X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Fri, 26 Aug 2005 12:35:44 -0400 Message-ID: X-Original-Return-Path: Received: from mail-relay-2.tiscali.it ([213.205.33.42] verified) by logan.com (CommuniGate Pro SMTP 5.0c1) with ESMTP id 682814 for lml@lancaironline.net; Fri, 26 Aug 2005 12:14:17 -0400 Received-SPF: pass receiver=logan.com; client-ip=213.205.33.42; envelope-from=robert.overmars@tiscali.it Received: from trottolino (62.11.3.207) by mail-relay-2.tiscali.it (7.2.063) id 42D2964B0032663C for lml@lancaironline.net; Fri, 26 Aug 2005 18:12:18 +0200 X-Original-Message-ID: <000001c5aa59$5a2df620$cf030b3e@interbusiness.it> From: "Robert Overmars" X-Original-To: "Lancair Mailing List" Subject: Thunderstorm Survival X-Original-Date: Fri, 26 Aug 2005 17:51:20 +0200 MIME-Version: 1.0 Content-Type: multipart/related; boundary="----=_NextPart_000_00AC_01C5AA66.C43C4F00"; type="multipart/alternative" 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_00AC_01C5AA66.C43C4F00 Content-Type: multipart/alternative; boundary="----=_NextPart_001_00AD_01C5AA66.C44576C0" ------=_NextPart_001_00AD_01C5AA66.C44576C0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Saluti tutti, Perhaps those pilots contemplating extending flaps in the case of = inadvertent penetration of thunderstorms should read FAR 23.345 (a) (1) = (2)appended below. Martin Hollman writes in M.A.D. vol I, "...A limit load factor of 0.5 x = n1 is used at Vf. This condition gives us the maximum twisting load on = the wing.... Twisting causes high in-plane shear stress and together = with twisting generates high rear spar loads" (n1 is the positive = manoeuvre limit load factor) Never having penetrated one of those nasty thunderies I still can't help = but think that compromising the aircraft G load limit, the gust design = strength, and restricting the aircraft speed envelope to Vf at a time = when the maximum strength/gust response/speed may well be needed is just = not a good idea. Test piloting the ultimate flap system or wing strength = at such a time could really spoil your day. By the way I do believe that the Vf G load limit is written up in = aircraft flight manuals. Anyone have a flight manual handy to confirm? ciao, Roberto d'Italia. =A7 23.345 High lift devices. top=20 (a) If flaps or similar high lift devices are to be used for takeoff, = approach or landing, the airplane, with the flaps fully extended at VF, = is assumed to be subjected to symmetrical maneuvers and gusts within the = range determined by- (1) Maneuvering, to a positive limit load factor of 2.0; and=20 (2) Positive and negative gust of 25 feet per second acting normal to = the flight path in level flight. (b) VF must be assumed to be not less than 1.4 VS or 1.8 VSF, whichever = is greater, where- (1) VS is the computed stalling speed with flaps retracted at the design = weight; and (2) VSF is the computed stalling speed with flaps fully extended at the = design weight. (3) If an automatic flap load limiting device is used, the airplane may = be designed for the critical combinations of airspeed and flap position = allowed by that device. (c) In determining external loads on the airplane as a whole, thrust, = slipstream, and pitching acceleration may be assumed to be zero. (d) The flaps, their operating mechanism, and their supporting = structures, must be designed to withstand the conditions prescribed in = paragraph (a) of this section. In addition, with the flaps fully = extended at VF, the following conditions, taken separately, must be = accounted for: (1) A head-on gust having a velocity of 25 feet per second (EAS), = combined with propeller slipstream corresponding to 75 percent of = maximum continuous power; and (2) The effects of propeller slipstream corresponding to maximum takeoff = power. [Doc. No. 27805, 61 FR 5144, Feb. 9, 1996] ------=_NextPart_001_00AD_01C5AA66.C44576C0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Saluti = tutti,
 
Perhaps those pilots = contemplating extending flaps in the case of inadvertent = penetration of=20 thunderstorms should read FAR 23.345  (a) (1) (2)appended=20 below.
 
Martin Hollman writes in = M.A.D. vol=20 I, "...A limit load factor of 0.5 x n1 is used at Vf. This condition = gives us=20 the maximum twisting load on the wing.... Twisting causes high in-plane = shear=20 stress and together with twisting generates high rear spar loads"  = (n1 is=20 the positive manoeuvre limit load factor)
 
Never having penetrated = one of those=20 nasty thunderies I still can't help but think that compromising the=20 aircraft G load limit, the gust design = strength, and restricting=20 the aircraft speed envelope  to Vf at a time when the maximum = strength/gust=20 response/speed may well be needed is just not a good idea. Test = piloting=20 the ultimate flap system or wing strength at such a time could really = spoil your=20 day.
 
By the way I do believe = that the Vf G=20 load limit is written up in aircraft flight manuals. Anyone have a = flight manual=20 handy to confirm?
 
ciao,
 
Roberto = d'Italia.
 
 
 
=A7 23.345   High lift=20 devices.
=20 top=20

(a) If flaps or similar high lift devices are to be used for takeoff, = approach or landing, the airplane, with the flaps fully extended at=20 VF, is assumed to be subjected to symmetrical maneuvers and = gusts=20 within the range determined by=97

(1) Maneuvering, to a positive limit load factor of 2.0; and

(2) Positive and negative gust of 25 feet per second acting normal to = the=20 flight path in level flight.

(b) VF must be assumed to be not less than 1.4 = VS or=20 1.8 VSF, whichever is greater, where=97

(1) VS is the computed stalling speed with flaps retracted = at the=20 design weight; and

(2) VSF is the computed stalling speed with flaps fully = extended=20 at the design weight.

(3) If an automatic flap load limiting device is used, the airplane = may be=20 designed for the critical combinations of airspeed and flap position = allowed by=20 that device.

(c) In determining external loads on the airplane as a whole, thrust, = slipstream, and pitching acceleration may be assumed to be zero.

(d) The flaps, their operating mechanism, and their supporting = structures,=20 must be designed to withstand the conditions prescribed in paragraph (a) = of this=20 section. In addition, with the flaps fully extended at VF, = the=20 following conditions, taken separately, must be accounted for:

(1) A head-on gust having a velocity of 25 feet per second (EAS), = combined=20 with propeller slipstream corresponding to 75 percent of maximum = continuous=20 power; and

(2) The effects of propeller slipstream corresponding to maximum = takeoff=20 power.

[Doc. No. 27805, 61 FR 5144, Feb. 9, 1996]

 
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