X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from gwa9.webcontrolcenter.com ([63.134.207.43] verified) by logan.com (CommuniGate Pro SMTP 5.3.5) with ESMTP id 4237342 for flyrotary@lancaironline.net; Wed, 28 Apr 2010 09:20:47 -0400 Received-SPF: pass receiver=logan.com; client-ip=63.134.207.43; envelope-from=rotary@cmowens.com Received: from mailb12.webcontrolcenter.com (mailb12.webcontrolcenter.com [216.119.115.141]) by gwa9.webcontrolcenter.com with SMTP; Wed, 28 Apr 2010 06:20:04 -0700 Received: by mailb12.webcontrolcenter.com via HTTP; Wed, 28 Apr 2010 06:19:29 -0700 From: "Chris Owens - Rotary" To: "Rotary motors in aircraft" Subject: re: [FlyRotary] Re: Eductor scavenging of radiator outlet, WAS 20B RV-8 cooling results Date: Wed, 28 Apr 2010 06:19:29 -0700 Reply-To: rotary@cmowens.com Message-ID: <7e277185$267cadad$14613e42$@com> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0001_7AD2BA08.B28E78B" This is a multipart message in MIME format. ------=_NextPart_000_0001_7AD2BA08.B28E78B Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable You know, I don't know if this has been discussed, but the whole pressure d= ifferential thing got me thinking of something that I'm surprised I hadn't = thought of earlier. Since the draw of air via low pressure on the output s= ide seems to be key, I wonder if an eductor type of scenario would work. Back in my Navy days, we used to use a device called an in-line eductor for= dewatering flooded spaces. Similar to a venturi, more or less, you pumped= water through it, it created a suction, and it was designed to suck as muc= h water through it as you put into it. 100 gallons per minute input would = dewater at 100 gallons per minute with 200 gallons per minute flowing throu= gh the output. A representative device is here (perhaps not for fluid use,= but the concept is similar): http://www.1877eductors.com/eductor_gas_dimensions.htm I presume a similar approach could be taken with a radiator setup, would yo= u think? I imagine it would work well for a center mounted radiator with a= centerline, below-the-nose scoop, so one could utilize the cheek inlets to= provide source air for the outlet side. ~Chris ---------------------------------------- From: "Ed Anderson" Sent: Wednesday, April 28, 2010 7:08 AM To: "Rotary motors in aircraft" Subject: [FlyRotary] Re: 20B RV-8 cooling results Hi George, As you know, taking heat away from your radiator cores requi= res sufficient air mass flow - a number of factors affect this - one of the= principle factors is pressure differential across your core. No pressure = differential =3D no flow. The primary positive pressure on the front side = of the core comes from converting dynamic energy of the moving air into a l= ocal static pressure increase in front of the core. This is basically limi= ted by your airspeed and efficiency of your duct/diffuser. The back side o= f your core air flow (in most installations) exits inside the cowl. Theref= ore any positive pressure above ambient under the cowl is going to reduce t= he pressure differential across your core. So once you have the best duct/= diffuser you can achieve on the front side of the core - the only thing lef= t to increase the pressure differential is to reduce the pressure under the= cowl. An extreme example is someone who flies with an opening (such as o= ne of the typical inlet holes beside the prop) exposed to the air flow. In= effect this hole with little/no resistance to airflow can "pressurize" the= cowl and raise the air pressure behind the radiator cores reducing the pre= ssure differential and therefore the cooling. Exhaust augmentation is theo= retically a way to reduce the under the cowl pressure by using the exhaust = pulse to "pump" air from under the cowl, thereby improving the Dp across th= e core and therefore your cooling. While exhaust augmentation can apparen= tly work - there was a KITPLANE issue back several years ago on the topic s= howing several installations where this was used. However, from what I rea= d (and think I understand), it takes some carefully planning to get an inst= allation to work correct and the effort is not trivial. Give the challenge= s you may encounter (such as motor mount struts, etc), fabrication of the a= ugmentation exit, the need to have the exhaust pulse exit at or inside the= cowl (or construct an extended bottom cowl tunnel) means you would have th= e bark of a rotary in front of your feet. Also, to gain maximum advantage = of these techniques, it is desirable to have the exhaust velocity at the ma= ximum - which implies little/no muffling. Having had my muffler back out o= ne time (at the cowl exit), I can tell you that you do not want to position= the pilot behind the exhaust outlet (in my opinion). It is much quieter w= hen you have the exhaust exit behind the position of the pilot {:>). Some= few people seem to have been able to achieve some degree of success, but e= ven in aircraft where you have an engine without the aggressive bark of the= rotary, you seldom see it used. The basic reason (in my opinion), is that= it offers few advantages (cooling wise) that can not be achieved easier an= d more reliability by other methods. For an all out racer where noise and = discomfort is secondary, it may have some benefit. Having said that, it's= clear that in some installations it appears to work well (see KITPLANE iss= ue), but if it were the magic solution, I think many more folks would be em= ploying it - but, again, just my opinion. Ed 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 B= ehalf Of George Lendich Sent: Tuesday, April 27, 2010 9:41 PM To: Rotary motors in aircraft Subject: [FlyRotary] Re: 20B RV-8 cooling results Ed/ Tracy, Can't sa= y as I understand Tracy's set- up completely, other than it's toward the lo= wer end of Rad sizes. I was thinking to myself how I could create a -ve pre= ssure in the rad outlet to create a suction on the Rad. We all know how the= exhaust augmentation works and I was wondering why we can't do the same th= ing with the rad outlets by running the rad outlets inro a larger outlet fe= d by outside air. At idle the air is fed by the prop air stream and at leve= l fight it is fed by outside air stream. The outside air could be could c= ontrolled by a butterfly - simple enough. I know there emphasis on using sh= utter /flaps to control the cowl outlet and I believe their good at restric= ting air flow, but I don't know if this equates to a good -ve pressure behi= nd the Rad. This presupposes the Rads are completely enclosed for both inle= t and outlet air. George ( down under) 75% of my cooling problems were = solved with the oil cooler change I did but still needed more margin for ho= t weather climbs. Made the decision to not change or enlarge the cooling = outlet (that adds drag) so went ahead and butchered the pretty inlets I ma= de. Ed Anderson's spreadsheet on BTUs & CFM cooling air required was instrument= al in deciding to go this way. It showed that without negative pressure o= n the back side of the rads, there would never be enough cfm to do the job = during climb at full throttle. Negative pressure is what I had when I flew= without the cowl on but oh what a draggy condition that was. The old inlets were 4.5" diameter for the radiator and 4.125" diameter for = oil cooler. New inlets are 5.190" for the rad, and 4.875" dia for the oil. This may not sound like a lot but it represents a 36% increase in inlet are= a. Results were excellent. Oil temp went down 19 degrees at the test speed (1= 30) and water temp dropped 9 degrees. On 80 degree day and 500 ft msl the = oil temp maxed out at 194F at 210 mph which is way faster than I would norm= ally go at this altitude. Temp was around 175 at 130. Oil Temp in climb= remained below redline (210) but the temperature lapse rate today made res= ults not very meaningful. OAT was dropping 14 degrees a minute at 3000 fpm= climb rate. now back to that nasty composite work to pretty up the inlets again. They = look like large stubby pitot tubes now. I hadn't thought of a good name for the RV-8 but a friend in California rec= ently came up with the winning idea which fit it well. "Euphoriac" It's a = term from a Sci Fi book (Vintage Season) meaning something which induces = euphoria. ------=_NextPart_000_0001_7AD2BA08.B28E78B Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable = You know, I don't know if this has been discussed, but the whole pressure d= ifferential thing got me thinking of something that I'm surprised I hadn't = thought of earlier.  Since the draw of air via low pressure on the out= put side seems to be key, I wonder if an eductor type of scenario would wor= k.

