Despite its rather simple appearance, the Hiller OH-23 Raven light helicopter line proved reliable even under the wartime stresses of Korea and Vietnam.
Hiller Aircraft began during World War 2 in 1942 under the operating name of Hiller Industries. The company carried the surname of Stanley Hiller (1924-2006) whose provided much of the early work in the field of helicopter flight. Indeed his first coaxial helicopter design was completed at age 15 and his XH-44 impressed the US Army at age 17. Hiller headed the first helicopter factory in the world out of Berkeley, California. Among his early developments (now under the "United Helicopters" name) included the UH-4 "Commuter" and the UH-5B "Rotormatic" which led to the single-seat UH-12 light utility helicopter of the late 1940s.
The UH-12 held origins in the company Model 360 and saw a first flight in 1948. The UH-12A was a follow-up modification to the original UH-12 and included a more powerful engine to go along with a new, two-blade main rotor. The US Army liked what it saw and contracted for a militarized variant of the UH-12A and this became the evaluation prototype designated YH-23. For the military form, crew capacity was increased to two in a side-by-side seating arrangement underneath a largely transparent bubble-style windscreen. The aircraft was powered by a single Franklin piston engine of 178 horsepower.
The overall configuration consisted of a front-mounted cockpit (originally single-seat and then seating for two or more) with a mid-mounted engine and rear-set stem. The engine powered a two-bladed main rotor blade fitted high atop the mast and drove a two-bladed tail rotor used to offset torque. The cockpit offered generally excellent vision and the undercarriage was of a basic skid-type design. While typically unarmed, some war-time models were outfitted with 2 x 0.30 caliber medium machine guns for basic offense.
Following successful trials of the YH-23, the system was formally adopted by the US Army as the H-23A "Raven" across 100 examples. The powerplant became the Franklin O-335-4 piston engine outputting at 178 horsepower. The type also piqued the interest of the USAF whom ordered five examples for official evaluation. The H-23A was followed into service by the revised H-23B. This new model series incorporated a combined skid-and-wheel undercarriage and was powered by a Franklin O-335-6 series piston engine of 200 horsepower output. The US Army then took on a stock of 273 units while an additional 81 served the export market. Some later OH-23B models were upgraded to the more powerful Lycoming VO-435-23B series engine of 250 horsepower.
The H-23C proved unique upon its arrival for it featured seating for three personnel under a single-piece canopy cover and also instituted use of metal blades. Some 145 were procured by the US Army. The H-23D was given an all-new main rotor design and powerpack to include the Lycoming VO-435-23B engine of 250 horsepower. US Army procurement numbered 348 examples. The H-23E was offered but never purchased.
The H-23F became a four-seat model with enlarged crew cabin. Additional changes included the use of the VO-540-A1B engine of 305 horsepower. The following H-23G offered seating for three personnel and dual-control features for both pilot positions. This mark was largely based on the preceding H-23F line.
The US Navy followed its own naming convention and tagged the UH-12A as the HTE-1. They were also two-seat airframes but offered dual-controls for both positions. Interestingly, this mark also showcased a tricycle-style wheeled undercarriage. Seventeen of the type were manufactured. The HTE-1 was then followed by the HTE-2 which was the H-23B and its Franklin O-335-6 piston engine of 200 horsepower. 35 examples were procured.
The Royal Navy followed suit and purchased the Hiller design under two marks - Hiller HT.Mk 1 and HT.Mk 2. The Mk 1 were ex-US Navy mounts (HTE-2 models) while the Mk 2 were UH-12E production models. Numbers totaled 20 and 21 respectively and primarily held as trainers out of RNAS Culdrose (Cornwall). The Canadian Army utilized the Hiller design as well, this under the C-112 "Noman" designation.
