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header or not

av8rtom

FRIEND
When I started my 12 project, there were no header tanks in the fuel system. I'm upgrading to either an 0-320 or 360. I've already put in Dakota 24 gal tanks and Dakota fuel selector, but haven't started plumbing yet. Someone a while back said if I didn't have a header to begin with, then don't worry about it. Should I install one (or two) or should I just not worry about it. What's the advantage other than a little extra gas? I added another door (seaplane) and the STC requires belly sumps. I'm trying real hard not to go experimental.
 
Tom, I did not use header tank(s). Two reasons:

First, that is extra gas right over my legs in the event of a wreck.

The other is that I think the header can actually operate in opposition to its intended purpose, at least as I understand. I think the intended purpose is to ensure gas feeding the carb in the event of temporarily unporting a main tank. However, if a tank is unported due to being low on fuel (or out of fuel), after switching tanks when the engine quits, it will take longer for gas from the other tank to reach the carb, because it will have to partly fill the header tank on the way to the carb. In this scenario more rapid recovery will occur without a header.

In the case of a low tank unporting in a steep descent, including a port at the front of at least one tank remedies that automatically.
 
I am curious, is there any evidence of a header-less fuel system using CC's design un-porting? I have never once stumbled my engine in over 300 hours. Been in many different descent angles, fuel levels.

Also more tanks means more weight and complexity.
 
I like headers. When you are landing up a steep grade, there is always positive fuel pressure above the carb. The forward mounted header is always above the carb. Unless you are going straight nose up...
 
The PA12 had two fuel valves. If you use the CC STC you do away with the two fuel valves. Is there another way to get this approved?
 
Actually Mike, you can't unport a header. You can run it out of fuel though. The whole idea of the header is to get you through the odd unusual attitude that may unport or starve the carb feed. Gravity feed fuel system have some inherent shortcomings. Envision where your aft main tank feed is located (in relation to your carb fuel feed fitting) when you are landing on a steep uphill landing area. Also in any steep high power climb. (high fuel demand). The less fuel you have in the tanks the lower the head pressure. That being said, av8rtom, I maintain and fly a PA-12-150 that has the same double doors and no headers. The fuel system is field approved with big Dodge tanks double plumbed fore and aft. One "both" fuel selector. Both aft lines have a belly quickdrain, because of the left door cutout. I haven't had any fuel starvation issues, but, I don't take it to some of the places I hunt with the PA-18 with Dodge tanks and headers.
 
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I have had my 12 since '75 with ho header and I like it that way. I have the two valve shut off system. I have heard, over the years, of pilots taking off with the gas turned off, using the gas in the header tank and then crashing when the header ran out of fuel. If I start to taxi with the valves off, the engine quits in about 100 feet while I am still taxiing. If I really believe that I am extremely low on fuel on a return to an airport I am just very careful in how I bank and descend. I do have a label on the top of the panel which states "no header".
 
I like headers because when low on fuel and flying uncoordinated such as slipping or skidding or making rapid changes in pitch, roll, or yaw you don't un-port the fuel pickup. It provides more safety when getting wild while low on fuel. 99% of the pilots would never need that ability but I like having it. You have to look at what is considered unusable fuel. With a header less systems I believe it's about 5 gal per side and it's even worse with bigger fuel tanks. Part of certification requires testing to determine min fuel required to operate in unusual attitudes. Even though header less tanks will empty dang near every drop a fuel in normal conditions the unusable fuel quantity is significantly higher than the stock header system. I also don't care for the cross feed on a header less system, I like two separate tanks. I don't buy the sales pitch that removing headers from the cockpit makes crashing any safer. Most crashes yank fuel lines apart regardless of headers and no one bitches about all the other airplanes that have nose tanks. Rule number one is don't crash :)


Jason
 
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I know of a cub with DC 24's and a CC header-less system that got a whole lot lower than that, once upon a time that is...
 
I am curious, is there any evidence of a header-less fuel system using CC's design un-porting? I have never once stumbled my engine in over 300 hours. Been in many different descent angles, fuel levels.

Also more tanks means more weight and complexity.
With the CC system, the only way you're ever going to un-port is to run completely out of fuel. Its an excellent system. At least one port is always going to be covered.
 
With the CC system, the only way you're ever going to un-port is to run completely out of fuel. Its an excellent system. At least one port is always going to be covered.


BULLSH!T.

Leave at least the front header in. There are a couple of reasons why, Jason has explained one.

If you really challenge yourself and your cub you will find times when you need to be uncoordinated, slipping, skids, abrupt pitch changes... part of the fun. In a slip you put the upwind wing down, and where does your fuel go??????? Right, to the outboards portion of the tank. Where are the ports?

Now do that on low fuel...

