Brake Line Torquing

Time: 1hr

I haven’t worked on the plane for about 2 weeks now. My wife (Rose) and I had a great trip to Germany to run the Berlin Marathon. I was almost able to meet my goal of running a sub 4 hour Marathon. I came in at 4:00:19 so missed it by 20 seconds. Oh well we have Chicago Marathon in a few weeks so maybe that might be the one. My mother and younger brother Jason went as well. My brother speaks a bit of German so that helped quite a bit, of course we were all completely lost when we got to Prague. We also went to Dresden and Heidelberg on our way to and from Prague. Unfortunately we didn’t have time to visit Peter V. and Pascal (2 other Sling builders) on the trip, but maybe we will try to do another Europe trip next year to run another Marathon and if they still want us to come we will be there. The other excitement was that I separated my AC in my shoulder the day we were leaving for Germany. So in addition to last minute packing we had to do an ER run. The good news was the doctor said that running wouldn’t make it any worse, the bad news was it was extremely painful to run. Of course being the stubborn person I am I ran the Marathon anyways and got a PR to boot.

Well back to airplane stuff. Today I went through and torqued all the AN4 brake line fittings. I’m thinking that I want to put in the brake fluid now rather then after I get it painted just to make sure I don’t have any leaks, etc. The brake lines that run down the back of the gear can be easily pulled away and masked off so they shouldn’t get in the way for painting. I need to read up a bit on how fill the lines with fluid. I watched a YouTube video and it seemed fairly straight forward. Basically you pump the fluid up from the fitting on the bottom of the caliper up through the cylinders on the pedals until it comes out of the reservoir on the firewall. There may be a bleeder valve that needs to be opened on the cylinders so I still need to look into that.

The other good news is that the box of upholstery (3 large cow hides and 25 ft of carpet) I sent to TAF in South Africa finally arrived there. It sat in the FedEx warehouse for almost a week because no one thought to call me to find out who was going to pay the duties on it, even though I put that I would pay them on the customs form. The shipping was outrageous. I figured it would be a few hundred dollars, but it turned out to be around $1000 to ship it to TAF. I probably should have just done the upholstery here in the US, but it will be nice to have the real TAF made seats and I want to support them in their business as well.

I purchased a set of crow foot wrenches to use on my torque wrench so I could torque the AN fittings. Since the crow foot wrench adds a bit of length to the torque wrench you need to do a little calculating to determine the exact setting of the torque value on the wrench. It’s a fairly simple calculation and I even found a site that has a calculator that figures it out for you.

The above screen grabs are from the Engineer’s Edge Website. I needed to torque to 11 lb-ft (132 lb-in) so after putting in the necessary distances it came out to 10.25 lb-ft (123 lb-in) and that is what the torque wrench was set to. Really 11 and 10.25 are pretty close so I probably didn’t even have to worry about the calculations, but what the heck.

Brake fittings installed

Time: .75hrs

I guess I’m getting pretty good at installing these fittings on the brake lines. Installing the two 45 deg. fittings on the brake line ends near the calipers only took 30-40 minutes. The spreader also helps a bit, but you still have to cut back the stainless steel braiding to get the olive to fit all the way onto the Teflon hose. The 45 deg. fitting also seems to work very well. The straight fitting put a hard bend in the hose and tended to pull the hose out of the channel, but now the hose sits into the channel much better. After I get the plane painted I’ll put some RTV in the channel and tap the hose into the channel with a rubber mallet to get it to seat in. I also found some nice plastic coated aluminum zip ties that I think I’ll use at the ends just to keep the hose in place. The zip ties will be hidden under the wing fairing and wheel pants so it will look clean.

The 45 deg. fitting works well to minimize the hard bend in the hose that the straight fitting would have had.

Hose run through the channel in the gear. The hose fits in fairly tight so it’s not completely seated right now.

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.

Brake Calipers

Time 0.5hrs

I don’t want the brake calipers to be sitting around because they’ll get lost or damaged so I put them back on the wheels. I’ll have to take the wheel spats off again to do the brake lines and I’ll torque  the caliper bolts then as well. 

The calipers slide into the large holes on the inside of the wheel rim. The new spat brackets allow you access to install or remove be the caliper. 

I put some high temperature anti-seize on the posts that slide into the holes. Don’t get it on the pads though. 

Sorry I forgot to get a photo of the assembled brakes. I’ll get one when I do the brake lines. 

