The Justification of Herr Dornier: An Examination of the Performance of the Do.X. Seaplane

WE are sure our readers will join us in thanking Herr Dornier for freely placing at our disposal for their benefit a lecture recently delivered by him in Munich. This forms the corollary to the slightly condensed translation of a previous lecture of his, describing the Do.X., published in the December, 1929, issue of Aircraft Engineering. That article contained very complete data on the construction, dimensions, and weights of the sea‐plane. These, coupled with the further data on performance now made available, give a tolerably complete picture of this seaplane. In his 1929 lecture Herr Dornier stated that the area of the main plane, including the auxiliary top plane connecting the engine housings, was 5,431 sq. ft. Since then the auxiliary plane has been removed. We have no data as to what its surface was, but we shall clearly not be understating the existing lifting surface, of the main plane alone, if we estimate it at the round figure of 5,000 sq. ft. The maximum gross weight, fully loaded, with which the seaplane has been taken off the water—at Lisbon—is stated to be 54·5 metric tons (120,0001b., or 53·5 English tons). This gives a wing loading of 24 lb. per sq. ft. It is interesting to note that, according to Herr Dornier, the Do.X. satisfied D.V.L. requirements as a freight‐carrier with a gross weight of 59 metric tons (129,800 lb.). This, however, was, apparently, when the auxiliary wing was still included in the design, so that the wing loading comes out about the same. It would have been interesting if Herr Dornier had given details of any alighting speeds actually measured. According to British standards, the wing loading is undoubtedly very high, and we doubt whether the resulting alighting speed—which must be in the neighbourhood of 80–90 miles an hour—would be acceptable for a British Certificate of Airworthiness.