Junkers G 31

https://en.wikipedia.org/wiki/Junkers_G_31

The Junkers G 31 was an advanced tri-motor airliner produced in small numbers in
Germany in the 1920s. Like other Junkers types, it was an all-metal, low-wing
cantilever monoplane. Compared to modern aircraft, only the corrugated duralumin
metal skin, so typical for Junkers aircraft, seems unusual. However, in the
mid-1920s all-metal construction and an aerodynamically 'clean' configuration
were remarkable.

Professor Junkers wanted to follow up on the commercial success of the tri-motor
G 24 with a new design that would be larger, more comfortable for passengers,
and simpler to operate and maintain.

The G 31 was the first Luft Hansa airliner to feature a flight attendant (Wagner
p. 264), who served food and drinks (which were not complimentary). This earned
the G 31 the nickname 'flying dining car' ('fliegender Speisewagen' in German).
Because of its large fuselage it was also called the flying moving van
('fliegender Möbelwagen' in German). Behind the cockpit were compartments for a
radio operator, baggage and an APU that provided compressed air for main engine
starting and drove a generator for electric power. The cabin was divided into
three compartments that held eleven regular passenger seats, four jumpseats for
passengers, a jumpseat for the steward, and an enclosed lavatory. Instead of the
passenger seats, ten beds could be made up for night flying. There was a baggage
and freight hold under the cabin. The wings had trailing edge flaps that reduced
the landing speed by ten percent (Wagner p. 267).

Professor Junkers originally requested the G 31 have landing gear that would
retract into the wings. After extensive wind tunnel experiments Ernst Zindel,
the leader of the design team, persuaded Professor Junkers that the gain in
speed provided by reduced air resistance, would not outweigh the increased
weight, cost and complexity of either retractable landing gear or simple wheel
fairings. The tailskid incorporated a roller, to avoid damage to grass
airfields(Wagner p. 262–263).

The intended powerplant was three Junkers L5 engines. When these proved too
weak, it was suggested to use the Napier Lion, considered to be the best aero
engine at the time ("the best engine for the best plane"). This however was too
expensive, especially since it would have had to be paid for in convertible
currency, not German Reichsmark. Most G 31s flew with foreign air-cooled radial
engines in the 500 hp range, which were licence-built in Germany (see list of
variants below)(Wagner p. 265–267).


Role
Airliner

National origin
Germany

Manufacturer
Junkers

First flight
1926

Primary user
Deutsche Luft Hansa

Number built
13

Originally, the G 31 had been intended to equip Junkers' own airline, Junkers
Luftverkehr, but this venture was merged into Deutsche Luft Hansa in 1926, and
the new airline purchased only eight G 31s, beginning operations in May 1928.
They were used on the long-range routes of Luft Hansa, particularly to
Scandinavia. They continued in this role until 1935, when replaced by the
Junkers Ju 52.

Four other G 31s were sold for freighting cargo in New Guinea. Operated by
Guinea Airways, one was owned by the airline itself, while the other three were
owned by the Bulolo Gold Dredging Company. Powered by Pratt & Whitney Hornets,
these differed from the G 31 airliners in having open cockpits, and a large
hatch in the fuselage roof to accommodate the loading of bulky cargo via crane.
In one particular operation, the G 31s were used to airlift eight 3,000 tonne
(3,310 ton) dredges (in parts) from Lae to Bulolo. Three of the aircraft were
destroyed in a Japanese air raid on Bulolo on 21 January 1942, and the remaining
aircraft was pressed into RAAF service ten days later. This machine
(construction number 3010, registration VH-UOW) was seriously damaged in an
accident at Laverton, Victoria on 31 October that year after it careened off the
runway and collided with and destroyed the Minister for Air's car. Although
judged beyond repair by the Air Force, it eventually returned to freighter use
in New Guinea for some time after the war.

Unlike the earlier Junkers G 24, the G 31 was not a commercial success, only 13
being sold, as opposed to 54 civilian G 24s (+30 military derivatives)(Wagner p.
267). Compared to the G 24 it offered passengers more comfort. Compared to the
more usual biplane airliners of the 1920s, the G 31 was faster, and its
all-metal construction made it safer. However purchase price and operating costs
were high. Instead of the newly designed G 31, a developed version of the G 24
might have sold better.

Specifications (G 31fo)

General characteristics
Crew: two pilots, one radio operator and one steward
Capacity: 15 day passengers or ten night passengers
Length: 16.50 m (54 ft 1 in)
Wingspan: 30.50 m (100 ft in)
Height: 6.00 m (19 ft 8 in)
Wing area: 102.0 m2 (1,097 ft2)
Empty weight: 5,250 kg (11,590 lb)
Gross weight: 8,500 kg (18,760 lb)
Powerplant: 3 × BMW-built Pratt & Whitney Hornet, 386 kW (525 hp) each

Performance
Maximum speed: 210 km/h (131 mph)
Cruising speed: 170 km/h (106 mph)
Range: 850 km (528 miles)
Endurance: 5 hours 0 min
Service ceiling: 4400 m (14,400 ft)
Rate of climb: 3 m/s (10 ft/min)





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