The Lublin R-XX was a large twin engined floatplane that was about to enter production for the Polish Navy when the Lublin company went bankrupt, and thus never got past the prototype stage.
Work on the R-XX began in 1930 after the Polish navy began to look for a new heavy torpedo bomber seaplane. A number of companies were interested, including Fokker, Heinkel, several French concerns and within Poland P.W.S., P.Z.L. and Lublin. The foreign companies were soon ruled out, leaving the P.W.S.62, P.Z.L.18 and Lublin R-XX as contenders. Progress on the project was slow, and the Navy didn’t create a full specification for the design until 1933. The R-XX design was then chosen, and Lublin ordered to produce a detailed design. This was completed by the spring of 1934, and a single prototype was ordered late in 1934. The design of the prototype was signed off on 17 January 1935 and work was finally able to start, almost five years after work had begun on the design.
The R-XX was a large low-wing cantilever monoplane, with twin engines built into the thick wings, and large twin floats carried below the engines. It was one of the largest aircraft yet to be designed in Poland, and by far the largest seaplane built in the country, with a wingspan of 83ft 4.5in
To put the size of the aircraft in context, the prototype had a wingspan of 83ft 4.5in and a loaded weight of 13,227lb, the R-XXA was to have had a wingspan of 77ft 7.25in and a loaded weight of 14,911lb. The rival P.Z.L. 18 was to have had an even longer wingspan. The P.Z.L. P.37 Los twin engined medium bomber, which did enter service, was a smaller aircraft, with a span of 58ft 10.25in but heavier, with a loaded weight of 9,436lb. The Cant Z.506B, which was ordered instead of the R-XX, was a three engined floatplane with a span of 86ft 11in and a maximum weight of some 28,010lb (and an empty weight heavier than the R-XX!). Overseas the roughly contemporary Heinkel He 59 had a wingspan of 77ft 9in and an gross weight of 20,104lb. The estimated performance of the R-XXA was better than the actual performance of the He 59, but is of course a far less reliable guide to performance.
The prototype R-XX was powered by two 600-65hp Bristol Pegasus II:2 radial engines, with cowling rings and exhaust collectors added to the original design. It had a flat fronted nose, with the bomb aimers position below and an open gun position on top. The pilot’s cockpit was partly open, but protected by a windscreen. The cockpit carried side-by-side seats for the pilot and navigator. Windows in the side of the fuselage above the wings show where there was internal crew space for the radio operator, and a second open gun position was placed just above the trailing edge of the wings. It had a twin tail, with the horizontal surface mounted directly on top of the fuselage and small triangular vertical surfaces on top.
The prototype was taken to the Naval base at Puck in the summer of 1935 for its first test flights. It handled well, and had a surprisingly short take off run, half of the original estimates. However by this point the Lublin company was close to going bankrupt. It’s assets were taken over by the newly formed (and largely government owned L.W.S. company), which was not terribly enthusiastic about the R-XX. At first L.W.S. continued to work on the design, now designated the L.W.S. 1, but it’s preferred option was to develop a float plane version of the L.W.S.4 (P.Z.L. 30B) Zubr bomber, as the L.W.S.5. Work on the R-XX/ L.W.S. 1 was thus abandoned. However the Navy lost interest in the L.W.S.5 after the prototype of the L.W.S.4 crashed, and instead on 30 July 1938 placed an order for six Cant Z.506B torpedo bombers, with the intention of ordering another 12 in 1940. Only one of the Cant bombers had arrived before the German invasion.
The Cant 506B was in every way a better design than even the estimates for the R-XXA, with a top speed of 220mph while it’s cruising speed of 186mph was 24mph faster than the top speed of the R-XXA. It had more than twice the normal range, a better endurance and a higher service ceiling.
The slow progress on the R-XX meant that by 1934 it was a somewhat outdated looking design. Late in the year Lublin began work on the updated R-XXA. This had a redesigned fuselage, with a longer nose, fully enclosed cockpit and gun turrets replacing the open gun positions. It had a shorter wingspan, and a redesigned tail, with the vertical surfaces lowered so part of each was below the horizontal surface. It would have been armed with two sets of twin machine guns (one in the nose turret and one in the ventral position) and a 20mm dorsal cannon in a turret. The engines were given low-drag NACA cowlings and airscrew spinners.
The R-XXA design was submitted to the Navy early in 1935, before the flight of the R-XX prototype. The Navy requested the addition of Swiatecki type bomb racks and release gear for larger bombs and depth charges, and the use of a single fin and rudder in place of the twin tail. Lublin made these changes, and at the same time began work on a land based bomber version of the aircraft, with a fixed undercarriage with the wheels contained within rather sizable looking spats.
In the early autumn of 1935 the Navy placed an order for six R-XXAs, with six more to be produced each year after that. However in October 1935 the Lublin firm went bankrupt, and in December was reformed as L.W.S. The R-XXA became the L.W.S.1/I but none were ever built.
In the summer of 1935 the Lublin design team produced a new version of the design. Once again the fuselage was redesigned, this time giving the pilot an all round vision blister type canopy (in effect an early version of the bubble canopy). The nose was redesigned again. In theory the R-XXB would have replaced the R-XXA on the production lines if production had ever begun. After L.W.S. took over the design the R-XXB became the L.W.S.1/II.
R-XXA (family date for dimensions, factory estimates for performance)
Engine: Two P.Z.L Pegasus VIII or two Pegasus III
Power: 660-680hp each or 750hp each
Span: 88ft 7.25in
Length: 54ft 7.5in
Height: 19ft 4.5in
Empty Weight: 9,920lb
Loaded Weight: 14,991lb
Maximum Speed: 162.1mph at sea level
Cruising Speed: 141.1mph
Climb rate: 1,027ft/ min
Range: 590 miles (normal), 1,025 miles (maximum)
Guns: two machine guns in nose turret, two machine guns in position, 20mm cannon in dorsal turret
Bomb load: 2,205lb internally or one 1,764lb torpedo under fuselage