I'm pretty sure I've seen a photo of MvR in a D.VII at the Jan '18 trials sitting in the cockpit of a D.VII. Of course I can't find it now.
I found this on acepilots.com searching for the photo.
"By January 1918 the DR.I triplane was becoming dated. In aviation's rapidly evolving early days of WWI, advances in fighter plane design and powerplant came so rapidly that an aircraft's period of air supremacy was measured in months, not years. (From the perspective of the 21st Century, when everything technological changes so rapidly, it's counter-intuitive to think that anything, especially something high tech, like military aircraft, changed more rapidly then than now. But it's so. The airframes of modern airplanes have essentially been optimized and the avionics and weapons are so complex that they require years of development and testing.) The 160 horsepower Mercedes D.III in-line engine powered several new models tested at Adlershof that January, among them the Fokker D.VII prototype. Reinhold Platz, Fokker's chief designer, largely created the D.VII, while Anthony Fokker tested the aircraft, guided critical improvements, and marketed the airplane to Germany's military. Fokker's egotistical personality led him to minimize Platz' important contributions. In his aiutobiography he did not even mention Platz by name.
During the January tests,
Manfred von Richthofen tested the new airplane. While delighted with its maneuverability, he found it a little unstable, especially in a dive. To improve stability, Fokker lengthened the fuselage and added a vertical rudder fin, among other changes. The result was easy to fly, maneuverable, and safe. The Red Baron endorsed it wholeheartedly. The Adlershof trials showed Fokker at his best, quickly modifying the plane to meet requirements, charming the German aces, and (most importantly) delivering a fighter that offered good, all-around perfomance.
So taken were the pilots with the new Fokker biplane that the Kogenluft (Kommandierenden General der Luftstreitkräfte) ordered 900, with 300 to be built at Fokker's Schwerin factory and 600 under license at Albatros factories in Johannisthal (Albatros-Werke G.m.b.H.) and Schneidemühl (Osdeutsche Albatros Werke). Fokker had not prepared any construction blueprints; the aircraft had been built from jigs and assembly sketches. So Albatros had to make its own drawings based on a finished airplane. The resulting airplanes inevitably differed in small ways. Surprisingly, the Albatros machines, designated Fokker (Alb) and Fokker (OAW), were felt to be of higher quality than those made by Fokker itself..
Manfred von Richthofen, a great influence on German fighter plane development, looked forward anxiously to the D VII, writing Kogenluft on April 2, 1918:
"When can I expect to receive the [new] Fokker biplanes with the high compression engines? The superiority of British single-seat and reconnaissance aircraft makes it even more perceptibly unpleasant here. Their single-seaters fight by coming over at high altitudes and staying there. We cannot even shoot at them. Speed is the most important factor. We could shoot down five to ten times as many if we were faster. ... Please give me news soon about when we can count on the new machines."
Of course, Richthofen never flew the new machine, as he was killed on April 21st."