Cowl Cutting & Baffle Tensioners

The Sika has cured on the rear window.  There's a bit of a mess for me to clean up, but for the most part everything lined up pretty well and the window is setting where it needs to. I still need to clean up the rollbar area and put a final bead of Sika on it to make the transition to the rear window look a little nicer.  I'm waiting to do that until I see if I need Sika out for anything else though - easier to do it all at once vs a little here and there.

I'm still chipping away at the lower cowl fit.  What a pain!  The right vertical side is where I needed to extend the edge.  The flox worked really well here, other than being a nightmare to sand.  This picture is before I took it down to the final edge - a lot of work for 1/32-1/16" addition.  It looks nice and consistent now though.

I had originally built up the bottom (inside) of the cowl with flox to try to get it to lay on the fuselage better.  About 5 hours of sanding later, it turns out that didn't work.  Oh well, there's a lesson in everything I guess.  So I pretty much sanded the entire flox addition off the bottom and am now almost back to where it was from the factory.  That factory shape still doesn't work though, so I need another solution.  The only thing I can think of at this point is to cut a relief in each corner to give the bottom the flex it needs to bend up toward the fuselage edge.

The cut lets the bottom snug up against the bottom fuselage flange since it's no longer constrained by the strong cowl corner.  I will push the cowl into position, then fiberglass over the cut to hold the shape. Once it's dry I will pull it back off and put more fiberglass (probably flox again - yippy) on the outside to fill the crack and smooth the outside shape.

The corners and bottom of the cowl need to be pushed in while the epoxy cures.  A few well placed boards did the trick.  I made a small square of fiberglass (3 layers about 2x2) and put it in position on the inside over the crack.  I'll know tomorrow if it was a success or not.

I can't do much additional fitting while the lower cowl dries.  The top cowl gets inlet ramps to help smooth the air out as it enters.  They don't fit very well (shocking, I know).  I put them in position as best as I could guess and drilled some holes to hold them.  They will get epoxied on once the top and bottom cowl are in place and attached to each other.  The instructions warn that epoxying them with the top off will cause fitment problems because they will make the top cowl more rigid.  So everything has to be in position while the epoxy cures.

This is a little out of order, but the other day before the lower cowl went back on I worked on the baffle tensioners.  Each cylinder has a couple of baffle sections that wrap down and around the cylinder fins.  These have to get pulled snug to the cylinders and held there (otherwise the air pressure will just push them away from the cylinder and allow air to leak past without actually cooling the fins).  Each cylinder on a side has a baffle on the outside and inside fins, then they get tied to the matching baffle extension on the other cylinder.  There are a lot of ways to do that, but the most common are with stainless rod that you thread each end of and use nuts on, or safety wire.  Van's supplies stainless rod.  All of the experienced builders say it's a real pain though, and safety wire is the way to go, so that's what I went with.

Each baffle has a flange with a hole in it that the safety wire can go through.  My first approach was to cut a small piece of stainless rod for the wire to wrap around.

I put the L on the rod to insert it into a second hole.  I'm using large safety wire, and it doesn't hold the rod very tight.  By having the second hole in the flange, the rod can't go anywhere.  I slid some old brake line over the safety wire to protect it from rubbing against stuff.

The rods worked fine, but then I saw that an even easier method that most people use is to simply wrap the wire around a washer.  There is very little tension on these baffle pieces, so the wire really just holds them in position vs pulling them much.  The washer is plenty of surface area.  When I pull out the high temp RTV to seal all of the baffle gaps, I'll put a dab on each washer to keep them from vibrating.

Fiberglass the Cowl

The fuel hose from the fuel flow sensor outlet still needed to be clamped to the engine mount.  I did that and also connected the wires for the sensor.

I made the rough cutouts for the louvers yesterday, but they still needed to be finished up.  I sanded all of the cutouts smooth and countersunk the rivet holes.  I'll probably wait to rivet in the aluminum pieces until I'm done with everything else on the cowl and it gets a coat of epoxy primer and paint to seal the inside.

