Editing Rotary engine (section)

====Siemens-Halske bi-rotary designs====
One clever attempt to rescue the design, in a similar manner to Redrup's British "reactionless" engine concept, was made by [[Siemens]]. The crankcase (with the propeller still fastened directly to the front of it) and cylinders spun counterclockwise at 900&nbsp;rpm, as seen externally from a "nose on" viewpoint, while the crankshaft (which unlike other designs, never "emerged" from the crankcase) and other internal parts spun clockwise at the same speed, so the set was effectively running at 1800&nbsp;rpm. This was achieved by the use of bevel gearing at the rear of the crankcase, resulting in the eleven-cylindered [[Siemens-Halske Sh.III]], with less drag and less net torque.<ref name="Gray_Profile">{{cite book |last=Gray |first=Peter L. |title=Aircraft in Profile No.86 — The Siemens Schuckert D.III & IV |year=1966 |publisher=Profile Publications |location=Leatherhead, Surrey, England }}</ref>{{rp|4–5}} Used on several late war types, notably the [[Siemens-Schuckert D.IV]] fighter, the new engine's low running speed, coupled with large, coarse pitched propellers that sometimes had four blades (as the SSW D.IV used), gave types powered by it outstanding rates of climb, with some examples of the late production Sh.IIIa powerplant even said to be delivering as much as 240 hp.<ref name="Gray_Profile" />{{rp|12}}

One new rotary powered aircraft, Fokker's own [[Fokker D.VIII|D.VIII]], was designed at least in part to provide some use for the Oberursel factory's backlog of otherwise redundant {{convert|110|hp|abbr=on}} [[Oberursel Ur.II|Ur.II]] engines, themselves clones of the [[Le Rhône 9J]] rotary.

Because of the Allied blockade of shipping, the Germans were increasingly unable to obtain the castor oil necessary to properly lubricate their rotary engines. Substitutes were never entirely satisfactory - causing increased running temperatures and reduced engine life.<ref>{{cite book| last = Guilmartin| first = John F. Jr.| title = Two Historians in Technology and War| year = 1994| publisher = [[United States Army War College]], [[Strategic Studies Institute]]| isbn = 1428915222| page = 10| chapter = Technology and Strategy: What Are the Limits? }}</ref><ref>{{cite book| last = Fisher| first = Suzanne Hayes| title = The European Powers in the First World War: An Encyclopedia| year = 1999| publisher = [[Taylor & Francis]]| isbn = 081533351X| page = 10| chapter = Aircraft, production during the war| editor = Spencer C. Tucker |editor2=Laura Matysek Wood |editor3=Justin D. Murphy }}</ref><ref>{{cite book |title=Tariff Information Surveys on the Articles in Paragraphs 44 and 45 of the Tariff Act of 1913 |year=1921 |author=[[United States International Trade Commission]]|page=40 |publisher=[[United States Government Publishing Office]]|location=Washington, D.C. }}</ref>