Showplanes Cowl Options on an RV 8

[claycookiemonster]

Showplanes cowl.

The oil door. There are no scribe lines to indicate where to place the oil door or how big is should be.
So: how big is an oil door? Is it square? Might it be round? Almost certainly hinged at the leading side. Almost certainly opening outward, though a part of me wants it to push in to open and then rest against a firm surround when pressurized in flight.

The cooling air and exhaust exit. I've got a simple 4-into-2 Vetterman set up on my IO-375. The "bulge" at the bottom of the cowl looks really HUGE, and I recall people reducing the exit flow to smooth out air flow. What should I do now for that? Change the profile of the cowl? Add a central body between the exhaust pipes to take up space?

 

[scsmith]

Hi Clay,
The oil door is hinged along the 'top' edge, the edge closest to, and parallel to, the airplane centerline. That way a straight hinge will work, since the cowl surface is straight there. The door opens outward. It requires a good Hartwell latch or Camlock latch, closing against a metal striker plate, or else two quarter-turn fasteners.

Do indeed stiffen the door substantially so it doesn't pillow out with internal cowl pressure. I used some 1/4" divynicell foam to make a sandwich out of it with two plies of glass on the inside over the foam. I shaped the foam to fit around the latch and the hinge.

You most likely can reduce your cowl exit area, especially if you are willing to install a cowl flap to let more air out during climb. A bulge on the inside will help with getting higher exit velocity, but won't reduce the airplane frontal area. I just closed off my exit to 37 sq in. from the original 58 sq in. (computed with the exhaust pipe area subtracted out). Here is a picture of what I ended up with, before paint. You can see the new (non-pink) fiberglass sides of the exit area. You can also see the cut-out for the cowl flap. I used a high-temperature epoxy (PTM&W 2080) since this part of the cowl is very close to the exhaust pipes (about 3/4"). Note that I have an angle-valve engine which puts a lot of heat load into the oil, so oil cooling is the main limiter on how much you can close off the cowl exit.
[/ATTACH]

 

[Mike S]

Showplanes cowl.

The oil door. There are no scribe lines to indicate where to place the oil door

As I recall, the cowl will work with a 540 also, so quite a difference where the oil door goes.

I would suggest you locate the cowl off the spinner back plate, then measure where the oil door needs to go.

 

[Taltruda]

I have seen a RV with an oil door that opens inward on an electric servo. He can open it in flight like a makeshift cowl flap, or after landing to let the heat or abs not cook his EarthX battery.