Wing Tank Bulk Purchase Update

[sonex1374]

Builders,

AirVenture produced a successful discussion with a fabrication shop, and I think we're ready to move forward on a bulk purchase of Sonex wing tank kits!

Here are the details that I have so far.

- The kit will include two cylindrical tanks, each holding about 5 gallons of fuel. One end of the tube connects to a filler neck and fuel cap that installs in the upper wing skin, near the wingtip. The other end (root end) connect to the transfer pump and plumbing into the main fuel tank.

- Weight of the kits will be about 25 lbs total. I'm working to pin this down better in the near future. No welding or fabrication is required, except for fitting the fuel filler caps to the wing skins.

- Tanks fit into the lightening holes just in front of the main spar. Kits can be built into the wing at initial construction, or "slid" into the finished wing so long as the wingtip is removed.

- Kits will come complete with all required parts, minus the common hardware items.

- Price depends on total kits ordered, and will almost certainly come in under $1500. I'll try to pin this down as soon as possible.

- Kits will be drop-shipped from the fabricator, with shipping expected to run about $200.

- 50% is due up front, with the remainder due at time of shipping.

Please send me your questions and I'll work to get answers. The goal is to firm up an order and final prices within the next 30 days, so if you're interested in participating, please respond to me as soon as possible, and be ready to write a check around the beginning of September.

For anyone on the fence about spending the money, consider that there may be no better time. This bulk order might be the easiest and cheapest way to get one of these kits, and there might be only one purchase.

Jeff

[JimP]

How are the tanks constructed and secured within the wing? Wouldn’t want it rattling or wearing the tank or ribs.

Will it essentially be in a neutral location for weight and balance? For example, it wouldn’t reduce the baggage weight limit (as long as it isn’t over gross)?

I haven’t bought a kit yet but a Sonex-B is at the top of my list. I am thinking that they probably wouldn’t be impossible to sell if I got a set and ended up not using them.

[sonex1678]

Wouldn't the location of the tanks at the wing tip be an issue if a fuel transfer problem developed? I would think an extra 50-60 lbs on a wing tip (fuel and tank) might cause a serious balance problem; not to mention that the wings may not be designed to support the extra weight at the tip. Any chance the tanks could be located on the root end of the wings?

[GordonTurner]

The tank runs the full span of the wing using the larger lightening hole in each of the nose ribs. The fuel is spread evenly from tip to root on each side.

[NWade]

I've just always wondered how tanks in the lightening holes don't "fret" over time, due to vibrations & metal-on-metal contact between the tank sidewall and the lightening hole edges.

--Noel

[kmacht]

The tank runs the full span of the wing using the larger lightening hole in each of the nose ribs. The fuel is spread evenly from tip to root on each side.

Until you bank the airplane even a little bit. Seems like the idea only works if the tanks are full or empty. Anything in between and you get weight shifting around each time you turn the plane.

[JimP]

Internal baffles can fix the quick weight shift problem. I assume that is part of each tank but it would be good to hear.

It’s a pretty elegant way to add the tanks really. Very non-intrusive to the structure and it should be close to the neutral position for balance. The dihedral gives you good gravity feed to the pumps.

Has anyone considered a small ~1 gal tank under the passenger seat, gravity fed through one way valves, and then pumped to main tank? That would keep the fuel levels in each wing the same and give either cheaper or redundant pumps.

The main downside to the configuration I see is that the surface to volume ratio is lower than a more cubical tank, and so it ends up a little heavier per gallon of capacity. But of course the passenger seat is the only place for such a tank.

[sonex1374]

These tanks don't have internal baffles, but I suppose a builder could add them if so desired. You could also fill the tank with fuel foam and accept the 5% loss of capacity.

As to the effect of fuel sloshing, perhaps Jim Hicke or Ed Lee could comment on the effect. Playing with some quick math: the moment created by a half-full fuel tank sloshing to the outside wingtip yields about 120 lb-ft (15 lbs gas x 8 ft to the center of gravity of that gas). This is roughly equivalent to a 120 lb passenger sitting 1-ft off the aircraft centerline. It's noticeable, but manageable.

Jeff

[SonexN76ET]

Jeff,

Two quick questions on the extended range auxiliary fuel tanks:

1- How do you plan on plumbing in a fuel sump for each tank to check for water in the fuel?

2 - When you transfer fuel from the auxiliary tank to the main fuel tank how will you determine when the transfer is complete?

Thanks,

Jake

[sonex1374]

For those that are still undecided on participating, I want to remind you that the deadline is August 31. There are currently 9 people that have confirmed, and several others are still considering. Please email or PM me directly if you think you're interested.

If you have remaining questions, please ask them. I have confirmed most of the details with the fab shop. Those answers are below.

Jeff

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- Price is $1300 per set. This might go down again if we get several more.

- Fabrication time is under 4 weeks. All the sets will be fabricated at once, then drop shipped to each person individually.

- Shipping is estimated at "under $200". It will come in a 10-ft long crate via truck freight carrier. Builders near each other can combine shipping if that works for you.

- Complete kit weight is estimated at 7.5 lbs each, and the hardware (pump, lines, filler caps, etc) at 5-10 lbs. That gives a weight of 20-25 lbs total installed.

- Chafe protection is applied to the tubes themselves and consists of a urethane tape. tape is located at each wing rib station, rather than over the entire tube, or affixed to the ribs themselves. This allows the tubes to be "slid" into the wing ribs (it's a tight fit, but doable).

- If you have pitot-static lines running thru the lightening holes in the standard Sonex-plans support brackets, those brackets will need to be removed and the lines relocated to the front lightening holes.

- Builders that have already closed their wings will need to remove the wingtips to gain access to the ribs. Assuming no obstructions, the tubes can be inserted from the tip end and all work done this way. If you do have obstructions, you may need to open the wing. This isn't that bad really, as all you really need to do is remove the wing from the airplane, flip upside down on a saw horse, and then drill out the forward wing skin rivets on the bottom side (from the spar forward to the leading edge, bottom side only). These will come out without too much trouble, and can be riveted back up easily afterwards. Seriously, this isn't that hard once you make the decision to just bite the bullet and do it!

- Kits will include the tanks and all related items. This includes the filler necks and fuel caps, transfer pump, fuel line, and general hardware. You might need minor additions, based on your own unique circumstances.

- Each tank has a Curtis drain valve at the root end of the tank, just outboard of the fuselage. You'll drill a hole for the valve/sump container neck thru the bottom skin.

- Tanks are pressure tested to 4 psi prior to shipping.

- The tanks don't have quantity marks or gauges, and you time the transfer rate using a known quantity of fuel. The pump will make a loud racket when it sucks air, letting you know your wing tanks are empty.

- This modification is not hard, and shouldn't take more than a couple weekends to accomplish. If you're plane is flying and you need to remove the wings and drill out rivets, that might be the most difficult part!

- Payment is due by August 31. I have to pre-pay 50%, and I'll send that in on September 1st. You can send me 50% and then the rest later if you like, or just keep it simple and send me the full amount up front. Check or Paypal is OK. Shipping will be billed prior to delivery from the shop.