What's new
Van's Air Force

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

James Aircraft Cowl - Catto Prop

rockwoodrv9

Well Known Member
Patron
I fit the Vans cowl for my 9A. I have the O-320 D2A engine with a carb and have a Catto 3 blade prop. I bought the 2" extension from Saber - beautiful by the way.

I hate the hinges and I want to install the Skybolt fasteners. Since I will be driving by the James Aircraft factory next month, I plan to pick up a new cowl but not sure what one to order.

My questions are:

1. Do both the standard and long cowls fit my engine - prop?
2. Is there a reason to choose one over the other?
3. Do the larger rings offer more cooling at a speed penalty?

If anyone has done the James cowl with a Catto prop, I would love to see some pictures and get your opinion.

Thanks
 
1. Do both the standard and long cowls fit my engine - prop?
2. Is there a reason to choose one over the other?
3. Do the larger rings offer more cooling at a speed penalty?

Long cowl requires a propshaft extension. I would choose the long cowl, in particular with smaller inlet ring sizes, as a high Vi/Vo inlet requires internal length. You're using a lightweight prop, so there's no W&B penalty to sticking it out there a bit further.

Several RV'ers have experimented with inlet size. Given a fixed exit and higher Vi/Vo inlets, decreasing inlet size initially resulted in slight incremental speed increase in return for higher temperatures, an expected result due to reduction of mass flow. A some point in the reduction trial, no more speed was found, but temperatures kept rising.

The same result can be expected with a larger, low Vi/Vo inlet by reducing the exit size. The empirical difference seems to be superior cooling at lower airspeeds...high AOA climb, 90 knots in from Ripon, etc. James doesn't make anything like that.

The Siren of Speed is hard to ignore, but most of us are better served by sticking closely to the Vans design mantra, balanced performance. We don't spend much time at max velocity, but we sure do spend a lot of time at Vy, economy cruise, or flying around a pattern.
 
As always, Dan has some great advice!

I went with the short Sam James cowl when I replaced my engine some time back. I selected this cowl for the looks, not performance, and I didn't like the idea of the extra prop extension. The cooling was much better with the stock Van's cowl, as Dan eluded to.

The short cowl is really designed for fuel injection and I had to modify the FAB extensively to work with the cowl. The good news is, it has worked out very wel!

Here is a thread on what I went through. You might have to move up or down a page to get the whole story.

Here are some pictures of my modified FAB.

Good luck!
 
Thanks Dan and Bill. I am more concerned with cooling than speed. Both the short and long say they can be used for carb or FI. I may add FI at some point so that is nice.

When I spoke with Will, he highly recommend the plenum. How do these setups sound?

1. Long cowl - 5-1/4" large rings, plenum - for max cooling
or
2. Short cowl - 5-1/4" large rings, plenum - for max cooling

I like the looks of both the long and standard length. I just want to make sure I do everything I can for good cooling.
Thanks
 
I like the looks of both the long and standard length. I just want to make sure I do everything I can for good cooling.
Thanks

Then go long; looks better and offers more space to get the plenum inlet shapes correct. Speaking of which, I'd buy Bill Lanes's plenum lid.
 
Then go long; looks better and offers more space to get the plenum inlet shapes correct. Speaking of which, I'd buy Bill Lanes's plenum lid.

That is good advice from Dan.

You must have some type of plenum with the holy cowl.

PS. See this thread.
 
Last edited:
Then go long; looks better and offers more space to get the plenum inlet shapes correct. Speaking of which, I'd buy Bill Lanes's plenum lid.

If it fits!! Is the 320 engine width the same as the 360? I.e 30.5" measured at rocker gasket bases -side to side?
 
Qualified Guinea pig

I have an IO-320 D2A with FI, the Sam James long cowl (with plenum) and a Catto 3blade. It all fit very well and I'm more than pleased with the cooling performance. In almost three years of flying I've only seen a CHT over 400 once... On a long climb on a 90F+ summer afternoon. Running LOP at 5000MSL and up my CHTs rarely exceed 330F.
I went with the long cowl primarily for the looks - I think the longer snout looks good on the A model. Compared to the experience of some, I was pleased with the air intake/filter/airbox configuration. it too has worked well for me.
Send me a PM and I'll send you a raft of photos showing any aspect you'd like to see.
 
James Cowl Catto Prop

Hi Rockwood,

I installed that combo back in 2005 and have been flying it since--only change being an updated Catto 3 blade to replace the 2005 vintage and a change from carb to FI.

You mention that you purchased a 2" (2.25") prop spacer. I believe you need a longer spacer for the long cowl--I believe mine (a Saber unit) is 4 inches.

It is also my opinion that the long cowl looks better with the 9a/3 blade Catto combo and it gives you more room for airflow ramping and installation of the induction system. I initially used the James conical filter housing on my carb (since converted to AirFlow Performance FI) but did not care for the way I had to support it on the engine-- so I modified my bottom cowl and incorporated the filter housing into the inlet scoop area --still using the large K&N conical filter.

Ref inlet ring size--I do not see why the 4 5/8 inch standard inlet rings would not cool well on your 320---assuming you have standard compression. They do just fine on my 360 (standard compression 8.5:1) and Terry's 320 and I do have EI. I believe the 5 1/4 rings are for the 540 engine??!!

