The Stinson O-49/ L1 Vigilant was the first slow flying liaison aircraft to be ordered by the USAAC, but turned out to be too large and too expensive for the role, which was eventually carried out by a variety of military versions of civilian light aircraft.
The O-49 was the first American observation aircraft to follow the European trend of using slow speed aircraft for artillery observation and liaison duties (most famously the Fieseler Storch). Previous American observation aircraft had been increasingly high speed aircraft, following the general improvement in aircraft performance, peaking with the 221mph North American O-47. By 1938 it was becoming clear that these aircraft were no longer suitable for close support work, as they needed decent airfields and a high level of technical support.
After some debate a design contest for a ‘short range liaison observation’ aircraft were initiated, with entries to be submitted by 23 February 1939. An impressive total of 117 requests for bids were sent out, but only ten were submitted. The designs from Stinson (O-49), Bellanca (O-50) and Ryan (O-51) were judged to be the winners by a board of officers that recommended ordering three of each type. By September 1939 orders had been placed for 100 Stinson YO-49s, which was seen as the best of the three, and three each of the O-50 and O-51. The O-49 Mockup Board, which met at Wright Field soon after the outbreak of war in Europe in September 1939 recommended that the three orders should be completed and also that commercially available light aircraft should be purchased to fill a gap in numbers.
The O-49 was a high wing monoplane. It had drooping ailerons and lowered by 20 degrees when the flaps were lowered, increasingly lift. It also had full span flaps and Handley Page leading edge slats. It could take off and land in 200ft. It had a top speed of only 129mph, and a stall speed of 35mph, allowing it to loiter over the relevant part of the battlefield. It was built around a metal tube framework, with fabric covering over most of its area and aluminium over the forward fuselage and cowling. It was powered by a 295hp Lycoming R-680-9 nine-cylinder radial engine. It had a fully glazed cockpit, including a glazed roof that rose just above the level of the wings.
In May-June 1940 the fighting in the Low Countries and France demonstrated just how useful the slow flying liaison and artillery observation aircraft was, but the YO-49 was still not ready. Different observers came to different conclusions after examining the events of 1940, with at least one US officer suggesting that only well armed fast light bombers could carry out the observation role, but in October 1940 the Air Corps Technical Committee recommended that two types of observation aircraft were needed – long range, twin engine armed aircraft for reconnaissance and unarmed short range liaison aircraft.
In mid 1940 the contract was increased to 152 aircraft. Soon afterwards the aircraft entered production, at Stinson’s parent company Vultee’s factory at Nashville.
The O-49 was slow to enter service. By the start of 1941 the US Field Artillery was getting impatient, and started to press for the use of existing commercial light aircraft. By the summer of 1941 the Army had decided to test out a series of commercial light aircraft in that summer’s manoeuvres, starting with the Second Army June manoeuvres in Tennessee. Piper, Aeronca and Taylor all provided aircraft, which despite a certain amount of disquiet within the USAAF, all performed well. These aircraft would enter service as the Taylorcraft O-57/ L-2, Aeronca O-58/ L-3 and Piper O-59/ L-4, all known as the Grasshopper. All three of these aircraft were much lighter and much cheaper than the O-49/ L-1. They were soon followed by Stinson’s own ‘76’, which entered service as the L-5 Sentinel.
Standalone pictures of the L-1 give a misleading idea of its size compared to the later L-2, L-3, L-4 and L-5. All five were high winged monoplanes, with the wing carried above fully glazed cockpits, giving them a very similar appearance. However the L-1 had a wingspan of 50ft, length of 34ft and loaded weight of 3,400lbs. In comparison the Piper L-4H had a wingspan 35ft 2in, length of 22ft 4in and loaded weight of only 1,220lbs!
It soon became clear that vast numbers of liaison aircraft were required. In November 1941 the General Staff suggested ordering 617 light aircraft, a mix of Taylorcraft O-57s, Aeronca O-58s and Piper O-59s and 275 of the somewhat larger Stinson L-5 Sentinel. In January 1942 the Ground Forces held a conference at which they requested some 4,000 liaison aircraft. The Air Corps ordered another 1,000, followed by 1,960 more six months later, but these were all of the smaller types – the L-2, L-3, L-4 and L-5. The L-1 might have been the most capable of these aircraft, but it was too complex and too costly to satisfy the demand that had suddenly emerged.
By December 1943 there were 178 L-1s in service, but no more were being produced.
The L-1 was also used by the British. In July 1944 Eisenhower actually asked General Arnold for a supply of ‘British Whizzers’, a fairly obscure name for the British version of the Vigilant. Eisenhower wanted the ‘Whizzer’ for his corps and division commanders. He specifically rejected the L-4 and L-5, on the grounds that they were too slow at take-of and didn’t descend fast enough to escape from danger.
His use of the Whizzer name was someone unusual, as the British actually called their L-1s the Vigilant Mk.I and Mk.II, but a US Air Force study of the development of Liaison aircraft suggests that this might have been a subtle dig at the USAAF’s failure to provide enough L-1s in the first place! By the time this letter reached Washington the L-1 was out of production and obsolete, and the Air Force suggested providing an improved version of the L-5.
The L-1 was also requested in the India-Burma front, where it was used as a casualty evacuation aircraft.
This was the initial version of the aircraft. A total of 142 were built, of which sixteen went to Britain where they became the Vigilant Mk.I.
The O-49A gained a 13in fuselage extension behind the wing root, making it 34ft 3in long. The fixed undercarriage could be replaced with two EDO Model 77 amphibious floats, each of which had a retractable nose and a main wheel, allowing for operations on land.
Stinson built 182 O-49As, which became the L-1A in 1942. One was used as a remote control for aerial targets, as the CQ-2. Fifty five went to Britain, where they became the Vigilant Mk.IA.
The O-49 and O-49A were the only versions of the aircraft built from new, giving a total of 324 aircraft. All further variants were conversions of existing aircraft.
This designation was given to four O-49s that were converted into air ambulances, with a fold down door added behind the wing root on the right to allow a litter to be loaded.
The L-1C was a second ambulance conversion, in this case with a loading hatch in the rear fuselage, and space in the cabin to fit the litter. 113 L-1Cs were produced by converting existing aircraft.
Twenty one aircraft were converted to act as target tugs for training duties, with the tow cable apparatus under the fuselage. They were used with the Aeronca TG-5, Taylorcraft TG-6 and Piper TG-8 training gliders.
The L-1E was the designation given to seven of the ambulance variants after they were given EDO Model 77 floats. Most were used on the China-Burma-India front.
The L-1F was an amphibious conversion of the L-1C, with the same EDO Model 77 floats as the other amphibious variants.
Stinson L-1A/ O-49A
Engine: Lycoming R-680-9 nine-cylinder air cooled radial engine
Span: 50ft 11in
Length: 34 3in
Height: 10ft 2in
Empty weight: 2,670lb
Maximum take-off weight: 3,400lb
Max speed: 129mph
Cruising Speed: 95mph
Service ceiling: 12,600ft
Range: 280 miles