The Bell L-39 served as an experimental aircraft designed to evaluate the properties of swept wings.
Following the conclusion of World War II, the United States military became intrigued by German aerodynamic research on swept wings.
In order to assess the low-speed characteristics of swept wings, the US Navy enlisted Bell Aircraft to modify two P-63s as experimental aircraft for the National Advisory Committee for Aeronautics (NACA).
These aircraft, identified by bureau numbers 90060 and 90061, were designated as L-39-1 and L-39-2, a departure from the typical Navy naming convention, with the “L” denoting Bell’s code and “39” representing the aircraft model number.
The modifications included straight inner wing panels and 35-degree swept outer panels based on the P-63E, both sections lacking dihedral.
Cameras were installed behind the canopy to capture the airflow patterns, which were visualized using tufts of string attached to the wings.
Additionally, leading-edge slots could be attached to the wings in various configurations.
The primary landing gear remained fixed, while only the nose gear was retractable.
All weaponry was removed from the aircraft, and the rear canopies were blacked out.
Following the initial flight of the L-39-1, a ventral fin extension was installed beneath the rear fuselage.
However, subsequent test flights revealed that the centre of gravity was too far forward.
To address this issue, the fuselage was lengthened by four feet and a lighter propeller was put in place.
Due to the high cost of a surplus three-bladed propeller, two P-39Q-10-BEs were acquired for their propellers, as they were more affordable.
The L-39-2 was designed with both the fuselage extension and a larger ventral fin extension right from the beginning.
Variants
L-39-2
Adjustments were incorporated from the outset.
Additionally, L-39-2 functioned as a test platform for the Bell X-2’s 40-degree wing design.
L-39-1
Subsequently, the team proceeded to NACA at Langley for wind tunnel testing, which yielded a wealth of valuable data.
Sources
U.S. Experimental & Prototype Aircraft Projects: Fighters 1939–1945-B Norton.
The American Fighter from 1917 to the present – E Angelucci.
Bell Aircraft Since 1935-A J Pelletier.
Bell P-63 Kingcobra, Xfl-1, P-39-Monografie Lotnicze 59-J Tomalik.
Warbird Tech 17, P-39-P-63 Airacobra & Kingcobra-F A Johnsen
