« Archives in May, 2012

Baffles infinity.

7 hours.

Memorial day weekend was decent. Got a bunch of stuff done, mostly trimming down the baffles. The final trimming still isn’t done, but I got the contour of the top inlet duct cut in. Very iterative, time-consuming process. I have to say, I’m still not altogether clear on how the airseal is supposed to work around the cowl inlets. There’s some airseal that’s supposed to go on the bottom inlet half, and I guess that’s supposed to overlap with the stuff on the baffle somehow.

the other problem I have is just how little metal I’ve got on the front baffle at the top of the arc near the governor drive gear. Still, that has to be fastened to the engine somehow, and I suppose I can reinforce it when I devise some clever system for attaching it to the engine.

I also drilled the fiberglass inlet ducts into place. Now that I have them locked in, I can glass them and fill in the inboard side so air doesn’t blow through and cost me pressure.

Apparently this game is all about air pressure, specifically, making sure that air flows through the engine compartment the way it’s supposed to, which is over and between the cylinders. I read somewhere that gaps totaling up 1 square inch where they’re not supposed to be will cost 20% of the cooling capacity. This would not be good. At all.

First thing that has to happen though is the baffles have to come off, get final trimmed, and deburred. Maybe painted. Not sure about that.

I’m starting to see one of two things: Either it’s the light at the end of the baffle tunnel, or it’s a train, which means I’ll wind up redoing them.

Baffles – Photos and things.

7 hours.

When I made the entry for yesterday, I was dead on my feet. After a day or two of standing/working, I sometimes don’t have the patience to write well, or clearly, and I certainly don’t have an excess of desire to deal with photos. I’m sure there’s some fancy wordpress widget that can handle it, but when I started this project, ‘blogging’ was a new buzzword heard only in elite circles of of the technorati, and as yet had no good tech for displaying images other than the tried and true html code, which is what I use, and still use.

Along with that, when I’m on the “here be monsters” part of the instructions, I don’t often stop to take photos because I don’t want to lose my train of thought. I envy the photojournalist’s muscle memory of shooting constantly while engrossed in other activities. I just ain’t got it.

So this entry is just a slew of photos, with comments as to what was going on, and hopefully they’ll tell some of the story of how I arrived at a solution for the interlocking puzzle of front-governor, snorkel, and baffles.

Like I’ve mentioned before, the O-540 front baffles from the RV-10 kit get dragooned into service on this particular -7. The biggest headache is finding all the chickens, all the eggs, and turning them into ducks, which go in a row. Barnyard metaphors aside, it becomes an exercise in problem-solving to figure out what to do first. The first thing to do is to fit the snorkel. I won’t go into that here, because it’s been described elsewhere, but the only way to get a solid enough structure from which to take any reference for cutting or fitting the front left baffle is to get as far as you can on the snorkel. This means riveting the side baffle and drilling the left front inlet ramp to fit it, with all the bends and adjustments done.

Like everyone else says, don’t trim the front of the inlet ramp until the last minute, because you’re going to need it to form the front air filter retainer angle, which is simply a bend in a section of the inlet ramp where the air filter edge stops. Mine’s just on the nice side of acceptable for this purpose. Making this bend also stiffens the inlet ramp, and that’s a good thing, because by the time you’ve cut the gaping maw of the air filter opening, things get a little wobbly.

From there, you can fight with the snorkel and the air filter retainers, and at the end of the process, you have a detachable airbox whose structure provides a rigidity suitable for measuring the final inlet floor angle.

This angle was marked on the engine case, but sure enough, it drifted around a degree or so during the install.

See that flat pad just below the governor? That’s where I marked the initial angle of the inlet ramp. This is done with the lower cowl on, because it’s necessary to make sure the inlet ramp comes up to the inlet on the fiberglass lower cowl. Also, don’t do like I did, make sure you cleco all your baffle-to-case hardware on so you can work without every bump moving something out of line.

I didn’t photograph this process but the way I measure’d the angle is by using a cheap plastic angle measuring thing (don’t remember the actual name of the device) which is like a protractor with a couple of arms and dials on it. You can use whatever you want, but the reference for this to line up the vertical are the two aft studs for the governor mount. With one arm of the device on those and the other laying on the inlet ramp floor, you get what you need. The governor should be off at this point, to give you room to work.

From there, it’s no big deal to transfer that angle to the O-540 front baffle, which has a sharper angle than the 360 baffle, and cut off the excess to line it up with the governor and the inlet floor.

With that done, you have a front baffle that more or less fits where it’s supposed to go. I didn’t take photos of the air filter retainers, VA-132-C and D, which hold the air filter in place inside its hole, but you need to make sure you have these on when you’re doing the final position of the baffle.

This photo shows the lower edge of the baffle laying along the inlet floor just inboard of the inboard air filter retainer. This is important, because the left front baffle needs to be detachable and accessible, as does the filter retainer.

The factory-formed tabs on the baffle are no longer there after the bottom has been cut away to match the inlet ramp angle, so you have to replace them with something. This is the first attempt. Initially I figured I’d only need to do the long side, but this isn’t really a good solution.

This little whisker proved to be the source of much head-scratching, pondering, and measuring. This forms to the angles of the baffle and the inlet ramp, replacing the tabs that were sheared away during the fitting of the baffle.

