Fuel cap lost

[mbaerobat]

The design as it stands doesn’t seem to be a problem. Very straight forward using easily available and replaceable parts; nothing that will be unobtainable due to a specialty manufacturer ceasing business.
The O rings probably can’t be tightened enough to do any damage to the filler neck.
Losing the caps is just a case of not being diligent on my part.

[AZBearhawk272]

Here I am!
Gas caps are on the to do list but not near the top…. : )

[rodsmith]

Wow, beautiful! Is that an IO-520, how much taller is the gear than plans?

[AZBearhawk272]

Rod,

IO-470 with a little bit of ignition and exhaust magic.
sits up 10 inches from stock, which makes it like a jungle gym to enter….. keeps me in shape.

[Nev]

I've been thinking further about how the left tank with the missing fuel cap was completely full after we landed, and the right tank (with the cap still on ) was missing 30 liters (over and above the fuel burnt enroute). I had the fuel selector in BOTH the whole time, so it's evident that the low pressure above the left wing was pulling fuel through the fuel selector from the right tank. No surprises.

A question in my mind for a while (from the extensive fuel discussion thread HERE ) was whether fuel could flow from one tank to the other via the fuel selector, and the engine keep running. Obviously it can, because around 30 liters (probably more) flowed across in a very short period of time, yet the engine kept running.

The next step would have been once the right tank was completely empty, whether the low pressure above the left wing would have prevented fuel flowing out of the left tank to the engine. If so, it may mimic what happens when flying out of balance. Thankfully I wasn't the one to test that scenario.

Has anyone who lost a fuel cap in flight seen what happens if a tank is completely drained ? Does the engine stop ?

[BTAZ]

I made my own per the plans and so far seem fine.

But if I was to make another set, I would turn a slight taper on the inside of the filler neck(slightly larger ID at the base then the top) so if the cap did try to "slide up" it would only become a progressively tighter fit in the neck.

Hard to retrofit but would be easy to do when making the filler neck.

[davzLSA]

Hey Brad, what are the V speeds for your LSA?

[swpilot3]

I've lost 3 caps in 4 years. I haven't figured out exactly what the cause is... sucking vs some hydraulic effect. I started using a crescent wrench to tighten them very tight... still lost one after doing that. The only thing I really don't like about my BH is the fuel caps. Hard to get off yet they fly away sometimes.

I used one of Kevins prototype caps and it was heaven!! :-) I know you've got a lot on your plate Kevin, but your caps were great and I would gladly pay a lot for them... even if they aren't perfect yet.

[Battson]

Are you putting lubricant on the O-rings?

[Nev]

Thanks for this info Bobby.

[swpilot3]

Yes, I use engine oil. But I’ll give fuel as lubricant a try.

[John Bickham]

Based on my experience................

It has become a huge red flag for me when someone walks up to me while I'm fueling and starts asking me about my Bearhawk. I kinda go to a place of euphoria and a bit of a distracted little kid. I've left a fuel cap on the ladder at KENV and took off across the desert. Pure pilot error, not fuel cap design.

To answer your question Nev. In flight, the tank with no fuel cap will show full and will suck the capped tank down rather quickly with the fuel selector in BOTH. Negative pressure above the wing. The engine will run fine. However, I did not test to one tank completely empty

I did notice the unusual gauge glass readings rather quickly and made a precautionary landing at the next available landing site. Boy, is that a dumb feeling. I put my extra cap on and returned to KENV to retrieve my cap and replace the lost fuel. The only bright spot was fuel was half the cost it is now.

[Battson]

I'm sure I am in the minority here, but I've had a decade of trouble free service from our caps - I find them easy to use, once I got them set up correctly and 'worn in'. They do need a few drips of fuel on them, or on the filler neck, if temperatures are freezing cold. I have also done a little tinkering with them to make them work smoothly.

You need to have fuel resistant grease inside the cap - on the threaded metal-on-metal parts only. I would not advocate putting any lubricant on the O-rings (other than fuel), based on what I have heard.

We've left a cap off once before, but pilot error not design issues. I have a refueling process which prevents that from ever happening again.

[whee]

I’m mostly with Battson though my experience is much shorter. While I’m not fond of the caps I’m never had any functional issue with them. I put lube on the threads so they don’t gall and if a cap is stiff to remove I get a couple drops of oil from my engine vent tube, smear it on the o-rings then it slides in nicely.

That being said, I don’t let anyone else touch the caps and I’ve had issues with lineman saying they won’t fuel my plane if they can’t remove/install the caps themselves. Some bologna about liability. For that reasons and some personal preferences I can see myself changing out the caps for standard J tube caps should I ever need to remove the tanks for some other reason.

[zkelley2]

There's close to a 0% chance they'd be able to put them on correctly.

[jonmiller0]

I’ve lost one when I first started flying the Bearhawk. I tried the fuel on O rings and it never worked so I use a small amount of plumbing grease. I hate putting on the gas caps…so challenging to get it lined up right. I really hope a new design will come out. I crank them now but keep a spare just in case. Judging by the regularity of this maybe I should buy a few more spares!

[Wyo Johnson]

I like the venting approach, but the chance of "loss in flight" outweighs the "simple to build" in my mind.

The pic shows a rough model I've been playing with and have most of the tolerances figured out. Before I "lean it up" I decided to have on 3D printed this weekend. I'll post better pics when we get it done.

The cap is 1.5" in diameter and retains Bob's vent feature. A threaded flange would weld to the tank, the Body of the unit would thread into it, allowing vertical height adjustment of the cap. There is a lock washer (tab type) that keeps the body and cap from rotating and is captured by the locking ring/nut, which is also safety wired (not shown in the pic).

To open the Cap, you push down on the vent fin slightly and rotate 30 degrees. This allows the "key" to disengage "anti-rotation notches" on the bottom of the body and then clear slots cut in the body to be removed. The Spring pushes up on the cap and key, so once the key is disengaged the cap is pushed vertically. The design in dummy proof (until the make a better one) so you can't partially install it, its either engaged or it sits proud of the top of the body. The Spring is currently at 5.5 lbs which should be more than enough to keep the key engaged even in a dive (150% air pressure margin). O-rings are Viton and found the manufacturer that makes them out of just about everything to be fuel (ethanol) compatible.

With a little luck I'll have a 3D printed "demonstrator" with me at OSH...and looking into a couple local CNC couple shops to build. I would like to get with Mark G to see if he and Bob are interested in them for the production aircraft. more to come...

Andy Johnson
1423B - Scratch

[zkelley2]

I've never had an issue of them coming off. Typically they're a pain to take off. If it's properly installed and clocked, there's no way in the world mine would come off.

[Gerhard Rieger]

This was my solution, I gave the BH caps I made to a friend and made these. They will have like an inspection plate covering it for access

[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