Bell L-39
American experimental aircraft
From Wikipedia, the free encyclopedia
The Bell L-39 was an experimental aircraft used to test the characteristics of swept wings.
| L-39 | |
|---|---|
| L-39-2 with fully swept wings | |
| General information | |
| Type | Experimental aircraft |
| National origin | United States |
| Manufacturer | Bell Aircraft |
| Status | Retired |
| Primary user | NACA |
| Number built | 2 |
| History | |
| First flight | April 23, 1946 |
| Developed from | Bell P-63 Kingcobra |
Design and development
After the end of World War II, the United States military took interest in German aerodynamic research into swept wings. To test the low-speed characteristics of swept wings, the US Navy contracted Bell Aircraft to modify two P-63 Kingcobras[note 1] as test aircraft for use by NACA.[2] These aircraft, assigned the bureau numbers 90060 and 90061,[note 2] were designated L-39-1 and L-39-2, based on Bell's code letter "L" and the aircraft's model number "39". Both aircraft were fitted with straight inner wing panels and 35 degree swept outer panels derived from the P-63E, both sections lacking dihedral.[1] A pair of cameras were mounted behind the canopy to film the airflow pattern, which was indicated by tufts of string attached to the wings.[3] Leading-edge slots could be bolted into the wings in different configurations. The main landing gear was fixed, with only the nose gear being retractable.[6] All armament was removed from the aircraft, and the rear canopies were blacked out.[2]
A ventral fin extension was fitted under the rear fuselage of the L-39-1 after its first flight.[2][3] During subsequent test flights of L-39-1 the center of gravity was found to be too far forward. To remedy the problem the fuselage was extended by four feet and a lighter propeller was installed. At the time, a surplus three-bladed propeller cost twice as much as a surplus P-39 Airacobra, therefore two P-39Q-10-BEs were purchased for their propellers.[2] L-39-2 was fitted with the fuselage extension and an even larger ventral fin extension from the start.[3]
Operational history
The L-39-1 made its first flight at Niagara Falls Airport on April 23, 1946, with Bell test pilot Alvin M. "Tex" Johnston at the controls.[2][4] Early flights revealed several handling problems, which were subsequently fixed with modifications to the fuselage and tail.[3] The L-39 was noted to have poor stall characteristics, stalling with little warning.[6] Different leading-edge slot configurations were tested, and pilots found that a 40 percent slotted wing improved stall characteristics. 60 and 80 percent slotted wings were found to have excellent stall characteristics, while 20 and 100 degree slots were unsatisfactory.[6]
The L-39 program was halted on August 26, 1946, and the L-39-1 was sent to Langley Field, where it was used for wind tunnel testing.[1] The L-39-2 was retained by Bell to support their X-2 program, being modified with a new fully swept wing of a design intended for the X-2.[1][3] On December 12, 1949, both aircraft were transferred to the Lewis Research Center before being sold for scrap in 1955.[4]
Variants
- L-39-1
- First aircraft
- L-39-2
- Second aircraft, later modified with fully swept wings.
Specifications (L-39-1, initial configuration)
Data from [1]
General characteristics
- Crew: 1
- Wingspan: 33.60 ft (10.24 m)
- Wing area: 250 sq ft (23 m2)
- Gross weight: 8,700 lb (3,946 kg)
- Propellers: 3-bladed, 10 ft 4.5 in (3.162 m) diameter
