Close this search box.

Junkers J.I / J 4

The Junkers J.I (manufacturer’s name J 4) was a German “J-class” armoured sesquiplane of World War I, developed for low-level ground attack, observation and army cooperation.

It is especially noteworthy as being the first all-metal aircraft to enter mass production, the aircraft’s metal construction and heavy armour was an effective shield against small arms fire over the battlefield.

It was an extremely advanced design for the period, with a single-unit steel “bathtub” running from just behind the propeller to the rear crew position acting as armour, the main fuselage structure and engine mounting in one unit.

Engine access was provided by armoured steel panels, one on either side of the nose.

The armour was 5 millimetres (0.20 in) thick and weighed 470 kilograms (1,040 lb) and protected the crew, the engine, the fuel tanks and radio equipment.

The flight control surfaces were connected to the aircraft’s controls by pushrods and bellcranks – not with the usual steel cable control connections of the era as pushrods were less likely to be severed by ground fire.

There was a significant size difference between the upper and lower wings the upper wing had an area of 35.89 m2 (386.3 sq ft), over double the area of the lower wing – 13.68 m2 (147.3 sq ft).

This is a form of biplane known as a Sesquiplane.

The aircraft had two fuel tanks with a capacity of around 120 litres (32 US gal).

The main tank (divided in two for redundancy) was supplemented by a smaller, 30-litre (7.9 US gal) gravity tank.

This was intended to supply fuel to the engine by gravity feed in the event of an engine fuel pump failure; it contained enough fuel for thirty minutes on full power.

There was a manual fuel pump for use when the gravity tank was empty.

The aircraft could be separated into its main components: wings, fuselage, undercarriage and tail, to make it easier to transport by rail or road.

A ground crew of six to eight could reassemble the aircraft and have it ready for flight within four to six hours.

The wings were covered with 0.19-millimetre-thick (0.0075 in) aluminium skin which could be easily dented; great care had to be taken when handling the aircraft on the ground.





9.1 m (29 ft 10 in)


16.00 m (52 ft 6 in)


3.4 m (11 ft 2 in)

Wing area

49.4 m2 (531 sq ft)

Empty weight

1,766 kg (3,893 lb)

Gross weight

2,140 kg (4,718 lb)


1 × Benz Bz.IV,

149 kW (200 hp)


Maximum speed

155 km/h (97 mph, 84 kn)


310 km (193 mi, 168 nmi)

Service ceiling

4,000 m (13,123 ft)


1 × trainable, rearward-firing 7.92 mm (.312 in) Parabellum MG14 machine gun;

Five, 200-round drums of ammunition.



Share on facebook