Originally Posted by
TheOddOne
I DO teach spill it onto concrete (not asphalt as it melts it) and watch it evaporate. If it's all water, it can still smell of AVGAS and have a blue tinge, but the evaporation test is positive for fuel.
If it's all water, it will be obvious to anyone paying attention as it drains out of the tank. Water and fuel have very different viscosities and look very different coming out the drain. No need to contaminate the ground with it.
Originally Posted by
TheOddOne
Also, as above, it's a waste of time doing drain checks unless the aircraft has been stationary for at least a couple of hours, as the contaminant will be in suspension.
OWT. If you're talking about right after fuelling, it's not a likely source of water and can take much more than a couple hours to settle out. If you're talking about water that has already accumulated in the bottom of the tank, moving the aircraft around is not enough to mix the water into the fuel. With high wing aircraft, if the bottom of the tank does indeed hold water you will get more of it out by moving the plane around before sampling. In fact if you do find water in your sample you'll definitely want to rock the wings to help the water make its way to the drain. In the worst cases where rain has been dripping into the tank through the filler cap it is best to start the engine so that the vibration helps the water move down to the drain.