J.Herris Pfalz Aircraft of WWI (A Centennial Perspective on Great War Airplanes 5)
Pfalz D.IV and D.V
In addition to the D.IIIa modifications, the Pfalz D.III was subject to a number of other experiments in a search for improved performance. One experiment was the installation of an experimental 195 hp Benz Bz.IIIb V-8 engine. This engine was not sufficiently developed and results were disappointing. This aircraft is thought to have been the Pfalz D.IV. Another experimental engine tested was the 200 hp Adler Ad.IV eight-cylinder; the aircraft with this engine likely was the Pfalz D.V.
Two experiments involved alternative engines built in the Austro-Hungarian Empire to allow license production there. First was a trial with the 200 hp Austro-Daimler engine. It was expected that the additional power would improve performance, but flight trials with this heavier engine demonstrated unacceptable flying characteristics. Next the lighter 160 hp Austro-Daimler engine was tried, but there was no improvement and the Pfalz D.III was not produced under license.