PDA

View Full Version : Fuel valve, lines & header tanks



JayH
01-11-2006, 10:16 PM
Hi Folks,
This greenhorn needs some expert advise. The Smith cub fuel system does not call for header tanks (24 gal per side with forward and aft fuel pick ups) I see that the Airframes Inc 24 gal tanks also say "headerless". My understanding of header tanks for the most part is to maintain fuel supply to the engine in sustained pitch up/down (unusual attitude) somewhat like a header tank in an aerobatic environment. My question is: with just a left/right section fuel valve, could you still starve the engine of fuel in a sustained right or left turn. Example: running off right tank and down about 1/2. In a sustained right turn, would the fuel fall away from the pick ups to the point you would get fuel starvation. Question #2: If this is the case, would a right/left/both fuel vale cure the problem in a headerless system. I'm thinking both fuel caps vented. I guess my Cessna ran this way but don't see a lot of Cubs set up with a "both" selection. Also, I think Cessna ran a crossfeed setup......? Insight on this would greatly expand my education in this homebuild adventure. Thanks, Jay (building a Smith Cub)

X18
01-11-2006, 11:25 PM
In a coordinated turn, the fuel pick ups will stay below the fuel level. There is a Smith Cub on the field with a left right both that has flown for over a year without a problem. I am in the beginning stages of building an experimental 18-95 with an O-200 and right and left wing tanks. The fuel tanks will be plumbed together and my fuel selector will have a both and off position. Simple is better.

Jim

JayH
01-12-2006, 06:55 AM
X18,
That makes sense on the coordinated turn. I,m just thinking extra safety and absolute positive fuel supply. I assume that the vented fuel caps are sufficient for positive pressure. Also, when you say " plumbed together", is that just at the "both" selection point, or would you have a cross feed tube of some sort. I 'm not quite sure why or how Cessna set up that way, but I suppose they were curing some kind of issue.

Thanks alot for the response.
Jay

Dan2+2
01-12-2006, 05:08 PM
I plan on the same type system in my exp. also. From what I have gathered here and cubclub etc, I will have a line connecting the two tanks in order for them to feed evenly, with vented caps on each tank. I will probably copy the 47 PA-12 system with a shut off valve for each tank. Located by my left knee. So will have single tank use, or both, with each valve open. Sight gauges in the wing root and maybe ram air vents on the caps. My tanks do have a vent fitting in the upper front outside corner, so I may run a small vent line to under the wing for ram air. I think that would let less water in if I fly though rain.
Ram air should help insure fuel flow. The interconnect line will go from upper front inside corner to the other tank. Across the top of the cabin. This is my first exp. so this is not gospel. Again I think the interconnect line is to insure even fuel flow when on both tanks.

JayH
01-13-2006, 08:58 AM
2+2,
Talking about that tank vent coming down through the bottom of the wing... my Cessna was that way and 90 degrees ram air forward. An inherent issue with that was when the plane vented with expansion in the warm weather, I had 100LL (a lot) all over the hanger floor. Not a big deal, that's what a vent is for. Anyway, I suppose that cross feed tube above the cabin was to get that ram air pressure to the other tank beings they only vented the one side. Would having the ram air vented caps on both tanks on the cub accomplish the same thing and eliminate the need for that cross tube over the cabin? Also, maybe someone running the ram air caps could jump in here and let me know the pros & cons of those caps i.e. venting out fuel, or water intake.... Thanks.

Having a lot of fun learning,
Jay

X18
01-13-2006, 10:00 AM
The fuel system will T the rear outlets together, T the front outlets together, and the front and rear lines will T together prior to the fuel valve. I will have a BOTH and OFF position on the fuel valve. The tanks will not be connected together directly with either a fuel line or a vent line. The fuel caps will be vented with ram air vents. Cessna has a vent line from tank to tank because they only have ram air vent under one wing. With both tanks vented, the fuel should feed as evenly as a Cessna 150 type system.

