Flight, June 1927

”THE SPIRIT OF ST. LOUIS"
The Ryan Monoplane Described

   Now that due homage has been paid to the human element of the splendid non-stop flight from New York to Paris, there is an opportunity to sit down quietly and contemplate the technical equipment used by Capt. Lindbergh in his historic flight. The personal factors that made for success were skill in piloting and navigation, unlimited pluck, and a magnificent physical constitution able to stand the strain of so many hours without sleep. It will be of interest to examine, in so far as we may, the technical factors that made the flight possible. Fortunately, we have been able to secure a good deal of technical documentation concerning the "Spirit of St. Louis," although it is regretted that at the moment detailed data relating to the Wright "Whirlwind" engine are not available. Some of these data can be estimated from information given incidentally in the calculations relating to the machine, but for others it will be necessary to wait for particulars to arrive from the Wright Aeronautical Corporation, the makers of the engine.
   The Ryan monoplane used by Lindbergh was designed by Mr. Donald A. Hall, chief engineer and designer of Ryan Airlines of San Diego, California, the firm which built the machine, and we are extremely glad to be in a position to present to our readers this week a number of graphs prepared by Mr. Hall in getting out his estimates for the transatlantic flight. No explanatory text accompanied the graphs, so that the following notes have been added by us mainly to assist in the task of interpreting the curves to those of our readers who are not very familiar with such work. Before doing so, however, a few words concerning the design and construction of the Ryan monoplane may be of interest.
   As the accompanying photographs will show, the Ryan N.Y.-P. type is a high-wing monoplane with strut bracing to the lower longerons of the fuselage, a radial air-cooled Wright "Whirlwind" engine in the nose, the pilot's cockpit situated under the trailing edge of the wing so that the view forward is entirely "blind," and a somewhat unusual undercarriage. The latter is of the divided type without wheel axle, the stub axles being the apices of two steel tube vees hinged to the lower longerons, and springing being by telescopic struts to the front wing spar strut, short sloping struts transmitting the load to the top longeron without imposing bending stresses on the wing strut, the structure being completed by a short vee to the lower longeron. The duty of this vee is, of course, to relieve the front wing strut of any bending load in a fore-and-aft direction. The arrangement does not make for "cleanness" particularly, but it does give a very wide wheel track and thus reduces the tendency of the machine to cartwheel on the ground.
   Structurally, the Ryan monoplane is of normal construction, the fuselage being a steel tube structure, while the monoplane wing is a wood and metal construction with box spars, wood ribs and tierod drag bracing. Generally speaking, the machine follows the lines of the Ryan M1 monoplane used for commercial work, the main difference being the larger petrol tankage and slightly larger wings. The wing section used is that known as the "Clark Y" section. The leading edge is covered over with three-ply wood so as to preserve a more exact wing curve and give greater strength. Ailerons of normal type and proportions are fitted. The tail surfaces are of steel tube construction.
   The "office" is, as already mentioned, under the trailing edge of the wing, and there is a window in each side and one in the roof. Diagonally forward and downward the view is good, but straight forward it does not exist, and a form of periscope has been installed to enable the pilot to look forward. This consists of a mirror which can be pushed out of the window and, in facing forward, reflects the view past the engine on to another mirror on the instrument board in front of the pilot. That this is anything but a makeshift arrangement can scarcely be claimed, but as Lindbergh was not likely to meet thousands of aeroplanes on his flight across the Atlantic, this compromise was chosen as being permissible for the particular flight, and the success of the flight proves this contention to have been justified. The shelter of a cabin, the relatively great distance away from the engine with its noise and fumes, were factors much more important than forward view, and the way Lindbergh handled his machine at Croydon under very bad conditions proved that sideslipping can be made to make up for poor view forward. In any case, the design of a machine for such a specific purpose involves endless compromises, and we have known of much worse than this one feature of the Ryan for which it has been criticised. In every other respect everyone agrees that the "Spirit of St. Louis" is a very good commonsense machine. That there is nothing startlingly remarkable in it from an aerodynamic point of view will be realised when we come to examine this side of its design.
   Following are the main dimensions, etc., of the Ryan monoplane: Wing span, 46 ft.; wing chord, 7 ft.; wing area, 319 sq. ft.; wing section, Clark Y; engine, Wright J-5-C, giving 223 b.h.p. at 1,800 r.p.m.; propeller, Standard Steel Propeller Company's, of Duralumin, set at 16 1/4 degrees pitch.
   The weight of the Ryan monoplane bare is 2,150 lb., and the load for the transatlantic flight was composed as follows: Pilot, 170 lb.; petrol, 425 gallons (Western at 6-12 lb./gal.), 2.600 lb.; oil. 25 gals, at 7 lb./gal., 175 lb.; total weight of load, 2,985 lb.; total loaded weight of machine at start, 5,130 lb.; weight of machine at end of flight, without petrol but with 10 gals, of oil left, 2,415 lb. Wing Loading: Fully loaded at start of flight. 16-1 lb. sq. ft.; light at end of flight, 7-57 lb. sq. ft. Power Loading: Full load at start of flight, 23 lb./h.p.; light at end of flight, 10-8 lb./h.p.
   Following is the estimated performance (r.p.m. data based on test and theory): Maximum speed with full load. 120 m.p.h.; with light load. 124-5 m.p.h.; minimum speed with full load, 71 m.p.h.; with light load, 49 m.p.h. Economic speed: with full load, 97 m.p.h. at 1,670 r.p.m.; with light load, 67 m.p.h. at 1,080 r.p.m. Fuel Economy at Economic Speeds: Full load with full rich mixture, 6-96 miles per gallon; light load with lean mixture, 13-9 miles per gallon. Range: At ideal speeds of 97 m.p.h. at start and 67 m.p.h. at end, 4,110 miles. At practical speeds of 95 m.p.h. at start and 75 m.p.h. at end, 4,040 miles.
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