Wasted fuel, wasted breath and wasted time.
Come on. Say what you really mean – don’t hold back!
Can you describe the physics and math in detail, Lucius?
You can describe how a plane moves through a fluid in a 3D space pretty accurately, given the various inputs at your disposals (static and dynamic pressure, gyros, ground speed, vertical acceleration, OAT, turning radius, etc…). There may be a few factors that we don’t know, such as air humidity, but they are minor. We can even calculate G forces without having a G meter. Agreed?
We also are able to capture the precise state at which the lift reserve is exhausted (stall) via calibration flight. From there, we can calculate how far away we are from that state, since we are able to describe the relationship of the state and AOA. I did not major in fluid dynamics to describe the physics and math in detail. But that is not required. All you need to believe is that such relationship exists, and has been described by some aerodynamists, which are magnitude smarter than me, like Ludwig Prandtl, Wilhelm Kutta, et.al. 70 years ago.
Let’s also not forget that Aspen software derived AOA, does not need to be perfect. It only needs to be equal or better than differential pressure AOA devices, which usually don’t distinguish between flaps up and down, because the inaccuracy between flaps down and up is seen as too small to matter for GA planes, surprisingly, I should add.
All you need to believe is that such relationship exists
“beleive” is not something that should be used in science.
The problem is, all the “derivations” I’ve seen in this thread might work for the steady state case, but that is actually the case that is totally uninteresting for an AoA indicator.
The problem is, all the “derivations” I’ve seen in this thread might work for the steady state case, but that is actually the case that is totally uninteresting for an AoA indicator.
I wouldn’t say that, because slow changes are very close to the steady state. An airframe slowly icing up during cruise while flying on autopilot, or an aircraft getting too slow on final after setting landing flap and not adding sufficient power can be considered to be in a steady state. These people might be saved by an AOA derived warning. But that’s already on board as the stall warner.
Of course, 45 degree banked turns from base to final in turbulent air are not steady enough for a “fake” AOA indication. But pilots who fly that way will not be saved by an accurate AOA readout.
An airframe slowly icing up during cruise while flying on autopilot
Any autopilots envelope protection that doesn’t already notice that by the diminishing IAS is not worth the ink it’s printed on the sales brochure.
Actually icing is a good example, because there the AoA display isn’t worth much anyway, because you have no idea where your critical angle of attack really is. So adding 5 degrees of AoA margin isn’t better than adding 20 knots IAS margin.
The only use of such an instrument is to be able to operate closer to the edge of the envelope (whether intentionally or unintentionally). Be it for more aggressive approaches (water, back country, or the normal madness on a busy GA airport in sunny weather), or closer to the coffin corner (Peter’s motivation). A 10 mile stabilized final is decidedly not interesting…
The question is what the accuracy of the AoA indication will be when taking into account the (in)accuracies of all the various input data you need to compute the AoA.
Have AoA sensors gone out of fashion?
They were all over the press 2-3 years ago, but one doesn’t hear of them much now.
One thing I realised when looking at them is that you have to get the optional heated version, otherwise it will be as useful as an unheated pitot tube (useless for N Europe, basically).
They’re very much in vogue, with the FAA having decided that allowing them to be installed easily was good for safety. For the PA46 where installation is non-trivial (pressurised vessel), STCs are coming in quickly, and the owners’ association is making a big push.
I don’t think there’s much point in having a heated AOA/LRI probe without full airframe de-icing. The reason being that airframe ice changes lift reserve, in which case whether the probe is iced or not, it will give false information.
Peter.
EASA’s CS-STAN also allows for easy installation on most EASA general aviation aircraft.
