27 Apr 2024

Installed edge protector on the rear fuselage floor ribs where the brake hoses and antennae wiring will pass through.

I have decided to modify the side vent system to address the concerns where hot air from the cabin heater loses temperature by the time it reaches the rear passenger air vents due to the cooling effect of the fuselage side skins being exposed to cold ambient air. The inner and outer side skins form the channel for air to be ducted to the rear passengers - a simple system, but with some room for improvement. I had previously modified the CF-CHL-S01 and CB-YPC-003 duct and Y-splitter components to simplify the system (see 28 January 2024). This is possible due to the use of Aerosport Products NACA duct controllers which can close off external air almost completely (the factory supplied units are completely ineffective). The benefit of this setup is that it also facilitates exterior ambient air to the rear passengers - which the original system design looks like it limits due to the nature of the ducting.

I disassembled the modified duct channel and then enlarged the hole in the ducting very slightly using a deburring tool so that the Y-splitter could pass through the hole into the duct. I then carefully snipped the support bracket, which previously held the Y-splitter in place, by less than 1mm at each tab and reformed the tab, then ground down the material between the tabs - the idea being to enlarge the inside hole for the bracket to also allow the Y-splitter to pass through it (the tabs were originally secured inside the Y-splitter, the new arrangement places the bracket and tabs outside the duct - not quite as pretty now, but it will be far more functional).

After checking the orientation of the Y-splitter, I cut off a section of the pipe protruding into the ducting - the angle chosen was simply to align vertically between the two rivets of the support bracket. This results in a C-shape inside the duct, with the closed side in front and the open side facing aft. The plan is that air entering the Y-splitter will then be forced to route aft. The three parts were then reassembled, with new rivet holes being drilled as required. I used the original orientation of the Y-splitter versus the support bracket to maintain the factory's angle relative to the ducting. This arrangement also moves the Y-splitter closer to the inside skins, thereby aligning far better with the vent holes in the dashboard, and it aligns the Y-splitter, NACA duct controllers and NACA ducts far better.

I then cut some 2 inch SCEET tubing to length (approximately 1.4m as a starting point) and flattened it to fit within the ducting cavity between the outside and inner skins. I used a piece of wood, around 1.4m x 50mm x 20mm (part of a Sling packing crate) as a rough form and inserted it into the tube, then after rough shaping I removed the wood and tried shaping by hand. This was originally a major challenge, I spent over an hour trying to massage it to shape, and it kept twisting into a propeller shape. I gave up on the original piece of SCEET and tried again, deciding to go low-tech. Same piece of wood, with the first roughly 40cm flattened using a rubber mallet. I then removed the wood and stood on the end whilst wearing rubber-soled shoes (flip-flops) and then slowed flattened the rest by standing on it. Result: perfect! Twice! They fit perfectly in the fuselage duct cavities.

I used the Y-splitter to mark an appropriately sized circle (50mm) near the one end of the SCEET tube, keeping the end of the tube flush with the edge of the duct and then cut a hole in the SCEET tube using scissors, snips and side cutters. The hole thus created fits over the C-shape inside the duct.

I need to seal the ducts properly with something like Proseal or Sika, but a test with a hairdryer found the airflow to be great, even with the few leaks due to lack of sealant.

I used the insulation from the firewall - which I have replaced with another product - inside the fuselage duct cavities. Between that and the SCEET tube, hopefully heat loss will no longer occur.

I'll need to create another 50mm hole at the back to match up with the vent position in the side skins and cut the SCEET to final length - that will come later. I may also make some flanges to go inside the SCEET tube and then rivet them in place around the holes to provide a bit of reinforcement.

I am also considering adding the foot-level heating at the rear as other builders have done - I've had a friend 3D print a 2" to 1" SCEET tube adapter based on a file supplied by a fellow enthusiast in the Sling Builders community (thanks both!) so should have the heating situation well under control!