The golden age of aviation was an era of rapid and fervent development for fixed wing aircraft. Many design innovations occurred during this period from 1919–1939 essentially between the two world wars.
This was a time when classic aerodynamic lines and popular characters dominated. Air races and barnstorming displays were common. Airports were deemed a necessity for any progressive minded community, and so they built them. Regulations were few, and daring pilots achieved fatality or fame.
Commercial use of airplanes was just beginning, and manufacturing firms were numerous and thriving. Among many private industries, light aircraft production was decidedly individual and personal. The use of aircraft, like mass production at the time, served wide-ranging purposes. Farming and ranching industries benefitted, as did prospectors of land and mineral resources. The U.S. was a vast and unexplored territory. Aviation served to make it less formidable.
Meanwhile, all of aviation’s civil applications would reflect upon the armed forces and a developing need to carry out missions on foreign soil. For military use, aircraft had been previously employed in two primary roles, assault and reconnaissance. These were the delivery of bombs and fire, and surveillance on the adversary. Airplanes were a powerful tool, the extent to which had not yet been fully understood, as ground forces had dominated national defense prior. However, a medial role that proved to be equally important would emerge—that of the liaison. Referring both to pilot and aircraft, liaison forces would quite simply permit ground armies to perform with greater accuracy, intelligence and expediency.
The key players in light aviation during WWII turned out to be Piper Aircraft and Stinson Aircraft companies. Despite their dominance, other aircraft manufacturers were prevalent, and collectively they contributed to the deployment, and success, of the liaison role.
L-birds that missed the cut in WWII
Most historians agree that one aircraft in particular had the greatest influence on the adoption of light aircraft for use in the armed forces. This was the Fieseler Fi 156 Storch—an oddity of German origin noted for its excellent short field (takeoff and landing) performance and low stall speed (around 31 mph). The aircraft looked strange in that it was slender, unusually svelte and angular. At 32.5 feet long, and nearly 47 feet in wingspan, its ability to float was derisively misunderstood. In comparison to the Piper L-4 or Stinson L-5 it was significantly heavier and less agile.
What made the greatest impression on lookers of the Storch was its unique ability to operate from short, unimproved and improvised landing fields—a daunting feat for aircraft large or small at the time. Following a public review of the Storch’s abilities, U.S. production of a similar such aircraft was commenced. The resulting Stinson L-1 Vigilant was eventually produced in a quantity of 324, of which only a handful remain today. The aircraft was notoriously complex and costly.
Aircraft similar to the L-1 (a.k.a. O-49), and Storch, must also be credited with with the liaison class coming of age. These included the Douglas O-46, of which 90 were built from 1936–1937. The O-46 was, if anything, more curvaceous than the Storch. It utilized a radial Pratt & Whitney R-1535 Wasp engine, big and heavy like the aircraft itself.
Likewise noteworthy was the Ryan YO-51 Dragonfly. It too was designed for optimum short takeoff and landing (STOL) capability. In 1940 three prototypes were built and testing proved highly successful. Full-span slots (gaps along the forward wing edge) and Fowler flaps (extensions beyond and downward of the aft wing edge) contributed to its STOL prowess. It again was large at 35.5 feet long and 52 feet in wingspan, and powered by a Wasp engine.
A third finalist in a 1938 U.S. Army Air Corps competition, with the Stinson YO-49 and Ryan YO-51, was the Bellanca YO-50. At the time all were considered observation (O) aircraft as the liaison (L) class had yet to be formed. In 1940 Bellanca built three prototypes, and with an inverted “V” Ranger V-770 engine it resembled the svelte Storch. Wingspan was a browbeating 55.5 feet.
The slot (similar to a leading edge slat which is moveable) was purportedly discovered independently in both Germany by Gustav Victor Lachmann and England by Frederick Handley Page. Lechmann subsequently joined the Handley Page Company and the device became known throughout the world as the Handley Page Slot. Handley Page manufactured a one-off example of a biplane, the H.P.39 Gugnunc, incorporating a slotted and flapped wing.
A more successful rendition of a STOL class, high-wing utility aircraft was the Helio Courier introduced in 1954. Used by the the U.S. Air Force and U.S. Army Special Forces, the so-designated L-24 Courier and L-28 Super Courier were used for liaison work, light cargo and supply drops, psychological warfare, forward air control, insertion and extraction by land and sea, and reconnaissance. The L-28 was later redesignated U-10. With a length of 30 ft 8 in, wingspan of 39 ft, and accommodation for pilot plus five passengers its overall size was in-between that of the L-1 and L-5. Some 500 Helio Couriers were built of which approximately 120 were L-28 / U-10 models.
