Installing the Retracts

Another little twist that popped up to complicate things was the dihedral joint. Being an 85" wing instead of the larger 100" version meant that the retracts ended up crossing out of the center section over into the outboard wing sections. This took about 1/2 of each retract past the dihedral joint, and put two of the mounting screws right on the joint. I didn't have any room for fudging it here either, they pretty much had to position in that one awkward spot.

This would also mean that my removable access hatches to get to the gear through a finished wing will end up crossing the dihedral joint too. I'll have to build access hatches that match the dihedral angle and include the wing joint "bead fairing" that goes around the wing. Fun, fun, fun!

I found the W4A ply "anchor rib" to be missing from my laser-cut parts, and decided to wait and cut it to fit once I got the rails to align properly. Satisfied with where the outer ends of the rails would hit, I hand cut the half-ribs in the W4A position and test fit them into place along with the rails and gear. I also had to notch the 2 rails to allow clearance for the screws in the sides of the gear and the air nipple in the cylinder to clear when sliding the retracts down onto the rails.

I have my 5" Dubro tires temporarily mounted to the retracts so I can check my fit and alignment with the wheel well area as I go. I went ahead and screwed the retracts down to the rails with 6-32 socket head screws and slid the assembly into position. Checking the 3 axis again, I went ahead and epoxied the rails into place.
As the slow epoxy was drying, I continually checked and adjusted the position of the rails to verify that they were parallel and in alignment to each other, as well as putting the axles in proper position to the leading edge of the wing.
I also made sure that the struts were providing a consistently accurate angle to the wing spar and that the tires were ending up in a good perpendicular right angle to the wing center section spar. Keeping the tires nice and straight up & down and parallel to the fuse should help make sure that the plane will track straight on the ground.

Setting up the Air System

Once the epoxy was good and dry, I removed the retracts and started on the Robart air system. When I bought the retracts, I ordered the Robart "Deluxe Air System" which came with the switch/valve, up & down airlines, filler valve & chuck, air pressure gauge, "T" connecters and some metal air line nuts.

My goal here was to get all the air system components installed that were going into the wing so I could finish up and sheet the wing. I will wait to complete the portions of the air system that go in the fuse later on.

So, I proceeded to cut an air system "bay" into the center of the wing, cutting out the sheeting on the topside of the wing. I mounted the Robart air valve/switch to the inside of the right side rib in the bay and mounted the Hitec HS-425 servo to the rear dihedral brace.

This gave me a right angle linkage line directly to the air valve's "switch plunger" to actuate the valve and switch the air flow for up vs down airflow. The servo lead will be secured into position and fed directly out of the top of the wing into the fuselage later.

Connecting the pink/red lines and the purple lines to the air valve (one for up and one for down), I fed them out a few inches to a couple of "T" connectors to split them out to each of the two wing halves.

To make it easier to fish the lines in and out of the wings in the future, I routed the lines through the red outer sleeves of a couple Sullivan Nyrods. This will make it easier when I need to replace my lines for scheduled maintenance or repair.

I looped an extra 10 inches or so out into the rib bays beyond the retracts so I will have enough slack to pull the retracts in and out of the bays when connected.

The rest of the system...

The remainder of the air system will go in the fuselage when I get to that point. This will include the Medium Size Robart Air Tank, the main supply line, and "T" connectors splitting out lines to the main fill valve and a "pressure gauge" which is more of an "idiot light" than a gauge. A little pin pops up when pressure is adequate, and retracts back into the gauge when pressure is too low.

Testing the system...

Once I had all the system installed in the wing, I temporarily hooked up the lines and tank to the retracts "offline" (outside of the wing) and tested the system for operation and leaks. No obvious leaks showed up and the system functioned perfectly. The Robart Medium Size air tank holds up to 150psi and I only pumped it up to 100psi for my test. Even so, I still was able to cycle the gear up & down at least 12 times on that 100 pounds of air!

The full 150psi should be more than enought to give me plenty of cycles, even if the air bleeds of a little over time. You may think that pumping 150psi would be a chore every time you go out to fly, but it wasn't... see the sidebar above on the RoadMaster air pump I used to do this with. It makes it super easy and takes less than a minute to do. Eventually I will have the entire system (wing and fuselage portions) all installed, and then I will pump the system up full and let it sit all day to see how much air bleeds of over time. I'll also have the pressure gauge installed and will test it to see how well it performs.

Call me lazy, but the idea of hand-pumping 150psi into my air system every time I fly was not an attractive option to me. So, I looked into my options for affordable electric air pumps and found what appears to be the perfect solution to "pump you up!"

Our local Odd Lots store had a sale on these RoadMaster roadside hazard/emergency pumps so I picked one up for about $20!!!! They are designed for roadside emergencies, so they also have a built in flash light, flashers, etc. that I won't need. The use a standard 2 toot airline hose and fitting that works for pumping up car and bicycle tires.

This device has it's own built-in 12-volt battery and has jacks so you can even use it as a portable 12-volt power supply. The unit has two storage compartments that handily store the supplied "wall-wart" battery charger, fuses, light bulbs and adapters.

I made an airline adapter for my air system by taking the supplied basketball needle, adding a 1/2 inch piece of Robart air hose, and then the Robart fill chuck.

When I tested this pump out on my retract system, I found that I was able to easily pump 100psi into the air tank in less than 30 seconds! The pressure gauge on top of the Roadmaster reads up to 300psi, so I should be able to fill up my tank to 150psi in less than a minute without breaking a sweat!