Retrofit AOA - What Does It Give You?

kontiki

kontiki

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Kontiki
I've seen a couple posts on retrofit AOA systems. Help me understand the value. Is it just an elaborate add on stall warning warning system?

Are the operating principles sound enough that there is accuracy through various attitudes and cross wind angles of flight?

Thanks,
 
Yes.

AOA is independent of speed. You can use it to fly a short field or optimum approach each time, every time, no matter what the temps, altitude or a/c weight is.

Because, the AOA your wing stalls at is the same, no matter what the condition is.

Now, truth be told, the stall speed for near empty and full gross on a spam can are pretty close together. On a navy bird with the ability to double it's weight in fuel and ordinance, and the difference is measured in tons, it's more practical.
 
Once you've flown with AOA, you'll have a really hard time going back. Instead of looking at airspeed on final, you just fly the AOA.
 
As the others alluded to, the beauty of AOA is that you don't have to compute your v-speeds based on weight, DA, etc. All you do is fly the AOA for best angle, best rate, best glide, optimum approach, etc, and the airspeed takes care of itself.
 
jwriteclub said:
Once you've flown with AOA, you'll have a really hard time going back. Instead of looking at airspeed on final, you just fly the AOA.
Click to expand...

Can't say I've ever looked at airspeed on final. Too busy looking at the runway and watching for traffic I guess.

Pilots have all sorts of instruments to keep them from stalling the airplane. Why one more is going to make such a big difference is beyond me.
 
I think it could be a great tool for when you're operating close to the edges of the envelope.

It's great to always double your runway length needed and use other tactics to have a big safety buffer, but some folks HAVE to operate with smaller margins in utility flying, and that's where an instrument like an AOA can really come in handy.
 
I'll bet the guys operating routinely at the edge aren't the ones in spin/stall crashes from base to final.
 
TMetzinger said:
And having an AOA indicator might be one reason why?
Click to expand...

Doubt it. Most of those guys are bush pilots and cropdusters. Don't know about the Ag aircraft, but the bush planes mostly don't have them so far as I know.
 
While I only have a few landings with mine, I do like it so far.
I put the AlphaAOA 4 inch indicator on top of the glare shield so it is in my peripheral vision but allows more concentration on the outside to Steingar's point.

I have been crosschecking airspeed with the LEDs and it is interesting to see the increase in speed at higher angles of bank on turn to final needed to keep the AOA at the same level..

For me it was an option to keep more outside view than popping in for a peek at airspeed and adding a few knots for safety, which made my final speeds probably faster than necessary. For my 5000 foot home drome, not a big problem but for shorter fields which I hope to do more of a bigger issue.

Hey I am new at this so I'll avail myself of as many tools as I can to be safer.

On several forums there is quite a bit of positive response to the AOA concept from some I consider to be way more experienced than I will ever be.

To the 2000 hour bush pilot, probably not important -- I will probably never see that many hours so it seemed like a good idea.

I still have my old nomex suit so feel free :D

PS the install in a 172 is pretty straightforward if you do not go for a heated probe.
 
steingar; said:
Pilots have all sorts of instruments to keep them from stalling the airplane. Why one more is going to make such a big difference is beyond me.
Click to expand...

it's useful for more than that. Best rate, best glide... They occur at specific AOA's. The speed in you POH is at sea level max gross.

You can use it to get in or out of a short field or stretch that engine out glide efficiently. You aren't glued to it but you incorporate it into your scan.
 
Thanks all for the replies. I understand much better, but I am not sure what to think about the accuracy of a system not specifically designed and calibrated for the aircraft it's going to be installed on.

When you purchase a system not specifically designed and tested for a specific aircraft, I imagine, you set it up, and somehow adjust it to reflect "bad AOA" at some stall condition (is that all there is?). Is it valid through the rest of flight envelope? Does it need to be? Can you get into trouble relying on it?

