I continued working on the main gear today. I removed the right hand axle from the gear leg and carefully marked the location for the cotter pin hole. I did this with the wheel and brake assembled to the axle and marked the location of the notch in the nut on the axle using a sharpie. The hydraulic brake drawings (SNX-L07) indicate that the hole for the cotter pin should be located after assembly. The SNX-L01 drawing shows this hole horizontal with respect to the axle assembly. I drilled the hole for the cotter pin and re-installed the axle stub on the gear leg. Next I greased the wheel bearings and installed the wheels. I left the cotter pins unbent in case I need to take the wheels off to work on the brakes.
I noticed that Sonex provides nuts to be used on the bolts that secure the brake discs to the wheel. I had originally used the incorrect nuts so I removed each nut and replaced it with the nut supplied by Sonex. Next, I spent some time dry fitting the bearings. This involved fitting the pistons into the half caliper. I used a bit of brake fluid to lubricate the o-ring and the pistons pushed in with a bit of force from my fingers. It was toughest to get the pistons past the initial tapper. Then the pistons when in fairly easily.
With the brakes assembled I fint the wheels and marked the left side for the cotter pin. I then dismantled it all and drilled the cotter pin hole.
Third times a charm?! I was still not happy with the fuel line routing/bending so I decided to try once more. I was very careful to avoid any uphill bends under the fuel tank. While the line runs downward on an angle when the fuselage is level, the line will move more towards the horizontal when the plane is in a steep climb. I had to put a slight upward bend in the portion under the tank but for the most part the joggle bend is horizontal. Forward of the firewall the line runs only down hill. This time I’m pretty happy with the outcome.
I also notched the bracket for the gascolator so that the gascolator could be removed without removing the bracket once the fitting was installed. I installed the plug in the gascolator but I still need to use some lock wire on them and the cotter pin the fasteners.
I worked on finishing the gascolator end of the fuel line. I started by shortening the line until it was the appropriate length to flare. Next I flared the line an checked the fit up. I’m not too happy with the routing inside the fuselage under the gas tank. I have a short segment that may be uphill when the plane is in a climb. I’d like to eliminate this if possible.
Today I went back to work on the firewall installing the bracket for the gascolator. There has been much talk about not using this but I’m going to give it a try along with insulating the fuel line so that I don’t get vapours causing hick-ups.
I finally got around to assembling one of my prototype boards for pressure measurement. I decided to go with the board measuring absolute pressure that I designed to determine pressure altitude. During the time that the boards and parts were on order I discovered that my idea of using 10V for the pressure transducer would not work as the differential output would not be in the correct range for the analog to digital converter. I decided not to populate the 10V section and ran a jumper to supply 5 volts to the transducer. This also meant changing the reference voltage to get the correct range for the output of the transducer since this would be half as large as originally planned.
While assembling and testing the board I found a couple of additional problems. I found that I had not connected the SET pin of the 5 volt regulator (MAX1659) to GND so I would not output the correct voltage. Next, I discovered that I had not wired the enable (ENB) line on the digital isolator (MAX14934) to 5 volts. This probably didn’t matter but at the time I was having difficulty getting communication to work on the SPI bus so I added a jumper anyway.
I finally started to get the board communicating with my Arduino but the value was off. I checked the reference voltage to the ADC and found it wasn’t correct. After looking at the specification sheet I found that I had created the voltage reference symbol incorrectly and swapped pins 4 and 5. This meant that I was not getting the correct output voltage. Back on the prototype I tried to lift that side of the reference IC (MAX6037) but it came completely off the board and I lost it. I installed one of my spares and installed jumpers to swap pins 4 and 5. With this complete the board started reporting what appears to be the correct voltages and hence correct pressure readings.
I started on the left gear leg engine mount attachment point. I needed a thin washer and a thick washer to get the hole in the bolt to line up correctly with the castle nut when torqued properly. I put the thin washer at the head of the bolt which allowed me to put the thick washer at the threaded end. The bolts still end up a bit long and the end of the bolts want to rub the firewall. I ended up putting a large flat washer or “fender washer” over the end of the bolt to provide a large bearing surface against fire wall. I saw this on another Sonex and it looks like it works. The cotter pin does not seem long enough. I’m planning to order some additional cotter pins that are longer for this bolts. I’m not sure why, but the Sonex specified cotter pin is a 5/16 inch diameter but the standard cotter pin for the AN4 bolt is only 1/8 inch diameter which would fit nicer. I’d also like a longer cotter pin since I need to wrap the legs around the nut instead of over the top. When putting the cotter pin in 90 degrees to the bolt it does not go into the castle nut as far as I would like.
I also installed, torqued and cotter pinned the fasteners in the lower end of the main gear legs for the front axles. This was easy but I needed two thick and two thin washers. I considered using a shorter bolt but I was not happy with how far the bolt came through the axle mount. I used the longer bolt so that the shank of the bolt was fully engaged in the mount to minimize the possibility of the holes becoming oval over time.
I went back to the wheels. Previously, I had assembled one of the wheels and found that the valve stem ended up very crocked. I wasn’t happy with the assembly. This time I made sure the valve stem was through the hole in the rim with the rubber resting against the rim. This time when I inflated the tire to 30 psi the stem remained straight. With one wheel assembled I proceeded to the second wheel. The bolts holding the wheels together are 5/16 inch diameter so I torqued them up to 85 in-lbs per the Standard Aircraft Handbook. I made sure my compressor was set to a max of 30 psi since this is the limit stamped on the side of the rim.
Today I worked on the landing gear some more. I wanted to install the 1/4 inch bolts to secure the main gear. I discovered the upper bolts specified were long enough but I needed a thin washer to get the hole in the castle nut to line up properly. I also need to get some fender washers for on the end of the bolt to spread the load from the end of the bolt over a larger area of the firewall. The shorter bolts to secure the axle stubs in place were way too long. I ended up ordering shorter bolts for these. I am using the disc brake setup from Sonex so it makes sense since I won’t be installing the cable deflector for the mechanical brakes. I worked at assembling one of the wheels. Once I put air the tube moved and I don’t like the position of the stem. I’m going to have to deflate these and reposition the tube.
I still need a number of parts to complete the landing gear. I reviewed the Sonex revisions list and prepared an order for Aircraft spruce of the hardware, wheels, tires and tubes. I’ll probably upgrade the tires later but I need something for now to get the fuselage on the ground.
I’ve been working on updating this site for a while and finally have it mostly finished. It shouldn’t look too much different but it will be easier for me to maintain.