RCU Forums - View Single Post - Incompatibility with CAT air trap and Kingtech/Jetcat engines?
Old 01-24-2016, 01:13 AM
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Originally Posted by marquisvns View Post
The function of an UAT is to trap air from the surface tension of the fuel from the filter media. Normally an UAT is not designed to be back flushed.

Wrong and wrong.

Modern air traps are not designed to eliminate cavitation but to reduce the likeliness of it by reducing the suction drag they create. However:

The primary function of an air trap is to work as a complement to the non perfect clunk.

As a reminder, air gets sucked into the system while performing maneuvers. No clunk system is perfect and no matter what, it will get into an empty portion of the tank at some point and pickup air.
When this happens, air is sent into the system downstream the tank and will be trapped by the air trap. The more aerobatics, the stiffer the clunk line, the more air will be sent into the system, especially towards the end of the flight. This is normal and cannot be avoided.

So it is essential to be able to back flush your air trap to refill it between each flight.

Otherwise, after a few flights, the air trap will be empty.

Also, there is a big mis-conception with the latest air trap. People believe that it is so good at trapping cavitation, that they do not need to have a big air trap volume in there. Once again, cavitation trapping is a secondary function of the air trap. The primary function is to block the air that is being sucked by the clunk and offer continuous flow to the engine. The main advantage of CATs or similar is to offer a various buffer volumes. Large volumes are important for big engines and I recommend chosing an air trap that offers 30 seconds of buffer at full thrust.

Down sizing an air trap is a big mistake and most system that I have seen getting people flame outs where either because of a drastic restriction in the system ( creating a cavitation condition ), wrong clunk line plumbing ( clunks blocking against a wall or stiff line due to hardening tygon ) and very small air trap buffer capacity.