue in

    2005 for a DIY AOA sensor/display package. Anyone

    got a copy in their library? I'd sure like to

    read a copy.



    The common thread that runs through these articles

    is an absence of discussion as to when the readings

    so carefully calibrated and displayed are not

    to be trusted.



   Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Sat Feb 12, 2011 10:31 am Post subject: AOA indicator

At 11:57 AM 2/12/2011, you wrote:

 	  Quote: 	
		  



Interestinb, but production units are out there.


	


    Yup, lots of them . . .



 	  Quote: 	
		  Lets not ignore what Elbie said about the AOA in icing contitions.

For sure he is the guru on these devices for all kinds of airplanes


	


    But what do YOU understand and are willing to pass

    along to the less informed as to the value of

    and AOA sensor and display system? What statements

    have been made by myself or anyone else that you

    find in error? Is it your understanding that Elbie

    claims that the "sweet spot" on his or any other

    AOA display is golden under all challenges that

    a pilot might face for comfortable arrival with

    the earth?



   Bob . . .

retasker(at)optonline.net
Guest

Posted: Sat Feb 12, 2011 12:42 pm Post subject: AOA indicator

If you are an EAA member you can see ALL back issues of Sport Aviation 

on http://www.oshkosh365.org



If that doesn't do it for you I do have the 2005 issues but I would have 

to see what issue it was in.  Do you remember what month?



Dick Tasker



Robert L. Nuckolls, III wrote:

 	  Quote: 	
		      There was an article in a Sport Aviation issue in

    2005 for a DIY AOA sensor/display package. Anyone

    got a copy in their library? I'd sure like to

    read a copy.


	


-- 

Please Note:

No trees were destroyed in the sending of this message.  We do concede, however,

that a significant number of electrons may have been temporarily inconvenienced.

--

pwmac(at)sisna.com
Guest

Posted: Sat Feb 12, 2011 2:05 pm Post subject: AOA indicator

I do noy have his message, but it went like any chance of icing 

forget about the aoa As the readings will be bad..

PaulW

==

At 09:27 AM 2/12/2011, you wrote:

 	  Quote: 	
		  

<nuckolls.bob(at)aeroelectric.com>



At 11:57 AM 2/12/2011, you wrote:

>

>

>Interestinb, but production units are out there.



    Yup, lots of them . . .



>Lets not ignore what Elbie said about the AOA in icing contitions.

>For sure he is the guru on these devices for all kinds of airplanes



    But what do YOU understand and are willing to pass

    along to the less informed as to the value of

    and AOA sensor and display system? What statements

    have been made by myself or anyone else that you

    find in error? Is it your understanding that Elbie

    claims that the "sweet spot" on his or any other

    AOA display is golden under all challenges that

    a pilot might face for comfortable arrival with

    the earth?



   Bob . . .

kuffel(at)cyberport.net
Guest

Posted: Sat Feb 12, 2011 5:09 pm Post subject: AOA indicator

<< How does it matter where and how some AOA value is measured or 

synthesized once the wing is iced? >>



The Dynon AOA sensor is a single heated probe with two holes which replaces 

the standard pitot sensor.  It has temperature control so you just leave it 

on all the time.  Thus is it relatively immune to icing.  This means I will 

have one less distracter when I follow Bob's (and others) great advice to 

get the heck out of wherever I am if ice is encountered.

Tom Kuffel

retasker(at)optonline.net
Guest

Posted: Sat Feb 12, 2011 6:05 pm Post subject: AOA indicator

While the AOA is relatively immune to icing, and it's output is accurate 

for your clean wings, it doesn't have any way to know the wings are iced 

up or how to take into consideration the degradation in performance when 

the wings have ice on them.  Therefore, if you pay attention to it's 

readings you could end up stalling.



That is what the original poster was referring to.  Even though the AOA 

is working perfectly, it is giving you false information.



