Wing Tanks Installation, Part 3

The next brief installment will detail some more work on the fuselage component of the wing tank installation.

The picture below shows the fuselage wing tank plumbing on the passenger side.  There is similar plumbing that needs access on the pilot side, so this procedure was actually performed twice.  A large, curved panel is what covers this section of the fuselage.  In order to gain access for maintenance, I stole a brilliant but fairly simple idea from another awesome RV-12 builder, Dick Gossen.

First step was to perform a relatively precise removal of material from the panel as shown below.

To arrive at that finished product required a few intermediate steps as shown below.  First, a CAD drawing was made and then applied to the panel with some contact cement.  The yellow line is the CORRECT cut out to make - did not want to cut to the wrong dimension, so checked it twice!

Now, a uni-bit was applied to give me some room for the business end of the hand-powered nibbler as shown below.

 Nibbling away....

And just when you think it will never end, it does.

Next, I needed to fabricate the access cover, so I used a piece of large diameter PVC tubing and a ratcheting strap and tried to put a permanent smooth curve into a piece of 0.040 inch thickness of 6061-T6 aluminum sheet.  I was skeptical it would work with this thickness.

To my surprise, the thing took a pretty nice bend, along with some additional encouragement by hand.  The photo below shows the access cover blank laying inside the larger fuselage side panel.

The finished product, trimmed to size, nutplates installed and holding the cover and panel together.  I think this will work - thanks Dick!

Wing Tanks Installation, Part 2

Next up in the tank install is the installation of the vent system.

The wing tank vent system actually begins at the filler neck of each wing tip.  Both tanks in each wing terminate at the filler neck. From a point just below the filler neck's fuel cap, an elbow connects to 1/4" aluminum tubing which runs back to the wing root where it ties into the vent line in the fuselage.

Before the vent line returns to the wing root though, it also picks up the interconnecting vent line between the tanks as shown below.

Next shot below shows the ventl ine running from tip to root.

At the root the line terminates into a bulkhead elbow in the second rib.

Another jog and another bulkhead elbow and the line terminates, awaiting a connection with a quick disconnect valve some fuel line and its connection with the fuselage vent.

The fuselage vent system begins at the fuel standpipe (like a header tank and mounted in the forward corner of the baggage compartment) and terminates with the fuselage belly vents.  The top bung with the tee sends one vent line to the belly vents and the other side runs to the interconnect between the left and right wing tanks.

The picture below shows the upper run of the fuselage vent line heading through the baggage bulkhead.

The view from the standpipe looking aft.

This bulkhead elbow on the backside of the baggage bulkhead sends this component of the fuselage vent system upward to the top of the fuselage.

 This picture will give you a better idea of the routing to the top of the fuselage.

The tee fitting in the lower portion of the photo above is emerging from the passenger side belly vent.  Both belly vents are shown below in the next picture.

The picture below shows the pilot side belly vent from inside the fuselage as its line runs aft toward the baggage bulkhead.

 Here is a side view of the pilot side belly vent plumbing.  Shown at the bottom is the fuselage interconnect vent line, which will be detailed later in this post.

Throughout the vent line routing, I have taken precautions to support the thin aluminum tubing with fuel line and safety wire as shown below.  A small 1/16" hole provides the attach point to the structure.

The shot below details the vent line connection between the two fuselage belly vents.  This line will be anchored to the tailcone floor in a manner similar to that shown above.

Another vantage point from the passenger side to pilot side.

If you're still following along, that concludes the one side of the fuselage vent system.

Now, back to the standpipe for a brief narrative of the other component of the fuselage vent system - the interconnect system.  We now follow the vent line downward from the tee fitting on the upper end of the standpipe.

Shown below is the vent line emerging from below the baggage compartment floor and into another tee fitting.  One leg of the tee runs to the elbow bulkhead fitting that protrudes from the passenger side of the fuselage.  The other leg of the tee fitting sends the interconnect line across the fuselage to a similar elbow bulkhead fitting on the pilot side of the fuselage.

 You can see the sheathed vent line running across the fuselage from here.  Note the control cables for the stabilator and rudder laying slightly above the vent line.

 
The photo below shows the termination of the pilot side of the interconnect.

Last two pictures illustrate the pilot side interconnect terminating on the fuselage skin.

