The Stinson O-62/ L-5 Sentinel was a larger and more capable liaison aircraft, which operated alongside the L-2/ L-3 and L-4 Grasshoppers, although needed more complex support than the lighter aircraft.
In the late 1930s the speed and complexity of all types of military aircraft rapidly increased, leading to a problem with observation aircraft. The standard types had become too large to be able to operate from unimproved fields, and a debate began about the type of aircraft that was required. Some favoured the light bomber type, believing that only high speed aircraft could survive over the front lines, while others wanted slow flying light aircraft. Early in 1939 the USAAC began a design contest for a slow flying liaison aircraft, which was won by the Stinson O-49 Vigilant, but although this physically resembled the famous Fieseler Storch, it was a somewhat larger aircraft, and proved to be rather slow to develop.
In 1941 the Army Ground Forces made their own arrangements to test Taylorcraft, Aeronca and Piper light aircraft during their summer manoeuvres, having got frustrated with the USAAF’s efforts. All three performed well, and the Ground Forces made it clear that they wanted large numbers of them.
The Air Force wasn’t at all impressed with these very light aircraft, so asked Stinson to design a more capable aircraft, somewhere in size between these ‘grasshoppers’ and the O-49.
In response Stinson produced a military version of one of their existing light aircraft of their own, the Model 76, based on their Model 105 Voyage. Late in 1941 the General Staff recommended purchasing a large number of commercial light aircraft to make up for the slow production of the O-49. The first order was for 617 aircraft, including 275 Stinson model 76s, which became the O-62 and almost immediately the L-5.
The L-5 was more advanced than the L-2/ L-3/ L-4 Grasshoppers. It had an 185hp Lycoming O-435-1 six cylinder air cooled engine (compared to 65hp on the L-4), and was twice as heavy. It had wing slots and flaps, which gave it the same performance as the L-4. It was a high wing monoplane, with a fixed landing gear and a heavily glazed cockpit, designed from the start to give a good view in every direction (in contrast the Taylor, Aeronca and Piper designs all started off with fairly poor rear views). The L-5 was similar in construction to the lighter types, with a steel tube fuselage, wooden wing spars and ribs and a fabric covering. Although it was almost twice as heavy as the various Grasshoppers, its more powerful engine and advanced wings allowed it to land at 45mph.
The L-5 was a more complex aircraft than the various types of Grasshopper. In 1943 the Field Artillery and the Air Corps disagreed about which aircraft the artillery should be using. The Field Artillery wanted the simple 65hp L-4, but the Air Corps preferred the L-5. The fundamental problem was that the Field Artillery wanted to operate their own aircraft, because they didn’t trust the Air Corps to provide them with enough aircraft, or not to divert them to other uses to satisfy their own whims. This was an entirely valid point of view, given the long delays in producing the Air Corps’s first slow speed liaison aircraft, the Stinson L-1 Vigilant. This required a simple aircraft, easy to maintain in field conditions, operating away from USAAF air fields. However these simple aircraft didn’t quite provide the required performance. The L-5 did have the required performance, but would have been difficult for the artillery to operate. The L-4 was also much cheaper – in 1942 it cost $2,432 to build one, rising to $2,701 in 1945. In contrast the L-5 began at $10,165 per aircraft in 1942, dropping to $8,323 in 1945.
By the end of 1943 there were 900 L-5s in service with the USAAF, and it was classified as a standard type. Production sped up in 1944 when 1,361 L-5s were built, although the L-4 was still more numerous, with 1,904 built. Eventually some 3,590 L-5s were accepted by the USAAF.
Although it was produced in large numbers, the L-5 wasn’t quite as satisfactory an aircraft as the more complex L-1. In 1944 Eisenhower even requested a supply of L-1s for his corps and divisional commanders! The Air Corps response was to try and improve the performance of the L-5 by developing a version with a controllable pitch propeller.
The L-5 was used as a liaison and observation aircraft by the US Army in the European, Pacific and China-Burma-India theatres. In the CBI it’s higher service ceiling was very useful, allowing it to operate around the Himalayan Mountains.
One hundred L-5s went to the RAF, where they became the Sentinel I and Sentinel II. These were mainly used in the CBI theatre.
The L-5 was still in use during the Korean War, when the Army, Air Force and Marines all used them. They served alongside the North American T-6 Texans as Forward Air Control aircraft.
In 1962 the L-5 became the U-19A and the L-5G became the U-19B, in the unified tri-service designation system. The last of the U-19s retired soon afterwards.
The O-62 was the initial production version. 275 were built by Stinson, along with 1,731 by their parent company Vultee, as the L-4-VW (VW standing for Vultee, Wayne Michegan). It had a 12-volt electrical system.
The L-5A was a modification of the basic L-5, with a 24-volt electrical system that allowed it to use radios that could communicate directly with attack aircraft. 688 were produced by converting existing L-5s.
The L-5B had a modified fuselage that allowed it to carry one patient on a litter or 200lb of cargo. It was given a deeper fuselage, with new observer’s windows and a hinged door along the right side of the fuselage that opened upwards, allowing the patient to be loaded underneath it. A total of 730 L-5Bs were built, starting in 1943.
Some L-5Bs were given a nose hook to allow them to be used with the Brodie Device. This was effectively a trapeze that could be used to launch and catch correctly equipped aircraft, and was installed on a number of Landing Ship, Tanks.
Some L-5Bs were given twin floats in place of the normal landing gear, and a ventral fin under the rear fuselage.
The L-5C was capable of carrying a K-20 aerial camera, which could be operated by either the pilot or observer. 200 were produced.
The L-5D was probably a version that would have had Handley-Page leading edge slots, to improve it’s high speed performance, but none were produced and the project was cancelled before any serial numbers had been allocated.
The L-5E was similar to the L-5C, with the same ability to carry a camera. It also had drooping ailerons that lowered when the flaps were operating, improving the low speed performance. A step was also added to make it easier to get into the observer’s position. A total of 750 were built.
The XL-5F was a single L-5B that was given a 185hp Lycoming O-435-2 six-cylinder air cooled engine for trials. After the tests were over it was converted back into a standard L-5B.
The last production version was the L-5G, which was similar to the L-5E, but with a 190hp Lycoming O-435-11 engine, enlarged wheels and tires and better brakes. It also had a SCR-274N radio that could communicate for the ground forces. This lifted its speed to 130mph despite a slight increase in weight. 115 were built.
The L-9 was the designation given to those civilian Voyagers that were taken over by the USAAF during the war.
The Navy received 306 L-5s from the Army, and designated them as the OY (O for Observation, Y for Consolidated, Vultee’s owner from 1943). The OY-1 was the standard version, the OY-2 an ambulance version. At least 29 of these were produced.
L-5/ O-62 stats
Engine: Lycoming O-435-1 flat six-cylinder air cooled engine
Length: 24ft 1in
Height: 7ft 1in
Empty weight: 1,472lb
Maximum take-off weight: 2,158lb
Max speed: 129mph
Cruising speed: 100mph
Service ceiling: 15,800ft
Range: 450 miles