Another in the utility/STOL class, however seating more than two and seeing service as a liaison aircraft, was the Bellanca 31-50 Senior Skyrocket. Stout in profile, the six- and eight-seat utility aircraft from which it derived was less gangly than the L-1 and Storch. Among 33 built only one was impressed into military service by the USAAF in 1942 in Alaska. It was identified as the L-11.
The Show Goes On
Stinson was steadily busy producing four- to six-seat Voyager and Reliant models preceding, and some concurrent with, the L-1 and L-5 beginning in 1933. The military L-9, derived from the Voyager, was labeled HW-75, Model 105, Model 10, YO-54, AT-19, and UC-81 at various stages. Its commercial availability enabled orders by the military for immediate use.
Various models of the Reliant were produced using a radial engine, even a gull wing modification. Eventually the four-seat Reliant was impressed into service with the USAAF during WWII as the L-12, comprising two SR.5A models and another two SR.7B models as the L-12A.
The Stinson L-13 was a bit more peculiar with its narrow aft fuselage. It arrived later in 1945. 28 Were converted for cold weather operations using a combination of wheels, skis and floats, and given the L-13B moniker.
Various Stinson configurations included ambulance (accommodating one or two stretchers), cargo, target towing, firefighting and photography. Stinson built 1,052 examples of the L-9 Voyager lineage, 1,327 variants of the L-12 Reliant type, and 302 of the L-13 including two XL-13 prototypes.
Taking the narrow aft fuselage to the extreme was the L-15, or YL-15, Boeing Scout, a two-occupant STOL observation concept with an aft-facing observer seat. Only 12 were produced by the airframer giant in an bailed attempt to enter the light aircraft market.
On the truly lighter side, the Cub was not alone in achieving its superstardom. Though Aeronca, Taylorcraft and Interstate made their mark in WWII, other Cub-like flivvers too were vying for a patch on the grass.
Standouts in the two-seater, high-wing class of aviation’s golden age include the Porterfield Collegiate. The series, CP-40/50/55/60/65 (Continental powered, while others were Franklin ‘FP’ or Lycoming ‘LP’ powered), is distinguishable by its parallel wing struts. Produced from 1936–1942, 476 were reportedly built, and the model is today considered light-sport per FAA rules. Many were used in the Civilian Pilot Training Program (CPTP) introducing civilians to military aviation. Importantly, company founder Edward E. Porterfield is credited with promoting, alongside William T. Piper, the use of light aircraft to the AAF in the early stages of WWII. Porterfield also designed the Eaglet 31 in 1930, of which approximately 93 were built.
Using the familiar Continental engines du jour, Rearwin Aircraft (later Commonwealth Aircraft) derived its Skyranger from earlier single-engine sport monoplanes. Produced from 1940 to 1947 (with a pause in the middle), 358 Skyrangers were built. Its construction also followed the Cub types du jour in being a fabric-covered steel tube fuselage with wooden wings. However, remarks that it was “too challenging to fly,” led to its exclusion from the CPTP training fleet.
Lesser known was the Welch OW (models 3, 5M, 6M, 6S, 7M, 8M) with progressively larger engines from 37–45 hp. An OW-9M concept with a Lycoming O-145 @ 55 hp was never built. Controls on the Welch were mounted overhead with an adjustable control wheel that could be positioned for either pilot (akin to the single throw control yoke of a Bonanza). Its appearance can be likened to the Aeronca C-3 with a forward bloated, aft tapering fuselage.
None of these three Cub-like flivvers ever received an L-designation. However, their similarity with the style du jour is apparent. All diminutive taildraggers, their reclined perch on the tarmac, level when aloft, gave one or two occupants shoulder mounted wings afore an undulating T-tail and a spring wheel.
Though introduced post-war in 1946, the same can be said of the Fleet 80 Canuck—a Canadian side-by-side, high-wing fabric covered tourer. 225 Examples of the Canuck were built before production ended in 1958.