Jim

Crash
01-13-2006, 10:58 AM
If you want to do it right, you should get a copy of Cub Crafters installation drawings, experimental or not. Some of the fuel line and fuel selector installations I've seen a few of you experimental guys install are going to kill some one. John Denver would agree with me if he were still alive. Crash

Bill Ingerson
01-13-2006, 12:14 PM
I agree with Crash. Cub crafters has a very nice fuel selector valve that reads Left/Right/Both. Im still learning also but have done alot of research on this. When installing the fuel lines make sure they alway flow down hill as much as possible in the direction of the fuel selector valve. Im not going to use header tanks, just don't like the thought of all that gas in front and in back of me inside the cockpit. Do like Crash said and get a copy of the fuel layout from CubCrafters. I know your right fuel tank has to have two threaded outlets on the inboard corners.
I still have questions also. I remember reading about a patrol officer landing a float plane (superCub) on a lake awhile back and parked on the beach at a angle. Left the plane for a couple of hours then jumped back in and did a turn at low altitude and the engine quit. It was reported the fuel might have drained from one of the wing tanks over time and when he took off the engine ran out of fuel. So Im left wondering if this is a possiblility ? Also it seems to me that it would be better to just leave the fuel selector valve on both. There will be alot of discussion from guys that know alot more than me on this, we need to do our home work.



Bill

Dan2+2
01-13-2006, 12:52 PM
According to Clyde Smith in Cub Club mag, some PA-12's did not have headertanks and only a rear fuel pickup in the wing tank. They would fuel starve in a long descent and quit. You had to lower the nose to get fuel flow. A front fuel line fixes that. With just a on/off valve some PA12 wing tanks would feed uneven with ram air caps. The two solutions, without adding a header tank, in cub club mags. were a interconnect line to equalize the pressure or a smaller ram air opening in the faster feeding tank. The cub crafters drawings sound like a good reference source, thanks Crash. This site is great cause someone will point out the weakness in design. Too bad John Denver did not have a site like this.

Bugs66
01-13-2006, 01:08 PM
Anyone care to share the CC drawings with us poor experimental types?

JayH
01-13-2006, 01:24 PM
I would definitely be interested in the CC drawings if they are available somewhere or if they are postable. Or even a PM would be greatly appreciated with that info.

Thanks,
J

kase
01-13-2006, 02:30 PM
From a old 337.

http://sparky.supercub.org/photopost/data/500/headerless_fuel_system.pdf

Bugs66
01-13-2006, 03:13 PM
From a old 337.

http://sparky.supercub.org/photopost/data/500/headerless_fuel_system.pdf

Awesome, thanks! I am going to use vented fuel caps instead of vent line.

kase
01-13-2006, 03:22 PM
I wouldnt but since your experimental go for it.

Bill Rusk
01-13-2006, 07:01 PM
Kas

For those of us that are "fuel system intelligence challenged" ......why?
What is the logic for connecting the two tanks with a vent line? Thanks.

Bill

Steve Pierce
01-13-2006, 09:09 PM
My understanding is the pressure in each tank is equalized and both tanks feed at the same rate when they are vented together. Vent by putting a tee in the top of the fuel site gauge fittings.

Ruidoso Ron
01-13-2006, 09:36 PM
You should be aware that, even with header tanks, you can eventually starve the fuel by flying in an uncoordinated fashion for a prolonged period. No, I'm not that bad a pilot, but I managed to flame out while on a photo shoot. My photographer was in the front seat, and I was flying from the back seat. We had a Sikorsky S-76 pull up to our right-rear quadrant, and tuck it in real tight. I put the airplane into a skid, so the front seater could shoot out the back without getting wing struts in the picture. After a couple of minutes, the engine quit, and we had an eyefull of rotorblades up real close. Scared the willies out of all of us. Then we prceeded to do it again in about 5 minutes! Talk about learning your lesson (eventually). :stupid

JayH
01-13-2006, 09:48 PM
Kase, great - THANKS - I printed a copy. This is how the Smith diagram is drawn with the exception of the vent line and the "off,right,left,both" fuel valve.

Bugs, I was planning the same with forward ram air caps. I think a ram air on both tanks would accomplish the same thing as the vent tube keeping in mind 2+2's post reference a little different feed rate - as long as they are positively feeding. I think the variance in feed rate may come from more restriction on one side than the other - longer lines, more corners, more fittings....

Steve, does the need to equalize the pressure stem from just one side being vented (earlier discussion ref Cessna)? And wouldn't both caps vented with the forward ram air accomplish the same thing? I could vent the two together using the top sight gauge fittings, but if not needed, would prefer to stay away from more potential leaky joints.

Thanks to all!!!!!!! This is why I'm on this sight.
Jay

P.S. Bill R. - if you saw my phone # on your caller ID a couple of times, this is what I was going to discuss with you. How ya been?

