VansAirForceForums  
Home > VansAirForceForums

- POSTING RULES
- Donate yearly (please).
- Advertise in here!

- Today's Posts | Insert Pics

  #21  
Old 02-13-2018, 08:04 AM
rv7charlie rv7charlie is offline
 
Join Date: May 2006
Location: Pocahontas MS
Posts: 2,760
Default

While I agree that the risk is minimal, I wouldn't think the risk is in-flight icing, but of getting enough moisture in the coils to later freeze on the ground. If that *did* happen (again, very low probability), you probably wouldn't know until long after departure on the next flight.
Reply With Quote
  #22  
Old 02-13-2018, 08:32 AM
PilotjohnS PilotjohnS is offline
 
Join Date: Jan 2016
Location: Los Angeles
Posts: 447
Default moisture

I am not sure how you would get moisture in there. water cant drip up from the vent hole, so it has to be from condensation. Not sure there could be enough condensation to form enough ice in the loop. Any "pumping" action from heating and cooling the fuel could force moist air in there, but would also bring the fuel vapors out, pushing the condensable moisture out on the next temp cycle.

My fear would be icing from flight in freezing moisture leading to fuel starvation.

I would be inclined to put the angle cut on the backside not the front; besides I cant see there being any noticeable "ram" air pressure from having the angle cut on the front anyway. The positive pressure should come from the wing doing its job, not the angle cut.
__________________
Thank you
John S

WARNING! Information presented in this post is my opinion. All users of info have sole responsibility for determining accuracy or suitability for their use.

Extra dues paid 2018, worth every penny

RV9A- Status: tail feathers done less tips
Wings done less tips and avionics
Fuselage started
www.pilotjohnsrv9.blogspot.com
Reply With Quote
  #23  
Old 02-13-2018, 08:56 AM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 2,655
Default

Quote:
Originally Posted by rv7charlie View Post
Have any of you guys who are talking about vent check valves and/or shutoff valves done the math on the air pressure change from, say, a 30 degree night temperature to a 80+ degree daytime temp, in a partially full tank?

I haven't, but I'd want to know before trapping that air in the tank.

Charlie
The check valve doesn't trap air in the tank. You tee off the main vent for the check valve, so that tank always has direct access to the main vent line. The check valve allows air into the vent line, under vacuum, if the main vent line is blocked. The primary purpose of the check valve is to prevent vapor from entering the cabin when you have a secondary vent ingress location.

Larry
__________________
N64LR
RV-6A / IO-320, Flying as of 8/2015
RV-10 in progress
Reply With Quote
  #24  
Old 02-13-2018, 09:00 AM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 2,655
Default

Quote:
Originally Posted by airguy View Post
Same here, just over 200 hours with several flights in rain and I regularly cruise in freezing temps. So far I'm stubbornly refusing to die. In this world there are plenty of "solutions in search of a problem", perhaps it's more effective to concentrate our time and effort on actual problems with a higher likelihood of occurrence. If you're flying in icing conditions in an RV, you've got higher priority problems than worrying about a fuel vent getting blocked. Your iced-up tailplane is going to kill you before the blocked vent does.
All of the icing literature that I have read indicate that the first things to ice on a plane are small protrusions into the air stream. This is why they recommend looking at a temp probe or similar object for signs of ice. Small protrusions will ice over well before the tailplane does. Further, it takes very little ice to block the opening on the vent port. Cutting an angle and facing it into the oncoming air makes it even easier for ice to plug the the 1/4" opening.

Larry
__________________
N64LR
RV-6A / IO-320, Flying as of 8/2015
RV-10 in progress

Last edited by lr172 : 02-13-2018 at 09:03 AM.
Reply With Quote
  #25  
Old 02-13-2018, 10:59 AM
cajunwings cajunwings is offline
 
Join Date: Jun 2007
Location: new iberia la
Posts: 540
Default Vents

FWIW: Many Mooney’s and Cherokee’s have the same 1/4” aluminum vent tube that we do on our RVs. It sticks down and out of the bottom wing skin about 3/8” and is angle cut on the front side just like ours. Only real difference is these vents usually tap into the outboard rib of the wing tank. I don’t have any numbers but i’m certain the certified fleet with similar vent arrangement to RVs have amassed many many 1000s of hrs without icing trouble. Gives me some confidence that the stock vents or the rocket style loops will work just fine.


