ORIGINAL: w8ye
ORIGINAL: Konrad
For a comparison that has a lot of examples all one needs to do is look at the old FAI F3A engines. These engines were held to a 10cc displacement for the two cycle and 20 cc for the four cycle. Now all one has to do is look at the record book to see that even with 200% advantage the four cycle engine was hard pressed to beat the 2 cycle for a myriad of reasons. So for aircraft that were/are critically judged the two cycle is the superior set up for our toys unless one give the four cycle an inordinate displacement advantage. Now in this example both engine types were competition engine. For the sport pilot the formula might not be the same.
All the best,
Konrad
And where are the 10cc engines in pattern today? Even the SPA is dominated by 15cc four strokes
The rules, SPA outlawed the true 10 cc pattern engine (no pipes). Now the modern 15cc four stroke is about as powerful as some of the high performance baffle engines that the Senior Pattern Association members flew when they were Juniors!
My point is that if left to compare power (flight pull) of a high performance two cycle verses a high performance four cycle one needs to give the four cycle at least a 2 to 1 displacement advantage over the two cycle. To support this statement I point to the FAI rule book. The FAI tried many formulas to try to bring the four cycle engine close to parity with the two cycle engine. They tried the 15cc route for a few month and quickly realized that the four cycle engine needs a lot more displacement to be anywhere near as powerful, hence the 20 cc limit for the four cycle, when there was an engine limit in the F3A class.