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Hi just purchased a saito 56 I am a little confused when looking at engine requirements on many of the models out there. Some say 40/46 2c 70/91 4c did the 56 fall through the cracks what is a good rule of thum for my 56 can I use it in a 46 2c application and have enough power I dont fly fast iI just want to feel like I'm not under powering any help appreciated Bob A
What the ARF and kit manufacturers try to do is recommend a series of engines that have similar weight, mounting dimensions and power.
Engines can be divided into, for the want of a better term, block size categories. For example, the ".40 block" engines include modern .40, .46 and .52/.55 size two-stroke engines. Also, four-strokes like the .40 - .56 Saito/OS/Magnums, the Saito .72/82a and YS .63 fit into this category. They are all about 36mm between mounting beams and they weigh about 500 grams, give or take. You often see ARFs recommending ".40 - .46 two strokes or .52 - .72 four-strokes" for this reason.
Same goes for the ".60 block" engines:, hence: ".61 - .75 two-stroke and "91 - 100 four-strokes", because engines in this range are typically about 42 mm between beams and weigh about 600 - 700 grams.
In my experience, in very general simplified terms, a good .52 four-stroke performs about the same as an average .40 - .46. A good .70 four-stroke about the same as a .52 two-stroke and a good .91 FS about as good as good .61 - .75 two stroke. YS fourstrokes are a bit different - they pretty much match or slightly exceed a two stroke cube for cube.
Notwithstanding the above, four strokes have some tangible advantages (spoolup and linear throttling) in applications like 3D flying, where response and throttle control is critical.