No question or applicability to stunt here, but since I had the Phantom P30 apart, I thought you might find the guts of it interesting since it is so unusual.
The engine was originally an Atwood design, but somewhere after Atwood quit, someone formed the "Phantom" company and continued making it. It is a "29", actually .298 to get just under the limit for class B. Ignition, of course, but this engine was later converted to glow (by someone who shall remain nameless aside from Richard Melvyn "Mel" Buck, my father, using a delicate technique involving a hammer to the timer case). It was reportedly used to set the last "B" Speed record that was below 100 mph, using a stripped-down hollow log P-51 Mustang kit and a 9-12 (!) prop. This was in Little Rock, Arkansas, at a flying site where Memorial stadium now sits, maybe in 1946-7. I say maybe and am equivocal because it appears to be one of those stories that got better over time.
What I found interesting about this engine is the gas path. Basically, the gas comes from the crankshaft passage in to the crankcase, then travels through a hole in the side of the piston on either side into small "pockets" in the sides of the cylinder, then gets trapped there as the piston comes down. As the piston moves further down, the pockets are then uncovered by the piston and the charge wafts gently into the cylinder, where it is compressed and then ignited, then out the exhaust. The exhaust is two long narrow tubes brazed to the cylinder fore/aft. ALL of the charge comes through the holes in the sides of the piston.
Several things about this - first, the dismally small size of the pockets severely limits the quantity of the charge and therefore the power. Unlike modern engines where the piston coming down forces the gas charge into the cylinder under some pressure and with some velocity, this one merely traps the charge under nearly no pressure. Nothing forces it into the cylinder, it just sort of drifts out. This is greatly inhibited by the exhaust gas left over from the previous stroke, where it would clearly just mix with it with no propensity to go up to the top of the cylinder and force out the exhaust. The result has to be absurdly dismal power, and extremely inefficient use of the charge. It had to be even worse on glow, where you need much more volume of fuel/air charge. I guess we know why you need a FOOT of pitch to go <100 mph, this guy was not going to spin very fast at all and had to have had power on the order of an TeeDee 049 at best (although at maybe 4000 rpm and a tenth of a horse or so, it was a fair bit of torque). That's actually reasonably consistent with a flight speed around 100 mph, presuming it was whipped heavily to get the prop unstalled - also as reported - it would have pretty decent prop efficiency at that low RPM.
My Uncle Donnie cracked the piston in an attempt to "grow" it as mentioned in the other thread, so it's no longer runnable, so I can't check the performance at this point, but it had to be pretty sad, and getting 100 mph out of it was quite an accomplishment, if true. I know the airplane existed with this engine in it, since I have the pictures of it with my dad holding it.
Here are some pictures of the cylinder, piston, and crankcase, so you can see what I am talking about.
Brett