Every time I put wing covers on I worry about the fuel vent getting snagged and broken off. There must be some compelling reason I have four tanks but only one fuel vent, but damned if I can figure out why. Any reason I cant add a second one on the other side? If the one gets bent and /or crimped, it may prevent the flow of fuel.
The main tank is on the right inboard fuel cell, this is where everything goes to..I see no reason to worry about damage to that vent, if you are careful it should be no problem
" If you are careful there will be no problems" Is what is scary. I would add another vent and not mention it to anybody if you know what i mean.
Just my 2 cents...
There is one fuel vent by design for an important reason... the vent on the left side is to help compensate for the longer fuel line runs (restricted fuel flow) with the primary system being located on the right. If you add another vent closer to the right you will create a new "path of least resistance" in the vent system and the fuel will draw much more readily from the right tank especially during high fuel burn like takeoff and possibly not at all from the left? I would highly recommend that you fully understand the fuel system before considering making any modifications to it. The vent is an integral part of the design and just as important as the fuel lines themselves.
On the 800, i have three vent. One for each outboard, located under the wing, one for the two inboards on the top. The system is inboard to the motor, outboard transfer to inboard by fuel pump.
I made my wing cover so they don't touch the vent on the top
Louis
(http://simonac.com/wingcover.jpg)
Quote from: lbpa18 on December 16, 2010, 12:41:57 PM
I have four tanks but only one fuel vent,.
Do you have the military version with the four valves ? If not, and you have two outboard tanks with pumps, i am surprise you have only one vent
Louis
My 295 that is the serial number one for a 295 had those two underwing vent for the outboards ( pumps too) Same as the 800 except for the inside clips. Kind of hard Velcro for the 800
Louis
Quote from: Louis on December 22, 2010, 05:28:30 PM
My 295 that is the serial number one
Louis
Hi Louis
You have picture of your H295 # 1201
Neil
Here we have serial # 1224 which is a 1967/8 H-295 model that clearly shows the single fuel vent. The H-800 had a new design with the improved Brent wing, the fuel system was also updated with additional vents as previously mentioned.
(http://i496.photobucket.com/albums/rr321/litburner/heliodepart.jpg)
The single fuel vent makes me nervous too. We had ours break off in flight during some turbulence, a few days after we bought it and were flying it home. Turns out it was only held in place by some bubble gum. Fortunately the turbulence turned us around before the lack of fuel flow did...
This thread seems confusing because the issue of what venting system is on 800s got mixed up with the questions of what venting is on the 295s when it has aux tanks. This is my belief:
The venting on the 295 with aux tanks is the same as the 800s. There are two vents on the aux tanks, one on each wing on the lower side, just outboard of the aux tank. These lower vents are easy to miss because they just barely protrude below the wing skin. The main tanks are both vented from one rather delicate cane shaped tube above the pilot's head on the outside of the fuselage.
Please show photos if you believe otherwise.
Quote from: Ken Berger on January 29, 2011, 07:55:43 PMThis is my belief:
My Helio 295 serial 1201 ( first one i think) was installed as you describe. (electric transfer pump model, not the military four valves system). My 800 was the same arrangement , and almost the same tanks ( the kind of clip that holds the bladder was different). Two other 800 that i saw were the same.
Louis
Quote from: mrhelio on December 23, 2010, 12:28:19 AM
Here we have serial # 1224 which is a 1967/8 H-295 model that clearly shows the single fuel vent.
On a 60 gallons helio or 120 gallons ?
Louis
Quote from: Louis on January 30, 2011, 02:14:28 PM
Quote from: mrhelio on December 23, 2010, 12:28:19 AM
Here we have serial # 1224 which is a 1967/8 H-295 model that clearly shows the single fuel vent.
On a 60 gallons helio or 120 gallons ?
Louis
Hi Louis 1224 is N61MU
is 120 gallon is my first Helio raide in 1988 in Florida ( at this time N61MA)
Neil
295 manual gives a three fuel vent system as standart for 120 gallons model. All serial numbers. As described by Ken Berger, two underwing vent for outside tanks ( number 16 on this page on auxiliary tank), plus one single overhead goose neck for the two inside tanks are shown on another page .
Louis
(http://simonac.com/H295_120G_sys.jpg)
This is really just a single vent fuel system with two main tanks tied to each other as if they are one. Each auxiliary tank is its own tank/system that simply transfers fuel into the main tank. The auxiliary tank vents only vent their respective auxiliary tank when fuel is being transferred by the transfer pumps to the main tanks. They do not provide any venting when the pumps are off and obstructing the fuel/airflow to the main tanks. The main tanks share the single vent. If the main vent becomes plugged in flight one could try running the transfer pumps to provide alternate fuel/venting. If the aux. tanks have fuel in them this will replace the fuel being drawn by the engine with fuel instead of air but serve the same purpose and prevent a vacuum and fuel starvation. One must be very careful doing this as with the main vent plugged pressure in the tanks could build resulting in an overpressure situation and a risk of a line coming off, the bladder itself rupturing and possible fuel in the cabin or high fuel pressure to the carburetor. The transfer pumps may cavitate and minimize this but I'm not positive on this and have not tried it. If the aux. tanks are empty running the pumps would provide venting through auxiliary tank vents, through the pumps and into the main tanks in this case the pumps will be cavitating and no risk of pressure build up should occur. These pumps are supposed to be self priming and able to be run dry although I would not try this for an extended period of time only long enough to get on the ground. I would also consider running the boost pump to help smooth out the fuel flow if the vent was restricted.
Very good analysis. I would be now a lot more suspecious of using tranfer pumps as a way to provide vent to the main tanks in case of a blocked goose neck. Four PSI is a lot of PSI on a surface as big as the tank. I will now choose to land ASAP with electric pressure pump ON if necessary until then.
Thanks.
Louis
I just found this post Nathan Mackeys site and thought I'd repost it here kind of an old thread; the part that caught my interest was what happens when a fuel vent is turned backwards. If I remember correctly there is nothing to keep this from happening but how tight you make the fitting its just a T in a copper line.
When I was putting 1233 back together my vent got broke off it was a homebuilt replacement. I was able to find a factory built vent and replace it. It seemed like it was a lot better. Later on when sweeping snow off I bent that one, but was able to bend it back without breaking it.
I always intended to make a copy of the factory vent out of stainless steel tubing but never got around to it. Another thing I briefly thought on was a better way to support it where it went through the the skin but didn't come up with anything simple what I wanted was a rubber grommet like you use for spots that wires pass through but couldn't come up with anything.
I was re positioning my U-10 from Hurlburt to Spartanburg for a Swift Strike exercise. Was told to get a low level nav mission on the way. Well, you know, weather was great so there I was skimming the tree tops when the engine quit!! Popped up and saw ONE cotton patch within gliding distance. All fuel tanks turned on, check everything and land. Found that the fuel vent on top of the wing was loose and turned around and instead of pressurizing the tank it siphoned all the fuel out! Even sucked the bladders up so that the gauges read Half tanks as they should have at that point in my flight. There was a big red fuel stain on the fuselage and tail that saved MY tail!
Yes, the reversed fuel vent problem you describe is just one loose AN nut away for all of us. I agree that a simple fix could easily be designed.
The only positive thought I have about this is that after rebuilding this area of my 295, I noticed that it doesn't take very much tightness on that fuel vent to keep it from turning. Naturally, I tightened it down regardless.