STEMME INNOVATIONS 

Unique in the world of sports aviation, STEMME is a synonym for innovative products that deliver performance at the highest level. Proven by world record long distance soaring flights, STEMME sets new standards right from the start. Creativity and state-of the-art methods for aircraft design, production and quality management are hallmarks of STEMME aircraft. For more than a decade, STEMME aircraft have delivered optimal flight performance and safety without compromising ease-of-use characteristics such as ground handling, ease of entrance, seating comfort, etc. The new STEMME-TSA family of Two Seat Aircraft expands on the company's history of break-through innovations in each of the following areas:

        Side-by-side cockpit and safety concept

Unique among high performance sailplanes, STEMME pilots enjoy side-by-side seating, a configuration common among power planes. This seating configuration offers numerous advantages.

        Drive Shaft - Propeller - Mid Engine

STEMME's most remarkable innovation is the patented propulsion design, consisting of a certified four-stroke aircraft engine mounted behind the cockpit, driving a nose-mounted propeller via a lightweight carbon fiber drive shaft. This light and cost effective drive shaft was brought to market in the early 1990s and enabled STEMME to position the engine in the middle of the airframe near the center of gravity with almost no cost or weight penalty.

No other powered sailplane design has combined the high performance of a sailplane with the practicality and convenience of a power plane. As a result, soaring was finally freed from local airfields and the requirement for ground handling support, creating a new class of gliders. Starting from convenient local airfields in the morning, owners fly under power to optimal soaring conditions anywhere within several hundred miles, soar all day, and still have time to return home the same day. The STEMME propulsion design makes high performance cross country soaring a convenient form of recreational, competition and record-setting flights.

The mid-engine layout offers numerous advantages. The pilot may transition between powered and soaring flight in seconds without moving any portion of the drive train. After shutdown, the engine remains safely out of the flow of cold slip-stream air, so there is no sudden thermal shock. The frontal drag is minimized yielding excellent handling qualities and optimized aerodynamics, resulting in high cruising speed and low fuel consumption.

For ultimate soaring performance and a glide ratio of  up to 50:1, the S 10 is equipped with the STEMME-RETRAC-PROP completely concealing the folding propeller inside the movable nose cone. The S6 and S8 will be equipped with electrical MÜHLBAUER constant speed propellers for high static thrust (for glider towing) and high cruising speeds. In feathered position they enable a glide ratio of 39:1 for the S6R with retractable gear.

Cooling air is drawn in from the lower front and exhausted up and rearward. This method of cooling is also environmentally friendly due to reduced noise emissions on the ground. The optional three blade MÜHLBAUER constant speed propeller in combination with a reduced propeller speed give an extra in noise reduction and more static thrust at the same. The result? A noise signature that meets the most stringent requirements.

From a maintenance point of view, the mid-engine layout also offers advantages. The S 6, & S 8 engines, together with their sub-systems are installed on a sub-frame as part of the center frame. As a result, the engine unit can be removed and replaced in 15 minutes, reducing maintenance and overhaul costs. Commercial operators, in particular, benefit from the ability to receive and replace complete STEMME certified propulsion units, minimizing downtime for overhauls and repairs.

As of 2002, more than 150 aircraft are operating throughout the world. While most are quietly enabling their owners to experience the shear joy of cross country soaring, others are using the aircraft to break longstanding records. Late in 2000, for example, Mr. Klaus Ohlmann set an astounding FAI-certified world record of 2.463 km (1,330 NM) in the category "longest distance’ in soaring flight using a STEMME S10VT.

In response to the overwhelming acceptance of the S 10 design, STEMME will offer a family of side-by-side motor gliders in the mid class segment – the S 6 and the S 8. The un-powered S 2 will also be available to address the demand for a side-by-side glider.

The overall conclusion: The clear benefits of the STEMME mid-engine layout are proven. Owners enjoy a host of advantages including improved performance, decreased fuel consumption and minimal noise levels.

        Landing Gear

Landing gear design is compromise. Weight and aerodynamic drag must be minimized, yet strength, ground handling and aesthetics have to be maximized. Once again, STEMME incorporates innovative design to address this conundrum to achieve optimal results.

The S 6 and S 8 will be available with fixed or retractable tricycle landing gear with steerable nose wheel. The retractable gear employs the well-proven S 10 electrical extension and retraction mechanism. Backup extension is provided by a manually activated gravity free-fall.

Spring and damping are realized by special non-linear elements, which contribute to safe and comfortable take-off and landings even on rough surfaces conditions. For strength, the main landing gear structure is directly connected to the center frame.

The wheel track of 2.0 m (6.6 ft) together and wheelbase of 2.0 m (6.6 ft) yields excellent ground handling. The comparatively large main wheels give extra flotation and shock absorption for unpaved runways. The hydraulic wheel brakes are taken from the S10 – with combined activation by a single hand lever.

The S 2 sailplane also enjoys a uniquely optimized landing gear design. The S 2 design is especially robust to meet the requirements of flight training. The main landing couples a large wheel 380 x 150 mm (15 x 5.9 in) with considerable shock absorber travel of 75 mm (3.0 in). A fixed nose wheel of 260 x 85 mm (10.2 x 3.3 in) yields easy ground handling. To improve safety, the main landing gear is placed at an aft c/g position, ideal for new students and gusty winds. Similar to other STEMME aircraft the wheel brake is activated by a hand lever mounted on the control stick. Pilots transitioning from the S2 to other STEMME aircraft will find the transition simple and easy, thanks to the common placement of controls and cockpit configuration.

