FK-11

Is the German FK-11 prototype a twin or a single? Yes. Twin propellers. Single engine.

With its side panels removed as for maintenance, the FK-11 belt drive system is revealed. A ballistic parachute system is installed aft of the engine.

A father and son design team, Otto and Peter Funk, are the brains behind Germany’s successful microlight company, B&F Technik.

Let’s check out the FK-11 ultralight.
How would you like to own a Mercedes-brand ultralight? Today you can’t, and maybe you will never be able to, but you may be able to purchase a slick little ultralight called the FK-11 that is well known to Mercedes. And if you want a Mercedes-powered ultralight today, one is being sold.
This month’s “Light Stuff” again ventures across the Atlantic to look at another fascinating aircraft coming from the European sport aircraft community. The pictures accompanying this column feature the FK-11, a prototype design from Otto Funk, lead designer for the German ultralight manufacturer, B&F Technik Vertriebs.
B&F is what Americans might call a family operation. Son Peter Funk runs the business. Otto is his father, who owns an engineering firm and works with Peter as B&F’s design team. Before starting his own enterprise, Otto was an engineer working for Airbus.
Twin-Prop FK-11
The FK-11 is a single-engine ultralight using two aft-mounted props that extend from the fuselage midsection on upward-angled supports. The pilot sits ahead of the wing in a smooth sailplane-like cockpit.
The FK-11 weighs 946 pounds, reports Otto. At this weight, it is well under the European ultralight limit of 990 pounds maximum takeoff weight. Made with a welded steel tube interior and a metal wing, FK-11 is conventionally built even though its lines have never been seen on any other ultralight I know.
With its 55 hp, the FK-11 manages better than a 100-mph cruise speed. But what makes it most impressive is its novel shape and rare powerplant.
FK-11 uses a three-cylinder engine developed by a Mercedes subsidiary for its really short Smart two-seat automobile. Quiet operation was mandated in the engine’s design, and Otto remembers that he once pushed the starter button again as he could not hear the engine running.
The engine is an important part of the low-noise package, but Funk also explained that locating the engine and prop aft greatly quiets it.
The FK-11 Smart engine runs through a dual belt drive system that Otto had to make himself. Funk had tried to fit a Raven gear drive, but he says the engine company would not sell the drive alone. Having his heart set on the Smart car engine, he was forced to make his own transmission.
Though Otto says he designed the FK-11 for a three-cylinder engine, he hadn’t really found the right combination until the Smart automobile came along.

Unusual Powerplant
Auto engines including Volkswagen, Subaru, Geo Metro and Honda have been used on several ultralights. Yet never to my knowledge has one been powered before by Mercedes. Talk about the right engine nameplate in a yuppy-oriented world! Bit this is somewhat less remarkable in Germany, its home country.
The three-cylinder, 55-hp, 145-pound, four-stroke engine is made for the tiny Smart car, a Mercedes joint venture that has become a mainstream automobile for space-tight Europe. In a recent trip to Germany, I saw many of these distinctive little autos.
Called the Suprex, Smart’s engine was created by a DaimlerChrysler subsidiary, Micro Compact Car (MCC). The developer’s engineers worked closely with Otto and report that as an aircraft engine, the Suprex has “significantly lower noise and fuel consumption… with the inclusion of an advanced control system.”
The engine was painstakingly designed for the Smart. The little turbocharged 600-cc engine develops peak power at 5250 rpm (a number quite close to the Rotax line of engines) and offers a maximum torque range between 2000 and 4000 rpm.
The control system automatically adjusts boost pressure, injection, and ignition to deliver a constant power regardless of altitude, says MCC.
The Suprex engine burns around 2.4 gph of premium unleaded auto fuel, which gives B&F Tecknik’s FK-9 ultralight more than a 500 mile range with two standard 5.8-gallon tanks. The company’s FK-9 model cruises about 115 mph and was recently featured in Flight International magazine for its cooperation with DaimlerChrysler.
Working with MCC engineers, the engine was carefully evaluated for use “above street level” and changed only to the extent that it replaced the auto’s sequential six-speed transmission with a 2.1:1 toothed belt transmission. Dual belts of the same construction are used on the unorthodox FK-11 prototype.
Even in the Smart car, the Suprex engine has dual spark plugs and, of course, these sufficed for aviation use. MCC says that development for light aviation use has the full support of Mercedes and especially the main Smart designer. In a country proud of its fine engineering, such statements are not made casually.
Although Suprex is a 55-hp engine while regularly employing its turbo, Funk says the engine can generate 65 hp for short periods like takeoff. He also indicated a more powerful engine is coming from MCC.
Arguably one of the main benefits is cost, reportedly less $6500, though production for aviation use is new and the figure does not include shipment nor a U.S. support network.

Sales Beginning
Though the Suprex engine is available now on the FK-9, the future of the innovative FK-11 has not been determined. It is a prototype to explore ideas; customer interest is what commonly drives an aircraft into production for an established manufacturer. B&F Technik is one of Germany’s leading builders of ultralights, selling a sleek folding-wing biplane in addition to the Cessna 150-like FK-9.
If you want Mercedes power today, you’d have to select the FK-9, and a kit system has not been approved for sales in the United States. But since engines for kit aircraft don’t need separate approval-and with a great brand name like Mercedes behind the Smart Suprex engine-I’ll bet we’ll see more German powerplants in the U.S. before long.