Now there's plenty of clearance between the hose and the engine mount. It's a little tight between the hose and the starboard exhaust pipe support, but I can tweak that part's position when I put the exhaust back on.

Another view looking up from below. The location given in the plans for the bulkhead fitting that brings fuel through the firewall is plain wrong, if you ask me. At least on my airplane it's very close to the starter solenoid, the resulting hose routing is problematic (see this post), and it's pretty difficult to get a wrench on the hose end nut. A better location would be straight below the heater air valve – you can see in this photo that it's completely open, and the hose routing from the firewall to the fuel pump would be very straightforward when using a 90-degree elbow on the engine side. Maybe they don't have you drill the hole there because they're reserving room for the nosegear weldment, but my airplane doesn't have one of those. Oh well, yet another thing to file away for next time.

]]> http://www.rv7blog.com/2013/03/09/fuel-hose-2/feed/ 0 http://www.rv7blog.com/2013/02/27/remote-transponder/ http://www.rv7blog.com/2013/02/27/remote-transponder/#comments Thu, 28 Feb 2013 02:00:09 +0000 Matt Burch http://www.rv7blog.com/?p=2335 I decided to sell my panel-mounted transponder and replace it with a remote-mounted unit instead. This is the GTX 23ES:

The unit itself is a faceless silver box – instead of pushing buttons on the transponder's front panel, you control it through the screen of your G3X system. It mounts in this sheet-metal tray, which I now have to find a place for.

The only practical place left in the airplane where I can mount something this size is the area under the baggage compartment floor on the passenger side of the fuselage. Needless to say, I'm glad I made my baggage floors removable.

The piece of aluminum angle shown here is riveted to the inboard floor rib with countersunk rivets, and it will act as a little shelf for the transponder tray to sit on. Some of the open holes visible in the rib are for tie wrap anchors that I temporarily removed to give myself space to work, but some are from little brackets and other things that I've since removed. This particular area of the airplane has undergone more changes than almost any other part, as I've installed various pieces of equipment and then later changed my plan and removed them in favor of something else.

Four pieces of angle plus some rivets became a pair of T-brackets, seen here riveted to the outboard floor rib. Keep reading to see what these are for.

I fabricated these two identical mounting braces out of some more aluminum angle. The mill was handy for removing excess material where it wasn't needed.

The braces attach to the transponder tray like so:

Closeup detail of how the braces attach to the tray, using #6 screws in the countersunk holes that are thoughtfully provided:

Here's how it all goes together. The transponder is oriented with the connectors facing towards the nose of the aircraft. The braces stay permanently attached to the tray, the tray sits on the longitudinal angle (not visible) and the braces are fastened in four places to the T-brackets and the inboard floor rib. It's kind of an odd setup, but it fits in the available space and is quite sturdy. Just as important, it is all fairly easy to remove if required.

Wiring… power and ground, RS-232 to the GSU 73, ARINC 429 to the two 430W's for TIS-A traffic display, and RS-232 for GPS position data from 430W #1 so I will be ADS-B Out compliant.

Wires routed and secured, all neat and tidy:

The transponder antenna coax carries high-power RF and shouldn't be routed with any other cable bundles (so says the install manual, anyway). I ran it inboard to the center tunnel, aft, and back outboard again to miss the elevator bellcrank on its way to the antenna. It's tie-wrapped to the floor rib with the usual plastic cable anchors.

You may have wondered earlier why I removed material from the middle of the mounting braces. If you look at this photo you can see that It's simply to prevent creasing the baggage compartment floor if I put something heavy on it (such as my knee!) that causes it to flex downward between the floor ribs. Well, it probably saves a few grams of weight too.

The overhead view shows why I had to make the tray removable, instead of permanently mounting the tray and just sliding the transponder in and out – no room! The under-floor avionics bay is physically not long enough to allow the transponder to be removed from the tray, even if I'd scrunched up the wiring and mounted it as far forward as humanly possible. So, to remove the transponder I'll have to undo four fasteners, lift the tray out of the floor, and then remove the transponder from the tray. I shouldn't have to do this too often, so hopefully it won't be too inconvenient.

Everything worked on the first try – after a few keystrokes for configuration, the transponder controls popped up on the PFD.

The only thing left to do on the transponder is to finish securing the antenna coax and connect it to the antenna on the belly. I'll tackle that eventually when I get around to venturing into the tailcone to finish up all the wiring back there. Right now that area is in a state of… let's go with "disarray".

Oh, you may be wondering why I decided to go to all this trouble in the first place. Why remove a perfectly good transponder from the panel just to put in a different one that's mounted somewhere else? Naturally, it was to make room in the panel for another toy… just what kind, I'm not telling yet.