Steve Pierce
01-13-2006, 10:13 PM
The FAA requires two tanks be vented together on a both system with two ways to vent the tanks. You don't have to worry about it on an experimental but I have seen certified airplanes suck tanks flat and think it is a simple enough precaution to make in my book. Another thought is the pressure vents might pressureize differently also. Not sure but with the prop wash I guess it could.

Frank T
01-13-2006, 10:46 PM
Do the 180 HP's use the 3/8 fuel line of go to 1/2 inch?

Frank

JayH
01-13-2006, 11:35 PM
Thats good enough for me Steve - I'll "T" the top sight guage fittings and vent em. Thanks.
Thanks again Kase for the drawing.

J

AkPA/18
01-14-2006, 01:15 AM
If I were going to do it I would run the vent line forward of the front spar carry through and install and inline quarter turn valve. Just my preference.

Mark

Bugs66
01-14-2006, 01:45 AM
On the CC drawings, where is the vent going after they are Tee-ed, up through the skylight to the atmosphere or are they just put together and you still rely on vented caps?

The Bearhawk guys seem to be doing regular ram air vented caps and I am not aware they are teeing any vents. I think most of the Smith Cubs are doing the same, no? Don't hear about any problems. I do hear that you want the ram air vented caps for the hungrier 180hp.

KelvinG
01-14-2006, 01:54 AM
If I were going to do it I would run the vent line forward of the front spar carry through and install and inline quarter turn valve. Just my preference.

Mark

Ok, I'm lost. Mark, why would you put a valve in the vent line?

Thanks,
KelvinG

AkPA/18
01-14-2006, 04:30 AM
Hey Kelvin

Just for the times that you need to park on uneven ground. If the tanks are full---the fuel tranfers to the low tank though the line to the lower tank(spills out the caps---bad deal). If you have a valve there, you can isolate the tanks. How is the project going??


Mark

Fortysix12
01-14-2006, 07:52 AM
I plan on the same type system in my exp. also. From what I have gathered here and cubclub etc, I will have a line connecting the two tanks in order for them to feed evenly, with vented caps on each tank. I will probably copy the 47 PA-12 system with a shut off valve for each tank. Located by my left knee. So will have single tank use, or both, with each valve open. Sight gauges in the wing root and maybe ram air vents on the caps. My tanks do have a vent fitting in the upper front outside corner, so I may run a small vent line to under the wing for ram air. I think that would let less water in if I fly though rain.
Ram air should help insure fuel flow. The interconnect line will go from upper front inside corner to the other tank. Across the top of the cabin. This is my first exp. so this is not gospel. Again I think the interconnect line is to insure even fuel flow when on both tanks.

The 12 layout is somewhat aniquated. Proper fueling requires the closing of the right tank which in the 12 is considered the aux. This is done so that while you fuel the other side the aux tank does not syphon or equalize into the left tank. The single vavle with the both left right option would be a better set up. However, never fuel an airplane with this valve in the both position or the same problem will occur. You will end up with less fuel than aniticipated,especially if you are interupted during the fueling process. There is nothing wrong with the 12 system just that you will be required to follow the original aircraft's fueling procedure that requires closing the right fuel valve before refueling. Aslo the left is fuel line is plumbed straight into the imperial two way valve then into the header tank than into the gasolator. The right valve and fuel line is T'd into the left fuel line prior to the main (left fuel valve), so closing the right tank valve would not terminate fuel to the engine unlike the closing of the left valve would. Hope this helps. There's a nice valve from the UK I always see at the show, that's the one I would use. Don't know the name of it,sorry. The header tank is there because there are fight attitudes under lower fuel conditions which could interupt fuel to the engine. The header tank is a buffer. I would opt for a both feature fuel selector.

