Motorgliders who want to upgrade their aircraft with a more powerful engine may well know Mainbullau airfield. At the airfield of this German city, south-east of Frankfurt, Rainer Korff and his company Korff & Co. have worked on optimizing a number motorgliders and light aircraft engines for a long time. Now the company's Luftfahrttechnischer Betrieb together with Limbach have finished the certification of the new L-2400 EFi. Thanks to an electronic fuel injection system the 4-cylinder water-cooled engine provides 8 HP more than its air-cooled brother.

L 2400 EFi inside of the Taifun engine room

Korff has a good name amongst motorglider pilots. Here the somewhat underpowered Fournier RF-5 and Puetzer RF-5b Sperber were fitted with a 80 HP strong Limbach L-2000 Twin carburettor engine. Limbach's largest engine, the L-2400 EB1 providing 92 HP, was certified by Korff for equiping the H-36 Dimona, the Grob 109-A and the Valentin Taifun. This has brought the performance of so called "first generation motorgliders" up to a more modern level.
Also by developing the L-2400 EFi-series Limbach and Korff & Co made a joint effort in introducing liquid cooled engines for motorgliders. Compared to the older air-cooled engines, the new liquid-cooled ones have become less noise pollutant and also thermal load during altering performance levels and airspeeds has been reduced strongly.

With a computer controlled electronic ignition and fuel injection system the L-2400 EFi provides 100 HP at 3000 rpm and still 90 HP at 2700 rpm. Because of this performance level there is certainly no need for a reduction drive. This saves maintenance time and money. Also high frequency vibrations as caused by reduction drives are avoided.
However, the larger engine also weighs a little bit more: All mountings, oil and cooling liquid together make a total weight of 91 kg for the 100 HP engine, some 7 kg more than the comparable 81 HP Rotax 912.

In Mainbullau we were able to make a test flight in one of the first motorgliders equipped with the new L-2400 EFi engine: a Valentin/TWI Taifun 2. With its MTOW of 850 kg this aircraft is one of the heaviest motorgliders available. In the old days the Taifun surely was the best touring glider in its class. Because of its higher weight and its tricycle retractable gear it was a little bit underpowered for a safe take-off on shorter runways. Therefore we thought the Valentin Taifun to be an ideal aircraft for testing the capabilities of the new engine. The L-2400 EFi is covered by a new cowling definitely more elegant than the air-cooled version. Because of the electronic ignition and fuel injection system there are fewer parts subject to damage or working loose. In the cockpit some innovations: The fuel pump switch also serves as master switch at the same time and the new ignition system makes there is no need for a choke and mixture control. Two pumps are placed underneath the co-pilot's seat providing enough fuel pressure. Only one pump is operated, the second one is switched on automatically in case of failure of the first one. Without fuel pressure the ignition engine doesn't run.

Certified for L-2400 EFi: Valentin Taifun. A more elegant cowling to this motorglider was constructed for the water-cooled engine.

Also new on the instrument panel is the emergency switch which turns off the computer controlled system and activates a simple emergency ignition program. This way the engine is not capable of providing maximum power with minimum fuel consumption, but it will take you home in a safe way.
A second battery is another safety feature. If the main battery runs empty the engine doesn't stop immediately: the automatic switch of ignition and fuel pumps to this spare battery is accompanied by a warning lamp on the panel. From then on there's still 20 minutes for the pilot to search for a safe landing spot.
The Taifun we flew has been equipped with a L-2400 EFi with single spark ignition, all that's required for a motorglider and, as experience has learned, all that's necessary too. But the engine has been designed for dual ignition by Limbach and if a customer wants this can be done.

 

Large capacity, little noise and vibrations
During wintertime the D-KRRK had been standing in the hangar for almost five months. Nevertheless the engine starts after a few turns without any extra help, also probably because the aircraft is fitted with special lead-gel starter batteries. A good decision! Already during warming-up the water-cooled engine runs very quietly. The electric controlled constant speed propeller (Mühlbauer) is adjusted to make 3000 rpm when starting.
With a light nose wind we accelerate at a fairly upslope runway at Mainbullau airfield. Despite the light rain we are airborne after only a short ground distance and with 3.5 m/s the heavy motorglider is ascending quickly. During ascent we leave throttle on full and reduce the L-2400 EFi to 2700 rpm. All along the ascent the engine runs at the right temperature. During touring flight the temperature even drops, something that will be overcome by a thermostatic value in the near future.

 

Injection nozzles at the cylinder head replace the carburettor and bring more power.

In case of an emergency: The "Engine-Emergency Switch" (white knob) can switch the computer controlled ignition into an emergency ignition program.

Noise levels inside of the cockpit are really low: A conversation with your co-pilot can be made with normal voice and while operating the radio there's no need for a headset. On top of that the engine is running almost without any vibrations at all. With this new Limbach the Taifun - at the moment- may even be the most quiet motorglider of the moment. During an official certification noise measurement it stayed 11 dB below the maximum level. Keep in mind that German standards for certification are very severe!
To cruise we reduced to 2600 rpm and 26 Inch Hg. A quick glance at airspeed and GPS showed us we were flying at 108 knots across the Odenwald.
During certification flights at 8000 ft with 75% of max power a cruise speed of 127 knots was measured. A comfort that few machines can provide, and if so most of them are more expensive Echo-machines.
Fuel consumption is kept very low, due to the computer controlled injection: Depending on weight and settings the L-2400 EFi swallows 12 to 18 litres of Super Plus or Avgas.
Touring and light aircraft scenes during the last years have been dominated by small cubic capacity liquid-cooled engines. With the L-2400 EFi Limbach/Korff have caught up in performance, power/weight capacity and torque curve. The new Limbach engines offer an amount of comfort and noise levels, up till now unknown in this class of aircraft. Also the overhaul period has been extended: right now this period is 1000 hours for the L-2400 EFi, but it is expected to rise to 2000 hours. Of course this is a weighty component in operational costs.
With the certification of the water-cooled L-2400 EFi for the Valentin/TWI Taifun 1 and 2 Korff company offers an appealing possibility to upgrade their motorglider. In case your looking for a used one, Korff has got some secondhand Taifuns that can be modified at customers wishes and specifications.

Brand-new Limbach: L-2400 EFiT, 130 HP and weighing only 104 kg.

A Turbocharger gives the extra plus. At 2600 rpm they still produce 120 HP.

Loaded Limbach: 30 HP extra
As this fliegermagazin-edition is being written the brand-new turbo-engine may well have had its maiden flight in a Grob G-109B: with 130 HP and an all up mounted engine weight of 104 kg, this engine can be described as a true power package. Even at 2600 rpm this variant still produces 120 HP. This turbo engine will give the Grob 109B (a widely spread motorglider, no longer in production) new possibilities, for instance as a towing aircraft. Also light motor aircraft are offered an attractive alternative with this L-2400 EFiT engine.

Jochen Ewald - fliegermagazin 5/99

 

This article originally appeared in German in "fliegermagazin 5/99". It has been translated for powerglidertaifun.de by powerglidertaifun.de with kind permission by fliegermagazin (www.fliegermagazin.de).

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