The German Giants The German R-Planes 1914-1918 GWHaddow Peter M Grosz The German Giants R-Planes 1914-1918 The German Giants The German R-Planes 1914-1918 GWHaddow Peter M Grosz '() 1962 G. W. Haddow & Peter M. Grosz First Published July 1962 Reprinted September 1963 Second Edition April 1969 CONTENTS Third Edition 1988 ISBN 0 85177 812 7 Acknowledgements IV Introduction VII PART I What is an R-plane'! "However, if 1 had waited long enough 1 probably never would have wriffen Operational History 9 anything at allsince there is a tendency when you really begin to learn something Eastern Front Operations 10 about a thing not to want to write about it, but rather to keep on learning about R-plane Raids on England 25 it always, and at no time unless you are very egotistical which ofcourse accounts for many books wi!! you be able to say'now I know all about this and wi!! write Western Front Operation 39 about it." Operational Losses 44 Post-War Operations 47 Ernest Hemingway Death in the AjiernooJl Appendix Flight Log of Staaken R.V 13115 52 Appendix 2 Organization ofR-plane Troops 53 Appendix 3 List of German Army Air Service Officers who died while attached to R-plane Units 55 Appendix ~ Operational Missions of Rfa 501 (Eastern Front) 56 Appendi>.. " Statistical Comparison of Bombengeschwader 3 and Rfa 501 during the England Raids 56 Appendix 6 Chart of R-plane Raids on England 57 Appendix 7 Operational Missions of Rfa 500 and Rfa 501 (Western Front) 58 Appendix 8 Performance of R-planes on Combat Missions 59 Appendix 9 Operational R-plane Losses 61 Appendix 10 Projected Delivery Dates for R-planes 62 Appendix II List of R-planes to be completed after 31 January 1919 63 Appendix 12 Description ofGerman Bombs 64 Appendix 13 Chart of R-plane umbers. Dimensions and Performance 67 Appendix I~ Sikorsky "Ilia Mourumetz" 70 PART II Printedandboundin Creat Britainfor Description of R-plane Types (Alphabetically) 73 Putnam, an imprint ofConway Maritime Press Ltd., 24 Bride Lane, Fleet Street, Selected Bibliography 303 London EC4Y8DR at the University Printing House, Oxford Index A Aeroplanes 305 Index B General Subjects 307 III ill-fated RML.I (VGO.I) and later test pilot of the Staaken E.4/20; Dipl.-Tng. Richard Llihr, technical officer of Rfa 500 during the early days on the Eastern Front; Wilhelm Pfaff, who served in Rfa 500 during the last months of the war and, as an engine mechanic on the R.45, par ticipated in several bornbing raids; Bruno Steffen, designer and test pilot, who provided much interesting material regarding the Siemens-Schuckert R-planes; Dipl.-Ing. Harald Wolff, chief of the SSW aircraft design bureau during the war, and to Frau E. von Bentivegni for details concern ingthe life ofher husband, the long-termcommander ofRfa 501. Working with the above has been a rewarding pleasure, and we hope they have enjoyed reminiscing about the past as much as we have enjoyed hearing and reading their stories. Our thanks and appreciation go also to the many air hi torians and enthusiasts who helped so much in providing material and photographs, in particular: the late A. R. Weyl, co-author ofthe classic engineering text on R-planes; Egon Krueger, who contributed valuable original material; Dr. Douglas Robinson for his friendly criticism and knowledge ofGerman aval history. AI 0, the following who generously provided assistance deserve our thanks: Mes rs. Peter M. Bower, Rex Brown, Bud R. Erb, Frank L. Greene, Alex Imrie, Albert L. Lang, Heinz Nowarra, William R. Puglisi, William W. Richardson and Douglas Whiffen. Staakcn tcst pilotscommemorating the completion ofthe 25th Staaken R-plane, an R.XIVa. Third from thc right IS Willy Mann who flew the first R-planc built by VGO. Our thanks also to Rear Admiral E. M. Eller, USN (Ret.). Director of Naval History, through whose kind offices the German Naval Archives were made available for inspection; A. J. Charge, Keeper ofPhotographs at the Imperial War Museum, London; The Still Photo Collection, USAF, Washington; Archiv fur Fluggeschichte und Luftschiffahrt, Berlin; Luftfahrt-Verlag Walter Zuerl, Munich; and the U.S. Air Force ACKNOWLEDGEMENTS Museum, Dayton. The authors also wish to express their thanks to Mrs. Peter Grosz for The authors owe a great debt of gratitude to the many individuals and valuable assistance in preparing the manuscript. organizations who so freely and graciously contributed to the compilation of this book. Particular mention is due to those veterans (now alas, very few) who actually participated in the development and operation of the ACKNOWLEDGEMENTS TO THE 2ND EDITION R-planes; they extended to us their records