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Beechcraft Twin Bonanza

The Beechcraft Model 50 Twin Bonanza is a small twin-engine aircraft designed by Beechcraft as an executive transport for the business market.

It was developed to fill a gap in Beechcraft’s product line between the single-engine Model 35 Bonanza and the larger Model 18.

The Twin Bonanza is dissimilar to the Bonanza, being much larger and heavier and using more powerful engines, while in its earliest form having only half the passenger capacity of the Model 18.

The United States Army adopted the Twin Bonanza as the L-23 Seminole utility transport, making it the largest fixed-wing aircraft in its inventory at that time.

According to Ralph Harmon, the airplane’s designer, during an initial demonstration flight for the Army, Beechcraft test pilot Claude Palmer crashed while trying to land over a 50-foot (15 m) tree line with the aircraft full of soldiers and sandbags.

Everyone on board walked away from the crash.

The Army was impressed with the structural strength of the Twin Bonanza, eventually purchasing 216 of the 994 examples produced.

It was also the first twin-engine aircraft in its class to be offered to the business market, but the Korean War was raging in the early 1950s and the US Army took almost the entire production for 1952 and 1953.


Model 50

Initial production version powered by two Lycoming GO-435-C2 engines, 13 built (six for the US Army, remainder civilian versions, with the first two production numbers for factory evaluation).

Model B50

Upgraded Model 50 with increased take-off weight, extra cabin windows and improved cabin heating, 139 built (40 for the US Army).

Model C50

Superseded the B50; fitted with 275 hp (205 kW) Lycoming GO-480-F1A6 engines, 155 built (one to United States Air Force).

Model D50

Superseded the C50; fitted with 295 hp (220 kW) Lycoming GO-480-G2C6 engines, 154 built (six to US Army).

Model D50A

Upgraded D50 fitted with GO-480-G2D6 engines, 44 built.

Model D50B

Upgraded D50A with new passenger steps and improved baggage area, 38 built.

Model D50C

Upgraded D50B with starboard airstair entry door, three rows of seats, improved air conditioning, larger baggage area, 64 built.

Model D50E

Upgraded D50C with extra portside window, squared-off rear starboard window, pointed nose and 295 hp (220 kW) Lycoming GO-480-G2F6 engines, 47 built.

Model E50

Supercharged version of the D50; with increased take-off weight and 340 hp (250 kW) supercharged GSO-480-B1B6 engines, 181 built (mostly for the US Army).

Model F50

Supercharged version of the D50A with GSO-480-B1B6 engines, 26 built including one converted to G50 standard.

Model G50

Supercharged version of the D50B with 340 hp (250 kW) IGSO-480-A1A6 engines, increased fuel capacity and increased take-off weight, one conversion from F50 plus 23 built.

Model H50

Supercharged version of the D50C with increased take-off weight and IGSO-480-A1A6 engines, 30 built.

Model J50

Supercharged version of the D50E with 340 hp (250 kW) IGSO-480-A1B6 engines and increased takeoff weight, 27 built.

 Excalibur 800

A modification designed originally by Swearingen Aircraft and taken over by the Excalibur Aviation Company which re-engines the Twin Bonanza with two 400 HP (298 kW) Avco Lycoming IO-720-A1A flat-eight engines in a new cowling and revised exhaust system.

Other optional improvements were also available.

L-23 Seminole

Military version






5 passengers


31 ft 6 in (9.60 m)


45 ft 3 in (13.79 m)


11 ft 4 in (3.45 m)

Wing area

277 sq ft (25.7 m2)

Aspect ratio


Empty weight

3,981 lb (1,806 kg)

Gross weight

6,300 lb (2,858 kg)

Fuel capacity

180 US gal (150 imp gal; 680 L)


 2 × Lycoming GO-480-C206 air-cooled flat-six, 295 hp (220 kW) each


Maximum speed

214 mph (344 km/h, 186 kn) at 2,500 ft (760 m)

Cruise speed

203 mph (327 km/h, 176 kn) at 7,000 ft (2,100 m) (70% power)


1,650 mi (2,660 km, 1,430 nmi) at 10,000 ft (3,000 m) and 160 mph (140 kn; 260 km/h)

Service ceiling

20,000 ft (6,100 m)

Rate of climb

1,450 ft/min (7.4 m/s)

Take-off run to 50 ft (15 m)

 410 yd (1,230 ft; 370 m)

Landing run from 50 ft (15 m)

458 yd (1,374 ft; 419 m)

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