]]> http://www.rv7blog.com/2013/02/27/remote-transponder/feed/ 0 http://www.rv7blog.com/2013/02/10/installed-new-cylinders/ http://www.rv7blog.com/2013/02/10/installed-new-cylinders/#comments Mon, 11 Feb 2013 01:00:22 +0000 Matt Burch http://www.rv7blog.com/?p=2320 After an unexpectedly long delay – due to schedule issues and also because ECI didn't send me all the expected parts on the first try – I finally managed to get my four new engine cylinders installed.

The cylinders are mounted and torqued, the pushrods and rocker arms are in, the oil drain tubes are back on, and the fuel injection lines are reinstalled and clamped. The intake and exhaust pipes are still off, since I want to get the EGT and CHT probes installed before I put them back on for good. And the rocker covers are not on yet because I ran out of steam and got tired of standing in the cold garage.

Grey cylinders with red pushrod tubes and crankcase is kind of a cool color scheme. Can't order 'em that way.

While I was complying with SB08-1, I also took care of SB12-1 by installing new stainless parts for the pushrod shroud tube retainer spring and lock tab.

Guiding me through this whole adventure was local engine guru Jerry Gippner, who taught me a lot about engine maintenance in the process. I think I could probably do it again on my own next time, so thanks Jerry for the education!

Next: Reinstalling baffles and other engine parts, hopefully for the last time (for the foreseeable future anyway).

I waited until I couldn't make any further progress on the engine without starting to attach things semi-permanently, then finally gritted my teeth and started unbolting things. I took off the baffles, dropped the exhaust (and sent it back to the manufacturer to fix a different potential cracking issue), pulled the spark plugs, and so forth.

One of the many piles of stuff that came off the engine:

I've owned and maintained Lycoming engines before, but I've never done any serious maintenance like removing a cylinder. I decided to hire out the job to a local A&P, from whom I learned a lot about how it's done. Definitely worth the cost of hiring a pro to show you the ropes the first time when you're working on an engine that costs as much as a nice new car. But now look how sad it looks with the jugs removed:

Four bad cylinder assemblies, ready to be shipped back to where they came from. If you've never seen an air-cooled aircraft engine cylinder up close, these are about the size of a gallon of milk (I guess that's why they call them jugs?) and weigh maybe twenty pounds apiece. I saved the valve covers, pushrods, rocker arms, injector nozzles, and wrist pins – everything else including the pistons and rings goes back and gets replaced with new parts.

Amazing how many little things have to be removed before you can take the cylinders off:

On the bright side, pulling the cylinders gives me a chance to look inside the engine for corrosion. I was slightly worried that some internal rust might have started during the (sadly) extended period the engine has been sitting in my non climate controlled garage, but happily everything I can see inside the engine looks shiny and new.

The ever-critical camshaft looks great as well. Once the cam starts to go, you're looking at a five-figure engine teardown. Luckily that date appears to still be a long ways off.

I boxed up the old cylinders and sent them on their way. Meanwhile I threw a tarp over the engine to keep stuff from falling into the open cylinder holes while I'm waiting for new jugs to arrive.

Although it is without a doubt an unfortunate backwards step, this chore is actually also a bit exciting, since it means that once the new cylinders are installed, I'll be able to start attaching things to the engine for the last time. Think positive…

The particular unit I picked is the Vertex LED lighthead by Whelen. These guys are known in aviation circles for making certified strobes and nav lights, but they make lots of automotive products too. This one is designed to work as a warning light for a cop car or other emergency vehicle, but it happens to also be the perfect size for an airplane too. Here's a photo I grabbed from the internet since I forgot to take a "before" shot prior to getting started:

I played with various mounting positions until I decided which one I liked best – it turned out to be the top of the tail, just like on your grandpa's Cessna. Then I got out the rudder cap and started cutting away at it with a unibit and Dremel tool.

The light will be held in place by two little pieces of scrap angle that will attach to the inside of the rudder cap.

A view from the bottom side. The beacon heatsink just fits into the widest point of the rudder cap.

That has the added advantage of putting the beacon about halfway back from the leading edge of the vertical stabilizer – farther back than on a Cessna – where the light shining directly forward will be blocked instead of getting into the cockpit and annoying me by glaring off the instrument panel.

The circuit board inside the beacon is flush with the top of the rudder cap. Now we just need to do something about the exposed shoulders of the heatsink sticking out into the breeze.

I covered the beacon with saran wrap and then laid up several plies of glass tape over it in a smooth shape:

It's a little late in the season to be doing fiberglass work – i.e. the temperature is a bit low in the garage – but for small projects you can cheat and use a heat lamp to get the resin to cure in a reasonable amount of time.

After sanding the initial layup, I installed the beacon again and followed up with a flox/cabosil mixture to build up the contour and give me a nice sharp edge around the opening for the lens.

