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AOA indicator



 
 
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  #1  
Old April 8th 16, 07:39 PM posted to rec.aviation.soaring
Jonathan St. Cloud
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Default AOA indicator

Was just reading about the Aspen suite of avionics for GA
http://www.flyingmag.com/way-to-aoa?...n=Aspen-FB-Ads.
Was wondering if Air-Avionics Butterfly, LX 90XX or similar modern glide computers would be capable of such algorithms to have a working AOA?
  #2  
Old April 8th 16, 09:17 PM posted to rec.aviation.soaring
son_of_flubber
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Default AOA indicator

WRT OP's question. I'd guess that Butterfly has the sensor input to compute AOA. I don't know if they have the computation resources to complete the calculation in the real time constraints (but they will in the future generation of chips). I don't think that offering this functionality would increase their revenue. It would increase their costs, in particular their liability costs. Has anyone ever been sued for an inaccurate vario reading?


The video raises other questions:

At :30 in the video "he steepens the bank, stalls and spins, even though the aircraft was well above the published stall speed".

I understand that steeper bank increases load factor and that increases the speed at which critical AOA is reached. What I don't understand is why do power pilots use such low Va (such that an increase in bank commonly causes a stall/spin!).

Is it because the stall speeds are so much higher in a power plane relative to the lengths of the runways? So a power pilot needs to fly slow, close to stall speed, to have an acceptable runout?

I also notice in power flying forums that the notion of increasing Va proportional to wind/gust conditions gets little attention.

I noticed power planes fly slow Va (a low multiple of their stall speed), shallow glide slopes and shallow bank turns. Gliders do the opposite. Why?

I'm curious because I'm planning to take some lessons in a tailwheel power Kitfox, and I'd rather not pay to argue these points with my CFI.
  #3  
Old April 8th 16, 09:25 PM posted to rec.aviation.soaring
Per Carlin
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Default AOA indicator

All modern computers has a stall varning algoritm, it doesn't need more than stall speed in strait flight, actual speed and load to calculate if you are above or below stall. With a total pressure sensor and g-meter is the math easy.

It is trickier with unknown variables as load and bugs,that has to be correctly inputted by the pilot.
  #4  
Old April 9th 16, 02:46 AM posted to rec.aviation.soaring
Dan Marotta
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Posts: 4,601
Default AOA indicator

The Dynon D10 in my Stemme has an AoA indexer display near the bottom
left corner of the display. I'll have to go up and watch that while I
practice stalls and falls. I'll report back if it actually works.

On 4/8/2016 2:25 PM, Per Carlin wrote:
All modern computers has a stall varning algoritm, it doesn't need more than stall speed in strait flight, actual speed and load to calculate if you are above or below stall. With a total pressure sensor and g-meter is the math easy.

It is trickier with unknown variables as load and bugs,that has to be correctly inputted by the pilot.


--
Dan, 5J

  #5  
Old April 9th 16, 07:04 AM posted to rec.aviation.soaring
SoaringXCellence
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Posts: 385
Default AOA indicator

On Friday, April 8, 2016 at 1:17:10 PM UTC-7, son_of_flubber wrote:
WRT OP's question. I'd guess that Butterfly has the sensor input to compute AOA. I don't know if they have the computation resources to complete the calculation in the real time constraints (but they will in the future generation of chips). I don't think that offering this functionality would increase their revenue. It would increase their costs, in particular their liability costs. Has anyone ever been sued for an inaccurate vario reading?


The video raises other questions:

At :30 in the video "he steepens the bank, stalls and spins, even though the aircraft was well above the published stall speed".

I understand that steeper bank increases load factor and that increases the speed at which critical AOA is reached. What I don't understand is why do power pilots use such low Va (such that an increase in bank commonly causes a stall/spin!).

Is it because the stall speeds are so much higher in a power plane relative to the lengths of the runways? So a power pilot needs to fly slow, close to stall speed, to have an acceptable runout?

I also notice in power flying forums that the notion of increasing Va proportional to wind/gust conditions gets little attention.

I noticed power planes fly slow Va (a low multiple of their stall speed), shallow glide slopes and shallow bank turns. Gliders do the opposite. Why?

I'm curious because I'm planning to take some lessons in a tailwheel power Kitfox, and I'd rather not pay to argue these points with my CFI.


Please research the V-G diagram, it describes the concept of Va, which is not what I think you're referring to. The Va speed is not selected by the "pilot" it is a construct of load factor, the angle of attack for a stall(both positive and negative), and the speed at which it occurs. It is often described as the speed at which a full control deflection (usually with regard to pitch) will result in a stall occurring before the load factor reaches a value that will damage the aircraft. Recent studies have shown that the other controls (for Yaw and Roll) may in fact cause damage below the Va speed.

