X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Thu, 03 Jan 2013 11:30:31 -0500 Message-ID: X-Original-Return-Path: Received: from imr-da06.mx.aol.com ([205.188.169.203] verified) by logan.com (CommuniGate Pro SMTP 6.0.1) with ESMTP id 5993224 for lml@lancaironline.net; Thu, 03 Jan 2013 10:49:49 -0500 Received-SPF: pass receiver=logan.com; client-ip=205.188.169.203; envelope-from=vtailjeff@aol.com Received: from mtaout-ma05.r1000.mx.aol.com (mtaout-ma05.r1000.mx.aol.com [172.29.41.5]) by imr-da06.mx.aol.com (Outbound Mail Relay) with ESMTP id 99A981C000151 for ; Thu, 3 Jan 2013 10:49:14 -0500 (EST) Received: from [10.151.185.121] (unknown [166.137.108.160]) (using TLSv1 with cipher AES128-SHA (128/128 bits)) (No client certificate requested) by mtaout-ma05.r1000.mx.aol.com (MUA/Third Party Client Interface) with ESMTPSA id 1FD16E0000CB; Thu, 3 Jan 2013 10:49:13 -0500 (EST) References: In-Reply-To: Mime-Version: 1.0 (1.0) Content-Type: multipart/alternative; boundary=Apple-Mail-CC0F4395-BFDC-4CBF-9191-C93BBFA5E30D X-Original-Message-Id: Content-Transfer-Encoding: 7bit X-Mailer: iPhone Mail (9B206) From: Jeff Edwards Subject: Re: [LML] Re: stalls X-Original-Date: Thu, 3 Jan 2013 09:49:07 -0600 X-Original-To: Lancair Mailing List x-aol-global-disposition: G X-AOL-SCOLL-SCORE: 0:2:464888992:93952408 X-AOL-SCOLL-URL_COUNT: 0 x-aol-sid: 3039ac1d290550e5a87925d0 X-AOL-IP: 166.137.108.160 --Apple-Mail-CC0F4395-BFDC-4CBF-9191-C93BBFA5E30D Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=us-ascii Fred, Well said! Jeff On Jan 3, 2013, at 9:16 AM, Frederick Moreno w= rote: > =20 > Bob wrote: > =20 > "Interesting: In all the twins I have flown not once was a stall an approv= ed procedure. Approach to stall sure, but never a full stall. So why must L= ancairs be stalled? > Seems that the Lancairs are in the twin situation. So learn the feel at t= he approach to a stall (I have), us an AoA (I do), and the planes are safe a= nd a joy to fly (they are!)."=20 > =20 > Much wisdom there. > =20 > I feel compelled to add a bit of technical content to the discussion. The= Lancair IV wing was tailored to maintain laminar flow as far as possible ov= er the top and bottom of the wing. The resulting wing profile has exception= ally low frictional drag, but an unpredictable stall performance, a common c= haracteristic of wing profiles with long reaches of laminar flow. Laminar b= oundary layers are just not very energetic and can separate from the wing in= a flash. The flow may separate at the root and stay there (conventional st= all), or the separated air flow zone may suddenly spread all the way to the w= ing tip in which case a snap roll into a spin will be the result. And the s= pin may be unrecoverable.=20 > =20 > The LIV is not certified, and its stall capability along with many other c= haracteristics mean it never could be. It is Experimental. Don't treat it l= ike a certified or aerobatic airplane. It isn't. > =20 > Most airplanes (SNJ's for sure, they are trainers), most aerobatic aircraf= t like the Zlin (which have big fat leading edges which are highly stall res= istant and relatively forgiving) and certified aircraft are relatively benig= n in stall. Aerobatic aircraft and many others are guaranteed to be spin re= coverable. Virtually all modern certified aircraft) must have wing designs t= hat are compromised to provide buffet in advance of stall, they quit flying= gently (and only slightly) with a straightforward relatively benign stall, a= nd provide normal straightforward recovery. I flew a friend's Cirrus and i= t was even more benign than my old C182. These airplanes were designed and c= omprehensively tested to assure this benign and forgiving behavior each and e= very time. > =20 > The Lancair IV most definitely was not. It was compromised in the directio= n of speed at any cost. And part of that cost is occasionally unpredictable= and potentially deadly stall behavior if not carefully and cautiously handl= ed. It is the nature of the laminar flow wing design that yields such low d= rag and high cruise speed coupled with other of the aircraft's characteristi= cs and design features. > =20 > I was instructed by a 20,000+ hour Qantas captain who also flew a Lancair I= V and was the Australian national aerobatic champion. This guy really under= stands unusual flight attitudes and aerodynamics. His instructions for the L= IV practice were approach to stall at 10,000 feet in the landing configurati= on, an IRONCLAD rule that the ball be kept EXACTLY in the center, and then i= mmediate recovery after the initial break. All this practice was done in th= e landing configuration except for a couple of very cautious approach to sta= ll tests with airplane clean which we did to establish a calibration point f= or my angle of attack indicator. He was adamant: once that data point is co= llected, there is no reason to go back there again. > =20 > He emphasized that there are airplanes that you just don't stall - ever - = because they bite. Many swept wing aircraft are in this category. On thos= e the stall can progress from root to wing tip very rapidly and the airplane= then immediately rolls on its back and drops into a spin. On the Lancair, a= deep stall with ball out of center can on occasion enter an unrecoverable s= pin. Let the ball get far enough out of center and it will almost certainly= drop into a spin. > =20 > In short, he said, there is absolutely NO REASON to put a Lancair IV into a= deep stall. Slow flight practice, fine. Nibble at stall (approach to stal= l) also fine subject to ball in the middle and 10,000 feet. Get ball out of= center and/or hold the stall a bit too long and the outcome maybe fine 9 ou= t of 10 times, but you may get an unrecoverable spin on the tenth. Without= a spin chute and a personal parachute, exploring that territory is definite= ly test pilot stuff, so you better train and equip accordingly. > =20 > Stay away from everything except the approach to stall with ball centered,= use an angle of attack indicator (should be mandatory in these aircraft), p= ractice some slow flight maneuvers at 10,000 feet, and practice forced landi= ngs.=20 > =20 > But deliberately putting the airplane into a deep stall is Russian Roulett= e. Many aircraft are like this. Why go there? > =20 > Fred Moreno --Apple-Mail-CC0F4395-BFDC-4CBF-9191-C93BBFA5E30D Content-Transfer-Encoding: 7bit Content-Type: text/html; charset=utf-8
Fred,

