747drvr

My Feedback: (5)

Hi Guys,

I'm new to the gasser game and was wondering about the use of header tanks with gas engines. I've had a few engine failures with my ZDZ 40 since I received it used and am trying to cover all bases.
Header tanks are very commonly used in turbines and helicopters to ensure bubble free fuel flow. How tolerant are gas engines to the occasional bubble of air if the clunk becomes exposed during manoeuvering ? I'm thinking it's not a problem since no one talks about it but I just wanted some educated opinions .

Thanks.

Big_Bird

My Feedback: (1)

Marc, IMHO a header tank is totally unnecessary on a gasser. The carbs are very tolerant of the occasional bubble. Unless you are very close to empty on fuel, you should be able to do any aerobatics that your plane can stand without a sputter or miss from the engine.

Ken

SAL98

My Feedback: (6)

I second that. Also a header tank is not only used to discourage bubbles, its mainly used to even out pressure going to the carb in different attitudes. Since the header is always full throughout the run of the main tank, the needle settings are not as likely to change as much. ( This is what the pattern guys did before pumper engines like the Y.S )

Also you must use throttle management when flying these bigger engines on bigger planes. No more full throttle loops. You then will be cutting the throttle back on your down-lines and not asking the tank for fuel when the clunk will be exposed to air

strato911

As I understand it (and I'm new to gassers too), gas engines are quite tolerant of the occaisional bubble in the fuel supply because their carbs have a pump integrated into them.

While bench running my WeedEater® conversion, as the tank ran dry, there was a steady flow of bubbles in the supply line, but not a hiccup from the engine till the bubbles exceeded the gas by about 2:1. The pump seems to overcome the bubbles quite well.

Big_Bird

My Feedback: (1)

Dennis, you are right on the money about the bubbles and the pump in the carb. Actually the clunk is probably not completely immersed in gasoline when the tank is getting low. There is a wild gyration of gasoline spray within the tank under these conditions. As long as the ratio of gasoline to air stays up in the fuel line, you probably won't notice any difference. Quite often a gasser will not give any warning before it runs out of fuel. I saw this happen with a 3D plane in a hover. Not a pretty sight. Always time your flight and land before you run out.

Ken

PAPE

wouldnt this fix the problems of the engine runing lean in high g manuvers?

Tired Old Man

My Feedback: (1)

It's reare that a header tank is used on a gasser. It's done on some specific platforms not used for normal R/C purposes but those engines run for many hours at a time. Using a filtered clunk eliminates many of the bubbles that are normally seen and also reduces the concerns of a clunk being partially out of the fuel supply. Their design is such that any contact of the clunk with the fuel supply assures a good pick up and delivery. They also generally use all the fuel in the tank if they have any means of making contact with the fuel. Check with Walbro for the correct part number.

I posted pictures and part numbers several times of a filtered clunk that works very well but I'm not in a position to find one of the filters to do it again. A search of this forum for gas filters and filtered clunks should turn it up again. I'd pass on the header tank unless your flying a jet or helicopter. The minor bubbles obtained with a gasser rarely have any effect on general fixed wing flying.

Zeeb

My Feedback: (41)

There is one more thought to consider...

The earlier ZDZ-40's had some problems with the supplied carb, you might get with RCS and see if you have the older carb. If so, it's my understanding that replacing the the older model carbs results in a much improved setup.

Just a thought since you say you got the engine used and I don't know how old it might be.

It might also help if you told us what the nature of the "engine failures" are? Sometimes when an ignition module is going out it will operate intermittently.

Rcpilot

My Feedback: (78)

The carb has a bowl. It only gets filled when the main jet opens. There is a constant supply of pumped fuel up to the main jet and it will open to fill the bowl when required. The fuel comes from the bowl and into the carb venturi.

Not a chance a bubble in the line will ever make it's way past the jet, into the bowl and then into the venturi to mess up your engine.

ram3500-RCU

My Feedback: (221)

Good explaination. Well stated.

I would like to respectfully submit this on filters, I have run them in the past, but don't anymore. I have found that, over time, the filter itself can deteriorate and be sucked into the crap trap in the carb, clogging it. I use a fliter on the fuel filling line and make sure the tank gets clean gas. I replace this filter each season (much easier to do than the one in the tank). I just don't have clogging problems anymore.

rc bugman

My Feedback: (30)

Hi,

If you are in a situation where you need to carry large amounts of fuel (1-2 gal) for long duration flights or shorter duration flights at full power, often the fuel has to be pulled a relative long distance from the various tanks or one large tank to the carb. In these situations, often you will experience a variation of fuel flow based on the status of the fuel load or position of the tank. The use of a head tank helps a lot in making sure that the flow of gas remains constant (and mixture to the engine remains constant) throughout the large quanity of fuel. I typically use a 8-16 oz head tank in these situations.

Usually, the use of a head tank is not benefical in most hobby RC applications.

Elson