Hobbies And Interests
Fuel
You might expect turning upside down would make an engine stop from fuel starvation. That's pretty much what would occur in a car or a lawn mower. Once the vehicle is inverted, fuel is no longer gravity-fed into the fuel intake in the bottom of the tank. That's because the bottom of the tank is now the top of the tank. However, aircraft fuel tanks have a "flop tube," which is a weighted, flexible tube with a fuel intake in the end. In normal attitude of flight, the weight sinks the tube to the bottom of the tank. When the plane inverts, the tube flops to the top of the tank, along with all the fuel, and continues to draw fuel into the system.
Carburetion
Standard internal combustion carburetors use gravity-operated floats to meter the fuel supply entering the intake manifold. This works fine as long as up is up and down is down. Turn the engine over, however, and the gravity-operated float now works in reverse, cutting off fuel to the engine just when it should be providing fuel to the engine. That's why fuel injection, now standard in all modern automobiles, was first developed for airplanes, not cars. A fuel injection system continuously pumps fuel under pressure to the cylinder injectors. The injectors meter the amount of fuel entering the cylinder without knowing, or caring, whether the plane is shiny side-up or not.
Oil
In an upside down world, wouldn't the entire contents of the engine oil pan swamp the cylinders, pour out of crankcase ventilation tubes and cause the engine to seize from lack of lube? If an aircraft had an oil pan -- or "wet sump" as it's called -- like a car in the first place, it might. But many airplanes have a dry sump. Oil is pumped in and out of the engine oil galleys from a sealed tank, not a gravity-dependent, automotive-style sump in the bottom of the engine. The oil tank contains a flop tube similar to the flop tube in the fuel tank, so it keeps pumping oil no matter what. On the other hand, many airplanes don't have dry sumps. And yes, for the brief period of upside down operation, oil indeed engorges the bottom of the cylinders. But aircraft engines are engineered with piston rings capable of sealing out the oil. Meanwhile, one-way check valves prevent oil spill through the crankcase ventilation system. A gravity-operated ball valve switches the oil pump from an oil pickup at the bottom of the sump to an alternate oil pickup at the top of the sump as the plane inverts, maintaining oil pressure and preventing seizing.
Coolant
Have some fresh coolant on hand if you're planning to run your car engine upside down. Coolant in the overflow reservoir will leak out with the force of gravity, eventually draining the entire cooling system. The majority of airplane engines have the ultimate defense against upside-down coolant loss: No cooling system or coolant. Air-cooled engines predominate in aviation.