Modern AOA disappointmentad

[Robert C.]

On 7/30/2016 at 9:44 PM, 201er said:

 AOA isn't just about stall or approach speed. It also relates to optimal performance as it relates to Vx, Vy, and best glide. This is extremely helpful in the turn where it is complicated to derive airspeed as it relates to weight, configuration, and bank angle. For example, you takeoff from an uphill runway and pitch for Vx. There is a mountain ahead and rising terrain so you need to hold Vx into your crosswind turn. With my AOA, I can pitch for Vx AOA on the departure climb and match the reduction in my pitch attitude in the turn to match the increase in required AOA in the turn to maintain Vx throughout the bank range. As bank angle and load increase, I can progressively lower the pitch attitude to maintain Vx in all parts of he turn. Although climb rate will suffer in the turn (due to the horizontal component of lift and increased load), I will still be able to maintain the best angle of climb attainable by maintaining Vx AOA. Flying Vx speed into an increasing bank is not only dangerously close to stall, it is also behind the power curve and will hurt climb performance further. The resultant poor climb may contribute to many panicked pull backs that lead to turning departure stalls.

Likewise I can optimize Vy climb and maintain best glide angle of attack in simulated engine out practice. Weight and speed will vary, but the AOA to maintain Vx, Vy, 1.3vso, and best glide remain the same. Even in the turns, without knowing the corresponding speeds in the turn, I can get optimal performance. So it's not just about avoiding stalls. It can help me avoid running into terrain by having the most efficient possible climb angle at all times.

It is a crying shame that some or most of the new AOA devices on the market are being sold as a stylish stall warning and not the fantastically useful device that it can be. I fault the instructors and old school pilot culture that thinks in terms of airspeed and not in terms of angle of attack. A change of culture is more important than just a change of devices. Using angle of attack indicators can do more than just prevent stalls, it can also help us maximize the performance of our craft for other forms of safety as well. It can help us think more fundamentally about how we fly and lead to better decision making. 

 

Mike, those who get an AoA to buy a tool rather than the latest gadget are likely wise to your point. Agree that it would be helpful if manufacturers stressed this more in their sales and installation litereature.

I corresponded with Don Kaye on calibrating my Alpha Systems unit and he helpfully described how he (and a safety pilot) had gone out, calculated for their weight the exact Vx, Vy, Vg numbers and ranges and then flew them while marking the AoA display so he always has immediate access to which light to illuminate to fly the desired AoA. I keep telling myself to go do the same but haven't yet...soon though!

[Robert C.]

Just now, PTK said:

Focus and answer the questions I posed to you Mike, if you can. 

...How much shorter, in feet please, are you landing with your AOA gadget?

and ...

How different is your Vso you fly with your AOA from what's in your POH?

We'll get to banking later.

I don't have hard data on ldg distance other than that I noticed the difference being visible when I fly the "blue dot," definitely less float.

Similarly, there is a good 5kt difference between my "blue dot" speed when at max landing weight and when I'm light. Flying straight and level on final....yep i could consult my old-tech paper cheat sheet which I still have....in downwind-base and base-final turns there is no time to consult cheat sheets and my brain is too full to add the memorization of speeds at different bank angles and landing weights. Am happy I can glance at the display and check I'm not below the blue-dot in those turns.

[PTK]

On July 30, 2016 at 9:44 PM, 201er said:

...For example, you takeoff from an uphill runway and pitch for Vx. There is a mountain ahead and rising terrain so you need to hold Vx into your crosswind turn. With my AOA, I can pitch for Vx AOA on the departure climb and match the reduction in my pitch attitude in the turn to match the increase in required AOA in the turn to maintain Vx throughout the bank range. As bank angle and load increase, I can progressively lower the pitch attitude to maintain Vx in all parts of he turn. Although climb rate will suffer in the turn (due to the horizontal component of lift and increased load), I will still be able to maintain the best angle of climb attainable by maintaining Vx AOA. Flying Vx speed into an increasing bank is not only dangerously close to stall, it is also behind the power curve and will hurt climb performance further. The resultant poor climb may contribute to many panicked pull backs that lead to turning departure stalls.

Likewise I can optimize Vy climb and maintain best glide angle of attack in simulated engine out practice. Weight and speed will vary, but the AOA to maintain Vx, Vy, 1.3vso, and best glide remain the same. Even in the turns, without knowing the corresponding speeds in the turn, I can get optimal performance. So it's not just about avoiding stalls. It can help me avoid running into terrain by having the most efficient possible climb angle at all times.

