Round & Round vs Up & Down fuel vent line

[Webb]

A couple of ~ 6” loops in the fuel vent line and exiting the wing root thru a fitting verses entering the cabin and making the high arc in the RV-8 gear tower and exiting thru a bushing on the gear cover plate.

Is it a coin toss or is one better than the other?

 

[cfiidon]

I used the loop method and have had no issues in almost 11 years. I did 3 loops if I recall.

Don

 

[Thierry A]

Take a look at this thread, post 43 and 47.

https://vansairforce.net/community/showthread.php?t=1062&highlight=vent+line+loop&page=5

 

[rv8ch]

I used the loop method and have had no issues in almost 11 years. I did 3 loops if I recall.

Don

I did the method recommended in the plans, but I'd do the loop if doing it again - no reason to make it too complex. If it's good enough for the rockets, it's good enough for the RV-8s.

 

[DavidHarris]

I did the loop method on my 7A. My DAR refused to sign off that way and I had to change it to plans. No clear explanation what was wrong with loops, but not worth arguing about.

David

 

[Webb]

I did the loop method on my 7A. My DAR refused to sign off that way and I had to change it to plans. No clear explanation what was wrong with loops, but not worth arguing about.

David

I saw that in another post. Makes no sense since both methods have a low spot that could hold water.

 

[Richard Connell]

Is a loop or series of loops even necessary?
The RV10 and 14 just exit straight downwards in the wing root.
The magnitude of thermal expansion of avgas (pumped in cold then heats up in the sun) is going to fill no matter how many coils you have. Maybe just the straight vent is the simplest?

 

[Webb]

Makes sense. No “valley” to catch water.

 

[PhatRV]

A couple of ~ 6” loops in the fuel vent line and exiting the wing root thru a fitting verses entering the cabin and making the high arc in the RV-8 gear tower and exiting thru a bushing on the gear cover plate.

Is it a coin toss or is one better than the other?

The vent loop through the gear tower is one of the most PIA part of the build. I had to redo mine a few times to get them right. I didn't know much about fuel venting back then so I followed the plan. I would use the wingroot coil method if I build another one.

 

[RV8RIVETER]

Loops fine

I have the rocket coils venting to modified naca style vent in the bottom wing root fairing. 391 hours without issue.

 

[Larry DeCamp]

Coils full of fuel, will they flow backwards ?

A question for the Aero Engineers. Is the pressure differential ( pump suction and/or dynamic air pressure) on a vent sufficient to draw air back past 2 or 3 coils full of gas ?
I used the coils on my RV3 with no problem, however, I did not leave tanks full to expand into the coils.

Frozen condensation in a low spot has real potential. I am surprised the Van design has not experienced that due to the long tube length to hold damp air . Apparently the pump and dynamic pressure can draw air past some amount of water head .

That said, my current project has a tube from the vent fitting, slightly down hill to toward the rear spar with a hole out the bottom into the airstream.