Fuel cap lost

[stinger]

2017-02-03 Fuel Tanks 003.jpg2016-12-15 Fuel Tanks 002.jpg2016-12-13 Fuel Tanks 003.jpg Different strokes I bought fuel caps and flanges from Van's same as I had on my RV8. I vented by way of tubing out with three loops in wing then out under wing . Flanges are inverted.and cap installed. It works for me . No lost caps. Stinger LSA 300 hrs

[Collin Campbell]

Stinger, I did the tanks on my first two Bearhawks in a similiar way. Since I had built an RV previously, I was familiar with the rivet/proseal procedure. I am curious how you did the venting with the loops in the wing. I looped my vent tubing in the tank itself, but still got some fuel out the vents at times. Collin

[Russellmn]

Collin, vent tubing should be on the outside of the tank (if we're talking about the 3 sides and down method) so the fuel can never siphon.

[stinger]

The vent line is indeed outside the tank on the out board side of the wing. The small amount of wing dihedral helps. I placed the three loops of the vent tube two bays out from the tank , putting the tubing as high as possible in the wing.with three loops then ran the tubing further outboard staying high and exit through the bottom of the wing outside the wing strut . Tubing is then bent forward for to capture air flow .. Works for me ! Stinger

[tailwind]

I have a question. Not having built a tank with rivets, is the sealing material going to seal the holes in the corners or are the holes for clecos and you are welding the corners and seams.

[stinger]

Pro seal does it all, however forming the aluminum in such a way making nice corners . No welding. Stinger

[Bcone1381]

I responded to a similar topic on another thread. Forgive me for repeating myself. A future builder a year from now might appreciate/benfit from my experience.

Before, I wished I had Stinger's or Collin Campbell's caps. My factory fuel cap was very difficult to remove.

Then I replaced the O-rings with a Dash 323 size which is one step smaller. Now I feel the Factory Cap fits just right. Before it was so difficult to remove I felt it was a hazard to me from multiple fronts....lubrication leading to a cap loss, ladder fall risk, damage risk to the cap/tank by using a tool to help pry/removal, etc.

The old O-rings were Dash 324, the new is Dash 323. This change was made through Mark, who consulted Bob. It was a quick, easy mod about the time and cost of a milk shake. I see no need for O-ring lubrication, and once released I gently rock the cab back and forth 2-3 times to work it out of the filler neck. The cap is very secure when I crank it down tight. I like the idea of tool to increase torque of the cap.

Beware, I'm still building so I have an experience issues in this arena.

[AKKen07]

Do you remember from where you sourced the rings Brooks? Looks like it’s not a standard size found at my typical shops.

[Bcone1381]

Oringsandmore.com. Part 323v. FKM heat resistant black oring size 323. This is fabricated from Viton rubber. Today they are .80 each.

https://www.oringsandmore.com/viton-heat-resistant-o-rings-size-323-price-for-1-pc-1/

[Bissetg]

Well, I joined the list of those that have lost fuel caps in flight today.

I’d filled to the gunnels for our days exploring. After about an hours flight Nev noticed we were streaming fuel from theRH tank. It seems it’s very tricky to get them tight enough to stay put without needing to be prized open with a screwdriver. I’m in the market for different caps.

[schu]

I heard Kevin was testing some caps that don't come out. I've never seen one, but I also have a design in my head that would lock into place and be easy to operate.... Now I'm super curious to see what Kevin came up with and how similar it is to my idea.

I have no intention of running any caps that don't positively lock in place, so for me it's whether it takes less time to machine my idea and test it or just cut the flange off the tank and install bayonet style caps that ride over a cam to lock into place. I suspect welding a new neck on the tanks is faster.

schu

So I have a design for locking fuel caps. It's in the 3d printed phase and seems to work well. I have contacted a machine shop about making them and they confirm the design is reasonable to manufacture.

I reached out to Bobby for feedback on the design and he confirms that my solution is completely different than Kevins so I don't feel like I copied him even though I've never seen his cap. It's pretty simple really, just a single o-ring on the body, single o-ring on the shaft so it's not a pain to get into the tank, then once in the tank you twist the top 1/4 turn and a cam engages a spreader of sorts that makes the cap under the filler neck spread out and lock into place.

My design also has an indexing pin that will require you to file a small notch in the neck. It's really no big deal, you remove the cap, insert a special plug I include, 2 minutes with a file, then vacuum out the aluminum dust, hit it with compressed air, then pull the plug out. The advantage of the notch is that the cap can't be fully inserted without being correctly indexed into the wind, and it can't be locked without being fully inserted. I believe this provides a bit of safety because having some consistency to the vent could potentially eliminate any pressure differential in the tanks in flight.

