SJ Cowl and Plenum

I will start fitting my Sam James cowl and plenum soon to my -7 and have some confusion on how the proper fit for the plenum around the front of the engine should look, especially the cylinders.

Does someone have detailed pics available I could review to hopefully find what I am looking for?

Thanks in advance,

Glenn Wilkinson

Fit the cowl first...forget about the plenum for now. Once the cowl is complete and the rings are epoxied in place, you can think of the plenum.

Now you can pull the upper cowl off and start working the plenum to the top of the engine. The plenum inlet must line up with the rings and the plenum top must have clearance under the cowl. Volume is your goal. I used the Vans Baffle kit and trimmed it to give clearance to the upper cowl.



My plenum fit poorly and I hacked it up pretty bad to clear the AFP FI spider and purge valve. also has to slice it so the front fit over the case properly and lengthen the inlets(i have the long cowl) Might have been easier to build a new one from scratch.

Here is the sized and painted but I had not finished trimming the baffles and drilling the sides for screws

Plenum

One other thing on the plenum...don't worry about getting the front to fit around the engine curves. It is easiest to just hack it off, wax the engine case real well, then lay new glass between the plenum and the case.

Scott
7A

Hi Brian, like you I've had to do a lot of work to get my Plenum to fit the way I want.

I've been thinking of extending the inlet tubes forward as well. How much of a gap did you leave between the metal rings and the Plenum?



Thanks, Terry.

Don't mean to change the subject but since you are here and I'm not, I have a question about the SJ Cowl, how much did you have to trim on the firewall side, someone one here spaced his engine mount 5/8 inch to move CG to compensate for a FP prop, is there plenty for this?

Brian et al,

Thanks for the info on how to best get started and I'm sure I'll be back with more questions in the future.

You've been a big help.

Glenn Wilkinson

bret said:

Don't mean to change the subject but since you are here and I'm not, I have a question about the SJ Cowl, how much did you have to trim on the firewall side, someone one here spaced his engine mount 5/8 inch to move CG to compensate for a FP prop, is there plenty for this?

Click to expand...

Bret, It depends....does that help?

no really it depends on what cowl you got, what prop spacer you got, etc.

I have a IO-360 parallel valve, WW200RV prop and 2.25" Saber spacer. I also have the James Long cowl for my -7. I trimmed off between 1"-1.5", if I recall.
If you have the short cowl version, I think it work with no spacer, but probably trimming the same amount....i think. Chad Jensen used a 320 engine mount with his 360 and a spacer with his Catto prop, but had James build him a custom length cowl.

hydroguy2 said:

If you have the short cowl version, I think it work with no spacer, but probably trimming the same amount....i think. Chad Jensen used a 320 engine mount with his 360 and a spacer with his Catto prop, but had James build him a custom length cowl.

Click to expand...

I have the long cowl with a Catto 3-blade ...it required a 4" prop extension. It was my understanding the short cowl (with a FP prop) gets the 2 1/2" extension.

I have the short cowl and you really don't know how much you need to trim until the engine and prop are in place. Once they are, set the top cowl in place and work from there.

Regarding the cooling plenum, I put mine fairly low, which was a good thing.

Two tips for you:

1. Reinforce the section behind #4 cylinder with some .063 AA. You will have to file off the point of the angle to get it to nestle in there. That will keep the baffles from cracking.

2. Slather the front of your engine with mold release (I used vaseline.), cut off the forward lip of the plenum, lay fiberglass over the front of the plenum right on the engine. That will guarantee you have a good, leak free fit.

N941WR said:

2. Slather the front of your engine with mold release (I used vaseline.), cut off the forward lip of the plenum, lay fiberglass over the front of the plenum right on the engine. That will guarantee you have a good, leak free fit.

Click to expand...

I notice you guys don't bother with fasteners across the front. It's difficult to imagine a good leak free fit along an unsecured edge when the lid is being pushed up by significant internal pressure.

At 180 knots and 3500 feet, even a James setup will load the plenum lid at 60 lbs per sq foot, the delta between plenum pressure and cowl pressure. You have 3 sq feet (or more), thus 180 lbs on a box lid with no fasteners across the whole front span...maybe 18"?

Need a familiar illustration? When we space fasteners 3" apart across the top center of a standard Vans cowl, out in front of the windshield, we can watch it bow up between them in flight. That's in response to lower cowl internal pressure, in this case about 20 lbs per sq ft. Sure, more area, but if the upper cowl has 3 times the area of a plenum (which can't be far from true), it is an apples-to-apples comparison.

you may be correct Dan.

