Firewall Rivnuts

Time: 0.5 hrs

Trying to just keep doing some things on the plane while I wait for parts. I installed a few rivnuts in the firewall. Now that I know I’m going to use the 914 I think these ones are safe to install. They’re for the TCU mount (M4), static pressure sensor (M4) and the starter solenoid (M5). The manual calls for M3 for the heater box, but then it says something about riveting it on the heater box construction page. I’m thinking I can drill out the 6 holes and put in rivnuts so the heater box is removal. The only odd thing is that the rivnut will also hold in the channel piece on the cockpit side so not sure how that will work out. I would imagine the end of the rivnut will fold over and hold it ok… just kind of weird maybe. I guess I’ll wait until I get the heat box just in case.

Since I’ll be using the LifoPo EarthX battery I bought a battery box for that from Aircraft Spruce. It should be here soon. Hopefully the install will go easy and I can reuse some of the existing holes. I just need a few more mounts from TAF and I should be able to wrap up most of the firewall stuff.

Put some screws in the rivnuts… boy that was hard 😁

Happy Thanksgiving!

Time: 0.75hrs

Just finished up the work from yesterday on the channel cut into the main gear for the brake lines. I filled a few spots where the router bit hit the edge of the channel with some fiberglass epoxy and primed it. Not perfect but looks good. When the brake line goes in it will look even better. I also found these polyester UV resistant clamps that would be good to use on the top and bottom of the gear to hold the brake line. The RTV will hold the line in fine along the back of the gear, but it may not be enough to hold it where it makes the bend into the brake caliber and at the top where it bends into the fuselage. I guess I’ll have to see when the time comes for that.

Now to cook some turkey.

Brake Lines Through Landing Gear

Time: 2 hrs

I wasn’t looking forward to this so it was hard to get motivated. Since I’m using stainless steel covered teflon brake lines I needed to widen out the channel that runs along the back of the main landing gear down to each wheel. I purchase a 9/32″ straight router bit (I couldn’t find a round nose one in that size). I put a block of wood on the router as a guide so that I couldn’t accidentaly slip out of the groove too much. I had to make three passes (probably could have done it in 2) down to a little over 1/4″ depth. It came out pretty good. There are a few spots that I have to fill because the bit knicked the edge of the channel. Also I had a quickly caught slight disaster that caused a few inches of the left side channel to be a bit deeper then wanted (the router bit started to move out of the chuck… got to make sure the chuck is tight ).

In other news. I’m still waiting for my GMU mounting bracket. It seems like everyone else got there’s but mine is still being shipped. I hope by next week or so. I real am not looking forward to installing that, but Peter was successful so it gives me hope that it may be doable. I also contacted California Power Systems and the lead time on the 914 is only 2 weeks so maybe January or so I’ll order the engine. I’d like to get the canopy and install that, plus any firewall forward parts I may need before the engine is ordered so that I’m ready to put it on the plane soon after it arrives. Additionally I verified that the fuel pumps and oil tank come with the engine so those don’t need to be purchased separately. I will need to get the oil cooler, radiator, and alternator.

Did a quick test in a block of wood. The brake line fit in nice and tight. Should be good to go.

Router bit set to a little over 1/4″. Didn’t get a photo of the wood block guide. Basically I just cut a small 1-1.5″ pieces of 1×1 wood and clamped it to the route base with a C-clamp on one side so that I could rest that on the edge of the gear and keep the router stable.

Came out pretty good. A few little knick to fill. This makes a mess.

The brake line fits pretty tight in the channel, you have to tap it with a rubber mallet to get it to seat. There’s a few spots where it’s not super tight though, but I’ll use some RTV when I install the brake line (after painting) that should keep it in place. Also I’ll probably use some kind of clamp on the bottom because it’s a fairly hard bend into the caliber. The clamp will be hidden inside the wheel pants. I was also looking at a way to use some adel clamps to hold the brake line down but I can’t really figure out a good way to install them. I don’t want to drill any holes in the gear for rivnuts.

Pitot and AOA Lines

Time: 0.5hrs

Almost forgot I had to run the pneumatic lines for the AOA and pitot. That should finish up any fuselage wiring/other lines that need to be run.

I used some colored 1/4 lines. One for the AOA and one for the pitot, both run to the pitot in the wing. I’ll have to install a connector here so it can join the lines from the wing. The hole is kind of packed. Might need a second hole on this side.

Cleaned up some of the wiring. I tried to route it where I think it will be going. The VPX will be in the middle so most of the wires go there. The ELT will mount on the right side on tabs and the COM2 and audio panel will mount on the left side on tabs.

Wiring Runs Done, More Fuel Lines, and Brake Lines

Time: 2.5 hrs

Things accomplished today:

  • Installed -4AN fittings on brake lines and ran brakes lines between parking brake area and wheel calibers
  • Ran wiring for wing strobe lights, taxi/landing lights and fuel sender
  • Ran fuel feed lines to fuel filters and installed fittings
  • Secured wiring and reviewed clearance from rudder cables

Today was a small milestone for the Sling project. As far as I can tell all of the wire runs through the fuselage are now done. I secured down most of the wire ties and also made sure that there is adequate clearance to the rudder pedal cables.

Not too messy and clearance to the rudder cables looks to be good. The rudder cable is a bit slack in the photo so there’s a bout 1.5-2″ of clearance to the wiring

The wring runs up the front of the last console support in the center. There’s a tie wrap mount in the center of the support to keep the the bundle in the center. I’m thinking to maybe adding a cross brace and another tie wrap mount towards the bottom just to keep the bundle from moving into the rudder cable path.

And there’s the mess. Actually everything has temporary labels on it so I know where everything goes… it really looks worse then it is.