I can't drag my feet any longer - it's time to tackle the awful fit of the cowl.  I wrote a bunch of notes on the cowl in an attempt to remember what needs to be done.  Here are all of the reference pictures for me.  Nothing interesting to see other than how ugly the cowl fits out of the box.

I mixed up a full cup of epoxy with flox and a little cabosil.  The flox is for structural strength, and the cabosil is simply a super light filler whose purpose is to help keep the epoxy from slumping with gravity.  Flox doesn't spreads very smoothly, so I know I'm going to have a lot of sanding in my future.  I tackled the right side vertical edge by sanding a scarf and adding flox so I can ultimately extend the edge about 1/16" to fit the firewall.  The lower edges that skybolt to the fuselage pucker out (have to be sucked up against the fuselage) and need to have more material to allow me to sand them even with the fuselage, so I added 1/8" of flox to the inside.  That will allow the inside to set against the ledge of the fuselage and give me enough meat so I can essentially taper off the original material on the outside.  I also added meat to the inside of the bottom corners (the round corners of the fuselage) so I have more material available to sand the outside to match the fuselage curves.  The front portion of the cowl is going to take the most work.  Matching the top and bottom cowl will be a lot of iteration I think.  I built up a lot of the areas that currently have gaps, then I'm just going to have to slowly chip away at sanding them to fit.  I don't expect to get perfect with the flox.  Once I'm close, I'll be able to fill in the small gaps and smooth it all out using micro.  Flox is very hard to sand and shape, but it's strong.  Micro (small glass balloons) is not nearly as strong, but much easier to sand and is what is usually used for the vast majority of fiberglass finishing.  Once the main shape is better, I'm also going to have to use glass cloth to fix the nosebowl flanges.

The cowl is going to take a day to dry, so in the meantime I started working on the rear window.  It's still too big and needs to be cut down to size.  The first thing I did was prop the front canopy up a little and scribe a line so I can make the first cut to get it parallel to the front.  I think Van's usually recommends something like 1/16" gap, but I'll probably do about 3/32 or 1/8".  I've heard of guys getting stuck canopies if they make the gap too small and the plexi swells because of heat.  1/8" sounds like a lot, but I'm 99% sure I'm going to do a fiberglass targa strip over the back edge of the canopy, which will cover the gap.  The targa strip is just a fiberglass/carbon fiber strip that goes from the side canopy rails, over the top to the the other side rail.  It's not commonly done, but from what I've read it provides a tremendous amount of stiffness to the canopy.  As is, the canopy flexes/twists pretty bad when lifted open and closed, making it super easy to catch the right side plexi corner on the roll bar when lowering it closed.  Do that too quickly or accidentally drop it and you've got a broken canopy corner.  The targa strip will also help me smooth out the uneven gaps on my side rails.

Fuel Hoses, Cowl Louvers

It's been a while.  Between being away from home for a bit and starting a new project for work, I haven't had much energy to work on the plane.  Hopefully I can get back to it now though.  I've done a number of random small items over the last few weeks, but nothing too exciting.  I finished up most of the FWF wiring, so I sealed the ends of the pass throughs with fire barrier.  then I wrapped them in silicone tape and put the hose clamp on (no picture of the final product).

I received the last few fuel hoses I needed.  The recommendation by the fuel flow sensor manufacturer is to mount the sensor in a way that just suspends in with the fuel hoses (with the hoses adel clamped within about 6 inches of the sensor), as opposed to rigidly mounting it on the engine anywhere.  I have quite a bit of room on the lower left firewall, so that's where I decided to locate it.  The one remaining task I have is to adel clamp the output hose that goes to the throttle body.

The last fuel hose is the one that goes from the firewall fitting to the intake of the mechanical fuel pump.  I ordered a 45 degree fitting to go on the firewall side to help the hose clear the engine mount and allow more room for the scat tubing to the cabin heat box (removed in this picture).  The one gotcha I discovered was that the fitting on the fuel pump was also a 45 degree fitting, which kind of torqued the hose in a very tight radius and made it rub the engine mount.  I ordered a new straight fitting from Aircraft Spruce, only to discover the next morning that I already had a spare straight mount.  Oh well, I guess now I'll have another spare that I can forget about.  With the straight fitting in place, the hose fit much better, although it's going to make for a very tight route for the cabin heat scat tubing.