In 1962, the United States military underwent a branches-wide designation revision which changed all H-23 designations to the "OH" format. H-23B became OH-23B, H-23C became OH-23C and so on (see variants section for complete list). Many OH-23 variants were based on existing civilian-minded Hiller marks including the original UH-12A. The UH-12B was the basis for the US Navy HTE-1 while the UH-12C was the H-23C. The UH-12 was the H-23D and so forth.
The OH-23 proved exceedingly popular on the world market beyond its use by the United States, United Kingdom and Canada. The list included Argentina, Chile, Indonesia, Israel, Mexico, the Netherlands, South Korea, Thailand and Uruguay among others.
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Specifications
Hiller Aircraft Corporation - USA Manufacturer(s)
Argentina; Canada; Chile; Colombia; Dominican Republic; Guatemala; Indonesia; Israel; Mexico; Netherlands; Paraguay; Peru; South Korea; Thailand; United Kingdom; United States; Uruguay Operators
CLOSE-AIR SUPPORT
Developed to operate in close proximity to active ground elements by way of a broad array of air-to-ground ordnance and munitions options.
SPECIAL-MISSION: MECICAL EVACUATION
Extraction of wounded combat or civilian elements by way of specialized onboard equipment and available internal volume or external carrying capability.
SPECIAL-MISSION: SEARCH & RESCUE
Ability to locate and extract personnel from areas of potential harm or peril (i.e. downed airmen in the sea).
INTELLIGENCE-SURVEILLANCE-RECONNAISSANCE
Surveil ground targets / target areas to assess environmental threat levels, enemy strength, or enemy movement.
TRAINING
Developed ability to be used as a dedicated trainer for student pilots (typically under the supervision of an instructor).
27.8 ft (8.47 meters) Length
35.4 ft (10.80 meters) Width/Span
9.8 ft (3.00 meters) Height
1,819 lb (825 kilograms) Empty Weight
2,712 lb (1,230 kilograms) Maximum Take-Off Weight
+893 lb (+405 kg) Weight Difference
1 x Lycoming VO-435-23B 6-cylinder engine developing 250 horsepower driving a two-bladed main rotor unit and two-bladed tail rotor unit. Propulsion
Usually none though some wartime models were outfitted with 2 x 0.30 caliber (7.62mm) Medium Machine Guns (MMGs) in special outboard mountings.
0 Hardpoints
H-23 "Raven" - Base Hiller company model designation
YH-23 - U.S. Army evaluation model; single example
H-23A - Initial production model; powered by Franklin O-335-4 engine; two-seat; 105 produced.
H-23B - Powered by Franklin O-335-6 engine of 200 horsepower; 354 produced.
H-23C - Three-seater; metal main rotor blade; 145 examples.
H-23D - All-new main rotor; powered by Lycoming VO-435-23B engine of 250 horsepower; new transmission; 348 produced.
H-23E - Proposed variant; not adopted
H-23F - Four-seater; Lycoming VO-540-A1B engine of 305 horsepower; 22 produced.
H-23G - Three-seater with dual control scheme; 793 examples produced.
HTE-1 - USN model; Franklin O-335 engine; dual control scheme in two-seat cockpit arrangement; wheeled undercarriage; 17 examples produced.
HTE-2 - USN model; Franklin O-335-6 engine; 35 examples produced.
HT Mk 1 - British Navy designation; 20 examples from USN stock.
HT Mk 2 - British Navy designation; 22 examples
CH-112 "Nomad" - Canadian Army designation
U-12A (H-23A) - Civilian model; Franklin O-335-4 engine of 178 horsepower.
UH-12B - USN trainer
UH-12C - Three-seat variant
UH-12D - Improved H-23C for US Army service
UH-12E - Three-seater with dual control scheme
UH-12ET - UH-12E with Allison 250 series turboshaft engine.
UH-12E3 - Improved three-seat form
UH-12E3T - Improved turboshaft version
UH-12E4 - Four-seater; Lycoming VO-540 engine
UH-12E4T - Four-seater with turboshaft engine
UH-12L-4 - Extended fuselage; enlarged cabin windows
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