Header Tank Sight Gauge

[danerazz]

Is the other one 7" in diameter? It would be about 6" shorter if it is.

[SheepdogRD]

The header tanks in N7340Z are 5" outside diameter and 19" long, similar to the standard SuperSTOL tanks, but 3" longer. They hold about 1.5 gallons each.

Both tanks have drains. There's no crossover, and the fuel valve is four-way. The return line will go to the right tank, and each header will be separately vented to its wing tank.

We put the interior fabric on the outer fuselage tubes and the stringer, rather than on the inside tubes, so there's more space to swing the header tanks outward. The bottom of each tank mounts on a bracket that rides on the cargo holddown loop.

The sight gauge seems fairly well protected between the tubes, but I may consider something more along the lines of Barry's system.

[R Rinker]

what were your reasons for going with two headers? Just curious to know the advantages. I know others have done that also..
Is your engine fuel injected? Or is the return actually needed?

[barry767]

Hmmm...I just did the math. My header tank has a radius of 2.5 inches and is 16 inches tall. That comes out to 314 cubic inches or 1.35 gallons. It replaced the smaller one that came with the kit that measured 1.25 inches radius and 18 inches tall. I always thought the smaller one was 1 gallon and the larger one that's now installed is 3 gallons, but apparently not. The existing one is big enough but now I'm tempted to call Just Aircraft to find out exactly what they sent me.

[danerazz]

When I ordered mine I didn't ask if they had a bigger one since they didn't advertise one in the options of their website. I spec'd it and asked if they could make it. It was well made and I like it, I wish I had gone just a little shorter to make mounting easier but again, I told them what to make. I wanted to avoid dual headers for system simplicity. I chose 3 gallons because I figured I would NEVER do a 30-minute full throttle descent, but calculated it at a 10,000 foot descent under power assuming worst case scenarios for fuel burn and then wanted fuel left in the header for an abrupt go-around. This put me at about 3 gallons. In reality it is overkill, but it is a good substitution for actual engineering.

The big point here is I told just exactly what I wanted and that is why my tank is the size it is.

Anything worth doing is worth over doing.

[SheepdogRD]

what were your reasons for going with two headers? Just curious to know the advantages. I know others have done that also..
Is your engine fuel injected? Or is the return actually needed?

Two headers were originally for more header capacity and to balance the additional moment arm caused by moving the engine forward 3" with the ring mount. I don't know what kinds of fuel I'll be able to find, because I don't know all the places I'll fly. I liked the idea that I could have a tank of avgas and a tank of mogas, and that I'd be able to keep them separate. When I decided a return line should be in the system, I realized I wouldn't be keeping them separate when the return only goes to the right tank. Since I'd really like to have them separate, I'm ordering a fuel valve that routes return fuel to the source tank: http://www.aircraftspruce.com/catalog/eppages/fuelvalvessprlv3.php. That should simplify fuel management a little. I'll have to add a return line from the valve to the left tank. Luckily, I made the ports in the tanks identical, so there's an available port in the left tank.

Our 912S isn't fuel injected. Rotax recommends the fuel return line, and I wanted to give the installation every chance to be problem-free and durable. The system includes an auxiliary fuel pump, and uses AN fittings, aluminum hard lines and braided flex lines rather than rubber lines and barbed fittings. I also installed Just's new aluminum wing tanks. I'll have a gascolator on the engine side of the firewall, and no inline fuel filter.

[danerazz]

Any pictures of the aluminum tanks?

[danerazz]

Any pictures of the aluminum tanks?

[SheepdogRD]

Here are a couple of them as received:

And here's one of them drilled and tapped:

We ended up moving the upper holes -- for vent and sight gauge -- apart, and moving the lower sight gauge hole an inch or so further from the rear main port. The front main port will be plugged.

I'll get some pictures of them in the wings tomorrow. Haven't made the tank covers, yet, so the wings are still open.

[SuperFly]

Looks good DIck!

Missed you at Billys this year! Hope all is okay.

Best,

Ben

[danerazz]

Wow, those look really nice. How are they mounted to the spars? Do you know what the factory is charging for a set? Also, is this going to be the "standard" highlander tank, or just an option?

[SheepdogRD]

Looks good DIck! Missed you at Billys this year! Hope all is okay.

I sure wanted to be at the Fly-In... but an upper respiratory infection has kept me down for a couple of weeks. Never felt terrible, but never had any energy, either. Decided I didn't need to infect anyone else, so I stayed home. Dangit!

Here's one of the tanks in the wing... it isn't bolted onto the brackets, yet, because I need to remove the tanks and clean them out before final installation. It's going to be a wrestling match getting them out and back in to stay, because they're a really tight fit. They're sized to make maximum use of the space available.

Because these tanks are bolted in, we needed a way to check the fasteners during inspections. One option was to cover both the top and bottom of the wing and install eight oblong inspection covers per wing -- four on the top, and four on the bottom. Instead, I decided I'd rather follow the SuperSTOL approach and build tank covers. I'll eliminate the need for access to the bottom by installing 10-32 nutplates on the bottoms of the spar brackets.

The .025" 6061-T6 tank covers will be held on by 6-32 stainless steel screws. Although you can only see them on the root rib, there are 6-32 nutplates all around the tank opening -- in the trailing edge, the ribs, and in an .032" 6061-T6 bracket I epoxied and riveted to the front spar.

The bottom of the tank bay is fabric covered. To hold the fabric off the tank bottom, I epoxied a capstrip across the opening by epoxying short pieces of rib web material at the false rib and at the front spar. When I do the final installation of the tank, I'll apply just a few dabs of caulk on that capstrip to hold it to the bottom of the tank so it doesn't drum in flight.

The tanks are flat-bottomed, so the adjacent ribs are, too. On existing wings, this means adding to the rib structure to flatten the undercamber, or replacing the ribs. I chose to modify the existing ribs, but the modified root ribs aren't very pretty, so I'll cover them with a Kydex insert panel. If I were doing it again, I'd simply replace the ribs.

The new butt ribs are also flat-bottomed, and that provides a bonus: the cover between butt rib and fuselage will be a simple flat part.

Thes wings will remain unfinished for a while... I have the engine in place, and I'm focused on the cowling and the windshield.

[SheepdogRD]

Wow, those look really nice. How are they mounted to the spars?

The tanks have angle aluminum brackets welded on. The factory provides 1/8" aluminum angle which is riveted and epoxied to the spars, and the tank brackets bolt to the spar brackets.

I chose to fabricate my own spar brackets:

I made each bracket from two pieces of .062" T6 that are epoxied and riveted to the spar. (The angle in the picture represents the tank bracket that bolts to them.) The upper piece was easy to form, but the bottom was a real bear because the material cracked as it approached a 90-degree bend. I had to fabricate a bullnose for the bender so it would make a larger radius bend. Fabricating each bracket part was a multi-stage, multi-machine process. Because I was hand forming them, it took a lot of fitting to get them just right. It didn't seem worth it to make tooling to form a few parts. Realistically, the factory solution -- angle aluminum -- requires no fabrication and is significantly simpler to install.

Do you know what the factory is charging for a set? Also, is this going to be the "standard" highlander tank, or just an option?

The tanks are $1400. I don't know the cost of the extra parts kit for installation in existing aircraft.

Yep, these tanks ship with new Highlander kits.