Nose Wheel Spat Finished

Time 1.25 hrs

Things done today:

  • Filled in unused holes in nose wheel spat (factory pilot hole for mounting)
  • Cut top of nose wheel spat flush
  • Drilled holes for tow bar
  • Connected and torque rudder pedal to nose wheel push rods

The forward part of the nose wheel spat is a little longer then the rear so I cut it flush with the rear and sanded it to finish the edge. The front part of my nose wheel spat sits about 15mm from the strut. The manual says 5mm, but it looks like the spat sits at a good angle and clearance to the front tire is good as well. Also the forward holes that screw into the mount were very close to the factory ones so I think it’s in a good spot. Also I checked the new manual and it doesn’t say anything about putting rivnuts into the nose wheel strut, but he old manual does so it’s possible that it’s not needed. I’ll have to check with the factory though.

Drilled the hole for the tow bar. That was kind of a paint in the butt. I measured the spacing from the rivnut to the center of the hole and then eyeballed the angle. Then I drilled a 1/16″ pilot hole and put a piece of wire in it and felt around the back to see where the wire came through the hole. I had to move the pilot hole back about 1/16″ or so. Then I drill a bit larger hole and then filed it out until I could see the edges of the tow bar hole. I then finished it using a step reamer to 3/8″. I’m going to consider the wheel spats done. The only thing left to do on them is to install the blond grommets for the air valve. I don’t have them so I need to find them online. Once I get them I’ll know exactly the size hole to drill.

This went quick. I just had to connect and torque up the AN5 bolts that connect the rudder pedals to the nose wheel. It’s steerable in the Sling. I also put some lithium grease on the rose joints (saw that at TAF).

Wheel Spats and Luggage Door

Time: 3.5hrs

Spent some time fitting the main and nose wheel spats on. I started with the main wheel spats. At first I was thinking that this was not going to work. They seemed so far off and parts were rubbing on the tires. I trimmed about 1/8″ or less from the top of the outer wheel cover. Things seemed to fit a bit better. I marked the top of the rear part of the cover (the part that bolts onto the gear) so that it lined up with the top of the front and cut that. The fit was even better. A little more light cutting and then a final sanding ended up with a pretty good fit.

A few photos of the fitment of the left spat. I’m pretty happy with it. Still need to cut the holes for air filling. 

I ended up glueing the washer to the inside of the spat since it was nearly impossible to get it to go on. 

One more look from the front

On to the nose wheel. Glad I didn’t use the factory provided holes as they were a little off. I ended up sharpening a M5 screw and screwed it into the hole then lined up the cover and hitting it with a mallet. This leaves a mark on the inside of the spat so you know where to drill the hole. 

Almost done. I still need to cut the top even and I believe the manual says to install two rivnuts at the top into the nose wheel strut. 

All spats on. Looking good 🙂

I also added some think neoprene foam to the luggage door. I had previously installed some neoprene rubber and it wasn’t really thick enough. Also it was kind of sticky so the luggage door would stick when you tried to open it. I just added the foam over the rubber and now it seems to seal up fairly well. 

The rest of the door will get covered with carpeting. 

Main Gear Mounted

Time: 2hrs

Well I guess a day makes a big difference. After failing to get the bolts installed a few days ago I had much better success today. I used a little different technic then previous and maybe this the reason for the better outcome. I started by lining up the gear the best I could and then checking the alignment of the metal spacer and hole in the gear channel. Once it was close I used a large punch in the hole and pushed it into the hole using wood as a pry bar against the main spar. Now rather the clamp that in place I did the same on the other side. Once both punches were in place I then clamped the gear in place. I removed the punches and used a small half round file to file down any burrs in the hole. Starting on one side I inserted one bolt, pushed it as far as I could by hand (which was only about 1/4″ – 1/2″ and then used the wood to slowly pry on it. To my surprise the bolt slowly moved in. I was able to pry it in until it hit the other side of the gear channel. Then I had to tap in it with a mallet. Now on to the other side. Same method and the bolt went right in. Prying the bolts in was the same as what I tried to do the other day, but bolts just wouldn’t budge. It must have been the tecnique of using the punches to line things up first that really helped. The next set of bolts went in using the same method. I’m so happy that this worked out. I was so frustrated the other day and just couldn’t see how this was going to work, but I guess a small change in process did the trick.

Using the main spar and a long piece of wood to put pressure on the bolt to push it in. It didn’t require too much pressure, but I would have never been able to push them in by hand. Note: I flipped this image so that it’s a little easier to see where things are. I’m actually working upside down)

Bolt on the left and one on the right are in… making progress.

The tool that saved the day. I used one on each side to line the gear up.

So next is to rivet the gear channel skin then fill and sand the bottom fuselage rivets.

Main Gear Mounting

Time: 6hrs

Well this has been very challenging. I think mounting the gear with the fuselage upside down was a good decision. It’s been very easy to check the fitment of the gear and accessing the bolts has been somewhat easy… though working inside the fuselage is a bit of a pain and somewhat cramped. The main issue is that I can’t seem to get two bolts (one on each side) in at the same time. Once I put one bolt in then the other side is a fraction of a millimeter off which makes it impossible to push the other bolt in. There is really no room to tap the bolt with a mallet. I did find a way to push the bolt in using a piece of wood placed between the bolt head and the main spar. After some research in the manual it appears that the bolts are to be installed with the head facing aft, but that’s not what the FAA says. I’d really like to install them in the correct orientation. 

