Here at the home of bad advice for VW Aeroengines, we get questions. As always, we have opinons based on the synthesis of research and other people's opinions, backed up by little or no practical experience. But hey, you get what you pay for.
>I read an old article a while back about a guy that competed in >aerobatics with a VW powered Tipsy Nipper.Then he upgraded to his own >design that was also powered by a modified VW engine.He had inverted oil >and the whole works!
Try the Tipsy Nipper site, there are links from my VW powered homebuilt page.
>Do you happen to know what I'm talking about
>or any other person that has tried this and was actually successful?
No, not personally. There was an article in an old MONINK newsletter about a guy in NZ that did acro in his Soneai, and started picking up metal in his oil in relatively short order.
>The reason >I ask is because I'm building a Sonerai 1 and plan on doing some >aerobatics in it with my buddy and his Sonerai 2. He does the basic >aerobatics in his 2 and wants to upgrade to an inverted oil vw engine >if at all possible.
There are a couple ways to approach this, and I'm only going to talk about oil. A flop tube and a fuel pump will take care of fuel, using either a POSA or Ellison carb.
First, you can do the whole Sportsman routine and stay positive the whole time, so who needs inverted oil?
Second, increase the oil capacity through an add on sump (Bugpack or Gene Berg) and an extended pickup tube, at least that way there will be more oil splashing around when you go upside down - some of it may find it's way to the main and cam bearings.
Third, HAPI (and later Mosler) used to sell an accumulator, that would add extra oil to the system when the pressure got low. This will give you a few extra seconds of oil. A current source for these things is Accusump, here's a dealer.
Fourth, you can check out the Christen system (see the Aircraft Spruce Catalog) and adapt it to your engine, with an auxiliary sump. The Aviat people, who make the bits, will sell you whatever pieces you need, and the critical one in the shuttle valve - a lead-weighted spool valve that switches the oil feed from the bottom of the engine to the top when you invert.
Fifth, there are dry sump systems available for VW engines, you'll need a special 2 (or 3) stage oil pump (SCAT sells 'em), an air/oil seperator, and a seperate sump. Or you can use an Auto-Stick oil pump, and use the second stage as a scavenge pump.
Sixth, call Steve Bennet at Great Plains, and see what he thinks.
Seventh, unless you go with a dry sump or the Christen system, you will probably puke a bunch of oil out of your breather, oil you can ill afford to lose. Check the oil level before and after every aerobatic flight. Great Plains has a new breather that may cut the oil loss down a bit.
Eighth, get ahold of these blokes, who built the Tipsy Nipper engine you seem to be referring to, and get their demon tweaks.
NONE of this stuff will fit forward the firewall on a II except a small added sump. A Sonerai I has some space between the back of the engine and the firewall where some of this crockery could be wedged.
What I would do is start building a spare engine, use a full flow filter, use oil analysis and change out the bottom end every 100 hours, or every winter, or when the metai numbers started looking bad. Chances are new rod, cam and main bearings would set you right again, and if you're careful, you wouldn't wreck your crank or cam.