The old Technopower engines and the Seidel really do have the ''look'' of the old radial.
I agree. I've also decided that the 7-cylinder Seidel 770 somehow looks more "scale" that the 9-cylinder 9-90 in terms of looking the part on a WWI model with a 9-cylinder rotary. The 990 is just too "busy" looking without enough space between the cylinders. Still, the Seidel is never going to be as scale in appearance as a top-notch dummy. One plus though is that, while a dummy engine has to sit in front of the engine which puts it too far forward in the cowl, one of these radials would sit right in the middle of the cowl where it's supposed to be.
What has always stopped me(aside from cost!), is the prop speed/rpm. Most the WWI rotary engines had an operating rpm of around 1200. This is what looks and sounds realistic.
The Seidel has an RPM range of 1000 to 6000 (with a 22 inch prop) and on a 1/4 scale Pup, for example, you'd probably only end up using about 1/4 throttle so you might very well get a pretty "scale" range of RPMs. But of course a radial isn't a rotary and doesn't sound like one. And in the end, it seems a bit silly to spend this much money for a "nice sound." For me the primary reasons for buying a Seidel would be:
1. The mock realism of having a functioning "round" engine (though still not a rotary and still not exactly scale).
2. The ability to swing a scale diameter prop without the expensive (and sometimes fussy) reduction gear.
And "real" to one person isn't necessarily "real" to the next.