Fuel Tank Jigs

I spent a few hours today building the jigs for the fuel tanks. I’m still waiting on the left fuel tank skin from TAF so I can’t build the tanks yet, but I should be able to get started with assembling a the fuel level and drain components on the ribs. I’ve been contemplating alodining all the fuel tank parts since some will not be primed (the surfaces that are expose to fuel). I will probably spray the other su5faces with primer after the tanks are assembled. So I’m wondering if it’s really worth the effort.

I’m also having a bit of a storage issue. I built a wing dolly (which I’ll post about later), but there’s not that much room in the garage to store the wings. I ended up reorganizing the garage so that the front of the plane faces in towards the back wall (rather than the garage door) so that I have more room towards the garage door side. I also was able to tempoarily put on the canopy doors because the garage door isn’t above the canopy in that area. This helps free up some space and I can also mount the hydraulic lifts for the doors.

I still have to finish up the left wing so I may try to get that done first before anything else. The weather is still really nice here in CA, but I’m sure it will start getting more windy and rainy soon and I don’t want to try to be building the wings and having to deal with that. The right wing is mostly finished so I want to try to get that into the garage this week.

The fuel tank jigs are finished, now I just need the left skin and the sealant and I can do the tanks. The jigs went together pretty quick. I used some left over plywood and had to purchase 2 2×3’s for the cross bar. I also did a test fit of all the ribs and Z channels for the right tank.


Right Wing Top Skins

Time: 13.5 hrs

Wow it’s been a few weeks since I posted. In that time I prepped and primed all of the top skins for both wings. I started with installing the skins on the right wing because it’s the easiest in that it doesn’t have the pitot tube. I finished up the wiring and double checked that everything was riveted on the wing structure. I also tested the wiring for continuity, just to make sure there were no breaks or shorts (you never know). I installed the short torque tubes for the flaps and ailerons and the long tub for the ailerons that runs to the fuselage. For the long tube I had to cut a hole in the wing jig so I could pass it into the ribs.

After everything looked good I clecoed the 2 main top skins on. I had tried to also cleo the leading edge skin, but I found that it pulled the wing in such a way that buckled the 2 main top skins so I decided the just get the 2 main skins riveted and do the leading edge skin after. I’m really happy with the way the top of the wing came out. There was one area of about 5-8 rivets the rear spar that needed to be elongated just a little bit to get the holes line up with the spar hole. It wasn’t a cleo pattern issue because all the hole before and after the area lined up fine.

Once the main skins were finished I clecoed  the leading edge and wing walk (wing root) skins. The wing walk skin lined up great. I think there was one hole that was a bit off. The leading edge skin was a real pain though. The tip part lined up fairly well, but as you moved towards the root it got out a bit. What helped was using clecos in every hole on the main spar and also I clecoed the ribs before clecoing the main spar. Still there were 2 holes toward the root end that just didn’t line up. One will get covered by the fuel tank skin.

Wire run to the landing and taxi lights. I used the lightening hole bracket that I purchased for the fuselage.

Had tp make a small how in the jig to get the long torque tube in. I could have waited until the wing was done, but I wanted to get this installed.

Aileron torque tubes installed

Flap torque tube installed

This rib is a bit wonky. I reriveted the front rivets that attaches it to the main spar, but it was still a bit bent. When the top skin went on it straightened out OK.

I installed an 1/8″ stainless steel rod to help support the strobe wire. It runs all the way to the wing tip and keeps the wire from hitting the bottom skin..

Celcos are in on the main skins and it’s ready to be riveted. Too late to rivet though so will wait until tomorrow.

All done. Happy with how it came out. Also the oil canning on the bottom of the wing seems to have gone away and no oil canning on the top.

I need to get started on the fuel tanks. I’m still waiting on the left tank skin from TAF since mine is really scratched (from shipping) and needs to be replaced. I guess I’ll start prepping the parts and maybe get some of the components installed on the ribs. I ordered the sealant and a SEMCO sealant gun so hopefully will have these in the next few days.