Switching gears - It doesn't look like much, but I spent an afternoon prepping the cowl hinges.  I drilled large holes in between the rivet holes.  It's not absolutely necessary, but it's recommended that in addition to rivets attaching the hinges, that epoxy or proseal is used as well.  The addition of an adhesive just gives the rivets some additional support and minimizes the chance that they'll work loose over time.  The holes provide space for the adhesive to get some extra grip.

I figured I needed to cut my teeth on something fairly simple to learn a little about fiberglass.  I scuffed up the area around the oil door and epoxied/riveted the doublers in place.  I already learned some lessons with it -  I didn't add quite enough flox to the epoxy, so it was a little runny after clamping/riveting and made more of a mess than it should have.  I've heard that the oil door can pucker out a little bit during flight due to the high pressure in the top of the cowl, so I decided to bond on the chunk I had cut out from the cowl to double up the strength of it.  With that in place, it's very stiff.

After spending hours and hours looking at the cowl fit and marking it up everywhere to help me remember where I need to thicken it up, extend edges, etc, I needed a more mindless task.  Nowadays Van's recommends adding an optional louver on the lower cowl to help with cooling.  Apparently the change from the simple front landing gear to the new elastomer type impacts the exit air enough to raise engine temperatures.  The louver provides a little more exit air.

I laid out where each louver would go and match drilled them to the lower cowl.

Once the marker holes were drilled, I expanded the holes that will form the sides of each cutout.

Lastly, I cut out the material between each hole.  The aluminum piece will be riveted to the inside of the cowl and the aluminum tabs will be bent inward to catch the air.

Misc. Odd Jobs

Even though the oil cooler is pretty solid with the added aluminum angle I put on the corner of the baffle, people tend to recommend still adding additional stiffness to the whole setup to keep the baffle from cracking.  One common approach is to add some sort of a brace from the inside edge of the cooler over to a rocker cover screw to essentially create a rigid triangle.  I had some leftover steel tubing from when I made my exhaust pipe hangers, so I decided to use that to create the brace.  I tried and failed 3 times - that tubing was just too thick to get bent at the exact angles needed (not only bent to go from the cooler out to the rocker cover screw, but also bent at a second angle to drop down vertically as well).  I finally gave up and ordered some steel tubing of the same size but half the wall thickness.  Still plenty strong, and bending was much easier.  With that in place, I think the cooler is rock solid to the shaking baffle, and the baffle is solid to the shaking cylinder.  Hopefully that means no baffle cracks.

With Dad here, we started to tackle all of the random work that is a little easier with a second set of hands.  The first up were the leading edge lights on the wings.  We reorganized the shop and pulled each wing out of the stand to lay them down so we could do the crazy part - cutting holes in perfectly good wings!  I didn't get pictures of the process, but after scratching our heads over the instructions (not Van's) to make sure we 100% knew where to cut the hole, we used a template and went to work.  Other than being a bit nerve wracking, it was relatively easy and uneventful.  Then we chopped down the install bracket to fit between the ribs of the last wing bay, drilled holes and installed nutplates for the mounting screws.  The brackets were painted black to help them disappear in the cavity a little better.  Then, using the wing cutout as a guide, we trimmed the lenses that get inserted and are held in place with nutplates and screws.  The lights themselves just drop into the bracket and are attached with screws.  Once the wings are on the plane, I'll have to aim the lights - the bracket has oversized mounting holes, so can be tilted up and down just by loosening the screws.  I'm leaving the lenses off until after I paint.

Next up was the part I'd been dreading - getting the forward top skin riveted on.  This is the last major item to rivet on the entire plane, and probably also the most awkward.  We pulled the canopy off, and after double checking all of the wiring to make sure there wasn't anything else I needed to do before my access to behind the subpanel was covered up, we got to work riveting.  Well, that was after we fought with the top skin just to get it in place.  We ended up having to use ratchet straps to pull in it down tight to get the longeron clecos in.

