Please do post links, Colonel.
In regard to the 1917 quote:
The first big improvement in aircraft design came as the result
of work by aeronautical engineers who demonstrated the powerful
influence of streamline form on the efficiency of the airplane.
I have read that the Wright Brothers built their own wind tunnel with small-scale models before their first flight. It measured drag and lift.
One finding was that the propeller is just another wing--going in a circle--and so needs attention to its streamline shape.
The Wrights preferred wing-warping for control of their "Flyer" after experimenting with twisting a long box. Others discovered that separate hinged panels for such things as 'ailerons' worked better.
The Wrights' experience as bicycle mechanics helped them enormously in working out the mechanical connections.
But they made their own engine!
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I believe it was German engineers who used wind tunnels to discover 'laminar flow'--the tendency of air to cling close to the aircraft surface. That's why you can't blow the dust completely off your car by driving fast. It's like "laminated" wood--there are layers of air, and the bottom one sticks.
Any disturbance or breaking of this smooth flow adds drag.
Rivets with round heads sticking up are an example of flow disturbance. The Bf-109 put the theory to use (I don't know that it was the first such aircraft to use laminar flow techniques, however).
There was much international visiting among engineers before the coming 2nd World War put a stop to that.
The P-51 Mustang is a production example of an American engineer who visited German aircraft factories pre-war, putting the new 'laminar' ideas to very good use.
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Kind of off-topic:
If you sharply cut off the rear part just right, the air continues to flow as though a 'tapered' tail is still there. This discovery was mostly used in cars rather than aircraft. Especially race cars.
You can see many "Kammbacks" around you on the highway today. Almost every car has some version.
German aerodynamics engineers Baron Reinhard von Koenig-Fachsenfeld and Wunibald Kamm of Germany discovered the effect.
They produced this low-drag "Kamm"-tailed prototype in 1944.
The American-made "Gremlin" and the 1962 Ferrari 350 GTO are other examples of Kammbacks.
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