I also laid up some flox inside the rudder cap to give the body of the beacon a nice solid shoulder to sit on, as well as thickening up the inside of the lens opening to avoid having a knife edge there.

After letting that cure and sanding it back down, the general shape of the "bump" for the beacon was basically done.

I applied one more coat of dry micro with a squeegee to fill in the low spots, then sanded it smooth.

A quick spray of primer dressed it right up. I'm quite happy with how the shape turned out. There are some small surface imperfections but I'll let the painter deal with those.

The beacon lens is very low profile. I still need to countersink the mounting holes in the sides, but that can wait until I get back the drawer full of #4 tinnerman washers I loaned out.

Now that it's all sanded smooth and blended in, the slight swell for the beacon is hardly noticeable:

What's that, you say you want to see my new rudder-mounted ground recognition beacon in operation? Very well:

It's hard to properly capture with the camera, but trust me, this thing is plenty bright.

]]> http://www.rv7blog.com/2012/10/28/red-beacon/feed/ 0 http://www.rv7blog.com/2012/10/15/tool-interlude-2/ http://www.rv7blog.com/2012/10/15/tool-interlude-2/#comments Tue, 16 Oct 2012 01:00:02 +0000 Matt Burch http://www.rv7blog.com/?p=2259 So yeah, it only took a few weeks for me to break down and buy a real milling machine. Like you didn't see that coming.

Actually I hadn't intended to get one right away, but I was unexpectedly lucky on eBay and got a very nice 12" Sherline mill to go with my 3.5×17" Sherline lathe. Judging from the few parts I've made with it so far, I can definitely see that a dedicated machine is a lot nicer and more capable than a lathe with a milling conversion attached.

The mill seems to have hardly been used at all, but since it's at least fifteen years old and doesn't seem to have gotten much TLC during its life, I decided to strip it down to its component parts so I could clean and lubricate everything. I also replaced the AC cord and switch, and added a power indicator safety lamp as I did with the lathe. After putting everything together, the mill worked a lot smoother and with less backlash, so it was worth the effort.

Then while I was at it, I tore down the lathe to individual pieces too, and gave it the same tune-up treatment. Then for some reason I decided to really get crazy and add DRO scales to it too. That was more challenging than I initially thought, and took a couple weeks to really get sorted out, but it did give me a chance to use the new mill to make real parts. And now that the lathe is back together, it too works better and has digital readouts to boot. (I may add DRO to the mill as well, but if I do I'll almost certainly take the easy way out and buy a kit!)

Hopefully this will all come in handy for the airplane project. Don't worry, I haven't totally forgotten that I have one of those too.

I chose to tackle both at once by modifying the bulkhead tee fitting that I previously installed through the firewall. I cut off the right angle leg, filed it flat (this was before I had a milling machine, or else I'd have used that) and tapped the hole for 10-32 threads. Then I installed a similarly threaded quick connect air fitting using Permatex #2.

Here's the modified air fitting re-installed in the firewall. The aft side, not shown here, is blocked off with an AN929 cap. This effectively turns the former tee fitting into a firewall-mounted right-angle hose-to-tube adapter.

This is a wider shot of the area in question. Manifold pressure is conveyed from a port on the back on the #3 cylinder to the fitting/adapter on the firewall via a hose, which is strain-relieved via an adel clamp attached to the engine mount. This originally had two attach points; I may hook the other one up again someday if it appears necessary.

From the firewall connection, the manifold pressure hookup transitions to 1/4" nylon tube, seen here as a black stripe because the camera wouldn't focus where I wanted it.

I attached a quick-connect tee fitting to the firewall using a simple aluminum tab affixed to an existing bolt hole. The middle leg of this fitting will eventually connect to the manifold pressure input on my ignition system (more on that in a future update) but for now it's just plugged. A pair of adel clamps keeps the manifold pressure tube from rubbing on the oil pressure hose and vice versa.

Here you can vaguely see the entire route of the black plastic manifold pressure line, from the hose transition on the starboard side, across the firewall through a tee to the sensor manifold on the pilot's side. In retrospect it's not exactly how I might have chosen to hook it up had I known I wouldn't need to bring it through the firewall, but it's not a bad arrangement regardless.

]]> http://www.rv7blog.com/2012/09/02/manifold-pressure-plumbing/feed/ 0 http://www.rv7blog.com/2012/09/02/engine-pressure-sensors/ http://www.rv7blog.com/2012/09/02/engine-pressure-sensors/#comments Mon, 03 Sep 2012 00:00:10 +0000 Matt Burch http://www.rv7blog.com/?p=2228 The electronic transducers that sense engine oil pressure, fuel pressure, and manifold pressure are all mounted on a manifold on the left side of the firewall. I ran the wiring to all three, then used some brass air fittings and the compressor to test the oil and fuel pressure sensors. Manifold pressure is easier to test since you can just compare the readout to ambient air pressure.