As far as fitment I’ve had the gear on and off a multitude of times. The top of the gear hits the rivnuts and also interferes with the rivets that will be installed to hold the rear seat floor panels on. Also the gear is a bit too wide at the bolt locations so that needs to be sanded down as well. 

Some photos and a bit more narrative below. Even after working in this for many hours I have not yet been able to get the bolts in… so the work will continue. 

This was a good method for me to allow placement and rough fitting of the gear. You can remove the wood block and check the fitment and then sand as needed. 

Here I thought I had the fitment right so I put some grease at the bolt area location as instructed by Jean from Torrance TAF. He said that this will minimize any creaking in the gear. It turned out that the top of the gear needed to be sanded as well so the gear was removed and sanded multiple times since this photo. 

I put a bevel on the top edge of the gear. This was done to get the gear to fit down without putting pressure on the rivnuts. Also it helped give some room to where the rivets will be installed for the rear floor panels. After this photo was taken I ended up taking out the belt sander with some 60 grit paper and sanded down the bevels even more. 

I think the fitments is good now and the gear seems to fit down into the channel without needed to be held into that position. This may help with the installation of the bolts which so far has been impossible to do. I spent nearly 4 hours trying to get two bolts in. The first bolt is fairly easy to install since you can get perfect alignment of the metal spacer in the gear and the holes in the gear channel so the bolt can be pushed in by hand or by using some wood to pry it in. The problem is the insertion of a second bolt on the other side. The top to bottom alignment can be tuned by pushing down on the gear and holding it with some clamps. The left to right positioning is really the problem. There’s not too much you can do about it and even if you have a small misalignment the bolt will not go in. I have tried to round off the edges of the metal spacers in the gear so that there are no hard edges for the bolt to catch on, but it only helps minimally. I’m thinking I may need to widen the hole in the gear channel just a small bit to get the bolts to fit. If you had room to tap the bolt in it would probably go, but there really isn’t much room. Hopefully I’ll get some time to work on this again in the next few days. 

Main Wheels

Time: 2hrs

Assembled the two main wheels. I had tried this before and ended up messing up two aviation tubes because they got pinched in then hubs. This time I was much more careful. I in flayed the tube a little and got the valve through. I then loosely screwed on the other side of the hub and then added a little more air in the tube. I tightened down 3 or the 6 bolts making sure the hub fit flush against the other one. Then a little more air in the tube. Then I let air out of the tube and put on the rubber o-ring (which actually isn’t necessary). I was able to seat the o-ring between the two halves of the hub by pushing down on one side of the tire until it disappeared into the crack of the joint. 

I also put together the saw horses to hold the plane when I turn it upside down. I made one about 4ft wide and 30″ high (to put under the center fuselage) and the other about 2.5ft wide and 36″ high (to put under the tail cone). I also used a swimming pool float tube for cushion. Now I just need some help picking up and flipping the plane over. 

Tube is in and these 3 bolts are just barely tight. If you can see the ride in the center of the hub then the tube isn’t pinched. I put a little more air in the tube at this point. Also forgot to mention I used some talc powder on the inside of the tire and rubbed some on the tube before putting the tube in the tire. 

Wheel all assembled with the brake disc attached. Note the cable is lined up with the red dot on the tire. 

My saw horses ready to go. 

More Main Wheel Spats

Time: 2.25

Things done today:

  • Finished up filling and priming the rear part of the main wheel spats
  • Primed and filled blemished in the front part of the main wheel spats

I finished dup the priming and fill on the rear portion of the spats that mount to the brackets. The main front parts were pretty good, but I wanted to fill few blemishes. I also noticed that I had a large dent in one of the wheel spats which I didn’t notice prior to doing all the work on it so I was a bit upset to see it know that not only will I have to wait for a new wheel spat but I’d also have to drill and mount all the rivet nuts and fit it again. So I though maybe if I heated up the material and used a cloth to push on it I could get the bump out. I used my heat gun at 400 degrees and carefully heated the inside. I was just about to use the rag to work out the bump and to my amazement I saw the bump disappearing before my eyes. I really couldn’t believe that heating it would have worked so well. In any case bump is completely gone.


Filling some low spots on the main part of the main wheel spats. I just used some epoxy resin then I sand with 320 grit paper.

Rear part of the main spats all filled and primed

Test fitting the main (front) parts of the main wheel spats. The bottom portion fits well, but the top is going to need some work.

Bottom fits well.

Top needs a bit of work. I think when the top edge  is cut back then it will pull in a bit. I’ll wait until the gear is mounted and things are right side up to do that work though.