AOA

[RV7A Flyer]

Originally Posted by boomer

I too wish there was a classic indexer readout, but there's not.

Don't know about other Dynon products, but lots of features have been added at users' requests to the Skyview line. Given that these sorts of things are "just software", I'd say go over to the Dynon forum and toss it into the mix as a requested feature. They've been pretty responsive in the past (although, for the life of me, they still don't have the capability to use flap position in the AOA computations/indications, which seems horribly wrong to me; that said, I do like the SV AOA indications/audio alerts very much).

[Brantel]

You could build your own AOA display and used Dynon's serial stream to drive it. The code to parse the serial data out of the stream is so easy even a hack like me did it.

http://www.vansairforce.com/communit...te+aoa+display

[carrollcw]

Originally Posted by mike newall

For those who are not aware, stick position is directly linked to aoa and therefore to stall. If you find yourself with the stick well back, you have to ask yourself why and are you comfortable ?

This is absolutely not true. As a prior fighter pilot, I can attest to this statement's falsity. AOA has nothing to do with stick position. In an RV-7 at 180 KIAS full aft stick (probably over G), you will not be in the same AOA as full aft stick at 80 KIAS (will stall). Instead, AOA is more easily understood as the airplane's energy state at a given stick position related to airspeed, altitude, attitude, and weight. If you calibrate it properly, it can help you understand the airplane's ability to perform the desired maneuver (based on the aforementioned factors). Calibrate the green circle for best glide. That should also correspond to best turn performance. Then strive to be in the green circle when in the final turn at 75ish KIAS, throughout a loop (between entry to the end), or if dogfighting and wanting your best sustained turn rate for a given airspeed. If your desire is to accomplish the best nose rate, you should be in the yellow chevron as best nose rate is not sustainable but for a few seconds.

[PCHunt]

Originally Posted by carrollcw

This is absolutely not true. As a prior fighter pilot, I can attest to this statement's falsity. AOA has nothing to do with stick position.

OK, all in fun now: This absolutely IS true. As a prior fighter pilot, I can attest to this statement's veracity. AOA has everything to do with stick position.

Yes I am a former fighter pilot, but that doesn't change what rules angle-of-attack follow. During my instruction and particularly when giving BFR's, I demonstrate that stick position equals "alpha" (AoA) by doing the following: I do a power off, level, one-G stall, and ask the other pilot to carefully note the stick position. Then I do an accelerated stall at about 2 to 2.5 G's, and again carefully note the stick position.

For all practical considerations, the stick positions are the same.

Now, I am sure that an aero engineer will comment and explain that there are small differences in stick position, but to the unaided eye, the stick position is the same.

Try it yourself, if you don't believe me.

"Screens up, Scotty!"

[PCHunt]

I believe that is exactly what was done on the Ercoupe.

One issue is that as the CG changes, so does the stall stick position. So perhaps to get a full CG range, it is necessary to have some additional control authority. Pure speculation on my part here!

Steve Smith, comments invited!

[rmartingt]

Originally Posted by PCHunt

Now, I am sure that an aero engineer will comment and explain that there are small differences in stick position, but to the unaided eye, the stick position is the same.

Those differences will creep in with CG (as you noted), transonic/supersonic effects (center of lift moving aft, etc; not a factor for RVs), landing gear extension (if equipped), flap/slat deployment (again if equipped), etc.

Originally Posted by curtis

Maybe this is a dumb question, but if the stick position indicates the AOA and is constant wouldn't the FAA regulate the manufactures to prevent the elevator travel to the "constant" position? If it is actually this easy and you could avoid stalls by just preventing the specific stick position one would think it would not be part of the rigging.

I'm no engineer, no fighter pilot, or anything else special. Just a ASEL pilot.

Originally Posted by PCHunt

I believe that is exactly what was done on the Ercoupe.

One issue is that as the CG changes, so does the stall stick position. So perhaps to get a full CG range, it is necessary to have some additional control authority. Pure speculation on my part here! !

Yep, that's part of the problem. Unless you have some kind of fancy auto-compensating limiter that looks at CG, you're going to set the stop for your worst-case condition. That leaves you running out of elevator authority at forward CG conditions, meaning you're landing faster and running the chance of landing nosewheel first.

If you're going to have said fancy auto-compensator, then instead of trying to predict CG and limit stick deflection, it'll almost certainly be easier just to pick off calibrated AOA to drive a stick shaker and use your autopilot servos as an alpha limiter (like Garmin has apparently just done). I think this is going to become a more common approach, especially as it looks like the newest round of certification requirements are getting tougher on stall/spin resistance. As much as it bugs a lot of people (and even myself sometimes), I think fancier and more involved systems than we're used to seeing--that is, AOA indicators, stick shakers, the EFIS-based limiters mentioned above, and so on--are going to be pushed harder and harder. Stall/spin accidents keep happening no matter how many times we admonish ourselves to "be a better pilot and practice"; we can keep trying the same approach and keep watching it fail, or we can try something else.

