Inverted and neg g's are different
but can they maintain inverted flight for longer than a second or two? Whats the longest someone has maintained inverted flight?
If you are asking how long oil pressure and/or engine power will last with out inverted oil and fuel (carb) when you go negative g's, I don't know, several seconds, not long. Depends on how negative as well. I really don't want to find out.
If you are asking what is the record invented flight (in properly equip planes), I don't know. I personally flew next to a guy in cruise enroute formation who was flying a RV-4 upside down for several minutes. He had all the inverted stuff. Frankly a RV with its highly cambered wing is terrible for sustaining inverted flight. It flies at a high angle of (negative) attack, so its draggy and hard to keep speed up. Pure acro planes often have symmetric airfoils and fly basically the same up or up side down.
There are records of people flying up-side down. Not sure what the max endurance record is, but I know there are records like max number if inverted spins. Not sure who keeps those records.
You should never intentionally fly negative g's for more than a second or two with out inverted fuel and more important, inverted OIL, in my opinion. I try hesitation rolls and hold the inverted for a second or two. I get very light in the seat, but I am trying to still keep + side of zero g's. It makes a mess on the belly when oil burps out the vent. If you do lose Oil P you know it when the engine surges, due to lack of oil to the prop gov (if the engine is still making power).
Yes you can fly inverted (pos g's) for quite awhile with out inverted fuel/oil systems. Example the top of a loop. You are inverted for many second but you are on the plus side of ZERO the whole time, at least that's the idea.
One maneuver you can do is pitch up to say 60 deg, half roll to inverted, than do a ballistic trajectory, allowing the plane to float and nose over slowly to say about 30 deg nose down, than half roll back and recover to level. You feed in just enough forward stick pressure to sustain it as long as possible while keeping it Pos G's. You don't have to look at the G-meter, you can feel it in the seat-O-pants. This inverted ballistic maneuver gets you time upside down but on the PLUS side of zero. It just has to be +0.1 or +0.2 g's, but you need that little bit of Pos-g's to keep the life blood juices going to the engine.
A true story, the T-28 radial engine trainers have a limited invented time due to engine oil limits, as I have read. I never flew one, but the famous Bob Hoover did. He borrowed a T-28 a few years back and held sustained negative g's too long, toasting the engine. The owner was not happy. The fear of damaging my engine keeps me away from intentional negative g's, but there's a whole world of Acro maneuvers on the Pos side of ZERO on the G meter.
, does the rv have enough downward elevator deflection to MAINTAIN (say for a minute or so) inverted flight?