Dick Tasker



The Kuffels wrote:

 	  Quote: 	
		   

 <kuffel(at)cyberport.net>



 << How does it matter where and how some AOA value is measured or 

 synthesized once the wing is iced? >>



 The Dynon AOA sensor is a single heated probe with two holes which 

 replaces the standard pitot sensor.  It has temperature control so you 

 just leave it on all the time.  Thus is it relatively immune to 

 icing.  This means I will have one less distracter when I follow Bob's 

 (and others) great advice to get the heck out of wherever I am if ice 

 is encountered.

 Tom Kuffel




	


-- 

Please Note:

No trees were destroyed in the sending of this message.  We do concede, however,

that a significant number of electrons may have been temporarily inconvenienced.

--

kuffel(at)cyberport.net
Guest

Posted: Sat Feb 12, 2011 9:13 pm Post subject: AOA indicator

Hi Dick,



<<  That is what the original poster was referring to.  Even though the AOA

is working perfectly, it is giving you false information. >>



And what I'm referring to is if I take avoidance action, as I should, the 

instant ice is encountered I don't have to worry about my Dynon giving me 

"false information".  It will still tell me accurately if my angle of attack 

is well above stall with clean wings.  While I don't know what my stall 

margin actually is at the moment I'm certainly better off than with no or 

incorrect AOA  information.



In other words, as compared to some other AOA systems the Dynon is giving me 

true information.  My job is to apply judgement to take actions which 

prevent the stall margin at normal cruise AOA from narrowing to zero.  And I 

get whatever benefit/insurance, however minor, of a heated pitot.



Tom Kuffel

nuckolls.bob(at)aeroelect
Guest

Posted: Sun Feb 13, 2011 7:08 am Post subject: AOA indicator

At 08:01 PM 2/12/2011, you wrote:

 	  Quote: 	
		  

<retasker(at)optonline.net>



That is what the original poster was referring to.  Even though the 

AOA is working perfectly, it is giving you false information.


	


    I think this is the 'nut' of what has

    yanked some folk's chains. Heated AOA

    or IAS will indeed continue to MEASURE and

    display the rudimentary stimulus that

    the sensor watches. IAS measures

    the DIFFERENCE of two pressures that

    is translated into a CALIBRATED IAS

    reading (complete with sweet-spots

     . . . or sweet-bands)



    AOA can be a vane that actually weather-

    cocks to align with relative wind -or-

    the system can measure pressure differentials.

    Both of those phenomenon are calculated upon

    interpreted, CALIBRATED data are displayed

    along with sweet-spots intended to be

    a guide for operation of the airplane.



    The concept often missed is that these

    sweet-spots are DERIVED numbers confirmed

    by repeated flight tests. In no case does

    either IAS or AOA directly measure the

    the conditions (shape) that set flying qualities

    of particular wing under  conditions that

    exist right now.



    So while the heated instrument is indeed

    performing as advertised in spite of icing

    elsewhere on the airplane, prior CALIBRATIONS

    for the sweet-spot are no longer valid. It's

    perfectly GOOD information. IAS is correct.

    AOA is correct. But the rules of application

    have changed in ways that are difficult to scale

    without taking off our GA pilot's hat and

    putting on the engineering test pilot's hat.



    Here the debate becomes purely personal.

    Do you understand what's necessary to re-

    interpret this data before you attempt a

    landing? If so, it's your choice. But if

    not so sure, then what behaviors (plan-b)

    are most likely to produce a happy outcome

    while ignoring previous calibrations of

    compromised sweet-spots.



    Bob . . .

Mark Sletten

Joined: 10 Jan 2006
Posts: 43
Location: St. Jacob, IL (Near St. Louis, MO)

Posted: Sun Feb 13, 2011 7:44 am Post subject: Re: AOA indicator

 	  kuffel(at)cyberport.net wrote: 	
		  It will still tell me accurately if my angle of attack is well above stall with clean wings.  While I don't know what my stall margin actually is at the moment I'm certainly better off than with no or incorrect AOA  information. 	




