Inlet ring to plenum gap?

[qtrmiledan]

Anyone with James cowlings or similar- what is the preferred distance from the air inlet rings to the plenum inlets for the flex- couplings made from the wet suit material? Thanks!!

[db1yg]

Hi Danny,

I have a 9a with the James Cowl/plenum and the aluminum James rings. Since I finished the plane in 2006 I have had a gap of around 2 inches. The problem with this amount of gap is that the "skin diver suit material" used for the tube seal will "balloon" and stretch over time due to the effects of air pressure. I have since extended the fg plenum nozzle to within 3/4 of an inch of the aft edge of the alum rings--this provides much less exposed seal, a smoother transition from alum to seal to fg plenum, reduces the chance of "ballooning", and still provides adequate spacing for engine movement.

Hope this helps.

Cheers,

db

[mannanj]

Originally Posted by db1yg

Hi Danny,

I have a 9a with the James Cowl/plenum and the aluminum James rings. Since I finished the plane in 2006 I have had a gap of around 2 inches. The problem with this amount of gap is that the "skin diver suit material" used for the tube seal will "balloon" and stretch over time due to the effects of air pressure. I have since extended the fg plenum nozzle to within 3/4 of an inch of the aft edge of the alum rings--this provides much less exposed seal, a smoother transition from alum to seal to fg plenum, reduces the chance of "ballooning", and still provides adequate spacing for engine movement.

Hope this helps.

Cheers,

db

Ahh Haaa! moment! Wonder if that is the reason for my engine temp increases over the last 18 months or so?????????

[qtrmiledan]

So one inch should do- providing enough room for movement. Would some lacing or cord around the outside of the "coupling" similar to scat tubing prevent the ballooning problem? Thanks!

[F1Boss]

Youu could make your own flexible adapter by using RTV as the 'resin' and 9 oz cloth as the base material. I doubt such a creation would baloon!

See DanH's postings for further help.

Carry on!
Mark

[Bob Martin]

Is there a good reason not to use 5" scat tubing?
I'm currently building a James Cowling set up now and extended the plenum snouts with fiberglass because I used the extended cowling. I purchased 5 inch scat hose and it appears to fit fine. BTW, I used 3/4" as a gap between the ring and the plenum also. So, has anyone tried the scat hose? Is there a reason to not use it ?? Thanks

[BillL]

Diesels use silicone hose as intake, pressured and suction. A few searches for "diesel intake hose" or "silicone hose" yielded many choices. You can consider the hump hose for aftercooler connections which handle pretty high boost pressure or simply straight hose.

http://www.siliconehose.com is one site that has 5" id, 4 ply straight, silicone hose by the inch. Diesel guys are cheaper that we are so the prices are not outrageous.

The 5" straight is $3.62 per inch.

or http://www.thermalflex.com/#!__silicone-hump-hose

Lots of options.

This will be what i look for, good sealing, flexible and smooth inside for good airflow.

YMMV

[DanH]

Originally Posted by mannanj

Ahh Haaa! moment! Wonder if that is the reason for my engine temp increases over the last 18 months or so?

Possibly. The reduced inlet area of a James cowl means each inlet operates at an increased velocity ratio as compared to a stock Vans inlet. As such, theory says more (or most) of the conversion of dynamic pressure to upper plenum static pressure is internal, after air passes the inlet face. Doing so requires an effective diffuser shape. A poor shape results in reduced upper plenum pressure. Pressure drives the system.

The typical James inlet ("inlet" meaning everything between the actual entrance and the plenum volume) has no actual diffuser shape, but rather a constant section duct leading to an abrupt expansion into the plenum.

Now throw in some misalignment between the ring and the duct snout, and connect them with a ballooned cross section. Even if you choose to discount the need for a diffuser, the misalignment and ballooned section combined with high velocity should result in disturbed flow.

Minimizing the gap between the ring and the snout will help the ballooned section problem. However, realize that if your snout and ring are perfectly aligned under static conditions, they are probably not aligned when subjected to engine torque.

[mannanj]

Dan:

Mine is the original James RV-8 cowl (not his new and improved version) and there is considerable mis-allignment between the inlet and the aluminum ramp bottom of the plenum/baffle interface on the starbord side. That has always been present though.

I was wondering if the ballooning spread the wet suit material where it goes over the aft section of the aluminum inlet rings. It is just a slip fit over the rings on mine and I wonder whether it becomes so stretched in that area that it allows a considerable air leak around that fit.

An air leak there would tend to equalize the pressure above and below the cylinders.

[DanH]

Mine is the original James RV-8 cowl (not his new and improved version) and there is considerable mis-allignment between the inlet and the aluminum ramp bottom of the plenum/baffle interface on the starbord side. That has always been present though.

I was suggesting it should be "misaligned" when static so it will be aligned when the engine is making torque. I have no idea how much.

Originally Posted by mannanj

I was wondering if the ballooning spread the wet suit material where it goes over the aft section of the aluminum inlet rings. It is just a slip fit over the rings on mine

There is no clamp?