 

Numbers Mike, show me the numbers man! Not your usual tactics of avoiding the question by talking bs!

I'll give you one more opportunity by asking you again: What were your actual speeds on a given day for your Vx climb, Vy and Vso and how do they compare to your POH? If you don't know say so. 

More importantly if you don't know you should not be taking off on that upslope runway with mountain and rising terrain ahead.

If you don't know that gadget will not help you.

Note, I haven't even asked you about banking yet.

[gsengle]

This group will spend all kinds of AMUs to add a few kts of speed. We like maxing the performance of our planes. And yet we probably mainly stay far from the low speed margins, unnecessarily far. I for one would like to get more performance in bank and in landing by getting closer to the margins with confidence.

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[jetdriven]

With proper training you can. I see it all the time with BFR training. The first landing is 3000' long.  The 4th one is 800'.  CNOE and I did it with a tennis ball on the pitot tube, that I forgot to remove.   Landed and stopped with 3 runway stripes and the touchdown zone aiming point markers in front of us.  Same with 201ER.   We did his as well m, by yes we had airspeed and AOA.  Burning ink he was too busy looking and sending to look at it much.. You can feel this, you don't need a gadget to tell you 1.2  Vso. A new gadget is nice but it will never replace proper airmanship. 

Edited August 1, 2016 by jetdriven

[PTK]

Just now, gsengle said:

This group will spend all kinds of AMUs to add a few kts of speed. We like maxing the performance of our planes. 

Not I! I do not spend money for the dubious knot here or there. I feel my airplane is perfect the way it is. 

[201er]

4 minutes ago, jetdriven said:

With proper training you can. I see it all the time with BFR training. The first landing is 3000' long.  The 4th one is 800'.  CNOE and I did it with a tennis ball on the pitot tube, that I forgot to remove.   Landed and stopped with 3 runway stripes and the touchdown zone aiming point markers in front of us.  Same with 201ER.   We did his as well m, by yes we had airspeed and AOA.  Burning ink he was too busy looking and sending to look at it much.. You can feel this, you don't need a gadget to tell you 1.2  Vso. A new gadget is nice but it will never replace proper airmanship. 

This is how instructors are responsible for the deaths of their students in stall/spin accidents. Student + Instructor + Fuel at Tabs leads to a false understanding of angle of attack. When you fly under the same weight condition consistently, you become accustomed to a certain pitch attitude, airspeed, and ground speed representing the target angle of attack. It works when you keep repeating the same training condition at the same airport flying the same traffic pattern.

Then some day that student loads up the plane not with his instructor but all his fat friends. golf clubs, and the kitchen sink. Now the airspeed or pitch attitude that corresponded to Vx with his instructor now puts him behind the power curve with his friends and the plane refuses to climb! The induced drag from the excessively high angle of attack won't let it climb. This is because some old fart instructor taught him to fly airspeed and not angle of attack.

The old fart instructor only flies with a student and set amount of fuel. He never sees alternative weight conditions. He gets accustomed to pitch attitude = airspeed = angle of attack. He only flies the same traffic pattern over and over again. Nothing changes. It all works. But when the student is taking off heavy into rising terrain off a short runway, the moment he puts in some turn, the angle of attack is no longer sufficient to support the weight of him and his fat friends and added load factor and they end up a smoldering crater of lard and aluminum on the ground. I'm sick to my stomach reading it happen over and over again. And the problem is the fundamental misunderstanding that airspeed is not the same thing as angle of attack. There are all kinds of things that can make the airspeed scale shift how it corresponds to angle of attack. On the other hand, the same angles of attack yield the same flight characteristics (although speed at which it happens will vary).

Instructors are making a deadly mistake allowing students to think that airspeed correlates to angle of attack (even if they're not saying it like that). If students were taught to fly by reference to angle of attack instead of airspeed, no matter how the weight, configuration, or bank angle would change in his subsequent flights, the method would work consistently and keep him safe! Flying airspeed KILLS pilots and passengers over and over again!

Airspeed only correlates to angle of attack under identical conditions (same weight, same power, same density altitude, same bank angle). Airspeed doesn't compensate for when lift vectors shift from directly vertical. When you have horizontal component of lift or vertical component of thrust, airspeed in anything but gross weight straight ahead climb is inaccurate for max performance speeds.

