After a series of proving flights at Hendon, "1456" was accepted by the RNAS and was flown to Manston for further trials. These revealed that despite a reduced balance area on the elevators, there was still a tail oscillation problem. A lack of directional stability caused by the increased forward side area was partly cured by adding a fixed fin but to find the cause of the tail oscillation, the Admiralty called in Frederick Lanchester from the National Physics Laboratory. Lanchester agreed that simple structural weakness was not the root of the problem and that resonance of the fuselage was the probable cause. Static tests on the third prototype which had a redesigned, stiffer, fuselage structure showed nothing. Lanchester flew as an observer in an amidships crew position on 26 June. The tail oscillations started at and Lanchester observed that the tail twisted by 15° to either side and that there was asymmetrical movement of the right and left halves of the elevators, which were connected by long control cables rather than being rigidly linked. He recommended that they be rigidly linked, that elevator balances be removed and additional bracing added between the lower longerons and the lower tailplane spar, measures which were successful in solving the problem.