Back in my Navy days, we used to use a device called an in-line eductor for= dewatering flooded spaces.  Similar to a venturi, more or less, you p= umped water through it, it created a suction, and it was designed to suck a= s much water through it as you put into it.  100 gallons per minute in= put would dewater at 100 gallons per minute with 200 gallons per minute flo= wing through the output.  A representative device is here (perhaps not= for fluid use, but the concept is similar):

http://w= ww.1877eductors.com/eductor_gas_dimensions.htm

I presume a similar approach could be taken with a radiator setup, would yo= u think?  I imagine it would work well for a center mounted radiator w= ith a centerline, below-the-nose scoop, so one could utilize the cheek inle= ts to provide source air for the outlet side.

~Chris



From: "Ed Anderson" <eanderson@carolina.rr.com>
Sent: Wednesday, April 28, 2010 7:08 AM
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net><= br /> Subject: [FlyRotary] Re: 20B RV-8 cooling results

Hi George,

 

As you know, taking heat away from your radiator cores req= uires sufficient air mass flow - a number of factors affect this - one of t= he principle factors is pressure differential across your core.  No pr= essure differential =3D no flow.  The primary positive pressure on the= front side of the core comes from converting dynamic energy of the moving = air into a local static pressure increase in front of the core.  This = is basically limited by your airspeed and efficiency of your duct/diffuser.=   The back side of your core air flow (in most installations) exits in= side the cowl.  Therefore any positive pressure above ambient under th= e cowl is going to reduce the pressure differential across your core. = So once you have the best duct/diffuser you can achieve on the front side = of the core - the only thing left to increase the pressure differential is = to reduce the pressure under the cowl.

