February 2012 Archives

Worked on Snorkel

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I've been traveling for work recently, so I haven't had much time to work on the plane.  I did manage to put a couple of hours in on the project today though,  First up, the mixture control cable interferes with the snorkel in the full lean position.  I marked the snorkel and will have to glass in a blister.

Next up, I mixed up some epoxy with flox and riveted the upper flanges on to the snorkel.

The rivets are flush on the inside (mostly) so that they don't interfere with the air filter.

On the outside, small washers were slipped over the rivet shanks before pulling to spread the load out on the glass.

Finally, I mixed up some proseal and sealed the corners between the flanges to prevent air leaks around the filter.

Finished Glassing Snorkel

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Instead of cutting and glassing in a dimple to clear the mixture arm, I heated the snorkel with a heat gun and simply pressed in with my thumb to create a depression.  There's just over 1/8" of clearance now, but the mixture arm is only in this position when the mixture is in idle cutoff.  When the engine is running, the arm is no where near the snorkel.

I also opened up the hole for the alternator clearance a bit and then prepped four layers of 9oz bid cloth between a couple of sheets of plastic (this picture was obviously taken after I cut out the piece to be applied to the snorkel).

Here's the glass applied to the snorkel.

I was having a hard time keeping the edges of the glass stuck down to the snorkel because of the tight curve, so I laid a piece of plastic over it and taped it tight.  I also wanted to keep the center depressed to provide additional clearance for the alternator bracket, so I taped a paper towel down over the depression.  I should have roughly 1/4" of clearance between the snorkel and the alternator bracket.

Started Filling Snorkel

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I mixed up some West System epoxy and lightweight filler and smeared a coat over the snorkel.  This will fill the weave and smooth out the transition to the new glass I applied yesterday.  This stuff is pretty easy to sand, so I don't have to worry too much about getting this really smooth right now.

Sanded Snorkel

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I sanded most of the filler off.  This thing is baby smooth now and you can't feel the weave or the transition to the new glass.  I still need to put some additional flox around the bolt holes since the surfaces aren't parallel there, and this will get a skim coat of pure epoxy to fill any pin holes.

Recharged Battery

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I accidentally left my master switch on a couple of weeks ago, and my battery was dead.  I mean really dead (1/4 volts).  It was so dead that the charger wouldn't even charge it since it didn't think it was connected to a battery.  I ended up tricking it by hooking up my bench top power supply in parallel with the battery.  This let the charger see about 12V, which was enough to trigger it into starting to charge the battery.  It's a little hard to see in this picture, but I have three multi-meters hooked up in addition to the battery charger and bench top power supply.  One of the multi-meters is monitoring battery voltage while the other two are measuring current delivered by the power supply and battery charger respectively.

Sealed Snorkel

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The battery is fully charged again and appears to be none the worse for the abuse I put it through.  The real test will be when I try to start the engine for the first time with it.

I finished filling the snorkel.  You can see a little bit of the reddish flox mix around the holes used to attach the snorkel to the fuel injection servo.  I did this to make the forward surface parallel with the aft surface so that the bolts would apply even pressure to the flange.  Afterward, I applied a coat of pure epoxy to fill any pinholes and seal the surface.  After a final sanding, this is ready for primer and paint.

Modified Plenum Mold

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The plenum mold I purchased was made on the old non-pink cowling and made the inlets too narrow to work on my cowling.  I cut off the ears and made a little mold with some stiff paper covered in packing tape.  The paper is attached to the other side (which is the top side) of the plenum mold with double-sided carpet tape.  I used four layers of 9 ounce cloth.  The dark lines along the edge of the mold and along the apex of the curve are epoxy/flox fillets to allow the glass to drape smoothly down onto the paper and to provide a hard corner along the apex of the curve.

I peeled off the paper and used some epoxy with lightweight filler to fill in the little gaps and provide a smooth surface to lay up the plenum.  I'll sand it all down tomorrow and see how it looks.
I sanded down the filler and then sprayed a few coats of enamel on the mold to provide a smooth surface to layup the plenum against.

This picture looks almost exactly like the one from yesterday, but I have applied several coats of mold release wax and a couple of coats of mold release agent.  The mold release agent is thinner than I expected and doesn't really flow out like it ought to.  I ended up using a brush to even out the surface a bit, but it still didn't make a nice even coating.

Started Laying Up Plenum

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I started laying up the plenum tonight.  I'm starting with two layers of glass because I'm going to have to narrow the inlets a bit and create little "ears" out the outer ends to attach the plenum to the baffles.  I'll layup a couple of additional layers once I've established the final shape.

I had been considering buying the equipment to do vacuum bagging, but it's fairly expensive and I don't expect to do much of it.  After thinking about it a bit though, I stumbled on a really cheap alternative.  This is one of those Space Saver storage bags.  Most of the bags they sell are too small, but they sell some larger bags labelled as hanging bags, the "suit" sized bag was perfect for the plenum and cost around $10.  The material isn't stretchy, so you'll have to coerce it into corners, but there's enough slack to do this.  Over the two layers of glass, I added a full layer of Dacron and a couple of layers of paper towels to absorb excess resin.  I then used our vacuum cleaner to suck out all of the air.  This worked surprisingly well, and the vacuum was still maintained the next morning.

Started Fitting Plenum

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I popped the plenum out of the mold and roughly trimmed it to the baffles.  The fit is pretty good, but there will definitely have to be some tweaks.

These corners were touching the underside of the top cowl.  I'll want a good 3/8" of clearance between the top of the plenum and the button of the top cowl to allow for engine movement.  I trimmed the forward aluminum baffles in order to lower this part of the plenum almost 1/2".  Unfortunately, this lowers the inboard edge of the ramps a little too much.  I'll have to cut and reglass the side of the ramp to raise the forward edge slightly.  I'm really glad I only laid up two layers of glass so far as it makes it really easy to bend and cut.  I'll probably end up laying up the additional layers right on the engine so that the plenum fit perfectly.

The outboard edges needs to come down quite a bit.  The inlets are quite a bit shorter at their outer ends than their inner ends.  I'll have to trim the side baffles to allow this to come down.

I wanted to ensure that there is sufficient clearance between the cowl and the plenum across the entire plenum.  I came up with the idea of placing blobs of something on top of the plenum and then installing the top cowl.  I wanted something that would deform pretty easily so that it wouldn't deflect the plenum, but stiff enough that it will stand up by itself without sagging.  My wife suggested a product called Moon Dough that my son had.  This worked perfectly.  It deforms with practically zero pressure, but won't move on it's on.  As you can see, the blobs flattened down nicely and perfectly reveal the clearance at each point.  I measured all of these, and they're all very close to 1/2".  I'm going to trim the baffles down another 1/8", but the thickness of the plenum and the screw heads will eat up some of the clearance.  I should end up with at least 3/8" all the way around.

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