X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from fed1rmmtao06.cox.net ([68.230.241.33] verified) by logan.com (CommuniGate Pro SMTP 5.0.6) with ESMTP id 916581 for flyrotary@lancaironline.net; Sat, 07 Jan 2006 10:50:29 -0500 Received-SPF: none receiver=logan.com; client-ip=68.230.241.33; envelope-from=ALVentures@cox.net Received: from BigAl ([68.7.14.39]) by fed1rmmtao06.cox.net (InterMail vM.6.01.05.02 201-2131-123-102-20050715) with ESMTP id <20060107154713.VHEN20050.fed1rmmtao06.cox.net@BigAl> for ; Sat, 7 Jan 2006 10:47:13 -0500 From: "Al Gietzen" To: "'Rotary motors in aircraft'" Subject: RE: [FlyRotary] Why rubber engine mounts? Date: Sat, 7 Jan 2006 07:49:46 -0800 Message-ID: <000001c613a1$fc535560$6400a8c0@BigAl> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0001_01C6135E.EE301560" X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook, Build 10.0.6626 Importance: Normal In-Reply-To: X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2180 This is a multi-part message in MIME format. ------=_NextPart_000_0001_01C6135E.EE301560 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable =20 If our engines are smooth and the entire engine is well balanced, why is it necessary to isolate the engine from the engine mount/airframe. =20 'Smooth' is a relative term. The rotary is much smoother than a Lyc; = but that doesn't mean that it doesn't vibrate. Add a prop that is trying to transfer all that power to the air, and the resulting turbulence and the various vortices adds more vibration. =20 Aside from contributing to noise and discomfort in the cabin, vibrations cause failures. Somewhere in your airframe there is a mounting bracket, = an electrical connection, or whatever that could have a natural frequency = that tunes to a vibration coming from your engine (resonance); and eventually succumb to vibration fatigue failure.=20 =20 The job of the engine mount dampers is to isolate the engine/prop from = the rest of the airframe. You can never get them all, but you can = significantly reduce their amplitude generally get most except the lower frequencies. = The objective would be to make the mount as soft as possible consistent with limiting the range of movement and not resulting is sag or failure of = the mounts in less than a thousand hours or so. Mostly in custom engine installations this becomes an educated guess. =20 FWIW, =20 Al ------=_NextPart_000_0001_01C6135E.EE301560 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

 

If our engines are smooth and the entire engine is

well balanced, why is it necessary to isolate the

engine from the engine mount/airframe.

 

‘Smooth&= #8217; is a relative term.  The rotary is much smoother than a Lyc; but = that doesn’t mean that it doesn’t vibrate.  Add a prop that = is trying to transfer all that power to the air, and the resulting = turbulence and the various vortices adds more vibration.

 <= /font>

Aside from contributing to noise and discomfort in the cabin, vibrations cause = failures.  Somewhere in your airframe there is a mounting bracket, an electrical connection, or whatever that could have a natural frequency that tunes = to a vibration coming from your engine (resonance); and eventually succumb to vibration fatigue failure.

 <= /font>

The job of = the engine mount dampers is to isolate the engine/prop from the rest of the = airframe.  You can never get them all, but you can significantly reduce their = amplitude generally get most except the lower frequencies.  The objective = would be to make the mount as soft as possible consistent with limiting the range = of movement and not resulting is sag or failure of the mounts in less than = a thousand hours or so.  Mostly in custom engine installations this = becomes an educated guess.

 <= /font>

FWIW,

 <= /font>

Al

------=_NextPart_000_0001_01C6135E.EE301560--