and recollections of those New contacts with surviving R-plane personnel, brought about by early days and generously allowed us to use photographs from their publication of The German Giants six years ago, has added many details albums. Our sincere thanks go to: Obit. a. D. Max Borchers, one of to the story of these fascinating machines, and made possible this revised the first members of Rfa 501 and last commander of Rfa 500; Paul second edition. Bi.ittner, a ground crew member in charge of gyro-compass installation We would like to extend our appreciation and thanks to all the following and servicing, whose excellent descriptions provided much background who were involved in the development of R-planes. Phillip Simon, the material on the activities of Rfa 501; Oberstabsingenieur a. D. Hans man responsible for quality control and stressing at VGO-Staaken, for Heitmann, a foreman at SSW, for his fact-filled and often amusing his first-hand account ofactivities at Gotha and Staaken. Max Schaefer, anecdotes offlights at Doberitz and at the Front; Dipl.-Ing. Wilhelm Hill one of the original employees of VGO, for his recollections and for mann, active as a designer in the early aircraft activities of Schlitte-Lanz; allowing us to delve into his superb photo album. Erich Bruno Schroter, Hptm. a. D. George Krupp, who first organized and commanded Rfa 501 Dornier test-pilot, who shared his early memories with us. To Direktor and later in the war was active in the testing and development of new Jager, who began a life association with Dornier as a test pilot in the R-planes for Jdflieg; Carl Kuring, second pilot and only survivor of the v First World War, who made available to us portions of the Dornier archives. Also to Werner Zorn, who as a young man worked in the AEG design office, for new material concerning the AEG R.I. Also to Mr. Fiedler, who witnessed the break-up ofthe AEG R.I from an accompany ing aircraft. Our most grateful thanks go also to the following veterans who flew INTRODUCTION R-planes on active service, for their fact-filled reminiscences: Waldemar Roeder, co-pilot of the R.13, R.SS and R.70; Heinrich Schmitz, pilot of The great technological progress made during World War II was the the R.9 and later 1st pilot of the R.13, and crew mate of Roeder; Joseph natural product of a time when the expenditure of vast sums of money Klose, wireless operator on the R.31, who by merest chance was replaced and material was secondary to the achievement of victory. The enormous just prior to the R.31's last take-off; and finally to Otto Neumann, former scientific endeavour, in which all nations shared, has provided the key to R-plane mechanic who survived several crashes, including that of the the harnessing of atomic energy and has placed mankind on the threshold R.28 when its bombs exploded after an emergency landing. of interplanetary flight. In World War I, technology played a similarly We would also like to thank Dr. Schildberger, who placed the album of dramatic role in advancing the science ofaeronautical engineering. Aero Robert Klein, his brother-in-law, at our disposal. Also Mr. B. Hulsen, planes grew from simple wood-and-wire flying machines to the sophisti of the Daimler-Benz Archiv, who made it possible to include the history cated all-metal aircraft which were being built on a production-line basis of the Daimler bombers. Our thanks go too to Erik Hildes-Heim, who at the close of the war. brought the Adlershof projects to our attention. Finally we gratefully No small part of this progress belonged in the field of giant aircraft acknowledge the valuable assistance provided by the Bayerisches Kriegs development, particularly in Germany. German engineers in a few short archiv and the Bundesarchiv-Kriegsarchiv in Freiburg. years had spanned the gulf between crude wooden biplanes and all-metal, muIti-engined, monoplane giant bombers. Much of the story of the German giant bomber has been forgotten or ACKNOWLEDGEMENTS TO THE 3RD EDITION not received its share of emphasis in the annals of aviation history. The Almost twenty-five years have passed since The German Giants was first purpose ofthis book, then, is to trace the evolution ofthe R-plane from its published. We never dreamed that there would be a second indeed even a inception, through the war and into the immediate post-war period. The third edition of this work. During the intervening years, our interest in first section ofthe book describes the R-plane and its operational history. German R-planes has remained active with the result that new documenta The second section traces the technical evolution of each R-plane