From Buchanan’s Jour­nal of Man, June 1887:

The air is cer­tainly yet to be nav­i­gated when a suf­fi­cient amount of power can be con­cen­trated in the machine, but at present we can do lit­tle more than float with the wind. It is prob­a­ble that an engine suf­fi­ciently strong, built of the best steel, and pro­pelled by the explo­sive power of gun cot­ton, or some sim­i­lar explo­sive, would over­come the dif­fi­culty. If I were to con­struct such an engine I would sub­sti­tute for the lift­ing power of a bal­loon that of a sail act­ing as a kite.