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  #1  
Old 03-30-2015, 10:40 AM
Mark Dickens's Avatar
Mark Dickens Mark Dickens is offline
 
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Location: Collierville, TN (KFYE)
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Default RV-8 Cowling Fitment

I'm working on fitting the cowling and started with the upper cowling, which I've positioned to my satisfaction and trimmed to the firewall. I've installed the skybolts and am happy (perhaps because ignorance is bliss) with how it hangs and how it's positioned relative to the spinner backplate (FP prop). I have not yet done any trimming on the horizontal.

The issue is with the bottom cowling, which fits to the upper cowling like high heels fit on a horse. To say that Van's fiberglass work is not up to their aluminum craftsmanship is a vast understatement and an old story. I could not find a way to fit the bottom cowling to the top cowling while mounted on the plane, so I removed it and began working with both cowlings on the shop floor per Dan Horton's recommendation (http://www.vansairforce.com/communit...t.php?p=461049). I have fitted the halves together so that the opening is 13" in diameter and have the back of the cowling matched to the height of the firewall. The inlets are equal in height as well.

Pics of current status:







My questions for the cowling gurus are:

1. Should I go ahead and trim the upper and lower cowling to each other while off the plane? If I don't do that, I don't see how I can match them up on the plane.

2. I am tempted to cut off the overlapping areas of the inner inlet sections because they fit so poorly and were so sloppily made. I'm thinking I can recreate that section later.

Thanks for any thoughts!
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  #2  
Old 03-30-2015, 01:11 PM
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DanH DanH is offline
 
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Mark, you're a bit off track, but hey, it's fiberglass. It's hard to make a mistake that can't be fixed.

From a previous post:

...trim either or both to an imaginary line which exactly bisects a 13" circle.

That means trim before clecoing them together.

Start by marking and trimming the upper cowl. Align a straightedge as shown; 6.5" at the center (half the spinner diameter), while maintaining exactly equal height on the two inlets. Mark at the four red lines. Trim just outside the line (maybe 1/16"), which leaves some room to clean up the edge with a long sanding board. At the outboard cuts, don't try to trim back along the sides of the cowl just yet. Just trim the leading edge of the inlet opening:



Now trial fit to the lower cowl, on the floor, with a spacer stick or two at the rear, and the long sides overlapped. If you're lucky, the lower cowl joggles will match the freshly cut upper cowl. By lucky, I mean won-the-lottery-lucky; you'll probably need to trim or fill to get a match.



BTW, if the joggles need a lot of work, it's easier to just cut them off, trim the lower to match the upper, then add new joggles. To do that, set up and trim the lower cowl nose pretty much as you did the upper. Cleco a temporary scrap joggle any where needed. Plenty of opportunity to fill the cleco holes later in the finishing process.

With the nose trimmed to a pretty good match, align the cowl on the airplane to trim the rear edge and the sides. Attach a steel or aluminum tab to the forward baffle attach points (1/4" screw) above each front cylinder. These support the nose of the upper cowl. The rear is supported by overlapping the boot cowl. Draw a centerline on the top rear center of the cowl. Draw a matching centerline on the top of the boot cowl. Adjust the length of the front supports so the cowl nose is dead behind the spinner and perfectly level. Install a block to set the spinner gap. Align the centerlines at the rear of the cowl. Now trim the rear edge of the cowl so it sits on your hinge line or camloc tabs. The upper cowl is now where it belongs.



Raise the lower cowl into position, install the two front clecos, and run a strap around the halves. Trim the rear edge. Now trim the sides. Start by drawing a level line back from the front of the cowl where you had already established a bisect line in the very beginnning. Trim both halves to this line.

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Last edited by DanH : 08-21-2018 at 06:54 AM.
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  #3  
Old 03-30-2015, 01:33 PM
Mark Dickens's Avatar
Mark Dickens Mark Dickens is offline
 
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Default

Quote:
Originally Posted by DanH View Post
Mark, you're a bit off track, but hey, it's fiberglass. It's hard to make a mistake that can't be fixed.

From a previous post:

...trim either or both to an imaginary line which exactly bisects a 13" circle.

That means trim before clecoing them together.

Start by marking and trimming the upper cowl. Align a straightedge as shown; 6.5" at the center (half the spinner diameter), while maintaining exactly equal height on the two inlets. Mark at the four red lines. Trim just outside the line (maybe 1/16"), which leaves some room to clean up the edge with a long sanding board. At the outboard cuts, don't try to trim back along the sides of the cowl just yet. Just trim the leading edge of the inlet opening:



Now trial fit to the lower cowl, on the floor, with a spacer stick or two at the rear, and the long sides overlapped. If you're lucky, the lower cowl joggles will match the freshly cut upper cowl. By lucky, I mean won-the-lottery-lucky; you'll probably need to trim or fill to get a match.

If the joggles need a lot of work, it's easier to just cut them off, trim the lower to match the upper, then add new joggles. To do that, set up and trim the lower cowl nose pretty much as you did the upper. Cleco a temporary scrap joggle any where needed. Plenty of opportunity to fill the cleco holes later in the finishing process.

