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Post by n3480h on Sept 6, 2011 22:37:40 GMT -5
So, since I am already making modifications to my cowl, I thought it might be interesting - and more efficient - to replace the stock cooling inlets with round inlets. Presume a GPASC 2180 at 80HP. Figuring (cipherin'?) cooling inlet area of .54 sq inches per HP x 80 HP = 43.2 sq inches total, yes? So two round inlets of ~21.6 sq inches = a radius of 2.622, or a Ø of 5.244 inches for each inlet. Correct? So if I form two round inlets of Ø 5.25" (a little surface friction loss?), I should have adequate inlet size with minimum cooling drag. If I understand the theory correctly, the outlet area has to be larger than the sum of the inlets. Forget the smiley inlet area because that will be ducted through an oil cooler under the sump - I'll use that for cabin heat or dump it overboard. Its late and I'm tired - am I figuring this correctly? Anyone see any downsides other than more sanding and itching? Tom
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Post by oahupilot on Sept 7, 2011 2:51:59 GMT -5
i hashed this out already on the old s net site. all the math and theory, unfortunately I don't have access to notes at this time. You can find it in the archive
If remember correctly your outlet should be .7 or .8 of you inlet
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peterzabriskie
Junior Member
"Did I make that part the best I possibly could have?" Unknown
Posts: 99
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Post by peterzabriskie on Sept 7, 2011 8:15:38 GMT -5
Well I wore out two pencils, but your math is right on, IF your assumtion that you have 80hp is correct AND your figure of 0.54 sq in per hp is correct. I think round inlets for looks are very cool and worth the sanding and itching....I have been paint scheming again see post for stolen Navy scheme from 2011 Airventure Midget Mustangs. -Pete
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Post by schrome on Sept 7, 2011 11:27:56 GMT -5
I question the premise of 0.54 s.i. per hp. Maybe it was right for draggier airplanes but I believe the ratio is or can be lower for a Sonerai. Kent Paser says he cooled the 160 hp engine in his Mustang with 30 s.i., after much testing and tweaking of course. That's 0.19 s.i./hp. The 'D' openings on the Sonerai's stock cowling are only about 20 s.i. combined and even when you add in the smiley it doesn't come up to 43. I too am reworking my cowling and likely will shoot for slightly smaller openings than the stock cowling and tweak from there.
Ed
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hans
Full Member
Posts: 166
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Post by hans on Sept 7, 2011 14:32:53 GMT -5
i hashed this out already on the old s net site. all the math and theory, unfortunately I don't have access to notes at this time. You can find it in the archive If remember correctly your outlet should be .7 or .8 of you inlet Wasn't that the other way around? Remember: as air absorbs heat it expands. I seem to remember that the outlet area should be around 1.2-1.25 of the inlet area.
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stick
New Member
Posts: 9
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Post by stick on Sept 7, 2011 15:50:53 GMT -5
I question the premise of 0.54 s.i. per hp. Maybe it was right for draggier airplanes but I believe the ratio is or can be lower for a Sonerai. Kent Paser says he cooled the 160 hp engine in his Mustang with 30 s.i., after much testing and tweaking of course. That's 0.19 s.i./hp. The 'D' openings on the Sonerai's stock cowling are only about 20 s.i. combined and even when you add in the smiley it doesn't come up to 43. I too am reworking my cowling and likely will shoot for slightly smaller openings than the stock cowling and tweak from there. Ed Don't forget that Kent Paser also used his engine exhaust as an augmenter, increasing the suction at the outlet. I think there was also a curved piece of sheet metal at the bottom of the firewall to smoothing the exiting flow.
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Post by n3480h on Sept 7, 2011 17:12:38 GMT -5
Oh boy, I apparently opened a can of worms here, lol. Its what I do best.
You guys have to agree on a factor for inlet area per HP, and the correct outlet area . . . or I'm going to come up with an ambient temperature adjusted, density compensated, mass airflow sensing, variable aperature inlet/outlet system that would make Bernouli barf. ;D And I KNOW you wouldn't do that to me, or would you? You really wouldn't want my cowl inlets to look like reversed miniature F-16 tailcones, would you?.
lol
So far, I have not gotten the archives to open in anything but raw html code. Not very helpful yet.
Tom
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Post by oahupilot on Sept 8, 2011 1:35:13 GMT -5
i hashed this out already on the old s net site. all the math and theory, unfortunately I don't have access to notes at this time. You can find it in the archive If remember correctly your outlet should be .7 or .8 of you inlet Wasn't that the other way around? Remember: as air absorbs heat it expands. I seem to remember that the outlet area should be around 1.2-1.25 of the inlet area. .7 to .8 comes from the book aircraft design:conceptual approach by Daniel P Raymer. The author has PHD in this sort of stuff so he might know what he is talking about
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Post by juergen on Sept 8, 2011 2:42:42 GMT -5
Hi Ohuapilot, you can not simply say .7 to .8 is the right factor, because Daniel P Raymer said it! The factor is very different in dependence of the aircraft (engine, speeds etc...) With >2000cc on a Sonerai1, the inlet is too big for the little outlet or the outlet is too small for this big inlet! To become a practical cooling on the S1 with big engine, you need a bigger outlet, additional venturi from exhaust and perhaps a bigger oil cooler. I go the way without bigger oil cooler and so, I must increase the speed on the cooling fins and do it with some modifications. Parts of the modifications, you can see in my Sonerai.net picture archive. Also I work on a article about the cooling situation on my plane and hope, that Sonerai.net will go new online as fast as possible. On this way, many thanks for Scott!! with best regards juergen
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4trade
Junior Member
Posts: 51
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Post by 4trade on Sept 8, 2011 13:10:54 GMT -5
Just build relative small round inlet, and if those are too small, change it bigger. Small and easy work for round inlet cowling that have bullet type shape.