type, tion and photographs have been gathered, but we were pleased to note that including as much historical material as has been possible to gather. It is in preparing this amended third edition, the text as originally published acknowledged that the story is not and perhaps never will be complete, required only minor additions and corrections. Some of the photographs but it is hoped that this work will provide a source of reference and a have been replaced by superior ones that we feel are more descriptive of starting-point for future researches in a fascinating field. the subject matter. We have dropped the individual photo credits since the Because the various R-plane types are described alphabetically by originals of most photographs are in the authors' possession or have been company, the following briefhistory will assist the reader in placing major supplied by several sources. All photograph contributors are given credit events and company activities in the proper chronological sequence. in the acknowledgements. The story of all large multi-engined aircraft began with Igor Sikorsky's In addition to the persons mentioned in the previous acknowledgements, "Le Grand", the world's first four-engined aircraft. This signal achieve we should like to express our thanks to Dr. Holger Steinle of the Museum ment stimulated the imagination of engineers, flyers and financiers fUr Verkehr und Technik in Berlin and Dr. Siegfried von Weiher of the throughout the world, for here was the true promise of flight; a vehicle Werner von Siemens Institut in Munich who have been most supportive of to conquer long distances at high speeds in relative safety. our efforts with documentation and photographs and finally to Dr. Volker In ]913 the Daily Mail established a £]0,000 prize to be awarded to the Koos of Rostock for his photographic contributions. first pilot to cross the Atlantic in an aeroplane. Among the many com Only a few of the R-plane pioneers who appear in the text are still with petitors were Glenn Curtiss, with his flying-boat "America" and Handley us. Our deep respect for these stalwart pioneers-engineers and aircrews Page with their HP L/200. Another aspirant was Hellmuth Hirth, one of alike-remains undiminished. To them and all those who helped and Germany's most skilful famous pilots. Hirth proposed a six-engined supported our endeavours through the years, our deep and grateful thanks. seaplane to Gustav Klein, the director ofthe Bosch Works, in the summer VI VII Concurrent with the beginning of the Staaken venture in late 1914, of 1913. With the financial backing of Robert Bosch, Hirth and Klein Graf Zeppelin, with brilliant foresight, commissioned Claudius Dornier planned to have the seaplane ready for the transatlantic attempt in the to design and construct all-metal R-seaplanes. At the end ofthe war both late summer of 1915 and then to place the aircraft in the San Francisco Dornier and Staaken R-seaplanes were under test at Navy experimental Exhibition of 1916. The outbreak of World War I forced all plans and aspirations to be stations. By 1918 R-plane engineering had reached a high level of development, shelved. However, Graf Zeppelin, Germany's "father ofthe airship", saw which made the construction of all-metal monoplane bombers feasible. in the Hirth-Klein project the potential vehicle for carrying large bomb These were to be high-performance and heavily armed aircraft capable of loads over long distances. To this end a corporation was formed and executing unescorted daylight bombing missions. None ofthese R-planes, backed jointly by Bosch and Zeppelin, and in September 1914 the con destined for Army squadrons, was completed, but their"design philosophy struction of the first of a long line of Staaken R-plane bombers started. One month later, in October 1914, Siemens-Schuckert began to construct was mirrored in the four-engined Staaken E.4/20, the first truly modern an R-plane based on the "Le Grand" formula. This aircraft was not a transport aircraft. This revolutionary all-metal monoplane was completed in 1920 at a time when the tide of German aviation was at its ebb. One success despite numerous modification, and further development of this look back at the early Staaken and Siemens-Schuckert giants is visible configuration was stopped. In December 1914 Bruno and franz Steffen proof of the swift progress which the German R-plane industry had made joined with Siemens-Schuckert to build an R-plane based on designs which the Steffen brothers had evolved before the war. A follow-up contract for in the war years. six additional machines was awarded in June 1915. The