        Fuselage

Designing optimal fuselage geometry for a single plane is a study in contradiction – to do so for an entire aircraft family is a real challenge to all disciplines of the development team.

The fuselage has to combine:

The STEMME team turned to state-of-the-art 3D-CAD software to find the best geometry for the TSA family. The final aerodynamic optimization, especially the fuselage-wing junction, was done by Prof. Boermans, known for his work in glider aerodynamics at the Faculty of Aerospace Engineering at Delft University of Technology in the Netherlands. The resulting design is highly aesthetic and, once again, confirms the adage that "an airplane that looks good flies well’.

Some of the low drag fuselage design elements include laminar airflow to the greatest extent possible. Much like a single seat sailplane, the side-by-side STEMME permits laminar airflow over a high percentage of the whole fuselage length. Aft of the pilot seats, the fuselage narrows to a slender tail cone to minimize turbulent wetted area. This reduction in diameter is done smoothly to avoid flow separation while also yielding sufficient space for all mechanical systems and a sizable baggage compartment.

The high wing position offers optimal wing aerodynamics, ensuring the wing upper side is free of fuselage influence. The fuselage camber line is optimized to follow the wing induced airflow. This is another step to minimize fuselage drag.

Close attention was given to the cabin frame to minimize gaps that spoil laminar airflow. Close inspection of the design reveals large radius gaps as a means to reduce airflow parallel to joint sections, a technique which avoids a large area of wedge shaped turbulent flow. This is another detail to minimize fuselage drag. Taken together, these and scores of other fine details in design and workmanship yield a remarkably low drag airframe which opens the door to truly high performance cross country soaring.

STEMME pioneered application of high quality paint to replace conventional high maintenance gel-coat surfaces. STEMME was the first glider manufacturer to use a paint finish instead of gel-coat. As anyone who owns a sailplane with a gel-coat finish knows; if the plane is flown regularly, the gel-coat finish deteriorates in a few years. The STEMME paint finish lasts many times longer and isn't as prone to surface cracks that plague gelcoat finishes.

        Polars and Wing Pressure Distribution

Manufactured to a tolerance of only a few thousandths of an inch, the STEMME-TSA wings are a work of art in themselves. Although of different spans, the S 2, S 6, S 8 will share the same basic wing geometry and flap design. For the new STEMME-TSA aircraft family new state-of-the-art wing, profiles were designed by Prof. Boermans at Delft University of Technology to obtain nearly ideal pressure distribution along the wingspan to minimize drag at all flap settings.

Special attention was paid to the fuselage-wing junction to minimize interference drag and special profiles were developed for the wing region closest to the fuselage to take into account the unavoidable turbulent airflow in that region.

Enormous attention was focused on flap design. When landing, the inner wing flap deflection is greater while the outer section is less. The resulting extra inboard high lift coefficient combines with more roll control for docile landing characteristics. Not merely for landing, however, properly designed sailplane flaps optimize flight performance throughout the aircraft speed range. The objective is to permit low minimum sink rate, high maximum glide ratio and low drag for high cruising speeds. This goal was achieved in the STEMME-TSA family of aircraft. When equipped with retractable landing gear, the ROTAX 914F powered S 6, S 8 motor gliders deliver astonishing cruise speeds in excess of 300 km/h (162 kt) TAS.

Flap travel for the S 2 has been carefully refined to permit highly competitive performance when the full range of flap configurations are used, yet excellent all-round performance when only using the 5º flap setting. The result is high enough performance to meet the expectations of the most demanding competition pilot, yet low workload for students learning to soar. This remarkable combination is especially well suited for flying clubs and commercial operators, because the S 2 is equally at home on basic training flights as the most ambitious soaring task. The S 2 is really a twin seat glider for everyone.

The result of all this aerodynamic fine-tuning is optimized aerodynamics over a wide range of flight regimes from narrow circling at low airspeeds in thermals to high speed cruising without need for cumbersome, high maintenance and expensive techniques such as active boundary layer control. Instead, owners of STEMME-TSA aircraft enjoy an ideal mixture of high performance and practical aircraft suited to daily use.

        Wing folding mechanism

All STEMME aircraft can be ordered with an optional folding mechanism, which reduces the wing span to 7.2 m (24 ft) [S 6 and S 8] or 9.2 m (30 ft) [S 2] or 11.2 m (37 ft) [S 10] with minimal effort. Dividing the wing at a span of 6 m (20 ft) results in a wing middle section of 100 kg (220 lbs) and two outer wings of 50 kg (110 lbs) each, which is similar to single seat gliders. This light weight allows one person to easily fold the outer wings. Strong enough to support the wing during taxi, the wing folding mechanism enables all ground operations to be performed single person, similar to that of single engine power planes.

        Stemme Folding Prop S10-VT (STEMME RETRAC) Click here

To restart the engine the nose cone is pushed forward and this also opens the cooling vents. Only when the engine is started do the propeller blades extend into the airstreams. Therefore, the S 10-VT suffers negligible drag or trim change during the restart period, and it can perform a normal glider circuit and landing if the engine fails to start. This is much safer than the situation of a fold-out engine motor glider which fails to start - becoming very dangerous very quickly.

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