Page 29 - MFW June 2024

side. I’m pretty sure the ever popular OS
Max- H series of engines are all Cross Flow
and therefore eligible for 25 second runs in
Duration events. (OS engines in the –FSR
series introduced in 1973 are Schnuerle
ported and have 25% to 30% more power)

So how does Schnuerle porting work?
This from Wikipedia;
In 1926, the German engineer Adolf
Schnüerle developed the system of ports
that bears his name. The ports were
relocated to both be on
the same side of the

Cylinder and ports viewed from above

cylinder, with the transfer port being split Finally I recommend a very good source of engine test reports if you are
into two angled ports, one on either side of looking to find the best motor for that new duration machine and to
the exhaust port. A deflector piston was no figure out its port configuration.
longer required. The gas Flow was now a
circular loop, flowing in and cross the piston Try This Spectre Flight site:.........................................
crown from the transfer ports, up and https://sceptreflight.com/Model%20Engine%20Tests/Index.html
around the combustion chamber and then
out through the exhaust port. It has many old and newer engine test reports. Some clearly state the
porting arrangement as well as showing RPM verses Propeller results
With Schnuerle porting, the piston crown and older reports even have full dynamometer results giving torque and
may be of any shape, even bowl shaped. power curves. Those were the days.
This permits a far better combustion
chamber shape and flame path, giving If still unsure about an engine then please contact the Vintage SIG and
better combustion, particularly at high ask for a ruling.
speeds. All the best until next time.

Any modern higher performance sport Allan Knox
engine with ball raced crank and front shaft
induction is almost certainly going to have
Schnuerle ports to give it that spritely
performance belying its low priced origins. A V intage
look in the exhaust port will likely show a flat
topped piston and definitely no built in gas
deflector. Thunder Tigers, SCs and ASPs Give it a go
and the likes come to mind. These relatively
powerful but cheap sport motors get 20
second run for duration events.

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