What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

a cowl observation

C

CATPart

Well Known Member
I notice some differences in the top silhouette of the RV4 cowl. Referencing the picture below, the left shows cowls that bulge on top, and the right shows cowls with a smooth transition. I wonder what this bugle means, if anything. Are their different cowls for different engines? I just don't see how this variation can be achieved if all cowls are the same, unless some engines have a higher crankshaft centerline, or the instrument bay cover is angled differently? For what its worth, 2 examples I know of with a bulge have o320-D1A. I understand that these aircraft are all hand built and all different, but even with respect to that, this variation seems strange, as if an engine was installed higher, or leaning upward slightly. I have seen stronger examples of the bulge, but I can't seem to find pictures. Yes a fairly unimportant topic, but I am curious.

410713416.jpg
 
No disrespect, but I'm not seeing it. From the photos you posted with the yellow line highlights, the angles of the photos as well as the temperate of the yellow highlights, it's hard to conclude the variables exist. In a nutshell, I don't think they do.
 
Part of it might be the top two have the older spinner and the bottom two have the newer longer spinner.

Bob burns

Rv-4 n82rb
 
You have a couple of reasons:
1) your viewing angle is not the same
2) the spinner changed from 12 to 13 inches
3) one of those pics looks like a constant speed prop (no prop extension)
4) cowl changed from long to shorter to accommodate constant speed props
5) 2 1/4 inch prop extension Vs 4 inch

Look at where the cowl cheeks end. They are not all the same. I put a 4 inch extension on my RV-4 and had to throw away the cowl cheeks. I also had to cut and regrow the glass around the firewall. If you move the prop forward everything moves forward and the cowl profile does not match or vice versa depending on the configuration that you bought.
 
It is not the viewing angle. They are all level with the top of the cowl which is the most important. The viewing angle of the 2 pics on the left causes a foreshortening that does help to magnify the situation, but that does not mean the situation is not there..think about it. Some people just can't see these sort of details, I accept that.

Anyway, I have actually run a straight edge along the top of some rv4s. some show a low spot of nearly 1/4 inch at the aft end of cowl , some show no low spot but just a continuous curvature making single point contact with the straight edge.

Good points about prop extensions and spinner diameter. I assume it would be a different cowl for the 13" spinner? Also, I assume the aft end of cowl is trimmed to fit the prop extension used? Spinner diameter seems the most likely culprit to me. I hope to conclude that thrust line and thrust angle are not the issue.
 
CATPart said:
Also, I assume the aft end of cowl is trimmed to fit the prop extension used?
Click to expand...


yes, you cut the back of the cowling depending on the extension used (or not). However, the location where you cut is not constant radius/angles (it expands). Think about it as a expanding cone originating at the spinner. If you cut the cone at 32 inches from the tip for a 2 1/4 inch extension, the profile will be different than if you cut the cone at 33 3/4 inch from the tip for the 4 inch extension. You have to make that up some how.

I guess I may not have the eye for detail, but I have worked on these issues during my build. Hope you find an answer that makes sense.
 
Oh I thought you saw it in the pics axo. I will admit that I am a bit fixated on it lol. It is so apparent to me in those left pics, looks like the whole cowl is pushed up like a pug nose. Just like when I look at Cindy Crawford I always see the mole :(

Anyway, like I said in the first post, this is an unimportant topic!...well, probably.
 
You must log in or register to reply here.
Back
Top