RV-7 Cowl , slider was too easy, guess this is payback

Where did you start the cowl installation, Top first or Bottom first.

Vans suggests connecting the two halves at the front as step one. Problem with this ( if you check the picture where the halves connect, at the spinner end) the two halves are not parallel.

There are no trim lines moulded into the top half, as suggested by Van's. Without a reference point from which to make measurements a had to assume the top half was already cut to size.

You will also notice the huge difference cowl to spinner spacing between the top and bottom halves.

Not a very well written thread, still a little frustrated. If you can make sense of this thread then please explain your installation sequence

http://i44.tinypic.com/1kx3q.jpg


Regards Peter

Peter, My cowl looks this bad also. Mine also has a twist in it that I'm undecided on how to take care of it. On yours, if it's otherwise okay, I'd split the top cowl vertically, about an inch behind the spinner. Cut it to within an inch or two from the top and move that cut portion foward and parallel with the spinner back plate. The cut will be easy to repair and fill in. This will also alow you to move the bottom cowl fowards. It looks to already be parallel with the spinner backplate. You will need to do the same with the outside portions of the cowl, moving the top cowl foward or the bottom one back. Even a combination of the two. It's a real piece of garbage in my opinion. Left me wondering how difficult and expensive it woud be to change to a Sam James cowling.
It's not a difficult fix, just another pain in the tail feathers.

top

Do the front first, as Van's suggests. The reference is the circle behind the prop spinner - get that round (circular) by trimming the flanges as necessary. Van's instructions work pretty well, once the circle is round, draw a reference line 2" or a bit more back from the front edge of the top skin along the front of the top skin, place the top skin in position the right distance back from the spinner, (I locked it in position with a bit of angle clecoed to the top of the top cowl and the the spinner bulkhead), mark the cut line on the rear of the cowl using the reference line you made on the skin,...it is slow and iterative. I also found the front face of the cowl was not parallel to the sinner rear bulkhead - but it seems to get better as the installation progressed. If still too much, it is glass and can be added to or sanded away.
Make sure the top skin is level across the front -I used a laser level horizontal line to the outer front edges, I don't think you can rely on the air intakes each side of the spinner to be exactly level and symmetrical. Then drill and cleco the top cowl to the firewall top and bottom. It becomes very solid and firm at this point.
The start on the bottom.....
Bill Brooks
Ottawa Canada
RV-6A finishing kit

Peter,
Bill is spot on with the overall instructions on how to do this. In your case though, like mine, you'll need to also repair the front piece. Dan Horton posted an excellent set of instructions to the forum. Find those and you'll be golden. He also posted great instructions on cutting out the cowl inlets completely and reforming them with round 'Piper' or "sam James" style inlets; very COOL!

Bill, Carl, thanks for the quick responses. You can see the wedge at the front where the two halves connect when they are positioned temporarily on the airframe.

I suppose I could just use one cleco at the very front to allow the two halves to maintain the wedge shape while clecoing the halves together as Vans suggests in step one. Is this what you did ?

Looks like I should correct the top cowl by doing the vertical split you suggest Carl, before clecoing it to the bottom cowl otherwise I will need a lot of fill to move the bottom half to the 1/4" spacing.

I notice that the split line, as defined by the bottom edge of the top cowl, is not parallel to the fuselage longeron ( right angles to the firewall), same for you?

I'll see if I can locate my copy of the instructions that Dan wrote. I couldn't find them on the forum.
Use a thin plywood disc the diameter of the rear of the spinner that you can mount to the engine hub to attach the cowl at the front. Make your rough cuts per Van's instructions. Make your vertical cut on the front of the cowl so the plywood lays flat and doesn't distort the cowl. Then using a LONG board with 80 grit paper glued to it sand the mating surfaced perfectly straight. Sneak up on mating them together. Rough cut the back and sneak up un fitting that, sanding with the long board. Be careful, the front of the fuselage isn't one straight line. Be patient and don't worry if you mess up. It can all be fixed. Unlike with the aluminum, you can add fiberglass back onto anything that was cut, ground or drilled away.

I mostly agree with the approach suggested by Dan in his link. The pink cowls seem to be all over the place in terms of fit. My lower cowl was easy to deal with; my upper cowl was so bad that, were I to do it over, I would have returned it for another. Not only did the spinner area slope forward, but there was a big flat spot on the pilot's side that I had to fill, and the upper/lower flange interface was so far out that it wasn't possible to force the top and bottom together without risking cracking something. A local friend's upper cowl matches his lower nicely, right out of the box. Go figure.

I fit the lower cowl to the fuselage first. With the square bottom corners of the side by side RV's, the corners naturally locate the cowl. Then it's a matter of sliding it fore/aft and, at the spinner, up/down to get the position right. After that, the plans approach to locating and marking the cut line at the firewall works well, or at least it did for me.