The original point of my post is that I don't like the newer led-blub AOAs because they are merely glorified stall warnings. A properly designed (and calibrated) AOA indicator is the most useful source of low speed performance information. It's not just for preventing stalls or making nice landings. It is there to inform the pilot the angle of attack that the airplane is currently flying, what performance change can be expected from a change of angle of attack (climb better or worse for example), the rate of change of angle of attack, performance angle of attacks (vx, vy, vglide), and stall avoidance.

Yes an AOA indicator is a better version of a stall warning. Even the ones I don't like I think are a better kind of stall warning system. However, as I pointed out, when properly used, it is an entirely different way of thinking about non-cruise airplane performance. It is not only safer but actually easier and more useful.

[gsengle]

Just now, gsengle said: This group will spend all kinds of AMUs to add a few kts of speed. We like maxing the performance of our planes. 

Not I! I do not spend money for the dubious knot here or there. I feel my airplane is perfect the way it is. 

This is more important than cruise speed. It is the difference between a stall spin death or overrunning the end of a short runway.

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[gsxrpilot]

I like my CYA-100. It gives me the confidence whether banking or just landing, regardless of weight, to know where I am in the envelope. As a result, I can regularly make the turn-off at this airport landing 17. 

If you don't like a tool, be it GPS, ADSB Traffic, XM-Weather, or AOA, don't buy one. But the disparagement of those who do chose to use them, seems rude and in poor taste.

[PTK]

To an even greater degree it is very rude and in very poor taste to engage in name calling toward those asking some questions. These are extremely relevant questions which remain unanswered. Some have so much to say but just can't answer a few simple questions about the use of a gadget they're touting.

If asking questions in the quest of seeking knowledge is considered disparaging by some, I don't think it is but some apparently do, then what is the name calling considered? Do they have an opinion on that they care to express?

[jetdriven]

2 hours ago, PTK said:

Not I! I do not spend money for the dubious knot here or there. I feel my airplane is perfect the way it is. 

How about an extra ten knots?  IDK, but I think it was worth it.

[Cruiser]

Some pilots like their AoA indicators and use them.

Some pilots think the AoA indicators can be much more useful in flight than given credit for.

Some pilots don't think AoA indicators are worth the money to install in their airplanes.

Some pilots don't have an opinion one way or the other.

If you like your AoA indicator you can keep your AoA indicator.

The FAA says it is a worthwhile instrument that can aid in SAFETY.

Anybody want to argue with me?

 

[Hank]

On July 31, 2016 at 4:39 PM, PTK said:

A problem that I have with these AOA gadgets for GA is the location of the sensor being on one wing. Since we can't put it on the nose would it not make more sense to have one on each wing and integrate the data somehow to present true AOA? Having it on one wing it only gives you AOA info for that wing. It says nothing about the other wing, except in coordinated flight. And if it's going to be dependent upon on say an uncoordinated base to final turn it has to be right.

Until this is addressed I have a hard time seeing the benefit of an AOA indicator in our small planes.

Peter, by that rationale the stall warning out on your left wing cannot be trusted because there is not also one on the right wing!

I don't have an AoA yet, because I'm still waiting for one I like to appear, with a reasonable-sized display that can go right beside my ASI. And yes, I do periodically check my ASI, along with Altimeter, while in the pattern and even on short final. I roll wings level on final at 85 mph, and slow to 75 by ~100 agl, but I reduce that by another 5 mph for every 300 lb below gross I am at the time.

Why? Because I got my license and was based for six years at an obstructed 3000' field, and am now on a cleared 3200' field. If I forget the extra 5 mph like I did today (or was it the extra flaps I added because I was a little high?) I touched down three additional stripes further down the runway than normal--today it was stripe #6, where I'm usually #2 or #3. Still needed only gentle braking to make the taxiway turn.

[Bob_Belville]

46 minutes ago, Hank said:

I don't have an AoA yet, because I'm still waiting for one I like to appear, with a reasonable-sized display that can go right beside my ASI. And yes, I do periodically check my ASI, along with Altimeter, while in the pattern and even on short final. I roll wings level on final at 85 mph, and slow to 75 by ~100 agl, but I reduce that by another 5 mph for every 300 lb below gross I am at the time.

 

Hank, I don't think you'll do better the the CYA 100 given your must have feature. It is only about 3/8" wide yet has 9 lights - the top 3 are green, the lowest 3 are red and there's an audio alert at the lowest light = the highest AOA. All for about 1 AMU installed. (Sold by Aircraft Spruce.) Pic below was taken with the lowest light lit - it's between the (backup) ASI and the aspen..