Don Broussard
RV9 Rebuild in Progress
57 Pacer
Reply With Quote
  #26  
Old 02-13-2018, 04:13 PM
DanH's Avatar
DanH DanH is offline
 
Join Date: Oct 2005
Location: 08A
Posts: 7,545
Default

Quote:
Originally Posted by pa38112 View Post
I like This !!! I am thinking the tank would need to have slightly more volume than the length of vent line leading to it. I am tired of linemen telling me I have a leak. I once came back to find two buckets under my vents...
Have you identified a supplier for the header tank ?
Yeah, my junk bin.

Seriously, it is the sort of thing I would just make...two lengths of 6061 tube and weld on some end caps. If you want to buy nice little tanks I'd look at standard Vans brake reservoirs.
__________________
Dan Horton
RV-8 SS
Barrett IO-390
Reply With Quote
  #27  
Old 02-13-2018, 04:26 PM
rv7charlie rv7charlie is offline
 
Join Date: May 2006
Location: Pocahontas MS
Posts: 2,760
Default

That was my 1st thought; IIRC, about 2 oz each.
Reply With Quote
  #28  
Old 02-13-2018, 07:42 PM
VA Maule VA Maule is online now
 
Join Date: Apr 2016
Location: Bucking ham, Virginia
Posts: 103
Default Venting

RV7A Flyer & DanH thanks for the comments. I think I'll give it a try with out the coils after all this is EXPERIMENTAL AVATION it will definitely vent and hopefully not burp too much, if it does easy enough to revise to the proven coils. It's still going to be a little while before first flight so further insights and comments are welcome & appreciated.

Dan you've just got all kinds of neat ideas please keep sharing.
__________________
The Best Government is less Government
Maule MXT-7(daily flyer)
Lancer 235(partner)
Raidial RV-8R Ephanage Done, Wings Done, Fuselage underway
Reply With Quote
  #29  
Old 02-14-2018, 10:35 AM
9GT's Avatar
9GT 9GT is offline
 
Join Date: Jan 2010
Location: Southern Michigan
Posts: 1,411
Default

Here is an example of why the tank vent lines drip fuel when "full". This is the per-plans method of venting the RV-9 tanks and probably the same for other models. You can see the vent lines have a straight termination after they attach to the filler flange. I was surprised when I checked my quick build tanks that I could almost fit the tip of my finger between the top of the vent tube and the tank skin. So there is about a 1/2" gap total that the fuel can siphon out through the vent line until the fuel gets below the lowest point of the vent line termination opening. Even if you fill the tanks to just below that point, as the fuel warms and expands a bit, it will rise and start dripping. When I built the RV-10 tanks, I turned up the vent line after the filler flange attach point leaving only 3/32" gap flush to the tank top skin. Never had a problem after filling unless I overfilled. When I open up my RV-9A quick build tanks to go over all the sealant areas and increase the capacity, I will re-work the vent lines also.
[IMG]DSC02010 by David C, on Flickr[/IMG]
[IMG]DSC02011 by David C, on Flickr[/IMG]
[IMG]DSC02012 by David C, on Flickr[/IMG]
__________________
David C.
Howell, MI

RV-9A: Under Construction. N161RV (Reserved)
RV-10: N959RV Completed 12/29/2013 SOLD 08/23/2016

"Donor Exempt" but donated through Dec. 2018
Reply With Quote
  #30  
Old 02-14-2018, 11:00 AM
PilotjohnS PilotjohnS is offline
 
Join Date: Jan 2016
Location: Los Angeles
Posts: 447
Default my take

When I built my 9A tanks, I left the vent tube a little longer so that it goes into the end as much as possible, I also turned the end away from the proseal so the tube wont get clogged when installing the back baffle. During filling the fuel will spill out the filler before the vent is covered by the fuel level, and during climb, the vent is at the highest point in the tank so that the air expanding in the tank I am not using wont push the fuel out. If the vent is towards the rear baffle, I figured it will be under the fuel level during climb out, pushing out raw gas.
__________________
Thank you
John S

WARNING! Information presented in this post is my opinion. All users of info have sole responsibility for determining accuracy or suitability for their use.

Extra dues paid 2018, worth every penny

RV9A- Status: tail feathers done less tips
Wings done less tips and avionics
Fuselage started
www.pilotjohnsrv9.blogspot.com
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 05:44 PM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.