More Cowl Confusion

[scotttro]

I’m working on my Waiex’s cowl, and I think I’m confused. Or maybe not. I dunno, I’m confused. I’m hung up on how the plane of the forward fuselage side panels extend to the plane of the side of the cowl. Looking at the plans, the flat of the fuselage side panels are supposed to continue on to the flat of the side of the cowl with a constant taper. But when I attach the front of the cowl to the alignment spacer, the flat side of the cowl doesn’t match the fuselage side panel - not even close. I made a sketch showing what I’m talking about -

When I saw the problem, the first thing I did was take a critical look at the cowl itself. I noticed for the first time that, when I laid it on the table centerline down, the flat that’s supposed to line up with the fuselage side panel was parallel to the centerline. No taper at all, though when completed that surface is supposed to taper at about 4-1/2 degrees. Basically, the front of the cowl is about 1-1/2 inches too wide, given the curve of the “cheeks” outboard the cooling openings.

Lest you think I have the motor out of alignment, both sides do it about the same, though I’ve thrashed around with the left side the most.

I’ve gone around and around about this in my head for a few days now, and frankly I’m stumped. The only cure I’ve come up with is to cut a wedge out of the whole thing to bring the “cheeks” in so I can match everything up. But that’d be a handful of fiberglass work, and I *hate* fiberglass work.

Suggestions?

[pappas]

I finished my Waiex B in 2019 and the forward fuselage maintains the same width from the pilot's shoulders to the firewall. From the firewall to the nose there is a slight compound taper.

If I recall, when I built my first Waiex Legacy model in 2006, there is a constant taper from the pilot's shoulders all the way to the nose of the cowl.
I think you are seeing exactly what you are supposed to have.

[Rynoth]

Scottro,

My inclination is to say: don't worry about it. My guess is that most if not all of the stock legacy cowlings have a similar shape of not following the taper shown in the plans 3-view drawing. The forward width of the cowling is pretty much set in the kit-provided cowling, and it definitely doesn't follow the same "taper line" as the fwd fuselage side panels.

This is the best pic I could find from my build showing how the side of my cowling lined up with the side panels:



It may be hard to tell from the pic, but the sides of my cowling are definitely more aligned with the longitudinal axis of the aircraft than the fwd fuselage side panels. Honestly, a bit more room under the cowling has proven to be a boon for me as I've stuffed it pretty full at this point.

EDIT: Just found another pic that might also show what I'm talking about. The "cheeks" of my cowling definitely don't taper along the same plane as the side panels.

[sonex892.]

With the A model there were a few different cowls supplied. Jabiru, Aerovee using blisters, and universal. The universal is quite a bit wider maybe 2 or 3 inches, it's now standard for the aerovee. The Jabiru cowl follows roughly the same line as the forward fuselage.

I modified a universal cowl to make it a similar width as the Jabiru cowl. I modified it to get the sides to follow the forward fuselage line and reduce flat plate area. These were the initial cut lines to set the width.

The final shape

Steve
Sonex 892

[Rynoth]

Nice post/pics Steve, the kit I received had the Universal cowl, and I have an Aerovee. To the OP, I'd say the decision is up to you. The cowling very much a custom-fit and it's still going to fly regardless.

[Area 51%]

If you trim your cowl to match the taper of the forward fuselage, get ready to cut holes in the sides to clear the valve covers. Find someone with a factory horizontal (Legacy) cowl and you'll see the sides are almost parallel.

The one dimension that's missing on the print, that probably would make the vertically split cowl easier to fit, would be the distance between the inlets. I have both vertical and horizontal cowls in the shop. If you nest the vertical cowl halves in one of the horizontal halves, it really tells a tale of how badly the verticals can be trimmed from the factory. Using the factory cuts as a starting point is probably why so many have had issues with puckers.

With the outlets matched up, there is 3/4 to 1in gap at the front, with the halves overlapping at the rear.

I have a picture if anyone cares to see it.

[Bryan Cotton]

I agree with Ryan. Don't over think this. My cowl flares out a little too.

[MichaelFarley56]

There have been several cowlings produced over the years. Originally, the cowling was designed for the Jabiru engine options and those follow the same line as the forward fuselage sides when looked at from the front. Unfortunately the VW engines are wider, so in order to fit an AeroVee under that cowling, builders had to graft cowling blisters onto the sides of the cowling.

Later, a “universal” cowling became the standard that is wider and thus allows the AeroVee to fit without the blisters. The final legacy cowling, the “horizontal split” cowling is the same “universal” size and all engines should fit under them.

My Waiex flew for the first 7 years with the universal cowling and I was glad to have the extra room. I would encourage the original poster to do the same and make it easier on yourself; it will work just fine!!

Good luck...cowlings can be a test of patience to fit. Take your time on it!

[NWade]

Also: remember that frontal area is going to be based on the fuselage at its widest point, which is at the forward end of the turtledeck and not at the cowling or firewall.

—Noel

[scotttro]

To follow up, I sent an email to Kerry who in reply suggested that the drawings do, indeed, show non-tapered plan views. Sure enough, looking at more than just B01 it seems there are, indeed, drawings with non-tapered sides. (In my defense, there are 6 that show tapered, and 4 that show parallel). P11 however is the one that differentiates them as "Aerovee" (parallel sides) versus "Jabiru" (tapered sides). Sadly, I hadn't truly studied P11 in as much detail as I should have - one of those situations where you look but don't see. Thanks for the assistance everyone (and especially Bryan Cotton who sent several P.M.s outlining the entire process in excruciating detail).