[Av8torTom]

Originally Posted by RV7A Flyer

Can you elaborate on that? Why?

Because AOA is NOT just about stall warning, it's about providing the pilot with detailed information about that the wing is doing. All of your V speeds for example can have an AOA value, but that requires an instrument that provides degrees AOA and not just some lights on a bar. The Advanced Pro AOA has both a light bar and degrees AOA readout.

I have not flown with the Advanced AOA, but have flown with another AOA instrument that provided a degrees AOA readout. I knew for example that on take off my airplane 8 deg AOA gave me Vx. There was no searching around with pitch chasing an airspeed indicator. I could instantly bring the wing to 8 degrees and I was done. The airspeed indicator would then settle on Vx some moments later.

Obviously I'm a huge fan of AOA information in the cockpit. I would like to see people's thinking evolve past just the stall warning information it provides. A good AOA instrument can provide much more.

[rmartingt]

A really interesting and relevant paper on the subject: NASA/TM?2014-218514: Review of Research on Angle-of-Attack Indicator Effectiveness

Some money quotes (emphasis mine):

No training on the use of the AoA indicator was given to the pilots beforehand. Pilots originally thought the AoA indicators were useless, but as they became familiar with and learned how to incorporate the information better, they understood the benefits and the resistance to the indicators subsided.

Several studies were done in the late 1960s through the 1970s. A study by Gee, Gaidsic, and Enevoldson (1971) evaluated whether AoA information was a useful addition to the General Aviation cockpit. The pilots, who did not receive any training with the display prior to flying in the experiment and varied widely in their piloting experience, appreciated the ease with which the AoA indicator allowed them to obtain trim and power settings. Piloting tasks that included take-offs, climbs, low speed maneuvers, approaches and landings were evaluated. The study found that an AoA indicator was a desired display to convey margin to stall as well as being a single reference point that allowed the pilot to select an approach trim condition which resulted in consistent flare and float characteristics regardless of weight or flap settings. It was concluded that displaying AoA was valuable during final approach as a way to maintain the flight path to the airport and in maneuvers to flare.

In the comments section of the paper titled ?Criteria for Stall and Post Stall Gyrations,? (Lamar, 1972) several commenters mentioned the desire to have an AoA indicator included in the cockpit display and one commenter questioned ?if the test pilot of an aircraft needed an angle of attack indicator to stay out of a stall, then shouldn?t every aircraft have one??

Odle (1972) tasked with studying and evaluating an AoA system for use in the United States Air Force (USAF) Air Training Command?s flight training program, found that AoA systems were most valuable in preventing stalls during the traffic pattern and landing phase.

Other studies cited in Karayanakis (1982) found that AoA feedback was useful during flight maneuvers such as: take-off, climb, turns, cruise, slow-flight, descent and landings. The AoA indicator gives the pilot a safe margin to stall that is independent of weight, bank angle, g-forces or density altitude variations.

The Navy evaluated AoA indicators to determine the optimum settings for the phases of flight where it determined it was most beneficial (Carlquist, 1960). They found that an AoA indicator provided useful information during steep turns, while gaining altitude where thrust was limited, maximum endurance flight at steady altitude, ground control approaches, normal field landings in smooth air, and carrier landings. It was impractical to use during cruise since the optimum AoA changed along with altitude, and it was difficult to use during times of turbulence. The AoA indicator was a primary reference during ground control approaches, stall warning, and smooth air landings and it was a secondary reference during other phases of flight. Following this study, it was recommended that AoA systems be installed according to military specifications. For the Navy, using AoA for low-speed control during carrier landings has shown a reduction in stall accidents and high energy landings (Forrest, 1969; Karayanakis, 1982). They also found that implementing the use of AoA on their other aircraft contributed to a substantial reduction in workload by providing a known margin to stall. This knowledge allowed pilots to achieve maximum aircraft performance during flight maneuvers. There was an almost complete elimination of early rotation during takeoff, and aircraft using AoA indicators were able to attain and maintain maximum range and endurance.

And yet... with study after study after study, spanning multiple decades, with entire books written on the subject, so many pilots still insist that AOA indication is "useless", "secondary to airspeed", "a distraction", a "gee-whiz gadget"; that a "Real Pilot" doesn't need those things but instead will just "feel" the airplane.

[Walt]

Originally Posted by rmartingt

And yet... with study after study after study, spanning multiple decades, with entire books written on the subject, so many pilots still insist that AOA indication is "useless", "secondary to airspeed", "a distraction", a "gee-whiz gadget"; that a "Real Pilot" doesn't need those things but instead will just "feel" the airplane.

Good post, I think that pretty well sums it up!

[F1R]

I can see it now, the RV-A320-A