The Stinson L-5 Sentinel is a World War II-era liaison aircraft used by the United States Army Air Forces (USAAF), U.S. Army Ground Forces, U.S. Marine Corps and the British Royal Air Force. It was produced by the Stinson Division of the Vultee Aircraft Company (Consolidated-Vultee from mid-1943). Along with the Stinson L-1 Vigilant, the L-5 was the only other USAAF liaison aircraft that was exclusively built for military use and had no civilian counterpart.
The origins of the L-5 can be traced to the prewar civilian Stinson HW-75. This 75 horsepower civilian high-wing design was built by the Stinson Aircraft Company at Wayne, Michigan and first flew in 1939. It was marketed as the Model 105 and was first introduced to the public at the New York World's Fair. The three-place HW-75 featured two side-by-side seats and a third "jumpseat" in back on which a small passenger could sit facing sideways. Economical, spin resistant and easy to fly, the plane was popular with aircraft owners and flight schools and by the end of 1939 Stinson was building three per day. In 1940 the Model 105 was upgraded to an 80hp Continental engine and with other small improvements this was marketed as the Model 10.[1]
Stinson became a subsidiary of the Vultee Aircraft Corporation in August 1940. Under Vultee management, an improved version was fitted with a four-cylinder 90hp Franklin engine for the 1941 model year and the type became known as the Model 10A Voyager. In the postwar era, the fuselage of the Model 10A was lengthened to accommodate four passengers and the four-cylinder powerplant was replaced with a Franklin 150 hp six-cylinder engine. This conversion became the Stinson Model 108 Voyager that was the only aircraft commercially produced by Stinson after WWII.
During the summer of 1940, Stinson built an experimental tandem-seat version of the HW-75, equipping it with a 100hp Lycoming engine. This was known as the Model 75B. Under Vultee management it was re-designated V-75B. Soon increased to 125 horsepower for better performance, this became the Model V-75C that was demonstrated to the military in August and September 1940.
The V-75C failed to meet military requirements, so the Stinson engineers went back to the drawing board and came up with a clean-sheet design that was similar in concept to the V-75C but was a far stronger, more powerful and completely new tandem-seat airplane that met rigorous Army-Navy engineering standards for the design of military aircraft. This was called the Model 76 and was adopted as the L-5.
The experimental 175 hp Model 76, dubbed "the Flying Jeep" by factory personnel, was first flown at the Stinson factory airport on June 23, 1941, by chief pilot Al Schramm. Accepted by the military after accelerated service trials were completed in September, the first contract for 275 planes was issued in January 1942. Originally designated O-62 ('O' for observation), this was changed to L-5 Sentinel ('L' for liaison) in April 1942, seven months before the first production airplanes were delivered. With minor changes, the six-cylinder Lycoming O-435 engine was upped to 185 horsepower, becoming the O-435-1 that powered all production Sentinel models through the L-5E-1.
Adopted by the Army Air Forces as their standard liaison aircraft, replacing the larger and more costly L-1 Vigilant, the primary purpose of the L-5 was short range officer transport, courier work and artillery spotting. The fuselage was reconfigured in January 1944 and the modified aircraft, designated as the L-5B, could be used as an air ambulance or for light cargo transport. With a wider and deeper rear fuselage section and a large rear door that folded downward, a litter patient or 250 pounds of cargo could be quickly loaded. Later iterations of the cargo / ambulance version were the L-5C with provisions for mounting a K-20 aerial camera, the L-5E with drooping ailerons for better low-speed control, the L-5E-1 with larger tires and heavy-duty brakes for better short and soft-field performance, and the final L-5G with a 24-volt electrical system and 190 hp version of the Lycoming engine.
In addition to the previously listed uses, L-5's were employed in many diverse roles such as reconnaissance, search & rescue, aerial photography, forward air control of fighter-bombers, laying communication wire, spraying pesticides, dropping para-cargo, dropping leaflets, and aerial broadcasting with loudspeakers. It also served as a test bed for radar tracking, firing aerial rockets, and airborne remote television. In uncommon instances, L-5 crews dropped grenades and fired wing-mounted bazookas at enemy targets.
The L-5 series was manufactured between November 1942 and September 1945, during which time 3,590 of the unarmed two-seaters were delivered for military service, making it the second most widely used light observation liaison aircraft of the war behind the Piper L-4 Cub.
The fuselage was constructed using arc-welded chrome-moly steel tubing covered with doped cotton fabric and the wings and empennage were constructed of spruce and mahogany plywood box spars and plywood ribs and skins, also covered with fabric. The use of aluminum, which was in critically short supply and more urgently needed for other aircraft, was limited to the engine cowling, tail cone, framework for the ailerons, rudder and elevator and the landing gear fairings. The L-5 through L-5E were powered by a six-cylinder 185hp Lycoming O-435-1 engine. The L-5G used a 190 hp Lycoming O-435-11.
Capable of operating from short unimproved airstrips, the L-5 Sentinel delivered personnel, intelligence and supplies to the front line. On return flights, wounded soldiers were often evacuated to rear area field hospitals for medical treatment. L-5s were primarily flown by the Army Air Forces liaison squadrons consisting of 32 planes each. One of these squadrons was attached to field army headquarters deployed overseas and an additional squadron was assigned to each Army Group headquarters. They saw action in Western Europe, Italy, the Philippines, New Guinea, and the China-Burma-India theater. In the hands of the U.S. Marine Corps artillery observation squadrons they were widely used during the Pacific Island campaigns of 1944 and 1945. The L-5 was used by generals and other high-ranking officers for short-range transportation.
An unusual use of the Sentinel was launch and recovery from a land-based overhead cable system designed by Lt. James Brodie that could be quickly set up in a large clearing that was otherwise unsuitable for a runway. The cable was strung between two tall masts and a braked carriage snagged an arresting hook attached to the top of the airplane. After successful tests of the "runway on a rope" in Oklahoma, it was demonstrated to the British in India who declined to adopt it. However, the unorthodox "Rube Goldberg" Brodie landing system was installed aboard the . Staff Sergeant R. A. Gregory made ten good successful launches and recoveries with a Stinson L-5.[2] During the Battle of Okinawa, L-5s operated from an LST equipped with the "Brodie System".[3]
The Navy and Marine version of the L-5 through L-5E were designated OY-1, and all these aircraft had 12-volt electrical systems. The 24-volt L-5G became the OY-2. Neither the L-5G nor OY-2 saw combat during World War II because production did not begin until July 1945, just weeks before the war ended, but they were used extensively during the Korean War. A further two dozen or so OY-1's were converted to OY-2's in 1948 and 1949. The British Royal Air Force (RAF) procured 40 L-5s and 60 L-5Bs in 1944 and designated them Sentinel Is and Sentinel IIs respectively. These aircraft were used exclusively in the India-Burma theater of operations by SEAC communications and medical evacuation units.
After World War II, the L-5 was used in the continental United States, Hawaii and Alaska by the Civil Air Patrol for search and rescue work. They were also employed by state law enforcement, forestry and Fish & Wildlife departments. Many other countries also received L-5s after the war. The largest quantities were sold to Italy, the Republic of the Philippines, and India. A few went to Pakistan after the partition of India in 1948, and a small number were used by the Japan Defense Force. Others were also sold to Korea, China, Thailand, Mexico, Venezuela, and Brazil.
Today there are about 300 known examples left worldwide and less than half are in flying condition.[9] A group called the Sentinel Owners and Pilots Association is dedicated to the preservation and enjoyment of this aircraft type.[10]
Greece