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The Loening OL was an unusual amphibian aircraft that used a single main float carried under the fuselage instead of the more standard flying boat hull. The OL was designed by Grover C Loening, a very talented aircraft engineer. His aim was to produce an amphibian with the performance of a landplane.
The same type of main float was used on the later Grumman JF and Grumman J2F Duck. This wasn't entirely surprising, as Leroy Grumman had worked for Loening, and the Grumman Company was originally founded to maintain existing Loening aircraft, with financial backing from Grover C Loening,
The OL was based on the Army's OA-1 (Observation, Amphibian). This had originally been developed in 1923 as the COA-1, powered by a 400hp Liberty V-1650-1 engine. The navy was interested in the design, and ordered two aircraft of its own, giving them the designation OL-1. These aircraft were similar to the COA-1, but carried a third cockpit (all in tandem) and were powered by a 440hp Packard 1A-1500 engine. The second OL-1 included a number of design improvements.
In 1925 the Navy bought five COA-1s for use on that year's Arctic Expedition. These aircraft were identical to the Army's COA-1, with the Liberty engine and a crew of two.
Next came the OL-3, which was based on the second improved OL-1, with the three-man crew and Packard engine. This would be the basis of all remaining versions, which eventually reached the OL-9, produced after Loening had merged with Keystone. The biggest change came with the OL-8, which used a Pratt & Whitney Wasp radial engine, and reverted to the two-man crew. The OL-8, OL-8A and OL-9 accounted for 66 of the 111 OLs of all types produced for the US Navy.
Variants
OL-1
The first two aircraft ordered by the Navy were given the designation OL-1. They were similar to the Army's COA-1, but with a third cockpit and used 440hp Packard 1A-1500 engines in place of the Liberty engines of the Army Aircraft. The second aircraft included a number of improvements and became the model for the OL-3 and most later entries in the series.
OL-2
Five aircraft were ordered in 1925 to take part in that year's Arctic Expedition. They were identical to the Army's two-man COA-1 and were powered by the Liberty engine.
OL-3
The OL-3 was the designation given to four aircraft that were identical to the second, improved, OL-1. They were thus powered by the Packard engine and carried a crew of three.
OL-4
The OL-4 was the designation given to six aircraft that were similar to the OL-3, but powered by the Liberty V-1650-1 engine.
OL-5
The OL-5 was the designation given to a small number of OL amphibians that were ordered for the US Coast Guard in 1926. Three were purchased late in 1926, and alongside three Chance-Vought UO-4s became the first aircraft to be owned by the Coast Guard. The first OL-5 was delivered in October 1926, making it the first aircraft to be built for the US Coast Guard. The OL-5 had a reinforced hull bottom and keel, modified wing-tip floats, higher rudders, extra fins and carried more fuel. Two of the three aircraft were written off after crashes and the third was retired in 1935. They were used for air-sea rescue and even armed with machine guns for police work.
OL-6
The OL-6 was similar to the OL-3, but with a more angular fin and rudder, first introduced on the Army's OA-1C. It was otherwise similar to the OL-3, with a three-man crew and the Packard engine. Twenty eight were built, making it numerically the most important variant.
XOL-7
The XOL-7 was a single OL-6 that was given experimental thick-section wings.
XOL-8
The XOL-8 was a single OL-6 that was given a Pratt & Whitney Wasp radial engine. This engine was adopted in the remaining production versions of the aircraft. The new engine had no real impact on speed, but it did almost half the time it took to climb to 5,000ft and improved the service ceiling.
OL-8
The OL-8 was the production version of the XOL-8. It reverted to the two-main configuration of the OL-2 and Army aircraft, but with the angular tail introduced on the Ol-6 and the Pratt & Whitney engine of the XOL-8. Twenty were built.
OL-8A
Another twenty aircraft were built as the OL-8A, which was identical to the OL-8 apart from the introduction of arrester gear to allow for carrier operations.
OL-9
The last twenty-six aircraft were produced as OL-9s. These was the same as the OL-8, but were produced after Loening had merged with Keystone.
Stats for OL-3
Engine: Packard 1A-2500
Power: 475hp
Crew: 3
Span: 45ft
Length: 35ft 1in
Height: 12ft 9in
Empty Weight: 3,673lb
Gross Weight: 5,316lb
Maximum Speed: 122mph
Climb rate: 10 minutes to 5,500ft
Service Ceiling: 13,000ft
Range: 423 statute miles