A Voice From The Past on Airplane Parasite Drag
"Ever since I first began to study aeronautics I have been annoyed by the vast gap which has existed between the power actually expended on mechanical flight and the power ultimately necessary for flight in a correctly shaped aeroplane. This annoyance is aggravated by the effortless flight of birds and the correlated beauty and grace of their forms. We all possess a more or less clear ideal of what an aeroplane should look like, a kind of albatross with one or two pairs of wings."
..."Apparently, large commercial airplanes of today would, were they ideally streamlined, either fly at present top speed for one-third of the present power, or alternatively, travel some sixty miles an hour faster for the same power."
..."There is a natural tendency to decide on one day that the gain - say 20%, on the total drag, or 7%, on the speed, - to be had by spending endless trouble on improving the undercarriage design, is not worth the trouble; on the next day to come to a similar conclusion about the drag of the engine cooling apparatus; on the next day about the wires, struts, and minor excrescences, and on the next day about the pilots view; omitting to notice that if all the improvements were made at once the total gain would not be some insignificant percentage of the whole, but might reduce power consumption to a small fraction of its original value and so extend the range and usefulness of the aeroplane into realms which would be otherwise attainable."
..."Reduction of drag will enable an aeroplane of a given power loading, either to cruise at higher speed or with a lower petrol consumption. This again will result in increased range or paying load, both factors of importance in aeronautical development."
..."We all realize that the way to reduce (total parasite drag) is to attend very carefully to streamlining."
..."It is, of course, well known that, unless bodies are carefully shaped, they do not necessarily generate streamline flow but shed streams of eddies from various parts of their surface. The generation of these eddies, which are continuously being carried away in the airstream, requires the expenditure of power additional to that required to overcome induced drag and skin friction.
...The power absorbed by these eddies may be, and often is, many times greater than the sum of the powers absorbed by skin friction and induced drag. The drag of a real aeroplane therefore exceeds the sum of the induced drag and skin friction by an amount which is a measure of defective (or lack of) streamlining."
Professor B. Melville Jones, Professor of Aeronautical Engineering at Cambridge University, Great Britain. Some excerpts from a lecture before he gave to the British Royal Aeronautical Society in May of 1929.