Header tank vs no header tank ..... why or why not

[Marty57]

After reading all the opinions on the posts about the Dakota Cub drawings for the headerless system; I have to ask the simple question ........ why remove the header tanks? Is it just for weight savings? Does it provide a better fuel system? The best improvement I can see in a fuel system is adding the front ports. We have two different scenarios here; certified vs Exp. With Certified, you have to follow the STC, so it's really not up for debate. On the Exp side, there seems to be a lot of options. If simple and light is an issue, why not just have front and rear ports on the two wing tanks and feed into one front header tank; avoiding the weight and complexity of running a lot of extra fuel lines around two doors. The use of vented fuel caps with a vent line from one site gauge across to the other takes care of venting issues. What is really gained by eliminating the simplicity of a header tank? Is it just weight? Is it really necessary to have Rt, Left, Both, and Off on the fuel selector? A Cessna 150 has an on and off fuel selector, very simple. It seems front and rear port fuel tank, with a front header system on a Cub with a seaplane door, would allow fuel lines to go more directly to a front header tank, eliminating the long path down the back of the door and than back up front to a selector than gascolator. I get the safety issue but let's remember, a J3 has a fuel tank right above your feet.

I'm not saying a headerless system is a good or bad idea; I'm just trying to better understand the generalities of the two systems when considering a simple, lightweight Cub type build.

Marty57

 

[stewartb]

Designing and installing a fuel system may be the most contemplative part of an exp build. It has to work. Not too difficult for airplanes within normal operating attitudes. Headers are a holdover from days gone by. The FAA resists change regardless of the merit.

 

[RVBottomly]

I think you at least want a way to shut off cross-flow between left and right tanks. Otherwise, being parked on even the slightest of lateral slopes may run full tank fuel out the vents.

The system in the Wag drawing scares me and I can see the absolute need for a header tank. It's ported at the rear but the line stays level with the wing until the leading edge. Seems like the worst of two worlds. On climb the fuel has to go uphill before going down (hope there is no bubble to break siphon), and on descent the fuel line would unport at around half tank.

My Commonwealth looks like it ports in the middle--lowest point in level flight, and it has separate fuel valves for each wing tank. It seems like something similar would work on your plane. I'm kicking around ideas but I'm also thinking of retaining the header tank in addition.

The main takeaway I've heard is to avoid going uphill near the tanks (where there is little to no head), and put drains on low spots.

 

[Marty57]

I think you at least want a way to shut off cross-flow between left and right tanks. Otherwise, being parked on even the slightest of lateral slopes may run full tank fuel out the vents.

The system in the Wag drawing scares me and I can see the absolute need for a header tank. It's ported at the rear but the line stays level with the wing until the leading edge. Seems like the worst of two worlds. On climb the fuel has to go uphill before going down (hope there is no bubble to break siphon), and on descent the fuel line would unport at around half tank.

My Commonwealth looks like it ports in the middle--lowest point in level flight, and it has separate fuel valves for each wing tank. It seems like something similar would work on your plane. I'm kicking around ideas but I'm also thinking of retaining the header tank in addition.

The main takeaway I've heard is to avoid going uphill near the tanks (where there is little to no head), and put drains on low spots.

Good points for sure; the stock Wag set up would not work without a header tank. On the Commonwealth, does the tank have front and rear ports; and where do they tie in and head to the header tank? My tanks are ported front and back so unporting in decent would not be an issue. A steep climb could unport the front port at anything less than full tanks, relying on the header tank during the climb. Even with the fuel lines at the rear port going aft and down around the door, the fuel still needs to flow uphill during a climb before it gets to a fuel selector or gascolator. On a headerless system like Dakota Cub, all fuel lines are routed down hill; bottom of Cub door opening is considerably higher than bottom of the door on a PA14, PA12, J4 or J5. Is there enough head pressure to overcome the uphill fuel travel and if so, would the same be correct for a fuel line run just below the bottom of the wing?

This is where my question stems from; does the header system make it a simpler routing of fuel lines vs non header running around and below doors? They both seem to have to travel uphill in a climb configuration but the header system gives you that positive flow during high angle of attack from the header. I must be missing something here as both systems seem to have the same uphill flow issues. I have added the front port in red in the attached picture; my thinking is this would eliminate the unporting issues. Would cross flow on unlevel parking be controlled by simple on/off valve on both tanks before the header tank?
Marty 57

 

[RVBottomly]

Marty, I’ll have to look again on my set up, but I do know left and right tanks have their own on/off valves before the lines merge in a sump behind the cockpit. No cross flow when they are off.

