Thanks to all for the education, opinions, and guidence
You are quite welcome! The internet, for all its faults, is an absolutely amazing resource for stunt fliers. When I was trying to learn 40 years ago, there was very little and you had to glean the meager information by reading every single magazine article you could find, and learn to read between the lines. Now you can have direct access to mutliple national champions and many very knowledgeable master modelers in seconds.
Back in the day, it was also common for experts to keep secrets, and you could actually do it. Now, absolutely anything anyone knows is immediately available and written down for you. No one can keep a secret any more, there are too many of us who will tell you anything we do, and, tell you what we think other people are doing.
There are a lot of arguments, and back-and-forth with differing opinions, but arguments in general are really helpful. What is not helpful is the people who are intentionally attempting to tweak people and in the process, promulgate gibberish or known wrong information. For the first time ever, I got real-life angry at someone in Muncie for this sort of thing this year. But that is one incident in ~25 years of internet activity since the old compuserve forum days.
BTW, I can describe the sort of modifications that most modifiers are doing -the same silly plan from 1980 when no one really knew what to do with the amazing power increase possible with schneurle engines. It's some combination of dropping the liner in the case (to reduce the exhaust duration), raising the intake port(s) by grinding the top edge of the ports (to reduce the blowdown), blocking the boost port (to reduce the high-RPM breathing), and stacking large numbers of head gaskets to decrease the compression ratio (to either reduce the 2-stroke power and/or overall power). The goal is to make it so you can run the engine at low RPM with a 6" pitch prop, and maybe in a 4-2 break. That's unfortunate because it once you make it run like a Fox 35, it has the same power as a Fox 35. This works sometimes, but in any case you toss away a huge fraction of what made the engine worth using in the first place, i.e. more effective performance.
A few people almost figured it out in the early 70's. The West Coast equivalent of the AMA was called WAM, Western Associated Modelers. It was formed in the late 40's, and was about equal in stature. One interesting thing about WAM was that they had skill classes in every event (carrier, combat, stunt, speed, everything) right from the beginning, and this was the model for the PAMPA classes when those started in 1974.
Anyway, another interesting thing about WAM was that they had engine size categories for every event including stunt. David Fitzgerald holds the WAM High Score Record for 1/2A, I hold the WAM High score record for both A* and BC, etc. At any rate, when Bay Area airline pilots Ted Fancher, Bill Fitzgerald, and Gary McClellan and their clan decided to fly stunt, they wanted to fly all the WAM engine classes. So they needed 1/2A airplanes (Cox 049) and A stunt airplanes. They experimented seriously, and came up with a more-or-less stock SIG Banshee using, wait for it, a Veco 19BB with a 10-4 prop running in a constant 2-stroke. This was in the mid-70's. The airplane flew so well that they may have been easier to fly than their "serious" airplanes at the time. But it never quite dawned on them to apply the same principle to the larger engines. Even when the OS 40FSR and other similar "schneurle of the month" engines came along, they still persisted in trying to run them like Foxes.
Still later, when doing the initial experiments with 4-strokes in the mid-80's (before the Johnny-come-latelys declared them a "revolution" in the mid-90s - about the time they sold their last St60 that had been rusting on the shelf for 10 years), once again, the best performer was Ted Fancher's Enya 46 with - wait for it - a 12-4 spinning at about 11000 RPM. This of course was quickly dropped when the drastic performance improvement and amazing adjustability of tuned pipe engines came along - also swinging, wait for it, 4" of pitch.
Ted and I, and then later, David, switched to piped engines about that time (1988-89) as did many others, and of course since then, this has been the de-facto system. Only recently has electric been a viable alternative.
Anyway, I spent a lot of time helping, or at least trying to help, beginners and others try to advance. Almost invariably, they were trying to use either vintage semi-slag engines like the Fox on profile mounts, or OS40FPs of some sort. The stock Fox needs no further description, burping/crash/die on every outside corner, and at the time, the bypass stuffer had not been discovered. Even if it keeps running, it shakes the airplane to bits in short order. The unmodified 40FP was notorious for "runways", AKA, running as designed, which led to grossly excessive power/speed when used with 6" of pitch, and even too much with 4" of pitch. The modified 40FPs were just as weak as Foxes, although they would keep running through maneuvers. Piped 40FP's worked fine, but that was far beyond the desires/means/interest of most of the guys we are talking about.
Anyway, during one of these sessions, out in the 100+ degree sun at Gilroy High School in Gilroy, California (home of the Garlic Festival), it finally dawned on my that the 40FP ran very well, but had about 2x the power it needed for the airplanes we were talking about. Say, if it has twice the power, maybe I need the same thing about half the size. Then it dawned on me what they had done with the Veco 19BB back in the 70's was analogous and how 4" of pitch was responsible for most of the performance increase from piped engine and for the 4-strokes. But it still didn't quite click.
Shortly thereafter, David and I were up flying at the old Napa site, and a guy comes up with a kit Ringmaster with a mere 15FP and about a 8.5-5 prop. Full paint job, probably weighs around 32-33 ounces. We know this is going to be a dog of the highest order. But, after we got his controls slowed down, it flew very well, better than most Ringmasters. We both take a flight, and it's amazing, this little "underpowered" airplane with the worst of the design characteristics from the late 40's and know to be one of the worst-flying models that is commonly built, flew like a regular airplane and had no problem with a 10 mph breeze.
It finally clicked. The very next day I went to PECs Hobbies in Mountain view, and what do I find but an OS20FP ABN, $47. The rest is well-documented. Spent a lot of time over the next few years out flying the Skyray 35 (originally built with a Dixon 40FP, then with a bypass-stuffer Fox) with various engines. The first 20FP flight was stunning, back-to-back with the Fox flights. It was like gravity had been turned off, the airplane flew up, down, horizontally at the same speed with me hardly having to help it at all. With the Fox, I could get it through patterns but I was a very accomplished Expert-caliber flier and NATs Top 20 qualifier. Most people would have had little luck with it. Anybody could fly it with the 20FP, it was dead easy.
ALL of the small engines I tried worked very well, far better than the Fox reference and all of them handled much better than a Fox and gave much better performance than a Fox. My rules (and still the rules to follow if someone wants to repeat it) - 4" of pitch, no internal modifications or head gaskets, and stock mufflers. The only engines that I tried that didn't work lwere just too big for the airplane, 32's and 36s. They also run much better in most cases than any of the modified/butchered 40's because those mostly ran like Fox 35s on 6" of pitch.
Brett
Topic: Follow on question o the OS 20 FP running with hole in crank case (Read 5653 times)
