The Hirth F23 2 stroke.

A few examples , with fuel injection and with carbruettors a cool muffler system.

I might pass on the pull start.

An F23 powered helicopter. If ever there was a great test for an engine, put it in a helicopter.

Some mounting systems and the specifications.

A rear view of the starter motor, fly wheel and fuel injection also the exhaust and engine mount on the SD-1.

The performance graph , these things are usually a bit of a yawn but this one has the fuel burn data which is useful.

It would be even more useful if they specified which carburettor they were using or if it was the fuel injected model.

Using 5000 RPM and a 46x46" prop turning at 2777 RPM would give a 102 MPH (90 Knots) cruse at 3 G/H or (11.35 L/H).

With the standard 6 Gallon fuel tank this would give 2H total flight time or 1H 15m with the standard 45m reserve.

BUT , with the addition of a 3 Gallon tank in each wing (3.5" dia x 72") would give 12 gallons total and 3.25 hours flight

time, plus 45 minutes reserve. 3.25 Hours at 100 MPH = 325 miles (About the limit of my endurance)