Engine basics > Four strokes only
Saito FA-82B ???
Brett Buck:
--- Quote from: Dan McEntee on September 09, 2023, 09:49:41 PM --- I had the whole nose of my Top Flite Score with a Saito .56 installed come flying off just after a demonstration at Oshkosh a few years back. Luckily, the engine hit no one, and the model survived well enough to be repaired and fly again. I think the incident had two causes. When flying the airplane before the nose separated, I often though how smooth the engine was running. I really felt nothing at the handle. It took me about three seasons to figure things out after reading up on Bob Reeves writings and few others. After that, I was liking what I had. Gilbert Berringer complimented me on how it rana nd flew after he put up a flight that year with it.
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I am not sure that this has anything to do with the 4-stroke, I have seen some pretty questionable workmanship in some of the Scores, it might have fallen off using a 40VF! One hallmark characterstic of a 4-stroke is the low fuel consumption for a given power. That means that each firing has to be very "clean", meaning very energetic, and while the average torque and force is less than a conventional engine, the peak is almost certainly much higher, meaning it it putting energy into higher-frequencies. Hence it can buzz up things that you wouldn't expect, like Gordan's flap horn upright. Think "ping ping ping" instead of "thud thud thud" of a 2-stroke engine running blubbery rich to the point of misfire and blowing 60% of the fuel out the exhaust.
For a given airspeed, you usually have less shaft power than a piped engine at the same speed, because the prop efficiency is much higher on the 4-stroke. But it's not the difference between 3 ounces a flight or 8.5 ounces a flight. This is also why the exhaust it much hotter on a 4-stroke, the only way to get more power/ounce of fuel is to burn it cleaner/hotter.
--- Quote --- The next airplane I build for a four stroke will have a nose similar to what you would build for an ST.60 or what I imagine you would build for a PA.75 for sure.
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None of David's airplanes are extraordinary nose construction, it's more-or-less the same as any other piped engine and not much different that what we have done since the ST46 era (which was also not exactly a jet turbine). The one thing I (and many others) did learn from Jim Greenaway was the degree to which the engine mount and fuselage rigidity affected the engine run quality. I never did it to the same degree he recommended with the ST60, but was very careful to make sure it was very solid, that's why my ST46 runs were generally much more consistent than some of my cohorts. Didn't fix the rings, of course.
Brett
Dennis Toth:
Just finished watching some development video's that Windy did leading up to the Tyfoon with the Saito 90. He did a lot of prop work with the OS Max FS70 and the Saito72 with a little on the Saito 82. It starts here:
Best, DennisT
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