Same with outlet, build 1.3 times inlet size and keep it that level if you need change inlet.
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Post by oahupilot on Sept 8, 2011 15:19:28 GMT -5
Hi Ohuapilot, you can not simply say .7 to .8 is the right factor, because Daniel P Raymer said it! The factor is very different in dependence of the aircraft (engine, speeds etc...) With >2000cc on a Sonerai1, the inlet is too big for the little outlet or the outlet is too small for this big inlet! To become a practical cooling on the S1 with big engine, you need a bigger outlet, additional venturi from exhaust and perhaps a bigger oil cooler. I go the way without bigger oil cooler and so, I must increase the speed on the cooling fins and do it with some modifications. Parts of the modifications, you can see in my Sonerai.net picture archive. Also I work on a article about the cooling situation on my plane and hope, that Sonerai.net will go new online as fast as possible. On this way, many thanks for Scott!! with best regards juergen Juergen you are right in stating that speed/ engine size and other factors will cause it to change from that factor. To actually derive a proper number for the sonerai or any other plane requires a computation fluid dynamic analysis of the entire system you would need a 3d model of the plane, cowl, engine, and anything else in the engine bay. You would also need a thermal analysis of the motor for model to be able to give you accurate results. Obviously thats a lot of work to get a good number, .7 to.8 is derived from empirical data of many working design that have been optimized through trial and error. Its a reference point from which to start and optimize the design. The book written by Dr. Palmer and published by the american Institute of astronautics and aeronautics, is a great source of industry data for initial aircraft concept design. Because its based in broad terms on what actually works its gets you close to the correct answer without having to go the long way of building the entire model. if you want to go the long way about it Open FOAM can actually do the cfd modeling and analysis. The program is free. Click the link below for a video demonstrating openfoam. www.youtube.com/watch?v=YFsmsi8uLAs
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Post by n3480h on Sept 8, 2011 17:30:54 GMT -5
Fascinating clip, oahupilot. And somewhat humbling. Juegen, I hope you will post your data as soon as you can. So, I am faced with complex goals: Minimize cooling drag while providing sufficient cooling at taxi, climb, and cruise, and make it look good. Hmmm. I think there is useful knowledge to be gained by placing a pitot tube in various locations in the engine compartment and recording airflow under these different conditions, AND recording engine temps. However, it appears that my only course for selecting a starting point for inlet size is the highly regarded P.O.O.M.A method. (Pulled Out Of what, he asks). ;D Gentlemen, thank you all for the lively discourse and the better understanding of airflow concepts as they apply to our beloved Sonerai aircraft. Tom
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Post by maddog on Sept 8, 2011 22:43:27 GMT -5
I know that adding a one inch (or so) lip to the bottom of the cowl at ~60* to the air flow can have a large improvement in reducing the CHT temps. We used this mod on the 601.
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Post by juergen on Sept 9, 2011 2:27:00 GMT -5
Hi Ohuapilot, the factor .7-.8 comes from fast planes without having cooling problems, like the p51. On this planes gives the reducing of the air outlet a increase of the airspeed on the outlet and so it do increase the speed of the plane: typical is P51. On our plane, we have the problem, that the VW engine only can cool about 50-60hp (said Bob Hoover). With the big engine (>2000cc) and in racing configuration we need more cooling and for this we must increase the airspeed on the cooling fins. For this, we should have high pressure inside the cooling baffles and low pressure inside the cowling, so the airspeed on the cooling fins go to the maximum. Other part to modify is the cooling tins below the cylinders: this tins are fine for a car, but not optimal for cooling. I had seen the molded replace part on Jeffs plane and had made a copy on mine and it works very well. with best regards juergen
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Post by lqbanotxano on Sept 9, 2011 23:02:54 GMT -5
This maybe a double post...havingcomputer problems...
This is from my own experience of myself designed & built holy cowl with entry 11 degree diffusers. I have an 85HP Continental. The inlet rings are 3-1/2" diameter...that is approximately 1/2 of a Sam James RV cowling for an O320 or O360. Sam James did all the RD all I did was cut his numbers in half. 160-180 HP is about double 80,85HP. My entry/exit sizing is about 1:1. With well wrapped box baffles, your CHT will go down but, your oil temps will probably go up. This is from me & most of the tightly cowled RV's (there are many) The exhaust or exit is the throttle of the cooling system...I would say a little bigger is better. You may have to try experimenting closing or opening the exit to get it to work. Sometimes smaller actually works better. The perfectly fined tuned cooling systems have .8 to .9 smaller exits to the 1.0 entry sizing. I got 1-1/2 years time (not counting paint) wrapped up in my cowling, inlets, exit, snorkel intake, snorkel oil cooler...yes the oil cooler air & the carb air are also fed from the (2) 3-1/2 diameter entry holes. The exit is also exhaust augmented with 4 equal 28' exhaust pipes exhausting from 2" inside the cowling. There is also a venturi rounded lip at the bottom of the firewall. It all works for very cool CHT’s but watch the oil temps. "No brag just facts" Anybody remember who said that?
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