Skydriller
By 'normal carbs' people are refering to a standard float chamber set up where fuel is pumped into the chamber at the top via a metering valve that is closed by the float rising when the camber is full, as fuel is used by being drawn into the venturi for mixing the float lowers, opening the valve and allowing more fuel in etc etc. As the fuel is drawn from a drain in the bottom of the chamber any inverted flight or sustained negative G would mean fuel starvation.
Most aerobats will use drirect fuel injection (no carb.) With this system fuel/air mixture is fed under pressue directly to an injector rail mounted just above the cylinder head where it's fed to the inlet valves and so making most of the previous problems obsolete. Of course, like everything, there are drawbacks to fuel injection, the main ones being difficulty in starting hot engines (very difficult for some) and fuel icing problems can also be a factor.
An aircraft designed for negative/inverted flight will have a dry sump oil system. In essence dry sump is similar to fuel injection where oil is stored in a seperate tank, scavenged by a pump when used and then fed at pressure to the vital areas in need of lubrication/cooling then returned to the storage tank.
A standard wet sump engine as found in your 152, chippy and tiger moth will work just as well for inverted/negative flight no problem, you may see a greater loss rate however. Wet sumps just has its oil load slushing around at the bottom of the crankcase (sump) or, if the engine is mounted 'upside down' such as the tiger moth and chipmunk then the oil simply sits around the pistons and exposed cylinder. This is the reason you should pull the prop through before start to clear any oil via the valves that has slipped past the oil and compression rings on the piston. Failure to do this can bend cranks as liquid is incompressible!
The reason for a moths engine being 'upside down' is not to provide the pilot forward vision (sorry, shaggy sheep driver) that just happens to be a nice side effect. It is because the aircraft is a taildragger and mounting the engine in the conventional sense would mean a smaller prop would be required to prevent contact with the ground upon raising the tail on take off. This larger prop due to better clearence also means a bit more thrust and christ knows those little piston engines need it if memory serves me correctly!
Anyway happy flying chaps, it could be worse you could be stuck with turboprops on nightfreight but that's another story