One of my coworkers pointed out that production airspeed on something like a C172 was really not all that accurate a lot of the time anyway, so AOA inaccuracies really wouldn't be any worse?

And, I suppose that variations in weight are really going to dominate the degree to which particular airspeed correlate to a particular AOA.

In a previous life, I supported the instrumentation on a very accurate flight test nose boom with AOA during pre production flight test of a fighter, about 15 years ago.

The "Team" flew a specific ship regularly. Actually one fighter pilot flew it and about a dozen people electronically patched into the flight at the range monitoring station to monitor data transmitted by the aircraft real time. Of course all data was recorded too.

I understood we flew test points located various places in the performance chart and that data would then be used to develop the lookup tables and functions eventually loaded into the production AOA computer.

Now there were a lot of differences between what we were doing and ordinary civilian flight operations. Calibration of the nose boom instrumentation was a GO/NO GO proposition for a lot of test points.

A lot of that was because the 30lb brains needed to do things like map the engine air inlet pressure down inside the intake ducts to be able to guarantee it wouldn't flame out.

I believe the production system eventually installed on the fighter jet probably worked as advertised at all attitudes, (inverted or not) all configurations etc.

After seeing what the Navy did and now observing that folks can just buy an all purpose generic AOA system, install it on their airplane, and just fly it, I just wonder what the limitations are and how much they matter.
 
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kontiki; said:
... I understand much better, but I am not sure what to think about the accuracy of a system not specifically designed and calibrated for the aircraft ....
Click to expand...

You calibrate it for your aircraft after installation by going up and doing some stalls. It saves that data and uses it for baseline to determine the wings AOA relative to that of it's stalling AOA.

Most add on AOA's use the pressure differential between two ports to determine %AOA with regards to stall. Those conditions are reproducible. As you approach that condition you get progressive indication.

That fighter flight test and production uses AOA data for all sorts of flight management stuff that allows the computer to fly the bird with the pilot as a non-majority voting member of the flight control system. The commercially available add on AOA goes to a standalone indicator with a few lights, or in some glass boxes, a colored scroll.
 
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Is AOA a simple linear function from stall? Is it influenced by wing camber or plan form?
 
I can see where you're calibrated to a stall at this point, but what about the other interesting points on the L/D curve like best glide?
 
patrick wentworth said:
While I only have a few landings with mine, I do like it so far.
I put the AlphaAOA 4 inch indicator on top of the glare shield so it is in my peripheral vision but allows more concentration on the outside to Steingar's point.

I have been crosschecking airspeed with the LEDs and it is interesting to see the increase in speed at higher angles of bank on turn to final needed to keep the AOA at the same level..

For me it was an option to keep more outside view than popping in for a peek at airspeed and adding a few knots for safety, which made my final speeds probably faster than necessary. For my 5000 foot home drome, not a big problem but for shorter fields which I hope to do more of a bigger issue.

Hey I am new at this so I'll avail myself of as many tools as I can to be safer.

On several forums there is quite a bit of positive response to the AOA concept from some I consider to be way more experienced than I will ever be.

To the 2000 hour bush pilot, probably not important -- I will probably never see that many hours so it seemed like a good idea.

I still have my old nomex suit so feel free :D

PS the install in a 172 is pretty straightforward if you do not go for a heated probe.
Click to expand...


Karl sure loved his
 
TMetzinger said:
I can see where you're calibrated to a stall at this point, but what about the other interesting points on the L/D curve like best glide?
Click to expand...

That sounds like a great idea. The indicator would be like a dial rather than a series of lights, similar to the ASI but the points would not vary based on factors like weight, etc.
 
Remos GX has differential pressure AoA-reporting pitot from the factory, with the ticker being created electronically by Denon PFD. I am used to assess the AoA by pitch and visible surface movement when close to the terrain, and I fly more conventional airplanes too, so I do not use it much. But I like looking at it in steep turns, to know if I'm getting close to accelerated stall. Unfortunately, the airplane is not aerobatic.
 
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