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James cowl help needed

dwranda

Well Known Member
I'm trying to decipher the first page of the James cowl instructions. From what I can figure out they want you to figure out the midpoint line of the cowl openings then use those lines to cut/file down the front so it is all in a nice level line. Then you attach that lower cowl to the plane and trim the upper cowl so it matches up. Is that right?
My issue is that I can't make a nice straight line across the midpoint of the openings because there are points in the fiberglass that are already lower than that line. The first pic shows a big view of the situation and the 2nd pic is a close up of the trouble spot. I can cut/file the front down so I have a line even with that low spot but as you can see the line would be at least 1/4" below those midpoint lines. I'm not sure if the upper cowl has enough material to match up with the lower cowl if I cut that much off. How do I proceed?
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The cut has to be at the mid point so the rings fit correctly and will be removable. Looks like you will have to build the low spot with fresh FG to make it work.
 
The key thing here is that both halves are right at 180 degrees of material - the inlet rings will need to slip in/out freely from both the bottom and the top, so you'll need to work the fiberglass (add/remove as needed) to achieve that.
 
I made a 1/4" plywood disc with an ID hole to match the crank guide, and OD to match the spinner. That was used to see how much could be trimmed to make the front edges of the cowl fit together relative to that disc. Later it was installed on the crank for positioning the front while come clecos were used to attach at the firewall. Fore aft etc etc. When doing the front, sitting on the floor with nose up, the sides will over lap. It is a progressive fitting process. Alignment holes were drilled in the disc and after a couple of adjustments, were used (clecos) to align the upper/lower every time it was reinstalled to the FW in the fitting process to the very end.

I remember very little trimming, very, very little. I used sandpaper on a long board to do the "trimming"
 
"How do I proceed? "

"How do I proceed? " I think SJ might like to see what he sent you to work with.

The next one might be a touch closer.
 
Here's another question. On this same lower cowl there are these spider web looking areas. It almost looks like something hit it and cracked the fiberglass causing it to look like shattered glass. There are a bunch of these all over it. There are none on the top cowl piece. Is this defective or normal. I have never worked with fiberglass before so just learning. Just counted how many there are on the bottom. 18!
Thanks!
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When you mount the plenum, mount it as high as you can to give the air a chance to expand and slow down.
 
When you mount the plenum, mount it as high as you can to give the air a chance to expand and slow down.

But not QUITE so high that the plenum rubs on the cowling, as mine does just ever so slightly. :rolleyes:
 
Here's another question. On this same lower cowl there are these spider web looking areas. It almost looks like something hit it and cracked the fiberglass causing it to look like shattered glass.

Take a really close look. Any actual cracks in the surface? If not, you're probably looking at the mirror image of surface defects (gelcoat cracks) in the mold.

Adding glass:

http://www.vansairforce.com/community/showpost.php?p=167693&postcount=14

http://www.vansairforce.com/community/showthread.php?p=620170&highlight=scarf#post620170
 
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David,
I would do what Bill said above.
The spinner is the matching point.
You CUT the inlets after everything else is done.

Try going edge point to edge point. Level that and
Fit bottom cowl.
Then match top. Spinner first.

It will come together and look great. Just
Seems a little backwards.

Boomer
 
One other thing I did was to cut the front of the plenum off, slathered the front of the engine with petroleum jelly, and fiberglassed the plenum to the engine so I had a perfect fit.
 
I made a 1/4" plywood disc with an ID hole to match the crank guide, and OD to match the spinner. That was used to see how much could be trimmed to make the front edges of the cowl fit together relative to that disc. Later it was installed on the crank for positioning the front while come clecos were used to attach at the firewall. Fore aft etc etc. When doing the front, sitting on the floor with nose up, the sides will over lap. It is a progressive fitting process. Alignment holes were drilled in the disc and after a couple of adjustments, were used (clecos) to align the upper/lower every time it was reinstalled to the FW in the fitting process to the very end.

I remember very little trimming, very, very little. I used sandpaper on a long board to do the "trimming"

Did you actually trim/sand the front to match the plywood disk before mounting the cowl on the plane?
 
Flyboy accessories cowling installation tool

Has anybody used the flyboy accessories cowling installation tool to fit up a S.J. cowling?

