I had dry the tanks twice. The time fully intentionally - I was to ferry flight a new microlight to Italy (I really mean new type) and wanted to get fuel gauges confirmed before setting up for several hundreds miles trip. Done above the airport at 3000 ft with Rotax 912. Engine started shaking and after switching to the other tank power was restored immediately. The second time I was flying on old 172 with Rolls-Royce 0-200. (it is a Continental you know). I was somehow not happy with the left fuel gauge reading, after visual inspection I made all take-offs and landings on the right tank. High enough I switched to left. And of course forget about chance the tank will be dry soon. When the power was lost, I didn´t even lowered the nose, just moved the fuel selector and power was restored immediately.
I also run a tank dry during my training to get my licence with my intsructor. As said previously, the engine did not stop suddenly, but coughed once or twice. I turned the electrical pump on, then switched tanks and the engine ran smoothly again immediately. The instructor had a point in showing it was a non event. However, in all the other clubs I have been after this one, rules were not to run a tank dry and pilots never had the opportunity to do it during their training. Too bad, in my opinion.
That rule could make sense for a club or group aircraft. If you run a tank dry you put air in the fuel line from that tank. The next time that tank is selected it could give somebody a nasty surprise when the engine stumbles. This obviously depends on the fuel system in that aircraft.
Do you really think that air stays in the pipes after the tank is filled again? I don't think so. Even if a little air stayed there, with the electrical pump turned on for take off, with the fuel used for heating the engine, there would be no air left in the circuit during take off. In my opinion that's not the reason for this rule. It simply a precautionnary thing. In France many pilots fly in aeroclubs with DR400. The 120 and 140 versions of the aircraft have but one tank. For many pilots, simply switching tank is a thrilling adventure... It would maybe have been one for me too, if I had not done it, including running the tank dry, with a instructor first.
It seems that carburetted engines recover very quickly, but my experience with injected systems ia about 10 seconds of rough running before the lines are flushed with fuel again.
I suspect this is down to the more direct supply of fuel to the engine and the sensitivity to fuel pressure.
In either event it is no great issue if planned for. There is little loss of RPM or altitude when I have tried it.
If you have refilled a tank that has been emptied, it's a very good idea to start and run on that tank on the ground to purge those fuel lines.
I suspect this is down to the more direct supply of fuel to the engine and the sensitivity to fuel pressure.
And probably also due to the fact that high pressure fuel pumps require by injected engines don't work properly when they are dry. Just like Diesel powered cars that are very difficult to get started again after being allowed to run dry. Some time ago I used to fly a C340 with six tanks. Unless you wanted unknown quantities of unused fuel in every tank you needed to run them dry before switching. When one was quick enough to switch tanks and turn on the electric boost pump at the first sign of coughing the whole process would not be noticed by the passengers. If you were slow and the engine coughed for a few seconds with the aircraft yawing, some passengers would get very scared.
