Fuel tank venting

This is a general low wing question, and tho I've pinged my builders group, just wanted to see how you guys do this.

In doing my fuel plumbing for the Mustang2 (a non-EFI setup), I discovered two vent references I wasnt aware of both out of FAA-H-8083-31 Ch14. One says that fuel tanks have to have two vents (page2); the other says if tanks are y-piped together, their vents must be interconnected.

So just talking about wing tanks only (not header tank installs) my questions are:

1. Do the VANs kits run two separate vents for your wings tanks?

2. If you interconnect vents, does that fulfill the 2 vent rule above?

3. Do you need to interconnect your wing tank vents if you are running a fuel selector with "L,R Both" positions?

FWIW I've got Usher flush fuel caps which are unvented, hence the questions.

Thanks for any wisdom.

The tanks on the RV's are vented separately and are not tied together. For low wing aircraft you can only have a LEFT & RIGHT, not a BOTH.
It is important to follow the manufacturer's recommendations with regards to fuel systems. Most fuel-related engine stoppage problems are due to modifications to the fuel system.

Vic

Thanks Vic. There are no recommendations on fuel systems for the M2 and therefore no standardization......or if you wish, its up to builders discretion. Hence the questions.

In the 'single digit' RV's, there's a fitting on the root end of each tank, and an internal run of -4 tubing that runs along the inside top of the tank & is attached behind the filler neck.

The norm ('to plans') is to bring the line into the fuselage, then up to the top longeron, forward to near the firewall, and down to the floor mounted vent. This minimizes spilling fuel out the vent with full tanks parked on a slope, due to fuel expansion in the sun, or during acro.

A few guys (I've heard that the Rocket guys do this) have used a coil of multiple turns inside the wing instead, but that might not be as effective with the M-2's relatively thin wing.

Charlie

Ok thanks Charlie. So sounds like some designs do, and some dont. Dealers choice.

FWIW, I've seen the Rocket guys coil setup and personally I dont understand why they would do that as it seems to me to be a water trap subject to freezing. I guess as long as you anticipate the limitations of such its ok, or if the coils are in some way heated like by cabin air or something so they dont experience a problem. No need to debate the issue here tho - I'm not going that route.

In anycase, can you guys or someone else shed light on if the vans setup covers the two vent per tank reference in the first post, or educate me on what it really means? Just a bit confused about that as I dont seem to see it or hear people talk about it.

Thanks again.

inverted

It as has been pointed out above and is that if you are going to do aerobatics and be going inverted you need to try a keep as much fuel as you can inside the tanks when going through your positive to negative flip-flops and knife edges or dull edges if you do those too. I tell people its like a pee trap in the plumbing and it kind is. If you are thinking of putting your Mustang through its paces you may wish to look at the vent set-up in an RV-4,8,3 or 6. You should be able to find one close to you, they seam to be all over these days.
Hope this helps. Yours R.E.A. III #80888

None of Van's designs that I've seen use dual vents. I suppose that having two separate non-interconnected tanks could be considered to meet the spirit of the requirement,but the early -3 had only a header tank. I don't know if it had 2 vents in it's design.

I took a quick stroll through the chapter you mentioned, & notice some other things that Van's designs might not meet, but there are also requirements that certified a/c don't meet. For instance, the requirement that

"Each tank must be isolated from personnel
compartments of the aircraft by a fume-proof and fuel-proof
enclosure that is vented and drained to the exterior of the
airplane."

The Cub & Taylorcraft are two that immediately come to mind.

These are experimentals, so we get a little more leeway, regardless of what the regs say. I don't know for sure, but I doubt that the M-2 landing gear meets FAR23. A lot of homebuilt designs' gear don't meet it.

Charlie

vic syracuse said:

For low wing aircraft you can only have a LEFT & RIGHT, not a BOTH.

Click to expand...

Color me curious. I fly a friends Scottish Bulldog (low wing) airplane once in a while and it has LEFT, RIGHT, BOTH and OFF on the fuel selector. AFAIK it came that way from the factory.

GalinHdz said:

Color me curious. I fly a friends Scottish Bulldog (low wing) airplane once in a while and it has LEFT, RIGHT, BOTH and OFF on the fuel selector. AFAIK it came that way from the factory.

Click to expand...

Do you have a fuel system diagram? It may be that both tanks plumb to a sump (or header) tank or that they used some other workaround to solve the issues associated with a "both" setting on a low wing.

Please heed Kyle's words. Don't go modifying fuel systems unless you know EXACTLY what you're doing.
Many accidents are attributed to fuel system modifications.

Kyle Boatright said:

Do you have a fuel system diagram? It may be that both tanks plumb to a sump (or header) tank or that they used some other workaround to solve the issues associated with a "both" setting on a low wing.

Click to expand...

Good point, and I honestly don't know. I was told it is fully acrobatic (I don't do acro) so maybe it has some setup. Looks like I will have to read more into the books for this particular aircraft.

Here is a copy of the Scottish Bulldog POH. It talks about the L-R-BOTH-OFF fuel selector on page 4-16 with a fuel system diagram on 4-17.