Mark
 
Some of them I can feel with my fingernail. There are definitely ridges.

As Dan said, if it got an interior mold, it could be an issue with the mold. It also could have been vacuum bagged on the interior and the ridges are from wrinkles in the plastic. If it were a crack, their wouldn't likely be ridges.

Larry
 
Could someone post some super close up pics of their aluminum rings and how they should look when completed? Is the outer aluminum edge even with the fiberglass?
 
Did you actually trim/sand the front to match the plywood disk before mounting the cowl on the plane?

Yes, also consider the inlet rings, too. Check them as you sand down to fit the cowl edges and be sure they are even side to side. The edges at the rings end up pretty sharp, not rounded to the air entry, more squarish. Mine did not align perfectly and used a long sanding board to square it to the upper/lower cowl and airstream. That surface also became the datum for ring alignment when bedding the flox behind it.

I'll take a pict today of the finished inlet ring(s).
 
As Dan said, if it got an interior mold, it could be an issue with the mold. It also could have been vacuum bagged on the interior and the ridges are from wrinkles in the plastic. If it were a crack, their wouldn't likely be ridges.

Larry

It is made from a mold for hand layup. When last I saw the molds, Will had them perfect. With Wills failing health, they were shipped back to Florida and likely (apparently) incurred some damage. Post cure damage would yield some white lines too. . . . . and no ridges.
 
This is all fantastic stuff guys!! Thanks for the help. I'm feeling a little more confident now. Keep it coming if anyone has anything else. On another note I think James also sent me the wrong air inlet ring. It seems way too big for that small lower hole. I will be calling them today. Yesterday I was kind of regretting getting this cowl vs the standard one. Hopefully today goes better!!
 
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Progress so far copying the Dan H photos. I've got the center circle a perfect 13" but the outer ones are still 1/4" to 3/8" too big. I sanded the top cowl straight across and if I keep sanding to get the outer circles right, the center one will be less than 13. Opinions?
 
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Progress so far copying the Dan H photos. I've got the center circle a perfect 13" but the outer ones are still 1/4" to 3/8" too big. I sanded the top cowl straight across and if I keep sanding to get the outer circles right, the center one will be less than 13. Opinions?

Please show or sketch what your reference points are for saying the inlets are off.
 
Well I went out to take a pic of what I was talking about and decided to sand a little more. I guess I got the outer holes close enough to 5 1/4. It's hard to fully tell when the sides are overlapping and things aren't lined up perfectly though. I think I'm ready to move on to the next step!
 
Fiberglass

Hey Dave, if you need any advice fiberglassing give me a call. Also, those "spider" marks you mentioned do indeed look like vacuum bag wrinkles and are most likely cosmetic. You can probably just fill with thickened epoxy and smooth.

I'm also planning on a SJ cowl so you better get this figured out! - :D
 
Define the intake diameter

I just went through this delimma. The intake opening is nebulus with regard to diameter due imperfections in resin/glass. It looks like your ? horizontal centerline? can be moved more toward the outer surface of the cowl . As stated above, the bottom line is a ? fit? to the aluminum ring bearing surface. As Dan says, the rest is just glass and subjective symetry.
 
Thanks Tom. Finally got the skybolts where they need to be around the firewall. Next is the skybolts on the seam. Hopefully they turn out alright.
As far as the cowl goes I am disappointed in the quality. The halves didn't line up very well together and there was hardly any overlap near the front. I ended up cutting one side too much(my mistake) so now I have to add some back on. This is my first plane but I had one builder tell me these cowls were a work of art. Mine wasn't. The upper cowl maybe but the lower not even close.
I also think they sent me the wrong metal inlet ring for that lower hole so I need to contact them about that.
 
One other tip

After you fit the cowling together, you will run either a hinge or brackets for quarter turn fasteners up the side but they will not make it all the way up to the round opening.

Fiberglass in a lip on the bottom section, that sticks up and behind the top section, from the end of the hinge or quarter turn fastener supports to the round opening.

This will help prevent air from entering the low pressure side (bottom) of the cowl and when you paint your cowl, it will get painted a well and help hide the black line from the cowl split.
 
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