Antonio wrote:
Does such an instrument really exist in a precise, reliable form?
I don´t know if any AoA instruments exist in a reliable form “available” to the lower segment of GA.
If one does – and it´s understood how to use it, it would be the best instrument available for many things, especially approach and threshold “speed” – since it would be totally independent of external weather conditions (density altitude, winds etc.) and actual aircraft weight and balance would be instantly considered.
They AoA indications on complex jets are obviously reliable and by far the most reliable indication of any sort related to critical AoA (wing “stall”).
We don´t have any pitot probes, nor AoA vanes, on Gulfstream G650 and later models – they are “smart probes” and provide AoA information (and a lot of other data, including IAS) between the 4 of them.
Antonio wrote:
They are used to drive flight laws being used (but not flight controls, other than stall-prevention)
I don´t understand this statement.
It is true that IAS/MACH (or VNAV/VIAS etc.) is what you mode SELECT and is used for “speed” and “drive”/controls the elevators (flight controls) and/or to maintain a speed.
The reason for IAS/MACH being the control mode, and not AoA, is not because of the reliability of the AoA data, but because we don´t aviate (operate) the airplane in AoA modes – we comply with procedural speeds and ATC instructions – all based on IAS/MACH.
Hey @Dan ! It is refreshing that you bring Larry Larrabure’s magistral example to the discussion.
I have been following him for years and it is amazing to see the places he puts his 182 down onto.
His use of AOA indicator is indeed different from what we are discussing here: he takes his airplane deep into the high AOA regime in a way which would likely be unsafe without such indication.
The rest of us mortals back-off once the stall warning goes off, not knowing how deep “into the stall” we are, he just pushes a bit further nailing his red AOA lights knowing he has a couple more of them to go…I note he does not do that in turbulent or windy weather…and for good reason.
You can however fly IAS on approach in turbulent and windy weather…but not onto a 500-ft long sandbar with a C182.
Yeager wrote:
I don´t understand this statement.
That is because you are speaking autopilot control modes, I am talking fly-by-wire control rules, one or two layers below autopilot.
Boeing’s logic in the Max disaster was that pilots do not normally need to know the underlying layer, just the top one, so I am bringing it up here :)
Typical “second-layer” control laws in pitch are attitude-command and normal accel (AKA G-load)-command, but never AOA-command…why would that be?
Friend of mine with lots of experience in these things came up with a quite plausible explanation of the rapid roll and disintegration…. what if the roll was a result of the initial impact? It may well have been wings level until then but it is not exactly unknown for wings to either break off or strike things on the ground, which could well lead to a roll over we’ve seen on the one video.
They were wings level until they disappeared behind the building and on the 2nd video where the roll is shown it is not clear if it happened while still airborne or as the result of ground contact.
Antonio wrote:
That is because you are speaking autopilot control modes, I am talking fly-by-wire control rules, one or two layers below autopilot.
Boeing’s logic in the Max disaster was that pilots do not normally need to know the underlying layer, just the top one, so I am bringing it up here :)
The fly-by-wire “rules” applies precisely the same to autopilot engaged or not engaged modes, there is no difference with regards to that. The protection modes will do the same – other than disconnecting the autopilot, it´s the same protection. Why do you think that the protection modes are based on AoA? The answer is that it is the only precise measurement of how close you are to reaching AoA crit (“stall”). Simple as that.
G-load is not a control law parameter in any airplanes I´ve flown (I think! ;-) ), including the A330, other than aileron levitation (structural “bending”), but even that I believe was based on AoA measurement, not any “physical” measurement.
Antonio wrote:
Typical “second-layer” control laws in pitch are attitude-command and normal accel (AKA G-load)-command, but never AOA-command…why would that be?
Well, you tell me? 
Antonio wrote:
His use of AOA indicator is indeed different from what we are discussing here: he takes his airplane deep into the high AOA regime in a way which would likely be unsafe without such indication.
On the Cessna CJx PFD in addition to the Aoa, you have another very good tool that is “green dot”, it’s a small green dot placed on the speed band, where it indicated the current 1.3Vs of the current attitude/configuration, and it’s based on the AoA sensor that we have too. Unfortunately, the Aoa is far from the direct view when in approach, and your scan is anyway going through the speed band.
This tool indicates that in any situation, you have the approach speed and your margin over it, and even if you didn’t have time to calculate your Vref/Vapp for any reason, you can still base your speeds on this.
And this green dot is really moving when your approach is shaky or when you’re in turn, making it a great tool.
Yeager wrote:
fly-by-wire “rules” applies precisely the same to autopilot engaged or not engaged modes
Exactly, that is why they are one (or more) layers below in the control loop, you know your stuff…I guess your G650 “beast” is FBW?
Yeager wrote:
G-load is not a control law parameter in any airplanes I´ve flown
Only some military fighter-type aircraft do, it may remain a limiting parameter on the others, AOA-style. On the F-16, IIRC, it is G-command (it used to be stick-force related, but later transitioned to a mixed stick force+position fed) , but on the F-18 and most airliners it is pitch-rate command, stick-position fed. On the F-14 and the L-1011, to use the one commercial airliner example, on approach, there was DLC mode where pitch was fixed and glideslope was controlled by the stick/yoke via spoilers…must have felt like an elevator, but pilots loved it.
Yeager wrote:
it adds value for “normal” ops
Unable to contest.
I guess the question is, to answer the concern raised by @gallois, whether AOA should be the main pitch guidance parameter used for inflight training for flying approaches in lieu of an IAS Vref
greg_mp wrote:
“green dot”
Very useful. As a minimum, it validates your Vref.
US Navy aircraft have had an AOA indexer since ages ago for the same purpose, but it was “digital” in the sense that it was either “on speed” , or “fast” or “slow”, but you would not know by how much.
Next one especially for @Dan
Some NAvy aircraft even used to have a repeater AOA indicator on the NLG for the LSO to see (and report to pilot) during approach
INteresting to see that the military do not call those “high- or low-AOA” lights, but “slow” or “fast” lights instead…just saying
Antonio wrote:
but “slow” or “fast” lights instead
Yes indeed, this is really a lot simpler to memorize.