Also when you are real low on fuel the stock 12 will not feed fast enough to keep the engine running. But using a fuller tank and letting the fuel flow to the header tank you can then switch and run till the header is dry, thus using the last gallon or two out of a tank.

Don't think you will need that? That is fine. But like a shoulder harness, if you ever do...
 
Also when you are real low on fuel the stock 12 will not feed fast enough to keep the engine running.
Based on nearly 30 years (ok, only 28 years) with my -12, I'll quote the gentleman from Haines --- "BULLSH!T".
 
BULLSH!T.

In a slip you put the upwind wing down, and where does your fuel go??????? Right, to the outboards portion of the tank. Where are the ports?
...

With a "Both" system and front back ports, almost impossible to un-port. I don't see it un-porting in your scenario. Also if you are running on fumes, why are you doing aggressive play time with the Cub?
 
With a "Both" system and front back ports, almost impossible to un-port. I don't see it un-porting in your scenario. Also if you are running on fumes, why are you doing aggressive play time with the Cub?

+1, given at least a little usable fuel in each tank.
 
With a "Both" system and front back ports, almost impossible to un-port. I don't see it un-porting in your scenario. Also if you are running on fumes, why are you doing aggressive play time with the Cub?

Ditto, provided that there are two fuel outlets in each tank. There needs to be an outlet at both the front and rear inboard corners with all four lines feeding the "both" position of the valve. Personally, I would like to be on the ground before the fuel gets that low. If not, I would be very careful about letting the fuel slosh in the tanks.

The headers are important when there is only one outlet per tank and are useful in both steep nose up and nose down conditions.
 
It unports in a flat spin, high centrifical force....might be the least of your worries at that point though....

A scenario in Alaska to consider. There is a psychosis that manifest itself around Aug. 9th every year. It involves little white sheep that hide way up in high places. Alaskan pilots put minimal amounts of fuel in their cubs so they can operate at elevations where they probably wouldn't be, if they were of sound mind. Flying amongst those windy turbulent peaks with minimum fuel, you can end up in some pretty unusual attitudes in mountain induced turbulence. I'll keep my forward header tank, just in case...
 
Nevermind. Discussing flat spin recovery on the internet is a bad idea.
 
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I have been in a flat spin (not a Cub) and the only thing that I could do to stop it was to increase power. Without the power there was no air flowing over the tail rendering the controls useless.
 
Nevermind. Discussing flat spin recovery on the internet is a bad idea.
Back to header tanks---or not.
 
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Based on nearly 30 years (ok, only 28 years) with my -12, I'll quote the gentleman from Haines --- "BULLSH!T".

Gordon, run one tank dry, switch tanks.

wait five minutes, switch back. You have fuel again and run for a while...

What, never tried it? Then don't say I am wrong.
 
12 has alot less dyhideral then a 18. Might not work as well as a 18 does?

Glenn


they have ~same dihedral ... 3" +/- 1/8"

MODEL PA-12 RIGGING PROCEDURE
.....
#2 Dihedral Angle: Stretch a length of string from wing tip to wing tip along the top of the wing at the front spar location. Measure down from the string to the top of the fuselage front wing hinge fitting a distance of three inches. Adjust the front lift strut fork fittings in or out to produce this dimension.

To check for equal dihedral in each wing, use a 30" level, held spanwise against the underside of the wing at the front spar location. Note the amount of off-level on one wing and see if the other wing has the same amount of off-level. Adjust the front lift strut forks in on one side and out on the other to get the same amount of off-level in both wings. Check the 3" dimensions after this adjustment to see that it has not been affected by the equalizing adjustments."
......

http://www.supercub.org/forum/archive/index.php/t-34286.html


pa-18
Dihedral Angle: To check Dihedral angle at the front spar, proceed as follows: Stretch a string along the top of the wings above the front spar, from wing tip to wing tip,and draw it tight.
Check the dimension vertically from the string to top of fuselage front spar wing hingefitting. For correct dihedral this dimension should be 3 1/8 inches.

I think they left out the +/- on that one??...
http://www.fadodge.com/fad_pdfs/Correct Procedures for Rigging a SuperCub.pdf
 
With the CC system, the only way you're ever going to un-port is to run completely out of fuel. Its an excellent system. At least one port is always going to be covered.

Which is why the CC 18 180 has six gallons of unuseable fuel, according to the TCDS? Apparently SOMEONE found SOMETHING there that suggested fuel starvation in certain attitudes.

As Nanook suggested, it's not just fully unporting a tank that's of concern, it's also how much fuel pressure arrives at the carburetor in certain pitch attitudes. A steep climb coming out of someplace you probably shouldn't have been anyway isn't where you want that O 360 to be hungry for gas.

notice the fuel cap "snorkels" required on some of the 180 conversions? Does that suggest a possible fuel pressure issue?

i like headers. That said, if there were none installed in a plane, I probably wouldn't install them.

MTV
 
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