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.

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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.

Parking Brake Lines

Time: 1.0hrs

Installed the 45º fittings on the parking brake and -4AN fittings on the lines. I wanted to finish this up because I will be making a mold of the throttle console piece for the carbon fiber part. BTW I have toe brakes so my parking brake is a little more involved then the simpler leveler brake type.

Left side of the center console. I have 90º fittings in the back and 45º fitting in the front. The lines are run kind of weird so that the bends in the lines aren’t too tight. The left and right lines run from the pedals and attach to the parking break with left on the left and right on the right, but then they leave switched. This is because it was just cleaner to leave the caliber lines on the sides on the channel that they came up on. The bend into the channel is pretty tight so from say the left brake caliper the line runs into the center channel and stays on the right side of the channel up to the parking brake rather then cross them back over.

Here’s the right side of the center console.

The 90º fitting will hit each other so I had to angle them a little oddly. I was thinking of putting an extension on the top one, but I think this angle works fine.

Here’s a side view of the parking brake. This is a little older photo when I had the straight fittings on the front. Those were changed out with 45º fittings to make the angle better on the brake lines.

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.

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.

Fuel Lines

Time 1.25hrs

Today I received most of the parts I ordered from Summit Racing. I did a rough install of the fuel lines that run between the fuel select valve (which I don’t have yet) and the wing tanks. The Fragola 8600 hose is very easy to work with. It doesn’t hold the coiled up shape so you’re not fighting to keep it straight and it seems to bend nicely around corners. I was a bit worried about putting the ends on because in the reviews people had said it was near impossible to get the ends on all the way so I tried putting one end on just to see. I heated the hose end with the heat gun set at 200 degrees and used a little spit on the fitting end (not as gross as it sounds… well maybe a little) and the fitting went on very well. The last 1/8″ was a little tough but still not as bad as I thought it might be.

I also put the 1/8″ NPT to -4AN fittings on the brake caliper and did a check on how the braided brake lines need to fit onto the gear. I don’t want to use tie wraps to hold the brake line in place on the gear so I’m thinking I can use a router to deepen the cut out in the back of the gear and then use some RTV to keep the line in place.


Box of fun arrived


-6AN fitting on the Fragola 8600 hose. I need the buy the tool to crimp the clamp, but I really don’t want to install the hose ends until I have the fuel select valve and I know exactly how long they need to be.

Hose routes down along the front of the main spar and out the hole in the side of the fuselage. The feeder hoses that run from the tank to the fuel select valve are -6AN while the return lines are -4AN (6mm). Also fuel filters get installed on each feeder line so I need to buy those as well.


The brake line and fuel feeder hose outside the fuselage. Hopefully will get the return lines in a few days. The grommet on the brake line isn’t installed. I think I’ll try to find a bit smaller OD grommet. I also need to figure out the wiring that needs to be run out to each wing. Both sides get similar wiring, but the right side (I believe) gets a few extra for pilot heat.


-4AN fitting on the caliper.