Return-Path: Sender: "Marvin Kaye" To: lml@lancaironline.net Date: Wed, 29 Sep 2004 19:35:09 -0400 Message-ID: X-Original-Return-Path: Received: from mail-relay-4.tiscali.it ([213.205.33.44] verified) by logan.com (CommuniGate Pro SMTP 4.2.3) with ESMTP id 436940 for lml@lancaironline.net; Wed, 29 Sep 2004 13:52:29 -0400 Received-SPF: none receiver=logan.com; client-ip=213.205.33.44; envelope-from=robert.overmars@tiscali.it Received: from trottolino (62.11.0.191) by mail-relay-4.tiscali.it (7.1.021.3) id 40F3EBEA0138D368 for lml@lancaironline.net; Wed, 29 Sep 2004 19:51:58 +0200 X-Original-Message-ID: <005b01c4a64d$ce4c0e40$bf000b3e@interbusiness.it> From: "Robert Overmars" X-Original-To: "Lancair Mailing List" Subject: Fw: [LML] wing incidence indifference X-Original-Date: Wed, 29 Sep 2004 19:57:34 +0200 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0058_01C4A65E.90207780" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2800.1158 X-MIMEOLE: Produced By Microsoft MimeOLE V6.00.2800.1165 This is a multi-part message in MIME format. ------=_NextPart_000_0058_01C4A65E.90207780 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable "Its a common procedure at Cessna. I am not aware of any accidents = attributed to it so if it is dangerous as you say don't you think it = would show up in the accident statistics?=20 Jeff Edwards LIVP"=20 Jeff and others.... Haven't there been enough Lancair fatalities already without adding to = the list to try to prove the point?=20 Have you read the compilation of Lancair accidents done by Lee Metcalfe? = Noticed the number of stall/spin accidents? The number of fatalities = (dreadful word fatalities, each fatality was a warm living breathing = person just like you and me and everyone else) from these stall/spin = accidents? Perhaps wing incidence/washout differences are very much a = factor in the all too common propensity of Lancairs to depart controlled = flight and crash except it's rather difficult to reassemble the broken = bits of aeroplane to check what was the original incidence = washout/incidence and if it was a factor. Cessna wings are to Lancair wings as chalk is to cheese. Cessna wings = with big fat leading edges, thick sections, slow speeds, big tolerances = and docile behaviour in that after max Cl lift falls off gradually. = Compared to Lancair wings with laminar flow, high speeds, small leading = edge radii, low tolerance for building error and in the case of IVs and = ESs, NACA 64212 tip profiles, quoting Martin Hollman "a good profile = with a high coefficient of lift but a sharp stall" Just how sharp is the stall? 3.5 degrees after max Cl (15 degrees AoA) = 20% of lift is lost. 7.5 degrees after max Cl more than 35% of lift is = lost. Little differences in incidence and especially tip incidence start = to become significant, especially at higher speeds, double the speed and = the lift quadruples. The LIV and ES wings have 2 degrees of washout, = does anyone seriously contend that a wing built with 1.7 or 2.0 degrees = more washout (an enormous 85% to 100% error in construction) than it's = partner wing can have it's incidence fudged by a degree or so with = eccentric bushes to average the lift in cruise flight and that that = aeroplane has safe stalling characteristics through ALL of the flight = envelope? That the stall will iniatiate at the wing root symmetrically = and progress outboard symmetrically as is the design intent? Gust loads and the structural limits are interesting.=20 Consider an ES cruising along at 8,000 feet at a weight of 2,800 lbs, = maintaining 220 mph. The MAC AoA is 2.32 degrees, the wing is working at = a coefficient of lift of .205. The aeroplane encounters a vertical = gust, lets say 50 feet / sec. The wing at MAC now sees an AoA of 11.12, = the Cl is .98968 and the wing lift is 13,515 lbs. Divide this by the = gross weight and the g is 4.83, more than the normal load limit of the = aeroplane. Lesson learnt...stay in the green arc of the ASI. While the MAC is working at a Cl of .98968 the wing tip with the correct = washout is working at 1 degree less AoA therefore the Cl =3D .90068. = Plug the numbers into the formula for lift and calculate the lift for = one sq ft at the tip equals 87.85 lbs lift. If the opposite wing tip has = 1 degree more AoA it's working at the same AoA and CL of the MAC and = merrily producing 96.5 pounds of lift. That's 8.7 lbs difference each = square foot at the tip, the difference progresively becoming less = towards the root, averaging about 300 lbs difference acting at MAC. Now our ES, after surviving that encounter slows down to 170 mph. The = AoA is 3.88 degrees, the Cl is .3439. Again it encounters that 50 fps = vertical gust, the AoA peaks at 15.28 degrees at MAC, the Cl is 1.36, = total lift is 11,071 lbs and the g is 3.95. Hooray! the airframe = survives. But the wing root has stalled (at 15.5 degrees) as it works at 1 degree = more than the MAC, however this is not a great problem as the falloff of = Cl past 15.5 degrees for the root profile is not so great (about 1/3 of = the falloff of the tip profile), and even if the incidence is a little = different side to side the rolling moment produced is not so much. With a wing built with 1.7or 2.0 degrees more twist at the tip than the = other installed on our hypothetical ES, in this situation you've gone = into test pilot land. It's feasible one complete wing has stalled and = part of the other wing, even the tip is still merrily working away at = max Cl. The downgoing wing sees an upwards vertical component in it's = airflow which effectively increases the AoA, which increase the drag, = the aeroplane starts to yaw...you get the picture..?? Purists will know that my figures are for illustrations purposes only. = In calculating gust loads there are finite delays allowed in the gust = onset and aeroplane response that skews the figures but not by such an = amount that these figures are meaningless. Nature doesn't always oblige = with nice convenient 50fps gusts or downdraughts etc and any aeroplane = can be involved in such a situation. Give yourself the best chance of survival and build 'em light and = symmetrical.....and keep 'yer tips flying! Ciao, Roberto d'Italia.=20 ------=_NextPart_000_0058_01C4A65E.90207780 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
 
"Its a common procedure at Cessna. I am not aware of any accidents=20 attributed to it so if it is dangerous as you say don't you think it = would show=20 up in the accident statistics?
 
