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Date: Wed, 09 Jan 2013 15:39:48 -0500
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From: Terrence O'Neill <troneill@charter.net>
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Subject: stalls and spins
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Greetings.
If I may respectfully offer a few more comments on this subject, this =
last time from the point of view of an airplane designer, rather than as =
a pilot. Though trained by the Navy I only flew 4 years there, and have =
much less experience than those pros I've been reading on this list.  My =
own primary interest has always been in designing better planes, =
starting with models in the late 1940s... and continuously as a hobby =
even to today, with but three years 'in the business' 1967-1971 getting =
a provisional TC for my Model W... where I did a lot of research on =
stalls and spins. ..though only testing of stalls, not spins per se.=20
So here are a few opinion-comments about current airplane design for =
stability and stalls and spins.

Most GeNav and experimental planes are heavily influenced by the =
designer's marketing concerns, some of which are not 'form follows =
function'.  I.e., the swept vertical tail-rudder is poor for high AOA =
airflow and spin recovery.  At high AOAs most of the airflow goes =
ineffectively right up the rudder hinge line... which is why the NACA =
and NASA and tests on spin recovery all refer to TDPF, for the airflow =
trapped under the horizontal tail and directed usefully back against the =
bottom of the rudder.  Exception  is Walt Mooney's forward-angle rudder, =
and the Ercoupe's twin tails. In my TC attempt I made the rudder hinged =
to angle forward for rudder control, though it's leading edge was swept =
back --for looks. On the Magnum I made the whole vertical tail into a =
stabilator which angled forward is deflected... for possible spin =
recovery force.

In developed spins, critical is yaw angle.  The yaw  depends on both =
area distribution and mass distribution both fore and aft (long =
fuselages, i.e. engines in the tail or out on the wing), and on the CG =
range, and on the shape of the fuselage and tail.  Also critical is what =
AOA will develop, This also depends on CG range, fuselage shape, h-tail =
area  ... rounded bottom aft fuselages (like the Howard GDA) let smooth =
high AOA airflow get to the vertical tail for more yaw-correcting power =
by the rudder, if not blanketed by the horizontal tail. I think the CAA =
had the Howard recover from a 6 turn spin, at aft CG.  Mass distributed =
out from the CG tends to make the spin go flat (high AOA), nice and slow =
turning, but not good. The flywheel effect can cause a high AOA, and =
popular h-tail design would be better for unstalling at high AOAs if the =
h-tail's aspect ratios were low, instead of high... because low ARs =
develop 3D flow vortices which can keep energy air available to the =
vertical tail-rudder... to stop the rotation.  Step on the ball; then =
stop the turn (with aileron), and then reduce the AOA to unstall... if =
the h-tail isn't stalled.

Our Lancairs are beautiful. When building ours I researched accidents =
and tech reports, which concerned me re pitch moments at deep stalls.  I =
didn't want to redesign the vertical and horizontal tail, so I finally =
decided to go with a band-aid partial mod to try to preserve the =
de-pitching power of the elevator to a higher AOA, and keep the h-tail =
unstalled perhaps another 10 ro so degrees, to give me more time to =
unstall the wing before the h-tail would stall.  I think and hope tan =
unstalled h-tail will also preserve smooth airflow over the rudder at =
wing-stalled AOAs ... as I said in the Kitplanes article.=20
I just mention these things so you can see where I'm coming from.  When =
my trusting soul-mate climbs into our Lancair kit #11 with me, and I =
drive us up into the beautiful clouds, and swiftly across the midwest to =
visit our kids in Colorado, I seriously want us to be safe, if some =
unforseen attitude happens, because our six kids would never forgive me =
if I was the cause of harm to their Mom. I'm sure many you share these =
concerns.