I used Permatex #2 to seal the sensors, plugs, and fittings as I screwed them into the manifold. The oil pressure sensor is hung off the side of the manifold, since the oil pressure switch (which drives the Hobbs meter and the low oil pressure warning light) is much too big to be placed anywhere else other than cantilevered straight out from the firewall. In fact, I discovered to my chagrin that the oil pressure sensor doesn't quite fit either – the radius is too big by an eighth of an inch – but I have a plan for that…

In classic style, I used this little challenge as an opportunity to buy a new tool. Seen here is a vertical milling table attached my lathe, which turns it into a very small milling machine of sorts:

I cut a piece of 3/16" aluminum bar stock, match drilled it to the transducer manifold, and then bolted/clamped it to the new milling table and milled out some lightening holes:

It's not perfect, but it's not bad for my first real part made using a milling machine. It's quite light, since most of the material in the heavy bar of aluminum has been milled out.

Now the manifold can be spaced out from the firewall, allowing the oil pressure sensor to fit:

…just like this:

I secured all the sensor wiring with tie wraps. Later I'll connect the three wires for the oil pressure switch.

The milling conversion attachment for the lathe wasn't all that expensive, but I have a feeling that it is going to end up costing me a more in the long run. Now that I've successfully made a useful part on a mill – something I never thought I'd be able to do – I'm already having impure thoughts about upgrading to a larger and more capable machine. I wonder if Mary would notice if I put a Bridgeport in the guest bedroom?

I connected and secured the standby alternator field wire and B-lead… note adel clamps and strain relief:

I had previously mounted the current sensor for the main alternator, but I never got around to wiring it or installing its twin that measures current from the standby alternator. The second sensor I installed with an adel clamp from the engine mount, right above the fuse holder where the standby alternator B-lead connects. Since these are 100-amp sensors and the standby alternator is only capable of 20 amps, I looped the wire through three times in order to achieve a little better resolution on the display. A calibration step in the G3X software allows you to apply a scale factor of 0.33 to account for this trick.

Here's a wider shot showing both current sensor hookups. To make them serviceable I used mini molex connectors, which are shown here prior to being secured in the wire bundles.

I wrapped the connectors with silicone tape in order to make them somewhat waterproof:

Then I powered up the avionics and calibrated both current measurements to zero. The machine is starting to wake up…

I started by squaring up the edges of the cowl cutout and making the corners nice and round:

Then lots of iterative fitting, trimming, and bending to get the aluminum door to fit the opening. The cowl has a gentle conic section at this point, a shape which the aluminum doesn't naturally want to follow without some smashing persuasion.

Here's the aluminum door, shaped and trimmed, sitting next to the stock fiberglass door that came with the kit:

Instead of the standard piano hinge, I bought a "hidden hinge" from Nonstop Aviation (whose name always makes me think of an old Brian Aldiss novel, which by the way was not great). Lots of folks install this type of hinge, including plenty of certified airplane factories. It's just a piece of regular hinge with a sort of gooseneck extension riveted on, thus allowing the pivot axis to be tucked cleanly out of sight underneath the cowl – I could probably make my own if I had a decent bending brake. It works the same as a piece of piano hinge, of course, but it looks a little nicer. It's spring-loaded too, although I left the spring out while I was fitting the oil door so it wouldn't launch itself across the garage.

Here's what it looks like with the door closed – no visible hinge line:

It takes some adjusting to get the door to open properly without binding, and without the inside edge crashing into the cowl and scratching the paint.

The hinge is flat and the inside of the cowl is curved, so I made it flat by laying up an epoxy/flox mixture and letting it cure with the hinge clecoed in place:

I wanted to use a push-button latch instead of the quarter-turn fasteners called for by the plans, so the oil door can be opened without tools and without anything sticking out into the breeze. There are basically two choices here: the Hartwell H5000, which holds very securely but is hard to make look nice, and the Camloc KM610, which is easier to install but trickier to make latch properly. The tie-breaker for me is that the Hartwell latch when operated tends to spring open like a demented mousetrap, and I've bruised my knuckles on them too many times to want to go to the trouble of having one on my airplane.

Also, pay no attention to the prices in the preceding links – those are new-certified prices, which are ridiculous. There's a surplus place in the neighborhood that sells new-condition Hartwells for ten or fifteen bucks and Camloc pushbuttons for five, so I picked up a handful of the latter in various sizes to play with:

Since they were so cheap, I removed the spring from one and drilled a hole in the exact center of the button, thus turning it into a drill jig for properly locating the mounting holes relative to the main hole:

It was then no sweat to drill the holes to mount it, although you do have to be super careful about where you position it relative to the edge of the cowl cutout. Too far forward, and it won't latch; too far back, and it will latch easily but it won't hold properly. Patience counts here.