Bottom Skins Done

Time: 16.25hrs

This week I was able to finish up the bottom wing skins. I also installed the rivnuts for the inspection panels and for the smaller panels as well. The smaller panels are supposed to be riveted, but I’d like to be able to have them come off for better access to the wing. I installed M3 rivnuts which worked fine.

I ended up purchasing a 4.9mm reamer from Amazon. The 4.9mm reamer is the absolute perfect fit for the M3 rivnuts. I first reamed the hole with the #11 reamer and then used the 4.9mm to enlarge it just a tiny bit. Perfect fit. I haven’t used too many M3 rivnuts on the build so I never bothered to find the exact fit. I think I had either used the #B reamer or the #11 and then just filed it slightly for the ones that I needed to drill out.

One time consuming thing was that while I was wiping off the skins after sanding the rivets I noticed a few spots that oil canned. One spot was especially bad so I had to start drilling out rivets and seeing how to relieve some of the tension in the skin so that it would sit better and not want to bubble. The right wing had the worst issue, but that was fairly easily fixed by drilling out the row of rivets on the leading and trailing edge between the ribs in the area with the issue, then reaming the holes, clecoing and riveting them again. I wasn’t able to completely fix the area near the first flap hinge on the the left wing and the area near the last aileron hinge on the right wing. I was able to minimize it, but it still has a slight bump in those areas. You can’t really see the bump but if you push on the skin in makes a sound like an oil can. It’s much better than before, but still does it a bit. I guess I can live with that and I noticed that maybe when the top skin is on and the ribs are straighter then it may solve the problem, but will have to see when the top skins go on.

Oh I also got my bag of stainless steel rivets from TAF (for the Service Bulletin 0014) so after I get some B2 sealer for the tanks I can install those as well.

Skins are on, rivets are filled and sanded.

I installed M3 rivnuts for the small and large inspection panels.

Bothe the left and right leading edge skins are riveted on the bottom. The top needs to wait because the top skins sit under this skin.

I also did a test fit of the fuel tank skins. One of my skins has a big scratch so I’m getting another one from TAF. Hopefully it will be here soon so I can start on the fuel tanks.

So now I need to flip the wings over so I can finish up the wiring and pitot tube install and get the top skins on.

More Wing Skins

Time: 2.5 hrs

Today I was able to attach one of the leading edge skins. I’m waiting on the other one from TAF so I can’t do that one yet. This went surprising well. It was a bit of work getting it to wrap around, but after getting a few clecos in the ribs it wrapped around fairly easily. I didn’t rivet the top portion since I still need to flip the wings over and do the top skins which fit under this skin.

I also riveted the portion of the inner most top skins (the wing walk area) so I could get all the bottom rivets done. I checked some of the top holes and they seem to line up OK. The   trailing edge didn’t fit as well on the right wing as the left, but not too bad over all.

The rivnuts for the lights also got installed without any issue. The newer bracket I resented from TAF actually had the correct hole size for the rivnuts so that saved some reaming time. SO just need to do the rivnuts for the inspection plate and fill/sand the rivets and then I can flip the wings over.

Outer leading edge on the right wing is partially riveted and rivnuts are installed for the lights. The rib to the left also gets the fuel tank skin attached to it so I can’t rivet that yet. I’ll also need to prep and prime the overlap area.

This is the inner top skin. This fit very well on the left wing and took a bit of work on the right. On the right side it seemed that the bend was a little off and I had to try to move it a bit, which is really difficult to do because it’s a very thick aluminum skin.