When I was chasing my phase 1 cooling. I sealed all the holes in the baffling with Red RTV. I also used the RTV to seal the front plenum to engine interface. I dropped temps about 15* that day. So don't know if it was the baffle holes or plenum lifting up.

I do now that it is sealed along the front now and I must cut it loose everything I pull the plenum cover and reseal when it goes back on. Good or bad I only do it a few times a year.

DanH said:

I notice you guys don't bother with fasteners across the front. It's difficult to imagine a good leak free fit along an unsecured edge when the lid is being pushed up by significant internal pressure.

At 180 knots and 3500 feet, even a James setup will load the plenum lid at 60 lbs per sq foot, the delta between plenum pressure and cowl pressure. You have 3 sq feet (or more), thus 180 lbs on a box lid with no fasteners across the whole front span...maybe 18"?

Need a familiar illustration? When we space fasteners 3" apart across the top center of a standard Vans cowl, out in front of the windshield, we can watch it bow up between them in flight. That's in response to lower cowl internal pressure, in this case about 20 lbs per sq ft. Sure, more area, but if the upper cowl has 3 times the area of a plenum (which can't be far from true), it is an apples-to-apples comparison.

Click to expand...

I will also be installing the SJ (long) cowl with the plenum cover. I understand what you are talking about there Dan, and will be keeping that in mind. Did you have any issues with your installation? How did you add attachment over this span? (I have many of your picts but don't remember this being illustrated)

Sealing the front of the plenum

My plenum followed the contour of the front of the engine case within about 1/4" on both sides of the case-split. I used some high temp (red silicone) weatherstrip I found at McMaster-Carr; sealed it up perfectly. Have never had a cooling issue from day 1. W'strip was cheap too.

One thing I didn't mention was that after using fiberglass to get the plenum to exactly match of the nose of my engine, I used high temp RTV to seal all around the plenum. This means the nose section, the sides along the aluminum plenum, in back, all around. I haven't noticed any indication that the high pressure air has moved past that seal.

hydroguy2 said:

...it is sealed along the front now and I must cut it loose everything I pull the plenum cover and reseal when it goes back on. Good or bad I only do it a few times a year.

Click to expand...

Whatever works. Given clean surfaces, I can believe a fat bead of cured silicone sealant will glue the edge to the case and withstand the load.

N941WR said:

..I used high temp RTV to seal all around the plenum. This means the nose section, the sides along the aluminum plenum, in back, all around. I haven't noticed any indication that the high pressure air has moved past that seal.

Click to expand...

Bill, yours is also glued to the case?

FWIW, you may not get much indication unless you go looking for it. Lots and lots of airplanes fly around with acceptable temperatures despite baffle leaks. However, eliminating all baffle leakage is the entire point of installing a plenum. Doing so allows the builder to take other steps and reduce total mass flow.

BTW, the stated pressure values are from measurement, not theory.

BillL said:

Did you have any issues with your installation? How did you add attachment over this span? (I have many of your picts but don't remember this being illustrated)

Click to expand...

The original install used a curved length of formed angle along the curved front bulkhead, one flange being riveted to the bulkhead and the other with nutplates for the lid. The pressure was enough to crack and fail that angle at each end, nearest the rubber inlet. This particular problem would not transfer to the James plenum, but it does illustrate the pressures.



The revision added a 90 degree flange to the lid, with fasteners in shear.



With the James plenum, it would be easy to add an attach point above the case split, in the middle of the unsupported span. Just need a small steel bracket attached to a case bolt, and one or more fasteners through the glass.

DanH said:

...
Bill, yours is also glued to the case?

FWIW, you may not get much indication unless you go looking for it. Lots and lots of airplanes fly around with acceptable temperatures despite baffle leaks. However, eliminating all baffle leakage is the entire point of installing a plenum. Doing so allows the builder to take other steps and reduce total mass flow.

BTW, the stated pressure values are from measurement, not theory.
...

Click to expand...

Yes, mine is RTV'ed to the case and you are correct. You wouldn't notice it, unless you went looking for it.

I recently posted a thread about how I reduced my CHT's by plugging all the holes. However, one thing I didn't mention was that some of the RTV by the nose had let loose and there was a small dirt stain/trail from the plenum forward, indicating an air leak.

This will be something I now look for with each cowl removal.

The one thing I did not like about the Sam James plenum was that the fit around the nose was not very good and when I questioned Will James about it, he simply said, "Fill in the gap with RTV." That would have been over a 1/4" of RTV, which seemed unacceptable to me.

