As engine fires occurred with the B-36's radial engines, some crews humorously changed the aircraft's slogan from "six turning, four burning" into "two turning, two burning, two smoking, two choking, and two more unaccounted for."
This problem was exacerbated by the propellers' pusher configuration, which increased carburetor icing.
The design of the R-4360 engine tacitly assumed that it would be mounted in the conventional tractor configuration—propeller/air intake/28 cylinders/carburetor—with air flowing in that order.
In this configuration, the carburetor is bathed in warmed air flowing past the engine, so is unlikely to ice up.
However, the R-4360 engines in the B-36 were mounted backwards, in the pusher configuration—air intake/carburetor/28 cylinders/propeller.
The carburetor was now in front of the engine, so could not benefit from engine heat, and also made more traditional short-term carburetor heat systems unsuitable.
Hence, when intake air was cold and humid, ice gradually obstructed the carburetor air intake, which in turn gradually increased the richness of the air/fuel mixture until the unburned fuel in the exhaust caught fire.
Three engine fires of this nature led to the first loss of an American nuclear weapon when a B-36 crashed in February 1950.
As engine fires occurred with the B-36's radial engines, some crews humorously changed the aircraft's slogan from "six turning, four burning" into "two turning, two burning, two smoking, two choking, and two more unaccounted for." This problem was exacerbated by the propellers' pusher configuration, which increased carburetor icing. The design of the R-4360 engine tacitly assumed that it would be mounted in the conventional tractor configuration—propeller/air intake/28 cylinders/carburetor—with air flowing in that order. In this configuration, the carburetor is bathed in warmed air flowing past the engine, so is unlikely to ice up. However, the R-4360 engines in the B-36 were mounted backwards, in the pusher configuration—air intake/carburetor/28 cylinders/propeller. The carburetor was now in front of the engine, so could not benefit from engine heat, and also made more traditional short-term carburetor heat systems unsuitable. Hence, when intake air was cold and humid, ice gradually obstructed the carburetor air intake, which in turn gradually increased the richness of the air/fuel mixture until the unburned fuel in the exhaust caught fire. Three engine fires of this nature led to the first loss of an American nuclear weapon when a B-36 crashed in February 1950.
Convair B-36 Peacemaker