During the Airbikes' design process, the proof-of-concept aircraft was reduced to the bare minimum and the entire aircraft rebuilt using proven, conventional methods and materials. The open fuselage consists of two steel tube frame sections, screwed together behind the cockpit. This fuselage frame carries the parasol-style cloth-covered wooden rectangular wing, held by V-struts and equipped with flaperons that cover nearly the entire trailing edge. The fuselage frame ends in simple tube-frame tail surfaces at its rear end. At the front, an aluminium alloy rectangular tube holds the engine, well damped by rubber blocks. A GRP cowling covers only the upper part of the engine; below it the huge exhaust system of the Rotax is left in the open air. A steel tube taildragger undercarriage, optionally equipped with elegant GRP wheel covers, completes this robust, simple aircraft. If there is not much hangar space available, the wings can easily be derigged, then folded back to the fuselage and fixed there.

The Tandem Airbike and the single-seater Airbike are currently being delivered in kit form by the German dealers, pre-manufactured for fast construction. This kit includes all plans and materials, the steel parts come pre-welded and the wooden parts are prepared for assembly. The average homebuilder should take around 400 hours to complete the kit. For those who don't want to build the ribs, spars or connection parts, they can order the parts in pre-assembled form. All that remains then is just the final assembly, cloth covering and painting. Hans Schaller and Thomas Jülich also offer the 'Airbikes' ready to fly, but nearly all of their customers prefer doing some work on their own aircraft which saves them some money!

The cockpit seat is actually just a simple saddle-type arrangement, just like you'd find on a motorbike! It is mounted on the topside of the fuselage's steel tube triangle. As the pictures clearly show, the cockpit continues the minimalist approach with the only concessions to comfort being the horizontally adjustable backrest of the front seat and the narrow windshield. The bike-like rudder pedals are fixed left and right outside the fuselage structure there are even 'stirrups' that prevent the feet falling off the dainty pedal tubes.

In front of the saddle is a small instrument panel; on the Tandem prototype it is equipped with just the basic engine control instruments and an altimeter. The ASI fitted to the prototype is of the conical tube type, a device well known to anyone from the hang-glider scene. It is fixed to the left wing's strut and calibrated in mph. Obviously, the builder can choose how to design his instrument panel, and Thomas Jülich equipped his single-seater with a 'nearly IFR' instrument panel!

With the central control stick and the throttle placed beside it, the front cockpit appears almost conventional, while the rear pilot has to peer over the shoulders of the front pilot to see the instruments. Because both pilots are sitting so close together, there is no space for a conventional second stick between them, consequently the rear seat has a 'sidestick' positioned on the right-hand side. This allows even large pilots to achieve full control movements. The rear throttle is situated on the left fuselage side beside the saddle, as is the wheel brake lever, which is designed to be operated from both seats. While the two sticks are connected by pushrod tubes, the connection towards the elevator is made by a 'Bowden' cable. The prototype is also equipped with the optional electric elevator trim, mounted directly on the elevator surface. As the flaps are interconnected with the ailerons another, bigger electric motor moves the bearing point of the aileron pushrods behind the rear backrest.

The master switch, ignition switch and starter knob have been placed above the pilot's heads in between the root ribs of the wings, as has the switch for the flaps, which can be set to '-1, 0, +1'. All the switches can be reached from either seat. Beside the switches are the two transparent polyethylene fuel tanks, each containing up to 4.4 gallons of two-stroke fuel. They are visible through the open root ribs of the wings and each is equipped with a fuel cock. For refuelling, there are screw lids on each wing's surface. Obviously, this aircraft does not have a baggage compartment or any form of stowage area, even the map has to be fixed to the rear of the front backrest!

A Junkers Magnum 450 aircraft rescue system has been fixed behind the saddle (a BRS being mandatory on microlights in Germany). If activated in an emergency, its rocket shoots out towards the rear right side, pulling the parachute out. Including this system, the optional GRP wingtips and the wheel covers, this Tandem Airbike prototype weighs just 441lb. With a maximum permitted take-off weight of 904lb, this aircraft is one of the few two-seater microlights which can be loaded and flown legally with two 'average-sized' adults aboard, even with the fuel tanks filled.

Like the old Piper J-3 Cub, the Tandem Airbike has been designed to be flown solo from the rear seat, although Schaller plans to offer a rear ballast weight, permitting the aircraft to be soloed from the front seat if customers prefer this (less windy) position. To enter the cockpit, I had to swing my leg right over the front saddle to sit down on the rear one. I then put my feet into the rudder pedal 'stirrups' and strapped myself in using the two-part, four-point harness. The seating position is upright, with my legs spread wide around the backrest of the front seat, but it is not uncomfortable. Sidestick, throttle and the wheel brake lever (unfortunately without a locking mechanism for parking and engine starting) are easily to hand. However, to reach the handle of the rescue system to the right of the instrument panel, I have to loosen my right shoulder strap a bit. Its position will be changed for serial aircraft. Before starting the engine I strap on my helmet, as good noise protection is a must owing to the open seating position in the stream of air behind the propeller.

The 50hp Rotax two-stroke engine starts easily and runs quite smoothly, thanks to its well-damped connection to the aluminium alloy front boom. The tailwheel, directly connected to the rudder, permits precise and easy taxying and the wheel brake is effective. There is minimal risk of 'nosing over' when applying the brake, as there is a high load on the tailwheel. There was a crosswind at Kropp's grass runway and some turbulence caused by the forest at the windward side, so I decide to leave the flap position at '0°' to obtain the best aileron efficiency.

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