One bereft among the early birds but carrying the L-moniker nevertheless was the L-7 Monocoupe 90 (Monocoupe aircraft would later become Universal Molded Products). Designed by Don Luscombe in 1928, the Monocoupe 90 was built into the late 1940s to a quantity of 324. A military version of the Model 90AF (sporting a Franklin engine vs. the previous radial engined versions) was bought by the USAAF. Designating 20 units as the Universal L-7, they were transferred to the Free French Forces. Equally noteworthy, Don Luscombe would later become known for his advanced sheet metal light aircraft—taking cues from larger aircraft of the time.
It is said that mocking is the sincerest form of flattery. Truth be known it is said of imitation. But all things being equal, and a mock-up being a prototype, to mock something means to draw attention to its perceived outstanding qualities, and that’s precisely what the L-birds and their influencers did. Though only a few received official L-bird notoriety, each made their contribution to the class. Many returned from battle with honors. The unifying characteristics they all expressed were short-range and short field superiority, availability practically anywhere and for nearly any task, and the quintessential quality of humans mocking birds for their extraordinary defeat of the boundary between surface and space.
While not a comprehensive inventory, but taking into account production notes in this article and known production of the most utilized L-2 thru L-6 aircraft of WWII, approximately 21,000-plus liaison aircraft have served the U.S. and its Allies. Considering post-WWII liaison types the total number of aircraft exceeds 28,000.
The L-3 essentially became the L-16 when in 1946 Aeronca began producing the improved L-16A (7BCM Champion), of which 509 were built, and the L-16B (7CCM Champion) of which 100 were built. These served in the Korean War.
The L-4 essentially became the L-18 and L-21. From 1947–1949 the PA-11 Cub Special was produced and given the L-18 designation of which 105 were built and delivered to Turkey under the Military Assistance Program. Beginning in 1949 Piper produced the PA-18 Super Cub building:
- 838 of the L-18C (95 hp Continental C90-8F engine) of which many were sent to other nations under the Mutual Defense Assistance Program
- Two YL-21 (135 hp Lycoming 0-290-D2 engine) evaluation units
- 150 of the L-21A (125 hp Lycoming 0-290-II engine)
- 584 of the L-21B (approved YL-21). These were redesignated U-7A in 1962.
The Piper NE-1 / NE-2 derived from J-3, while the Piper AE-1 / HE-1 derived from J-5.
The Piper YL-14 derived from J-5. An order for 845 of the L-14 was cancelled after five/eight units were built.
The Piper L-4F / UC-83 derived from J-5A Cruiser (Continental A75-8 engine), four built and served in Panama, additional 39 built.
The Piper L-4G derived from J-5B Cruiser (Lycoming GO-145-C2 engine), 34 built.
Piper L-birds served in many Allied countries where many can still be found today including: Argentina, Austria, Belgium, Germany, Greece, Iran, Italy, Israel, Japan, Katanga (central Africa), Netherlands, Nicaragua, Norway, Portugal, Sweden, Switzerland, Uganda, Uruguay.
A single low-wing three-seat Ryan S-C-W with a radial engine was impressed into service in 1942 as the L-10. Though a taildragger it had little other similarity with the L-bird class. Ryan also built 246 L-17 low-wing four-seat Navion aircraft that were later designated U-18.
The O-1 / L-19 Birddog was developed in 1949 serving after WWII. Cessna built 3,431 units.
The DHC-2 / L-20 Beaver also came later in 1952. L-2 designation was changed to U-6A, de Havilland Canada built 1,657 of the type.
Built in Czechoslovakia the L-60 Brigadýr resembled the Storch. Aero Vodochody produced 273 examples from 1953–1960.
YO – Indicates an aircraft was a pre-production, or evaluation (Y), observation (O) aircraft. It was thus assigned a military designation number (Serial Number if USAF/USAAC/USAAS/USAAF or a Bureau Number [buno] if Navy/Marines) and a manufacturer’s serial number (MSN).
XO – Indicates the first test unit, or experimental (X), observation(O) aircraft
XL – Indicates experimental (X), liaison (L) aircraft
YO-57 (four built) and O-57 would become Taylorcraft L-2; Total 2,168
YO-58 (four built) and O-58B would become Aeronca L-3; Total (including L-16) 2,248
YO-59 (four built) and O-59 / J3C-65D would become Piper L-4; Total (all) 7,752
O-62 would become Stinson L-5, then later U-19; Total 3,590
XO-63 would become Interstate L-6, 251 built (one XO then 250 L-6), L-6 differs from the L-8 of which only eight were built for Bolivia; Total 259
In 1962 a new single letter designation system was implemented while the L-designation was dropped. U – Indicates a utility aircraft.