DanH said:

Click to expand...

Great idea!

Thanks, Dan, I did not realize which was the final configuration. I only had the earlier configuration pict with the vertical fasteners across the center and did not know you had further development. The feature of removal with only 1/4 tun fasteners seems very attractive for ease of inspection. It would seem silly for me to have quick release fasteners for the cowl, just to have the plenum glued in, although there is still some good advantage to that. While I loathe pondering too much in favor of building, my path is well invested now, so I may as well give it appropriate consideration.

N941WR said:

... the fit around the nose was not very good and when I questioned ... it, he simply said, "Fill in the gap with RTV." That would have been over a 1/4" of RTV, which seemed unacceptable to me.

Click to expand...

I felt the same way. That's why I searched out the hi-temp weatherstrip. That solution is working well; no signs of leakage or deterioration after a year and 110hrs.

N941WR said:

However, one thing I didn't mention was that some of the RTV by the nose had let loose and there was a small dirt stain/trail from the plenum forward, indicating an air leak.

Click to expand...

That's a good clue.

By all reports your 360-powered -9 is fast enough to generate significant plenum pressure.

BillL said:

The feature of removal with only 1/4 turn fasteners seems very attractive for ease of inspection. It would seem silly for me to have quick release fasteners for the cowl, just to have the plenum glued in, although there is still some good advantage to that.

Click to expand...

All the plenum lid fasteners are machine screws. The trouble with 1/4 turns is that the spring usually sets the maximum tension, at least if you want the heads flush. Given enough airspeed the edge of the plenum lid would lift up off the flange.

Rupester said:

That's why I searched out the hi-temp weatherstrip. That solution is working well; no signs of leakage or deterioration after a year and 110hrs.

Click to expand...

Do you have a photo for us Terry?

Dan,

I would be interested in seeing a close up of how the 90 degree flange at the front of the plenum attaches. There must be some really short baffle piece affixed to the case?

Thanks,
Scott

Dan,
From my perspective, I would like to see any and all pics you have of the work you did documenting the process of cowl and plemun installation.

Glenn

Scott, it's just a curved aluminum baffle wall. No recent photos. Here's an old one from original construction. Most of the formed angle was later removed and replaced by nutplates with the screws horizontal. The baffle wall is attached to the case at the ends and at the center split, then sealed to the case with silicone.



Glenn, that would be a rather long post

Hi Gang:

Here's some shots of my installation. I started with Van's Baffle kit and worked from there. You'll see that across the front portion on either side of the crankshaft I have mounting holes about every 1.5 inches. Everyplace you see a cleco will be a machine screw and nut plate.

I have redone the front portion up and over the crankshaft centre section. I have that down to about a 1/16" gap and I hope that some sort of high temperature weather stripping will seal that off completely.

I have had to modify the James plenum to accommodate the stock oil cooler complete with shutters.

You'll see the foam plugs installed that I used last night to extend the inlet tubes. I have the extended cowl and will be using a 4 inch prop extension.

I was hoping Hydroguy2 would say how much of a gap he left between the rear of the metal rings and the start of the inlet tubes. I'm thinking 3/4" would allow movement with out the fear of the neoprene flexible seal not holding the pressure.


Did I mention that fibreglass is not my favorite medium to work with?

Terry.

I didn't extend the snouts of the plenum. The gap between the polished intake rings and the plenum snout is just a hair under 2". The thick wetsuit/foam material Sam furnishes for the "ducts" worked well, and are still fine after a year and 110 hrs. No plans to change them at this time.

I looked for pics of the front of my plenum install at the engine case and alas, found none. Won't be able to take any for another week or so.

terry.mortimore said:

...

...

Click to expand...

I would drill out those blast deflectors and make them removable so you can trim them later, if needed.

I also have about a 2" gap.

No problems after 230hrs. I do check the clamps often as one slipped off once.

Hey Guys,

Keep the posts coming, I'm learning something with each one.

And Dan, I understand that would be a problem, would you happen to have a website where your build is documented?

Glenn

I'm pulling a blank. What do yellow cylinder fins mean? +20?

chart

See post #2.

http://www.homebuiltairplanes.com/f...l-system/174-mystery-solved-engine-codes.html

glenn654 said:

And Dan, I understand that would be a problem, would you happen to have a website where your build is documented?

Click to expand...

Sure...VAF. Seriously, I posted a lot of content here over the years.

