X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Fri, 30 Nov 2007 17:51:20 -0500 Message-ID: X-Original-Return-Path: Received: from mta15.adelphia.net ([68.168.78.77] verified) by logan.com (CommuniGate Pro SMTP 5.2c3) with ESMTP id 2520954 for lml@lancaironline.net; Fri, 30 Nov 2007 09:36:41 -0500 Received-SPF: pass receiver=logan.com; client-ip=68.168.78.77; envelope-from=glcasey@adelphia.net Received: from [75.82.212.14] by mta15.adelphia.net (InterMail vM.6.01.05.04 201-2131-123-105-20051025) with ESMTP id <20071130143600.OHGY13145.mta15.adelphia.net@[75.82.212.14]> for ; Fri, 30 Nov 2007 09:36:00 -0500 Mime-Version: 1.0 (Apple Message framework v752.2) In-Reply-To: References: Content-Type: multipart/alternative; boundary=Apple-Mail-17--917172926 X-Original-Message-Id: <39717222-C648-4CC5-9772-8FD12144119A@adelphia.net> From: Gary Casey Subject: Re: Removing ram air duct from 360 cowling X-Original-Date: Fri, 30 Nov 2007 06:35:59 -0800 X-Original-To: "Lancair Mailing List" X-Mailer: Apple Mail (2.752.2) --Apple-Mail-17--917172926 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed In the interest of balancing the comments, I'll post some reasons in favor of eliminating "ram air", but first have to note that there are really two questions implied: Is it good to use ram air and is it good to provide a filter bypass? I'm not sure which question is being asked. Regarding the use of "free" ram air, most all airplanes, from C150's to 747's use some feature that attempts to recover the velocity pressure of the engine inlet air. I think you always want to capture as much of this as practical, regardless of whether the engine is naturally aspirated or supercharged. The standard 320/360/RV inlet location is pretty good in this regard, being pointed roughly in the direction of air flow and being about the right area. Does that design add drag? I'm sure it does, but I doubt if it is even close to negating the benefit from the ram effect. I suppose the inlet could be somewhere else - some use a flush NACA-type inlet, but I don't know which would result in the best tradeoff. The second part of the "ram air" question is whether it is worth it to bypass the filter and for this question I say it is seldom worth it. Most ram air system designs favor the ram air option with regard to restriction, reducing the size of the filter or relegating it to drawing from a heated source without benefit of dynamic pressure recovery. This makes the "ram air" appear to give a big advantage, when actually it is just eliminating the "badness" of the other inlet path. You want to use filtered air the most on the ground and less the higher you go - but doing all takeoffs with heated inlet air just to get the filtration is not the kind of thing I would like to do. Some people take off with unfiltered air, but then why bother installing a filter in the first place? I propose the best approach is to keep some kind of pressure- recovery inlet and use a full-time large paper filter element. Then add a blow-in door to bypass the filter if it becomes plugged (happened to me once). An adequately-sized paper filter will have a pressure drop of only a few inches of water (a foot of water is about an inch of mercury). I calculated the drop in my system at about 0.1 inches. Regardless of what you design you still have to make the interface between the cowl and the engine inlet, unless you draw the engine air from the cooling inlets. That can be done, but there is always a little less recovery there than in a good dedicated inlet. I designed an inlet for what I thought was maximum ram air recovery and used the largest aircraft filter I could find with an automatic bypass door and I am completely satisfied with the result. I believe that if you want to use a filter at all the paper variety will offer the best compromise between filtering efficiency and pressure loss. I think the weakest link in the 320/360 carburetor system is the shape of the transition to the carburetor inlet. A better design would be worth the effort, in my opinion. Gary Casey > > From: kneaded pleasures > Date: November 29, 2007 8:28:44 AM PST > To: lml@lancaironline.net > Subject: Removing ram air duct from 360 cowling > > > Unless persuaded otherwise by commentary from this august body, I > intend to remove the ram air duct from my 360 cowling for these > reasons: > > *Never use ram air; *It doesn't work (doesn't add inches of > air pressure); * It is draggy (perhaps add a knot of speed by > removing); *Making a tight seal of cowling to ram air aluminum > structure has always, for me, been problematic causing some loss of > ram air pressure and adversely affecting cooling air; *Saves > weight and complexity (remove one long cable and and air valve and > replace with simplified, gently-sweeping 90-degree elbow into fuel > injection from air-box/filter); *Doing previous step permits > further streamlining of cowling; *Plane is now in a repaint cycle > so this is logical time to modify cowling; *Aircraft will > hereafter use only clean filtered air; *Facilitates removal and > installation of cowling (less time on my back; less dirt and fewer > expletives); *Most spam can planes have only a single source of > filtered air (...I think); *Air filter will be parallel to airflow > entering the plenum making it very highly unlikely that the air- > box can ever be plugged so as to suffocate the engine. Oh, yes, > did I say that I never (except for test) use the ram air feature in > flight? > > My loins are girded. What thinkest you of this plan? Greg Nelson > --Apple-Mail-17--917172926 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=ISO-8859-1 In the interest of balancing the comments, I'll post some reasons in = favor of eliminating "ram air", but first have to note that there are = really two questions implied: =A0Is it good to use ram air and is it = good to provide a filter bypass?
I'm not sure which = question is being asked. =A0Regarding the use of "free" ram air, most = all airplanes, from C150's to 747's use some feature that attempts to = recover the velocity pressure of the engine inlet air. =A0I think you = always want to capture as much of this as practical, regardless of = whether the engine is naturally aspirated or supercharged. =A0The = standard 320/360/RV inlet location is pretty good in this regard, being = pointed roughly in the direction of air flow and being about the right = area. =A0Does that design add drag? =A0I'm sure it does, but I doubt if = it is even close to negating the benefit from the ram effect. =A0I = suppose the inlet could be somewhere else - some use a flush NACA-type = inlet, but I don't know which would result in the best tradeoff. =A0The = second part of the "ram air" question is whether it is worth it to = bypass the filter and for this question I say it is seldom worth it. = =A0Most ram air system designs favor the ram air option with regard to = restriction, reducing the size of the filter or relegating it to drawing = from a heated source without benefit of dynamic pressure recovery. =A0This= makes the "ram air" appear to give a big advantage, when actually it is = just eliminating the "badness" of the other inlet path. =A0You want to = use filtered air the most on the ground and less the higher you go - but = doing all takeoffs with heated inlet air just to get the filtration is = not the kind of thing I would like to do. =A0Some people take off with = unfiltered air, but then why bother installing a filter in the first = place? =A0I propose the best approach is to keep some kind of = pressure-recovery inlet and use a full-time large paper filter element. = =A0Then add a blow-in door to bypass the filter if it becomes plugged = (happened to me once). =A0An adequately-sized paper filter will have a = pressure drop of only a few inches of water (a foot of water is about an = inch of mercury). =A0I calculated the drop in my system at about 0.1 = inches. =A0Regardless of what you design you still have to make the = interface between the cowl and the engine inlet, unless you draw the = engine air from the cooling inlets. =A0That can be done, but there is = always a little less recovery there than in a good dedicated = inlet.

