Re: Q2 Revmaster Cooling

Jon Finley



The basic premise of efficient engine cooling is to get the air into the cowling, slow it down/increase pressure, get it thru the cooling fins, speed it up/reduce pressure, and get it out of the cowling.  Sounds easy but it isn’t – especially with limited space.  Air wants to move from high pressure to low pressure. So, the cowl exit needs to provide that. The Citabria photo is a classic example of little to no engineering/design – just a big hole with a lip at the front to create low pressure. Probably works fine at 80mph and with no regard to efficiency.  At cruise, air tends to hit the nose of the aircraft at a slightly upward angle.  This means the lowest pressure area (near the firewall) is the top of the cowling and not the bottom.  I experimented top air exits years ago but just didn’t have enough instrumentation.  Most don’t do that because ‘it just isn’t done that way.’  As Dave says, very good baffles are important.  After that, I would focus on the cowling exit – much to be gained there IMO.


Oh, also… The VW engine was designed to cool something around 30hp with a fan. When extracting 70hp (stock heads), there just aren’t enough cooling fins for all situations.


Years ago, most of us had no idea what our engine was doing. We had one cylinder instrumented and assumed all were the same (they aren’t). Instrumentation is cheap these days (e.g. GRT EIS with all four cylinders instrumented) so no need to repeat those omissions (which led to problems).


Cowling design (and baffles) has been beat pretty severely by numerous groups – especially the boys doing the racing (check out Sam’s setup while at FOD). I suspect lots of good stuff can be found with a bit of Googling.

Jon Finley
Somewhere in the Southwest flying an RV-4

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