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Cooling Schemes for Water Cooled Engines

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wsimpso1

Super Moderator
Staff member
Joined
Oct 18, 2003
Messages
11,353
Location
Saline Michigan
Subaru Cooling Options

I am investigating options for cooling my bird’s engine. Just how should we arrange the stuff and the inlets, outlets, do it while minimizing drag? I am considering the following configurations. I have my own thoughts on each, but I am looking for learned opinions on pros and cons of each one, which one you would choose and why, and any special tricks for each.
  1. Standard Lycoming style and sized cowling and inlets next to the spinner, heat exchangers placed obliquely in standard openings, outlets to cowling interior, cowling outlet below firewall;
  2. Standard Lycoming style and sized cowling, heat exchangers on ducts from standard openings, outlets on cowling sides;
  3. Air inlet below prop with a splitter, duct under engine to oblique heat exchangers, outlet to cowling interior, cowling outlet below firewall;
  4. Air inlet below prop with a splitter, duct under engine to oblique heat exchangers, outlet to cowling interior, cowling outlet along sides;
  5. Air inlet below prop, entire cowling as diffuser, heat exchangers and outlets on cowling sides;
  6. Air inlet below prop, entire cowling as diffuser, heat exchangers in A-frame box between engine and firewall, outlet below firewall;
  7. P-51 style scoop on belly with splitter, diffuser, heat exchangers, and controllable exit. Cowling can then be relatively tight.
In recognizing that any air flowing through the system but not put to work or leaked overboard costs speed and fuel, all schemes should be tight except where we want them to flow, and then only flow as much as we need. Likewise any air that encounters more drag than it needs to, is costing speed and fuel.So, in each scheme, what are the losses and the internal drag with each system?

My firewall is 43” wide and 28” high. If the engine does weigh in at 320 lbs, its CG will have to be about 30” ahead of the firewall. I suspect that there will be a bunch of room around the engine, so maybe we can use the volume between engine and cowling as a high expansion ratio diffuser. There will also be space either below the engine or behind the engine (depending upon turbocharger position) to allow for heat exchanger placement. If it turns out that the cowling is still too small, I can make the cowling tighter and use the P-51 style scoop. Maybe someone has the dimensions for the EJ257 with SOHC heads. I can update my thinking on this idea.

Billski
 
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