Header Tank Info

Back to Main Page

  
What is a header tank good for? You may get some various answers from others. I will try to cover the technical concepts behind them. First I will start with the true reason for a header tank. It is a bubble trap. When doing hard 3D the clunk line may pick up some air as it gets thrashed around inside the tank. The header tank provides an air bubble free supply of fuel to the engine. The second valid reason for a header tank is to add a little extra flight time.Personally I don't use a header tank. I 3D upstairs until I get to 1/3 tank then I do ground maneuvers. Also, my carb settings stay the same from the top of the main tank to the bottom. I figure adding a header tank is just one more thing that could fail so I don't use one.
Installation: The header tank should be placed at the center of height of the main tank. Why there? Because you want to average the fuel rate. How do the engineers pick the place for the main tank? They place the tank so that the top of the tank is no higher then the top of the carb. Gravity helps feed the fuel to the carb. If you take an engine on a test stand and hold the tank in your hand while you run the engine, you will notice that if you hold the tank above the carb, the engine will run rich. If you go below the carb, it will run lean. So if the engineers placed the tank so that it was in the middle, then we would never be able to get a consistant needle setting. The difference in the mixture setting from a full tank to empty would be a lot more then with a tank placed under the carb. Just like in the above test, if you move a header tank up or down, you will change the fuel flow. By placing the header tank in the middle of the main tank, you will minimize the difference as the main tank empties.
Why do some say a header tank cures the problem of the engine getting too hot toward the end of the flight. It has to do with a couple of reasons, incorrect engine/throttle-pitch/mixing or vibration. The effects of either of these two will cause the engine to get hot. If it's due to vibration, then the header tank will help take the air bubbles out and therefore mask the true problem. If it's due to incorrect engine/throttle-pitch/mixing settings, then by having a header tank up high will give a rich run toward the end of the tank which would help cool the engine and therefore again mask the true problem.