X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Wed, 29 Dec 2010 09:23:29 -0500 Message-ID: X-Original-Return-Path: Received: from imr-db03.mx.aol.com ([205.188.91.97] verified) by logan.com (CommuniGate Pro SMTP 5.3.11) with ESMTP id 4657295 for lml@lancaironline.net; Tue, 28 Dec 2010 22:28:33 -0500 Received-SPF: pass receiver=logan.com; client-ip=205.188.91.97; envelope-from=Sky2high@aol.com Received: from imo-da04.mx.aol.com (imo-da04.mx.aol.com [205.188.169.202]) by imr-db03.mx.aol.com (8.14.1/8.14.1) with ESMTP id oBT3RoVq021539 for ; Tue, 28 Dec 2010 22:27:50 -0500 Received: from Sky2high@aol.com by imo-da04.mx.aol.com (mail_out_v42.9.) id q.e8f.4a758e3 (37558) for ; Tue, 28 Dec 2010 22:27:45 -0500 (EST) Received: from magic-d18.mail.aol.com (magic-d18.mail.aol.com [172.19.155.134]) by cia-mb03.mx.aol.com (v129.7) with ESMTP id MAILCIAMB037-92b64d1aaab13c2; Tue, 28 Dec 2010 22:27:45 -0500 From: Sky2high@aol.com X-Original-Message-ID: X-Original-Date: Tue, 28 Dec 2010 22:27:45 EST Subject: Re: [LML] Re: Cowling Deformation X-Original-To: lml@lancaironline.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="part1_df70.4ad183f.3a4c04b1_boundary" X-Mailer: AOL 9.5 sub 5400 X-AOL-IP: 24.15.17.119 X-Spam-Flag:NO X-AOL-SENDER: Sky2high@aol.com --part1_df70.4ad183f.3a4c04b1_boundary Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit All of them allow some movement. I would say the lower cowl to fuselage are the worse because there are so few attach points. In a message dated 12/28/2010 8:53:53 P.M. Central Standard Time, colyncase@earthlink.net writes: I meant which locations on the cowl... On Dec 24, 2010, at 2:30 PM, _Sky2high@aol.com_ (mailto:Sky2high@aol.com) wrote: I think it is the 2400 series (small ones, spring loaded). In a message dated 12/23/2010 1:08:58 P.M. Central Standard Time, _colyncase@earthlink.net_ (mailto:colyncase@earthlink.net) writes: 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 N91CZ Chris Zavatson N91CZ 360std _www.N91CZ.com_ (http://www.n91cz.com/) ========================================= Rob, 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/_ (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 = --part1_df70.4ad183f.3a4c04b1_boundary Content-Type: text/html; charset="US-ASCII" Content-Transfer-Encoding: quoted-printable
All of them allow some movement.  I would say the lower cowl to= =20 fuselage are the worse because there are so few attach points.
 
In a message dated 12/28/2010 8:53:53 P.M. Central Standard Time,=20 colyncase@earthlink.net writes:
I meant=20 which locations on the cowl...=20

On Dec 24, 2010, at 2:30 PM, Sky2high@aol.com wrote:

=
I think it is the 2400 series (small ones, spring loaded).
 
In a message dated 12/23/2010 1:08:58 P.M. Central Standard Time,= colyncase@earthlink.net=20 writes:
Scott, WHICH camlocs do yo= u think contribute to the problem?=20  I was planning on having hinges everywhere except the back (in= front=20 of the windshield) where I would replace the screws with camlocs.=20  (This is on a IVP).   The screws are problematic as they= tend=20 to make a crater in the countersunk zone.=20

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 ac= tually=20 represent movement under load, but a slight misalignment.  Se= e=20 photo below of the cowl spinner junction of the same aircraft whil= e=20 parked on the ground.
Also, I have many in-flight photos of= N91CZ=20 showing no detectable movement (second photo).  Do you use=20 camlocs?  That might be the biggest contributor to movement.&= nbsp;=20  
Continental bed-mount vs Lycoming dynaf= ocal=20 mount may also be a factor based on another post. 
The cow= l=20 scoop is certainly a weak spot near the rear.


<image001.jpg>
Aircraft=20 in LOBO photo

 

<image002.jpg>
N91CZ

 

 

Chris=20 Zavatson
N91CZ
360std
=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,
 
A well built normally aspirated cowl se= tup with=20 no internal engine cooling plenum is subject to high internal uppe= r cowl=20 pressures (ballooning of the upper cowl), low air pressure over the top of the cowl and=20 some high pressure on the underside of the cowl.  This leads= to=20 cowl distortion and lifting.
 
A perfect example is the picture of the= =20 aircraft on the LOBO home page ( http://lancairowners.com/=  ) - notice=20 the cowling quite a bit higher than the prop spinner.&nb= sp; I=20 spent some time on my own aircraft trying to figure out how bug sp= latter=20 could be on the upper 3/4" face of the cowl right behind the= =20 spinner when everything lined up so nicely on the ground.  Re= ad=20 on.......  
 
Builders, like myself, that used= Camloc=20 fasteners (spring loaded) find that there is a lack of rigidity -= that=20 is the cowl can move under the forces encountered in flight. = Those=20 builders that made extensive use of hinges or screws would fi= nd=20 much more rigidity and less opportunity for the cowl to lift durin= g=20 flight.
 
If the bottom air exit bulge is no= t=20 supported as Lancair recommended (stiff arm between the bottom and= the=20 firewall), it can certainly deform.  One way to eliminate the= =20 support and obtain stiffness is to consider the use of some extra= foam=20 and carbon along the trailing edge.  Rather=20 than a sharp edge that creates turbulence, drag and a virtual= =20 reduction in the air exit size, consider a flared exterior al= a=20 some Diamond aircraft and/or some interior build up to form= a sort=20 of nozzle effect to accelerate the exit air.  Either or both= will=20 stiffen that part of the cowl.
 
Good Luck,
 
Scott=20 Krueger



=3D

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