So does test-fitting:

Here's a view from the underside. Note how the latch tongue is pretty short as well as pronouncedly rounded, which is what causes the difficulty.

To get the clecoes out of the way and make sure the whole works was properly rigid, I riveted the latch and hinge to the door:

As pictured, the latch tongue bears on an un-reinforced fiberglass surface, which of course won't do at all. To fix this I fabbed a little striker plate out of some thin stainless steel material I bought from the K&S display down at the local hardware emporium:

A single flush rivet holds the striker plate to the cowl:

Once I had the metal parts built and the overall mechanism working (which was fun) it was time to make the fiberglass look cosmetically acceptable (which is never fun).

I protected the door with packing tape, then latched it in place and squeegeed a flox/microballoons/cabosil mixture into the gaps between the door and the cowl.

After a couple iterations of sand-fill-sand, the cowl was a good match to the shape and contour of the oil door. But I had a problem – there wasn't enough gap around the door to let it actually open. Hmm, obviously zero-clearance is no good here.

What I wanted was something I could put around the circumference of the door to provide a uniform separation between the metal and fiberglass for a cast-in-place operation. I experimented a bit with some of this nylon grommet edging material I had laying around, but it wasn't quite right. Kind of an interesting idea to keep in mind for the future, though.

In the end I hit upon the idea of using some silicone fusion tape instead. This is close to ideal, since it's fairly thick, resists epoxy, and follows the curved corners without wrinkling. I dremeled out a gap around the cowl opening, then wrapped the door with two layers of silicone and latched it in place.

Then I spackled in a new layer of filler:

The result, after puling the door out and sanding down the high spots, was a set of nice straight edges and round corners. I forgot to take a photo of it, but this technique gave me a fairly uniform 1/16" gap all around the door opening.

As I expected, the clearance was a bit less around the corners where the rubber tape stretched, but I got that cleaned up pretty well with a file.

I attached the hinge to the cowl with stainless screws and tinnerman washers, the better to keep the fasteners from pulling through the fiberglass. The grey splotch here is just a misting of primer I sprayed on as a guide coat to help me sand down the filler.

Inside, I made a little hinge pin retainer out of some angle stock and a leftover hinge eye I found in the scrap pile. It picks up one of the mounting screws and keeps the hinge pin from getting away.

Here you can see how the gap looks – it's a bit deceptive in a photo because the coloring is uneven where I sanded, but in person it looks pretty nice. I'll let the painter fix up the last 10%.

Here's a video I shot showing how the whole thing operates. Dig that solid latching action!

And now I need to clean up the garage before I do anything else. What a complete mess.

]]> http://www.rv7blog.com/2012/06/10/oil-door/feed/ 0 http://www.rv7blog.com/2012/05/06/orthodontia/ http://www.rv7blog.com/2012/05/06/orthodontia/#comments Sun, 06 May 2012 21:00:56 +0000 Matt Burch http://www.rv7blog.com/?p=2131 When I was a young lad, I had to suffer through years of braces and other painful torture devices in to correct an unsightly overbite. In fact, I only narrowly escaped being required to wear headgear to junior high (the horror!). So it was not without a certain sense of deja vu that I set out to correct a similar condition on my airplane cowling. It's a bit hard to see here, but the way my upper and lower cowl halves fit together causes the one to be out of alignment with the other by about an eighth of an inch:

Knowing what I know now, I could probably have corrected this early on when I was initially fitting the cowl halves together. But now that everything is trimmed and drilled, it would be impossible to shift the relative alignment of the upper and lower cowl without affecting everything else, including the parts that actually turned out pretty good. Still, no matter – even though it's a pain to work with, fiberglass can erase many sins. I first obtained some 1/8" thick closed-cell foam, and cut a half circle to fit the cowl. With a sanding block I matched the contours, then epoxied it to the lower cowl. (the notched-out area in this photo was repaired before subsequent steps}

A weighted board covered with wax paper ensured the foam would adhere evenly all around and leave a flat surface:

On top of the foam I laid up three plies of 8-ounce bid cloth. The foam is just a substrate, of course – the epoxy and glass will provide the actual strength.

After several hours of sanding and fitting, I had the excess glass ground away and the shape looking pretty good:

It took a lot of on-and-off fitting and work with the grinder before the top cowl would fit again:

Now the two halves are roughly even, but there's still room for improvement:

I stuck some packing tape to the top cowl as a release agent, and reinstalled both halves on the airplane. I then squeegeed a thin layer of microballoons and cabosil over the new layup, as well as the cowl joint behind the spinner:

After another couple hours of sanding, the surface is getting pretty smooth:

In case you were wondering, sanding fiberglass is dusty and hot and no fun at all. Not even a little bit.

Now we're talking!

Nice and flat all around:

As a bonus, the fit behind the spinner is greatly improved as well. Good enough to give to the painter for the final detail work.

