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Why was the D.V's headrest removed?
Short answer
Because it interfered with the pilot's field of view: early D.Vs carried a large headrest that was almost always removed in service. The model entered service in May 1917. British trials with a captured D.V found it slow to maneuver, heavy on the controls and tiring to fly.

A headrest that blocked the view
Early production Albatros D.Vs left the factory with a large headrest, but in service it was almost always removed, because it interfered with the pilot's field of view. The fighter entered service with the German air force in May 1917.
A poorly received fighter
Manfred von Richthofen criticized the new aircraft in a letter from July 1917, describing it as so outdated and so ridiculously inferior to British aircraft that nothing could be done with it. British trials with a captured D.V concluded that the aircraft was slow to maneuver, heavy on the controls and tiring to fly.
Airframe changes and service numbers
Compared with the D.III, the D.V's upper wing sat 121 mm (4.75 in) closer to the fuselage. Albatros later responded with the D.Va, which featured stronger wing spars, heavier wing ribs and a reinforced fuselage. That model also restored the D.III's aileron cable routing, which ran outward through the lower wing and then up to the ailerons. By May 1918 there were 131 D.V and 928 D.Va in service on the Western Front.
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