Gropp wren

Gropp wren
Type:	Motor glider
Design country:	German Empire
Manufacturer:	Gropp
First flight:	1930
Production time:	1930
Number of pieces:	1

The Gropp Wren was a motor-powered glider developed in the Weimar Republic , only one of which was built.

development

Herbert Gropp designed this motor glider in 1930 during his studies at the Chemnitz State Academy for Technology in order to be able to provide the members of its flight engineering working group (FAG) with an aircraft for practical training. He completed the building on his parents' property in Siebenhöfen near Geyer . As a drive, he decided on a motorcycle engine from JAP , which developed 9 HP at 1200 rpm and initially powered a pneumatic screw made of duraluminium that was adjustable on the floor , but Gropp soon decided to replace this with a wooden propeller. The construction essentially consisted of the hull boat with the engine in the rear area and the tail unit connected to the hull by struts . A sprung runner served as the chassis. The glider could still be completed in 1930 and Gropp carried out the first flight of 200 m length at a height of about 1 m at Chemnitz Airport using a rubber rope launch . Since Gropp was only in possession of the glider license A and his aircraft was also not licensed , the airport authorities forbade him to make any further attempts. He therefore assigned it to FAG Chemnitz, which named it Wren in a ceremony on December 7, 1930 in the presence of the Academy's professors .

Gropp successfully completed his studies in March 1931 and then took up a job in the test department of the DKW -motorenwerke in Zschopau, where he succeeded in arousing interest in the wren in August Prüssing , chief engineer of the racing department , so that the latter provided him with a self-designed boxer engine as a new drive, which weighed just 17 kg with the same power as the JAP engine. The FAG students made a new wooden propeller and made some changes to the glider; an additional strut was drawn in from the rear of the fuselage to the fin to strengthen it . Modified in this way, the wren was flown in public on September 27, 1931 by Hans-Joachim von Hippel, a former fighter pilot of the First World War , in front of an audience at the Chemnitz airfield. The wren proved to be completely self-launching and stable in flight.

After von Hippel's experiences on these flights, the following year the aircraft received modified tubular steel ailerons and plywood planking for the leading edge of the wing . Flights were no longer carried out, however, and the wren, who was placed in the premises of the Chemical Institute, showed serious storage damage after some time due to penetrating moisture, which attacked the glue joints. Finally, in May 1933, a wing was dismantled to be used as visual material for the academy. This also meant the end of the wren who, apart from Gropps' brief maiden flight in 1930, had only made ten flights with von Hippel. However, it later served Hans Wünscher, who also worked at FAG Chemnitz, as a suggestion for the construction of the C 10 motor glider .

construction

The wren was a braced shoulder-decker . The fuselage consisted of a tubular steel framework offset with wood , which was partly covered with fabric and partly covered with wood. The cabin was covered by a molded hood, which, although aerodynamically clinging to the contours of the fuselage, offered a very limited view of the front. The engine was located behind the pilot in the middle on the rear edge of the wing, the associated drop fuel tank was integrated in the tensioning tower above.

The wing was designed in two parts and consisted of a wooden frame with a main and an auxiliary spar . The leading edge of the wing was initially lined with cardboard , which was later replaced by plywood. The tail unit was attached to the fuselage and the rear wing spar by two struts. Due to the lack of rigidity of the fin , it was later reinforced with an additional strut that ran towards the lower fuselage. The landing gear consisted only of a skid attached to the underside of the fuselage with six suspension struts.

Technical specifications

Parameter	Data
crew	1
span	13.00 m
length	5.85 m
height	2.5 m
Wing area	15.0 m²
Wing extension	11.3
Wing loading	14.6 kg / m²
Power load	24.4 kg / hp
Preparation mass	≈130 kg
Takeoff mass	220 kg
1. Drive	an air-cooled two-cylinder - two stroke - V-engine J.AP (600 cm³) with adjustable two-bladed Duralumin- or rigid Holzluftschraube (⌀ 2.35 m)
2nd drive	an air-cooled two-cylinder two-stroke boxer engine DKW Prüssing (586 cm³) with a rigid wooden propeller (⌀ 1.6 m)
power	both 9 HP (7 kW)
Top speed	55 km / h
Cruising speed	50 km / h
Minimum speed	39 km / h

literature

• Frank-Dieter Lemke: Positions of a German aerospace engineer. Herbert Gropp was only 32 years old. Self-published, 2nd edition, Berlin 2015, ISBN 978-3-95735-032-9 .