This little mini project was one of those things that isn't strictly necessary to make the airplane fly, but it would have bothered me to leave it undone. I think they call that craftsmanship. I'm just glad the airplane won't have to wear headgear.

A view from the other side… I may replace these nuts with all-metal locknuts later, after my next parts order:

To keep air from leaking between the aluminum baffles and the rubber seal strips, I put down a thick bead of black RTV before I started riveting. This also means that I didn't get any pictures of the process, since my hands were too filthy to hold the camera.

Fast-forward a couple hours… my hands are all black with glue, and all the rubber pieces are attached to the baffles with large-head blind rivets. I cleaned up all the squeezed-out RTV and made sure there was an adequate bead all along the top seam.

One hole on either side gets a screw and nut instead of a rivet, so I can peel back the associated rubber strip to install or remove the metal seal tabs.

While I was in sticky-finger mode I dabbed some orange RTV in the gaps and tooling holes around the top of the oil cooler area. Don't ask me why I used two colors of glue.

Here's the finished product. The next step after this is "go all around the engine and seal every little gap between the engine and baffles with RTV", but I'm not going to do that just yet. There is an AD out on my ECI cylinders that I'll have to deal with first, which unfortunately means everything will have to come apart one more time before it's all said and done.

Finally, done with the baffles! I collected a ton of scrap cuttings of rubber seal material from around the garage – and this is probably only about half of what I generated, not counting what's already gone into the trash.

Oh, and tonight's beer is an excellent spring seasonal from a brewery just down the road from my airplane factory.

Once again the angle drill is worth its weight in… something heavy and expensive. You can see in this photo that I drilled an extra hole on the inboard end of each attach strip, so I could put a screw on the "upright" portion. I found that helped the rubber seal stay in place a little better when installing the cowl.

Here's what one of these seal strips looks like when being test-fitted. Since the bottom cowl is installed from below, these strips have to pass up and over the metal baffles as you raise the cowl, which can be awkward. You want to start with an oversized piece and gradually cut it down until you find the balance point between too hard to install and not enough overlap with the metal baffles. I ended up with about 1/2" of overlap, which is similar to other RV's I've seen. These strips have also been a pain in the rear on every other RV I've ever taken the cowl off of, so I think I must have them sized about right.

I added a countersunk screw at the outboard corner on each side, the better to keep the rubber seals from folding up when installing the cowl. This was only possible thanks to the extended attach flanges I laid up a while back. The screw and tinnerman washer are hidden beneath the upper cowl when it's installed.

Here's how it looks at the inboard end:

The cowl seal overlaps and sits on top of the "ears" on the crankcase baffles (exaggerated here for clarity). You can sort of see the upper leg of the metal attach strip here too:

That's the last of the rubber baffle seals to be fitted! Everything from here onwards is assembly, at least as far as the baffles are concerned.

The plans tell you to permanently attach the mounting strips to the rubber seals with Pliobond. What they don't tell you is that this stuff is also the most evil, nasty, noxious, horrible-smelling gunk on the planet. Worse than Proseal even. I had to vacate the garage while it cured so I wouldn't get gassed.

The result, a couple days later:

I countersunk the cowl for #6 tinnerman washers and attached the seal strips with screws and nuts:

]]> http://www.rv7blog.com/2012/04/08/lower-cowl-baffle-strips/feed/ 0 http://www.rv7blog.com/2012/03/17/crankcase-baffle-seals/ http://www.rv7blog.com/2012/03/17/crankcase-baffle-seals/#comments Sun, 18 Mar 2012 01:00:53 +0000 Matt Burch http://www.rv7blog.com/?p=2087 The baffles on the forward part of the crankcase, just behind the prop hub, are deceptively difficult to get shaped correctly. So, it should come as no surprise that the associated rubber seal strips are also hard to get just right. After much trial and error, I ended up making the seals out of nine separate pieces of material in order to get them to lay against the upper cowl without wrinkling. Also, pay particular attention to the "ears" at the front:

Those ears have nothing to do with directing airflow – instead, they are there so you can tuck the rubber seals inside the inner face of the spinner opening on the bottom cowl, to prevent the oncoming air from peeling them back and trying to turn them inside out. I'd seen this before on other RV's but never really comprehended what I was looking at until I was deep into the baffle process.

Here's what it looks like with the top cowl on:

I had an especially hard time figuring out how these seals were supposed to go, so I'll try to help out the next guy by posting a few more detail photos of this area. When you get to this part of the build, you'll know what you're looking at.

