The ULF-1 single seat foot-launched sailplane was designed by Dieter Reich and constructed by Heiner Neumann of Germany. Designed for ridge soaring and marginal thermal currents (Microlift), it has full three-axis aerodynamic control. Its first flight was in November 1977; its first public appearance was in August 1978 at the 3rd International Hang Glider Meeting at the Wasserkuppe, the historic German soaring site.
Since that appearance different pilots on a number of ULFs have accumulated many hours of flight time. The prototype alone has more than 150 hours total flight time in 200 flights, most of them starting from foot-launch.
More than 40 ULFs are believed to have been completed and flown. Fifteen ULF-1s are in operation in Germany. The longest flight lasted six hours; the maximum distance achieved 140 km. Both of these flights started with a foot-launch.
In July 1980, the ULF-1 design received an airworthiness certificate issued by the German authorities, after all required calculations and tests had been provided by the designer. In 1983 the Australian authorities gave approval for the ULF-1 to be built and flown in Australia. ULF-1 is, as far as we know, one of the best-performing foot-launched aircraft to date.
The aircraft can be foot-launched from slopes of more than 15 degrees even at small wind speeds. The pilot supports the weight of the aircraft on shoulder straps and uses the side stick for lateral control. The self-launch is rather simple and does not require any special skill. As the pilot starts the take-off ground run, the elevator stick should be in slight nose-down position to lift the horizontal tail. The moment the pilot feels a pronounced seat pressure; the control stick is pulled back until the aircraft lifts off. After take-off the pilot retracts his legs and puts them on rudder pedals. A sliding slat-type construction behind the pilot’s back can be released in flight to provide a seat.
Because of a low sink speed (0.8 m/s at max. take-off weight) and its good manoeuvrability, ULF-1 is sensitive to marginal thermal conditions. The best L/D of 16:1 is at around 55 km/h (about 34 mph). To reduce the aerodynamic drag of the fuselage, hinged doors have been fixed to the front superstructure of the fuselage. They are kept open during take-off ground run and closed manually after lift-off. For “record-breaking” flights a closed Plexiglas windscreen is recommended.
It is estimated that both measures, the “landing gear” doors and the windshield, improve the L/D by ten to fifteen per cent, resulting in an L/D of 18. Since this glide-performance is also at a relatively high speed, the average cross-country cruising speed, including time for circling is at least fifty percent higher compared with conventional hang gliders.
Landing the ULF-1 is done on a nose skid located beneath the pilot’s seat. The airplane can also be launched by bungee rope (down hill), winch, car and air tow.
Infolge der relativ geringen Sinkgeschwindigkeit (0,8 m/s), den kleinen Kurvenradien und seiner guten Wendigkeit ist mit dem ULF-1 auch das Segeln an kleinen Hängen möglich. Die beste Gleitzahl von 16 liegt bei einer Geschwindigkeit von ca. 55 km/h. Um den aerodynamischen Widerstand des Rumpfes zu verringern, wurden an der vorderen Rumpfstruktur aufklappbare Bodentüren angebracht. Sie sind während des Startvorgangs geöffnet und werden nach dem Einziehen der Beine manuell geschlossen. Für Leistungsflüge wird die Verwendung einer geschlossenen Plexiglas-Kabinenhaube empfohlen.
Eine Rechnung hat ergeben, dass mit beiden Maßnahmen zur Verringerung des Widerstandes, die beste Gleitzahl auf 18 erhöht werden kann. Da diese Gleitleistung bei einer relativ hohen Fluggeschwindigkeit erzielt wird, errechnet sich eine mittlere Überlandfluggeschwindigkeit – einschließlich Kreisen in der Thermik – welche mindestens 50 Prozent höher liegt als die konventioneller Hängegleiter.
Die Landung erfolgt auf der Kufe. Neben dem Fußstart lässt sich ULF-1 auch mittels Kfz-Schlepp, Drachenfliegerwinde, UL-Schlepp und Gummiseil von der Kufe weg in die Luft bringen. Er kann von den vielen Drachenfluggeländen und UL-Flugplätzen gestartet werden.
The three-axis aerodynamic control greatly reduces the pilot’s workload compared to a conventional hang glider with its two-hand yoke bar, and frees one of the pilot’s hands.
Dynamic pull-ups to about 20 degrees result in a smooth nose-down movement after the wing has stalled. In turns or in turbulent air, there is some wing drop in a stall. Recovery is properly and promptly achieved with opposite rudder. The loss of height is usually less than 10 meters (30 feet).
For sailplane pilots there will be no problems flying the ULF-l. However, experience with conventional hang gliders is not sufficient to handle the aircraft. At least some solo flight experience in conventional gliders is recommended.
ULF-1 is specially suited for selfbuilders. The basic construction materials are spruce, birch plywood and balsa wood. The airframe is covered with doped fabric. For hinges, fasteners and fittings, aluminium, steel sheet and fibreglass/resin are used. Steel tubes are employed only for the control stick, control parts in the cockpit area and rudder drive.
The ULF-1 prototype is equipped with a ballistic recovery system for both pilot and aircraft, located immediately behind the main bulkhead and activated by means of a mechanically released pull-out rocket.
For road transport, the two-piece wing can be detached. In addition, the horizontal tail can be removed. The aircraft can be taken off a trailer and assembled in about ten minutes.
A plan pack is available comprising of:
A complete set of 31 blueprints (14 sqm) most of them are full scale, including full scale computer generated lines for wing and tail.
A 37 page construction manual (with sketches) including a list of materials with their American, British and German designations, in addition many photographs, showing construction details.
An inspector’s test and check list.
An 18 page flight-/operation manual.
A cut-away drawing (A3).
All descriptions and manuals are in English language (metric units).
The cost of materials amounts to about EURO 2500. The aircraft can be built in about 1000 hours. Kits or materials are not supplied.
In Germany all ULF-1 airplanes constructed under license are considered airworthy and permitted to be flown, provided the following requirements are met.
1. Construction supervision by an authorised inspector, according to the check-/test instructions as written in the ULF-1 construction manual, followed by a detailed final inspection.
2. Condition inspection by an authorised inspector every two years.