I feel like adding my two cents here... This is all from first hand experience and my impressions...
The high rpm/low pitch run style as I understand it developed as a work around for the schneurle engine run away. The run away is defined as setting the needle on the ground, and it stays at that setting in the air until sometime after the first few maneuvers where suddenly it picks up a bunch of RPM and flies out the tank in a fast 2 cycle to the tune of 4.5 second lap times. The problem comes from using RC engines that are tuned for high RPM power and are controlled by the carb. When used with a venturi they tend to run away. Workarounds include reducing compression, restricting exhaust with mufflers, restricting intake with smaller venturi's, etc. While any number of these work arounds can work for an indiscriminate period of time they usually tend to act up at the worst possible time (at the contest during an official flight) resulting in over runs and/or sloppy maneuvers. By running a lower pitch prop and setting the needle to a higher RPM the engine is already closer to its peak and is less likely to run away. But, the plane typically is flying faster, or at least a consistent speed through all maneuvers and doesn't provide the throttle action of a 4-2-4 break.
These 'runaway' characteristics are normally applied to the OS FP series. The LA series is basically a cosmetic update to the FP series, incorporating the gimmick square head, etc to make the RC guys feel like they're keeping up with the Jones'. At the same time the LA seems to lack a lot of the quality and finesse of the FP. Note the plastic (cheap) backplate, phillips screws, heavy RC muffler, RC style remote needle, etc. The only real difference in the LA is the lack of a boost port in most of the later ones that cuts the power output. This isn't anything new, since people were stuffing the boost port on FP's a long time ago. The problem is that the LA still is capable of running away, and while I've gotten a few good runs out of the one I've tried, I don't see it as being enough better then the FP to justify changing over.
Even with a constant speed, its not really constant because the plane is going to slow down in climbs and accelerate in dives. The point I want to emphasize here is that you have to react quicker when dealing with a high rpm/low pitch configuration because the plane doesn't slow down for you. With a 4-2-4 the engine comes on and speeds up when you're climbing, and slows down when you're diving, resulting in more time to react and a more consistent speed overall.
The entire need for a work around for the run aways was because there weren't many C/L engines being produced. Just the Fox 35, the OS FP's, and some of the more unusual imports like the Enya and Merco. The Fox 35 is fairly tempermental and is low on power for most designs, so its discounted leaving only the OS as a viable option for many people. That's what has led to their popularity.
The persuit of the 4-2-4 break (note the 4 at the end, cause it comes back to the 4) is how the engine reworking community has succeeded. Several cottage industry engine specialists have popped up and have modified engines to run more suitably for C/L stunt. Having run several engines that have been reworked, I can tell you some are better then others. Unfortunately I would say my opinion is that its better to buy an engine that will run a 4-2-4 to begin with, rather then try to reinvent the wheel.
I've found a couple engines that run a very nice 4-2-4 break, there are others I'm sure, but these are the ones I've tried that I can vouch for...
Fox 35
OS Max-S 35
Super Tigre 46
Super Tigre 51
Topic: general setups (Read 2289 times)