Perhaps some of you may agree with my opinions on airplane stall-spin =
design, and I hope that if they make sense, they'll help others =
understand what's going on in their birds as they fly at high AOAs.

terrence


=20=

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<html><head></head><body style=3D"word-wrap: break-word; =
-webkit-nbsp-mode: space; -webkit-line-break: after-white-space; =
">Greetings.<div>If I may respectfully offer a few more comments on this =
subject, this last time from the point of view of an airplane designer, =
rather than as a pilot. Though trained by the Navy I only flew 4 years =
there, and have much less experience than those pros I've been reading =
on this list. &nbsp;My own primary interest has always been in designing =
better planes, starting with models in the late 1940s... and =
continuously as a hobby even to today, with but three years 'in the =
business' 1967-1971 getting a provisional TC for my Model W... where I =
did a lot of research on stalls and spins. ..though only testing of =
stalls, not spins per se.&nbsp;</div><div>So here are a few =
opinion-comments about current airplane design for stability and stalls =
and spins.</div><div><br></div><div>Most GeNav and experimental planes =
are heavily influenced by the designer's marketing concerns, some of =
which are not 'form follows function'. &nbsp;I.e., the swept vertical =
tail-rudder is poor for high AOA airflow and spin recovery. &nbsp;At =
high AOAs most of the airflow goes ineffectively right up the rudder =
hinge line... which is why the NACA and NASA and tests on spin recovery =
all refer to TDPF, for the airflow trapped <i>under</i> the horizontal =
tail and directed usefully back against the bottom of the rudder. =
&nbsp;Exception &nbsp;is Walt Mooney's forward-angle rudder, and the =
Ercoupe's twin tails. In my TC attempt I made the rudder hinged to angle =
forward for rudder control, though it's leading edge was swept back =
--for looks. On the Magnum I made the whole vertical tail into a =
stabilator which angled forward is deflected... for possible spin =
recovery force.</div><div><br></div><div>In developed spins, critical is =
yaw angle. &nbsp;The yaw &nbsp;depends on both area distribution and =
mass distribution both fore and aft (long fuselages, i.e. engines in the =
tail or out on the wing), and on the CG range, and on the shape of the =
fuselage and tail. &nbsp;Also critical is what AOA will develop, This =
also depends on CG range, fuselage shape, h-tail area &nbsp;... rounded =
bottom aft fuselages (like the Howard GDA) let smooth high AOA airflow =
get to the vertical tail for more yaw-correcting power by the rudder, if =
not blanketed by the horizontal tail. I think the CAA had the Howard =
recover from a 6 turn spin, at aft CG. &nbsp;Mass distributed out from =
the CG tends to make the spin go flat (high AOA), nice and slow turning, =
but not good. The flywheel effect can cause a high AOA, and popular =
h-tail design would be better for unstalling at high AOAs if the =
h-tail's aspect ratios were low, instead of high... because low ARs =
develop 3D flow vortices which can keep energy air available to the =
vertical tail-rudder... to stop the rotation. &nbsp;Step on the ball; =
then stop the turn (with aileron), and then reduce the AOA to unstall... =
if the h-tail isn't stalled.</div><div><br></div><div>Our Lancairs are =
beautiful. When building ours I researched accidents and tech reports, =
which concerned me re pitch moments at deep stalls. &nbsp;I didn't want =
to redesign the vertical and horizontal tail, so I finally decided to go =
with a band-aid partial mod to try to preserve the de-pitching power of =
the elevator to a higher AOA, and keep the h-tail unstalled perhaps =
another 10 ro so degrees, to give me more time to unstall the wing =
before the h-tail would stall. &nbsp;I think and hope tan unstalled =
h-tail will also preserve smooth airflow over the rudder at wing-stalled =
AOAs ... as I said in the Kitplanes article.&nbsp;</div><div>I just =
mention these things so you can see where I'm coming from. &nbsp;When my =
trusting soul-mate climbs into our Lancair kit #11 with me, and I drive =
us up into the beautiful clouds, and swiftly across the midwest to visit =
our kids in Colorado, I seriously want us to be safe, if some unforseen =
attitude happens, because our six kids would never forgive me if I was =
the cause of harm to their Mom. I'm sure many you share these =
concerns.</div><div><br></div><div>Perhaps some of you may agree with my =
opinions on airplane stall-spin design, and I hope that if they make =
sense, they'll help others understand what's going on in their birds as =
they fly at high =
AOAs.</div><div><br></div><div>terrence</div><div><br></div><div><br></div=
><div><br></div><div><br></div><div>&nbsp;</div></body></html>=

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