I don’t think going uphill when the lines are lower than the fuel tank is a worry because head (pressure from the fuel tank level) pushes the fuel uphill. What is concerning is when lines go uphill at or above fuel level in the tanks. In that case you are relying on suction from a siphon.


Sent from my iPhone using SuperCub.Org

 

[ak49flyer]

I like the stock -18 system. No crossfeeding ever, run on 4 gallons in left and right tank dry for shuttling out of somewhere short with no worries. On a long trip, run one dry, and know exactly how much you have in the other. Hard to beat the simplicity. I’ve never really understood the advantage of a both position… that being said, in the 180 I use both 90% of the time, but I do really hate the crossfeeding and/or vent leaks when parked on a side hill…

 

[stewartb]

Turn the valve to either L or R. No cross feeding. Pretty simple.

 

[RVBottomly]

View attachment 63959

Another concern jumped out at me with the drawing. Is the red dot indicating another port? If so, consider what happens if your tanks are half-full or less and you are taxiing in a three-point stance. It looks like the front port could be exposed to air--no siphon effect to help draw from the rear port.

Which means you are running only on the header tank. Taxiing, runup, delays for clearance, etc., all eat into what is in the header tank. On take-off you might have less in that header than you hoped for.

 

[DENNY]

Tanks with a rear only port have issues with prolonged nose down approach to runway. If you only have a few gallons left it gos to the front of the tank and rear /middle starts sucking air This can be a cub and early Cessna 180 issue. The right rear header tank in a cub helps with this issue. Cubs with only a few gallons in the tank can have issues with prolonged VX climb because you will loose the head to push fuel to the carb. That is why the cub are takeoff and land on Left tank only front header tank gives you some time. Having said that I just fly stock right tank for all procedures until it gos dry and never had a issue. The reason not to have just a both is fuel management. Gauges and site tubes are just not that good you are going to land with over a hour of fuel left because you don't know what you have. I have seen same thing with guys that like to keep switching tank at three hours they say they need to land because they don't know how much they really have. I like the front and rear outlets on both tanks with a header tank after the fuel valve. Is there enough room on the firewall to put a header tank that sits below the fuel valve? Any reason not to move the fuel valve higher? Can we just get the header tank volume with 1 inch aluminum fuel line laid back and forth on the fire wall? Not quite sure what the right answer is. A stock left tank with header tank and outside crossover vent should solve any problem that comes up. Rig the right however you want, if it coughs go to left. I have coughed a Right tank 10 feet AGL on both landing and takeoff flipped to left and it was not a issue, passenger did not even notice it on landing. DENNY

 

[Marty57]

Another concern jumped out at me with the drawing. Is the red dot indicating another port? If so, consider what happens if your tanks are half-full or less and you are taxiing in a three-point stance. It looks like the front port could be exposed to air--no siphon effect to help draw from the rear port.

Which means you are running only on the header tank. Taxiing, runup, delays for clearance, etc., all eat into what is in the header tank. On take-off you might have less in that header than you hoped for.

Hmmmm; I think you are right about that being an issue where the header might run out of fuel if delay in takeoff is excessive. You are correct; the red is a front port and is connected to same line as rear port. That would have to be verified in testing to see what would be lowest fuel level for takeoff. I can see this could cause there being enough fuel for landing but not safe for takeoff; maybe that's ok? Placard to the effect "Max taxi and run-up 20 minutes below 1/2 tank"? That is a little scary thought.

Let's look at this change. The red front port connects directly to the header; independently from the rear port line. The vent is now a line connecting the top of the site gauges. Should one of the vented fuel caps become clogged; both tanks and header are vented from the one clear cap. In a 1/2 fuel or less capacity taxi, the front port could become unported; would siphon continue flow from rear port to header? This set up would not allow for an independent shut off valve for the right or left tank. I would think that would be the same angle for that rear port fuel line as if it were running uphill along the floorboard then up to a gascolator or fuel selector. Would this be any better vs first concept? Both tanks have same set up, ports on front and rear of the tanks.

Marty57

 

[TurboBeaver]

One of the simplest setups is to simply install hardware in the forward plug that's already in your LEFT tank and come right down back of the windshield then back and T into the rear fuel line before the selector. That will get you
away from needing a header tank in the front of the airplane. If you don't want to get into the expense of pulling right tank, to tig weld in a front port, on the right tank, Simply leave right side alone completely! Then anytime you need all the fuel you got on long trip run on your right tank First; until it quits in level flight........ switch tanks to left side with no header but front and rear ports plumbed up like a Pacer. And the attitude won't effect your ability to get all the fuel on that side. Experimental only of course. Poor man's fuel system that gets rid of front header tank, So if that isn't important to you, then I am guessing you have never been hanging in the seat belts, upside down with av gas dripping on your legs???
Good luck with your decision.
Fly safe
E

 

[Steve Pierce]

Search the subject and you will find a lot of threads here with pros and cons of each system.