Anyway, I'll need another month or two to finalize the design and get the first few in the field, but I'm curious how many people would want to buy one? Assuming it's everything I claim it is, is this something that people would be willing to part with $300/pair for?

I know that's expensive, but they are billet, and have a dozen machining operations, and it takes time to design, test, and produce stuff like this.

If it was just for me I'd just cut off the factory filler neck and weld in a bayonet style bung, but if there is interest then perhaps I can solve this problem for others and retain the bearhawk tank design myself.

Thanks,
schu

[Utah-Jay]

schu I look forward to seeing your caps

[Battson]

I think an alternative design would be welcomed by the market schu

While I wouldn't personally be in the market for a new set, I think the demand is definitely there.

[Tim213]

Schu, Based on so many folks losing caps I would be interested in purchasing your caps when they become available.
Tim

[schu]

Here is a sneak peak of the design. I'm missing the o-ring groove in the render and of course I need to build several that will get thrown away while working through the tolerances. One concern is how consistent are the filler necks? Right now the outside diameter is 1.72 which is .0035 smaller than measured in one bearhawk. I'll probably want to take this to 1.71. Perhaps some of you can tell me the diameter of your necks to see how close they are.

As far as safety, the bottom screws will have notches cut and staked like an andair valve to ensure they don't come loose.

Also missing the notch that will indicate them in the filler neck.

[AZBearhawk272]

Schu,

I have caps out there flying. Right now, completing my Bearhawk is my Home priority and I am not going to get distracted at the last 3.258 %
I like several features of your design.
If you care, send me your e-mail and I can answer directly some of your questions and share my discoveries.

Kevin

Bearhawk#272@

Drop the # and add Geemale

[schu]

Kevin, check your PM for contact info.

schu

[Battson]

Here is a sneak peak of the design. I'm missing the o-ring groove in the render and of course I need to build several that will get thrown away while working through the tolerances. One concern is how consistent are the filler necks? Right now the outside diameter is 1.72 which is .0035 smaller than measured in one bearhawk. I'll probably want to take this to 1.71. Perhaps some of you can tell me the diameter of your necks to see how close they are.

As far as safety, the bottom screws will have notches cut and staked like an andair valve to ensure they don't come loose.

Also missing the notch that will indicate them in the filler neck.

I like the mechanism which you have selected. I have been imagining solutions, your design is similar to what I had in mind. I think it's perhaps the most elegant design achievable without changing the filler neck design. Part of me thinks the best solution may be a different filler neck, but I haven't really thought it through.

If there was some way to ensure a good seal with downward pressure.... Perhaps if the O-ring was at the top up against the rim, in a recess, and then the design allowed the mechanism to close and apply a small downward force on the cap (tapered locking arms perhaps?). Just thinking out loud, you probably don't need extra ideas

[schu]

I like the mechanism which you have selected. I have been imagining solutions, your design is similar to what I had in mind. I think it's perhaps the most elegant design achievable without changing the filler neck design. Part of me thinks the best solution may be a different filler neck, but I haven't really thought it through.

If there was some way to ensure a good seal with downward pressure.... Perhaps if the O-ring was at the top up against the rim, in a recess, and then the design allowed the mechanism to close and apply a small downward force on the cap (tapered locking arms perhaps?). Just thinking out loud, you probably don't need extra ideas

Speaking of changing the filler neck design: I'm still considering a bayonet style cap for myself. Not only is it quarter turn on a cam that locks the cap on and against a rubber gasket, but it's also a bit larger so you can see the fuel level easier.

As for the caps I'm designing to fit in the existing kits, it seems that there are some differences between the plans and the factory tanks. The plans for the cap call for a bung that has a 2" OD and 1.75 ID, with the cap OD at 1.74 however the tank I measured was 1.7235, which is a bit of difference, enough that the cap as drawn wouldn't fit in the tank I measured. More measuring of different kits should reveal more info. Also, I thought of tapered locking arms, but that really wouldn't work because I'm not betting that the filler necks are consistent enough in height, because there really isn't much room to build all of this inside of 1.7", because the locking arms are only .100 tall and only stick out .060 with the cam engaged, so that would be a really steep ramp, and because I'm trying to limit ways this can hang up because the cap getting wedged more than the spring can retract would equal stuck cap.

I think the solution is to just put the locking arms a solid .020 below where i expect the tank to be and if the cap slides up that much in flight I don't care as long as it's locked, the notch prevents rotation, and the o-ring is deep enough to work.

[schu]

[Utah-Jay]

Ok, that video is pretty impressive. Timeframe?