to fully retract. Cruise climb needs a fuel burn in the 25 lph range, with a modest 300 fpm up at 90 knots. Despite having three fuel tanks, fuel
SOARING While the S12 may be a more than competent
management is straightforward with a panel-
cross-country tourer, it is first and foremost a
mounted selector valve. The electric fuel pump is
superlative glider. The appeal of the S12 is the
switched off when passing through 1000 feet.
ability to shut its engine down and soar wherever
To accelerate to best cruise speed, the flaps are
and whenever you wish. To do that, the propeller
deflected upward, or in a negative configuration.
is moved into takeoff mode and the power reduced
The flap positions are zero, 5, 10 or 15 degrees
to keep the CHT and oil temperature cool. With
down, with 15 being optimum for landing. But they
the cowl flaps fully open, the Rotax cools quickly,
also reflex 10 degrees up from the streamlined
which helps to reduce the risk of overheating
position. This cuts drag at high speed by reducing
during engine restart. Before shutdown the
unnecessary lift and aligns the fuselage more
airspeed is reduced to approximately 54 knots.
closely with the relative airflow.
Once slowed and cooled, simply turn the
Cycling the propeller into cruise pitch mode (or from cruise to takeoff) takes approximately two minutes. As a genuine cross country tourer, the S12 has easy and benign handling. Stemme has
Solar PV cells keep batteries charged while gliding.
added an electric pitch trim to the S12, which makes it easy to trim for level flight. The flight controls are pushrod driven and the rudder system uses cables. Breakout forces are reasonably light – especially considering the number of connections to the distant ailerons. The rudder pedals are adjustable, but the seating position is not. Once in cruise, the beautifully streamlined S12 has impressive speed and good range. Stemme claims the S12’s maximum cruise speed at 140 knots true at 10,000 feet. Vne is a low 142 KIAS which is a tight safety margin, especially considering the forces on those long wings. Cruising in a no-wind scenario, you could fly for 950 nautical miles. The Rotax can burn as little as 20 lph and it’s approved to run on both mogas and avgas so fuel supplies should not be a problem. November 2020
65