We Fly: Stemme S12

An impressive way to soar.

Soaring is quite unlike any other kind of flying. Plunk yourself down in an open field on a warm, sunny day, as I did last fall, and watch a hawk, wings outstretched, wingtips moving only slightly to adjust the flight path as they trace seemingly endless patterns across the sky in search of a meal. Natural soaring is silent, so quiet, in fact, that a hawk circles unnoticed unless eyes happen to turn skyward.

In an airplane, soaring is often a silent activity as well, once the airplane leaves the ground. But for pilots who get to try it, soaring is equal parts science and emotional experience in a continual search for the next thermal of rising air required to keep their airplane aloft.

A glider, or sailplane — the terms are interchangeable — is often towed behind a powered aircraft to become airborne before it’s cut free. After that, making it back to the original airport or to some distant locale is pretty much up to the skill of the pilot in the cockpit. Misread the weather or lose track of the best thermals and glider pilots might find themselves putting down unexpectedly in an open field along the way — what’s known as landing out. At that point, the chase crew normally springs into action to retrieve both plane and people.

Flying a sailplane variant like one of the German-manufactured Stemme motorgliders reduces off-airport-landing anxiety considerably because the airplane carries a Rotax engine in case the weather gods play tricks on even the sharpest of soaring enthusiasts.

The high-performance Stemme S12 I was invited to fly last fall hides its 115 hp turbocharged Rotax in the center of the fuselage behind the pilot. Of course, the engine doubles for the takeoff power that frees the pilot from the need of a ground crew or even a towplane, making it the best blend of both worlds. Once the S12 is airborne and the Rotax is shut down, the propeller slips into an adjustable nose cone that completely removes it from the slipstream, morphing the aircraft into a true touring sailplane.

I don’t hold a sailplane pilot certificate. In fact, this was my first launch in a sailplane of any kind. As if flying a motorglider like the Stemme S12 wasn’t unique enough, my chance to soar like an eagle began from Montrose, Colorado’s regional airport at the western foot of the Rocky Mountains. Those hours I spent over a weekend with the S12 and Stemme demo pilot and instructor Wes Chumley took us right up close to the granite that, until that day, I’d only spied out the window as I floated over at FL 410. But rather than a hindrance, being a powered-aircraft pilot all my life and a Midwestern flatlander to boot probably made me the ideal candidate to evaluate the airplane. Chumley was just the fellow to offer a beginner a solid look at the soaring experience in the Stemme, having spent 300 hours showing off the S12 to pilots and enthusiasts around the United States over the past year.

For those unacquainted with the American Rocky Mountains that divide the United States into west and east, the few-billion-year-old mountain range stretches nearly 3,000 miles, from New Mexico northwest through Colorado, Wyoming, Idaho, Montana and on into British Columbia, with mountaintops reaching nearly 14,500 feet. My flight coincided perfectly with the foliage’s change of color on the ground. But the Rockies are also known for extreme weather conditions — including winds — along with an uncanny ability for everything to change on short notice. Of this, I knew very little.

While the surface winds at Montrose tend to be mild, all sorts of things happen once they strike the up-sloping terrain and the jagged peaks along the mountain rims. The resulting updrafts and downdrafts can lead flatlanders into trouble, but they’re what soaring pilots live for. After a few conversations with the owners of earlier Stemme models such as the S10, the consensus was that the company has evolved the earlier and already impressive airplane into the S12, a truly magnificent sailplane.

Stemme S12
The Stemme’s cockpit is compact yet incredibly comfortable. Philip Powell

Inside the S12

The wing of a true soaring aircraft differs vastly from that of a powered aircraft, and the S12 is no exception, with a whopping 82-foot wingspan, only about 12 feet shorter than that of a Gulfstream G550. In the tradition of making certain the Stemme motorgliders can be handled by one person alone, the wings of the S12 fold backward toward the tail after a bit of unfastening work. The resulting shape, tipping the scales at 2,000 pounds, will then fit into a 40-foot T hangar small enough to hold a Mooney.

That big S12 wing delivers an impressive 53-to-1 glide ratio, perfect for the airplane’s mission of duplicating the soaring I’d watched that hawk demonstrate. That translates into the aircraft moving forward 53 feet while losing only a single foot of altitude. Try that in your Cirrus SR22.

