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Tue, 20 Jul 2021 17:39:00 +0000 Received: by kubenode510.mail-prod1.omega.bf1.yahoo.com (VZM Hermes SMTP Server) with ESMTPA ID 63b28844acdc7a3041392a7e79b0fbf3; Tue, 20 Jul 2021 17:38:54 +0000 (UTC) Subject: Re: [FlyRotary] Re: Cooling Inlets-shape To: Rotary motors in aircraft References: Message-ID: <9b0c0b70-202a-155e-ec37-1258ec01c058@verizon.net> Date: Tue, 20 Jul 2021 13:38:51 -0400 User-Agent: Mozilla/5.0 (Windows NT 5.1; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: Content-Type: multipart/alternative; boundary="------------DFDD5CFEBC4777C891BEE82C" Content-Language: en-US X-Antivirus: Avast (VPS 210720-4, 07/20/2021), Outbound message X-Antivirus-Status: Clean X-Mailer: WebService/1.1.18469 mail.backend.jedi.jws.acl:role.jedi.acl.token.atz.jws.hermes.aol Content-Length: 27195 This is a multi-part message in MIME format. --------------DFDD5CFEBC4777C891BEE82C Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit See my original post below "On 4/28/2011 9:07 AM, Tracy wrote:" Subject is: Re: Cooling Inlets-shape Finn On 7/20/2021 1:11 PM, Marc Wiese cardmarc@charter.net wrote: > Can someone post pictures of Tracy’s inlets or point me to where they > are in the archives? > M > > Sent from my iPhone > >> On Jul 20, 2021, at 10:58 AM, Finn Lassen finn.lassen@verizon.net >> wrote: >> >>  >> Thanks Ed. >> >>  Not been making much progress on the RV-4 over the last month. I >> guess the heat and humidity is getting to me ... >> >> Finn >> On 7/13/2021 11:57 AM, eanderson@carolina.rr.com wrote: >>> Hi Finn, >>> >>> Its been a long time since I dove this deep into cooling ducts/lip >>> contours etc.  But, here goes. >>> >>> The duct (lip + diffuser) is suppose to convert air velocity to air >>> pressure with minimum loss/drag and turbulence.  However, like >>> almost everything else involving flight - there is no single best >>> answer - only an optimization or approximation to the best (that you >>> are going to get with the compromises you have to make).  So in our >>> case one set of compromises might be between cooling effectivness >>> and cooling drag.  As you know the larger your radiator the more >>> heat you are going to get rid of, but, the larger your core the more >>> cooling drag you are going to encounter. >>> >>> Now at low speeds you might get away with sticking the radiator out >>> in the airstream without any ducting and get adequate cooling, but >>> it will have higher drag - now at biplane/slow airspeed the drag >>> might be acceptable, but at 200 mph quite unacceptable.  Again, it >>> depends on what you are trying to achieve. >>> >>>  Its been quite a while, but Ill give it a shot on trying to explain >>> the charts.  I presume that External refers to air factors prior to >>> the lip and Internal refers to air factors after the lip of the >>> diffuser (or internal to the duct).  you mention wanting a 100-20 >>> mph slow down.  That is a data point, but as I recall that is the >>> overall slow down which would include the slow down across the lip >>> of the duct and the across the radiator combined.  Also for a faster >>> aircraft where Vo is quite high, perhaps Vi/Vo =  0.40 makes for >>> less drag but  gives you all the cooling needed as opposed to >>> selecting cooling as a Vi/Vo = 0.20. >>> >>> Also the Positive CPs are all below the horizontal line for Internal >>> flow.  With lower Vi/Vos resulting in higher positive CPs.  That >>> makes sense because if we have Vi/Vo = 1.0 then that would imply the >>> least conversion of velocity to internal pressure, and we get a >>> negative ratio Cp =  -0.6.  Conversly if Vi/Vo = 0 then that would >>> imply all the velocity energy is coverted to pressure Vi/Vo = 0 then >>> Cp = max or approx positive 1.0 which tends to jive with the graphs. >>> >>> The Cp external magnitude tends to increase as A (lip Curvature) >>> becomes more pronounced (with A=40 being the most pronounced and >>> A=10 the less pronounced lip curvature).  External pressure would be >>> considered a drag component in my opinon, so you want the least of >>> that possible consisten with other objectives (such as cooling). >>> >>> So I think A=20 was chosen as the best compromise of lesser drag and >>> adequate cooling. Also, other  lip curvatures might have had >>> "Separation" or other problems at different angles of attach (from >>> 12 to -12 degrees).  