The Curtiss Model 31 CS was a reconnaissance and torpedo bomber aircraft used by the United States Navy during the 1920s.
It was a large single-engine biplane with single-bay unstaggered wings, the design conventional in all respects other than that the lower wing was of greater span than the upper.
The CS was built to allow its undercarriage to be quickly and easily interchangeable between wheeled, tailskid undercarriage, and twin pontoons for operation from water.
Provision for the carriage of a torpedo was semi-recessed into the underside of the fuselage, blended in behind an aerodynamic fairing.
The pilot and gunner sat in tandem open cockpits, while accommodation inside the fuselage was provided for a third crewmember who served as bombardier and radio operator.
This station was also provided with a dorsal hatch aft of the gunner’s position, and a ventral blister aft of the torpedo recess, which was used for aiming bombs or torpedoes.
Curtiss produced six CS-1 prototypes for the Navy in 1923, which were mostly used for engine tests.
Two examples of the improved CS-2 were built the following year and set a number of world speed, distance, and endurance records for seaplanes in its class.
The Navy ordered both the CS-1 and CS-2 into production, but when Curtiss tendered with a price of $32,000 per aircraft, Martin undercut them with a tender of $25,200 for each CS-1 and $19,863 for each CS-2 and won the contract.
Curtiss refused to provide full sets of drawings and data to Martin, so Martin-built machines were in part reverse-engineered from a Curtiss-built CS-1 provided by the Navy.
By the time the Martin-produced aircraft were delivered in 1925–26, the Navy’s designation system had changed, and they entered service as the SC-1 and SC-2.
Martin-built SC-2s suffered from poor handling characteristics and soon earned the nickname “Sea Cow”.
Meanwhile, the Naval Aircraft Factory made extensive modifications to the two Curtiss CS-2s leading them to be redesignated CS-3.
Further development of the design was carried out by Martin as the T3M and T4M, and eventually by Great Lakes as the TG.
Variants
Curtiss CS-1
Initial prototypes/production, powered by 530 hp (395 kW) Wright T-2 engine.
Six built by Curtiss.
Curtiss CS-2
Improved version with 600 hp (448 kW) Wright T-3 engine and more fuel.
One converted from CS-1 and two new-built aircraft by Curtiss.
Curtiss CS-3
Modified CS-2, with geared engine.
One converted.
Formed basis of Martin T3M.
Martin SC-1
Martin built production version of CS-1. 35 built.
Martin SC-2
Martin built production version of CS-2. 40 built.
Martin T2M
Alternative designation for the Martin built SC series.
Martin XSC-6
Conversion of SC-1 with 730 hp (545 kW) Packard 1A-2500 engine.
Martin SC-6
SC-1 fitted with 1A-2500 engine.
XSC-7
Conversion of CS-1 with T-3A engine and increased gross weight.