Well said!

Jeff

On Jan 3, 2013, at 9:16 AM, Frederick Moreno <frederickmoreno@bigpond.com> wrote:

 
Bob wrote:
 
"Interesting: In all the twins I have flown not once was a stall an approved procedure.  Approach to stall sure, but never a full stall.  So why must Lancairs be stalled?
Seems that the Lancairs are in the twin situation.  So learn the feel at the approach to a stall (I have), us an AoA (I do), and the planes are safe and a joy to fly (they are!)." 
 
Much wisdom there.
 
I feel compelled to add a bit of technical content to the discussion.  The Lancair IV wing was tailored to maintain laminar flow as far as possible over the top and bottom of the wing.  The resulting wing profile has exceptionally low frictional drag, but an unpredictable stall performance, a common characteristic of wing profiles with long reaches of laminar flow.  Laminar boundary layers are just not very energetic and can separate from the wing in a flash.  The flow may separate at the root and stay there (conventional stall), or the separated air flow zone may suddenly spread all the way to the wing tip in which case a snap roll into a spin will be the result.  And the spin may be unrecoverable. 
 
The LIV is not certified, and its stall capability along with many other characteristics mean it never could be.  It is Experimental.  Don't treat it like a certified or aerobatic airplane.  It isn't.
 
Most airplanes (SNJ's for sure, they are trainers), most aerobatic aircraft like the Zlin (which have big fat leading edges which are highly stall resistant and relatively forgiving) and certified aircraft are relatively benign in stall.  Aerobatic aircraft and many others are guaranteed to be spin recoverable.  Virtually all modern certified aircraft) must have wing designs that  are compromised to provide buffet in advance of stall, they quit flying gently (and only slightly) with a straightforward relatively benign stall, and provide normal straightforward recovery.   I flew a friend's Cirrus and it was even more benign than my old C182.  These airplanes were designed and comprehensively tested to assure this benign and forgiving behavior each and every time.
 
The Lancair IV most definitely was not. It was compromised in the direction of speed at any cost.  And part of that cost is occasionally unpredictable and potentially deadly stall behavior if not carefully and cautiously handled.   It is the nature of the laminar flow wing design that yields such low drag and high cruise speed coupled with other of the aircraft's characteristics and design features.
 
I was instructed by a 20,000+ hour Qantas captain who also flew a Lancair IV and was the Australian national aerobatic champion.  This guy really understands unusual flight attitudes and aerodynamics.  His instructions for the LIV practice were approach to stall at 10,000 feet in the landing configuration, an IRONCLAD rule that the ball be kept EXACTLY in the center, and then immediate recovery after the initial break.  All this practice was done in the landing configuration except for a couple of very cautious approach to stall tests with airplane clean which we did to establish a calibration point for my angle of attack indicator.  He was adamant: once that data point is collected, there is no reason to go back there again.
 
He emphasized that there are airplanes that you just don't stall - ever -  because they bite.  Many swept wing aircraft are in this category.  On those the stall can progress from root to wing tip very rapidly and the airplane then immediately rolls on its back and drops into a spin.  On the Lancair, a deep stall with ball out of center can on occasion enter an unrecoverable spin.  Let the ball get far enough out of center and it will almost certainly drop into a spin.
 
In short, he said, there is absolutely NO REASON to put a Lancair IV into a deep stall.  Slow flight practice, fine.  Nibble at stall (approach to stall) also fine subject to ball in the middle and 10,000 feet.  Get ball out of center and/or hold the stall a bit too long and the outcome maybe fine 9 out of 10 times, but you may get an unrecoverable spin on the  tenth.  Without a spin chute and a personal parachute, exploring that territory is definitely test pilot stuff, so you  better train and equip accordingly.
 
Stay away from everything except the approach to stall with ball centered, use an angle of attack indicator (should be mandatory in these aircraft), practice some slow flight maneuvers at 10,000 feet, and practice forced landings. 
 
But deliberately putting the airplane into a deep stall is Russian Roulette.  Many aircraft are like this.  Why go there?
 
Fred Moreno
--Apple-Mail-CC0F4395-BFDC-4CBF-9191-C93BBFA5E30D--