4 Stoke Experience

Recently, I went to visit some friends and both had retrofitted planes with Saito 56 engines. Both were using ST 60s previously. Both engines ran very well and the planes performed quite well. As well as before but quite different. I flew both and I have to admit, I'm starting to understand why when I have asked others how they liked flying the 4 stroke, I get a sort of mixed response.

First, both planes had a gob of power. As much or more than with the ST60. But the power is quite different. I had a lot of problems at first getting the planes to turn where I wanted. Not because of any trim problem or really anything to do with the planes themselves, but because my reflexed are tuned to the power going on and off. With the 4 stroke, that didn't happen. You launched the plane and the power you have is the power you have. Everywhere and always. We were flying at altitude (about 3000 feet) and it was hot (about 85) and a bit windy (not too bad, 15-20 mph). The most noticable different came in overheads. The ST60 will turn the power on into the wind so that the speed changes, while noticable, don't seem to effect the way the plane flies. With the 4 stroke, the planes really slowed down into the wind. There wasn't any noticable change in line tension and I had control all the way, but you really had to wait for the plane to power through the wind. Coming down hill was pretty noticable too. The plane would climb into a loop (or whatever) and the speed coming toward the ground was pretty much the same. No really noticable change in air speed. I wouldn't say from the experience that the 4S was better, but it's different. did some things very well and others not so well (as they were set up).

Seems there's a lot that can be done with props. We messed with a lot of props. From an APC 12x6 to a number of B,Y&O 12 and 13, 4, 5 and 6s. and a couple of others. Much like a piped engines, if you can let the engine rev a bit and lessen the pitch, the results are changed. Air speed and power. I won't say it's better, but you get a change. Just depends on what you're comfortable with. These guys are using a sort of aluminum venturi mount in place of the carb with the ability to change venturis much like a two stroke. I plan to mess with mine quite a bit with different venturis and props.

I don't think the 4 Stroke signals the death of other types of power or anything, but they are definately different than running a 2 stroke. I'm anxious to mess with mine to see if I get similar results a sea level. The guys I flew with did some very clever tank, muffler and crankcase venting. Interesting how you can change the run significantly with changes in how you go about venting this stuff.

Randy,

I have about twenty flights or so with an OS 40 Surpass in a profile Force. I had previously run an OS 40 FP. I really enjoy the change of flight characteristics with this particular airplane and setup. I too have tried a few tank variations and vent setups and am amazed at the change in the engines performance from setup to setup. I was able to fly this airplane with each motor on the same day and that was when I really got to see the big differences. It held line tension better and, for me at least, I felt more in control. I felt more comfortable with lower bottoms and sharper squares. I realize that it is a little more nose heavy than I origianlly had it set up for which may attribute some of the handling changes.

I'm having fun and looking forward to burningg more fuel and building another plane for a four stroke.

Later,
Zuriel