That depends on how you interpret and use the data it provides. If you are flying with an iced wing, the only data even the most accurate AOA indication provides is that the wing is not stalling at the current AOA.



An AOA indicator is only that; an indicator. It tells you the current angle of attack. Its only value lies in knowing a second crucial piece of data: at what AOA the wing will stall. If your wing is iced you no longer have the second crucial piece of data.



Given that you have not stalled, the AOA indicator is not providing data you don't already have, that you have, in fact, not stalled. How does an accurate AOA indication help in this scenario?



Mark Sletten

pwmac(at)sisna.com
Guest

Posted: Sun Feb 13, 2011 8:14 am Post subject: AOA indicator

Bingo

Bob, Thanks for the summary

PaulW

=========

At 07:04 AM 2/13/2011, you wrote:

 	  Quote: 	
		  

<nuckolls.bob(at)aeroelectric.com>



At 08:01 PM 2/12/2011, you wrote:

>

><retasker(at)optonline.net>

>

>That is what the original poster was referring to.  Even though the 

>AOA is working perfectly, it is giving you false information.



    I think this is the 'nut' of what has

    yanked some folk's chains. Heated AOA

    or IAS will indeed continue to MEASURE and

    display the rudimentary stimulus that

    the sensor watches. IAS measures

    the DIFFERENCE of two pressures that

    is translated into a CALIBRATED IAS

    reading (complete with sweet-spots

     . . . or sweet-bands)



    AOA can be a vane that actually weather-

    cocks to align with relative wind -or-

    the system can measure pressure differentials.

    Both of those phenomenon are calculated upon

    interpreted, CALIBRATED data are displayed

    along with sweet-spots intended to be

    a guide for operation of the airplane.



    The concept often missed is that these

    sweet-spots are DERIVED numbers confirmed

    by repeated flight tests. In no case does

    either IAS or AOA directly measure the

    the conditions (shape) that set flying qualities

    of particular wing under  conditions that

    exist right now.



    So while the heated instrument is indeed

    performing as advertised in spite of icing

    elsewhere on the airplane, prior CALIBRATIONS

    for the sweet-spot are no longer valid. It's

    perfectly GOOD information. IAS is correct.

    AOA is correct. But the rules of application

    have changed in ways that are difficult to scale

    without taking off our GA pilot's hat and

    putting on the engineering test pilot's hat.



    Here the debate becomes purely personal.

    Do you understand what's necessary to re-

    interpret this data before you attempt a

    landing? If so, it's your choice. But if

    not so sure, then what behaviors (plan-b)

    are most likely to produce a happy outcome

    while ignoring previous calibrations of

    compromised sweet-spots.



    Bob . . .

raymondj(at)frontiernet.n
Guest

Posted: Sun Feb 13, 2011 8:45 am Post subject: AOA indicator

do not archive



***Disclaimer: I've never had an icing encounter in an airplane. The 

following is pure speculation based on several icing encounters I have 

had in cars.***

I think the value that a working AOA or AI has after an icing encounter 

is to allow you to return to a known AOA or airspeed.  The knowledge 

that your airplane will fly at a particular AS/AOA even with the ice 

load that has accumulated, has value if you deviate from the point while 

distracted by other tasks. It allows you to return to a point where you 

know the aircraft will fly.  During any change in attitude it would give 

a known AOA/AS value that can be adhered to to assure continued flight. 

  Clearly ANY deviation from that know AOA/AS carries additional risk.



I'm guessing that some of the intuitive clues that help seat of the 

pants flying might be altered by an ice accumulation. The specific one 

I'm thinking of is the sounds. I know this to be true in cars. I believe 

this is another reason to take steps to avoid having to fly the aircraft 

without an AOA/AS.



