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Robert,
I'm no aeronical engineer and can't
read that graph with anything but wonder, but your interpretation of it is most
illuminating. It's very believable though as once flow separates on
laminar wings like ours, my limited understanding is that AOA must be
reduced beyond the separation point before the flow reattaches.
I'd love to hear some of our other LML readers (like Gary Casey and
Professor Regan) who may also be qualified to comment on this weigh in
on the subject. I have some questions:
1. Since the ES and IV wings are so different
in size and loading, is this tip stalling effect more pronounced in one plane or
the other?
2. Does CG have any impact on the chart
or does it merely impact the ability to reduce AOA enough to recover once
the plane departs?
3. How much of the wing is considered
the "tip"? Outboard of the ailerons or including
them?
4. Do the tips stall in advance of the wing root and if so, by how
much?
5. How much effect would some vortex
generators ahead of the ailerons have on this graph?
It would seem to me that the key to
avoiding this phenomina is keeping the ailerons flying through a stall (assuming
you allowed yourself to get that far in the first place). It would appear
that Lancair Certified addressed this on the Columbia by placing leading edge
cuffs ahead of the ailerons. The effect is akin to slats on an
airliner, which keep the airflow attached to the wing
longer in slow flight regimes like takeoff and landing. On the
Columbia, they keep the part of the wing behind the cuffs (where the
ailerons are) flying past the point where the rest of it stalls, ensuring
roll control throughout. Vortex generators also delay the onset of flow
separation, though they're normally only used on STOL aircraft which often fly
in that part of the envelope. I believe our best prevention tool is giving
stall speed a very wide berth.
Thanks for bringing this
up. Every small morsel of information which helps us better
understand the characteristics of our machines hopefully enhances our
ability to safely fly them.
Skip Slater
N540ES
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