For example perhaps if A=40 was choose, >>> separation may have occured at angles below 12 Degs and for that >>> reason alone been unacceptable. >>> >>> Best this old brain can do perhaps someone of the younger generation >>> can jump in and clarify. >>> >>> Ed >>> >>> >>> ------ Original Message ------ >>> From: "Finn Lassen finn.lassen@verizon.net >>> " >> > >>> To: "Rotary motors in aircraft" >> > >>> Sent: 7/11/2021 11:12:23 AM >>> Subject: [FlyRotary] Re: Cooling Inlets >>> >>>> So Ed, you're bored? >>>> >>>> Want to take a stab at helping me understand the below graphs and >>>> how they lead to the selection of the optimum outside/inside lip >>>> radius ratio? >>>> >>>> I understand that Cp is pressure coefficient, pressure relative to >>>> other pressures in the vicinity. >>>> >>>> Not clear to me if we're looking for positive or negative Cp inside >>>> the diffuser, I assume positive? (Converting airspeed into pressure) >>>> I also assume we're looking for a profile with maximum Cp over a >>>> wide AOA range. >>>> Why did they pick A-20 and Vi/Vo = 0.4 for figure 36d? >>>> Aren't we shooting for a Vi/Vo of 0.2 or better? (slowing 100 mph >>>> down to 20 mph) >>>> >>>> Finn >>>> >>>> On 6/30/2021 11:18 PM, Finn Lassen finn.lassen@verizon.net wrote: >>>>> Thanks. I guess I kept missing it because I don't understand what >>>>> I'm looking at. >>>>> Can anyone help me understand the following and show me the >>>>> optimum inside/outside radius ratio (which I assume is one of the >>>>> A-10 to A-40 contours): >>>>> >>> >>>>> >>>>> >>>>> Finn >>>>> >>>>> On 6/30/2021 9:45 PM, Charlie England ceengland7@gmail.com wrote: >>>>>> Seems likely; I don't recall seeing a CR3485 referenced anywhere, >>>>>> either. >>>>>> >>>>>> On 6/30/2021 4:42 PM, Finn Lassen finn.lassen@verizon.net wrote: >>>>>>> I tried in vain to find NASA_CR3485 (well, I found a NASA >>>>>>> contractors report on animal studies). >>>>>>> >>>>>>> I wonder of he meant 3405? >>>>>>> >>>>>>> >>>>>>> >>>>>>> Anyone found a better match? >>>>>>> >>>>>>> Finn >>>>>>> >>>>>>> On 4/28/2011 9:07 AM, Tracy wrote: >>>>>>>> Finally got around to finishing my cooling inlets. (pictures >>>>>>>> attached)� Up until now they were simply round pipes sticking >>>>>>>> out of the cowl.�� The pipes are still there but they have >>>>>>>> properly shaped bellmouths on them.�� The shape and >>>>>>>> contours were derived from a NASA contractor report >>>>>>>> (NASA_CR3485) that you can find via Google.� Lots of math & >>>>>>>> formulas in it but I just copied the best performing inlet >>>>>>>> picture of the contour.�� Apparently there is an optimum >>>>>>>> radius for the inner and outer lip of the inlet.�� There >>>>>>>> was no change to the inlet diameters of 5.25" on water cooler >>>>>>>> and 4.75" on oil cooler. >>>>>>>> >>>>>>>> The simple pipes performed adequately in level flight at >>>>>>>> moderate cruise settings even on hot days but oil temps would >>>>>>>> quickly hit redline at high power level flight and in climb.� >>>>>>>> >>>>>>>> The significant change with the new inlet shape is that they >>>>>>>> appear to capture off-axis air flow� (like in climb and >>>>>>>> swirling flow� induced by prop at high power)� MUCH better >>>>>>>> than the simple pipes. �� First flight test was on a 94 >>>>>>>> deg. F day and I could not get the oil temp above 200 degrees >>>>>>>> in a max power climb. �� They may have gone higher if the >>>>>>>> air temperature remained constant but at 3500 fpm the rapidly >>>>>>>> decreasing OAT kept the temps well under redline (210 deg F). >>>>>>>> >>>>>>>> I have an air pressure instrument reading the pressure in front >>>>>>>> of the oil cooler and was amazed at the pressure recovered from >>>>>>>> the prop wash.� At 130 MPH the pressure would almost double >>>>>>>> when the throttle was advanced to WOT. � That did not happen >>>>>>>> nearly as much with the simple pipes.�� >>>>>>>> >>>>>>>> These inlets ROCK! >>>>>>>> >>>>>>>> Tracy Crook >>>>>>>> >>>>>>> >>>>>>> >>>>>>> >>>>>>> Virus-free. www.avast.com >>>>>>> >>>>>>> >>>>>>> >>>>>>> <#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2> >>>>>> >>>>> >>>> >> --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus --------------DFDD5CFEBC4777C891BEE82C Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: 8bit
See my original post below