Segmenting helps the rubber follow the shape of the top cowl:

Adjacent pieces overlap from front to back to keep the air from getting underneath:

Tabs and carefully-cut angles help go around corners:

]]> http://www.rv7blog.com/2012/03/17/crankcase-baffle-seals/feed/ 0 http://www.rv7blog.com/2012/02/19/ignition-wire-seals/ http://www.rv7blog.com/2012/02/19/ignition-wire-seals/#comments Mon, 20 Feb 2012 00:00:33 +0000 Matt Burch http://www.rv7blog.com/?p=2071 To pass spark plug leads through the baffles, you use these two-piece plastic wire seals, which require an oddly shaped hole. The bit of aluminum in this photo is a drill template I made out of scrap.

Ideally I would have cut the required holes in the baffles earlier so I didn't have to mess around with removing and reinstalling them, but my ideas about ignition systems have been evolving recently so it can't be helped. I'll discuss that further in a future update. Here I've used one of the existing rivet holes to locate the upper fastener for the wire seal in the the left rear baffle, per the plans:

#10 screws will be used to attach the plastic seal to the baffle, after the wires have been passed through and the two halves snapped together:

Testing the wire routing… it looks like with a bit of securing, I should be able to keep the wires well away from the fuel injection lines:

Same deal for the right rear baffle. I chose to file the holes to an oblong shape instead of a figure-eight. Not sure why, since it doesn't really matter.

While I had the right rear baffle off the engine, I took the opportunity to fill a little gap towards the bottom with red RTV:

I had a complaint recently that I haven't posted any beer pictures in a while. So here's today's selection, a nice pint of Guinness – it's too cold in the garage for anything else.

]]> http://www.rv7blog.com/2012/02/19/ignition-wire-seals/feed/ 0 http://www.rv7blog.com/2012/02/05/baffle-tension-rods/ http://www.rv7blog.com/2012/02/05/baffle-tension-rods/#comments Mon, 06 Feb 2012 02:00:00 +0000 Matt Burch http://www.rv7blog.com/?p=2053 The forward and rear parts of the baffles are tied together underneath the engine cylinders with steel tension rods. These pull the baffles down and around to keep them in contact with the cooling fins, which forces air to go through them and do useful work cooling the engine. You make these out of raw stock, bending as required to clear various protuberances that stick out of the engine.

Threading the stainless rods is kind of a chore, but relatively ordinary all the same. Forward a half-turn, back a quarter-turn, repeat until done, and use plenty of cutting fluid.

Here's a view of the general area where this is going on. You can see where the left inboard tension rod is in place, and the outboard rod has yet to be fitted.

A closeup of the left inboard tension rod being fitted. The hardware is only temporary – this will use all-metal locknuts when it's installed for good. The portion of the rod between the forward and aft attach tabs is covered with nylon tubing in order to keep it from chafing on the bottom of the cylinder.

Here's the inboard rod on the right side of the engine being fitted. You can see how it's bent to fit through the available space:

It's hard to see, let alone get a photo of, but the hose clamp near the center of the image was in the way of the right outboard tension rod. I managed to remove the clamp, shorten the band, and reinstall it in a friendlier orientation.

Test-fitting the right outboard tension rod. This has quite a significant Z-bend at either end, although from this angle it's hard to notice.

A view from the side, peeking through the exhaust pipes and intake tubes:

You want to ensure that there's sufficient separation between the steel rod and the aluminum oil return line to keep one from chafing through the other and letting out all your engine oil:

I wanted to put nylon tubing over the outboard rods as well, but they're bent too sharply to let it fit past the bends. So instead I split the tubing along its length, by cranking my drill press spindle down almost to the table, and carefully running the plastic tube against a cutting wheel. (while wearing heavy gloves, of course!)

Perfect fit:

Here you can see how the outboard rod has to dive down to clear the oil tube, then turn back up again at the far end. But one thing I found worrying about this arrangement was the fact that there was nothing to keep the bent rod in the correct orientation required to prevent it from rubbing on the oil tube.

I solved this by using an extra nut and washer at one end, to clamp the rod firmly to the attach tab. Now it can't rotate on its own. At the other end, I kept the default single nut so that the rod can still slip through the hole in the other attach tab, to handle the cylinders shaking around independently while the engine is running.

Various things have been going on to prevent me from working on the airplane recently, but hopefully I'll be able to do a lot more work going forward. Feels good to be back to fabricating stuff out of metal.

Before I got the tools out, I did a bunch of thread-reading on VAF, then went to the airport and looked under the cowl of as many RV's as I could find (five). It turned out that every one of airplanes I encountered had its baffle seals done in a different way, but it was interesting to see which ones fit well and which ones had leaks. In the end I came away with some good ideas that I'll try to put into practice.

In places where the baffles are curved, I used multiple overlapping strips to avoid wrinkles that could cause leaks. Each one overlaps its neighbor in such a way that the incoming airflow will tend to flatten it against the baffles and top cowl – sort of like bird feathers. The fastener holes are 3/8" from the edge of the baffles, spaced approximately every 1 1/2". Eventually the rubber seals will be riveted to the metal baffles with large-head blind rivets.