 

[skywagon8a]

Of your two sketches, this one is better. I didn't say it would be my choice. I don't like it.

View attachment 63960

There are so many "what ifs" in this thread they need to be addressed separately.

Venting between tanks: If you desire (optional) to vent between the tanks, the vents should be connected to the outboard forward upper sections of the tanks to prevent cross feeding when parked on other than level ground. If vented as shown, the fuel will flow across ship. The only connection between the two tanks in my Cub is the "Both" position of the shutoff valve. There have been no issues in any flight or ground attitude. Each tank is vented independently of the other through a 1/4" snorkel on each filler cap. Your choice of vent may differ. That becomes a separate issue with it's own considerations.

Header tanks: Are they needed? What is their purpose? Their purpose is to ensure some fuel is available to the engine when an unusual attitude exists whereby fuel will not flow downhill by gravity from a wing tank. In that case the header tank must be higher than the carburetor in all attitudes. To answer this question, make a quasi scale sideview drawing of the fuselage with the wing, tanks, fuel lines, shutoffs, gascolator and carburetor. Then move this drawing through any and all unusual attitudes you can imagine the airplane ever being in. Is there ever an attitude when the lowest outlet from a tank is below the carburetor? If yes, install a header tank. If no, skip it. What is this maximum unusual attitude? The Cub wing stalls at between 15 and 18 degrees nose up AoA. Any steeper angle would be produced by extra horsepower, not withstanding zoom climbs. A header tank must be vented (from the top) to it's respective feed tank to prevent a build up of air within the header.

During the routing of the fuel lines, is there any attitude whereby air has the possibility of being drawn into the lines? Air will not be drawn in by gravity. If so, eliminate it.

If you are reduced to making a placard to remind you to manage your fuel a certain way, change the system so the placard is not necessary. The existence of that placard is an indication the fuel system was not designed to be fool proof.

It appears to me the installation of a header tank creates an unnecessary amount of extra components and weight in the fuel system. A cub type plane can be built and operated reliably and safely with a header less system. Those Cubs with higher horsepower should be given the most consideration for the ability to exceed high nose up attitudes. I believe you have said you are using an 0-290 or a 0-235? Even an 0-320 is low horsepower for your plane.


Edit: The OFF position also connects the two tanks as well as the BOTH position.

 

[bob turner]

If it helps, we have an "Ellis" J3 with no header tanks. I got a field approval for a PA-11 style header, and a field approval for the hookup I found. Over its 20-year existence set up without a header, there have been no problems.

Clarence Witte apparently got approval for a headerless single wing tank in a J3.

 

[Gordon Misch]

I agree with Sky, #13. Your sketch in #10 effectively joins the front and rear ports DOWN LOW, WHERE IT MUST BE. The sketch in #4 will pull air in an up-pitch attitude (the siphon will be broken).

 

[JustusSJ]

Our "new to us" PA18-95 has left and right 19gal tanks with 2 header tanks (front and rear). It also has a L-R-Both-Off fuel selector. I was taught to take off and land on the LH tank only.

I still do not fully understand why, though. If I am on "both" at an unusual high nose-up attitude, the Front (L) header thank is still higher than the engine, thus creating a positive pressure over eventual air, coming from the aft (R) header tank, right?
Like you said, air will not be drawn in by gravity - so why not leave it on both all the time?

Thanks for the heads-up!

Regards from Germany,

JSJ

 

[DENNY]

post deleted due to bogus info.

DENNY

 

[Steve Pierce]

I guess I haven't seen that placard on a Super Cub.

 

[DENNY]

Damm you are right it was just a flashback from my Pacer days.
DENNY

 

[OLDCROWE]

in my opinion they are worth the weight. on take-off if you have a fuel selector malfunction, header tanks will allow you to climb higher before fuel starvation thus increasing your options. I've had it happen as well as a close friend, mine came out ok my friends not so much. This is why I kept header tanks in my rebuild and changed the stock front one for an Atlee Dodge Heavy Duty one. But I did use the Dakota Cubs (4 way) Valve and cross over system.

 

[skywagon8a]

in my opinion they are worth the weight. on take-off if you have a fuel selector malfunction, header tanks will allow you to climb higher before fuel starvation thus increasing your options. I've had it happen as well as a close friend, mine came out ok my friends not so much. This is why I kept header tanks in my rebuild and changed the stock front one for an Atlee Dodge Heavy Duty one. But I did use the Dakota Cubs (4 way) Valve and cross over system.

