RE: OS drops .32SX
I must take exception with the remarks about the OS .46AX design. It seems obvious that the author has not compared the design with that of the FX. I am attaching 3 photos so you can see the differences in the cylinder and head design. It is not a rehash of the older FX engine, but a new and different design for OS. The first time I saw this same type cylinder-head configuration was on a Super Tigre engine many years ago. I think the .91 still uses this design and a 4-bolt head.
In the first photo where both the AX and FX have cylinder heads, the FX is on the left and the AX is on the right. Note the light area back of the fins on front. This is the front transfer port. Notice it is wider on the AX. You'll also see that the head bolts go into the eages of the transfer port area. If they had used a 6-bolt head on the AX with the wide transfer port, the bolts would extend into the transfer area.
The solution is the method I mentioned I first saw on Super Tigre engines. Note in the 3rd photo that the cylinder of the AX on the right extends upwards above the cylinder block. On the FX, the cylinder sits down into the bloch and it flush with the top. Now look at the two heads. The AX head has a deep groove machined into it to fit down over the raised cylinder, giving a tight seal. The FX head sits generally flush with the top.
Works good on Super Tigre and on OS and doesn't need 6 bolts.
As for the rpm range of the AX engines, specifically, the lower rpm and higher torque of the AX series, I think OS is manufacturing to sell to the greatest number of fliers. Most people do not fly speed planes, not very many, actually. The really popular kit now are scale, acrobatic scale and warbirds, and 3D planes. Both of these types tend to drive the flier to a larger prop. If I am selling the most RC engines in the world, I figure I would aim right for the casual scale and 3D/fun fliers.