The third Model 264 was completed as the YP-29B with an open cockpit configuration similar to that of the YP-29A. The serial number was "34-25". The only outward differences between it and the YP-29A were the addition of a one-piece wing flap similar to that of the YP-29, an additional one degree of dihedral in the wing, and an oleo tail wheel assembly similar to that of the YP-29. The YP-29B was sent to Chanute Field in Illinois for service testing. It was eventually redesignated P-29B, adding to the bewildering succession of designations for essentially the same model.