This is the original setup to form the plenum lid and male molds for the rubber intake ducts. The basic plenum lid was just a 4-ply layup over the taped yellow foam:



The ducts got their own thread.
http://www.vansairforce.com/community/showthread.php?t=43391

Later the plenum lid got the front flange, additional flanges at the front corners, and an oil cooler supply duct. The corner flanges tie the lid directly to the #1 and #2 cylinder ears with 1/4-20 screws. The duct supplies a remote oil cooler without preheating the air 15 degrees before it gets there. It also stiffens the lid a lot. The black part with the flange is installed in the rear baffle wall. The duct plugs into it when the lid goes on.



The holes for the 1/4-20's are not yet drilled in this photo...it's on the way to the airport for fitting:



The cowl started as a fully fitted stock Vans cowl. The easy way to establish the round inlet shape was to cast core rings in a machined nylon mold; two plies of 8.9 oz 8-harness and some wet micro.



With rings in hand it became easy to visualize the new shape and placement using tape, then graft them in.



I didn't absolutely know how to do any of this when I started. It's the creative process which makes it so much fun.

"I would drill out those blast deflectors and make them removable so you can trim them later, if needed."

Excellent point, Bill. I'm still fine tuning my deflectors in front of #1 and #2 to get perfectly even CHT's. All are within 10F now. My deflectors are screwed into the aft end of the plenum intake snouts. I can even remove the L side deflector thru the intake opening!

Rupester said:

"I would drill out those blast deflectors and make them removable so you can trim them later, if needed."

Excellent point, Bill. I'm still fine tuning my deflectors in front of #1 and #2 to get perfectly even CHT's. All are within 10F now. My deflectors are screwed into the aft end of the plenum intake snouts. I can even remove the L side deflector thru the intake opening!

Click to expand...

Good move. I simply replaced the 470 rivets with plate nuts and made the deflectors accordingly. Cap screws are used to hold them in place because they are easier to remove without taking the plenum off. This also allows those who live in very cold climates to make different deflectors for the different seasons. Simple and easy modification.

aerhed said:

I'm pulling a blank. What do yellow cylinder fins mean? +20?

Click to expand...

My camera let me down, the paint is Orange. Standard size chrome Superior cylinders.




Terry.

Since we do have such a great source of information on the SJ Cowls, I think that if someone (ones) with the experience and knowledge would set up a step by step procedure, with pictures showing how to best make these installations would be a great benefit for us "newbie" builders.

Since the SJ instructions are quite sparse and make as a "sticky" (not sure that is the right word) so that that thread would be easily accessible anytime.

This I believe this would be a great resource many years since those of us facing this for the first time would not need to ask the same questions over and over.

What to you think?

Glenn Wilkinson

glenn654 said:

Since we do have such a great source of information on the SJ Cowls, I think that if someone (ones) with the experience and knowledge would set up a step by step procedure, with pictures showing how to best make these installations would be a great benefit for us "newbie" builders.

Since the SJ instructions are quite sparse and make as a "sticky" (not sure that is the right word) so that that thread would be easily accessible anytime.

This I believe this would be a great resource many years since those of us facing this for the first time would not need to ask the same questions over and over.

What to you think?

Glenn Wilkinson

Click to expand...

Agreed - please!! I'm just about to tackle putting the James cowl on my 9A (IO360, cold air sump, WW200RV) and I've got WAY more questions than I have answers...

glenn654 said:

Since we do have such a great source of information on the SJ Cowls, I think that if someone (ones) with the experience and knowledge would set up a step by step procedure, with pictures showing how to best make these installations would be a great benefit for us "newbie" builders.

Since the SJ instructions are quite sparse and make as a "sticky" (not sure that is the right word) so that that thread would be easily accessible anytime.

This I believe this would be a great resource many years since those of us facing this for the first time would not need to ask the same questions over and over.

What to you think?

Glenn Wilkinson

Click to expand...

When I did my install I followed one of the mil spec/ sky bolts website instructions. They had a great detailed photo/instructional PDF. Can't remember which?

Found it:

https://m.app.box.com/view_shared/dntsplb9725iz4lzt5ze

Those instructions are on the sky bolt website. They only cover the firewall and side/half connections.

Do a search here ( I am lazy at the moment or would do it for you) for cowl and DanH. Dan has made it simple for all.

None of these really address the plenum and cooling airflow.

