Breather/Vent Tube Protection

[skippydiesel]

My new, almost completed (took +12 months intensive work to get her into the air) homebuilt aircraft came with fine mech SS grills epoxied to the outside of the fuel tank breather vents. Presumably to prevent the ingress of foreign material, particularly mud wasp activity.

 

I have never seen this before. Quite like the idea but am concerned that there may be some negative aspects to the innovation - comments?

Edited November 1, 2023 by skippydiesel

[facthunter]

They will only be a problem if they increase the back pressure.  Nev

[skippydiesel]

20 minutes ago, facthunter said:

They will only be a problem if they increase the back pressure.  Nev

Thanks Nev - The original builder has the vents (x3) facing into wind & on lower surface of wing/fuselage (high pressure) . Even with the mesh (looks a lot like window fly wire) there is likely to be some posative pressure at flight speeds.

[facthunter]

That's not desirable. It will be added to what's already needed to get the oil up the pipe from the engine.  Nev

[skippydiesel]

4 hours ago, facthunter said:

That's not desirable. It will be added to what's already needed to get the oil up the pipe from the engine.  Nev

Nev - This fuel tank breathers.

 

Posative air pressure in the fuel tank is generally assumed (not so much by me) to be a good thing ie assist the pump in delivering the fuel to the tank or carburettor.

 

Back to the topic - gauze on the breather - the gauze is to prevent undesirables (eg mud wasp nests/ wind blown chaff) from entering. The alternative is nothing or removable plugs, that must then be carried in the aircraft. Seems to me what needs to discussed here is;

• The potential/likelihood of something blocking (partial/total) the breather pipes?
• The desirability of foreign object entry prevention?
• If the above deemed desirable - what is the most effective system - ie removable (before flight) plugs, a gauze, some other system?

[facthunter]

Rotax's oil return system is nothing like a fuel system  Rotax are very clear about not altering anything in that  engine oil scavenge system. Pipe dia length and orientation. Nev.

[skippydiesel]

Nev - the breathers I have referred to are fuel tank breathers 

[skippydiesel]

Wow! 117 views and only one respondent (Nev) - what's the matter  non of you have an opinion?

[Thruster88]

We need a picture. I have seen bush dweller Cessnas with mesh cable tied over the under wing breather.

 

If the mesh is very fine it might block if wet or hit by a splatter bug. 

[RFguy]

The locals tell me they overfill the tanks daily and spit fuel out the breathers which kills anything living in there....

[IBob]

FWIW Savannahs traditionally have a 3mm nylon breather line for each tank. These poke out under the wind and are cut off at 45deg into wind to give a degree of positive pressure. It's not the tidiest setup, but seems to work though it can be difficult to get equal pressure in all tanks as the pipes do not sit straight or perpendicular to the underwing due to the natural curve of the pipe itself.
At one stage I had very uneven L/R fuel feed, and was able to partly correct this by adjusting the angle of the pipe cutoffs. If I were  building again, I would run and anchor solid pipes down through the wings, rather than flexible line, allowing the cutoff angles to be precisely adjusted.

 

I did try converting to (much tidier) forward facing underwing vents, using tiny 90deg garden irrigation fitting, but changed back after just one short flight that saw massive crossfeeding. Part of the problem there was a poorly moulded integral fuel tank filler point, that allowed that tank to 'blow'. However, it does not do this with the standard setup, so clearly the forward facing vents were delivering a lot more pressure.
 

Mason bees/mud wasps are a whole class of critters: over here they are just a little smaller than a german wasp, but far too large to enter or nest in a 3mm pipe. They may be different where you are.

Part of my preflight is to visually check the ends of the breather lines. This is easy as the the nylon is semi transparent. To date I have never found anything in there.

[skippydiesel]

I do think that a fuel tank breather is an unlikly nesting spot for  mud wasps or similar. There would always be a fuel vapour rich atmosphere inside the tube which most insects would find very uncomfortable BUT I would only have to be wrong once, for there to be a heart stopping moment, as the tank went from posative to negative pressure as fuel is drawn off and the engine started to loose power due to fuel starvation.

 

I do check all my external fixtures, before flight but mud wasps can sometimes nest well up inside a pipe , no external tell tail allerting me to their presence.

[IBob]

Maybe check the size of your mudwasps, Skippy? And take note of where they nest in your area. Remember they have to be able to get in and also turn round in order to lay eggs etc. So if the hole is round it has to be a reasonable diameter to allow that.
Here they will get in a dowel sized hole  or a keyhole (which allows turning). I haven't seen them in anything round much smaller than that.
They also nest between flat surfaces and in curtain or hung clothing folds, but that's not relevant here..........

[RFguy]

Well. I just found a  small mudwasp  nest up behind my Directional Gyro !!!!. way up behind everything.....A  1/2" cube of mud....

During the annual , we found one fuel tank breather was partially blocked with debris..... 

[3rd harmonic]

3mm is a pretty small vent tube, I'd be more worried about it getting blocked by dust and/or mud flicked up off the ground than wasps.

But mud wasps are an absolute bugger where I live in the Adelaide Hills.

They blocked up the air inlet on my compressor and so when I turned it on the dirt was sucked in and damaged/broke the spring steel check valve in the cylinder head!

Then last year went to start our generator during a power outage and it would sort of fire but then stall. Didn't take too long to work out the little sods had blocked up the exhaust right down inside the muffler!

We decided to run it without the muffler, running any motor without a muffler is fun for a abit but the novelty quickly wears off...

Took me ages to clean it out flooding it with water from the hose and the long compressed air jet nozzle.

They did the same to my neighbours fire pump muffler with partial blockage and the mud had been baked into hardened ceramic by the heat.

Little vandels!

[facthunter]

A good condition Stihl chainsaw here would only idle and was the muffler blocked by mud, a month ago, so it's a potential problem. It West Maitland it was always happening to the Pitot Tube. Mant got proficient at doing a circuit without airspeed indication.  nev

[skippydiesel]

1 hour ago, facthunter said:

A good condition Stihl chainsaw here would only idle and was the muffler blocked by mud, a month ago, so it's a potential problem. It West Maitland it was always happening to the Pitot Tube. Mant got proficient at doing a circuit without airspeed indication.  nev

Don't know about the circuit without airspeed, I guess I might have doe it in my last aircraft (10 year's experience) but the new aircraft is a very diffrent beast, so it might be some time before I have that sort of  simpatico with her.

 

As for the chainsaws and for that matter all small motors - checking the exhaust pipe after a failed attempts to start, is now routine and almost always a mud wasp nest.

[danny_galaga]

Dunno about your situation, but my simple setup just has the breathers poking out the bottom. To prevent mud wasps, I simply drilled a small hole in the breather about 10mm from the end and put a split pin through it. I got real fancy on one of them and used the split pin to hold the breather in place too 🙂

[Blueadventures]

Here are my covers for fuel tank vent and pitot. A mud wasp started building on my pitot cover.