RE: Knowledge Quiz for Warbird wiz
You guys are good. metaldriver was very close but mustang1971 got it exactly.
Mustang 1971 gets next question.
The rest of the story... For much of 1916 the Germans had lost their advantages as new allied scouts like the DH.2 and Nieuports bested the slow Eindecker. Things changed again with the introduction of the First Albatros fighters, their 160hp Mercedes engines giving more speed and the carrying capacity to haul 2 guns. The Germans again had the upper hand in late 1916 so long as they stuck to boom and zoom tactics. However, pilots who tried to win a turning fight with the nimble Nieuports didn't fare as well.
Looking to close the maneuvering advantage, in the summer of 1916, Idflieg ordered the Albatros werke to copy the one unique feature of the Nieuport, its sesquiplane (1.5 wing) configuration. This they did, fitting a D.II fuselage and engine with a V-strut sesquiplane wing to make the D.III prototype, that went to the front in late December.
It wasn't long before reports came in of wings ripping off in a dive. The authorities didn't believe them at first because the few pilots who survived it reported the wing ripped off *downward*. What happened was that the lower wing spar was too far forward for the centers of mass and lift for that wing. This allowed the wing to flex in flight and its been calculated in modern times that the critical flutter speed was around 120-135mph. The D.III could only make about 109mph in level flight but in combat dive speeds well over 120 were common.
As you guys noted, in 1917 they didn't know what flutter was and assumed the spar was just too weak. So for the D.V and D.Va they strengthened the fuselage attachment and spar structure and also added an auxiliary strut from the V to the lower LE. All these changes added a lot of weight so they also added a 180hp Mercedes to compensate. The result was an increase in top speed to 115 or 117mph making the margin of safety to the critical flutter speed even lower. This is why the failures got worse in the D.V.
If they had today's knowledge they could have instead added weight to the LE of the lower wing (field modification) or moved the central spar back and completely solved the problem.
~Jeremy