I laid underneath the panel (bent backwards over the spar carry through - super comfortable!) and bucked rivets while Dad used the rivet gun.  It took a good chunk of the day, but we got it done!  There were a few rivets that were just impossible for me to reach due to where I had mounted some of the electronics boxes, so I ended up using a couple of pop rivets in those locations.

I reinstalled the canopy pin mechanism (I had to take it out earlier in order to buck the rivets along the center subpanel), and we reinstalled the canopy.  I can't say that I look forward to taking the canopy off and on very often!  That might have been the most stressful part of the entire build so far.  It's very difficult to get the hinges to line up with the pins, all the while trying to hold the canopy in position so you don't snag the leading edge skin on the fuselage.  I've read horror stories of people creasing that canopy frame skin and essentially having to rebuild the canopy frame to fix it.  We did manage to get it back on without any damage.

I will still have to crawl back under the panel at some point to put proseal in the gaps of the subpanel to waterproof the seam.  I need to wait for my back to return to a normal shape before I try contorting under the panel again though.  I didn't get a picture, but we also fit some weather stripping to the underside of the canopy frame where it sets on the fuselage canopy rail.

Switching gears, we moved back up to the firewall forward stuff.  We spent a while just staring at things trying to sort out the last bit of fuel hose routing I need to do.  The area is getting so full of stuff that there really isn't a perfect routing to take, but I think we landed on the best option.  We took measurements and I shot them off to the guy who I use to make hoses.  I ordered the fuel hose that goes from the firewall to the mechanical pump, then one from the outlet of the pump to the fuel totalizer, and from the totalizer over to the fuel servo.  I'll get those hoses next week sometime.  Fingers crossed they're the right length.

The hose that Titan installs for the fuel servo up to the distribution spider took some thinking too.  It's the perfect length for their setup of course, but I'm using crossover exhaust, which while it's fairly standard in the RV world, isn't the normal straight pipes option that is on most engines.  What that means is that Titan's planned routing for the fuel line takes it right between the sump and one of the crossover pipes.  There's clearance, but we're talking like 1/4".  I don't know that I could insulate that well enough to not have some heat issues with the fuel.  What we landed on instead was routing the fuel line over the front air intake pipe and down in front of the rear one.  I'll need to come up with a way to adel clamp it to the rear intake pipe.

Next up is the air intake box that hangs below the fuel servo.  The FAB, as it's called, is a fiberglass scoop with a couple of aluminum plates.  As simple as it looks, it took the better part of a day to get it "finished" (not finished).  The top plate is put in place to be able to apply just enough squish of the air filter to keep it in place.  One of the issues I've seen over the years is that the K&N filter tends to shrink over time.  When it does that, it no longer stays squished between the top plate and the fiberglass bottom of the FAB.  Then it starts to vibrate with the engine and eats its way through the fiberglass.  From what I've gathered, as long as you watch out for that and replace the filter before it shrinks too far, everything is fine.

Part of the fiddly nature of getting the FAB set up was getting it lined up with the cowl scoop.  Since the engine is angled and not pointing directly ahead (offset thrust for a host of aerodynamic reasons), the FAB has to be angled back to center to meet up with the cowl center line.  We first bent the top plate of the FAB up to match up to the top edge of the scoop, then did a lot of back and forth to get it centered laterally.  It's still not perfect because of the poorly shaped fiberglass, but it's close enough that I'll be able to match it up when I do the finish fiberglass work.  I have to mold a fiberglass extension to the scoop to bring it aft a few inches and mate up with the baffle material that will be attached to the front of the FAB intake.

Moving on from the engine, we went back to the wings.  The wing tips also get lights in them, although these are position/nav lights, not the landing lights that are in the wing leading edges.  I built these lights from a kit a long time ago.  They are LEDs attached to circuit boards that will set in the wing tips and get covered by a lens.  The circuit boards have resistors and other bits on the back side, so the wing tips need to have cutouts.  We used the provided template and made the cuts.  The circuit boards can be installed using screws, but the company says double stick tape works just as well. So that's what I'm going to go with - got some heavy duty automotive body trim tape.

The "lens" that goes over the area comes as one big piece for both wing tips.  It has to be cut down to size.  That was an iterative process, not wanting to take too much off by accident.  The fiberglass is pretty sorry, making the fit a little harder.  I'll have to do some clean up when I work on the wing tips.  One nutplate and screw on the top and bottom corners will be all that is needed to hold the lens in place.

