‘L’ IS FOR LIAISON
5 = the fifth liaison type adopted by the U.S. military.
The primary purpose of a liaison airplane was to provide messenger, courier and liaison services for the ground forces and serve as aerial observation posts for the field artillery. They of course did far more than that during WWII, but artillery spotting and messenger service within friendly territory was their official raison d’être. By order of the Secretary of War, the liaison (L) designation was officially recognized in March, 1942 for this newly adopted category of light, unarmed courier airplanes. Prior to that time they were classified as observation aircraft and were identified by the prefix ‘O’.
The official military name for the L-5 type was Sentinel. The suffix VW was appended to the main designation to signify the manufacturer and factory location – in this case, Vultee, Wayne. (Ex: L-5-VW, L-5B-VW, L-5C-VW, etc). Stinson was a subsidiary division of the Vultee (later Consolidated-Vultee) aircraft company, and the factory was located in Wayne, Michigan, just west of Detroit, hence “VW’.
The Stinson engineering name was Model 76, while the Vultee designation was V-76. The unofficial name Flying Jeep was coined in 1940 by factory personnel and was used to refer to the design even before the initial prototype was flown That nickname stuck and became popular among military personnel and with the news media. It was also commonly used in official Stinson and Vultee correspondence and public relations literature.
ARMY AND ARMY AIR FORCES TYPE AND MODEL NUMBERS
O-62: Total built: 275. This observation designation applied to the first batch of aircraft ordered by the government in December 1941. It was dropped in March 1942 when the USAAF officially established the liaison (L) sub-category of light unarmed aircraft. These 275 planes and all other models were delivered under the L-5 designation but for convenience we usually call them O-62’s to identify them as early production airplanes.
L-5: Total built: 1,538. The standard Stinson L-5 was an improved version of the O-62 and incorporated many small engineering changes throughout the airframe, especially in the electrical system. This model was the mainstay of Army Air Forces liaison squadrons from mid- 1943 until the late summer of 1944 when the L-5B ambulance model began to join it in the field.
L-5A: None built. Since it’s inception, the follow-on to the O-62 was often popularly referred to as the “A” model, so it became a part of L-5 lexicon even though it is incorrect. The real L-5A was in fact going to be a 24 volt, Ranger-powered version with an aluminum monocoque aft fuselage and all-metal tail. It did not progress beyond the planning stage because the Ranger L-440 engines manufactured by Fairchild were not available in sufficient quantity and aluminum was still in critically short supply. The hybrid fuselage design was resurrected after WWII and became the basis for the Convair L-13 that was also designed by Stinson.
L-5B: Total built: 712. The B model was the first ambulance / cargo version of the L-5 and it first appeared in service during the summer of 1944. It was designed for casualty evacuation and light cargo transport. The aft fuselage was substantially enlarged and a two-piece downward hinged door was added to accommodate standard U.S. Army, Navy and British litters. The large doors made loading and unloading extremely easy. Cargo capacity was only 250 pounds, but more was often carried and bulky, lightweight items such as mail sacks could easily be accommodated. In common military verbage, all ambulance models were typically referred to as L-5B’s, regardless of whether they were later versions or not.
L-5C: Total built: 200. This model was identical to the L-5B except for a sliding camera aperture in the belly and a vertical mount located behind the rear seat that could hold a Fairchild K-20 aerial camera. This modification expanded the utility of the basic ambulance model to include short-range reconnaissance and mapping missions. With a 200 foot film roll in the magazine, four hundred 4×5″ photographs could be taken either singly or in rapid succession to create a “strip map”. The expensive, sensitive cameras were not permantly mounted inside the aircraft and were only installed when needed.
L-5D: None built. The D model was designed to incorporate a Ranger L-440 engine and 24 volt electrical system, similar to the still-born L-5A. The USAAF planned to procure 1,200 of these aircraft but the contract was cancelled in favor of additional, much cheaper Piper L-4 Cubs. A single modified L-5 based on this design is known to have been created in Brazil in the 1950’s where Ranger engines were built under contract.
L-5E: Total built: 500. This was an improved L-5C that incorporated manually drooping ailerons that slightly shorttened the takeoff and landing run, lowered the stalling speed and slightly improved low-speed controllability with up to 15 degrees of droop available. The first E models were built in February, 1944 but didn’t reach combat theaters until April.
L-5E-1: Total built: 250. The dash-1 was an improved L-5E that utilized 8.00×6″ main wheels and tires and heavy duty brake drums, instead of the 700×6″ rims and tires used on earlier models. The larger tires made it somewhat better for negotiating rough fields and they provided extra “floatation” on soft ground. The taller tires created a slightly higher angle of attack in the 3-point attitude for slower anf slightly shorted takeoffs and landings, and it increased propeller clearance for operating in brushy off-airport areas.