"On 4/28/2011 9:07 AM, Tracy wrote:"
Subject is:
Re: Cooling Inlets-shape

Finn

On 7/20/2021 1:11 PM, Marc Wiese cardmarc@charter.net wrote:
Can someone post pictures of Tracy’s inlets or point me to where they are in the archives?
M

Sent from my iPhone

On Jul 20, 2021, at 10:58 AM, Finn Lassen finn.lassen@verizon.net <flyrotary@lancaironline.net> wrote:


Thanks Ed.

 Not been making much progress on the RV-4 over the last month. I guess the heat and humidity is getting to me ...

Finn
On 7/13/2021 11:57 AM, eanderson@carolina.rr.com wrote:
Hi Finn,

Its been a long time since I dove this deep into cooling ducts/lip contours etc.  But, here goes.

The duct (lip + diffuser) is suppose to convert air velocity to air pressure with minimum loss/drag and turbulence.  However, like almost everything else involving flight - there is no single best answer - only an optimization or approximation to the best (that you are going to get with the compromises you have to make).  So in our case one set of compromises might be between cooling effectivness and cooling drag.  As you know the larger your radiator the more heat you are going to get rid of, but, the larger your core the more cooling drag you are going to encounter.  

Now at low speeds you might get away with sticking the radiator out in the airstream without any ducting and get adequate cooling, but it will have higher drag - now at biplane/slow airspeed the drag might be acceptable, but at 200 mph quite unacceptable.  Again, it depends on what you are trying to achieve.

 Its been quite a while, but Ill give it a shot on trying to explain the charts.  I presume that External refers to air factors prior to the lip and Internal refers to air factors after the lip of the diffuser (or internal to the duct).  you mention wanting a 100-20 mph slow down.  That is a data point, but as I recall that is the overall slow down which would include the slow down across the lip of the duct and the across the radiator combined.  Also for a faster aircraft where Vo is quite high, perhaps Vi/Vo =  0.40 makes for less drag but  gives you all the cooling needed as opposed to selecting cooling as a Vi/Vo = 0.20.

Also the Positive CPs are all below the horizontal line for Internal flow.  With lower Vi/Vos resulting in higher positive CPs.  That makes sense because if we have Vi/Vo = 1.0 then that would imply the least conversion of velocity to internal pressure, and we get a negative ratio Cp =  -0.6.  Conversly if Vi/Vo = 0 then that would imply all the velocity energy is coverted to pressure Vi/Vo = 0 then Cp = max or approx positive 1.0 which tends to jive with the graphs.

