Oxygen Cylinder Installation
The following is a step-by-step process for installing the Mountain High Oxygen cylinder for the Lancair Legacy. There may be other methods for securing the cylinder in the Legacy; however, after researching several other methods, I decided this one would work best for my aircraft. Please note that I mounted my oxygen cylinder behind the pilot seat as close to the aft console as possible.
Cover the entire surface of the cylinder with a single layer of duct tape. Be careful to also protect the valve assembly with plastic.
Do a six-bid layup of carbon fiber over the entire flat length of the cylinder around approximately ½ of the cylinder circumference. Dimension of layup should be approximately 13” in length and 11” around half the circumference of the cylinder. It is helpful to draw these dimension lines on the duct tape for easy positioning of the layup.
After the carbon fiber is cured, carefully release it from the duct tape. Then place it back in the same position on the cylinder. Using plywood, fabricate three braces which fit the cylinder’s external radius as shown. Use Bondo to bond the three braces to the outside of the carbon fiber at the two ends and the middle. The only purpose of these external braces is to hold the carbon fiber radius securely and accurately while accomplishing the next step.
After the bondo has cured, remove the carbon fiber with external bracing from the oxygen cylinder. Using 1⁄2” plywood, fabricate three braces which fit the cylinder’s internal radius as shown. Use Bondo to bond the three braces to the inside of the carbon fiber at both ends and the middle.
After the bondo for the internal braces has cured, carefully remove the external braces, and sand off remaining bondo from outside of carbon fiber.
Using blue polyurethane foam, fabricate two cradle brackets (foam core molds), approximately 2” wide, with the approximate shape shown below. Note 1: My forward bracket had to be cut down due to an access panel in the aft console. If you don’t have a forward access panel in your aft console, both brackets can be the same shape. Note 2: The height of the cradle bracket cannot be more than approximately 1” in height outboard of the cylinder radius as this will prevent easy installation and removal of the cylinder with the baggage floorboards in place. You should make the cylinder radius in the foam slightly undersize for now; it will be sanded to perfection later. Locate the foam core molds on the belly skin. Mark their location with a Sharpie pen. Make sure these cradle brackets will provide the support and spacing you want for your cylinder and the aft console. Verify you can easily install and remove the actual cylinder with the baggage floorboards in place. Use micro to bond these cradle bracket molds in place on the belly skin as shown below. Ensure the micro is fully cured before proceeding to the next steps.
Clean the exterior surface of the internally-braced carbon fiber structure. Apply approximately 7-10 layers of duct tape on the outer surface of the two ends of the structure. Then stick on 40-grit “Stick-it” sandpaper to the outside of the duct tape as shown below.
Use this structure to sand the foam cradle bracket radii to final shape. It is necessary to get the radius in the forward cradle bracket mold within 1/8” of the belly skin, and the aft cradle bracket mold radius must be level with the inside belly skin aft of the foam mold. This is to ensure clearance between the top of the oxygen cylinder and bottom side of the baggage floorboard access panel. Just like everything else, it’s a fairly tight fit!
Use 40-grit sandpaper to form nicely rounded radii on all edges and corners of the foam cradle bracket molds. Then use duct tape as a release tape to protect all surfaces adjacent to the foam molds. Also, form micro radii at all inside corners/intersections.
Apply a micro slurry to the foam mold. Apply 5-bid e-glass to each mold using standard fiberglass layup procedures. Ensure a minimum 1” flange is completely “wetted out” around the blue foam mold. After the fiberglass is cured, drill cleco holes through the fiberglass cradle brackets into the belly skin and aft console so the brackets can be accurately re-located. Remove the cradle brackets from the belly skin. Trim the brackets leaving approximately 1” bonding flange all around. Grind the blue foam out of your new cradle brackets. A mini die grinder with carbide wheel works well for this.
In this step, the internally-braced carbon fiber structure will be bonded to the two fiberglass cradle brackets (the brackets are not yet bonded to the floor). Secure the fiberglass cradle brackets to the belly skin using clecos. Fit and locate the carbon fiber structure into the cradle bracket radius and secure to each cradle bracket using an 1/8” cleco. Prepare all surfaces for bonding. Tape off any surfaces where you don’t want epoxy/flox to stick. Bond the carbon fiber structure into fiberglass cradle brackets with epoxy/flox using standard bonding procedures. Note: In addition to the two clecos holding the carbon fiber structure to each of the cradles, I filled the carbon structure with spare clecos for added weight.
After the assembly has cured, remove it from the fuselage. Remove the internal wood bracing from the carbon fiber structure. Cut and trim the carbon fiber so it forms a “liner” to the fiberglass cradle bracket radii. Cut holes in the cradle brackets as shown for the stainless cylinder holddown straps. Trim to final shape. This would be a good time to cleco the cradle brackets to the belly skin, temporarily install your left baggage floorboard, and verify you have sufficient clearance to easily install and remove your oxygen cylinder from their cradles. This would be the ideal time to fix any clearance issues by sanding down the height of the bracket on the outboard side of the cradle radius.
In this step, the fiberglass cradle brackets are bonded to the belly skin with epoxy/flox using standard bonding procedures. The stainless straps are also permanently installed at this time. There is not enough clearance for the straps to be installed after bonding the cradle brackets in. Prior to bonding the cradle brackets to the belly skin, install the stainless steel straps into the cradle brackets. It will be necessary to hold these straps up and out of the way during bonding so they are not inadvertently contaminated with epoxy/flox and/or bonded to the belly. For this purpose, I made two 3⁄4” plywood disks, equal in diameter to the oxygen cylinder, which are gently clamped into the cradle bracket. After all mating surfaces have been properly prepared for bonding, bond the fiberglass cradle brackets in place using 1/8” clecos. Note: Special-length stainless straps are required due to the increased circumference created by the fiberglass cradle brackets. They are available through Mountain High. Request item #CMK0055-02 when you order your oxygen system from Mountain High.
Remove clecos. Remove wood disks, and ensure the straps are free to rotate. Clean up excess epoxy/flox. Fill cleco holes. Install oxygen cylinder.
John Kleber #117