## Wilbur Wright to Octave Chanute

Dayton, January 1, 1905

We have your letter of Dec. 26th and thank you for the kind wishes expressed therein. We trust that you also will enjoy health and prosperity through the new year.

Your suggestion regarding the power expended by birds found us considering that very point, having been led to consider the subject by the very ingenious calculations of Sir George Cayley as published in the Aeronautical Annual for 1895. He attempts to compute the power expended by a consideration of the thrust possible to be obtained by a crow in its flight, but the result obtained was too favorable, in his opinion, and I am inclined to think the same, though I have been unable to complete some calculations of a somewhat similar nature from lack of definite information regarding the tip to tip measurement of a crow. Do you possess any information on this point? It is my present impression that 75 lbs. to the horsepower is about the limit of what a flying machine will be capable [of] at a speed of thirty miles an hour; 35 lbs. at seventy five miles; and less than 20 lbs. at one hundred miles. I see no hope, based on any information at present accessible, for any considerable advance on what we have already done in the matter of dynamic efficiency. I think I the great room for improvement will be found to be in mechanical details and methods, and especially in the skill of the operators. If it could be definitely proved that the birds do very much better, it would lead to a revision of our present views, and therefore we are intending to give bird flight careful study when opportunity can be found. If it can be proved that a crow raises and lowers the tip of its wings less than twenty two or twenty four inches, it evidently flies with less power than is yet possible with a gliding machine or flyer. For if it be estimated that the crow moves twelve feet with each wing stroke it would have to raise itself the equivalent of eighteen inches vertically in order to maintain horizontal flight, assuming its gliding angle to be one in eight. We do not find the January copy of Moedebeck's paper in our files and cannot now recollect that we have ever seen that number. We had copies of the February and March numbers. With best wishes.