ORIGINAL: ThumbSkull
ORIGINAL: NM2K
ORIGINAL: shaggy48
I'd like to replace the OS 46 LA on my tower trainer 40 and would love to put a 4 stroke on it. I do have a brand new Saito FA-56 looking for a home. But I just cant see how I could mount the 56 without some serious modifications mostly because of the way the carb sticks out the back of the engine a good inch or more. Also the throttle lever is on the opposite side of the engine unless. I could easy enough re-route the throttle linkage to the other side but the carb sticking out the back seems to be a real show stopper. Are all small 4 strokes made this way? I really like Saito engines at the moment and I know the 56 would overpower the trainer but it would be nice to fly the trainer again with a little more power and a reliable engine. I know I could go with a 2 stoke like the OS 55 AX but from what I've read, they seem just as problematic (as the LA) so I'm not impressed with OS at the moment.
Looking for suggestions for a reliable replacement for the 46 LA.
TIA
Shaggy
The Saito .56 will be lucky to make as much power as your OS .46LA two-stroke. Four-strokes are not as powerful as two-strokes of the same displacement. The .56 Saito might have enough of a displacement advantage to come close to matching the .46 two-stroke, but certainly not more powerful.
Lots of folks mistake the better slow speed performance obtained when swinging larger diameter/lower pitched props for more horsepower. Put the same prop on the OS .46 LA and be prepared for a surprise. Yes, you MUST retune the two-stroke for the larger prop before passing judgement.
You could cut a notch in the firewall to accept the carburetor that projects rearward from the four-stroke engine. You won't need as large a fuel tank for a four-stroke engine, so the rear projecting carb won't be a problem when it interferes with the fuel tank. Get a smaller fuel tank.
I'm not familiar with the trainer that you are flying. The above advice was meant for a model that utilized wooden crutch bearer mounts. If your model uses a bolt on mount, simply buy one that fits the four-stroke and fit her up. Good luck.
Ed Cregger
Many people confuse HP with thrust. A Saito 56 will have plenty of thrust for that airframe.
You could put a 3 horsepower pylon engine on there and get less thrust than a 56 Saito.
The Pylon engine uses RPM to get high HP numbers with a small prop.
The Saito 56 will use a large prop to give a low HP number but will have greater thrust.
More horsepower makes more thrust every time, when the proper propellers are chosen. I said in my post to mount the four-stroke's large prop on the OS .46LA and watch it out turn the four-stroke, which will provide the same or more thrust.
If you're a mild type of flyer that floats around at half throttle most of the time, you might not notice the difference in power between similarly sized two and four-strokes. You could even begin to believe that the four-strokes better throttle response makes it a stronger engine You could, because after all, your model is already grossly overpowered. But when it is time to takeoff from a dew moistened wet grass field, the extra power provided by a two-stroke of near the same displacement will impress you. Just do what I do - use a larger four-stroke! <G>
Ed Cregger