Jeff Edwards
LIVP"
 
 
Jeff and others....
 
Haven't there been enough Lancair fatalities already without adding = to the=20 list to try to prove the point?
 
Have you read the compilation of Lancair accidents done by Lee = Metcalfe?=20 Noticed the number of stall/spin accidents? The number of fatalities = (dreadful=20 word fatalities, each fatality was a warm living breathing person just = like you=20 and me and everyone else) from these stall/spin accidents? Perhaps wing=20 incidence/washout differences are very much a factor in the all too = common=20 propensity of Lancairs to depart controlled flight and crash except = it's=20 rather difficult to reassemble the broken bits of aeroplane to = check what=20 was the original incidence washout/incidence and if it was a = factor.
 
Cessna wings are to Lancair wings as chalk is to cheese. Cessna = wings with=20 big fat leading edges, thick sections, slow speeds, big = tolerances and=20 docile behaviour in that after max Cl lift falls off gradually. Compared = to=20 Lancair wings with laminar flow, high speeds, small leading = edge=20 radii, low tolerance for building error and in the case of IVs and = ESs,=20 NACA 64212 tip profiles, quoting Martin Hollman "a good profile with a = high=20 coefficient of lift but a sharp stall"
 
Just how sharp is the stall? 3.5 degrees after max Cl (15 degrees=20 AoA) 20% of lift is lost. 7.5 degrees after max Cl more than 35% of = lift is=20 lost. Little differences in incidence and especially tip incidence start = to=20 become significant, especially at higher speeds, double the speed = and the=20 lift quadruples.  The LIV and ES wings have 2 degrees of = washout, does=20 anyone seriously contend that a wing built with 1.7 or 2.0 degrees = more=20 washout (an enormous 85% to 100% error in construction) than it's = partner=20 wing can have it's incidence fudged by a degree or so with = eccentric=20 bushes to average the lift in cruise flight and that that aeroplane = has=20 safe stalling characteristics through ALL of the flight envelope? That = the stall=20 will iniatiate at the wing root symmetrically and progress outboard=20 symmetrically as is the design intent?
 
 
 
Gust loads and the structural limits are interesting.
 
Consider an ES cruising along at 8,000 feet at a weight of 2,800 = lbs,=20 maintaining 220 mph. The MAC AoA is 2.32 degrees, the wing is working at = a=20 coefficient of lift of .205. The aeroplane encounters a  vertical = gust,=20 lets say 50 feet / sec. The wing at MAC now sees an AoA of 11.12, the Cl = is=20 .98968 and the wing lift is 13,515 lbs. Divide this by the = gross=20 weight and the g is 4.83, more than the normal load limit of the = aeroplane.=20 Lesson learnt...stay in the green arc of the ASI.
While the MAC is working at a Cl of .98968 the wing tip with the = correct=20 washout is working at 1 degree less AoA therefore the Cl =3D .90068. = Plug the=20 numbers into the formula for lift and calculate the lift for one sq ft = at the=20 tip equals 87.85 lbs lift. If the opposite wing tip has 1 degree = more AoA=20 it's working at the same AoA and CL of the MAC and merrily = producing 96.5=20 pounds of lift. That's 8.7 lbs difference each square foot at the tip, = the=20 difference progresively becoming less towards the root, averaging about = 300 lbs=20 difference acting at MAC.
 
Now our ES, after surviving that encounter slows down to 170 mph. = The AoA=20 is 3.88 degrees, the Cl is .3439. Again it encounters that 50 fps = vertical gust,=20 the AoA peaks at 15.28 degrees at MAC, the Cl is 1.36,  total = lift is=20 11,071 lbs and the g is 3.95. Hooray! the airframe survives.
But the wing root has stalled (at 15.5 degrees) as it = works at 1=20 degree more than the MAC, however this is not a great problem as the = falloff of=20 Cl past 15.5 degrees for the root profile is not so great (about 1/3 of = the=20 falloff of the tip profile), and even if the incidence is a little = different=20 side to side the rolling moment produced is not so much.
With a wing built with 1.7or 2.0 degrees more twist at the=20 tip than the other  installed on our hypothetical ES, in this=20 situation you've gone into test pilot land. It's feasible one complete = wing has=20 stalled and part of the other wing, even the tip is still merrily = working=20 away at max Cl. The downgoing wing sees an upwards vertical = component in=20 it's airflow which effectively increases the AoA, which increase the = drag, the=20 aeroplane starts to yaw...you get the picture..??
 
Purists will know that my figures are for illustrations purposes = only. In=20 calculating gust loads there are finite delays allowed in the gust=20 onset and aeroplane response that skews the figures but not by = such an=20 amount that these figures are meaningless. Nature doesn't always = oblige=20 with nice convenient 50fps gusts or downdraughts etc and any aeroplane = can be=20 involved in such a situation.
 
Give yourself the best chance of survival and build 'em light=20 and symmetrical.....and keep 'yer tips flying!
 
Ciao,
 
Roberto d'Italia. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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