FVA 1 “Schwatze Düvel”

The “Schwatze Düvel” was the first glider built by the FVA. On the occasion of the first Rhön glider competition in 1920, some students under the leadership of Wolfgang Klemperer and Professor Theodore von Kármán decided to take part in the gliding competition and started the construction of the “Schwatze Düvel”. This was based on the fundamental ideas of aircraft designer Prof. Hugo Junkers, who was teaching at the TH Aachen at the time, and the result was a two-skid low-wing monoplane. The Structure was made of wood and covered with black Fabric.

Technical director Wolfgang Klemperer reported on the FVA’s first aircraft in the “Flugsport” magazine 1920 (edition 23):

“Decisive for the design and success seemed to us to be great maneuverability and control efficiency in connection with sufficient inherent stability. These requirements led to the choice of a cantilever, monoplane with a skid frame growing out of its wing and a cantilever tail unit growing out of its fuselage. The number of non-load-bearing, drag-only elements has been kept to a minimum, and these parts have been most carefully clad and streamlined. All transitions have been made as smooth as possible. The construction material used is almost exclusively wood, in the form of a consistently executed plywood:truss construction. There is no tension wire anywhere on the aircraft. Sheet metal fittings are also avoided. Only the clamps with which the tail can be separated from the tailplane and the attachment of the trailing edge cord to the rib ends are made of sheet aluminum. All other joints are made with cold glue, using shims and shims where necessary.

The main part on which the whole machine is built is the wing framework. The wing is undivided for greater strength and lighter weight. The tail end was made separable from the front part of the fuselage to allow for rail and road transport. To take advantage of the overall height of the thick airfoil, three spars were arranged. In place of the largest airfoil height was a particularly strong spar designed as a recessed plywood box girder, joined by a front and rear spar each designed as a double-T girder. The main spar still had five times the safety if it had had to carry the entire load on its own. With a span of 9.50 m, it weighed 7.5 kg.

The ribs have an outwardly decreasing airfoil height and are similar in shape to those of Junkers airplanes. The innermost rib has the unusual thickness of 0.42 m at 1.90 m length. All the ribs together weigh 3.74 kg. They are artfully inserted through the recesses in the spars and their webs are glued to the spar webs with special strips. The frontal pressure is absorbed by a diagonal strut construction. A special system of spatially diagonal straps gives the framework excellent stiffness against torsion. Instead of a leading edge, the part of the wings in front of the front spar is covered with cardboard. Seen from the front, the wings show V-shape. In fact, they are slightly bent in the manner of bird wings.

The plan of the wing is trapezoidal. Ailerons of 0.75 m are hinged to an auxiliary spar, which show a slight bend on the outside. One aileron flap weighs 870 g! It is dimensionally rigid without pretension. The complete, fully covered wing has a surface area of about 15 m and a weight of only 24 kg. A particularly fine black voile fabric was used for the covering, which was impregnated with a special collodion-containing agent used here for the first time and weighed just under 90 g/m² at 6 kg/cm tensile strength. The impregnation proved excellent in the wet weather on the Rhön.

The driver’s seat is installed between the main and front spars and rests mainly on the latter. The stick, made of duralumin tubing weighing 130 g, is mounted for all-round movement with a hollow steel ball weighing 46 g in a hollow spherical shell ring of 32 g machined from aluminum alloy. The joint is attached to a pyramid-like plywood support on the front spar. The foot lever for the rudder control is assembled hollow and weighs 150 g with great strength, including the sheet aluminum foot rests. The fuselage nose, which was built so strong that it also protected against rollovers, carries a clad body of bamboo skeleton. The fuselage leading edge, which grows out of the wings, ends behind the trailing edge of the wing in the plywood separating bulkhead.

The landing gear bodies are designed in a somewhat peculiar manner, growing out of the wing spars without lateral support. They have proven to be of excellent strength and allow an extremely comfortable landing on the all-round rubber-sprung ash runners. Their completely streamlined fairing ensured the lowest possible air resistance. An unfavorable influence of the same on the directional stability has not been shown.

The tail is supported by a low spur formed from canes tied together. The continuous elevator, weighing 1400 g, and the rudder, weighing 600 g, are mounted on duralumin pins in duralumin bushings and are easily removable. The control cables can be disconnected on peculiar, very safe snap hooks and released with safety pin-like steel spigots on the control arms without the need to release the turnbuckle safety device made with steel wire. Disassembly or assembly of the entire tail, which incidentally weighs only 11 kg complete, can be accomplished in 2 minutes by three men. For road transport, the main part of the apparatus could be driven transversely on a specially built two-wheeled cart.

Takeoff was accomplished by pulling out a rubber cord looped around hooks at the rear skid ends, which the auxiliary crew kept in their hands after takeoff. With an empty weight of 62 kg and a wing loading of about 9 kg, the machine took off with the guide already smoothly in 4 m/s wind. On the other hand, it kept very stable even in the strong gusts of the last Rhön flying days.The excellent visibility, the correct position of the center of gravity, the good control sensitivity and maneuverability, as well as the good characteristics of the thick airfoil in fast and slow flight make it a type of extremely pleasant flight characteristics and suitable for sailing experiments by utilizing gust energy as well as for training.”