X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Thu, 06 Mar 2014 14:15:04 -0500 Message-ID: X-Original-Return-Path: Received: from mail-wg0-f47.google.com ([74.125.82.47] verified) by logan.com (CommuniGate Pro SMTP 6.0.8) with ESMTPS id 6763061 for lml@lancaironline.net; Thu, 06 Mar 2014 12:54:39 -0500 Received-SPF: pass receiver=logan.com; client-ip=74.125.82.47; envelope-from=pjdmiller@gmail.com Received: by mail-wg0-f47.google.com with SMTP id x12so3549221wgg.18 for ; Thu, 06 Mar 2014 09:54:03 -0800 (PST) X-Received: by 10.194.2.70 with SMTP id 6mr12190308wjs.25.1394128442914; Thu, 06 Mar 2014 09:54:02 -0800 (PST) X-Original-Return-Path: Received: from [192.168.4.214] (mailhost.letts.co.uk. [80.76.116.1]) by mx.google.com with ESMTPSA id ga10sm20412931wjb.23.2014.03.06.09.54.01 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Thu, 06 Mar 2014 09:54:01 -0800 (PST) Subject: Re: [LML] Re: Canopy Latch modeling References: From: Paul Miller Content-Type: multipart/alternative; boundary=Apple-Mail-C981B902-001E-4F8A-B367-0B9723AC69D4 X-Mailer: iPhone Mail (9B206) In-Reply-To: X-Original-Message-Id: X-Original-Date: Thu, 6 Mar 2014 17:54:00 +0000 X-Original-To: Lancair Mailing List Content-Transfer-Encoding: 7bit Mime-Version: 1.0 (1.0) --Apple-Mail-C981B902-001E-4F8A-B367-0B9723AC69D4 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=us-ascii Charles, understood on all points thank you. But, if the canopy generates l= ift and the lift is removed, like a spoiler deploying, is there a further ef= fect from the loss of lift considering we were trimmed for flight prior to u= nlatching beyond the canopy weight? What kind of lift can we guesstimate? Paul On Mar 6, 2014, at 1:06 PM, Charles Brown wrote: > a) The canopy is generating lift when closed. More to your point, the pre= ssure on the inside of the canopy is higher than the pressure on the outside= . I'll assert that without citing several reasons why it's true. Next, th= e canopy lift will decrease when it's unlatched; the canopy will rise until t= he sum of the moments around its fwd hinge point are equal. That is, it wil= l rise until the delta P from bottom to top decreases to *just enough* to of= fset its weight minus the gas strut contribution. >=20 > b) The cg moves forward trivially when the canopy opens all the way. If t= he canopy weighs 50 lb, and it opens 90 degrees, a rough hack indicates that= the cg would move forward about 0.6 inches, or 7% of the total allowable cg= range. And the canopy won't open 90 degrees; at small openings the cg chan= ge is completely negligible. >=20 > c) The drag increase will be significant. If the canopy opens six inches,= then using a typical Cp for an aft-facing step of -0.1 and assuming no chan= ge to the pressure on the upper surface (that means I'll calculate a minimum= value for the drag; the real drag will be greater), you'll introduce a delt= a Cd of about .002. Cruise Cd is around .014 so that's a drag increase of 1= 5% -- at least -- for a 6" opening. >=20 > d) Recent posts suggest keeping the angle of attack low. That makes sense= to me. Adding power makes sense to me; offsets the drag and keeps alpha lo= w. Takeoff flap makes sense to me; reduces fuselage alpha without adding mu= ch drag. >=20 > Charley >=20 >=20 > From: Paul Miller > Date: March 4, 2014 6:21:39 AM CST > To: lml@lancaironline.net > Subject: Re: [LML] Canopy Latch modeling >=20 >=20 > Let me ask these questions to the group, speculation is permitted since we= have no data: >=20 > a) is the canopy generating lift when closed? If so, does that lift decrea= se or increase when unlatched? > b) Does the CG of the aircraft change between open and closed canopy in fl= ight? > c) Does drag increase between open and closed in flight? > d) What does a pilot do when all that noise and flying paper occurs? Full= throttle, decrease power? >=20 > Paul >=20 >=20 --Apple-Mail-C981B902-001E-4F8A-B367-0B9723AC69D4 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=utf-8
Charles, understood on all= points thank you.  But, if the canopy generates lift and the lift is r= emoved, like a spoiler deploying, is there a further effect from the loss of= lift considering we were trimmed for flight prior to unlatching beyond the c= anopy weight?

What kind of lift can we guesstimate?=

Paul

On Mar 6, 2014, at 1:06 PM, Charles Brown <browncc1@verizon.net> wrote:
<= br>
a) The canopy is gen= erating lift when closed.  More to your point, the pressure on the insi= de of the canopy is higher than the pressure on the outside.  I'll asse= rt that without citing several reasons why it's true.   Next, the canop= y lift will decrease when it's unlatched; the canopy will rise until the sum= of the moments around its fwd hinge point are equal.  That is, it will= rise until the delta P from bottom to top decreases to *just enough* to off= set its weight minus the gas strut contribution.

b)= The cg moves forward trivially when the canopy opens all the way.  If t= he canopy weighs 50 lb, and it opens 90 degrees, a rough hack indicates that= the cg would move forward about 0.6 inches, or 7% of the total allowable cg= range.  And the canopy won't open 90 degrees; at small openings the cg= change is completely negligible.

c) The drag incre= ase will be significant.  If the canopy opens six inches, then using a t= ypical Cp for an aft-facing step of -0.1 and assuming no change to the press= ure on the upper surface (that means I'll calculate a minimum value for the d= rag; the real drag will be greater), you'll introduce a delta Cd of about .0= 02.  Cruise Cd is around .014 so that's a drag increase of 15% -- at le= ast -- for a 6" opening.

d) Recent posts suggest ke= eping the angle of attack low.  That makes sense to me.  Adding po= wer makes sense to me; offsets the drag and keeps alpha low.  Takeoff f= lap makes sense to me; reduces fuselage alpha without adding much drag.

Charley


<= b>From: pjdmiller@gmail.com= >
Date: March 4, 2014 6:21:3= 9 AM CST
Subject: Re: [LML] Canopy Latch modeling

Let me ask these questions to the group, speculation is permitted since= we have no data:

a) is the canopy generating lift when closed? If so= , does that lift decrease or increase when unlatched?
b) Does the CG of t= he aircraft change between open and closed canopy in flight?
c) Does drag= increase between open and closed in flight?
d) What does a pilot do when= all that noise and flying paper occurs?  Full throttle, decrease power= ?

Paul


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