Here's a pretty good Video:
https://www.youtube.com/watch?v=ZjBXAosfcco
  #6  
Old April 9th 16, 02:56 PM posted to rec.aviation.soaring
son_of_flubber
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Posts: 1,550
Default AOA indicator

On Saturday, April 9, 2016 at 2:04:16 AM UTC-4, SoaringXCellence wrote:
On Friday, April 8, 2016 at 1:17:10 PM UTC-7, son_of_flubber wrote:
WRT OP's question. I'd guess that Butterfly has the sensor input to compute AOA. I don't know if they have the computation resources to complete the calculation in the real time constraints (but they will in the future generation of chips). I don't think that offering this functionality would increase their revenue. It would increase their costs, in particular their liability costs. Has anyone ever been sued for an inaccurate vario reading?


The video raises other questions:

At :30 in the video "he steepens the bank, stalls and spins, even though the aircraft was well above the published stall speed".

I understand that steeper bank increases load factor and that increases the speed at which critical AOA is reached. What I don't understand is why do power pilots use such low Va (such that an increase in bank commonly causes a stall/spin!).

Is it because the stall speeds are so much higher in a power plane relative to the lengths of the runways? So a power pilot needs to fly slow, close to stall speed, to have an acceptable runout?

I also notice in power flying forums that the notion of increasing Va proportional to wind/gust conditions gets little attention.

I noticed power planes fly slow Va (a low multiple of their stall speed), shallow glide slopes and shallow bank turns. Gliders do the opposite. Why?

I'm curious because I'm planning to take some lessons in a tailwheel power Kitfox, and I'd rather not pay to argue these points with my CFI.


Please research the V-G diagram, it describes the concept of Va, which is not what I think you're referring to. The Va speed is not selected by the "pilot" it is a construct of load factor, the angle of attack for a stall(both positive and negative), and the speed at which it occurs. It is often described as the speed at which a full control deflection (usually with regard to pitch) will result in a stall occurring before the load factor reaches a value that will damage the aircraft. Recent studies have shown that the other controls (for Yaw and Roll) may in fact cause damage below the Va speed.

Here's a pretty good Video:
https://www.youtube.com/watch?v=ZjBXAosfcco


I meant Vat (V approach) not Va (maneuvering speed) which makes no sense in the context of my comment.
  #7  
Old April 9th 16, 03:16 PM posted to rec.aviation.soaring
Jonathan St. Cloud
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Posts: 1,463
Default AOA indicator

Several decades ago the SSA sponsored a contest to design an AOA, now we have the technology to have a viable solution. Just saying
  #8  
Old April 9th 16, 04:58 PM posted to rec.aviation.soaring
Dan Marotta
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Posts: 4,601
Default AOA indicator

Wasn't there something years back that was attached to the trailing edge
of the wing? It included two holes, one above the wing and one below.
These holes were connected via tubing to an instrument in the cockpit
which displayed the difference in dynamic pressures between the top and
bottom of the wing which, I would assume, could be marked to show where
a stall could be expected.

Or was that one of Dick Johnson's devices for measuring drag?

On 4/9/2016 8:16 AM, Jonathan St. Cloud wrote:
Several decades ago the SSA sponsored a contest to design an AOA, now we have the technology to have a viable solution. Just saying


--
Dan, 5J

  #9  
Old April 10th 16, 12:01 AM posted to rec.aviation.soaring
firsys
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Posts: 36
Default AOA indicator

On Friday, April 8, 2016 at 2:39:56 PM UTC-4, Jonathan St. Cloud wrote:
Was just reading about the Aspen suite of avionics for GA
http://www.flyingmag.com/way-to-aoa?...n=Aspen-FB-Ads.
Was wondering if Air-Avionics Butterfly, LX 90XX or similar modern glide computers would be capable of such algorithms to have a working AOA?


At the epoch of the SSA AoA indicator, I did some work on another approach.
It consisted of a microphone, amp., and a variable Hi/low pass filter
to select airflow noise in a limited band. It was sucessfull in
showing approach to the stall in a Puchaz by a rise in the
low frequency flow detachment near the TE. I concluded that it was insufficiently robust to be generally usefull.

John f
  #10  
Old April 11th 16, 08:59 PM posted to rec.aviation.soaring
SoaringXCellence
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Posts: 385
Default AOA indicator

I've done some research into developing a pitch/yaw AOA device. It can replace the Pitot tube and provide the angle of yaw and pitch as well as airspeed. It's based on a 5-port pitot combined with today's very small, sensitive, pressure transducers, computed by a micro-processor like an Arduino or Raspberry-Pi, Including the display screen, I think it can be constructed for under $100.

Unfortunately it's a ways down on the task list, and I just spent all my pennies on a Trig22. Maybe next year.

MB

Websites to peruse:

Here's a patent for a three-port Pitot/AOA system
http://www.google.com/patents/US4378696

Dynon makes a Pitot that is a simpler two port system for positive AOA only (page 1-4):

https://www.dynonavionics.com/downlo... _-_Rev_C.pdf

 




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