The S12 carried through some design elements from the S10, such as the electrically operated retractable landing gear, but placed the new wheels 6 inches farther apart to improve crosswind handling. As a nonsoaring pilot, I found the flaps to be a bit of an oddity until Chumley explained the system that brings the airfoils into use when soaring. The flap positions are zero, 5, 10 or 15 degrees down, with 15 being optimum for landing. But they’re also incredibly handy “if they’re set at negative 10,” Chumley said. At that point, they’re reflexed 10 degrees up from the streamlined position. This cuts drag at high speed by reducing unnecessary lift and aligns the fuselage more closely with the relative wind.

Unlike the earlier Stemmes, the S12 is equipped with a single 31.7-gallon fuel tank hidden in the fuselage behind the cockpit. At 55 percent power, the Rotax will burn about 3.4 gallons per hour. By mixing powered aircraft time with soaring, the S12’s range can be enormous despite being officially listed as only 950 nautical miles. At 10,000 feet, the S12 will speed along at upward of 140 knots true.

The aircraft’s 12-volt battery can be charged by a set of solar panels embedded in the outer fuselage behind the canopy to extend the use of avionics during flight. Also nestled near the solar cells is the opening to a rear baggage compartment capable of holding 44 pounds of goodies, turning the S12 into a true cross-country soaring machine. In case a couple of hefty pilots happen to choose the S12, the aircraft is equipped with a water ballast system to make moving the center of gravity rearward a snap. The S12 also includes provisions for two optional oxygen bottles for high-altitude flight.

The cockpit seats two in a side-by-side configuration that turned out to be perfect for Chumley to keep an eye on me as I learned the simple yet unique aspects of soaring, such as pulling those flaps negative to increase overall lift. With the side-by-side seating, each pilot can easily reach everything in the cockpit.

The wraparound bubble canopy makes visibility in all directions excellent, and each side of the canopy offers a small sliding window to allow in some outside air under slipstream pressure.

Optional avionics in the S12 include an LX soaring computer with eVario, a nifty device that helps the pilot locate and remain inside those invisible thermals needed to remain aloft. An AHRS can also be added to the Dynon EFIS-D10A display. Other options include a Garmin GPS, a Mode S transponder, a compass and a Flarm, a device that functions like a TCAS to point out other similarly equipped soaring aircraft nearby.

The wait for a new Stemme S12 is currently about nine months. It can be had for a U.S. price of $349,000 to $369,000.

Stemme S12
The initial part of the soaring experience focused on finding the most exotic terrain to crisscross, a strategy that turned out to work pretty well for enhancing the entire flight. Philip Powell

Come on Aboard

Climbing aboard the S12, assuming some wonderful ground-support person ahead of you already unfolded the wings, demands a little training, which Chumley happily provided. Because the Stemme’s bubble canopy is hinged at the front, I learned the trick to getting aboard while wearing the required parachute was to back up to the left side of the fuselage at the cockpit first and then pull myself up with two arms before allowing my butt to gently slide backward into the pilot seat. Coming out of the cockpit, the process is essentially reversed. The S12 includes a pair of quick-jettison handles to blow the canopy in case of an emergency.

The angle of the seat struck me at first as too reclined, but once I was able to stretch my legs out beneath the instrument panel it became clear that all the switches and controls, such as the flaps and speedbrakes, were within easy reach. The flight controls are connected to a short stick that sits between the legs of each.

The aircraft I flew, German registry D-KSIZ, featured the Dynon EFIS unit with an AHRS, Garmin GPS and the LX soaring computer to support the few other basic airplane instruments: an altimeter, airspeed indicator and vertical-speed indicator. After a thorough preflight, starting the Rotax on the ground first required pulling the red propeller dome handle to be sure the blades were clear, opening the fuel cock, turning the propeller switch to takeoff and cranking the starter. The cowl flaps were used as needed to keep the Rotax warm.

Taxiing the S12 is similar to moving any taildragger on the ground using a combination of rudder and wheel brakes. Pilots new to the airplane also need to remember there’s quite a bit of wing sticking out just behind them when they taxi, so avoiding narrow taxiways near parked airplanes is a must.

Before takeoff, I ran up the Rotax 914 to check its operation. Max power on takeoff to take advantage of all 115 horses should indicate about 5,500 to 5,600 rpm. With takeoff flaps set to 5 degrees, the fuel pump switched on and the propeller also set for takeoff, the airplane was ready. Taxiing onto Runway 31 at Montrose with very light local winds offered me a 100-foot-wide surface — just enough to keep the wingtips over the runway. With the airport already sitting about 5,700 feet above sea level, Chumley and I planned to climb to about 12,500 feet after departure.

