Careful not drawing errant conclusions from
… the small tailed Lancairs don't have enough tail authority to even do a full stall touchdown without getting into 'unsociable' sink rates.
(
@hindsight2020, not saying you are thinking such, but a casual reader readily could misinterpret)
This does not mean such is an unstallable airplane. Ground effect shifts the aerodynamic center making the wing’s nose down moment stronger the further you are into ground effect. Aero for Naval Aviators, H.H. Hurt, has some interesting discussions for early lift offs and some planes while being unstallable in ground effect being mushy and unable to escape ground effect in such condition. These discussions apply here. The Aussies put together a nice report while looking into sea skimmers that also applies showing the shifting ac (Wing in Ground Effect Craft Review, Halloran/O’Meara). Canard Boulevard also has a good inadvertent early liftoff takeoff video showing good corrective action bunt the nose on the departure side of it for any plane that shows the ground effect kinda concerns. What you’re seeing with unarrestable sink in landing is in part due to increased longitudinal stability and increased speed sensitivity due to being in ground effect with this increased wing down moment.
if the sensor is a probe like the one from Alpha Systems which is on one wing, isn’t the reading less correct turning in one direction vs the other? And if so, on this particular model plane, wouldn’t it be a safety issue due to erroneous reading and dependence on it?
A valid technical concern though most probes are adequate through a range of beta rendering this particular issue moot.
Specific to the pressure diff, you can have an issue with accelerated stall measurement though such can be resolved in one of two ways and is still far less an error than is airspeed if left unmitigated. The easiest is to have the critical angle occur at a point half way between the forward and the lower pressure sensing points. This is why many probes have thirty-six degrees between ports as many GA stall in the vicinity of eighteen degrees. The other method is to electronically crunch it out.
Note further concern comes with systems that normalize as they may introduce common points of failure. Dynon normalizes by tapping off the static port to enable it which means static issues affect their AOA as well as ASI. Garmin uses a separate static to normalize and also account for speed-pressure concerns but they like Dynon still share the pitot as forward AOA sense port. So shared block vulnerabilities. Lift and Alpha are nice in being truly independent. Search for “Vac”on Van’s Air Force, follow his postings for more info; also see Fly Onspeed organization and the technical papers tab.
.. if the consensus, seemingly from the things I see above, is that you shouldn’t mess with stall testing, how would one ever calibrate the AOA indicator like the Alpha Systems?
Yes and no. You can calibrate it to the highest AOA of comfort having it derive values relative to this as if this be the stall. But, I agree with your sentiments, and would want to calibrate through stall. And would want to document stall characteristics. Note, if you did calibrate to the non-stall highest AOA of comfort, you might want to make “onspeed” something other than 1.3 so as not to be landing too fast.
Don’t let such worries deter from AOA systems. They are by far the best things you can have for helping your flying. Except maybe APM (airfoil performance monitor (listens to the vorticity of the boundary layer)) though such is essentially AOA with healthy wings only becoming something better should your wings be contaminated (iced) or damaged.
www.clarin.com