 

An extreme example is someone who flies with an opening (s= uch as one of the typical inlet holes beside the prop) exposed to the air f= low.  In effect this hole with little/no resistance to airflow can "pr= essurize" the cowl and raise the air pressure behind the radiator cores red= ucing the pressure differential and therefore the cooling.  Exhaust au= gmentation is theoretically a way to reduce the under the cowl pressure by = using the exhaust pulse to "pump" air from under the cowl, thereby improvin= g the Dp across the core and therefore your cooling.

 

While exhaust augmentation can apparently work - there was= a KITPLANE issue back several years ago on the topic showing several insta= llations where this was used.  However, from what I read (and think I = understand), it takes some carefully planning to get an installation to wor= k correct and the effort is not trivial.  Give the challenges you may = encounter (such as motor mount struts, etc), fabrication of the augmentatio= n exit,  the need to have the exhaust pulse exit at or inside the cowl= (or construct an extended bottom cowl tunnel) means you would have the bar= k of a rotary in front of your feet.  Also, to gain maximum advantage = of these techniques, it is desirable to have the exhaust velocity at the ma= ximum - which implies little/no muffling.  Having had my muffler back = out one time (at the cowl exit), I can tell you that you do not want to pos= ition the pilot behind the exhaust outlet (in my opinion).  It is much= quieter when you have the exhaust exit behind the position of the pilot {:= >).

 

Some few people seem to have been able to achieve some deg= ree of success, but even in aircraft where you have an engine without the a= ggressive bark of the rotary, you seldom see it used.  The basic reaso= n (in my opinion), is that it offers few advantages (cooling wise) that can= not be achieved easier and more reliability by other methods.  For an= all out racer where noise and discomfort is secondary, it may have some be= nefit.

 

Having said that, it's clear that in some installations it= appears to work well (see KITPLANE issue), but if it were the magic soluti= on, I think many more folks would be employing it - but, again, just my opi= nion.

 

Ed

 

From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of George Lendich
Sent: Tuesday, April 27, 2= 010 9:41 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: 2= 0B RV-8 cooling results

 

Ed/ Tracy,

Can't say as I understand Tra= cy's set- up completely, other than it's toward the = lower end of Rad sizes. I was thinking to myself how I could create a = -ve pressure in the rad outlet to create a suction on the Rad. We all know = how the exhaust augmentation works and I was wondering why we can't do the = same thing with the rad outlets by running the rad outlets inro a larger ou= tlet fed by outside air. At idle the air is fed by the prop air stream and = at level fight it is fed by outside air stream.

The outside air could be could controlled by a butterfly - simple eno= ugh. I know there emphasis on using shutter /flaps to control the cowl outl= et and I believe their good at restricting air flow, but I don't know if th= is equates to a good -ve pressure behind the Rad. This presupposes the Rads= are completely enclosed for both inlet and outlet air.

George ( down under)

75% of my cooling problems were solved with the oil cooler chang= e I did but still needed more margin for hot weather climbs.   Made th= e decision to not change or enlarge the cooling outlet (that adds drag)&nbs= p; so went ahead and butchered the pretty inlets I made. 
Ed Anderson's spreadsheet on BTUs & CFM cooling air required was instru= mental in deciding to go this way.   It showed that without negat= ive pressure on the back side of the rads, there would never be enough cfm = to do the job during climb at full throttle.  Negative pressure is wha= t I had when I flew without the cowl on but oh what a draggy condition that= was.

The old inlets were 4.5" diameter for the radiator and 4.125" diameter for = oil cooler.
New inlets are        5.190" for the rad= ,  and   4.875" dia for the oil.

This may not sound like a lot but it represents a 36% increase in inlet are= a.

Results were excellent.  Oil temp went down 19 degrees at the test spe= ed (130) and water temp dropped 9 degrees.  On 80 degree day and 500 f= t msl the oil temp maxed out at 194F at 210 mph which is way faster than I = would normally go at this altitude.  Temp was around 175 at 130.  = ;  Oil Temp in climb remained below redline (210) but the temperature = lapse rate today made results not very meaningful.  OAT was dropping 1= 4 degrees a minute at 3000 fpm climb rate.

now back to that nasty composite work to pretty up the inlets again.  = They look like large stubby pitot tubes now.

I hadn't thought of a good name for the RV-8 but a friend in California recently= came up with the winning idea which fit it well. "Euphoriac"  It's a = term from a  Sci Fi book (Vintage Season)  meaning something whic= h induces euphoria. 


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