ORIGINAL: edaf1246
I am getting ready to start building my third airplane. My initial instructior has recommended that I use an OS 90 4 stroke engine, in lieu of the OS 55AX I was planning to use. I keep hearing that the sound is better with a 4 stroke, and that they are more fuel efficieint, but is that really worth over $100 more for the engine? The kit manufacturer suggests a .40 to .60 2 stroke or a .60 to .90 4 stroke, so both are within the suggested limits. If I go with the 4 stroke, what are the differences I should expect from my previous experience with 2 storke engines? Thanks.[sm=50_50.gif][sm=50_50.gif]
You need to compare more than just price and sound. And the difference in fuel efficiency isn't even noticed by most.
The FS91 is listed as 24 ounces.
The 55AX is listed as 14 ounces.
They both list basically the same horsepower.
There is $105 difference in the price.
My first experience with 4strokes was using an OS71 FS in an airplane that wound up with a 46AX 2S in it's place. I discovered that the FS was a b****h to start in that airplane. I discovered that the FS really didn't like my 10% fuel. All the FS guys told me right away that FSs take more nitro to run good. So I bought some more expensive fuel and discovered that b***h still didn't like to start in that airplane. I discovered that the airplane flew almost exactly the same with either. The FS used a bigger diameter prop doing basically what the 2S did with a smaller prop. That didn't strike me as mattering at all. After running the FS awhile in another plane, I was told by a FS expert that I really ought to adjust the valves and I'd get more power. I did. And I didn't. I adjusted them and I didn't see any difference. The guy says I didn't waste my time because you need to learn how to adjust valves anyway. Yeah?
If I sum up what I got out of the FS experience, I'd say.......... I got part of a gallon of more expensive fuel. The backfiring FS ruined a couple of plastic spinners that would have lasted on the 2Ss for years. I've got some nice big props now. I've learned how to adjust FS model engine valves (I enjoy adjusting automobile valves lots more.). I've got some spare FS plugs that cost me way more than 2S plugs cost. I've got a spare FS that I might someday use if I find a model that needs more noseweight than expected, but doesn't need any extra power to go with the weight.
Ask yourself if the model you're considering is probably going to need 10 ounces of nose weight?