The Cp external magnitude tends to increase as A (lip Curvature) becomes more pronounced (with A=40 being the most pronounced and A=10 the less pronounced lip curvature).  External pressure would be considered a drag component in my opinon, so you want the least of that possible consisten with other objectives (such as cooling).  

So I think A=20 was chosen as the best compromise of lesser drag and adequate cooling. Also, other  lip curvatures might have had "Separation" or other problems at different angles of attach (from 12 to -12 degrees).  For example perhaps if A=40 was choose, separation may have occured at angles below 12 Degs and for that reason alone been unacceptable.  

Best this old brain can do perhaps someone of the younger generation can jump in and clarify.

Ed


 
------ Original Message ------
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: 7/11/2021 11:12:23 AM
Subject: [FlyRotary] Re: Cooling Inlets

So Ed, you're bored?

Want to take a stab at helping me understand the below graphs and how they lead to the selection of the optimum outside/inside lip radius ratio?

I understand that Cp is pressure coefficient, pressure relative to other pressures in the vicinity.

Not clear to me if we're looking for positive or negative Cp inside the diffuser, I assume positive? (Converting airspeed into pressure)
I also assume we're looking for a profile with maximum Cp over a wide AOA range.
Why did they pick A-20 and Vi/Vo = 0.4 for figure 36d?
Aren't we shooting for a Vi/Vo of 0.2 or better? (slowing 100 mph down to 20 mph)

Finn

On 6/30/2021 11:18 PM, Finn Lassen finn.lassen@verizon.net wrote:
Thanks. I guess I kept missing it because I don't understand what I'm looking at.
Can anyone help me understand the following and show me the optimum inside/outside radius ratio (which I assume is one of the A-10 to A-40 contours):


<kbdejbnihmgdehea.png>

Finn

On 6/30/2021 9:45 PM, Charlie England ceengland7@gmail.com wrote:
Seems likely; I don't recall seeing a CR3485 referenced anywhere, either.

On 6/30/2021 4:42 PM, Finn Lassen finn.lassen@verizon.net wrote:
I tried in vain to find NASA_CR3485 (well, I found a NASA contractors report on animal studies).

I wonder of he meant 3405?
<bnmfmdnlndmefidc.png>


Anyone found a better match?

Finn

On 4/28/2011 9:07 AM, Tracy wrote:
Finally got around to finishing my cooling inlets. (pictures attached)� Up until now they were simply round pipes sticking out of the cowl.�� The pipes are still there but they have properly shaped bellmouths on them.�� The shape and contours were derived from a NASA contractor report (NASA_CR3485) that you can find via Google.� Lots of math & formulas in it but I just copied the best performing inlet picture of the contour.�� Apparently there is an optimum radius for the inner and outer lip of the inlet.�� There was no change to the inlet diameters of 5.25" on water cooler and 4.75" on oil cooler.

The simple pipes performed adequately in level flight at moderate cruise settings even on hot days but oil temps would quickly hit redline at high power level flight and in climb.�

The significant change with the new inlet shape is that they appear to capture off-axis air flow� (like in climb and swirling flow� induced by prop at high power)� MUCH better than the simple pipes. �� First flight test was on a 94 deg. F day and I could not get the oil temp above 200 degrees in a max power climb. �� They may have gone higher if the air temperature remained constant but at 3500 fpm the rapidly decreasing OAT kept the temps well under redline (210 deg F).

I have an air pressure instrument reading the pressure in front of the oil cooler and was amazed at the pressure recovered from the prop wash.� At 130 MPH the pressure would almost double when the throttle was advanced to WOT. � That did not happen nearly as much with the simple pipes.��

These inlets ROCK!

Tracy Crook



Virus-free. www.avast.com





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