A Zero G Ride for a Mere $2,950!

[USMCmech]

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Two really bad things come to mind when doing such a thing in a 172: fuel exaustion due to the fuel being gravity fed into the engine and a lack of an inverted oil system. Do it too much and your engine will stop due to lack of gas. Continue to do it and it won't turn back on again because it dosen't have any oil.

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Cessnas have an engine driven fuel pump just like everybody else, graviety is their back up.

Both the fuel and oil pumps create a suction that will keep things flowing for the few seconds you are 0 or even negative G. The engie start time is far worse to your engine.


As for the airframe question, NASAs KC-135 performes a 1.5-1.8 G pull out on the bottom of their parabollas. Hardley a strain on the wings. Since it is subjected to this constant strain they have carefully examined it for weakness. The genral consensous is that the frequent G loading isn't an issue.

The main factor leading to metal fatigue is pressurization cycles of the cabin. Rember the Aloha plane that lost it's roof, it had almost as many pressurization cycles as hours.

 

[RPM]

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If you start paying attention to aerobatic airplanes, they have inverted fuel/oil systems for a reason. Only reason I mention it.

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Even the unlimited aerobatic oil systems aren't set up for prolonged knife-edge or vertical flight...you generally have to watch your oil pressure gauge or follow the 10 second rule for that type of flying even in unlimited aircraft. Most inverted systems basically just add a modified oil pickup in the top of the engine in addition to the one in the oil pan and add baffles in the pan to keep the oil sloshing to a minimum.

If the plane is going vertical or knife-edge you only have around 10 seconds max for the maneuver before oil starvation becomes a problem....unless you go with a dry sump system which hardly anyone uses.

The fuel thing isn't a big deal in the cessnas....yeah, you can get the carburated ones to sputter and even die sometimes if you get real agressive with em, but they start right back up once you level out. It's more of a fuel metering problem with the carburator not fuel starvation due to gravity feed systems like people think. You should always be at a sufficient altitude doing stuff like that in a Cessna anyway. The only time i've ever had serious carburator issues in a Cessna was doing a falling leaf stall (falling backwards) then going into a spin in a 152...at about 3-4 seconds falling backwards it started sputtering and just about died, so I kicked the rudder to the floor to bring it around into a spin and get the nose pointed down and it smoothed right out /ubbthreads/images/graemlins/grin.gif I've never had any issues with oil press. or fuel starvation just doing short 5-7 second vertical dives...any longer than that and you'd pick up too much speed anyway and have a whole new set of problems to deal with, like wings ripping off /ubbthreads/images/graemlins/ooo.gif

Cessnas are lame, I want a Pitts!!! /ubbthreads/images/graemlins/cool.gif