LS8-st: 15/18 Meter Standard-Turbo made by DG
a Report by Jochen Ewald in the “Segelfliegen” magazine of Sept/Oct 2005.
Some time ago LS developed a non-selfstarting hydraulically retractable engine, but only ten units were produced. DG has taken this development further by creating the LS8/18 from the LS8-s with a completely redesigned mechanically retractable engine now known as the Turbo LS8-sT.
For more than 10 years the LS-8 has been one of the most successful Standard Class sailplanes. Five years ago they started a new trend by increasing the wing span to 18 m, which proved popular with clubs and private owners, and which was followed by most well known sailplane manufacturers. Financial problems forced LS to close, and DG Flugzeugbau in Bruchsal undertook to continue service to LS customers, as well as the further development of the successful series LS-8 and LS-10.
As I get ready for a test flight of the LS8-sT prototype in Bruchsal everything looks familiar except for the engine. The configuration is basically the same as the LS8-s with a few differences from the old Schneider design. The big 5 undercarriage wheel combined with a strengthened wing structure allows a higher take-off weight of 575 kg in the 18 m configuration. It also increases the angle of attack on the ground compared to the original LS8 and results in an earlier lift-off.
|The instrument panel goes up together with the canopy and gives an unhindered entry. The canopy emergency release becomes possible with the complete pulling of both red opening handles.
Cockpit comfort was increased. A pocket in the side upholstery helps keep the cockpit uncluttered, and the batteries were moved from the luggage space to under the seat. So even in the motorized version an acceptable stowage space is available next to the fuel tank. The spoiler handle was equipped with a Piggott Hook which prevents the accidental deployment of the possibly unsecured spoilers The instrument panel is attached to the canopy for easy entry and exit and the ergonomically designed seating and cockpit arrangement are in accordance with the popular LS tradition, as goes without saying.
Pilots not familiar with the gear levers reverse operation (back means out) and the wheel brake on the rudder pedals need to take note.
New in the motorized LS8-sT: the compact DEI-NT engine control and operating unit at the bottom of the instrument panel, the fuel shut off valve on the right side of the canopy frame (the prototypes was a bit awkward to reach small grey knob, which will be better positioned in the production models) and the decompression lever needed for starting and stopping the engine is on the left side behind the spoiler handle.
The new wheel design is an improvement so that from the initial ground roll the airflow attaches to the wing and the ailerons respond immediately. The angle of attack on the ground is big so the LS8-sT lifts off on reaching flying speed together with the Super Dimona tow plane. The canopy does not quite reach as far down as usual with DG, but visibility is still excellent and the tow plane is clearly visible over the instrument panel even with low tow speeds. The undercarriage goes in and out easily with a smooth movement of the lever, and locking at either end is clearly felt and visible.
DEI-NT controls the engine of the LS8-st. It is positioned at the bottom of the fixed instrument panel.
After release I test the engine operation. The compact DEI-NT reduces the work load normally required for main and ignition switches so the location of the DEI at the bottom of the instrument panel does not present a problem.
At 90 kph main switch on, ignition switch on and the propeller appears in the mirror on the right side close to the canopy. The pictogram in the DEI shows the raised propeller. Now pull the decompression lever on the left side of the cockpit and accelerate to about 140 kph until the propeller turns firmly. Now close the decom lever and the engine starts and runs set optimal power. As soon as it runs properly speed is reduced to the best climb speed of 90 kph. 15 to 20 seconds and 100m are required for the start before climb is achieved for a worst case (colder engine not operated for while) the manual mentions a height loss of about 150m. Similar values are applicable to nearly all Turbos without an electric starter. The height loss required for a start must be added to the safe height required for the selection of a field and circuit height for an out landing.
Many pilots believe that regardless of the type of motor glider they can rely on a fail safe start of the engine. Accident statistics show quite clearly that this is a mistake. No engine ( even the much stricter requirements for airplanes with engines) can achieve a completely fail safe start reliability. A motor glider pilot is only safe when he keeps enough altitude in reserve to fly a proper circuit with the dead engine extended and keeps the reduced flying characteristics and capabilities in mind. (With luck hardly ever in an LS8-sT).
At a speed of 90 kph the engine runs at 5100 rpm and delivers about 1.25 m climb. Horizontal flight is possible with a continuous maximum of 5500 rpm at 140 kph. That gives a range of 220 km. Obviously it is more economical to use the dolphin method with intermittent use of the engine. That extends the full tank range to about 400 km. A maximum allowable short time engine speed of 6000 rpm guards against overreving when starting or short higher flying speeds.