Wing Bottom Skins

Time: 24.0 hrs

Over the past few weeks I did quite a bit of work on the wings. I haven’t posted much because the bulk of the work is prepping and priming parts… not too exciting The wings have been going along fairly well, no big issues or problems. The only problem so far was with the fitment of the bottom skins. One particular area is the row of rivets that attach the fuel tanks to the main spar. The main bottom skin also uses those holes and if you line up the bottom skin so that most of the other holes align then this row is fairly far off. I had been waiting for the factory to let me know what to do about the alignment issue. The final fit come was that this is an issue on the Sling 4’s and to just widen up the hole in the skin (not the spar). So with that answered I could finally move onto riveting the bottom skins.

It’s a bit hard to see in the photo, but the row of hole in the primed area are a bit off. TAF said just to open them up a bit. I checked the fuel tank skin and the holes seem to line up OK so these holes will just be sandwiched in between the spar and the fuel tank skin so I guess it’s OK if the rivets don’t fit tight.

Prior to riveting the skins I installed the REV1 of the rear spar lower join angle (WG-ANG-005). When doing inventory I notice that I had a REV0 of the right one and a REV1of the left one so I had TAF send me REV1 for the right. The difference is the notches in the ends of the bends to help prevent cracking. The upper left one in the photo is REV1 and the lower right is REV0. I suppose I could have just made the REV0 a REV1 by notching it… Oh well.

Right wing bottom skins are done. It actually went pretty quick. I think only about 1.5-2 hrs. Now they need to be filled 😦

I have a stray hole in the skin. I will need to drill it out from the other side (to make a hole in the correct location) and then fill this one. I don’t want to drill out this hole because it seems like it will hit the actual rib and not the flange on the rib.

That rivet there will need to be cut. It hits one of the parts that make up the bracket that holds the bell crank for the ailerons.

Left wing ready to rivet.

And it’s finished. Only took about 2 hours. I hand riveted the rivets around the aileron and flap hinges since the pneumatic riveter didn’t fit well.

So next I’ll rivet on the leading edge skin I have (for the right wing I think). Still waiting on the other from TAF. I’ll also rivet the bottom part of the top inner skins, the wing walk area so that I have those bottom rivets done. After that I can fill and sand the rivets.. oh and install the rivets for the inspection plates.

Engine Work Complete

TIme: 6.75 hrs

Over the past week or so I worked on getting the engine finished up. I’m sure I’ll still have a few things to do on the engine, but I wanted to get as much finalized as possible so I can move onto other things. There’s just too many open projects going on at once and I’m starting to lose track of where things are at when I come back to them.

I took a bunch of photos so I’ll just describe what I did after each of the photos. I know I still have a few pending things firewall forward but the bulk of the engine work should be finished. Items remaining are:

  • Purchase and install EarthX battery – I don’t want to by this too soon since it will just need to be charged periodically and should be pretty easy to wire up.
  • Adjust alternator belt, torque bolts and safety wire – I need to get the prop installed before doing this
  • Finalize the throttle and choke cables – I need to wait until the panel is installed or I at least have a good idea where the choke knob will be mounted so that I can cut the cable to the correct length.

I installed the External and Internal Alternator fuses in the engine compartment. I know some people have used circuit breakers in the cockpit, but I didn’t like the idea of running long high current wires unfused and if the breakers were to blow you’re not really supposed to reset it anyways so I decided I’d just put them closer to the source. I also uses a braided ground strap rather than just a wire. It’s easier to see if it’s broken.

Here’s what I ended up doing for the left side coolant hose. NOTE: I should get a picture of the bracket that’s mounted to the exhaust. In any case the hose is supported by a bracket that mounts on the exhaust and then attaches to that using an M8 bolt through the adel clamp. I used a very flexible silicone hose for the coolant hoses. For this side I had to also fit a 60º bend to this main hose since I wasn’t able to get this main hose to bend that tight into the radiator.

You can also see I wrapped the exhaust which I found a few other people doing and one of the guys at Torrance TAF had said was good to do. And you can also see the EGT sensor which I only ran to the rear mounting holes on each side. I had read that doing all four is not really necessary.