I would also recommend using Vans standard baffle wall kit and using a carbon fiber plenum top. I used the James plenum on mine and it was an absolute nightmare to fit properly---much cutting and reglassing required. Maybe they have improved since but that was my experinece.

Given my experience, on my brothers 7a build we used Vans baffle wall kit and the available carbon fiber top----greatest challenge for you will be to adapt the square plenum inlet to your round cowl inlets. This approach went MUCH smoother that using the James plenum and was less expensive. Take a look at Dan H's pics on how to build the plenum to ring transition.

Skybolts look good but are expensive and do not protect against vibration wear--I used SS #8 Phillips screws/#6 SS Tinnerman washers (dimpled to accept the #8 screw)/ and platenuts. Look much like the SkyBolts cosmetically, fit flush, are readily available, provide excellent strength, and cost much less.

Hope this helps.

Cheers,

db
 
Ref inlet ring size--I do not see why the 4 5/8 inch standard inlet rings would not cool well on your 320---assuming you have standard compression. They do just fine on my 360 (standard compression 8.5:1) and Terry's 320 and I do have EI. I believe the 5 1/4 rings are for the 540 engine??!!

The notion that some particular inlet area is for some particular engine size is one of those bad concepts that won't go away. Almost ANY ring size can be made to work. A small inlet area merely means the builder must put special emphasis on internal diffusion. A large, low velocity inlet may not need any internal duct work at all; external diffusion means it can just dump into the plenum volume.

The reasons to choose one over the other have little to do with engine size. For example, W&B may preclude pushing the prop way out on an extension, so the smart designer goes low Vi/Vo (the large inlet); it works fine with limited distance between the inlet and the engine cylinders. A racer may prefer a fuselage shape with the best possible fineness ratio (a pointy nose), so a long prop extension, tiny inlets, and well designed internal diffusers are the order of the day.

See a Mooney Acclaim or Cessna TTX for examples of low Vi/Vo inlets. See a good Reno F1 or the Anequim project for a high Vi/Vo example. Closer to home, my RV-8 is a low Vi/Vo, while Chris Z's Lancair is high Vi/Vo.
 
GEEEZZ

The OP asked for opinions from people who have EXPERIENCE with a James Cowl and a Catto Prop. That is what was provided. If one wants to convince him of the benefits of a Low Vi/Vo system-and a course of action that mimics theirs then that is a different discussion.

See ya!

db
 
Lets get the inlet dimensions correct here.

Hi Rockwood,
<snip>
Ref inlet ring size--I do not see why the 4 5/8 inch standard inlet rings would not cool well on your 320---assuming you have standard compression. They do just fine on my 360 (standard compression 8.5:1) and Terry's 320 and I do have EI. I believe the 5 1/4 rings are for the 540 engine??!!
<snip>

Hope this helps.

Cheers,

db

the 4 5/8 rings ARE the 5 1/4 rings. One is ID the other is OD.

Screen%252520Shot%2525202015-11-23%252520at%25252011.20.52%252520AM.png
 
If one wants to convince him of the benefits of a Low Vi/Vo system-and a course of action that mimics theirs then that is a different discussion.

I'm not rooting for a team here. As noted, either approach (high or low velocity ratio) will work. Which to choose depends on a number of design factors, but engine size isn't one of them. My own design driver was W&B.

You might be surprised to learn your 4.625" dia James inlets are not particularly high ratio. At 16.8 sq in per inlet, they're really middle of the range. The 9.6 sq in inlets (3.5" dia) on Chris Z's Lancair operate at a ratio near 1, and the late Paul Lipps used even smaller inlets with the help of some exhaust augmenters. So, just considering these examples, we have total inlet areas ranging from 19 to 56 sq in, successfully cooling engines with less than a 25% variation in HP.
 
Last edited:
I appreciate all the info all of you are giving. I don't understand the cooling - plenum - baffles engineering enough to even know what to ask. As of now, I will be ordering the following:
1. Long James Cowl
2. 5-1/4" rings
3. Im working with Bill to make a plenum for my O-320 carb engine
4. Carb air intake from James aircraft

Hopefully that will give me both good looks and good cooling. Links to other's work are really appreciated.
 
James Cowl/Etc

Hi Rockwood,

You are welcome--pm any time.

You are going to love that 9a. If aerobatics is not your thing, the 9a airframe provides an incredibly capable, fun to fly, and efficient cross country and local flyer!

All the best and of course,

Cheers,

db
 
Full disclosure

I'm glad to see db1yg (Dave) chimed in on this thread. He was incredibly helpful - and encouraging- to me during my build. I copied a number of his details and am really glad I did. His gorgeous 9A with the long SJ cowl was the clincher for me in my cowl choice, not to mention the Catto 3-blade. My SJ cowl and plenum were fabricated 5 yrs or more after Dave's, and I perceive that Will and Sam made "fit improvements" in that interval. I didn't have to do the mods that Dave did.
One more thing ... I have the Milspec fasteners on the firewall and love 'em. Would do the same again in a heartbeat. :)
 
Back
Top