Like so. This provides a good place to mount the platentuts that hold the baffle to the inlet ramp. It looks fine now, but getting to this point was insanely difficult. At some point in the build, you realize you’re off the map entirely, and you wind up being designer, engineer, and installer, sometimes all on the same day.

This is why I can’t stress it enough: If you’ve never built a plane before, or you don’t have a lot of experience with fabrication or mechanical work (like working on airplanes, for instance), don’t deviate from standard configurations or construction, because you’re going to get your ass kicked. The whole reason I’m in this mess is because I bought a weird engine. If I had to do it over again, I’d have gone with the recommended 360, with its aft-mount governor. Would have saved two or three weeks, possibly more. Seriously.

Anyway, back to the narrative. With the angles cut, bent, deburred and drilled, the platenuts go on, then this piece gets riveted to the inlet ramp.

The right hand side is similar, except in this case I’m using a slightly thicker piece of angle stock, since there isn’t as much of it in contact with the baffle. Not shown in this photo is the small piece of angle on the front edge of the baffle, which provides enough beef to keep everything solid. You can also see the conical gusset clecoed into place. This is an interesting bit of business, because the aft-most hole on the conical gusset goes through the inlet ramp and the bend in the side baffle. The two forward most holes are done with flush rivets so the airseal material can lay flat against the surfaces.

From time to time, it’s necessary to put the lower cowl on to check fit and lineup. In this shot, you can see a slight conflict between the aft platenut on the cowl and the forward edge of the baffle. Trimming away a small bit of the baffle fixed this.

This is another view. The aft angle piece took care of the gap between the baffle and the inlet ramp frame, but there’s still a small one on the first bend. This is why the archengineers of aerospace spec’d out high-temp RTV.

Back to the left side. It’s a little hard to see, but there are four flush screws holding the front baffle to the angle from earlier, which is riveted to the inlet ramp.

Here, everything is screwed on and riveted, except for where the two upper baffles join. I’ll have to fabricate a bracket that will connect to the case bolt just above the governor drive gear. Sorry for the blur. the iPhone 3g has some issues compensating for the light levels present in my shop during daylight hours.

The next phase of this is to cut down the top edges of the baffles to allow the top cowl to be installed. This is another iterative, bit-by-bit process, taking care not to remove too much metal, but enough to allow the cowl to sit where it’s supposed to with the hinge pins installed.

As you can see from this photo, there’s plenty of metal that needs to go away before the top cowl will sit where it’s supposed to.

I started the rough cut, and rough is definitely the word for it, but the idea is to get the cowl to fit again. There isn’t too much reference for this step, in the plans or on the Interwebs, But it becomes obvious what to do after a while. There was a lot of anxiety reaching this point; nothing on this up to now has been simple or easy, why should this be any different? But eventually, you just need to sack up and start trimming the baffles.

Just check for fit frequently.

After this is done, you’ll need to make the final trim, which is 1/2″ of clearance between the top edge of the baffles to the cowl, uniformly, all the way around. There are various methods for doing this, although I foresee a little more chicken-and-egg when it comes time to do the upper inlet ramps, which are fiberglass, and attached to the top cowl. I’ve decided I’m going to cut down the side baffles to fit the upper inlet ramps rather than having them ride outside of them, as some have done. I think this will provide a better seal and reduce the amount of dependency on interlocking parts.

Mostly the process involves deriving a reference line on the baffles to use as a cut guide. Some have done it with paper clips: put a crap-ton of paper clips on the baffles and the cowl pushes them down and lets you mark along the contour. Also there’s the wheel-and-sharpie method, where you cut the end off a fine-point sharpie and put a 1″ disk of aluminum on the felt tip, rolling that along the contour of the cowl to mark the line, although I don’t see that working real well except for anyone besides Plastic Man or an octopus, given the space constraints you have for arms and hands.

Baffles 8-9

10 hours.

Today and yesterday.

My motivation this week was at an all-time low, and the anxiety factor was at an all time high. Some of these tasks that look like nothing turn out to be major headaches. I’m currently working on the forward baffles, and there is no way this could have gone smoothly. This front-governor nonsense has proved itself to be a recurring pain, and fitting the O-540 baffle elements to the O-360 kit is a pain.

But yesterday I sucked it up and made attach brackets for the left front baffle. This is hard, because the angle has to match the inlet ramp and the baffle at the same time. I got it done though, and put a bunch of platenuts in it so I can detach the baffle from the inlet ramp to facilitate working with the prop governor. It should work OK, but it bears watching. I also riveted the inlet ramp and baffles together, where applicable, plus set up the air dam that attaches to the main angle bracket of the left front baffle. Fortunately on VAF, there was a post about putting this on with platenuts, because it will probably need to be shaped a little during flight testing to adjust cooling properties. I also finished the snorkel/inlet ramp interface, and bent the leading edge of the inlet ramp down to serve as a barrier for the air filter. It all works.

With the exception of one of the brackets, and the sealing of the area around the corners of the snorkel intake, the left front baffles are done.

Today I worked on the right front baffle. I drilled in the conical gusset, plus the air dam got the same platenut treatment, and I started fabricating the bracket setup for the front baffle/inlet ramp connection. There’s no governor to get in my way, but the retention system is different, so I have to fab a couple of brackets for it. I did one, but I need to do two more. I might be able to finish that up tomorrow.

The goal is to get the baffles in a state where I can start cutting them down to fit the cowl. After that, it’s plumbing, cabling and wiring.