I also ran the bundle of wires out to the wing roots. This bundle includes wiring for the fuel sender, Strobe/Nav Lights and Tax/Landing lights. I used different color striped wiring to tell the difference between the landing and taxi lights. I suppose you can also use a multicore-core cable and get some shielding as well. The LED lights don’t draw too much current so EMF should be relatively low.

Brakes lines are run out to the brake calipers from the parking brake area. I need to look at making the groove on the rear of the landing gear a bit deeper and see if I can get the brake line to secure into that groove. I don’t want to use zip ties to hold the brake lines on.

I received the 30º fittings a few days ago so I was able to get the fuel feed lines connected to the fuel filters. The fittings worked well to turn the lines in towards the middle away from the rudder pedal cables. I’m going to leave the ends that attache to the fuel selector unfinished right now until I get the fuel sender and know the exact length they need to be. I’ll also secure the hoses a bit better once I know they don’t need to be moved at all.

I purchased some “cobra” tie wraps also called low profile tie wraps to secure the fuel lines. These tie wraps have a more even grip on the hose so they won’t tend to pinch in on the hose like a regular tie wrap. I also will wrap the area with silicone tape prior to zip tying. I secured the return fuels to the console support behind the fuel filters using a single tie wrap and mount.

Pitot Heat Wiring and Fuel Lines

Time: 2.0 hrs

Things done today:

  • Installed the second -6AN bulkhead fitting to firewall
  • Installed the right side fuel return line
  • Ran wiring for pitot heat to left wing root
  • Mounted second fuel pump 

I received a few of the parts I was waiting for from Summit Racing as well as some wire from ProWire USA. I was able to finish running the fuel return lines and also ran the wire for the pitot heat to the left wing root. 

Prepping the 2 12AWG wires for the pitot heat. I couldn’t find any 12-2 multicore wire so I used single wires and twisted them to cut down on EMF. The pitot heat can draw up to 12A at 14V so it’s got to be a beefy cable for the 25ish foot run out to the pitot tube. I also ran a single 22AWG wire for the heater sense connection since I’ll probably use the regulated pitot heater for better  heat management. I’m hoping it will help keep the amperage lower because that little 40A alternator is going to be taxed with all the electronics being used.   

Pitot heat wires run out to the left wing root. Only one more bundle to run for the lighting. Looks like it should all fit. 

It’s getting a little tight under the angle cut out of the center console. I have one more good sized bundle to run for the strobe/nav and landing/taxi lights.

Both -6AN bulkhead fittings are in. 

Mounted the second fuel filter. Still waiting on the 30° fittings to finish up the hoses. 

Fuel Lines and Fuel Filters

Time: 2.5 hrs

Things done today:

  • Mounted one of two fuel filters
  • Ran left side fuel return line
  • Installed -6AN bulkhead fitting in firewall for fuel feed line
  • Cut out soundproofing hole for the flap and aileron control tubes

I spent some time today contemplating the placement of the coarse fuel filters. The manual calls for two filters one on each tank feed line before the fuel selector. I’ve seen at TAF Torrance that the Sling 2’s have one filter in the engine compartment right after the fuel line comes through the firewall. While this is a bit simpler and probably easier for maintenance I’m thinking maybe two filters is better just in case one gets clogged. You could always run off the other tank then. I purchased two 40 micron filters and some Adel Clamps from Summit Racing. These fuel filters are nice because they have -6AN fitting on them so they will connect right up to the fittings on the fuel lines without any adapters. I guess one thing to note is that I’m probably note buying the full firewall forward kit (just the parts I need) since I’d really like to make all the fittings AN type which is more prevelant in the US. A lot of the TAF parts and fittings are metric.

Pieced together the console and instrument panel to get an idea of exactly where the fuel selector is located. That’s not the throttle console I’m using since I have toe brakes, but it’s the same size as the toe brakes one so that will work. It was way too tempting not to sit in the plane. I actually haven’t sat in it yet so well… I did… didn’t get a photo though, maybe I’ll take a selfie tomorrow in it. Does anyone know how the throttle console mounts to the instrument panel? I saw on another builders blog that they had an angled metal plate (not sure if they made it or not) behind the fuel selector mounting area. So I’m wondering do you drill a hole into the leather and fiberglass and install rivnuts? Just curious.

So I’m thinking that I’ll mount the fuel filters vertical on the console support though the manual shows them on the floor. It should make it easier for maintenance and I don’t want them banging around so I want them secured to something. I’m going to use 30º AN fittings on the bottom so that I can angle the hose in and away from the rudder cables. Unfortunately I could only mount one because I only had one M5 rivnut (will need to order more). I also ran the -4AN (6mm) return line. I couldn’t run the return line for the right side because well I kind of melted the little yellow plastic part. Note to self don’t heat hose with heat gun when the fitting is on it. The best part is you have to buy a whole new fitting to get the .02 yellow plastic part :-(.

Right now I’ll just use the one hole for both lines and also the electrical wiring seems to be big enough. I ordered the wiring for the left and right wing connections so I should be able to work on that next week.

I installed a -6AN bulkhead fitting to the firewall. I will do the same for the return line, I just need to order more seal washers for that side. This the the engine side of the firewall with the -6AN fitting.

And the cockpit side of the firewall with the other end of the bulkhead fitting. I’m thinking maybe I should do the same for the brake line rather then using the grommet…Hmmm. The thing is the more fittings you have the more potential for leaks… though probably not much of a concern. The main reason I want to put in the bulkhead fittings is because I’m going to switch to SS braided hose for the engine compartment fuel lines with fire sleeve. The rubber hose I’m using is only rated to around 300ºF. Also by using the teflon SS braided hoses rather than the Rotax rubber hoses you don’t have to do the 5 year hose replacements since the teflon hoses will last a lot longer under the higher heat conditions… so maybe 10-15 year replacement.