Since the seal material (rubberized fabric) comes rolled up, it has a natural curve to it. I took advantage of this by cutting parallel to the axis of curvature and orienting each piece of material so it naturally wants to bend inwards.

A leather punch is about the best way to put the fastener holes in the rubber strips. The rubber doesn't drill well with a normal twist bit, but the punch makes a clean hole without tearing.

Looking into the cowl inlet during a test-fit. I purposefully left the rubber strips overly long so I could trim them to fit later. The forward end especially will need some work, since there will also be a separate set of rubber strips attached to the lower cowl.

I managed to fit rubber seals to all the outboard and aft cylinder baffles before I got tired. The prop hub and flywheel will have to come off again in order to do the crankcase baffle seals anyway, so this is a good stopping point.

]]> http://www.rv7blog.com/2011/11/27/started-baffle-seals/feed/ 0 http://www.rv7blog.com/2011/11/13/finished-baffle-riveting/ http://www.rv7blog.com/2011/11/13/finished-baffle-riveting/#comments Mon, 14 Nov 2011 01:00:58 +0000 Matt Burch http://www.rv7blog.com/?p=1994 After trimming the baffles to their final shape, I finished riveting together all the parts that I had been leaving clecoed together for fitting purposes. First I made some doublers out of scrap to reinforce the outboard corner of the #3 cylinder baffle:

Here's what it looks like riveted together:

Another view. I'm not sure if reinforcement is strictly necessary here, but it was easy enough to do and adds almost no weight.

Here's the previously-seen #1 cylinder baffle, newly riveted to the starboard side crankcase baffle.

Closeup view of the joint… flush rivets towards the front where the rubber seal material will go:

And now the #2 cylinder baffle, also riveted to its corresponding crankcase baffle. I later used RTV to fill those visible gaps where the parts come together.

A view of the #2 cylinder baffle from the aft side. The angle reinforcement piece has almost no rivets through it, since it will primarily be secured by the screws that hold the air filter retaining ring.

All the baffles are now riveted together permanently, and back on the engine temporarily:

It's a bit hard to see in a photo, but there are substantial gaps between the forward baffles and the nose of the crankcase that will have to be caulked up when I put them on for good. You can also see some of the RTV previously mentioned.

The plans tell you to rivet little tabs to the forward cylinder baffles where they overlap the aft ones, to make a sort of expansion joint. I wanted these to be removable without drilling out rivets, so I sized the holes for #6 screws instead.

Screw heads are flush on the inside to accommodate the rubber seals:

I cut the tabs slightly oversize so they would seal up the tooling hole that's visible in the previous photo:

One small step at a time…

I put a bead of RTV between the baffle and the cover plate to keep air from leaking past. I'll have to wait till I buy the heat muff to figure exactly where I'm going to relocate the heater air supply.

]]> http://www.rv7blog.com/2011/11/13/heater-duct-cover-plate/feed/ 0 http://www.rv7blog.com/2011/11/13/1988/ http://www.rv7blog.com/2011/11/13/1988/#comments Sun, 13 Nov 2011 17:00:33 +0000 Matt Burch http://www.rv7blog.com/?p=1988 After a seemingly never-ending process of measuring, marking, trimming, and test-fitting, I finally have the forward baffles trimmed to fit the cowl inlet ducts.

I ended up totally re-making the center crankcase baffles from new parts. It was really tough to figure out the proper shape here, so I'll post plenty of photos.

The key thing here is to try for a nice smooth transition up the side of the inlet ducts to the inside surface of the top cowl. This is highly dependent on how you shape your inlet ducts so there is a feedback effect as you work on the shape of the various parts.

Close-up of how the parts join together just behind the spinner:

All the various baffle parts are cut about 3/8" behind the aft edge of the cowl opening:

A view from the other side:

I bent the forward edges of the crankcase baffles inward to help the rubber baffle seal material bridge the gap:

Trimming the outboard baffle on the #2 cylinder was fairly easy. I already made the corresponding modifications to the outboard #1 cylinder baffle in a previous work session.

I had to grind away more baffle material in front of the #1 cylinder to make room for the back of the flywheel:

A view with the cowl on… the gap between the crankcase baffle and inlet duct looks huge due to the camera angle. In real life it's between 3/8" and 1/2".

Same area on the left side. This photo shows where I still need to do some fiberglass work to square up the face of the cowl behind the spinner… that can wait till next summer, though.

Looking in through the spinner cutout. This is the best photo I could get of how the crankcase baffle runs up the side of the inlet duct towards the apex of the cowl. It's almost impossible to see in real life – you mostly have to figure it out by sticking your hands in through the inlets and feeling around. Naturally this makes trimming the baffles a long and tedious process.

On to the next step…

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