I posted a bunch of pictures here. You can see how I had to nearly detach the spinner interface on the upper cowl to get it to fit correctly. I initially clamped the upper and lower cowls together with a circular 13" diameter (same size as the spinner) plywood disc, drilling through disc and cowl and using clecos. With the halves joined that way, the top to bottom measurement at the aft end of the cowl was considerably less than the height of the firewall. That's when I broke out the die grinder with cutoff wheel and started hacking. When all the (fiberglass and epoxy) dust settled, it fit very nicely.

Oh yeah; a heat gun was one of the tools I used, along with die grinder, files, fillers, glass cloth, epoxy and lots of sanding. I should be annoyed looking back at the experience, but I'm not. I learned a ton about glass work.

Dan, thanks for the info. I believe I will do it exactly the way you suggest.

To take care of the foreward lean of the top cowl at the spinner, I will cut a wedge starting at the top of the cowl a push it back and use the wood disk in your picture to help alignment while I glass it in.

The bottom cowl is already parallel to the spinner.

No one commented about the split line not being at right angles to the firewall, cant see any option here.

Cant remember the RV6 with the old white cowl being this bad

Thanks for all the help folks

Peter

WOW, you guys are equally skilled in plastic as you are in aluminum!

Nice work!

I have my cowling to do soon and this information is quite timely for me. Thanks in advance!

I hope my skill set will come up to a level so that I can be HALF as good as you guys!

CJ

My cowling sequence. I produced a series of videos called the Cowling Chronicles as I navigated my way through the process. It's a series of head-scratches, basically. I haven't done the last one yet, but the cowling turned out fine. So maybe these will walk you through the process a little bit.

Episode One
Episode Two
Episode Three
Episode Four

petersb said:

To take care of the foreward lean of the top cowl at the spinner, I will cut a wedge starting at the top of the cowl a push it back and use the wood disk in your picture to help alignment while I glass it in.

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I'd do the flat behind the spinner last, after all other cutting and fitting is complete, including the firewall attachment and side seams. Until then it will keep changing. And it may be easier to add micro to the low flange rather than cut and move the high flange.

No one commented about the split line not being at right angles to the firewall, cant see any option here.

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That angle will also change a little. For now don't worry about it too much. Search "scarf joint". You can always scarf on some additional glass and sand to change the angle. Again, that's detailing for after you have mated the parts to each other and the airplane.

Don't forget to work the front side of the lower cowl flange and the rear side of the upper cowl overlap so they nest nicely. You see a lot of those with lumps and poor fit holding them apart.

Remember, you're working to an imaginary split line; there's nothing to say the molded flange is in the right place. You can move the inset on the lower cowl flange just as well as you can lengthen or shorten the overlap. Just add glass to the back side so you have enough material thickness, cut the new flange location with a square edge sanding stick or a vixen file, then radius the edges and sand away any excess glass.

Cowl Tool

See my post on Cowl Tool,, in the fiberglass section. that might help

Thanks Dan. Searched for your original posting for an hour and couldn't find it. Probably "operator error"!
You are certainly correct that things will keep moving around. I found that getting everything "close" but a little oversized; relieving the distorted parts with the appropriate cuts; then sneaking up on the final fit worked the best for me. I was amazed at how much a little change on one side would so much affect the other side. Your posting was instrumental in getting me thru - THANKS!
Too bad that these layups are such garbage.

ColoCardinal said:

Thanks Dan. Searched for your original posting for an hour and couldn't find it. Probably "operator error"!

Click to expand...

I always had the same trouble until one morning Doug pointed out the "Search By User Name" feature in Advanced Search. Put search words in the left frame and a particular user name in the right frame.

Too bad that these layups are such garbage.

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They're not so bad. Somebody supplied the glass contractor with a finished cowl, they pulled molds from it, and we all get a faithful copy. So, maybe the shape isn't perfect but the actual layup fabrication (the honeycomb, foam, and fabric, the bagging and cure, etc) is pretty good.

You wouldn't have any joy of accomplishment if it all just bolted together like a Christmas bicycle. And there's a learning curve. You might be shocked to see how fast somebody like Jay can trim and hang a cowl.

Dan,
I will admit that you're right about it being more fun than putting together the Christmas bicycle. It's certainly educational and that's a good part of why we're doing this. I'm certain that it would take me less than half the time to fit another cowl but don't think I want to find out.
It has given me some ideas of things I could make that I never would have thought of before this experience.

Hi Peter-
The advice above seems pretty good, so I don't have much to add, except:
1. You really have to start doing before you fully understand. Kind of a catch-22, but seemed to be true in my case. Eventually, it all makes sense.
2. Make sure you pay attention to the cowl to spinner gap distance. I originally used a 1/4" spacer (because that's the gap I wanted). However, I ended up with a closer-than-desired 1/8" somehow. If I eventually get fed up with how hard it is to get the cowl on and off, I may do what Dan suggests and build up the inside of the cowl so that I can sand off some the exterior. I'm not the artist that Dan is with fiberglass, however, so I'll wait at least until just before painting to do that, if its still an issue to me.
Good luck.