One thing - the side split should be parallel to the fuse rail, and intersect the center of the crank (prop, etc). I used the sky bolt instructions as a guide, but regarding spacing there are some others for that here too. On top I have a closer spacing than down the side. If you are going to use SB or MilSpec to connect the halves, then you can make the line down the side intersect with one on the firewall for esthetic value. I used a water tube level to determine the split line intersection on the fuse and spaced the fasteners to match. BTW. To be easy on myself ( lazy) I mounted the engine made all measurements, then removed engine w/mount and installed the firewall perimeter tabs. This is wrong!!

Correction: I located my skybolt positions along the side of the firewall so that the line of fasteners along the cowl split would would exactly match one on the firewall. The cowl line split line intersects the firewall at about 1.25 " HIGHER than parallel to the crank. I called Vans and they said there was no "design" intent for that split, they made a cowl in place, then sent it to a supplier who made a mold. I urge you to just fit the top cowl and then locate the split at the firewall so it is even from side to side. I over thought this and it bit me. I had to remove and relocate the fastener locations along the firewall to make the lines right.

While you are at it, install a tab along the bottom of the fuse for an aero streamliner for cooling air exit. Picts on request.

I am right here with you, I have not begun the actual cowl fitting, just prep.

Question for flying Sam James owners ...

Do any of you see cooler CHTs on the R side than the left? I have my front baffle deflectors perfected now and the R side CHTs are always 10 to 15 F cooler than the left side. I have no differential between F and rear .... Just the 10 to 15(max) difference R to left. It's not a problem for me in any way - my cylinders cool great under all conditions. I'm just curious if anyone else sees the L vs R difference.

Plenum Fitting Help Needed

I decided to add to this thread rather than start a new one. I hope it get some responses.

So, I have fitted the cowl with SB fasteners and glassed the inlet rings. SJ builders, please read below and tell me what you would do or did differently. After rebuilding the back flange, I will cut off the front inlets, make some from styrofoam, and re-glass them to fit properly against the forward heads. Also allow for a gradual expansion of inlet air. I really need some experienced opinions here.

Not addressed yet is the fact that 1/3 of the oil cooler is blocked with the rear at this plenum cover level and I have not formulated the details of how to fix that yet.

The baffles have been trial fitted on side and back, but before getting into the fitting at the front of the engine I searched and studied and even cut out the SJ templates. In order to understand the baffles, I got the Lycoming engine installation drawing and used it to overlay the baffles and understand what the exact dimensions are for the Vans baffles.

To begin - the SJ plenum is a "universal fit", it does not fit anything. I have an early one, but Sam says the new ones are the same. I am not going to argue with him.

Here is a box built with the exact dimensions expected to fit the engine. It is parallel, spark plug locations provide a good datum for fore/aft locations. Inserted is the SJ plenum. There are a couple of dimensions on the plenum that are good, the side span is perfect and parallel, the forward contour fit to the case is pretty good. The back is bad, are the air inlets are bad. Not shown is that the height above the heads is the same as measured at the center of each head (inline with plug 2" above valve covers).

I used the contour and the plug locations to affix the engine. The contour is tight against the from of the case and down as low as it can go. The inside flow area is 2 inches above the top of the valve covers. Meaning, it can not go lower or I runout of cooler flow area and risk possible air flow throttling at the inlet over the front head/cylinders.



Here is the back - and how the original glass does not follow the baffles. it is off in every way. I will cut off the flange and re-glass that.




Here is the left and right view of where the inlet snouts "match" to the forward baffles. There is a significant gap on both sides. The left side inlet is centered with the cowl, the right is 1/2" low. it can not be moved anyway with the other constraints.

Right side -



Left:


EDIT - I did look at HydroGuy's, RonDuren, and Mike Bullocks pictures. Rupsters posts had some good pictures too, but he has a 320. All of these contributed immensely to my understanding. I also looked at ALL pictures on the yahoo SJ group. These are just ill fitting parts, and I would suggest making your own.

Rupester said:

Do any of you see cooler CHTs on the R side than the left? I have my front baffle deflectors perfected now and the R side CHTs are always 10 to 15 F cooler than the left side. I have no differential between F and rear .... Just the 10 to 15(max) difference R to left. It's not a problem for me in any way - my cylinders cool great under all conditions. I'm just curious if anyone else sees the L vs R difference.

Click to expand...

Short or long cowl?

The short cowls struggle with cooling because there is limited space to expand the incoming air prior to hitting the front cylinders.

If I were to do it again, and I may, I would raise the plenum as high as I could on my short plenum.

I have the long cowl. The L to R temp difference makes me wonder if it relates to the way the air corkscrews off the prop. If that were true, others should see the same effect. That distance between prop trailing edge and the intake rings is minimal .... ~2".