I = designed an inlet for what I thought was maximum ram air recovery and = used the largest aircraft filter I could find with an automatic bypass = door and I am completely satisfied with the result. =A0I believe that if = you want to use a filter at all the paper variety will offer the best = compromise between filtering efficiency and pressure loss.

I think the weakest link = in the 320/360 carburetor system is the shape of the transition to the = carburetor inlet. =A0A better design would be worth the effort, in my = opinion.

Gary = Casey=A0

From: = kneaded pleasures <kneadedpleasures@sbcglobal.= net>
Date: November 29, 2007 8:28:44 AM = PST
To: lml@lancaironline.net
Subject: Removing ram air duct from 360 = cowling

=
Unless persuaded otherwise by commentary from this august body, = I=A0intend to remove the ram air duct from my 360 cowling for these = reasons:
=A0
=A0=A0=A0=A0 *Never use ram air;=A0 = *It doesn't work (doesn't add inches of=A0air pressure); =A0* It is = draggy (perhaps add a knot of speed by removing);=A0=A0*Making a tight = seal of=A0cowling=A0to ram air aluminum=A0structure=A0has always, for = me, been problematic=A0causing some loss of ram air pressure and = adversely affecting cooling air;=A0=A0*Saves weight and complexity = (remove one long cable and and air valve and=A0replace with simplified, = gently-sweeping=A090-degree elbow into fuel injection from = air-box/filter);=A0 *Doing previous step=A0permits further streamlining = of cowling; =A0*Plane is now in a repaint cycle so this is logical time = to modify cowling; =A0*Aircraft will=A0hereafter use only clean filtered = air;=A0=A0*Facilitates removal and installation of cowling (less time on = my back; less dirt and fewer expletives);=A0 *Most spam can planes have = only a single source of filtered air (...I think); =A0*Air filter will = be parallel to airflow entering the plenum=A0 making it very highly = unlikely that the air-box can ever be plugged so as to suffocate the = engine.=A0 Oh, yes, did I say that I never (except for test) use the ram = air feature in flight?
=A0
My loins are girded.=A0= What thinkest you of this plan?=A0=A0 Greg Nelson