The Ju-87 Stuka's bomb-release trapeze mechanism and design

Engineering Description -- Ju-87 Bomb-Release Trapeze

One of the most innovative and successful aircraft of the early World War II era was the German Junkers 87 "Stuka" dive bomber that actually pioneered the concept of dive bombing as a military aviation tactic (Crosby, 2007; Jackson, 2003). That tactic turned the aircraft into an airborne form of highly accurate artillery because it allowed pilots to dive directly onto their targets and to release their bombs to follow the trajectory of the aircraft before pulling out of the dive. The Ju-87 "Stuka" was the first dedicated dive bomber in the world and its design specifications reflected two critical advances: the autopilot pullout feature and the swing-out bomb trapeze (Crosby, 2007; Jackson, 2003). The first was necessitated by the fact that the intense G-forces of the vertical dive often caused pilots to black out (Reinhart, 2008); the second was necessitated to allow the plane to release a bomb in the vertical orientation without the bomb hitting the propeller. To ensure that the bomb would clear the propeller arc, the Junkers designers installed a trapeze device that held the bomb and swung away from the fuselage to allow the bomb to clear the propeller arc on release (Crosby, 2007; Jackson, 2003).

II. Description of Whole

Generally, the apparatus consisted of two parallel longitudinal arms braced by diagonal and perpendicular struts. The bomb was secured in between the longitudinal arms by a hinge and the aft ends of the arms were hinged to the aircraft fuselage in a manner that allowed the pilot to activate the bomb release cable and drop the bomb when the device swung out away from the aircraft under the natural pull of gravity. The device was constructed of aircraft-grade aluminum and painted to match the underside camouflage battle paint of the fuselage. The aircraft was used extensively and very successfully by the Nazi Luftwaffe throughout the Spanish Revolution in 1937 and in the initial campaigns of World War II in Poland and France (Crosby, 2007; Jackson, 2003). However, the Stuka was a relatively slow aircraft that proved incapable of defending itself effectively against the superior Allied fighters and interceptors such as the Hawker Hurricane and the Super Marine Spitfires employed by Britain. It was withdrawn from the air war for control of British skies in the summer of 1940 but used in the Eastern Campaign in Russia (Crosby, 2007; Jackson, 2003).

Figure 1 below depicts the typical installation and configuration of the bomb trapeze on the aircraft.

Photo 1 (Jackson, 2002)

III. Description of the Parts

The main parts of the bomb trapeze are listed below and correspond to Figure 2 that follows the parts list.

1. clevis

2. jack

3. bolt

4. housing

5. tranverse rod

6. spring bolt

7. knurled nut

8. tranverse cross-support

9. resting plate

10. rubber buffer

11. ball heads

12. cable holder

Figure 2 (Jackson, 2002)

The bomb release trapeze operated according to very simple mechanical principles and relied on gravity. Upon activation of the bomb release lever, a simple cable-catch attached directly to the exterior of the bomb released the hook and allowed the bomb to fall under its own weight. The trapeze prevented the bomb from detaching until the device had swung out 180 degrees from the aircraft fuselage at which point notches on the inside of each longitudinal tranverse arm (visible in Figure 1 near the bomb attachment) allowed the pins holding the bomb to the tranverse arms to fall away from the tranverse arms.

V. Conclusion

The Junkers Ju-87 "Stuka" was the world's first operational aircraft designed for the role of dive bomber. During testing, it became clear to the Junkers design team that the traditional bomb release fixture in which bombs were attached directly to the fuselage of the aircraft would require alteration to avoid having the bomb strike the aircraft's propeller as it passed the aircraft in the vertical flight orientation. The bomb release trapeze allowed the bomb to be carried in the traditional configuration for aerodynamic purposes but to be safely released without the risk of striking the propeller. It was an innovative design that allowed the Stuka to become a devastating tactical aviation weapon and a precursor of all modern dive bombers that followed it.