X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from cdptpa-omtalb.mail.rr.com ([75.180.132.123] verified) by logan.com (CommuniGate Pro SMTP 5.2.16) with ESMTP id 3819279 for flyrotary@lancaironline.net; Thu, 20 Aug 2009 09:51:43 -0400 Received-SPF: pass receiver=logan.com; client-ip=75.180.132.123; envelope-from=eanderson@carolina.rr.com Received: from computername ([75.191.186.236]) by cdptpa-omta01.mail.rr.com with ESMTP id <20090820135104008.VCDB29812@cdptpa-omta01.mail.rr.com> for ; Thu, 20 Aug 2009 13:51:04 +0000 From: "Ed Anderson" To: "'Rotary motors in aircraft'" Subject: Cowl Flap/Exit was [FlyRotary] Re: back in the air Date: Thu, 20 Aug 2009 09:49:57 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0012_01CA217B.93EFF0F0" X-Mailer: Microsoft Office Outlook, Build 11.0.5510 In-Reply-To: Thread-Index: AcohlKwdPNnnsZBBT/u6EaY0dd8YygAB4GVw X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.5579 Message-Id: <20090820135104008.VCDB29812@cdptpa-omta01.mail.rr.com> This is a multi-part message in MIME format. ------=_NextPart_000_0012_01CA217B.93EFF0F0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Past a specific inlet area to core frontal area (this ratio in the vicinity of 0.30, no additional flow is achieved by further opening of inlets - the exit area becomes the controlling factor. As Tracy stated, probably better to look to a cowl flap than mess with your inlets if you are getting good cooling with your present inlets. Here is an extract out of a study of cooling of small aircraft engines that points out the two functions of your exit area. Exits The exit has two basic functions: to regulate the cooling air flow and to exhaust the cooling flow into the external flow so as to result in minimal drag penalty. To adequately perform the regulation, the exit must act as both a throttle and a pump. Throttling is necessary in cruising flight to minimize the cooling drag by reducing the cooling flow to that sufficient to meet cooling requirements. In ground operation and in climbing flight, the exit must act as a pump to induce sufficient cooling flow through the system. Both of these functions can be performed by a hinged flap. The fundamental principle here is that for any subsonic flow system, the flow rate through the system will always adjust itself so that the static pressure at the exit will match the local external flow static pressure surrounding the exit. The static pressure at the exit is controlled by the exit area. Thus, regulation is obtained by varying this area. Opening the flap beyond the contour of the airframe creates a low-pressure region that induces additional flow through the system. It became common design practice during World War II to serve the exit flap to a coolant temperature sensor to optimize the system operation. Ed Anderson Rv-6A N494BW Rotary Powered Matthews, NC eanderson@carolina.rr.com http://www.andersonee.com http://www.dmack.net/mazda/index.html http://www.flyrotary.com/ http://members.cox.net/rogersda/rotary/configs.htm#N494BW http://www.rotaryaviation.com/Rotorhead%20Truth.htm _____ From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Tracy Crook Sent: Thursday, August 20, 2009 8:49 AM To: Rotary motors in aircraft Subject: [FlyRotary] Re: back in the air "So far its looking like I could stand to shrink both inlets a little - maybe a lot. " Mike, Glad your EC2 & cooling issues are under control. I'd go with a cowl flap to restrict air flow (and increase exit velocity) rather than reduce inlet size. Probably less fiberglass work for the cowl flap as well. Won't go into the mind numbing formulas and laws that govern the principal but here is what I have boiled them down to: It is not the absolute SIZE of the cooling inlet that determines drag but the amount of air that goes through it. Main thing is to make sure the air that is diverted around the inlet has a clean path. (you've done a good job there). Restricting the inlet will also restrict the flow but why reduce your options for other conditions (hot weather, max climb, etc). Tracy On Wed, Aug 19, 2009 at 11:30 PM, Mike Wills wrote: I seriously considered a water oil exchanger. Fluidyne also made some of those that looked really good. Dont know if they still do. Ultimately decided not to go that route. So many people were having cooling issues when I was designing my system and it seemed that using seperate air oil exchangers would ease potential debug hassles. I'm mostly happy with my choice. Its working well so far. And using a $25 wrecking yard RX-7 oil cooler was about as cheap as it gets. My only complaints so far are that I am not real happy with the looks of the extra scoop I added for the oil cooler, and my braided stainless oil cooler lines are fairly long and heavy. I probably will redo the cowl somewhere down the road after I get a good handle on just how well the cooling is on hot days. So far its looking like I could stand to shrink both inlets a little - maybe a lot. On my flight the other day coolant temp never went over 180. And that included taxi from the extreme west end of the airport to the other end of an 8000' runway. Mike Wills RV-4 N144MW ------=_NextPart_000_0012_01CA217B.93EFF0F0 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

