M-19 Cowling
Engine Cowling Construction
Updated May 4, 2008
Here's the airframe moved to its new home, our garage in San Antonio, TX. I had hoped to have a workshop or a hangar by now, but no joy... so we keep on working with 1/2 of a 2-car garage. The airplane was moved out of storage on October 4, 2003... exactly 5 years to the day after starting this project. In this photo, I've started fitting the foam pieces to build the engine cowling. The starting point was to get a nose piece the size and shape of the prototype's (about 7"x10") cut out of plywood, bolted to the prop flange, and a corresponding foam nose piece attached. Then the top piece was rough-shaped and fitted, during which I discovered some interference with the engine oil filler/breather cap and one or two other things.
A little better view of the top piece. Simple, single curve.
Side view of the pieces as they fit. My engine mount is longer than stock due to the magneto on the rear, but it doesn't look too bad with the slightly longer nose (3" longer than stock). Weight and balance will be calculated and adjusted accordingly.
Starboard side pieces fitted. The process involves slowly measuring, trimming, and rough-fitting in place, then mixing up some 5-minute epoxy and gluing into place. Hot glue could be used instead. Duct tape around the nose of the fuselage at the firewall will prevent the fiberglass cowling layups from sticking to the fuselage..
Starboard side view, showing the bottom piece fitted. The bottom piece is nearly a straight, flat piece so should be fairly easy to glass (fingers crossed!) The aft line of the bottom of the cowling should fair right into the belly panel of the airplane, which is not installed yet.
This is a head-on view of the cowling, and don't worry if things look out of whack. Remember that all the square edges get sanded to a round shape, and everything should get trued up if my eyes work right. I'm thinking of adding a small opening in the nose piece right below the prop hub, to let some blast air hit the oil pump and ventilate the cowling in general.
My idea is to create a carb air intake like the one on this Super Cub. Whattya think?
Port side, with panels rough fitted. Note that I've added a piece of foam on top, from which I'll create a 'blister' to clear the oil breather/filler cap. I think I'll include the blister in a hinged access door to allow access to the filler and dipstick.
And here's the assembly after shooting all the cracks, gaps, and holes with expanding "Great Stuff" urethane foam. It really dries hard! Sanding is next...
Here's what it looks like after knocking off the hard edges and most of the gooshed-out white foam. The blister on top is pretty well smoothed into its final shape, most of the corners and edges are symmetrical (but not all!), and it's starting to look like something. Keep that Shop-Vac handy for all the sanding dust!
A head-on shot with the intake manifold and carb installed show a few things. For one, nothing seems to be working out as far as symmetry. Note that the bottom edge of the cowling is not square with the bottom of the firewall, the nose piece is not square, the top edge of the cowling is out of square a little bit, the carb isn't exactly centered on the cowling centerline, and so forth. But this is the beauty of foam: you just sand things till they get squared up or add some more foam to build it back out. In my case, you just shrug and keep going ;o) Actually, I'll be adding a piece to the bottom to take care of the worst of it, but the rest will sand out. Note also where I'll be adding an air intake right under the prop hub.
Side shot shows where the cowling part line will be (some of it, anyway), and also shows that the carb really hangs out there. But I'll have my oil cooler mounted aft of the carb so the cowling will have to be at least that deep to 'swallow' the oil cooler. And my carb heat air box will have an offset outlet to the carb, allowing me to tuck the box up against the underside of the cowling. You'll see as the work develops in the weeks to come.
This view shows that the edges are starting to soften up, although I'm not using radii as large as Marvin's because I didn't build the foam up thick enough in the corners and I'll sand through if I round off the corners too much. Anyway, this view also shows the top blister for the oil breather/filler and my idea of where the access door will go for the filler and dipstick. Two camlocs will hold the door in place and a short piece of piano hinge along the back edge of the blister will allow it to swing out.
Here's the oil cooler mounted on the lower edge of the firewall. The connections are on top, so it hooks up nicely. It's a 10"x4" size cooler (VW aftermarket). Mounted on two 1/4" studs with some aluminum angle stiffeners and all-metal locknuts. This is the last piece needed in place before I can start figuring out what the 'chin' will shape up to be. It's got to enclose the intake, carb heat box, carb, and fair into the oil cooler.
I fabricated a carb heat plenum out of cardboard to see how things were going to fit. Black part on the front is a cardboard representation of what the air filter will fit like.
Here's the mockup from the port side. I will relocate the overboard "dump" outlet from the carb heat box to the other side so it won't interfere with the linkage operation. It is the aftmost outlet on the top of the box. The hole on the forward side is the heated air inlet from the exhaust stack muff. And all of this, including the carb, will be inside a 'chin' under the cowling.
Here's what it looks like after finishing the rough-shaping of the underside and "chin". I laid on the drywall mud pretty thick and it's drying in this photo. Once dry, I'll sand it smooth and apply touch-up to any low spots or voids, then sand that, then apply a couple of layers of paste wax in preparation for laying up fiberglass.
Here's the cowling after a couple of sessions of filling and sanding. Since the layup will go on over this, it isn't essential that the surface be perfect but it helps. Also, resin from the layup will get in cracks and crevices and make it harder to pop the finished cowling from the plug, but any remnants can be removed later using a Dremel or sandpaper. I just got tired of filling and sanding so I proceeded to the next step, which was the application of a couple of coats of enamel. I had yellow on hand so I used it. I marked the part lines with a black magic marker so I could see them through the finished layup later.
View of the front, showing the part line, cutout for the prop hub, and top blister for the oil filler.
View of the underside chin, air inlet, and the air outlet past the oil cooler. We'll see how well it works once the engine is ready to run. And yes, I know- there are some little imperfections and everything isn't quite symmetrical.
Hard to see what this is because I have laid out my glass cloth and plastic patterns on a sheet of plywood that has a white and grey patterned Formica on it, but basically just showing that I've removed the plastic patterns after fitting them around the cowling plug, then started cutting cloth using the patterns. They will also be used for the layup later. More to follow.
So, if you're not building yet.......why not??
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