L-5F: Total built: 1. This plane was a modified L-5B, serial number 44-17103, that was used as the mock-up and testbed for development of the 24 volt electrical system used on the L-5G.
XL-5F: Same aircraft as above. In 1948 the single L-5F above was temporarily modified with a low noise exhaust system and a special five bladed propeller used in “quiet airplane” studies by NASA. It was the predecessor of the USAF stealth aircraft program and pilots said it was “eerily quiet”. When flying at only a few hundred feet, ground observers couldn’t hear it over ambient daytime noise levels outdoors.
L-5G: Total built: 115. This final production model was an improved L-5E-1 with a 24 volt electrical system and an upgraded radio package that allowed air-to-air as well as air-to-ground communications on multiple frequencies. It also incorporated a better carburetor and revised air induction system, increasing engine performance by five horsepower while reducing fuel consumption by up to ten percent. The 115 G-models delivered between July 13th and November 1st 1945 do not not include approximately 45 other L-5G’s that were assembled in 1946 and sold on the civilian market. It also doesn’t include a number of E-models that were upgraded to 24 volts and redesignated as L-5G’s by the Air Force between 1947 and 1951.
L-5H: Total built: 1. This model was in the prototype testing stage and not ready for delivery before the war ended. It incorporated all the latest features of the L-5G, but had a hybrid fuselage whose shape was halfway between that of the ambulance models and the original observer type. The reason for the fuselage re-design was that the full bodied ambulance was not as suitable for observation and artillery work due to limited rearward visibility. The fate of this airplane is unknown but there is a photograph of it sitting on the factory ramp in 1945, so we know it existed. Numerous technical drawings of it can be found in the blueprint set maintained at the National Archives and accessible through the SOPA..
U.S. NAVY, MARINE CORPS and COAST GUARD DESIGNATIONS
OY-1: Total delivered: 288. This was the Navy and Marine Corps designation for all of the 12-volt L-5’s that were diverted from the USAAF and assigned to the Marine VMO (artillery observation) squadrons that operated in the Pacific theater. The Navy Bureau of Aeronautics did not bother to differentiate between the L-5 observer and L-5B/C/E ambulance models.
OY-2: Total delivered: 18. This was the Navy / Marine Corps designation for the Air Force L-5G. While only 18 were delivered, numerous earlier models were upgraded to 24 volts by the Marine Corps O&R facilities in San Diego and Cherry Point starting in 1947. These were re-designated as OY-2’s. Again, no differentiation was made between observer and ambulance models.
TN-OY-1 / TN-OY-2: These were the designations adopted by the U.S. Coast Guard when they received a half-dozen cast off OY aircraft from the Navy Department in 1948 and 1949.
BRITISH ROYAL AIR FORCE DESIGNATIONS
Sentinel I: Population 40. This was the RAF designation for the observer-type L-5 Sentinels received through the Lend-Lease program and deployed to the CBI (China-Burma-India) theater for use by the Southeast Asia Air Command (SEAC). They were primarily used by communication squadrons.
Sentinel II: Population 60. This was the RAF designation for the ambulance-type L-5B Sentinels received through the Lend-Lease program and deployed to the CBI theater for use by the Southeast Asia Air Command. They were primarily used by casualty evacuation squadrons. The Chindits and other British forces often referred to them as Jungle Angels.
U-19B / U-19B: The U.S. Air Force designation for a very few L-5’s still remaining in inventory in the early 1960’s. One such aircraft was used as a glider tug at the Air Force Academy. It was a confusing designation given the widespread use of Cessna L-19’s and the propensity for the uninformed to mistake the Stinsons for Cessna’s, and vice-versa. The prefix letter ‘U’ stood for Utility.
Clevenger: Approximately 20 built. This was a biplane crop-dusting modification of the L-5 used in the 1950’s and 60’s by Wayne Clevenger, an aerial applicator from Salinas, California. Designed and constructed by Clevenger and mechanic Larry Lujan, also of Salinas, the odd-looking planes were fitted with Continental W670 radial radial engines and modified Luscombe wings that were used for the lower wing panels. The rear seats were removed for the installation of a dry chemical hopper or liquid chemical tank. A few later versions used the Lycoming W680 engine. While the stock Stinson L-5 had a gross operating weight of 2,200 pounds, the restricted-category Clevenger dusters typically operated between 3,800 and 4,300 pounds with full loads. A single restored Clevenger in full biplane configuration still exists in Yuma, Arizona. Several others are still flying as in a monoplane configuration. All are operated in the experimental or restricted category as sport planes.