Gravity fuel flow and aerobatics

[larry]

I'm just curious - at least theoretically, you cant' do aerobatics in any of the planes that don't have a fuel pump. Or can you? Were early 1900 airplanes fitted with fuel pumps, then? Folks were doing loops and what not in them...

[sideslip]

Aerobatic planes are fitted with inverted oil and fuel systems. That way they can still have the engine operate upside down. I'm not very familiar with what all is involved with those systems.

[skid]

A loop is a positive g manuever so fuel flow is not a problem. Many manuevers can be done without an inverted system. A cuban 8 is almost all positive,so is an emmelman. A simply aleron roll can be done by raising nose,relaxing elevator input and applying full aileron, remaining positive entire time. A properly done slow roll has 1 negative g for a short period of time, but can be done in most airplanes. A slow roll has nothing to do with the speed of the roll, the nose is held on a point throughout the roll. The engine will quit during neg portion because of float in carburetor. Oil pressure will go to zero and will probably dump small quantity of oil out of cankcase breather. Continued arobatics will leave the engine low on oil. Many of the older airplanes had pressure carburetors that were essentially a single point fuel injection. Radial engines usually have a dry sump system that keeps the engine supplied reasonably well with oil. Modern inverted systems are very simple. A valve with two heavy balls in it picks up oil from the sump when upright and from the top of the motor when inverted, and then to the oil pump. Gravity moves the two balls to cover and uncover the proper port. A catch can collects oil from breather when inverted which drains back to sump when upright. Any fuel injected airplane will continue to run inverted. The only addon is a flop tube in gas tank or a headertank with flop tube; roll inverted and pickup hose flops to where fuel is. I think most of the manuevers your refering to are probably really still positive G. Those old airfoils had lots of lift; and very little lift inverted. Would take a tremendous amount of horsepower to do hard outside manuvers. Flying well negative G and just keeping the motor running while inverted are two different things. Many modern arobatic aircraft have symetrical airfoils to fly the same upright or inverted. By the way even though any Cessna will loop or roll, don't for several reasons. If you fall out of a manuver, there is little room for error and you can overstress it easily. Even if the airframe is strong enough, seat frames ,battery mounts etc, are not strong enough to withstand high G. Battery acid can be spilled, you get oil all over the belly,etc.Besides all that, what's the point in doing sloppy figures to keep from overstressing the airplane?