With the nose trimmed to a pretty good match, align the cowl on the airplane to trim the rear edge and the sides.
Aha...the part I didn't get earlier is the part about not cutting along the sides yet. Makes sense. I think the light just came on that the first step is getting the inlet portions to decently match and once that's done, you attack the sides and firewall sections.

Dan, THANKS for taking the time to explain this! Very appreciated!
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  #4  
Old 11-20-2018, 10:38 AM
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wjb wjb is offline
 
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Quote:
Originally Posted by DanH View Post

BTW, if the joggles need a lot of work, it's easier to just cut them off, trim the lower to match the upper, then add new joggles. To do that, set up and trim the lower cowl nose pretty much as you did the upper. Cleco a temporary scrap joggle anywhere needed. Plenty of opportunity to fill the cleco holes later in the finishing process.
Just did this with my pink -7 cowl ... Now, it's soo much easier to get everything to fit. I'll add them back later. Great tip, DanH!
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  #5  
Old 06-10-2019, 12:20 PM
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IowaRV9Dreamer IowaRV9Dreamer is offline
 
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Default should I even have "joggles"?

I'm finally trying to fit my RV-9A cowl using the excellent techniques in this thread, but have a noob question. There are much talk of "joggles" which I take to mean a flange on the inside of the lower cowl that lives behind the upper cowl.

I have a pink cowl, and it seems to have no flanges or joggles. My DWG 44 has a section A-A which actually shows removing the flange "TRIM AWAY FLANGE" but I don't think that applies to my cowl.

I'm planning on quarter turn fasteners, which means I'll be adding an aluminum strip to the lower cowl which will act as a joggle, I guess.

So, before I make the big side cut - I just want to be sure: my goal is to have top and bottom both cut such that they touch (or come close), similar to section N-N and P-P in the plans? No Joggle?

Right now, I have the top fitted and attached to the plane, and the bottom is cut on the firewall. It is underlapping the top cowl by maybe 0.5" at the firewall. I'm not sure how I'm going to cut both of these cowls to match. Probably a laser, mark and cut the top, then put it back and mark and cut the bottom to match the top...
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  #6  
Old 08-13-2019, 07:00 AM
Sam_B Sam_B is offline
 
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Location: Boyceville, Wi
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Default Engine sag

Quote:
Adjust the length of the front supports so the cowl nose is dead behind the spinner and perfectly level.
Vans instructions say to allow for 1/8” to 3/16” of engine sag. What are previously built RVs experiencing for how much the engine sags, or is it insignificant and just “line it up” with the spinner?
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  #7  
Old 08-13-2019, 08:15 AM
PhatRV PhatRV is offline
 
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There is a webinar on eaa.org website that mentioned the engine should complete its "sag" after about one month. After one month, the airplane can be readied for painting or things like that. I forgot who was giving the webinar, the owner of Synergy or some airplane painting guy.
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  #8  
Old 08-13-2019, 02:16 PM
Sam_B Sam_B is offline
 
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Does that mean one month of the engine just sitting on the airframe, or does it mean one month of use so the engine “shakes down” to its final sagged position?
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  #9  
Old 08-13-2019, 04:19 PM
DaAV8R DaAV8R is offline
 
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Default Cowl Fit

I've never understood the logic of setting the cowl low in anticipation of the mounts sagging. I figure the thrust line is properly set when installed with 4 new mounts. If/when the engine sags at a later date the thrust line could be re-established with shims at the firewall. While I'm moving at a snails pace over here I can attest to the fact that my engine has been hung for a while (I"m not admitting how long ) with no appreciable change to the cowl/spinner relationship.
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  #10  
Old 08-13-2019, 01:54 PM
scsmith scsmith is offline
 
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Quote:
Originally Posted by Sam_B View Post
Vans instructions say to allow for 1/8” to 3/16” of engine sag. What are previously built RVs experiencing for how much the engine sags, or is it insignificant and just “line it up” with the spinner?
I definitely experienced 3/16" of engine sag on my angle-valve 360. But I was ready for it. I fit the Lord mounts with two large diameter, thin (0.032?) aluminum spacer washers on the top motor mounts. Then I fit the cowl to be about 1/8" low at the spinner, meaning the spinner was 1/8" above the smooth line of the cowl.

Once I was flying, about half way through Phase I, I noticed that the engine had settled enough that the spinner was now just slightly below the cowl line. So I took those spacer washers out. That pulled the engine up just enough that the cowl fit perfectly.

Over time, it has settled a little more, and so I put those thin spacer washers on the lower mounts, once again raising the nose of the engine enough to get a good fit between the spinner and the cowl.

One odd thing I notice with using the quarter-turn fasteners to hold the cowl to the firewall is that they shift around a little bit. Mine are Mil-spec brand. When I have the cowl off and on for oil change or inspection, I find that the cowl sits a little bit high above the line of the spinner. One short run-up and it settles back to where it is supposed to be. I assume the quarter-turn fasteners are settling in within the range of float that they have.
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