lml@lancaironline.net Mailing List Archive

Stall strips are good, they widen the stall warning zone.

Cuffs are good, they do more of the same.

But once you are in a spin in spite of those devices, what is there to help you recover ?

. . . I'm thinking more tail moment and further forward CG . . . neither of which improve efficiency but do help stability.

. . . but that needs to be built in, it's not something that can be glued on after the fact.

. . . . . . the "kangaroo tail" might be an exception.

Wolfgang

----- Original Message -----

From: John Smith

To: lml@lancaironline.net

Sent: Tuesday, January 08, 2013 6:20 AM

Subject: Re: [LML] Re: Stalls & Spins

From my perspective, the key phrase is spin resistance.

Having researched the NASA material and having also seen the Lancair videos of actual flight testing, rightly or wrongly, I installed the wing cuffs to the Legacy on the basis that they seemed to offer the opportunity to make it harder to get into trouble, but accepting that if pushed too far into a spin, then the aircraft may or may not be recoverable. So, if one accepts the view of many which is that "as was", the aircraft was not spin recoverable, there would only appear to be upside from installing the cuffs. The flaw is, of course, that if indeed the Legacy is spin recoverable without wing cuffs, then the addition of the wing cuffs may preclude spin recovery!

Unless someone goes to the trouble of spin testing the Legacy, or any other type fitted with cuffs, one will never know whether spin recoveries are possible under what flight and loading circumstances and, of course, with or without wing cuffs.

Meanwhile, per my prior post on this, all I can say is that the albeit very limited flight testing (straight and level, and continuous 30deg AoB turns) in my Legacy fitted with the cuffs shows that there is plenty of warning of the impending stall – stall strips give the first "gentle" warning", followed by the more severe intermittent "shuddering" as the centre section drops in and out of the stall (whilst the outboard sections are still flying).

I'm happy to talk to anyone if they are interested to talk about this more…. numbers below, but please note time is UTC + 8!!

Regards,

John

John N G Smith
Tel / fax:    +61-8-9385-8891
Mobile:      +61-409-372-975
Email:         john@jjts.net.au

From: <marv@lancair.net>
Reply-To: Lancair Mailing List <lml@lancaironline.net>
Date: Tuesday, 8 January 2013 2:25 AM
To: <lml>
Subject: [LML] Re: Stalls & Spins

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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