Stick Jammer wrote:
Then explain why an engine running on the ground that for one reason or another is getting air bubbles in the fuel line runs noticeably erratic.
The difference between the two situations is that when you get a stream of small air bubbles in the fuel tubing from a leak or fuel foaming in the tank you are effectively leaning out the engine over a longer period of time. This tend to alter the RPM of the engine which in turn will have an effect on the two-phase flow (air and fuel mixed together) in the fuel tubing which again will have an effect on the RPM. The engine will run erratically and be very hard to tune.
When in a dive one air bubble will enter the the fuel line. The size of the bubble will depend on engine RPM and for how long the dive is maintained. The air bubble will get out of the system very quickly, especially at high RPM.
Even at low RPM (engine at idle when diving) you will probably not notice anything special because the air bubble will be a lot smaller (less fuel consumed at low RPM) and also the inertia of the rotating propeller together with the windmill effect on the propeller will tend to keep the engine running during the brief time it takes for the air bubble to be 'sucked' through the carburettor.
/Red B.