I ended up replacing all the nylon locking nuts for the engine mount with all metal locking nuts. I also did this for all the various clamps, etc. You’re not supposed to use nylon locking nuts firewall forward, though I see a few on the Rotax engine (from the manufacturer) so I would expect they should hold up OK.

Just a overview photo of the wiring routing and fuel lines in/out of the fuel regulator.

I’m using silicone and stainless steel teflon hoses so that I have minimal hose replacement when I have to do the 5 year rubber swap outs. The only rubber hoses left are what’s on the engine and in the fuel pump assembly. When that time comes I’ll try to replace those with appropriate non rubber hoses. The one silicone oil hose (connected to the oil tank) is special and is fluorosilicone lined to hold up the the oil.

I used adel clamps to hold the oil and fuel drain lines… kind of overkill I guess. I also combined the left and right side fuel drains so I only have one hose fuel drain exiting the cowling. I still need to cut the drain line hoses a bit shorter.

Another overview photo. I made a few short clamp extensions from stainless steel sheet. One was used to connect the 2 adel clamps for the main oil line that runs from the oil tank to the thermostat. The other connects the 2 adel clamps that are used to hold the fuel line from the fuel flow sensor to the right carb. I also made a bracket to hold the fuel flow sensor.

I ended up running both the oil lines between the thermostat and the oil cooler on the right side. There was just no good place to secure the hose if I ran it on the left side and it comes very close to hitting the cowling and alternator.

Just a shot of the rear portion of the engine. You can see the red wire that runs to the starter and quite a few adel clamps that were used.

UPDATE (09/05/2019): Adding below photos that I forgot to take and some more info.

I was able to get the extension loom from Air Master for about $100 with DHL shipping. This is an extension cable so there are connectors on both ends and Martin (at Air Master) said to leave about 20″ from where the slip ring will be installed which on the Rotax 914 in the center of the engine on the top where I believe the vacuum pump is mounted if you had that option. Having this cable allowed me to close up the firewall for where all the cabling goes through. It’s made from 2 pieces of 1/16″ stainless steel that screw onto the firewall there are grommets also in there for the cables to pass through. Then I put the stainless steel grommet guards on.

Here’s what I ended up doing for the left side cooling hose. I purchased a stainless steel exhaust hanger (9″ JEGS 309002) from Amazon and bent it at around the first hole. I also purchased a stainless steel 1.5″ U clamp to clamp the bracket to the exhaust. It seem pretty sturdy so should work well. This keeps the cool hose away from the exhaust manifold and secures it from moving around.

I didn’t have a photo of how I did the fuel flow sensor. I made a bracket to mount it to the same mounting holes as one of the engine sensors. The hose coming off the regulator is split and feeds the flow sensor and will also the pressure sensor which is mounted on a plate on the engine mount. My only worry is that the 90º bend it pretty close to the inlet of the sensor and the Red Cube manual said not to do that. I spoke to a few people about it and they think that because I’m only pulling 5 gallons an hour it shouldn’t matter, it might matter with a higher volume of fuel since the bend can create some turbulence in the flow and mess up the sensor readings. If I get inaccurate readings I have an alternate idea of how to run the hose so will have to see.

On the ride side of the engine it’s a tight fit for the exhaust manifold, cooling hose and oil line. I probably should add something to hold the oil hose to the cooling hose to keep it from touching the exhaust.My other worry is that the box that goes around the air filter will hit the cooling hose so I’ll have to move it… will have to wait to see when I get the air box.

TAF Service Bulletin #0014

TAF sent a Service Bulletin on 8/18/2019 on replacing rivets in the wing spar and fuselage with stainless steel rivets. I guess the aluminum ones will start to give too much and cause cracking in the paint. Fortunately I haven’t riveted the skins onto the wings yet so at least that part I don’t have to redo, but I will need to drill out and replace all the rivets along the bottom to the main spar in the fuselage.