The FL-23 prototype was designed and built as a private venture, it was a high-wing cantilever monoplane with an all-moving tailplane mounted at the top of the fin. It had a fixed tricycle landing gear and powered a 225-hp (168 kW) Continental E225 piston engine. It had room for a pilot and observer in tandem; the observer had an unusual acrylic plastic enclosure to give an all-round visibility.

The US Army issued the specification for a two-seat liaison and observation monoplane and the prototype was entered into the competition. During trials the aircraft was badly damaged in a flying accident when it lost its tail, and was withdrawn from the competition. The competition was won by the Cessna 305A which became the L-19 Bird Dog.

Powerplant: 1 × Continental E225, 235 hp (175 kW)
Propeller: Hartzell 7 ft (2.1 m) diameter
Wingspan: 33 ft 4 in (10.16 m)
Length: 28 ft 4 in (8.64 m)
Height: 8 ft 1 in (2.46 m)
Wing area: 277 sq ft (25.7 m2)
Airfoil: NACA 4412
Empty weight: 1,500 lb (680 kg)
Gross weight: 2,450 lb (1,111 kg)
Fuel capacity: 60 US gal (50 imp gal; 230 L)
Maximum speed: 133 mph (214 km/h, 116 kn)
Cruise speed: 118 mph (190 km/h, 103 kn)
Stall speed: 38 mph (61 km/h, 33 kn) (flaps extended)
Range: 485 mi (781 km, 421 nmi)
Service ceiling: 19,500 ft (5,900 m)
Rate of climb: 1,180 ft/min (6.0 m/s)
Crew: 2

John Thorp was interested in armed light aircraft and in 1948 he demonstrated the prototype Sky Skooter at Fort Bragg. At the start of the Korean conflict Thorp sold his basic armed lightplane concept to Wendell and Maurice Fletcher. The result was the FD-25 series. Developed by the Fletcher brothers and John Thorp it was aimed at a perceived need in the US armed forces for a cheap and lightweight counter insurgency (COIN) attack aircraft.

The prototype FD-25, N90802, received the green light from the Fletcher management on 1 November 1950. Five engineers, including Thorp, and five engineers were assigned to the project. The prototype flew on 14 April 1951. The single seat FD25 was manufactured from Dow magnesium rather than aluminium. According to Thorp was “economically marginal because of the extra processing, equivalent to anodising, that was required to resist corrosion”.

The FD-25A two-place version was begun before the single-place flew. The aircraft, N90609, had a magnesium wing and aluminium fuselage. Heavy navigation equipment resulted in a critical aft c-of-g condition that contributed to the FD25A crashing during flight trials in 1952, killing several Fletcher employees.

It was the two-place version that was built in Japan.

Fletcher then took nine months to complete the all-aluminium FD-25B N91316. Two 30-calibre machine guns were imbedded in the wings, mounted outboard of the fuel cells and firing outside the propeller arc procured on bailment from the office of Admiral Richardson, then Chief of Naval Aviation. Each gun had space for 1000 rounds of ammunition.

Thorp, who made the initial flights in all the FD-25s, also fired the first in-flight rockets on the range at Inyokern, California. In preliminary ground firing, the cap on the back of the 5-in HVAR rockets ejected with such force that it damaged the stabiliser. The rocket rails were then moved farther outboard.

The plane was to depend on surprise attack and was built without armour plate or self-sealing tanks. The FD-25 was created to stop Russian T-36 tanks used by the North Koreans.

The FD25B undertook very successful demonstrations with the US armed forces. The FD25B was a performer and was enthusiastically supported by US military personnel but unfortunately received no US Government support.

Senator Barry Goldwater flew the experimental FD-25B solo, as did Chuck Yeager.

The FD25B armament consisted of a pair of wing mounted racks for two 33-gallon napalm tanks. Additionally two 250 lb. fragmentation bombs and up to 40 2.75 inch folding fin air rockets of four 5.0 inch heavy rockets or twenty 80 mm Oerliken rockets could be fitted.

Fletched ceased production after three examples to then concentrate on the development of the FU-24. However, further FD25 production was undertaken under license in Japan by the Toyo Aircraft company.

The first Toyo example, a FD25B, was flown in March, 1953 and soon after sales of four FD25A and four FD25B were made to the Royal Cambodian Air Force. These were followed by an unclear number, possibly two each FD25A and FD25B, to the North Vietnamese Air Force. The fate of these airframes is unknown.

Much of the demonstration life of the FD-25B was flown with a full dull black paint job. The FD-25 was designed to sell originally for $25,000 or less.

Ex-WW2 fighter pilot Jim Castor took over the FD-25 project after Don Downie and obtained the only known 25 in existence. He obtained it from the company after it had collected dust for eight years and refurbished it in his garage in La Mirada, California. Part of Castor’s agreement with Fletcher Aviation was to demonstrate the airplane to any potential customer on request.

Gallery

Engine: Continental E225-8, 225 hp.
Wingspan: 30 ft
Length: 20 ft 11 in
Height: 6 ft 3 in
Wing area: 150 sq.ft
Empty weight: 1228 lb
MTOW: 2500 lb
Fuel capacity: 50 gal
Max speed: 187 mph SL
Cruise speed: 162 mph SL
Service ceiling: 16,500 ft
Range: 630 mi
Armament: 2 x 0.30in mg
Hardpoints for: 2 x 33 gal nalpalm, 2 x 250 lb bombs, 40 x 2.75in rockets, or 4 x 5in rockets

FD-25B
Engine: Continental E225, 250 hp
Propeller: Hartzell controllable pitch
Wingspan: 30 ft
Wing area: 150 sq.ft
Airfoil: NACS 652-415
Aspect ratio: 6-1
Chord: 60 in
Outer wing dihedral: 6 deg
Length: 20 ft 11 in
Height: 6 ft 3 in
Gross weight: 2700 lb
Empty weight: 1428 lb
Useful load: 1272 lb
Fuel capacity: 60 USG
Max speed: 187 mph
Cruise speed: 162 mph
Landing speed: 45 mph
ROC: 1725 fpm
Service ceiling: 16,500 ft
Cruise range: 630 mi
Take-off distance: 500 ft
Landing distance: 330 ft
Fin area: 8 sq.ft
Rudder area: 4 sq.ft
Wlevator area: 9 sq.ft
Stabiliser area: 21 sq.ft
Seats: 1

The designer/builder was American Mr. Jim Flemming, although the XNU-1 was built in the Philippines.

The all-metal aircraft was reportedly briefly tested during the late-1960s or early-1970s. The engine was reported as a 185hp Lycoming.