Past a specific inlet area to core = frontal area (this ratio in the vicinity of 0.30, no additional flow is achieved = by further opening of inlets – the exit area becomes the controlling = factor. As Tracy stated, probably better to look to a cowl flap than mess with your = inlets if you are getting good cooling with your present = inlets.

 

Here is an extract out of a study = of cooling of small aircraft engines that points out the two functions of = your exit area. 

 

Exits

 

The exit has = two basic functions: to regulate the cooling air

flow and to exhaust the cooling flow into the external flow = so

as to result = in minimal drag penalty. To adequately perform

the = regulation, the exit must act as both a throttle and a pump.

Throttling is = necessary in cruising flight to minimize the cooling

drag by = reducing the cooling flow to that sufficient to meet

cooling = requirements.

 

 In = ground operation and in climbing

flight, the = exit must act as a pump to induce sufficient cooling

flow through = the system. Both of these functions can be performed

by a hinged = flap. The fundamental principle here is

that for any = subsonic flow system, the flow rate through the

system will = always adjust itself so that the static pressure at the

exit will = match the local external flow static pressure surrounding

the exit. The = static pressure at the exit is controlled by the

exit = area.

 

 Thus, = regulation is obtained by varying this area.

Opening the = flap beyond the contour of the airframe creates a

low-pressure = region that induces additional flow through the

system. It = became common design practice during World War

II to serve = the exit flap to a coolant temperature sensor to optimize

the system = operation.

 

 

Ed = Anderson

Rv-6A N494BW Rotary = Powered

Matthews, NC

eanderson@carolina.rr.com=

http://www.andersonee.com

http://www.dmack.net/mazda/index.html

http://www.flyrotary.com/

http://members.cox.net/rogersda/rotary/configs.htm#N494BW

http://www.r= otaryaviation.com/Rotorhead%20Truth.htm

From: = Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Tracy Crook
Sent: Thursday, August = 20, 2009 8:49 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: = back in the air

 

"So far its looking like I could stand to shrink both inlets a little - maybe a lot. = "

Mike,
Glad your EC2 & cooling issues are under control.  I'd go with = a cowl flap to restrict air flow (and increase exit velocity) rather than = reduce inlet size.   Probably less fiberglass work for the cowl flap as = well.

Won't go into the mind numbing formulas and laws that govern the = principal but here is what I have boiled them down to:

It is not the absolute SIZE of the cooling inlet that determines drag = but the amount of air that goes through = it.

  Main thing is to make sure the air that is diverted around the = inlet has a clean path.  (you've done a good job there).  Restricting = the inlet will also restrict the flow but why reduce your options for other = conditions (hot weather, max climb, etc).

Tracy

On Wed, Aug 19, 2009 at 11:30 PM, Mike Wills <rv-4mike@cox.net> = wrote:

I seriously considered a water oil exchanger. = Fluidyne also made some of those that looked really good. Dont know if they still = do.

 

Ultimately decided not to go that route. So many = people were having cooling issues when I was designing my system and it seemed that = using seperate air oil exchangers would ease potential debug = hassles.

 

I'm mostly happy with my choice. Its working well so = far. And using a $25 wrecking yard RX-7 oil cooler was about as cheap as it = gets. My only complaints so far are that I am not real happy with the looks of = the extra scoop I added for the oil cooler, and my braided stainless oil cooler = lines are fairly long and heavy.

 

I probably will redo the cowl somewhere down the road = after I get a good handle on just how well the cooling is on hot days. So far = its looking like I could stand to shrink both inlets a little - maybe a lot. = On my flight the other day coolant temp never went over 180. And that included = taxi from the extreme west end of the airport to the other end of an 8000' = runway.

 

Mike Wills

RV-4 N144MW

 

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