X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Thu, 23 Dec 2010 14:08:41 -0500 Message-ID: X-Original-Return-Path: Received: from elasmtp-scoter.atl.sa.earthlink.net ([209.86.89.67] verified) by logan.com (CommuniGate Pro SMTP 5.3.11) with ESMTP id 4652409 for lml@lancaironline.net; Thu, 23 Dec 2010 11:42:20 -0500 Received-SPF: none receiver=logan.com; client-ip=209.86.89.67; envelope-from=colyncase@earthlink.net DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=dk20050327; d=earthlink.net; b=jVf7oRmzPGP0s7jVwqnnpTAqscOX6PmaM1BRfUrEZsFjYVSI3zaFDHshTO8pd/6w; h=Received:From:Mime-Version:Content-Type:Subject:Date:In-Reply-To:To:References:Message-Id:X-Mailer:X-ELNK-Trace:X-Originating-IP; Received: from [216.57.118.85] (helo=[192.168.1.103]) by elasmtp-scoter.atl.sa.earthlink.net with esmtpa (Exim 4.67) (envelope-from ) id 1PVoEa-0001AX-76 for lml@lancaironline.net; Thu, 23 Dec 2010 11:41:44 -0500 From: Colyn Case Mime-Version: 1.0 (Apple Message framework v1082) Content-Type: multipart/alternative; boundary=Apple-Mail-179--864792486 Subject: Re: [LML] Re: Cowling Deformation X-Original-Date: Thu, 23 Dec 2010 11:41:43 -0500 In-Reply-To: X-Original-To: "Lancair Mailing List" References: X-Original-Message-Id: <85310C86-285A-40C5-A892-603343210DAE@earthlink.net> X-Mailer: Apple Mail (2.1082) X-ELNK-Trace: 63d5d3452847f8b1d6dd28457998182d7e972de0d01da94021080e36296c0e1d18f89d28ce6c040c350badd9bab72f9c350badd9bab72f9c350badd9bab72f9c X-Originating-IP: 216.57.118.85 --Apple-Mail-179--864792486 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=us-ascii Scott, WHICH camlocs do you think contribute to the problem? I was = planning on having hinges everywhere except the back (in front of the = windshield) where I would replace the screws with camlocs. (This is on = a IVP). The screws are problematic as they tend to make a crater in = the countersunk zone. On Dec 23, 2010, at 10:11 AM, Chris Zavatson wrote: > Scott, > Interesting. Some more data points. > The offset in the LOBO photo may not actually represent movement under = load, but a slight misalignment. See photo below of the cowl spinner = junction of the same aircraft while parked on the ground. > Also, I have many in-flight photos of N91CZ showing no detectable = movement (second photo). Do you use camlocs? That might be the biggest = contributor to movement. =20 > Continental bed-mount vs Lycoming dynafocal mount may also be a factor = based on another post.=20 > The cowl scoop is certainly a weak spot near the rear. >=20 >=20 > > Aircraft in LOBO photo > =20 > > N91CZ > =20 > =20 > Chris Zavatson > N91CZ > 360std > www.N91CZ.com > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > Rob, > =20 > A well built normally aspirated cowl setup with no internal engine = cooling plenum is subject to high internal upper cowl pressures = (ballooning of the upper cowl), low air pressure over the top of the = cowl and some high pressure on the underside of the cowl. This leads to = cowl distortion and lifting. > =20 > A perfect example is the picture of the aircraft on the LOBO home page = ( http://lancairowners.com/ ) - notice the cowling quite a bit higher = than the prop spinner. I spent some time on my own aircraft trying to = figure out how bug splatter could be on the upper 3/4" face of the cowl = right behind the spinner when everything lined up so nicely on the = ground. Read on....... =20 > =20 > Builders, like myself, that used Camloc fasteners (spring loaded) find = that there is a lack of rigidity - that is the cowl can move under the = forces encountered in flight. Those builders that made extensive use of = hinges or screws would find much more rigidity and less opportunity for = the cowl to lift during flight. > =20 > If the bottom air exit bulge is not supported as Lancair recommended = (stiff arm between the bottom and the firewall), it can certainly = deform. One way to eliminate the support and obtain stiffness is to = consider the use of some extra foam and carbon along the trailing edge. = Rather than a sharp edge that creates turbulence, drag and a virtual = reduction in the air exit size, consider a flared exterior ala some = Diamond aircraft and/or some interior build up to form a sort of nozzle = effect to accelerate the exit air. Either or both will stiffen that = part of the cowl. > =20 > Good Luck, > =20 > Scott Krueger >=20 >=20 --Apple-Mail-179--864792486 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=us-ascii Scott, WHICH camlocs do you think contribute to the = problem?  I was planning on having hinges everywhere except the = back (in front of the windshield) where I would replace the screws with = camlocs.  (This is on a IVP).   The screws are problematic as = they tend to make a crater in the countersunk zone.

On = Dec 23, 2010, at 10:11 AM, Chris Zavatson wrote:

Scott,
Interesting. Some more data points.
The offset in the LOBO photo may not actually = represent movement under load, but a slight misalignment.  See = photo below of the cowl spinner junction of the same aircraft while = parked on the ground.
Also, I have many in-flight = photos of N91CZ showing no detectable movement (second photo).  Do = you use camlocs?  That might be the biggest contributor to = movement.   
Continental bed-mount vs = Lycoming dynafocal mount may also be a factor based on another = post. 
The cowl scoop is certainly a weak spot near the = rear.

Aircraft in LOBO photo

 

<image002.jpg>
 

Chris Zavatson

N91CZ
360std

 
A well built normally aspirated cowl setup with no = internal engine cooling plenum is subject to high internal upper cowl = pressures (ballooning of the upper cowl), low air pressure over the top of the cowl = and some high pressure on the underside of the cowl.  This leads to = cowl distortion and lifting.
A perfect example is the picture = of the aircraft on the LOBO home page ( http://lancairowners.com/ ) - = notice the cowling quite a bit higher than the prop = spinner.  I spent some time on my own aircraft trying to figure out = how bug splatter could be on the upper 3/4" face of the cowl right = behind the spinner when everything lined up so nicely on the = ground.  Read on.......  
Builders, like myself, that = used Camloc fasteners (spring loaded) find that there is a lack of = rigidity - that is the cowl can move under the forces encountered in = flight.  Those builders that made extensive use of hinges or = screws would find much more rigidity and less opportunity for the cowl = to lift during flight.
 
If the bottom air exit bulge is not supported = as Lancair recommended (stiff arm between the bottom and the firewall), = it can certainly deform.  One way to eliminate the support and = obtain stiffness is to consider the use of some extra foam and carbon = along the trailing edge.  = Rather than a sharp edge that creates turbulence, drag and a = virtual reduction in the air exit size, consider a flared exterior = ala some Diamond aircraft and/or some interior build up to form a = sort of nozzle effect to accelerate the exit air.  Either or both = will stiffen that part of the cowl.
Good Luck,
 
Scott = Krueger



= --Apple-Mail-179--864792486--