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Amen to Pete's comments.

A review of Part 23, several texts, NASA 1977 Tech Paper 1009, TN2016, TN1779 and others, and a letter from James Bowman, ass't director at Langley in 1972 when I was trying to type certify my Model W, in which he noted "a need or additional research for light planes... the influence of tail design, tail length, center of gravity, mass (wing loading), and mass distribution, on spin recoveries of both high and low wing airplanes... to be correlated with existing Tail Dampening Power Factor criterion..." etc.

That is, NASA Langley was still working on the problem.

All these relevant factors indicate the complexity of the problem of achieving reliable spin recovery once an airplane's configuration is set.

It's much easier to prevent the problem in configuration design, as with aerobatic designs. Too late for that for the experimental Lancairs.

I think FAA certified Part 23 standard category aircraft only have to demonstrate recovery from an incipient spin (first two turns) at an aft CG, during which most aircraft will unstall themselves once.... and after that, you're in the 'twilight zone'.

I read somewhere that before WW II planes had to demonstrate recovery from a 6-turn spin... and I suspect that after the war the big powerful aviation companies (North American, Republic, Ryan etc.)persuaded the CAA/FAA to reduce this 'business risk and cost' to the present requirements which only placard against deliberate spins, but ignore the accidental, developed spins.

Since NASA's 1977 spin tunnel tests tested spins involved 2deg to 33deg sideslipping, and AOAs from 15 to over 68 degrees, the yawing demonstrates why rudder power is needed to stop it, and the high AOAs indicate why the horizontal tail (and CG position) has to be able to reduce the AOA to unstall the wing. If the planes' configuration blankets the rudder or horizontal (blanketed or stalled) tail, stopping a spin is less than likely.

Since a plane can't spin unless it stalls first, stall resistance and prompt recovery is a priority... like, keeping the CG forward helps. I added slots to my horizontal stabilizer, and it seems to keep de-pitching control strong at the stall.

Just offering a few comments to broaden an understanding of the problem.... hopefully they might be helpful.

Terrence

On Jan 7, 2013, at 12:25 PM, <marv@lancair.net> <marv@lancair.net> wrote:

Posted for "Peter Field" <pfield.avn@gmail.com>:

Dear Lancair Drivers:

I've been following the discussion on stalls and spins and I want to add
some additional factual information purely for your personal consumption and
reflection.  Attached are excerpts from 10 different 1980-90 NASA flight
test final reports on a series of GA airplanes in which NASA evaluated the
use of cuffs on leading edges to improve the behavior of the test airplane
approaching the stall.  For various reasons the cuffs improved lateral
control entering the stall, but had the adverse effect of destabilizing the
aircraft once a fully developed spin was achieved.  Essentially, stall
behavior was improved at the sacrifice of spin recovery.  Cuffs on wing
leading edges are an add on design fix, the more elegant solution is
"washout," where the wing is twisted so the outer portions of the wing
always operate at a lower angle of attack.

To my knowledge, Lancair has never subjected any of their aircraft to a
fully developed spin matrix complete with appropriate instrumentation and a
spin recovery chute.  There is no FAA requirement for them to do so - it's
an Experimental Category airplane.  Early on they may have lightly touched
on such testing; but I have never seen any documentation on a fully
completed spin matrix, which would involve at least 160 spins at various
cg's and lateral loadings.  In my opinion, it would be highly risky to fool
around much beyond the stall in any Lancair - there is no documentation that
indicates any of these airplanes can always be recovered from a one turn
incipient phase spin or any fully developed spin.  Being good at spin
recovery isn't so much a matter of how skillful a pilot you are, it's a
matter of how many spins you've experienced in airplanes known to be
recoverable.  Being familiar with the stall characteristics of your own
airplane should be a matter of personal preference.

Best regards,

Pete Field (LNC2)

USNTPS graduate & spin recovery instructor

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