Cowling mod on RV-3

Hey guys...Not sure if the new RV-3 kits have a cowling with round holes (like an SR-22) or if they still have the old style. I have a 30 yr old -3 and I am thinking of modifying my cowl to the round inlets....anybody done that?
Or if the new ones have the round holes...how incredibly hard would it be to match up a new cowl to my old airframe?...I'm thinking hard:-(
I am really good with fiberglass, but it will be a big job and keep me out of the air...and nobody likes that.
Any opinions, suggestions, shortcuts?
Thanks
Dave Cronwall
N66GB

I think the Sam James cowls have the round inlets. As of a couple years ago, the standard RV-3B cowls sure didn't.

Dave

yes that is correct. the same James cowl. The 3s and 4s have the rectangular inlets.

No help from Vans

I checked with Vans...only thing they have is a cowl kit, and it is the same as what I have....but completely starting from scratch. At this point, I am looking for a molded part that I can section and attach to what I have. That way, it's already symmetrical and easier to adapt to my 30 yr old cowl. And though it's still a lot of work, I'm wouldn't be molding everything new.
I'm reaching out to LoPresti Aviation to see if something they make will work, but looking for any and all suggestions.
Dave

Maybe you can find someone with a cowl that has those round inlets, take a mold from their cowling, and then you'd have the parts you are looking for.

Dave

I kinda copied DanH and made round cooling air inlets for my stock Van's cowl on my 7, follow the link below.


http://www.vansairforce.com/community/showthread.php?t=94648&page=32

Why round ?

Looking for education. Is round aesthetically more appealing, more efficient or what ? Talk to Dan at Panther SPA, he might have a reject cowl you cold use to put round holes on yours.

According to some NACA reports done long ago, the round inlet is more efficient.

dacronwall said:

I checked with Vans...only thing they have is a cowl kit, and it is the same as what I have....but completely starting from scratch. At this point, I am looking for a molded part that I can section and attach to what I have. That way, it's already symmetrical and easier to adapt to my 30 yr old cowl. And though it's still a lot of work, I'm wouldn't be molding everything new.
I'm reaching out to LoPresti Aviation to see if something they make will work, but looking for any and all suggestions.
Dave

Click to expand...

The Sam James cowling, or the front part of it, will work, but you would have to fork out $$$ for something you would only use 1/3rd of. The only other thing I could think of is the nose bowl that William Wynne sells for the Corvair. flycorvair.net or something like that. But I have no idea if it would fit.

Sam James sells round outlet kits

Dave, if u go to www.jamesaircraft.com they sell 4 different sizes of aluminum cowl inlet rings from 3 to 6 inch diameter out of their north shop (850) 342-9929, regards, Al.

Another source for round-inlet cowls is from the Panther kit plane. I think I read somewhere that this cowl was developed from an RV-3 cowl, so who knows? It might fit.

Dave

Cowl mods progressing

I spoke with Will James about his cowls, and decided it was going to be way too much work to fit up new fiberglass to my 33 yr old RV-3. So I have been about the business of cutting, foaming, shaping and glassing...oh...and don't forget the itchy sanding! I had to make my own inlet rings, but based them on the James design.
The mod is about 90% complete, with only the piano hinge left to replace, and final sanding and prep for paint. I still need to make the forms for the plenum to mate up to the inlet rings, but that should not be too bad.
I will try to get a couple pics posted up soon.
Dave

sblack said:

According to some NACA reports done long ago, the round inlet is more efficient.

Click to expand...

Not aware of any NACA report measuring efficiency of round inlets vs others. Got a lead?

The report referenced most often is NASA CR3405. Because the inlets shown to have the best coefficient of pressure in CR3405 happened to be round, "round is better" seems to have become a common conclusion. Reality is that the report showed low velocity ratio inlets to be better. The actual shape isn't so important.

I'd also recommend AIAA 80-1242R and AIAA 80-1872R. I'm sure there are others.

Round inlets can help with auxiliary issues. For example, round can be easier to seal to a plenum. A round inlet also seems to be less affected by spinner effects, and reduced propeller-induced inflow velocity near the spinner. Put another way, there is less inlet area located in the slow region near the spinner, aft of the blade roots, so less pressure delta across the width of the inlet.

My own reworked inlets move area outboard of the original RV-8 inlets, and upward. Based on a limited data set, measured pressure recovery of a stock RV-8 inlet is quite good; the outboard locations seems to be of most benefit during high power climb, when they better utilize higher velocity propeller outflow.



To the OP's interest; having reworked a standard RV-8 cowl, I would say that simply fitting a whole new cowl would be a LOT less work, assuming you can find one with suitable inlet diameter. Apparently not

I thought that you could purchase the front end of a SJ cowl at one time. This was just a generic nose bowl, IIRC. If still available, grafting the new nosebowl on would be a head start on a cowl facelift.

Contact Dayton from DJM manufacturing out of Carson City, NV. I believe he makes the rings for Sam James.

Here is my progress

Fiberglass continues. I made my own rings.



Still have to build the plenum....
Dave