June 18 is the anniversary of a very significant letter for our project's current activity. Here is a brief summary of Wilbur's letter to Octave Chanute.

  "The only point of importance in the Maxim articles is the statement that the speed in his final trial was about 37 miles... (This) agrees better with our calculations of what it should be possible to attain with the screws and engines he used, and seems to confirm the correctness of our theory.

  "The papers on screws, by various authors, do not seem to me of very much value... Very little is known about the action of screws in motion forward. The action of screws not moving forward presents a very different case, and experiments based on such conditions are not applicable to the conditions met in practical flying... We think we have a method of figuring a screw in action... We will know more about its correctness when we have had a chance to try it.

  "Our engine develops at the brake 15.6 horsepower and we are convinced that this is very close to what we will be able to reach as a maximum. It furnishes in foot-pounds at the brake energy equivalent to 23 percent of the heat units contained in the fuel, so its efficiency is some twenty percent higher than the usual efficiency of gasoline engines which ranges from 14 to 18 percent of the total power contained in the fuel."

  Wilbur discussed the engine and propeller used in a balloon by Santos-Dumont and concluded that the 19 mile per hour speed reported and Wilbur's estimate of the balloon's drag indicated his propeller was about 50 percent efficient. This included an estimate of his engine power and an observation that French motors seemed to be rated at about twice their actual power. In summary, the power in Santos-Dumont's engine was sufficient to achieve the performance reported in news reports. (This is a remarkable set of predictions and observations supported by concise engineering estimates and explains why the Wrights chose to design and build their own engine.)

  Two final paragraphs further illuminate Wilbur's character:

  "That portrait business is a real nuisance, however, if we can get pictures pretty enough to do us justice (?), we will try to send you some within a few days.

  "I have finished the manuscript of my address and find that it contains about 5,500 words. In delivery I may not follow the manuscript very closely in some places but the matter will probably be about the same in amount."

  This address was the remarkable "Experiments and Observations in Soaring Flight" for the Society of Western Engineers that he delivered in Chicago on June 24, 1903.

Regards,
Gary A. Moir, PE

Reference, pages 316-318, The Papers of Wilbur and Orville Wright, Volume One: 1899-1905, Marvin W. McFarland, Editor, 1953, republished by McGraw Hill, 2001.

P.S.: See my bio and our current activity in our website at www.wrightflyer.org