gas cap venting

[Steve Fisher]

Has anyone experienced a bug smashed into the gas cap vent in flight? Seems like this could be a problem and lead to reduced fuel flow. While the probability may be low, it is definitely a possibility with bad results. If the vent is turned backwards to avoid being plugged by a wayward bug, the fuel tank pressure be slightly reduced and will result in a reduction in fuel flow. Has anyone tried installing the vents backwards and was the fuel flow adequate?

[geraldmorrissey]

In 50 plus years of flying it has not happened to me. I suppose it could. Reversing the vent might possibly cause fuel to flow overboard. Others might chime in with smashed bug stories, but I think having one crawl in and nest is more likely. I've had a pitot tube blocked once by a mud dauber in Southern California. That will get your attention.
Cheers
Gerry
Patrol #30 Wings

[Mark Goldberg]

Do not turn your gas cap around with the vent facing aft. An excellent way to pour all your fuel out of your tank and make things very quiet in the cockpit.

I have never heard of a bug or rain or anything blocking up that vent. Theoretically it might could happen. But a lot of 1,000's of hours in the field with these caps and it has never happened as far as I know. Mark

[Blackrock]

Over 1,000 hours on mine without a fuel vent plugging. I smash lots of bugs too coming out of ranch meadows, backcountry strips, etc. I don't think you have much to worry about there.

I did lose a fuel cap at night over the middle of Nevada and it sucked 20 gallons of fuel out before I could land. The idiot who last fueled the plane left the cap loose (me). On another trip, the same dip attempted a partial fuel transfer from the aux tanks, forgot and left the pumps on, and dumped 10 gallons of fuel overboard. I've also forgot the fuel selector was set to one tank, unported that tank and killed the engine; that will also get your attention, much like Gerald's mud dauber event. The point of my confessions is that pilot error when it comes to fuel management may be a bigger concern. That has certainly been my experience and while it is embarrassing to share, I hope others can learn from my mistakes to avoid the same.

The sight gauges work well and will indicated a flow problem, should it arise and as long as they are periodically checked. However, installing a fuel flow transducer and fuel flow monitoring system is the single most important safety addition built into my plane, in my humble opinion. That has significantly improved fuel management and has provided a level of accuracy (combined with the fuel sight gauges) that has certainly improved in-flight decision making. I don't think I'd own another plane without fuel flow. Especially one used for much x-country flying. I've got a lot of examples about how that has saved the day, but won't go into that now except to say that it has paid for itself many times over.

Mike

[Bcone1381]

Sounds like you have experience and remedies that would make for a good article in Beartracks.

[jaredyates]

For real Mike! You could have a regular column.

[Chewie]

Mike, if you pm me I'd be interested to hear more fuel flow examples. That very issue has come up on many occasions at work.

[Blackrock]

Mark,

PM sent.

[Mark Moyle]

There are a bunch of bug smashers up here with O360's. The most of the STC's for the supercub upgrade call for Atlee Dodge gas caps. These things have 5/16" tube welded to the cap pointing forwards.....I'll post a pic...


Sent from my iPad using Tapatalk

[whee]

There are a bunch of bug smashers up here with O360's. The most of the STC's for the supercub upgrade call for Atlee Dodge gas caps. These things have 5/16" tube welded to the cap pointing forwards.....I'll post a pic...


Sent from my iPad using Tapatalk

That looks just like the gas caps on a Luscombe. In 500hrs we never had a problem and I've never heard of anyone having an issue on a stock Luscombe. The one time I know of was on Speedbird. A mud dauber plugged the vent while parked and it wasn't known till the plane was in the air. Speedbird was a highly modified Luscombe with a 150hp turbine.

Like Mark G. said, putting the caps on backwards is a bad idea. My grandpa did that once on his Luscombe after refueling in a hurry. It caused enough suction to vent all his fuel rather quickly.

[bway]

This thread got me to wondering why in 50 years of flying I have never had a fuel vent like these get stopped up in flight. Every time it happened, the aircraft was on the ground. Same thing with pitot tubes. One would think that in thousands of hours I would just not be that lucky as I live in the south where there are lots of bugs. Here is my theory. There is virtually no air flow through these tubes once they are pressurized, so there must be a high pressure cone shaped area that forms immediately ahead of the opening. I think that high pressure air simply deflects the bugs out of the way in flight.

[Battson]

I think that high pressure air simply deflects the bugs out of the way in flight.

All the thousands of bugs dead on my leading edges might disagree with the high pressure theory!

I think a hard shelled bug with soft insides, hitting a metal orifice travelling that fast, is always going to be smashed into smithereens. Then you have the air pressure to clear any remnant blockage which might exist post-impact. The chances of it causing a long lasting blockage must be less than winning the lottery, and then you have two tanks, so you have to win twice in a row...

[JimParker256]

Rainbird water sprinkler filters of the right outside diameter will prevent bugs from entering your fuel vents, and do not block the "venting" effect. They are tapered mesh, so there is very little obstruction to air passage, but they do a great job of keeping bugs out. Grumman American Tiger/Cheetah/Traveler pilots use these on their airplanes. I've heard that some who have REALLY picky IAs will pull them before the annual inspection and reinstall afterward, but on an experimental it should be no issue. Just make sure you do your fuel flow testing with them installed if you're going to use them.

[bway]

"All the thousands of bugs dead on my leading edges might disagree with the high pressure theory!"

Yes, I've had lots of bugs on leading edges, etc., but they would have had to change direction much more abruptly to miss those surfaces. Clearly something keeps the bugs out of these vents. If not a high pressure area, then what? The bugs would only have to be moved about 1/8 inch to miss the vent opening. I'm not saying it could not happen, but it must be very rare. Bob

[Phil]

Kit Planes just finished a really good 3 part series on fuel systems that's worth a read. Aft facing vents are a big no no because they can create a vacuum in the tank and suck them both dry if you have a cross over or are running from both tanks. I believe they even referenced AC 43.13 on that one.

If you're really worried about bugs plugging it up you could use a Cessna style vent exiting behind the strut, but that's a lot more complex.

Edit: I've also never had a bug plug a fuel vent, but I did have a giant dragon fly gum up the stall warning tab on my C-150.

[Battson]

True story - when you pull a high G turning or climbing manoeuvre in the BH (especially with full tanks) it flushes fuel out of the cap vents at very high pressure. We observed this during formation flying. I guess this is because the fuel is compressed into that area of the tank for whatever reason, I can't really understand that part. But we did see a lot of fuel going overboard and streaming aft. A negative G push over would probably do the same with almost empty tanks?

Anyway, if you happened to get a clog in the vent, you could always use that technique to flush it out. Hahaha! (kidding)

[Bdflies]

Very interesting! I have a theory; at 'high G manuvers' the wings are producing more lift. More lift = more pressure on bottom and less pressure above. We've all seen condensate form above jet fighter wings, at high G. Now, an average Bearhawk may not be able to create enough negative pressure to condense mousture, but my guess is that you've created a enough of a pressure drop to blow fuel out of the vents.
Heck, I could be all wrong, but it sounds cool! That would definitely be my story! BTW, how many G's are we talking about?

[Battson]

The most we've ever pulled is 3.4, at very light weight. Usually about 2.2 is the max with any load on.
I can't recall what it was on this occasion, but would not have been more than 2.5 from memory.

[tailwind]

Of concern for me would be ice build up. It would not take much to close the opening.