Stemme S12
At soaring speeds of around 65 knots, a Stemme pilot and passenger have time to take in the beauty of the nearby terrain thanks to the impressive visibility possible through the large canopy. Philip Powell

Soaring with Eagles

As I brought the Rotax up to full power, I kept the aircraft heading straight up the runway with the rudder pedals, adding a bit of forward pressure on the stick around 45 knots to raise the tail and improve visibility over the nose. With a little back pressure on the stick the S12 left the ground at 60 knots. Chumley suggested the best rate of climb speed at 62 knots. Once we had 100 feet or so between the runway and us, I raised the gear.

We departed the traffic pattern, climbing in the general direction of Telluride, about 35 miles to the south. Out of 1,000 feet, I pulled the power back to max continuous of 5,400 to 5,500 rpm. I quickly noticed that the S12 is not the kind of airplane you fly with your feet flat on the floor. Those big wings need some help in the turns, with an adequate amount of rudder to keep the turns coordinated. Once I caught on to the airplane’s demands in a turn, however, the S12 handled well.

The September day I flew could not have been more beautiful, with the colors beneath us just beginning to change as they prepared for the coming winter. The crisp air, about 50 degrees Fahrenheit on the ground, and the rain that passed through the previous evening produced visibilities of at least 25 miles. We kept climbing as I tried some steeper turns with more rudder to get a feel for the airplane. Before I realized it, we were through 12,000 feet and the time had arrived for the big power switch, as in switching off.

Once I leveled off, the airspeed picked up to just over 80 knots as Chumley took me through the shutdown procedure. Actual shutdown requires the aircraft to be flying slower, so I slowed to about 55 knots by reducing power to idle, leaving the cowl flaps open. Once the engine cooled down a bit Chumley told me it was time to shut down the engine. For soaring pilots, this is no big deal. For me, though, the thought of turning off the only good engine seemed more than a little odd. But switch it off I did, and the propeller quickly stopped with a gentle pull on the propeller brake handle. Once I’d nudged the prop to the closed position, I pulled the dome closed as well and the prop vanished.

It took me a few a minutes to realize we were soaring and that the Stemme’s big wing kept the airplane aloft with almost no loss of altitude. The cockpit grew very quiet, except for some occasional radio chatter on the Montrose unicom frequency. I tapped the fuel gauge, gently reminding myself we had plenty of gas and the potential for power if we needed it. Transitioning from glider to powered airplane can actually happen in as little as five seconds with an experienced pilot at the controls.

“Now what?” I asked Chumley.

“We just fly,” he responded matter-of-factly. And we did just soar for the next hour and a half as my sailplane indoctrination continued. It didn’t take long to get used to the quiet in the cockpit, with just the sound of the wind passing around the canopy, as Chumley explained the search for clouds that might produce the thermals we needed to remain aloft. He showed me how the LX navigation computer with eVario came in handy. The unit emits a beeping sound that rises in frequency as the aircraft enters an updraft. Want to stay there? Turn as needed to keep that little baby beeping at the same frequency. It did make me wonder how sailplane pilots without an LX found thermals, but I assumed that kind of knowledge was a few lessons down the road.

The Stemme S12 includes an electric trim tab. S10 pilots who’d tried it said it almost sells the airplane on its own. Our demo airplane included an autopilot that I only tried for a moment. True cross-country fliers told me they were excited about the option, which would offer just the break they needed on long flights. Hand-flying the S12, I found it to be rock-stable even in the bumps.

Despite truly breathtaking views everywhere through the canopy, I found that flying near the hills, the ones with huge chunks of rock sticking out in all directions, took a little getting used to. Headed southeasterly at one point, Chumley suggested we reverse course. With the nearby rocks staring back at me out the left window — at least they appeared that way to me — I began a right turn before Chumley stopped me. “We can turn left and still clear the hill by quite a bit,” he said. I entered a 40-degree left bank and watched the S12 appear to almost pirouette around a point below. Chumley was right. We did have plenty of room left.

By my second flight the next day, I was shutting the engine down like a pro, although skimming the tops of the hills is probably an acquired taste. The view out the canopy is indeed breathtaking, and the silence aloft will offer most pilots an opportunity to experience flight like never before.


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