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  #1  
Old 08-15-2021, 08:37 PM
ghatch ghatch is offline
 
Join Date: Nov 2006
Location: San Angelo, TX.
Posts: 78
Default Fuel Tank Vents

Has anyone either put a 90deg bend in the fuel tank vent with the vent hole facing forward or added a 45deg forward facing cut in the fuel tank vent?
The reason being to the negate a lower pressure in the tanks caused by the vents being on the bottom (low pressure area) of the wing and again to stop the Venturi effect on caused by the vent pointing straight down with the end being 90deg to the airflow? I found that I need to do the above to allow the engine driven pump to suck fuel from the tanks in either high altitude, high temp or both situations. Has anyone heard of doing this ?
Thank you in advance for your input.
Gerry

Last edited by ghatch : 08-15-2021 at 08:38 PM. Reason: Forgot to say this is for an RV-10
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  #2  
Old 08-15-2021, 09:16 PM
philb philb is offline
 
Join Date: Apr 2005
Location: Salt Lake City
Posts: 197
Default

Yep, my plans called out a 45 degree bevel facing forward- assuming this is still the case….
P44-7 on my 2004 era plans

Phil
Rv-10
Bountiful, Utah
KBTF

Last edited by philb : 08-15-2021 at 09:19 PM.
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  #3  
Old 08-16-2021, 12:17 AM
Taltruda Taltruda is offline
 
Join Date: Oct 2017
Location: Las Vegas, NV
Posts: 1,137
Default

Quote:
Originally Posted by ghatch View Post
Has anyone either put a 90deg bend in the fuel tank vent with the vent hole facing forward or added a 45deg forward facing cut in the fuel tank vent?
The reason being to the negate a lower pressure in the tanks caused by the vents being on the bottom (low pressure area) of the wing and again to stop the Venturi effect on caused by the vent pointing straight down with the end being 90deg to the airflow? I found that I need to do the above to allow the engine driven pump to suck fuel from the tanks in either high altitude, high temp or both situations. Has anyone heard of doing this ?
Thank you in advance for your input.
Gerry
The bottom of the wing isn’t “low pressure” area, it’s high pressure.
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  #4  
Old 08-16-2021, 01:46 AM
dmn056 dmn056 is offline
 
Join Date: Aug 2014
Location: Sydney, Australia
Posts: 56
Default

Quote:
Originally Posted by Taltruda View Post
The bottom of the wing isn’t “low pressure” area, it’s high pressure.
And, Van's have said previously that ram effect is not needed for proper operation of the fuel vents:

Quote:
Originally Posted by vic syracuse View Post
... I have always been concerned about inadvertent ice accumulation on the RV's. ... The main thing bothering me was the fuel vents, so I decided to try something. I asked at Van's if we really needed the ram air into the tanks, and since the answer was no, I decided to put one of the cable fairlead covers like we use where the rudder cables exit the fuselage ahead of the fuel tank vent. The vent line does not protrude below the depth of the cover. I have made many flights now, at all pwer settings and altitudes, and I have not noticed any difference in fuel flows or pressures.
If you're not getting adequate fuel flow in some conditions, maybe you need to look at any restrictions in your vent lines or fuel lines.
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  #5  
Old 08-16-2021, 07:18 AM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 7,002
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I didn't go the plans route and also don't believe ram pressure is necessary. I made a smooth round disc with a hole for the vent (think static port) and mounted it on the bottom of the wing. No issues getting fuel to the engine.
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  #6  
Old 08-16-2021, 07:28 AM
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Champ Champ is offline
 
Join Date: Apr 2012
Location: Kingsville, Ontario, Canada
Posts: 390
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I left mine cut straight with no ram effect. I’ve considered this a builders/my error but have never had a problem with it so decided to just leave it. If it isn’t broke don’t fix it. I’m hangered but have still added sticking a wire up the ports in my preflight to make sure nothing has nested up there. Made some port plugs for when I’m tied down outside.

Edit - Like Mel suggested I’ll angle file my vents toward the front. Good point.
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Last edited by Champ : 08-16-2021 at 05:40 PM.
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  #7  
Old 08-16-2021, 03:44 PM
mdaniell mdaniell is offline
 
Join Date: Oct 2009
Location: Albury, NSW, Australia
Posts: 22
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Refuelling the tanks to full has two consequences, firstly making a mess and spilling a small amount of fuel and secondly a full stream flushes the vent lines and ensures they are clear.
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  #8  
Old 08-16-2021, 04:08 PM
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Mel Mel is offline
 
Join Date: Mar 2005
Location: Dallas area
Posts: 11,389
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I recommend cutting the vents at an angle towards the front as per the plans. Even though ram air is not necessary, a cut that is square and/or slightly angled to the rear, can have a venturi effect causing a small negative pressure in the tank.
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EAA Flight Advisor/Tech Counselor, Friend of the RV-1
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  #9  
Old 08-16-2021, 05:05 PM
Carl Froehlich's Avatar
Carl Froehlich Carl Froehlich is online now
 
Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 3,593
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Reposting what I do.

I worry about two things for tank vents:
- Mud daubers
- Ice
Either one will block a vent which could lead to tank collapse.

Here is a mod I did for the RV-10. Note:
- The piece out in the breeze is 3/8” tubing, cut on a bevel with a piece of aluminum screen JB welded across the bevel. This is for the mud dauber risk. The 3/8” tubing bevel cut provides more surface area for the JB Weld.
- The black nylon thing is a vacuum breaker suitable for fuel use. It only takes a few inches of vacuum to open the valve. Here if ice forms on the outside piece you suck in are from the wing root area. I never had a problem with fuel leaking past the valve.

The valve is very light and available from McMasters.

Carl
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  #10  
Old 08-16-2021, 05:12 PM
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Jetmart Jetmart is offline
 
Join Date: Sep 2019
Location: Windsor, Ontario
Posts: 521
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Quote:
Originally Posted by Carl Froehlich View Post
Reposting what I do.

I worry about two things for tank vents:
- Mud daubers
- Ice
Either one will block a vent which could lead to tank collapse.

Here is a mod I did for the RV-10. Note:
- The piece out in the breeze is 3/8” tubing, cut on a bevel with a piece of aluminum screen JB welded across the bevel. This is for the mud dauber risk. The 3/8” tubing bevel cut provides more surface area for the JB Weld.
- The black nylon thing is a vacuum breaker suitable for fuel use. It only takes a few inches of vacuum to open the valve. Here if ice forms on the outside piece you suck in are from the wing root area. I never had a problem with fuel leaking past the valve.

The valve is very light and available from McMasters.

Carl
Would you have a part # or a link from McMasters?
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RV-14 A - Kit Ordered February 8, 2022
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