X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Thu, 24 Apr 2008 16:46:26 -0400 Message-ID: X-Original-Return-Path: Received: from mta21.charter.net ([216.33.127.81] verified) by logan.com (CommuniGate Pro SMTP 5.2.2) with ESMTP id 2870240 for lml@lancaironline.net; Thu, 24 Apr 2008 11:41:14 -0400 Received-SPF: pass receiver=logan.com; client-ip=216.33.127.81; envelope-from=troneill@charter.net Received: from aarprv04.charter.net ([10.20.200.74]) by mta21.charter.net (InterMail vM.7.08.03.00 201-2186-126-20070710) with ESMTP id <20080424154036.DTOK23078.mta21.charter.net@aarprv04.charter.net> for ; Thu, 24 Apr 2008 11:40:36 -0400 Received: from axs ([75.132.241.174]) by aarprv04.charter.net with SMTP id <20080424154035.PTUB4495.aarprv04.charter.net@axs> for ; Thu, 24 Apr 2008 11:40:35 -0400 X-Original-Message-ID: <009301c8a621$8a2b6350$6501a8c0@axs> From: "terrence o'neill" X-Original-To: "Lancair Mailing List" References: Subject: Re: [LML] Re: Window Strength X-Original-Date: Thu, 24 Apr 2008 10:40:35 -0500 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0090_01C8A5F7.A1139760" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.3138 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.3198 X-Chzlrs: 0 This is a multi-part message in MIME format. ------=_NextPart_000_0090_01C8A5F7.A1139760 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Amen, Brent. Strength is only half of it; stiffness i.e. torsional or bending = frequency tuning is probably more important... especially balance of the = control surfaces. Sympathetic vibration at some (unmeasured) frequency, = which one does not want to match some energy input from engine torsional = pulses, or airlow pulses from prop blade, etc. I had an interesting conversation with the survivor of a flutter = (unbalanced but irreversible horizontal tail) failure at about 500 mph = and going up through 100 ft. (one hundred feet) altitude. Like, = hummmmmm-BAM. His black XP-89's tail came off at the star, his ejection = seat failed to fire, Gs locking him down, then one wing snapped off and = spun the fuselage throwing him out. His guardian angel smiled a second = time causing the 600 ft/sec airflow to rip open his chute before he = could pull the ripcord, blowing out two panels... so he could land in a = lone peach tree in Hawthorne, CA, thence to the hospital for dislocated = shoulder, leg, broken pelvis, etc. The pitch control was irrevesible, but the hydraulic lines back to the = actuators could flex a little. Flex, as in vibrate.... Terrence N211AL L235/320=20 ----- Original Message -----=20 From: Brent Regan=20 To: lml@lancaironline.net=20 Sent: Thursday, April 24, 2008 09:52 AM Subject: [LML] Re: Window Strength "I am sure 8' deep girders will be sufficient." Leon Moisseiff, Chief = Engineer, Tacoma Narrows Bridge "If you cant find 20' lengths of All-Thread then substitute two 10' = lengths" Jack D. Gillum, Hayatt Regency hotel "Tea Dance" walkway = designer. "Sure, it's a little stronger with the window bonded in, but that = small amount of extra strength is not required. The fuselage is strong = enough even with the big hole in it." Rob Wolf Rob is correct that the static strength of the fuselage is determined = without the windows BUT the windows do have significant "in plane" (npi) = shear strength which will have an effect on the torsional stiffness of = the fuselage. This, in turn, effects the natural frequency of the = empennage. Making the fuselage less stiff by decoupling the window = reduces the empennage flutter margin. Only analysis and testing will = tell us by how much. Pushing the aircraft faster with bigger engines and = making the fuselage less stiff will eventually result in structural = failure. I know of at least one IV -P that disintegrated in a 0.63 Mach = dive. Rob may be correct that the structural effects are negligible but his = confidence is unsupported by analysis or testing. I doubt he has the = factory's agreement on this matter. Prudence, and experience, dictates a less cavalier approach to = structural modifications. Regards Brent Regan ------=_NextPart_000_0090_01C8A5F7.A1139760 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Amen, Brent.
Strength is only half of it; = stiffness=20 i.e. torsional or bending frequency tuning is probably more important... = especially balance of the control surfaces. Sympathetic vibration = at some=20 (unmeasured) frequency, which one does not want to match some = energy=20 input from engine torsional pulses, or airlow pulses from prop blade,=20 etc.
I had an interesting = conversation=20 with the survivor of a flutter (unbalanced but irreversible = horizontal=20 tail) failure at about 500 mph and going up through 100 ft. (one = hundred=20 feet) altitude.  Like, hummmmmm-BAM. His black XP-89's tail came = off at the=20 star, his ejection seat failed to fire, Gs locking him down, then one = wing=20 snapped off and spun the fuselage throwing him out. His guardian angel = smiled a=20 second time causing the 600 ft/sec airflow to rip open his chute before = he could=20 pull the ripcord, blowing out two panels... so he could land in a lone = peach=20 tree in Hawthorne, CA, thence to the hospital for dislocated shoulder, = leg,=20 broken pelvis, etc.
The pitch control was = irrevesible, but=20 the hydraulic lines back to the actuators could flex a little. = Flex, as=20 in vibrate....
Terrence
N211AL = L235/320 
 
----- Original Message -----
From:=20 Brent=20 Regan
Sent: Thursday, April 24, 2008 = 09:52=20 AM
Subject: [LML] Re: Window = Strength

"I am sure 8' deep girders will be=20 sufficient." Leon Moisseiff, Chief Engineer, Tacoma Narrows = Bridge

"If=20 you cant find 20' lengths of All-Thread then substitute two 10' = lengths" =20 Jack D. Gillum,  Hayatt Regency hotel "Tea Dance" walkway=20 designer.

"Sure, it's a little stronger with the window = bonded=20 in, but that small amount of extra strength is not required.  The = fuselage is strong enough even with the big hole in it." Rob = Wolf

Rob=20 is correct that the static strength of the fuselage is determined = without the=20 windows BUT the windows do have significant "in plane" (npi) shear = strength=20 which will have an effect on the torsional stiffness of the fuselage. = This, in=20 turn, effects the natural frequency of the empennage. Making the = fuselage less=20 stiff by decoupling the window reduces the empennage flutter margin. = Only=20 analysis and testing will tell us by how much. Pushing the aircraft = faster=20 with bigger engines and making the fuselage less stiff  will = eventually=20 result in structural failure. I know of at least one IV -P that = disintegrated=20 in a 0.63 Mach dive.

Rob may be correct that the structural = effects are=20 negligible but his confidence is unsupported by analysis or testing. I = doubt=20 he has the factory's agreement on this matter.

Prudence, and=20 experience, dictates a less cavalier approach to structural=20 modifications.

Regards
Brent = Regan
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