third company to undertake construction of an R-plane prior to 1916 was the Deutsche Flugzeugwerke, but technical difficulties prevented their bomber from reaching operational service until 1917. During 1915 and early 1916 the few Staaken and Siemens-Schuckert R-planes flying at home and at the front were beginning to show relatively promising results, contrary to the expectations of the majority of the military leaders. The maturing of the R-plane's war potential came at a time when mounting airship losses made the future of the airship as a weapon seem dim indeed. The R-plane, superior in almost every respect, was the natural replacement for the airship as a long-range bombing and reconnaissance weapon. Therefore, the German Army High Command set in motion a large R-plane production programme in mid-1916 which eventually embraced many companies throughout Germany. By early 1916 two Army R-plane squadrons had been formed to evaluate the fledgling giant bombers, to gather experience under front-line con ditions and to prepare for the more powerful R-planes to follow. Known as Riesenflugzeugabteilung 500 and 501 (Rfa-R-plane Squadron), these two squadrons were initially stationed on the relatively quiet Eastern Front. After the collapse ofthe Russian Army Rfa 500 and 501, equipped with new aircraft, were transferred to the Western Front, where they saw action over England and France until the war's end. The German Navy did not neglect to investigate the possibilities of the R-plane for naval warfare. Jndeed, the Navy supported the Staaken venture from the beginning, and actually placed an order for the first two R-planes built by Staaken. In 1916 a Navy R-plane squadron Aew along side Rfa 500 for a short period of time. Land-based R-planes, however, were abandoned by the Navy in favour of R-seaplanes, the development of which was actively fostered. VIII IX PART I What is an R-Plane? All aeroplanes used by the German Army in World War I were classified according to their "c" function by one or more letter subscripts. For example, aircraft classified by a were observation aircraft, "D" stood for fighters, "G" for bombers and so forth. The letter "R", the functional classification given to large bombing machines, was an abbreviation of "Riesenftugzeug" (giant air craft). Although an R-plane's function, like the G-types, was bombing, the R-plane differed not only in size but in more significant aspects, which are discussed later in this chapter. Actually the earliest R-planes were. for a time, classified as G-type bombers, and the "R" classification was not authorized until late 1915.1 The functional letter classification was preceded by the manufacturer's name and followed by a Roman numeral to indicate the model (or design) number of the aircraft, i.e., Staaken R.JV. In addition, all Army aircraft were assigned a military serial numberfollowed by two digits representing the year in which the aircraft was ordered, for example: AEG R.I 21/16. In the case of licence built aircraft the manufacturing firm was represented by an abbreviation of its name as follows: Staaken R.YI (Schill) 27/16. Because relatively few R-planes were built during the war, it was cus tomary to refer to individual machines by their functional letter and serial number in official documents. a practice which is retained in this book, i.e., R.21, R.55, R.75, etc. The allocation of the military serial numbers for R-planes differed from the conventional system in which the serial numbers were renewed each year. It was possible, for instance, that two different fighter aircraft could have the same serial number, differing onlyin the year the aircraft were ordered. i.e. D.1220/17 and D.1220/18. On the other hand, R-plane serial numbers were not re-issued yearly, but ran consecutively from R.]/15 to R.86jl8. Another exception to the rule was madein ]916, when a block of serial number in the R.200 range was set aside for advanced R-plane project which were still in the design stage or under construction at the close of the war. What were the criteria by which an aircraft was given the "Riesenflugzeug" classification? Ifsheer size, weight or horse-power were the hallmarks ofan R-plane, then one would expect to find orne yardstick by which to measure them. But such was not the case, and the best way to answer the question is to study excerpts from the Bau und Liefervorschriften fiir Heeresj1ugzeuge (BLY-Con struction and Delivery Specifications for Army Aircraft), which regulated the construction of all German Army aircraft. A similar set ofspecifications which applied to the construction and delivery of all naval