August 24, 2014 - 4.5 Hours

Cowling Plans, Decisions, and Getting Started

I'll be honest here, I was not looking forward to working on the cowling. I guess I've read too many builders' web pages and logs, seen the frustrations, and the amount of time they invest. I was not looking forward to a monumental task like that, especially after all the time and work I invested on the canopy project. But one day when I was down at Vans picking up some stuff, I was talking with Ken Scott and he asked me how my project was coming along and where I was at. When I mentioned that I needed to get started on the cowling, he said "oh, the cowling is a cinch!" Well, I guess that's all I needed to hear. So I decided to come home and dive in. It turns out, he was just a bit over-simplistic. Or call it optimistic, or whatever. It actually turns out to be quite a project. But it's really the last major project on the airplane. And it's something other than aluminum. You can look at that as a glass-half-full or glass-half-empty scenario, whichever you wish. I choose to be positive about it. Then, once I dove in, the old enthusiasm comes alive. It's exciting to see things progressing and taking shape!

So the first thing you need to do is make some decisions. How are you going to attach the cowl to the airplane? Using Vans standard hinges-and-pins method? Or something else popular these days, the sky-bolts, or cam-locks? Most of us have had this question on our minds long before we actually jump in and get started. So I'll tell you right up front, I decided a long time ago to go with the standard Vans method, with hinges and pins. There are several reasons I chose this. One, the cost is significantly less. Those cam-locks are expensive! Next, the cam-locks hold things together with a finite number of points around the cowl. And in between each pair, there's space where nothing is holding it together. This works okay from an engineering standpoint, if you do it right. But I've actually been flying in some RV's where you can see the cowling pooched up in between the cam-locks, from the air pressure underneath. It just makes more sense to me to have nearly an infinite number of holding points with a hinge riveted (and mine will also be expoxied or glued) to the cowling halves. But the biggest reason, by far, at least for me, is that I don't like the way they look. The cam-locks, that is. I know they're convenient and all, but nothing ruins a good paint job quite like a cowling that's shot full of holes with all those cam-locks showing. At least, that's how it comes across to me. Many people don't care; and that's perfectly fine. I just don't like the way they look and this is the way I'm going. It's a proven design, with thousands of finished RV's flying with them. So with that in mind, it was time to get started.

I pulled out the manual and read all I could. I studied the drawings. Another decision I made early on was to get some wider hinge stock than what you get in the kit. One thing that irks me about some cowling jobs, is that you can see the hinge eyelets in between the cowl halves if you look close. You're going to have a tiny gap there, and you can see in between. By offsetting the hinge just a bit, you can make it so you'll never see any of those hinge eyelets. You'll see what I mean as we progress here.

Another decision I made somewhat early on, was to use a plenum over the engine baffles, rather than the standard rubber stuff that most people have on top of the baffles, to seal it against the cowl. For a while, I was seriously considering a Sam James Cowl instead of the stock Vans cowling. But I finally chose to stay with Vans. Saved a bunch of money, and while I really like the look of the Sam James Cowl, especially the round intake rings in front, spending the extra money for that just didn't seem worth it to me in the long run. So here I am. But during all that decision-making, I learned a lot about the plenum and I'm really excited about it. I believe I'll get it to seal better, take pressure off the top of the cowl, and ultimately get more efficient cooling of the engine. More on that theory later. Time will tell. We'll see. But that's what I'm doing. What sealed the deal for me, was when I met a guy down in Independence, Oregon, who is an expert in fiberglass, painting, and he's done a lot of work with Lance-Airs, Glass-Airs, and RV's, too. He strongly recommended the plenum and he made a mold to use to make plenum blanks! So for not too much money, he made a very nice plenum blank for me. (He can make one for you, too!) As I said, I'm excited about it! Stay tuned, and you'll see the process as it all comes together for me.

Now, it's time to get going! It all starts with the hinges that are riveted to the firewall, across the top. I clecoed the top forward skin on, just to make sure things were where they're supposed to be, and then proceeded to clamp, drill, and cleco the hinge pieces on. You have to study the drawings carefully to get the right size hinge material. This is different, for example, from the hinge material that goes horizontally along the sides between the top and bottom halves. These cleco clamps came in very handy for this job, and you can see that I started on the left side and worked my way up to the top.

A little while later, I'm working my across the top. I should mention, there's an .020" spacer strip that goes in between the hinge and the flange on the firewall, so don't forget that! The holes you drill may not line up as precisely as they should if you try and do it later.

Here's a close-up of the drilling and clecoing operation. I used every clamp in my toolbox, to make sure this was as tight-fitting and good as possible.

Finally, I'm working my way down across the other side, on the right side. You can see a gap just to the right of the last clamp. You need this gap to be able to insert and remove the hinge pins. The plans detail how to make this and where to put it. Now, for a detail item. I've looked at a lot of cowls, and you can see this gap from the outside of the cowl if you look close between the gap. I decided to go ahead and continue with the .020" spacer strip through this gap area, and have it extend out beyond the firwall flange just a bit. This is so that the cowl gap will not show here with the cowling in place, and you won't see it! It also serves the purpose of not letting any air escape there either, giving you a better seal.

After this comes the usual work... undo everything, deburr, dimple, scuff, clean, and prime everything. It's very tempting at that point to rivet things together, as you've been doing the whole time on this airplane. But you can't to it yet, unless all of your wiring is finished under that top skin! And mine is far from finished... so no riveting for now.

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