Short or long cowl cheeks?

My -3B was built with the sort of cut-off cowl cheek afterbodies that Vans had on the RV-1 and early RV3’s. So half the length of the typical ones and with a fairly decent size opening at the back of them.

While I am sure that it will aid in flow for cooling air, there must be a reason vans went for the closed ones on later 3’s and the 4.

Anyone knows the full story on these? And the pros and cons?

Thanks

Quick thought

Tuft the exits and look for an aerodynamic "afterbody"

More or less the completion of an imaginary streamline body, a rain drop. In this case - approximately a 1/2 cone, sliced from the point to the base.

If the tufts at the edges (or more) curl "into" the imaginary afterbody, then you have some choices to make.

Hint, this can get into lots of development time and work, so consider having your target where you spend the most time, i.e., cruise etc.,

FWIW

I wish I could remember what Van told me when I asked that question during the restoration of the -1... but I don’t. I can tell you that all the later models went with closed ends.....

Paul

I believe that the RV-3 and RV-4 tends to run relatively cool, or perhaps that's just the oil temperature. There are probably threads here that will tell you. Seems to me that the cheek cowl exits offer a possibility for lower drag, if designed as an exit, but a greater opportunity for fumes to migrate into the cabin.

I'm building my RV-3B with the full-length cheeks to avoid that.

Dave

side cheeks

My RV-3 has full length (1/2 ice cream cone). My buddy has the cut off ones.
My engine ran very cool when I got it. The oil cooler is up front, and I had trouble getting oil temps up above 150. The Vans oil shutter solved that.
As far as cooling, I re-shaped the cowling to more/less what the Sam James cowl is, (2) 4" round inlets connected to an engine plenum. My interpretation is that the inlets are generous on the stock cowl. I run my oil shutter full closed until its over 90 deg OSA, and even then I just crack it to get the oil around the 200 mark.
My CHTS all run in the 330 -350 range even on hot days, all the cooling air is directed out the belly where the exhaust comes out.
The round inlets are cleaner with less frontal area, and the ram air effect keeps temps in control even when its 100 deg. I can get some flashing of the fuel in my injector lines on top of the engine if I shut down and restart before it cools...But running the boost pump solves that and once airborne, it settles back out.
I like the sleek look of the round inlets, and I filleted and faired out the side scoops when I was prepping for paint. My leg fairings are integrated to the cowling so I have only the vertical seam where the cowl meets the firewall, and the horizontal hinge seam down the sides. Super clean.
Best
Dave