Upgraded Oil Tank Getting Fixed

Viking advertised an upgraded oil tank, which I immediately purchased when I first heard about it.  The upgrade was made to address the adhesive mounted top and bottom of the oil tank.  The upgraded tank featured an all welded assembly.  In addition to the welded structure, a new bung was added to the tank in order to facilitate oil circulation into and out of the PSRU via the upgraded oil tank.

Unfortunately with the upgraded oil tank, Viking changed the location of the oil pickup line to a more forward (and unconservative) location which caused problems with intermittent oil starvation.  Most probably the forward location during high angle of attack (climb) and perhaps cavitation as well appear to have contributed to the problem.

Viking has not provided any solution to the problem for whatever reason....so a few of us builders have taken matters into our own hands.

Shown below are pictures of the modified upgraded oil tank's drain plug plate.  The cap with the holes is what we have called an anti-vortex device, designed to halt any tendancy of the oil pump to "out suck" the oil level in the tank.  The second feature is an AN elbow fitting that, like the anti-vortex device, has been TIG welded onto the aft end of the drain plug plate.  Hopefully, these changes will faciliate a more conservative location of oil pickup and also eliminate the pump cavitation issue.

New and primed oil hatch getting installed with Right Stuff onto bottom of Upgraded Oil tank....looking upward.

 Another couple of pictures showing flexible oil pickup line routing up to the engine block from the tank.

Ultimately, the only way to test this mod is to flight test it, so stay tuned for that.

Wing Tanks Installation, Part 1

Before I get started, let me recognize another RV-12 builder, who is also a Viking RV-12 Wing Tanks builder and has been at this gig for bit longer than myself.  Bill Dye has pioneered a very nice installation and I am unabashedly following almost all of his techniques.  He has made a thorough analysis and resulting thoughtful installation.  Give credit where credit is due.  He has taken a very rough and quite frankly, unfinished installation procedure rendered by Viking Aircraft Engines and re-engineered it into a very nice and complete assembly.

Now, some of the more significant procedures for wing tank installation.  First picture shows the "saddle" into which the tubular wing tanks will be seated.  McMaster-Carr describes it simply as an edge grip with rubber seal.  A 15" long piece with appropriately sized cutouts is manufactured for each of the designated rib lightening holes.  Upon installing the edge grip onto the edge of the circumference of each hole, I elected to follow that up with some Right Stuff adhesive on the outboard side of each rib for some extra (and probably unneeded) holding power.

Edge grip installed with other tank temporarily resting in place.  This shot is looking at the "root" side of the ribs.

A shot below of the 3 inch diameter rear wing tank laying in its new home.  The dish soap was very successfully used to ease the friction of the tank as it passed through each of the edge grips.  The soap made the installation through the 8 or so edge-gripped holes a non-event.  It worked great.

Next shots show both tanks installed.  Looking at the tip end of the wing on the right.

 
Looking from the root on the left, to the tip on the right.

Wing is now inverted and the filler neck assembly is starting to get rigged at the wing tip.  The large rubber filler neck hose was another major coup that Bill pioneered for this installation.  Viking's proposed use of Kinar elbows was lacking and this solution proves to be a major improvement.  The brass tee fitting at the base of the filler neck was discarded in favor of AN fittings as will be seen in later photos.

With the filler neck hoses removed, the vent line plumbing can commence.  Below is the vent line interconnect between the two tanks at the wing tip.

Next, a mechanism for securing the tanks from any potential span-wise movement was improvised using a trimmed aluminum angle and hose clamp with some rubber padding.

Backside of the rib where the angle is riveted.

Next, the main tank fixture is in work.

Viking did provide a pair of access panels for the wing tank installation.  Below, the process of marking the location of the panel in the wing skin and then the removal of the material is under way.

The finished cut out is ready for the access panel frame to be fitted, drilled and finally riveted into position.

Next up is the vent line plumbing from the wing tip to the wing root.  Shown below is an intermediate termination point in rib #2.  From that elbow bulkhead fitting, a final run of aluminum tubing will proceed to the mid-rib point and then across to the root rib, where it will terminate in another elbow bulkhead fitting.  That fitting will transition to rubber hose and a quick disconnect fitting, which will interface with the rubber hose from the fuselage pickup point. 

More to come. It's getting exciting!