Take a look at Piper drawing #12458 and then explain to us how a header tank will still feed the engine with a fuel selector malfunction. The selector is the last item in the fuel system prior to the fuel passing through the firewall to the engine.
http://www.supercubproject.com/drawings/pdfs/A3250013.pdf

 

[Scott A]

Unrelated to the OP but what is the purpose of the "Plane Duct" - the two short pieces on the main lines aft of the valve? - it is very specific that they are 12 and 8.5 inches from the valve.

Edit: Reference the drawing in the post above.

 

[frequent_flyer]

Unrelated to the OP but what is the purpose of the "Plane Duct" - the two short pieces on the main lines aft of the valve? - it is very specific that they are 12 and 8.5 inches from the valve.

Edit: Reference the drawing in the post above.

I guessed it was a protective sleeve to stop something rubbing on the fuel lines or the fuel lines from rubbing on something else. I later found this ref - https://www.supercub.org/forum/showthread.php?37330-What-is-a-Plane-Duct-in-the-SC-fuel-system

 

[Steve Pierce]

Unrelated to the OP but what is the purpose of the "Plane Duct" - the two short pieces on the main lines aft of the valve? - it is very specific that they are 12 and 8.5 inches from the valve.

Edit: Reference the drawing in the post above.

It is a woven cloth cover that was used to keep the two aluminum lines from rubbing on the carb/cabin heat controls.

 

[Steve Pierce]

 

[frequent_flyer]

Reading through most of this thread seems to show there is general agreement that deleting the header tanks saves weight.

My CubCrafters FX-3 Carbon Cub has a headerless system with a pair of tanks in each wing for a total capacity of 44 US gallons. Sounds good at first glance but 5 gallons of that is declared unusable. If one really believes that 5 gallons is unusable then one is carrying 30 lb of dead weight all the time. I doubt a dual header system would have added 30 lb.

How honest are you going to be when determining unusable fuel? If you follow FAA rules it isn't the fuel left after you drain all fuel from the tanks in level flight attitude.

 

[Scott A]

Unrelated to the OP but what is the purpose of the "Plane Duct" - the two short pieces on the main lines aft of the valve? - it is very specific that they are 12 and 8.5 inches from the valve.

It is a woven cloth cover that was used to keep the two aluminum lines from rubbing on the carb/cabin heat controls.

Thanks Steve! I figured it was chafing protection but couldn't figure out what for, makes sense now.

 

[courierguy]

In the RANS S-7 world, a common location for a 3 or even 4 gallon header tank ( tapered, outlet at the bottom of course, with a sight gauge) is behind the rear baggage station, up high against the upper longeron. It takes up little space, being only 3 or 4" at it's widest, and while still being low enough for the wing tanks to gravity flow into, it's high enough to always flow to the fuel pump and carbs. With it having a sight gauge, I can fly until the motor stops, and there will not be a drop of fuel in the plane, AND I can accurately predict to within 30 seconds exactly when the motor will die. A header tank down low, with no sight gauge, non tapered, no thanks.

 

[stewartb]

My C-180 has the best fuel system I know. L-R-Both. Takeoffs and landings on Both per the POH, because the dual feed works perfectly. I’ve built two Cubs. One with headers and one without. Both had L-R-Both valves. Both worked perfectly. I love having the valve on Both and not thinking about it. It works. It’s easy. I like it.

 

[courierguy]

I liked being able to eliminate 2 extra tank fittings (the front ones) and their associated fittings and lines. More than anything I like being able to know EXACTLY when the motor will die! Meaning, while still being compliant with the min fuel duration (45 min, an hour...one of those) before landing, I can cut it closer with full confidence. the result is like having extra fuel capacity, without having to pack the weight. IF I ever run down the mains enough to be operating purely off the 3 gallon header, I would make sure to first rock the wings to get every dribble out of the mains, doing so as a test once, and running it until it quit, and then opening the fuel drain showed no measurable fuel left on board. Turning my head 180 degrees to eyeball the header sight gauge is almost impossible, until I need to, then I get real limber, quick. Testing this also showed that having my 8 gallon marine bladder ferry aux tank ready to go when all other fuel was totally exhausted, took only a few seconds, like 5 maybe, for the engine to run normal once I hit the transfer pump and opened a valve, I thought it may take a minute or so of rough running, not so. IF I ever make an emergency landing ddue to fuel exhaustion, someone kick my butt, I will deserve it, with all the clear advance notice I have in my "system."