Inverted systems and completion aerobatics
I really wanted to attend this one but ended up missing it. However, I did go by the IAC building and sign up for a free six month membership. One of my buddies competes with his Super Decathalon and can help me get started.
Question for the competetors: How necessary is it to have an inverted oil system to compete when starting out? The plane already has a flop tube in one tank for gas.
Obviously I meant COMPETITION aerobatics in the title!
Hi Mike,
The short answer is - NOT NECESSARY. Now to the full story.
Were I building an airplane, as you apparently are, I would definitely include an injected engine and a full inverted oil system.
That said, I'm competing in my RV-4 and I started without either. After my first contest, I installed the Raven air/oil separator (commonly called a Half Raven System). I'm debating injecting my O-360 but have many hours now flying the Sportsman level figures with just a carbureted motor.
The lack of injection will result in your engine cutting out during many of the figures that produce less than one G. That alone is no big deal, it just limits your performance some. At the Primary and Sportsman level, you won't spend enough time inverted for that to be a big limitation. A heavy, constant speed prop like mine really helps as it keeps the engine turning even when you get slow.
When it comes to oil, I would highly recommend either a Raven or a Christen air/oil separator as a minimum configuration. Unless you have an inverted fuel system, and want to do extended inverted flight, the full Raven or Christen systems really won't provide much benefit. The air oil separator though is a BIG deal because without one, you'll lose quite a bit of oil during a Sportsman level sequence, and especially during practice flights. That's not a safety issue but the oil will make a terrible mess of the bottom of your airplane and your ramp / hangar. It also makes tracking your oil consumption for analytical purposes or doing any meaningful oil analysis program practically impossible. You have to add too much makeup oil.
With a constant speed prop, the other limitation with a setup like mine is keeping oil pressure to the prop. Since the prop drives to full increase RPM when you lose pressure, you'll risk an overspeed if you don't pay close attention. I use a two quart oil accumulator to combat the overspeed problem. A full inverted fuel / oil system would almost eliminate the overspeed risk but not entirely. A counter-weighted aerobatic prop that goes to high pitch (reduce RPM) with loss of pressure is the only true solution but those are rare in a multi-purpose airplane like our RVs.
Bottom line - install a Raven or Christen air/oil separator at a minimum. If you have an inverted fuel system (injection), consider the full Raven or Christen system. An accumulator is a nice addition (with or without a full inverted system) as an aid to maintaining oil pressure.
Good luck with your plane!
Randy