I don’t think the AoA indicators designed for light aircraft are primarily intended for high altitude use – more as an aid during low and slow phases of flight such as final turn from base to final.
Why would a non-heated version be a waste of time?
…more as an aid during low and slow phases of flight such as final turn from base to final.
You have two such aids already installed in your aeroplane: An airspeed indicator and an independent stall warning device which is nothing else but an AoA indicator with a digital readout: not close to the stall <> close to the stall. Nothing else is required, even if the industry has been trying to push these AoA things on the market for some time.
I don’t think the AoA indicators designed for light aircraft are primarily intended for high altitude use – more as an aid during low and slow phases of flight such as final turn from base to final.
If it actually measures AoA then it should work at any altitude.
The ones in GA tend to have 2 holes and the device measures the pressure difference. This may or may not be a direct AoA measurement. I really don’t know if this will work at altitude. Obviously the magnitude of the difference, for a given AoA, will be smaller at FL200 than at 2000ft and much depends on whether they compensate for the absolute pressure. The avoiding replies I got from the vendor didn’t give me a lot of confidence.
On bizjets, the sensor is a rotating vane which AFAIK measures the AoA directly.
Why would a non-heated version be a waste of time?
It will ice up, below 0C. Same as the pitot tube will ice up, even in VMC (though in VMC it can take quite a while). I would regard a non-heated pitot as highly dodgy because one has to only pop into a little cloud below 0C and the tube could get iced over. The feeling I get is that these GA AoA products have historically been aimed at the homebuilt market where this is less of a concern, and in Europe it cannot “officially” be a concern at all 
The heated version costs only a bit more, fortunately.
Fair concerns, Peter, although I think there may be something to be said for capitalising on the added safety which these systems appear to offer – whilst remaining mindful of their drawbacks, of course – rather than waiting for perfection?
You have two such aids already installed in your aeroplane: An airspeed indicator and an independent stall warning device which is nothing else but an AoA indicator with a digital readout: not close to the stall <> close to the stall. Nothing else is required, even if the industry has been trying to push these AoA things on the market for some time.
Personally, I’m always happy to examine the merits of a new idea or a new approach 
If nothing else is required, why are these systems commonly used in other areas of aviation (air forces)?
rather than waiting for perfection?
Nooooo – only perfection will do for me
But, seriously, I am not going to screw something onto my plane which costs a k or two to buy, takes a day or two to install (wiring and CB for the heater, and mounting the indicator somewhere neatly) but becomes useless when I pop into a cloud.
I flew this morning (short local) and saw -2C. If I flew into some cloud then, there would be a fair chance the AoA indicator would stop working there and then.
why are these systems commonly used in other areas of aviation (air forces)?
Probably because they are able to incorporate AoA approaches into their training. That isn’t ever going to happen in the PPL.
Also in some ops they really do have to use AoA e.g. aircraft carrier landings.
If I was flying a Lancair or some other type with “interesting” low speed behaviour I would probably install it right away, but on my TB20 I don’t see the need. And the system will fail in the one scenario I can imagine happening: having to land with a lot of ice. It senses the airflow angle only, and is calibrated in flight with the aircraft clean. So it will indicate a “good” AoA even when the (iced-up) wing is not producing any lift.
If nothing else is required, why are these systems commonly used in other areas of aviation (air forces)?
About air forces I know nothing, but a lot about civilian aircraft. As I wrote, two independent systems for measuring the apporoach to potentially dangerous low speed regimes are required. In smaller (mostly part 23 certified) aeroplanes this is usually the ASI with colour markings and the stall warner, either electric or pneumatically operated. The stall warner of a C152 for example is nothing but an AoA indicator that will give an acoustic signal whenever a specific AoA is reached. As a C152 is such a simple and benign aircraft, one single AoA value gives sufficient protection at every load and flap setting. This already changes with light twins, where a broader speed range and more configuration options result in different critical AoA values. A Piper Seminole (Pa44), one of the lightests and simplest piston twins on the market already needs two AoA vanes that are activated depending on the flap setting.
The more bigger, faster and complex aircraft become, the larger their range of speeds (a typical light jet can fly between 90 and 450KT IAS) and the broader their payload range, the more dependencies will influence the occurrence of the stall. Therefore an analog sensor like an AoA vane is the easiest option. But wether or not the pilot is presented with the measured data is at the discretion of the aircraft manufacturer. Many of them do measure the AoA but there is no indication for the pilot other than a stick shaker, a marking on the speed tape in the ASI and/or an acoustical alarm. Most Airbusses for example have no AoA indicator and many turboprops don’t have one either. The pilot really only gets the same kind of stall warning like in a Cessna 152. If that’s good enough for an airliner, why should an lightplane require anything extra?
“The pilot really only gets the same kind of stall warning like in a Cessna 152. If that’s good enough for an airliner”
Clearly wasn’t good enough for AF 447…
Clearly wasn’t good enough for AF 447…
Sorry, but if they didn’t notice 30 degrees of pitch then they certainly won’t have noticed an unusual AoA value either. It’s exactly the same as with stall/spin accidents in the traffic circuit: If you monitor your instruments from time to time, you won’t stall. But you can add as many instruments as you like, they are useless if no one looks. Therefore the typical light aircraft setup with an ASI for those who look at the instruments and an acoustic stall warner (or stick shaker in lager planes) for those who don’t is the safest approach. Adding another instrument to the panel in the form of an AoA indicator will do nothing to improve safety.
[Peter] Probably because they are able to incorporate AoA approaches into their training. That isn’t ever going to happen in the PPL.
The militaries maybe, but the typical ATPL pilot with a typical jet or turboprop rating does not receive much AoA training (again: many airliners do not have an AoA indicator so there is nothing to train!). The AoA triggers the stick shaker, and your training consists in the proper reaction to that event just like the blaaaahhhh in a C152. The only other “AoA training” that I received was that they told me which AoA value gives best glide endurance in case of both engines out…
Another use for AoA is to be able to set the correct final approach speed for different configurations of loading in particular. In the Pa46 we all seem to fly to the MTOW final speed which is essentially always too fast unless you started very overloaded. I don’t see AoA as stall avoidance just a more accurate way to judge slow airspeed flight.