Single seat standard class 15 m glider with retractable auxiliary power plant and wing tips to 18 m. Wing with fork and tongue connections and 2 main wing pins, automatic connections for ailerons, spoilers and water ballast release. Each wing has integral water ballast tanks with a coupled release for a total maximum 188 liter, filling through the release valves. The connection with the outer wingtips is with spring loaded secured slotted nuts, the outer ailerons connect automatically, the fuselage with (now with enlarged and more ground clearance) 5 inch retractable main wheel and a wheel brake coupled to the rudder pedals. 7,5 Liter water ballast tank in the fin to compensate the forward moment of the wing tanks, filling likewise through the release valves. Centre of gravity correction by a battery in the tail and fuselage front possible. Elevator with automatic connections by spring loaded secured slotted nut. Retractable 2 cylinder, 2 stroke SOLO 2350 engine with a directly coupled Technoflug KS-1G-079-L-050-W propeller, DEI-NT engine control unit and 17 liter tank with electrical filling pump in the luggage room.
In addition to the engine speed the DEI-NT also shows the fuel content, the power plant status (out, running or in), the outside temperature and the engine time to inspection. It also serves as an engine total time indicator and warns of exceeding engine parameters or potential problems.
Stopping the engine is also simple: at 90 kph switch off the ignition, and the engine retracts a bit. A pull on the decom lever quickly reduces the speed to 1000 rpm. After releasing the lever the propeller stops and the engine retracts a bit more while the propeller stopper enters into the propeller turning circle. A bit of a pull on the decom lever lets the propeller come to the stopper and the engine retracts completely into the fuselage and the bay doors close with an audible click Stopping and retracting the LS8-sT engine required only 18 seconds.
Flying the LS8-sT confirms its well known good characteristics. The 18m wing has an easy roll rate of 4.5 seconds from a 45 degree bank at 105 kph. The control balance at 90 100 kph is excellent, at slower thermalling speeds a bit more rudder is required to compensate for the negative turning moment of the 18m wings. At around 85 kph it thermals easily even in rough thermals and proves itself as one of the best climbers. The stall characteristics are outstandingly docile. Below 75 kph the controls begin to feel sloppy, at 73 kph a light shudder occurs that increases with the increased angle of attack until at 70 kph the LS8-sT goes into a light mush. Stalling while circling does not show a tendency to an uncontrolled wing drop. With spoilers out the behavior is similar but occurs at about 4 kph higher speeds. The ensuing mush is quite stable.
The approach flight path is easily controlled at a basic landing speed of 95 kph thanks to the effective Schempp-Hirth spoilers. In addition, a easily controlled sideslip allows very steep approaches. If fully held off the LS8-sT settles itself with the tail wheel just before the main wheel. The well sprung and enlarged main wheel evens out rough landing spots and there is sufficient load on the tail wheel to avoid belly scratching when the brake is applied a bit too enthusiastically. To use the pedal wheel brake the pedals have to be sufficiently rearward, or they must be adjusted backwards if necessary before the final flare. Benign characteristics and well balanced controls result in a pleasantly relaxed flight in the LS8-sT.
Many contest flights have proved the top performance of the old Schneider LS8s. The LS8-sT is not only a top performing competition sailplane but is also quite suitable for club operations, even as a first solo sailplane. The 18m wings make it eminently suitable for European weather conditions and the increased weight to 575 kg makes higher wing loadings for super weather possible. Compared to the pure sailplane the extra weight of the engine does not materially affect the flight characteristics Because the LS8-sT is not only an excellent cross country sailplane and is quite suitable for club operations it will keep its value for a very long time.
Control of the engine with the newly developed DEI-NT is in accordance with DGs proven philosophy of keeping the engine operation simple and effectively reducing the pilots work load by using electronics.
|Max take off weight(kg)
|Max waterballast wing(kg)
|Max waterballast fin(kg)
|Wing Loading kg/m2
|Power Plant SOLO 2350 2 cyl, 2 stroke
|Power 15,4 kW 22HP at 5500 rpm
Propeller drive direct
Tankvolume 17,3 l , 17 l ususable
Propeller 2 blades
Translation: Albin Schreiter, CDN