RCU Forums - Header tank

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- - Header tank (https://www.rcuniverse.com/forum/gas-engines-142/460838-header-tank.html)

Has anyone tryed using a header tank set up on their gas motors. Pros,cons and ideas? Think this is necesary to smooth out the mixture change from full to empty?

Gasser carbs have built in pumps. There is no mixture change.
No header tank required...

Agreed. . not required. . but still not a bad idea.

I run 40-50 ounce tanks on all my big stuff, which would, in theory, give me 25+ minutes of flying time. I set the timer for 15 minutes, though, and follow it religiously. Why? Practicing IMAC sequences has shown me that below 1/2 tank level it is very possible to starve an engine for gas, especially in the middle of low-G meandering maneuvers such as spins where the gas may go to ne side of the tank and the clunk may not follow because there is not enough G force to make it go that far. The result is fuel starvation at low throttle (especially in nose-down attitudes where the gas goes to the front of the tank) which is a bit exciting when you come out of the dive/recovery at 50 feet wayyy out THERE on the backside of the IMAC Aerobatic box. Try it on a windy day and it gets to be even more fun. . .

I have one of the BVM Header tanks that I will be experimenting with in a 38% 260. It holds 4 ounces of gas and I'll be mounting it inside the engine box. This is to not only make sure I have a "bubbleless" fuel supply near the engine, but to add a touch of noseweight (the tank is always FULL). I'll be using a 32 ounce Main tank over the wing spar instead of my normal 50 ounce tank. My figuring is this. . I'm only using about 25-30 ounces of gas out of a 50 ounce tank anyway, so why not make SURE I have a readily available and consistent fuel supply (with the header tank), and get rid of 8-12 ounces of unnecessary weight at the same time? Since the fuel system, except for the vent to the main tank, is totally sealed, the carburetors pump will easly pull fuel from the entire system, and any air bubbles (as long as they are small) will be trapped in a corner of the header tank while the centralized pickup tube is totally immersed in gas at all times.

It's just an idea I am going to try, but if we never try things, we never progress, right? I'd rather give this a shot than constantly worry about fuel starvation at less than 1/2 tank level. Lose a $5000+ IMAC plane just ONCE to a long-distance deadstick and you'll appreciate the lengths some of us go to in order to ensure it never happens again.

Hey Kris , the part about the $5000.00 possible lose is all the motivation I need to try this. I have been doing this for years on DF jets. I was thinking of using a 2 oz dubro, not a waste of money BVM.

Meaningful Ballast

My original use of header tanks goes back several years on glow motors, and the reason was to correct a tail heavy position...

Now, running lighter ZDZ engines, I'm finding the same situation....rather than lead, why not GAS ? Makes perfectly good sense to me, and I'll likely do it on my next project coming up.

I need about 8 oz to balance things....so....I figure a 8 or 10 oz header tank, then a much smaller tank amidships.

Great ideas!!

Is there any special hook -ups for making sure both tanks can be defueled???? Thanks Captinjohn

is easy....the hook up that I use is;
OUT of Header tank is "T"d and goes to the carb, and is how we're fueled.
VENT of Header tank goes to OUT of Main tank...
VENT of MAIN tank is vented to atmosphere.

How much fuel you get out is controlled by the clunks' fit in the tank....but this morning, when I did a test of this, it was very obvious that the header tank drew all the fuel out of the main tank, then it started emptying.

The amount left in both tanks was negligible.

Hi Aerobob , could I use 3 lines in the header tank. So the carb line would stay full or would this make a difference.

should work...you just want to have it drawing out of the header tank...

Header tank on a pumped engine???

How would you benefit here? I might be way off base but it seems to me that if you have no external pressure going to the rear tank, e.g., from the muffler, how do you keep the header tank from emptying before the rear tank? Since tanks require venting you wouldn't benefit from a syphoning or bladder effect a closed system would give you.

The header tank, if empty, is the same as a verrry long fuel line..A Walbro carb will draw fuel at least 4 feet straight up...You could have as many tanks in line as you wanted, set up like AeroBob says....

Hey rcign I have a ? for you. My zdz 40 does lean out on the low neddle as the tank emptys. I adjust the carb at half tank, as instructed.After filling the tank the motor richens a bit, if I lean it back out a bit it runs great untill half tank. Then the throttle won't respond smoothly, almost cuts off. Land the plane , richen the neddle 1/8 to a 1/4 , everthing is fine again. The engine has a bing carb on it now. ZDZ has replaced it with a walbro carb but I have not installed it yet. Engine run well ,has 5 gals of fuel thru it. The fuel tank is 6 in from the carb and has been inspected for any air leaks. Thanks Kent

Might be a characteristic of the Bing carb.The pump side of the carb fills the cavity under the diaphragm when the engine is running...Tank fuel level should have no effect at all....Maybe you have a partial restriction somewhere between the carb and wherever the pulse comes from..Be sure the carb and block are aligned so the pulse hole is clear.....If the diaphragms are at all stiff they won't work right either....

How is the walbro different from the bing==Kent==

K_Hunt: You may also have an airleak in intake area... that gets worse as engine warms up after running. You can check by blocking off carb and exhaust..... then apply 1/2 -1 lb air pressure. Use soapy water to check all gaskets, seals anywhere you think it could leak. Do not over pressure, or you will blow the seal out around propshaft. CaptinJohn

hilleja - it'a about

BALLAST...on an airframe (any flavor) that is designed around one of the "beefier" engine packages, when one puts on a ZDZ of comparable power, the NOSE gets lighter (not bragging, that's JUST THE WAY IT IS)....so...on a new project, if you need a handy 8 oz of airborne ballast that makes sense, and doesn't add more than planned to the all up weight, just divide the fuel between a CG located tank, and the header tank. Have the CG tank sized for your "normal" burn, and the header tank sized for the correct "ballast" value.

For example, my 12 oz Dubro tank with gas in it weighs exactly 11 oz. I don't use 12 oz of fuel in my typical flight, so the MAIN tank of 16 oz becomes the primary supply....and unless something REALLY ugly happens, I never start burning down the header tank volume.

It's just about ballast.