[jetdriven]

3 hours ago, gsxrpilot said:

I like my CYA-100. It gives me the confidence whether banking or just landing, regardless of weight, to know where I am in the envelope. As a result, I can regularly make the turn-off at this airport landing 17. 

If you don't like a tool, be it GPS, ADSB Traffic, XM-Weather, or AOA, don't buy one. But the disparagement of those who do chose to use them, seems rude and in poor taste.

I do that too, with no AOA and and varying weights, too You know Boeing airplanes have the weight in the FMC and put a VREF speed for the weight. it works. Landing speed varies with weight, I get that, but as Don Kaye says you can calculate that.  

 

its about 71 MPH over the numbers at minimum landing weight and, as Hank said, add 1 knot per 300 lbs.  But you dont need an airspeed indicator in a 747-400 and you dont need one in a M20J. You simply fly the speed that gives you a 2 degree nose up attitude on final. Particularly short final.  The -400 is 2.5 to 3 degrees ANU, but its the same concept.  if the airplane starts to sink you're too slow.  If you got to scooch up in the seat to lift up and see the runway numbers on final, you're too slow. if you are pointed at the runway you're too fast. nose down too fast. 100 MPH too fast.  If you're in doubt, you're too fast.  This isn't hard stuff. The 1900, the CRJ, the 747-200, the 747-400, the Aribus A320, all variants of the 737, the 727, the 757, 767,  none had an AOA gauge.  They all have AOA vanes to set off the stick shaker, but the VREF was calculated by weight and seems to work.  

 

Edited August 2, 2016 by jetdriven

[201er]

3 minutes ago, jetdriven said:

I do that too, with no AOA and and varying weights, too You know Boeing airplanes have the weight in the FMC and put a VREF speed for the weight. it works. Landing speed varies with weight, I get that, but as Don Kaye says you can calculate that.  

Yeah, it calculates it for you! Also you're not flying steep turns in a tight traffic pattern with your head out the window and nobody in the right seat. I agree that flying 20 miles straight in finals on an autopilot coupled ILS is very safe and extremely unlikely (and unreasonable) to stall. Flying GA airplanes with a single pilot, little to no autopilot, single engine, tighter margins, less power, etc is a whole other story.

When I take off, I usually pitch to my best guestimate for Vx. Leaving for Oshkosh, we were loaded with fuel and baggage to the limit. Even with full fuel and wife on board, I have about 100 pounds till gross weight. So I pitched for Vx (mostly based on pitch attitude, secondarily based on airspeed), look down at AOA and sure enough it was a tad higher angle of attack (too slow for you guys who don't understand aoa) than ideal for this weight. I pitched down a little to improve the climb. It's counter-intuitive to push forward to go up more. But when you're already climbing worse than usual, you can use all the climb you can get.

By getting the best possible climb now, I can defer the liklihood of making a mistake later on. At the moment, everything is going dandy. Let me get more altitude now and fly the best AOA. In a minute when ATC gives me vectors or I have to dodge a plane, it's good that I was already flying the right AOA and had the best ground separation available. Now I'm ready to continue to maintain the pitch I had already established based on the instrument earlier and a distraction won't push me closer toward a stall.

Edited August 2, 2016 by 201er

[Bennett]

I rather like my CYA 100 AOA. I have had it mounted alongside my vertical compass (no discernible effect on the compass) where it is in my constant line of sight. I find it most useful on take-off where I want to make certain that my initial climb is between Vx and Vy. At Vx I am in the orange zone, and green at Vy. I don't want to see the red zone at anytime on takeoff. My J's rate of climb is initially less than after about a minute of WOT/2690 RPM/takeoff flaps. I usually retract the gear as I pass 2/3s of my home field 2600' runway, and retract flaps at about 500'. With the AOA constantly in my sight, I can deal with the other aspects of take-off. In landing I still see the AOA, but I do glance at the ASI to make sure touchdown speed is where I want it to be.. The AOA is a useful tool that I use with the many other tools in our panels, and on our heads.

[jetdriven]

2 minutes ago, 201er said:

Yeah, it calculates it for you! Also you're not flying steep turns in a tight traffic pattern with your head out the window and nobody in the right seat. I agree that flying 20 miles straight in finals on an autopilot coupled ILS is very safe and extremely unlikely (and unreasonable) to stall. Flying GA airplanes with a single pilot, little to no autopilot, single engine, tighter margins, less power, etc is a whole other story.

