On Thursday, September 6, 2018 at 8:21:39 PM UTC-5, Mike Borgelt wrote:

To digress from the vario topic slightly:
Which is why I said that flying attitude can kill you. I think this is what happened to an ASG-29 pilot at Waikerie about 2 and a half years ago, turning final with what seemed to be plenty of airspeed, into a strong thermal encounter and the next thing he was in the grapevines. Fortunately the wires and vines cushioned the stop enough and the spin wasn't fully established, that he survived. Encounter a fairly sharp 10 knot core at 60 KIAS and the AoA increases by 10 degrees. The AoA may be around 7 degrees before the encounter. What AoA do thin subsonic wings stall at?
This, I believe is one answer to the unexplained spin ins that occur from time to time.
Attitude is fine in equilibrium or very close to equilibrium situations. Doesn't work very well in other situations. How many have died in the winch launch failure scenario where you bury the nose well below the horizon, then roll and pull and the thing flicks in to a spin? Unfortunately all too many merely in practice.
A guy who was Chief Test Pilot for the Royal Australian Air Force during the 1950s and 1960s once told me if the aircraft is wanting to go a certain way and you are trying to force it to go another, just go with the aircraft as it is departing from controlled flight. Good advice IMO.

To continue this excellent digression from the original thread: This whole "pitchdown in the pattern due to a thermal" is the reason we should be using AOA in the pattern instead of Airspeed. An AOA gauge would immediately indicate the AOA changing due to a gust or thermal - before the ASI shows any change in airspeed. Couple the AOA system with a visual (or even better, an aural) indication, and you can fly the pattern safely without ever looking in the cockpit.

Caution, war story: The F-4 had a really nice AOA system with both visual (cockpit gauge and coaming AOA lights) and aural cues, that worked much like a vario audio, with different tones from fast down to on-speed and down to slow and dangerously slow. Very distinct tones which made it easy to fly the pattern at a nice safe speed (regardless of gross weight or bank angle) until on final, then slowing down to final on-speed for touch down - never looking at the airspeed indicator other than to cross check AOA vs airspeed at the start of the approach. Flying approaches from the back seat, you couldn't even see the airspeed indicator (due to having to lean way over and look around the pilot's seat - a crosswind or a bit of rudder helped ;^) so you relied entirely on the AOA tones to fly the approach - and it was the easiest, most natural thing to do, keeping the touchdown point in view the whole time.

Here is an idea for you smart guys: come up with a simple AOA sensor system consisting of small low drag bluetooth-enabled "pods" attached about mid-span on both wing leading edges, transmitting to the AOA system in the cockpit. When the gear is down (and/or spoilers open for fixed gear ships) the vario audio would be turned off and replaced by the AOA audio (which would be distinctive enough not to be confused with a vario), backed up with a set of FAST/ONSPEED/SLOW indexer lights on the top of the panel. To use, in the pattern drop gear or crack the spoilers, verify the AOA tone matches your approach speed on downwind (to check for stuck or failing AOA system), then fly the audio to touchdown, looking for a fast or slightly fast tone until short final when you slow to on-speed tone. If you hit a gust or thermal that bumps up your AOA dangerously, you would get an immediate SLOW or DANGEROUSLY SLOW tone and could react accordingly. Same if you have a PTT down low full of ballast and have to turn back to the field - the AOA tones would still be correct for your increased bank angle and wingloading.

Kirk
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