jon
01-14-2006, 09:22 AM
3/8 " but must use ram air type tank caps. I used C.C. type of routing
of the lines. Be cautious of line pitch If you have extend gear and
thinking larger tires. Position your fuselage with the 3' gear and
say just 8.50 tires. It is almost impossible to get forward pitch.
I installed 2 tees in rear lines with drains to help with this problem.
Photos in gallery name (Jon)
Jon

cubunltd
01-14-2006, 11:37 AM
In the CC system the fuel equalizes through the fuel valve with in the "BOTH" position. If you are parked on a slope, simply choose "right" or "left" position to stop the transfer of fuel from one tank to the other.
The cross-vent line between the tanks if mounted properly does not transfer fuel unless you are filled all the way to the top and then it will only transfer until the fuel gets below the vent installation point in the tank, which should be installed as high as possible.
I run 3" gear and 26" tires and there is no problem keeping the fuel lines on a down hill run to the fuel selector valve. From the valve it's down hill to the gascolater.
The ram air caps are a must with 3/8" lines if you're running a 180hp. Not necessary on a 150 or 160hp.
I can probably find some pics, if anyone is interested, email me.

cubsunlimited@verizon.net

John

Dan2+2
01-14-2006, 01:48 PM
A lt/rt/both fuel valve is best, if you can remember the name of the valve from the UK? I believe the front fuel line eliminates the need for a header tank. Using two on/off valves, I was planning to connect the lines after the valves. Bugs, the interconnect line is not vented to the atmosphere, It just connects the two tanks to equalize and also if the vented cap clogs up that tank will still be vented through the other tanks cap. That gives you an extra vent like Steve Pierce mentioned.

Bugs66
01-14-2006, 02:17 PM
The UK valve is Andair.
See: http://www.andair.co.uk/system/index.html

You can get at Spruce, Chief, etc. These valves look great, albeit pricey. You can also order direct from Andair and get black anodizing, which looks the best. Sometimes you need to splurge.

JMBreitinger
01-14-2006, 05:49 PM
We got a field approval for a headerless system with separate left and right on / off valves. This gives us the option of left right or both. it is so simple that even I could not screw it up.

Nearly two years ago, I had an engine failure due to fuel starvation on departure. I was +/-100 feet off and 3/4 of the way down the runway in a dense urban area. It turned out to be a bad needle valve in the carburetor that precipitated the problem. When I started trouble shooting (under extreme duress) I found the multi-position switch to be confusing.

A better pilot would have likely had less trouble with this but these problems are apt to plague us at the worst possible time.

I opted to continue straight ahead and now have the opportunity to replace the entire fuel system.

KelvinG
01-14-2006, 11:46 PM
Just for the times that you need to park on uneven ground. If the tanks are full---the fuel tranfers to the low tank though the line to the lower tank(spills out the caps---bad deal). If you have a valve there, you can isolate the tanks. How is the project going??

Mark

I knew that, I had mentioned the problem of uneven ground and isolating the tanks to someone else in another thread.
I was hung up on it having something to do with venting. :drinking:

What about this for vent lines without a valve? If you loop the line to the outer end of each tank it shouldn't siphon.

http://sparky.supercub.org/photopost/data/611/Fuel_Tank_Vent.JPG


The project slowed up a bit. My wife gave birth to a 9lb. 6oz baby girl on 1/7/06. The little girl gave us quite a scare, but both wife and baby are doing fine now. Yesterday was the first day Iíve worked on it in about a month.

KelvinG

gdafoe
01-15-2006, 10:03 AM
John, I for one would sure like to see detailed pictures of the system. I'm doing a Smith Cub and have been fixing to work on the 'in the wings' part of the system.

The Andair valve is really nice. My friend put it in the RR3 that is out in the hangar. You have to push the button in to get it into the OFF position which is a nice safety feature.

JMBreitinger
01-15-2006, 10:23 AM
Next week, I'll run down and take some photos. I'll get my builder to help sketch it out too. I think that it was inspired by a PA-12 system.

Bugs66
01-15-2006, 02:30 PM
Kelvin,
For the CC drawing I don't believe the interconnect vent line between the tanks has a vent on it going up through the roof. It merely serves to connect the tanks at their highest point for equalization. You then still need the ram air vent caps for the actual vent. That is how I interpret it, but someone can correct me if I am wrong.

kase
01-15-2006, 05:28 PM
Kas

For those of us that are "fuel system intelligence challenged" ......why?
What is the logic for connecting the two tanks with a vent line? Thanks.