When I take off, I usually pitch to my best guestimate for Vx. Leaving for Oshkosh, we were loaded with fuel and baggage to the limit. Even with full fuel and wife on board, I have about 100 pounds till gross weight. So I pitched for Vx (mostly based on pitch attitude, secondarily based on airspeed), look down at AOA and sure enough it was a tad higher angle of attack (too slow for you guys who don't understand aoa) than ideal for this weight. I pitched down a little to improve the climb. It's counter-intuitive to push forward to go up more. But when you're already climbing worse than usual, you can use all the climb you can get.

By getting the best possible climb now, I can defer the liklihood of making a mistake later on. At the moment, everything is going dandy. Let me get more altitude now and fly the best AOA. In a minute when ATC gives me vectors or I have to dodge a plane, it's good that I was already flying the right AOA and had the best ground separation available. Now I'm ready to continue to maintain the pitch I had already established based on the instrument earlier and a distraction won't push me closer toward a stall.

We have maneuvering speeds for each flap setting, lets call it flaps up, takeoff and landing. Its basically V2 plus 80 clean, and V2 plus 5 landing configuration, but in any case, it guarantees your 45 degrees of bank, 1.6G, without approaching the shaker, which is still above stall.  

The thing that gets me, is none other than the CYA actually measure AOA.  So you're relying on an instrument placarded as not to be relied on for primary flight information, to make critical flight decisions. 

[gsengle]

What I find amazing is everyone arguing that they can keep a 3 or 4 dimensional chart in their heads, and rely on it at critical stages of flight. Computing stall speed for each combination of weight, density altitude and bank angle.

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[201er]

Just now, jetdriven said:

The thing that gets me, is none other than the CYA actually measure AOA.  So you're relying on an instrument placarded as not to be relied on for primary flight information, to make critical flight decisions. 

Yeah. But it's still more accurate than the ASI. In 5 years I've had about 4 ASI issues (mostly cause of water or gear override switch) and none with AOA. I think ASI is prone to many more potential problems. Air leaks, instrument calibration errors, icing, bugs, etc. Not sure that the differential pressure AOAs are better but the stall-tab-like ones are really robust. Short of a full electrical failure, hard to see what would make it stop working.

[201er]

Just now, gsengle said:

What I find amazing is everyone arguing that they can keep a 3 or 4 dimensional chart in their heads, and rely on it at critical stages of flight. Computing stall speed for each combination of weight, density altitude and bank angle.

And for Vx, Vy, and Best Glide. But hey, dentists must have a knack for those sort of things.

[gsengle]

Just now, gsengle said: What I find amazing is everyone arguing that they can keep a 3 or 4 dimensional chart in their heads, and rely on it at critical stages of flight. Computing stall speed for each combination of weight, density altitude and bank angle.

And for Vx, Vy, and Best Glide. But hey, dentists must have a knack for those sort of things.

Those are three approximations and I bet you only know the published number for max gross. The reality is that we all just use safe numbers, and stay far from stall to be safe. I'd like to get better performance than that.

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[jetdriven]

Just now, 201er said:

Yeah. But it's still more accurate than the ASI. In 5 years I've had about 4 ASI issues (mostly cause of water or gear override switch) and none with AOA. I think ASI is prone to many more potential problems. Air leaks, instrument calibration errors, icing, bugs, etc. Not sure that the differential pressure AOAs are better but the stall-tab-like ones are really robust. Short of a full electrical failure, hard to see what would make it stop working.

your system uses a stall vane which moves up and down. But it doesn't measure AOA directly.  How accurate is it with flaps up, 15 degrees, or full down? What about with ice on it?

[201er]

7 minutes ago, jetdriven said:

your system uses a stall vane which moves up and down. But it doesn't measure AOA directly.  How accurate is it with flaps up, 15 degrees, or full down? What about with ice on it?

Probably no less accurate than the ASI. The probably get affected equally. Doing tests to compare AOA to ASI wouldn't necessarily prove anything.

[gsengle]

The fact is, using aoa is a primary measurement for stall, and always works if measured accurately. Using IAS, adding weight, density altitude, bank angle, and hoping your airplane matches the test airplane is using a calculated derived number... In truth you could get rid of airspeed and fly only aoa...

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