Archive for June, 2011

Plenum Progress

Here’s a bird’s-eye view of the new plenum pieces painted and installed. I’m very happy with how they turned out. Now it’s just a matter of connecting the dots–joining the original plenum with the new pieces by fabricating a fiberglass lid.

Once again my good friend Phil came to my aid with my fiberglass work. He’s got more fiberglass experience and tools than any sane person ought to have. Using Phil’s equipment and expertise, we made a vacuum-bagged layup consisting of 2 layers of cloth, a 1/8″ layer of foam and another 2 layers of cloth. To complete the vacuum bagging package, we laid on a layer of peel ply and then a layer of breather cloth. The whole mess then goes into an airtight bag and a vacuum is drawn.

This little pump supplied the vacuum. We placed the whole package on the top of my engine with bags of lead shot to hold everything down nice and tight against the existing plenum and my new metal pieces. It took about 6 hours to cure to the point where I could remove the vacuum. I left the weights and everything else in place until the next morning.

I was back at it again first thing Saturday morning. This is what it looked like as I started pulling the peel ply and breather cloth off the cured part. The gold color is the foam core as the 2 layers of fiberglass are pretty much transparent once all the excess resin is sucked out. The piece is surprisingly light.

I laid the piece back on the engine to get a feel for just how much I’d have to trim. It fit surprisingly well, but will obviously need to be trimmed.

With the front-to-back trimming complete, I next marked strips along each side. I’ll use a Dremel tool with a small cut-off wheel to carefully remove the first two layers of fiberglass from the strips along the edge. This will allow the fiberglass, without the foam core, to rest on my new metal flanges.

Once the first two layers of fiberglass were removed, I just had to scrape the foam core out to leave the remaining 2 layers of glass exposed. This wasn’t a difficult process.

To finish the flange, I used a Dremel tool with a cone-shaped grinding tool to grind a 45 degree bevel in at the edge of the remaining foam core along the length of the flange. Even using the vacuum process, it’s easier to get fiberglass cloth to lay down over something less than a sharp 90 degree angle. After the bevel was cut, I applied another 2 layers of cloth tape along the flange so that the finished flange is 4 layers thick. 4 layers of cloth wouldn’t be enough for the entire plenum (without the foam core), but it’ll work well for the flange.

I drilled and clecoed the new fiberglass piece in place. I laid the blue tape on a flat surface and made my marks for the holes so they’d be equally spaced. It’s tough to determine the spacing on a curved surface so the tape works well. I drilled through the new plenum and into the flanges of my new baffle pieces. I also drilled and clecoed a few holes through the new plenum into my old plenum pieces.

I took the entire plenum off as a single piece. My plan is to remove 2 layers of cloth and the foam core where the new piece will mesh with the old plenum halves. This should make it easier to graft the new piece to the old pieces and create an invisible transition so that the entire plenum will be a single piece. Obviously there are some openings in the corners that I’ll have to address with additional wet layups.

More cooling issues

Looks like I did the victory dance a little early with my cooling issues. When I went out to fly my plane in 74 degree temps, the oil temperature went straight past redline. I landed as quickly as I could to prevent any damage. I’m convinced that the oil cooler isn’t doing much at all. I’m thinking the only reason it worked last year when it was mounted on the top of the case is that cool air blew through the cooler and cooled the case itself.

Before I started on more drastic measures, I decided to bypass my new thermostat to make sure it wasn’t causing my cooling issues. In this picture and the last picture, I’ve capped off the thermostat and joined the hoses with AN couplers. No change. Still ran right to 225 degrees and was headed higher when I landed after 3 laps overhead the airfield.

I dug through all the junk that came with my airplane when I purchased it 7 years ago and found the original baffles. There’s no way I’m putting this junk back on my shiny new airplane, but maybe it’ll be good for a pattern. Or not. In the end I decided I like the plenum over the cylinders and how it fits… I just need to extend it over the top of the case to (hopefully) provide better cooling.

I used my contour tool and some foam core board to make a few patterns. I have previously used poster board in these situations, but find that it gives too much for an accurate pattern. My plan is to seal off the case from just behind the spinner to just in front of the engine mount bolts.

Here’s the aft piece fabricated from .032″ aluminum. It fits the contours of the case well enough that it shouldn’t be a problem sealing it up airtight with some RTV. If the combination of the RTV and the plenum isn’t enough to hold the piece in place, I could always attach a few brackets to mechanically hold it in place.

Here’s the nose piece just setting in place for a preliminary test fitting. There are two attach holes on either side of the crank flange that will allow me to attach this piece to the case. I think the holes were used as part of the stock baffling installation. In any case, a quick trip to the aviation aisle at Ace Hardware and I’m all set with the proper 1/4″ coarse threaded bolts.

With the fore and aft partitions in place, it was time to plug up the irregular-shaped holes on either side of the front of the case. Again, I used foam core board and my contour tool to come up with the shape. After I took this picture, I marked the patterns to be trimmed so they’ll just meet up with the forward partition.

I needed a flange along the top of the forward and aft flanges so I broke out my stock of Van’s-supplied stiffener material. Van’s fabricates this stuff for use as control surface stiffeners. It’s the greatest thing since sliced bread as far as I’m concerned. I ordered a bundle of it and have found many uses for it during the Midget Mustang project. Here I’ve cut notches along one side so it can follow the gentle contour of my new baffle.

Here’s a shot of the baffles after priming and after the flange has been cleco’d in place. I always get excited when things start to come together like this.

With the flanges in place it was time to fit the pieces at the front of the case to the left and right of the crank flange.

I’m pretty happy with the way these fit. After a few tweaks I separated all these parts, primed the remaining pieces and riveted everything together. The next day I painted everything black to match the existing pieces at the valve covers. I don’t have a picture of the freshly painted pieces because they were still tacky when I left the hangar on Saturday afternoon.

While waiting for the paint to dry, I decided to tackle another little squawk that’s been bugging me for almost a year. I just don’t have enough elevator trim authority. At different phases of flight I find myself trimming to the full up and full down positions and wishing I had more. The painted piece to the right side of this picture is my existing trim tab. The one on the left is the replacement.

Here’s a better shot to see the difference in size between the old and the new. Believe it or not, the new tab is more than 50% larger in surface area. I’ll start with this and if it’s too much I can always trim it down a bit. I can’t believe I put this project off for almost a year. Once I got started on it, the project probably only took me 30 minutes to complete.
I was really busy at work during the months of April and May, but I’ve vowed to be less busy during the month of June. I’ve already missed some fantastic flying days so I’m highly motivated to return my Midget Mustang to flying status as soon as possible. I’m off work for 5 days in a row starting next Thursday. I’m hoping for some serious progress during that time.

Gotta show a picture of my new beater truck. I bought this in anticipation of my next project… finishing my basement! 4 x 8 sheets of drywall will certainly fit better in this truck than they’ll fit in my VW Passat! It’s not much to look at and it doesn’t get very good gas mileage, but it’ll serve a purpose. I’m finding it really fun to not have to worry about where I park for fear of door dings, too!