X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from ispmxmta05-srv.windstream.net ([166.102.165.166] verified) by logan.com (CommuniGate Pro SMTP 5.1.11) with ESMTP id 2281585 for flyrotary@lancaironline.net; Thu, 23 Aug 2007 23:58:06 -0400 Received-SPF: pass receiver=logan.com; client-ip=166.102.165.166; envelope-from=montyr2157@alltel.net Received: from ispmxaamta08-gx.windstream.net ([71.29.241.244]) by ispmxmta05-srv.windstream.net with ESMTP id <20070824035726.HKXI19750.ispmxmta05-srv.windstream.net@ispmxaamta08-gx.windstream.net> for ; Thu, 23 Aug 2007 22:57:26 -0500 Received: from Thorstwin ([71.29.241.244]) by ispmxaamta08-gx.windstream.net with SMTP id <20070824035726.CBIR7089.ispmxaamta08-gx.windstream.net@Thorstwin> for ; Thu, 23 Aug 2007 22:57:26 -0500 Message-ID: <002d01c7e602$e5268b20$6501a8c0@Thorstwin> From: "M Roberts" To: "Rotary motors in aircraft" Subject: Engine Mounts Date: Thu, 23 Aug 2007 22:57:31 -0500 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_002A_01C7E5D8.FC318970" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.3138 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.3138 This is a multi-part message in MIME format. ------=_NextPart_000_002A_01C7E5D8.FC318970 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Bill or anyone, I guess I need to change my question to more specifics. For example, = what do you think of the single point attachment on the rear of the = s-beam verses the more substantial attachment of the flat plate mount. I = personally don't know if I feel comfortable with a single point of = attachment in the rear. For example, there may be times when the engine = gets torqued around due to sudden changes of flight direction. Robert Robert,=20 Flight loads are really not that large. Even if you design for 10 gs you = are only looking at 3000 lbs or so on the mount.=20 A more realistic number is 5 Gs. so 1500 lbs. At that loading, each = side of the mount must hold up around 750 lbs.=20 750 lbs is not much for a steel truss structure. Most mounts are = hopelessly over designed. It would probably scare you to see a mount = that was designed for a factor of safety of 1 for actual flight loads.=20 Stiffness is a different matter. Whirl mode oscillations can cause huge = loads and are usually initiated by a perturbation flight load. So your = instincts are correct to be concerned about this issue.=20 Most mounts (even poorly designed ones) will work under normal = circumstances. Where you get into trouble is departure from controlled = flight and turbulence. So what if your engine mount weighs 5 lbs more? When in doubt make it stout....(within reason) ;-) Monty ------=_NextPart_000_002A_01C7E5D8.FC318970 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Bill or = anyone,
I guess I need to=20 change my question to more specifics. For example, what do you = think=20 of the single point attachment on the rear of the s-beam verses the more = substantial attachment of the flat plate mount. I personally don't know = if I=20 feel comfortable with a single point of attachment in the rear. For = example, there may be times when the engine gets torqued around due to = sudden=20 changes of flight direction.
Robert
 
Robert, 
 
Flight loads are really not that large. = Even if you=20 design for 10 gs you are only looking at 3000 lbs or so on the mount.=20
 
A more realistic number is = 5 Gs.  so=20 1500 lbs. At that loading, each side of the mount must hold up = around=20 750 lbs.
 
750 lbs is not much for a steel truss = structure.=20 Most mounts are hopelessly over designed. It would probably scare you to = see a=20 mount that was designed for a factor of safety of 1 for actual flight = loads.=20
 
Stiffness is a different matter. Whirl = mode=20 oscillations can cause huge loads and are usually initiated by a = perturbation=20 flight load. So your instincts are correct to be concerned about this = issue.=20
 
Most mounts (even poorly designed ones) = will work=20 under normal circumstances. Where you get into trouble is departure from = controlled flight and turbulence.
 
So what if your engine mount weighs 5 = lbs=20 more?
 
When in doubt make it stout....(within = reason)=20 ;-)
 
Monty
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