Raymond Julian

Kettle River, MN



On 02/13/2011 09:44 AM, Mark Sletten wrote:

 	  Quote: 	
		   

 kuffel(at)cyberport.net wrote:

> It will still tell me accurately if my angle of attack is well above stall with clean wings.  While I don't know what my stall margin actually is at the moment I'm certainly better off than with no or incorrect AOA  information.

 That depends on how you interpret and use the data it provides. If you are flying with an iced wing, the only data even the most accurate AOA indication provides is that the wing is not stalling at the current AOA.



 An AOA indicator is only that; an indicator. It tells you the current angle of attack. Its only value lies in knowing a second crucial piece of data: at what AOA the wing will stall. If your wing is iced you no longer have the second crucial piece of data.



 Given that you have not stalled, the AOA indicator is not providing data you don't already have, that you have, in fact, not stalled. How does an accurate AOA indication help in this scenario?



 Mark Sletten





 Read this topic online here:



 http://forums.matronics.com/viewtopic.php?p=330881#330881

nuckolls.bob(at)aeroelect
Guest

Posted: Tue Feb 15, 2011 4:33 pm Post subject: AOA indicator

At 03:39 PM 2/12/2011, you wrote:

 	  Quote: 	
		  

<retasker(at)optonline.net>



If you are an EAA member you can see ALL back issues of Sport 

Aviation on http://www.oshkosh365.org



If that doesn't do it for you I do have the 2005 issues but I would 

have to see what issue it was in.  Do you remember what month?


	


   Sorry, no. It was mentioned on another forum.

   Had an EAA membership for 20+ years but gave it

   up about 10 years ago. So if anyone could find

   and capture the article, I'd sure appreciate it.

   Bob . . .

user9253

Joined: 28 Mar 2008
Posts: 1919
Location: Riley TWP Michigan

Posted: Wed Feb 16, 2011 6:44 am Post subject: Re: AOA indicator

Bob,

I did a search of past EAA articles and found the following pertaining to AOA:

Better Way to Fly - May 1998

Carrier Pilots' Secret - July 1999

Test Pilot: Angle of Attack - April 2001

Test Pilot: Angle of attack and lift/drag - May 2001

Test Pilot: Angle of Attack - November 2003

Shop Talk: Angle of Attack Indicator - December 2008

I could not find anything in 2005 about AOA.  The December 2008 article by Dave Barker might be the one that you are looking for.  It describes how to build the AOA sensor using a hall effect transducer and LED bar graph display.

Here is a link to the December 2008 EAA article: http://www.oshkosh365.org/saarchive/eaa_articles/2008_12_21.pdf

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

_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Feb 16, 2011 9:36 am Post subject: AOA indicator

At 09:44 AM 2/16/2011, you wrote:

 	  Quote: 	
		  



Bob,

I did a search of past EAA articles and found the following pertaining to AOA:


	


   <snip>  thanks to all who responded to my query about S.A.

   articles. I now have several. It's interesting/useful to see

   what kinds of things have been published for the OBAM aviation

   community. I've added all your contributions to my library.



   Bob . . .

raymondj(at)frontiernet.n
Guest

Posted: Wed Feb 16, 2011 2:29 pm Post subject: AOA indicator

Are they online somewhere?  Or am I looking in the wrong place?

Raymond Julian

Kettle River, MN

On 02/16/2011 10:32 AM, Robert L. Nuckolls, III wrote:

 	  Quote: 	

 <nuckolls.bob(at)aeroelectric.com>

 At 09:44 AM 2/16/2011, you wrote:

> 

> <fran4sew(at)banyanol.com>

>

> Bob,

> I did a search of past EAA articles and found the following pertaining

> to AOA:

 <snip> thanks to all who responded to my query about S.A.

 articles. I now have several. It's interesting/useful to see

 what kinds of things have been published for the OBAM aviation

 community. I've added all your contributions to my library.

 Bob . . .

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