Swiss aeronautics engineer August Hafeli went on to develop a series of military biplane aircraft for Swiss Air Force consideration, this after coming over from the A.G.O. concern of the German Empire. His experience in working on the German C.I and C.II twin-boom biplanes (both detailed elsewhere on this site) led to the similar Swiss-originated "DH-1" (also detailed elsewhere on this site). The move to the DH-2 saw the twin-boom concept dropped in favor of the more traditional inline arrangement and this led to the successful DH-3 armed biplane scout of 1917 - total production yielding 110 units.
Against the backdrop of World War in Europe, Hafeli continued to push designs such as the "DH-4" of 1918, another conventional biplane approach with single-engine performance and fighting function centered around an operating crew of one. This entry relied on the successes and strong qualities of the preceding DH-3 but did away with the two-man crew and its reconnaissance role.
Its construction was completed in the early part of 1918 and the fighter exhibited expected fighter qualities such as an over-under biplane wing arrangement, open-air cockpit, and fixed, wheeled undercarriage with tailskid. The fuselage was given slab sides and the engine was installed at the nose in the usual way - the Hispano-Suiza HS-41 8-cylinder, liquid-cooled engine of 150 horsepower driving a two-bladed, fixed-pitch propeller at the nose. The upper wing member had a section of its central trailing edge cut away for improved vision for the pilot.
Dimensions of the aircraft included a running length of 19.7 feet, a wingspan of 32.1 feet, and a height of 8.5 feet. Empty weight was 1,410lb against a Maximum Take-Off Weight (MTOW) of 1,950lb. Armament was a single 7.45mm machine gun fitted ahead of the pilot and synchronized to fire through the spinning propeller blades. Construction was of the typical fabric-over-wood approach of the period.
Eidgenoessische Konstruktionswerkstaette (K+W) headed manufacture of the one and only airframe completed. This example was flown in 1918 and tests were had from May until August of that year - after which the design was shown to have unsatisfactory performance and handling. K+W took the specimen back for modification and additional testing but the aircraft never flew in a meaningful way again.
As tested, the DH-4 showcased a maximum speed of 92 miles-per-hour and a range out to 190 miles - able to fly for some 4.5 hours. Rate-of-climb was 890 feet-per-minute and 6,000 feet could be reached in fourteen minutes.
(OPERATORS list includes past, present, and future operators when applicable)
✓Air-to-Air Combat, Fighter
General ability to actively engage other aircraft of similar form and function, typically through guns, missiles, and/or aerial rockets.
✓X-Plane (Developmental, Prototype, Technology Demonstrator)
Aircraft developed for the role of prototyping, technology demonstration, or research / data collection.
SYNCHRONIZED / INTERRUPTOR GEAR
Automatic weapons are synchronized to fire through the spinning propeller blades via special mechanical gear arrangement.
Addition of more mainplanes to enhance inherent agility, providing a tactical edge in tight engagements.
Inherent ability of airframe to take considerable damage.
Can accelerate to higher speeds than average aircraft of its time.
EXTENDED RANGE PERFORMANCE
Capability to travel considerable distances through onboard fuel stores.
19.7 ft (6.00 m)
32.2 ft (9.80 m)
8.5 ft (2.60 m)
1,433 lb (650 kg)
1,951 lb (885 kg)
+518 lb (+235 kg)
(Showcased structural values pertain to the Hafeli DH-4 production variant)
biplane / over-under / straight
Design utilizes a dual-plane wing arrangement in which one mainplane member is seated above the other; biplanes enhance agility at the expense of added drag.
Dual mainplane configuration seating the members in an over-under fashion and poisitoned at different points along the fuselage.
The planform involves use of basic, straight mainplane members.
(Structural descriptors pertain to the Hafeli DH-4 production variant)
1 x Hispano-Suiza HS-41 8-cylinder liquid-cooled inline piston engine developing 150 horsepower driving two-bladed, fixed-pitch wooden propeller at the nose.
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