X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Fri, 04 Jan 2013 01:50:37 -0500 Message-ID: X-Original-Return-Path: Received: from mail16.tpgi.com.au ([203.12.160.231] verified) by logan.com (CommuniGate Pro SMTP 6.0.1) with ESMTPS id 5994249 for lml@lancaironline.net; Thu, 03 Jan 2013 20:01:15 -0500 Received-SPF: pass receiver=logan.com; client-ip=203.12.160.231; envelope-from=domcrain@tpg.com.au X-TPG-Junk-Status: Message not scanned X-TPG-Antivirus: Passed X-TPG-Abuse: host=60-241-193-89.static.tpgi.com.au; ip=60.241.193.89; date=Fri, 4 Jan 2013 12:00:36 +1100 Received: from 192-168-1-2.tpgi.com.au (60-241-193-89.static.tpgi.com.au [60.241.193.89]) by mail16.tpgi.com.au (envelope-from domcrain@tpg.com.au) (8.14.3/8.14.3) with ESMTP id r0410YE0032155 (version=TLSv1/SSLv3 cipher=AES128-SHA bits=128 verify=NO) for ; Fri, 4 Jan 2013 12:00:36 +1100 From: "Dominic V. Crain" Content-Type: multipart/alternative; boundary="Apple-Mail=_FF1C5874-A033-4E83-A178-EE58E3760A14" X-Original-Message-Id: Mime-Version: 1.0 (Mac OS X Mail 6.2 \(1499\)) Subject: Re: [LML] stalls X-Original-Date: Fri, 4 Jan 2013 12:00:34 +1100 References: X-Original-To: "Lancair Mailing List" In-Reply-To: X-Mailer: Apple Mail (2.1499) --Apple-Mail=_FF1C5874-A033-4E83-A178-EE58E3760A14 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=iso-8859-1 AND much wisdom here. On 04/01/2013, at 2:16 AM, Frederick Moreno = wrote: >=20 > =20 > Bob wrote: > =20 > "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!)."=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 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.=20 > =20 > 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. > =20 > 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. > =20 > 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. > =20 > 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. > =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 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. > =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 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. > =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), practice some slow flight maneuvers at 10,000 feet, and = practice forced landings.=20 > =20 > But deliberately putting the airplane into a deep stall is Russian = Roulette. Many aircraft are like this. Why go there? > =20 > Fred Moreno --Apple-Mail=_FF1C5874-A033-4E83-A178-EE58E3760A14 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=iso-8859-1 AND much wisdom here.

On 04/01/2013, at 2:16 AM, Frederick Moreno <frederickmoreno@bigpond.com> wrote:

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