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Successful Auto Conversion Trials, Tribulations and Tips

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slociviccoupe

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Apr 1, 2011
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269
Location
Palm Bay Fl.
Im in for this since i live in florida and its ungodly hot all the time.

Russel do you have any sketches with dimensions. Width and height of inlet entrance, any radius', length from inlet to front of core, diffuser angle or curve, exit length and sizes. I read your whole conversion but didnt know enough to apply it.
 

pfarber

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Feb 21, 2019
Messages
560
Location
Pennsylvania
Car aero add ons are very rarely particularly good aerodynamically. Read some aero books and you can almost certainly do better yourself.
Because most are done by non-engineers. There are MANY good installs. Are they perfect? Well, they ARE flying. What better metric is there??
 

pfarber

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Feb 21, 2019
Messages
560
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Pennsylvania
Pfarber, your calculations for a 200 HP radiator match fairly closely with the one flying in my Glasair / Subaru EG33. My rad is 16” x 15” x 2.75”.

However, I find that in my case, your 30% inlet size is too large. My opening is about 33 sq/in …. In fact when we race this plane or during the winter, I have a sleeve that goes over the front opening and reduces it to about 27 sq/in.
Russell Sherwood
So about 11-12% opening area? I cited the information from articles in Contact Magazine and a few Meridith effect studies I was able to understand.

My comparison is from an known, flying auto conversion BD-4 V8 (475hp) using a belly scoop and a huge 19x26 radiator (494sq in) with a 45sq in scoop opening. That's 10% opening and he reported no cooling issues. My rad size for 200 hp is only 10x20 (200 sq/in) single row with 30 Sq/in opening (15%) but chin mounted.

I plan on building a bottom half of the cowl that will easily allow for changing the inlet size. Basically the inlet will be screwed to the cowl, allowing easy changes to the opening and the geometry.

Oil cooling and air inlets will probably be from other holes in the cowl. The throttle body can be moved because I am scrapping the stock car intake (its huge and tuned for low speed, for high RPMs I need short runners).
 

Russell

Active Member
Joined
Nov 29, 2015
Messages
43
Location
Ft Worth, Texas
Toolbuilder & Slociviccoupe;
I have inserted a few photos to give you a better idea of what I have … pardon me if I have already posted these. All my sketches during construction have long ago been thrown away.

The scoop is for water cooling only, the air inlet is approximately 10.5” wide x 3” high. Length from inlet to the radiator face is about 39” … if the reducer sleeve is installed the length goes to 42”. The interior of the scoop expands at a fairly shallow angle for the first 20”. After 20” the expansion rate increases, sorry I don’t have angles. To help the air expand I added guide vanes, the guides were necessary to reduce turbulence within the scoop.

The exit squeezes down fairly quickly. Apparently the squeezing action and passing thru the radiator keeps the air well organized with little turbulence. Total exit length is about 20” and can be closed from 10 sq/in. or opened to 60 sq/in. We generally fly with the exit open around 25 sq/in, but with summer OATs between 95F and 105F it is set closer to 35 sq/in.

In addition to water cooling I have a 3.75” x 1” NACA scoop for the oil … yes, NACA scoops do not do well when trying to push air through a radiator, but they do look sexy! :)

Cool air for the engine enters the cowl through a 2” x 2” opening in the cowl. All air hot exits in the conventional location at the bottom aft of the cowl.

Photo 1 gives a good side view of the scoop.
Photo 2 shows the location of various inlets.
Photo 3 is the reducer sleeve that is added to the front of the cowl for racing or cooler weather.
 

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rv7charlie

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Nov 17, 2014
Messages
847
Location
Jackson
Hi Russell,

It's great to see more data from successful cooling installations. Can you expand (pardon the pun) on your inlet to exit area ratio? The reason I'm asking is that the really fast Lyc guys are finding that they can run inlets that are oversized for climb cooling (as long as the inlet lips are shaped correctly), and with attention to smoothing flow into the exit, reduce cruise power outlet area to as little as less than 1/2 the inlet area. I realize that the 'heat exchanger' makeup is radically different (the engine itself), but it's still surprising that inlet/outlet ratios are reversed for air cooled engines.

Thank you for any insight you can offer.

Charlie
 

Russell

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Nov 29, 2015
Messages
43
Location
Ft Worth, Texas
It's great to see more data from successful cooling installations. Can you expand (pardon the pun) on your inlet to exit area ratio?
Charlie
Charlie, I am not sure if this is what you are asking for ... if not let me know. The inlet is about 13% of the radiator area. My reducing sleeve brings the inlet area down to about 11%. The outlet varies from about 4 to 25% of the radiator area,
 

rv7charlie

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Joined
Nov 17, 2014
Messages
847
Location
Jackson
Ah, yes! When I read the earlier post, I saw
Total exit length is about 20” and can be closed from 10 sq/in. or opened to 60 sq/in. We generally fly with the exit open around 25 sq/in, but with summer OATs between 95F and 105F it is set closer to 35 sq/in.

Which had me thinking that your exit area was always larger than inlet. If you can go down to 4%, with inlet at 13% (outlet area about 35% of inlet area), that makes a lot more sense to me. As I said, the best Lyc installs are running about 50% outlet area to inlet area, and the proper duct possible with an actual heat exhanger core should allow a bit better ratio than the chaotic flow around a Lyc engine.

Thank you for the clarification.

Charlie
 
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