Bill

Looks like that has already been answered. If it was my plane I would want a fuel system that has already been proven in the field with data to back it up. Such as the original system or the headerless CC system and not try to envent my own.

http://sparky.supercub.org/photopost/data/513/PA18_fuel_system.pdf

Im not so sure the headerless system elimantes a fire hazard compared to having HD header tanks. If you tweek the frame or pull the wings back your going to separate the fuel lines and have fuel run out anyhow.

labdad32
01-16-2006, 12:43 AM
I started out with a different valve until I had all my plumbing finished and was leak testing the system. I was not happy with the lack of feel in the detents, so, I called CC and ordered-up the valve they use (Allen). It fit right in without any change to my plumbing and it feels great. Perhaps the best $220. I have spent to-date. I used the CC drawings and am using the Dakota Cub tanks. I had Dakota Cub weld in another fitting high in the left tank for my belly tank to feed into.

Steve Pierce
01-16-2006, 08:47 AM
Wicks also sells the Allen valve as does Univair. That is what I have used in the Clipers that I have rebuilt the fuel system in.

Bill Ingerson
01-16-2006, 10:33 PM
If I remember right there is a check valve for each tank, this would keep the fuel from draining from one tank to the other. Find out for your self I could be wrong. The pressure cap facing forward helps with the tank pressure. Seems like water would get in, every time I ask about that, no one answers ?

A friend was putting one of the CubCrafter valves in and while doing that the fuel line snapped off the header tank in the dash, gas everywhere.
Just makes me worry about vibration, check your header tanks.

In the interest of safety, Im removing my two header tanks, so I can sit over the top of a belly tank full of gas ??? :crazyeyes:

Crash
01-16-2006, 10:58 PM
The pressure cap facing forward helps with the tank pressure. Seems like water would get in, every time I ask about that, no one answers ?
:

There is a small hole drilled in the back side of the pressure tube about 1 inch before it goes into the cap. Any water entering the cap is suppposed to be blown out this drain hole. I've run through some extream rain storms and never had any water in the tanks or gasolator afterward. Crash

Steve Pierce
01-16-2006, 11:16 PM
I flown through rain also and haven't gotten any water in the fuel with the pressure caps.

Bill Ingerson
01-16-2006, 11:37 PM
Thanks guys on the Drip proof caps, thats good to know, I will be buying some soon for the 180 which uses the bigger tube.

cubunltd
01-17-2006, 12:02 PM
If you have a good original valve, it can be modified very easily.


John

kase
03-31-2006, 11:35 AM
On the CC drawings, where is the vent going after they are Tee-ed, up through the skylight to the atmosphere or are they just put together and you still rely on vented caps?

.

Bugs, looked at a CC fuel system yesterday and took a picture of the vent line routing.

http://supercub.org/albums/Mods-and-Alterations/vent_line.thumb.jpg (http://supercub.org/albums/Mods-and-Alterations/vent_line.sized.jpg)

selector with placards

http://supercub.org/albums/Mods-and-Alterations/valve.thumb.jpg (http://supercub.org/albums/Mods-and-Alterations/valve.sized.jpg)

plumbing from another project for no header tanks

http://supercub.org/albums/Mods-and-Alterations/plumb_1.thumb.jpg (http://supercub.org/albums/Mods-and-Alterations/plumb_1.jpg)

Bugs66
03-31-2006, 02:37 PM
Excellent photos Kase, much appreciated. It looks like they just interconnect. Easy to accomplish.

Side topic: What's the secret to make your own labels that have that factory look? DIY silkscreen? I'll have to do some Googling.

behindpropellers
03-31-2006, 02:43 PM
Excellent photos Kase, much appreciated. It looks like they just interconnect. Easy to accomplish.

Side topic: What's the secret to make your own labels that have that factory look? DIY silkscreen? I'll have to do some Googling.

My dad has been making some with his laser printer and clear film with adhesive. Looks pretty good.
Tim

TDTerry
02-28-2007, 11:35 AM
2+2
According to Clyde Smith in Cub Club mag, some PA-12's did not have headertanks and only a rear fuel pickup in the wing tank. They would fuel starve in a long descent and quit. You had to lower the nose to get fuel flow.

You are totally correct! It happened to me going into Leon, Mexico. A long decent with light fuel. I landed after noticing the prop needed painting. Tower got excited with my landing in 90 degree cross winds of 30knots. Then they quit being excited and were angry when I figured out what happened, re-started the PA-12 and taxied to the parking ramp. Man! They have more different kinds of uniforms!! :roll:

MaxMotoring
03-28-2007, 03:29 PM
Well, I don' t want this happen to me!

I looked for the front port drawings in previous posts but files are missing. Does anybody know where to look for them?

Cheers.