I ran an OS .40 non-surpass in 1984. Ron Sheldon's Hobby Shop got 2 in, and I bought this one for $90.
I installed it on a scratch built profile biplane I built for test purposes, to satisfy my dilemma with top wing incidence. (top wing was incidence-adjustable) 36" wingspan, 28" fuse length, silkspan/dope finish.
Adhering to the old rule "just one adjustment at a time", I was cautious to bench run the engine prior to installation. An associate and I took turns running it just outside the Service Dep't at Allison BMW, where we worked. After 8 tankfuls of 6 oz., I was satisfied with its performance. Consistent as could be, only it would backfire on starting and lose the prop nut! (the cleanliness of the area was tantamount in recovery of that nut! In desperation, I simply applied a length of silicone fuel hose to the end of the threaded crankshaft. Never loosened it again. It was as though the nut 'took the hint'!)
11/5 Top Flite prop, 10% Sheldon's fuel. The plane balanced a trifle nose heavy, and seemed to weigh a ton...
I took off with the throttle blocked wide open, engine not 'screaming', just making unbelievable prop draft...It taxied for 1/4 lap, I held 'down' to raise the tail; when I gave a little 'up', the plane caught up to the engine.
Climbs, dives. The first wingover gave no hint of engine strain, it didn't lose ANY RPM! It was effortless!
Took some getting used to, but when I tried the "C/L Immelmann" (at the top of the wingover, crack full down)
the Bipe did a quick roll, swooping downward, then doing a slow loop (on its own, 20 ft. slack in the lines!) then returned to the end of the lines at about 20 ft. up, gently wagging and returning to that super smooth constant!
I would fly that plane over that year, then again in '86 & '87.
I got my final adjustment figures, (wasn't that far off with incidence) and received all kinds of "advice" and other verbal insubordination... ("4 strokes don't work for C/L", etc.) but I enjoyed the plane, to this concensus: The 4-stroker never gave me any trouble, besides the occasional backfire starting. Its performance and consistency left plenty of carefree room to get to the purpose of the airplane: the tests.
Heavy, yes. But not too heavy on the lines. It did land a little fast...