We needed something fun, so decided to go ahead and get the interior fit and mounted too!  While a lot of the interior just uses velcro strips stuck to the skins, there are a few screws necessary, so I figured we might as well do it now and ensure it fits before I start doing all of the final finish work.  We started with the glare shield trim.  I had already drilled the holes for the screws a while back using the template the company provided. Lo and behold, all holes matched up with the trim except the outermost ones on each side.  It looks like they may have sent the wrong template or something.  I'm going to have to remove the trim and locate where the holes are supposed to be.  It's a little irritating to have extra holes sitting in my new glare shield, but I can probably just 3D print a tiny black plug to cover them up.

The rest of the interior install went very well (minus me managing to break my pop riveter while installing a rivnut).The fit is pretty amazing and the quality is great.  The only thing not shown in the pictures is the front and baggage area carpet and seats.  Once we verified it all fits, we pulled it back and out so I don't accidentally get paint on it when I'm spraying the fuselage.

Oil Shutter Control Cable

I had always figured I'd be drilling another hole through the firewall for the oil cooler shutter cable.  After a lot of contortions trying to figure out how to route the cable without interfering with anything else, the obvious solution hit me - just route it through the existing penetration on the right side firewall where all of the wires go through.  I clamped the cable to the right rib and wrapped the portion in the firewall passthrough with spiral wrap and silicone tape to keep it from chaffing wires.

I put an adel clamp on the baffle as well as the engine mount.

I still don't love that the push/pull direction is the opposite of what it would ideally be (push to close, pull to open - I'd prefer it to be push to open since that's where it will be 90% of the time), but reversing it would have been a real pain.  I'll get over it.  I'll have to figure out how to change the label on the panel without causing too much damage though.

EGT/CHT Wires & Crankcase Vacuum Kit

I finished up the lower spark plug and EGT/CHT wire routing tonight.  The EGT and CHT wires are all differing lengths since they ship the same length but obviously have different distances to travel to get to each cylinder and exhaust pipe.  They already come with spade connectors crimped on, so I took the lazy way out and just bundled them up to get them to land in the same general location.  Then I trimmed the sensor wires that come from the engine black box and crimped connectors on (I doubled back those wires to give myself some extra length to put a new connector on should I ever need to).  For now the connectors are all just hanging out so I can test the connections, but I'll eventually put some wire wrap on them to clean them up.  The left and right side are done about the same - I just forgot to get a picture of the finished right side. 

I fired up the EFIS to see if I at least had some sensor readings.  Success!  All CHT readings are the same, which they should be, and all of the EGT readings are also the same.  I put a heat gun on one of the cylinder heads and exhaust pipes to make sure the sensors were indeed reading correctly.  Everything seems to be working as it should.

The other day I connected the oil breather crankcase vacuum valve to the left exhaust pipe.  I removed the Van's rubber hose that was on the oil breather port and replaced it with the much nicer silicone tube that came with the Antisplat kit.  This is the bright blue tube in the picture.  While it is getting pretty tight behind the engine, the picture actually makes it look tighter than it really is.  Everything has room and is not rubbing anywhere.

The tube swings down behind the oil cooler and drops down to the exhaust valve.  I split the tube to insert a blow off valve and tube.  This is a one way valve that will pop open if the valve at the exhaust ever gets plugged - theoretically saving me from a blown front seal on the engine.  I plan to check the exhaust valve at every oil change, so it should not ever get to the point where it can clog up, but better safe than sorry.

I haven't routed the blow off valve tube yet.  I think I'll just clamp it to the firewall where the Van's oil breather line was supposed to be clamped, then just let it hang over the exhaust. There shouldn't ever be anything coming out of it unless it's an emergency, and if that's the case I don't really care about the oil that'll be on the belly from it.

I pulled the tube off of the exhaust valve for now so I could put the engine dehydrator on it.  I think in the long run I can probably attach the dehydrator to the end of the exhaust using a big stopper, but for now I'll just keep the tube detached for it.