aircraft. R-seaplanes included, was known as the Allgemeine Baubestin1l111111gell fur Marinej1ug::.euge (ABB-General Construction Specification for Naval Aircraft). Initially R-planes were built within the framework ofthe existing BLV specifications, and by 1916 the BLY already included a handful of special regulations for R-planes. However, these were not nearly comprehensive enough considering the breadth and unique requirements of an R-plane. As a result, by the end of 1916 a BLY intended solely for R-planes was drafted by the Inspektion der Fliegertruppen (ldflieg-Inspectorate of Aviation Troops) and distributed to the various R-plane manufacturers for approval. Known as the BLYR, this document went into effect on 22 January 1917. Although it drew heavily from the existing BLV, it did contain several specifications which set the R-plane apart from all other German aircraft. The BLYR consisted ofmany pages ofdetailed technical and engineering regulations; consequently only the most pertinent and illustrative para graphs are quoted. Excerpts from the "Construction and Delivery Specifications for R-Planes-1917" (BLVR) I The "R" classification was authorized sometime after 8 August 1915 for on that date an Idflieg document still refers to the VGO.I as the Zeppelin G.T and the SSW R.I and R.II as G.T and G.1l respectively. 1. Arrangement of the Fuselage stopping any engine. Friction clutches must be protected against oil. For the preservation A. General-The R-plane is distinguished from G-type and smaller aircraft by its ability ofgearteethand conservation ofuniform rotary movement, theenginesshall haveflywheels, to fly for severalhours with very large loads. Correspondingly, it is equipped with powerful or the clutches must be built as such. engine, means for self-defence, navigation instruments and communication devices. The The gear-oil temperature shall not exceed 80° C even in hot weather, otherwise forced R-plane must be capable of performing short flights with a great load of bombs or very oil cooling must be employed. For control ofgear-oil temperature, each gear-box shall be long-range flights without bombs, in which case it should utilize its total lifting capacity to fitted with one mercury and one thermo-electric thermometer. Engine and gear spaces must carry extra fuel. Provisions must be made to replace the bombs with fuel tanks on such be well ventilated so that the efficiency ofthe flight mechanics is not impaired by oil fumes, occasions. steam or exhaust vapours. From a military standpoint the ability of the crew to change places quickly is of great B. Attendance ofEngines-Throttles and master ignition switch must be capable ofbeing value. The fuselage must protect the crew against wind and weather without obstructing controlled separately or in unison from the pilots' position. Independent throttles, starters the pilots' vi ibility ahead and to the sides and, above all, the horizon must be visible at all and ignition switches mu t be provided for the flight engineers. The starting device, clutch times. levers, oil and fuel valves and hand pumps shall be located in the flight mechanics' position. B. Commander's Position-The aircraft commander must have a position from which he C. FuelTanks-There shall betwo emergency tank (gravity or pressure tank) and several can easily communicate with the pilots and other crew members. In particular, there mu t main tanks. Larger fuel tanks must be divided into several compartments. Each tank or be means for rapid transmittal ofmessages to and from the wireless operator. Ifthe flight compartment shall have shut-off valves. mechanics' positions are outside of the fuselage, then communication among commander, D. Exhaust Pipes-Exhaust pipes must be constructed to minimize noise and to trap pilots and crewmust be accomplished by special devices. flying sparks and exhaust flames without becoming red-hot. The e~hau.st pip~s must be C. Pilots'Positions-Duplicate flight controls must be fitted so that they can be operated mounted outside the airframe. Each exhaust pipe shall have an operatinglIfe ofsIxty hours. singly or simultaneously by both pilots. The flight controls must be arranged so that even E. Radiators.-Radiators must be so proportioned and arranged that, even in the summer, in most unfavourable weather they can be operated by a man of average strength. Hand engines may be run at full throttle on the ground for 5 minutes without the cooling .wat~r and foot controls must be constructed of non-magnetic materials in order not to influence coming to the boil. Controls must be provided to enable the flight mechal1lcs to maintain .the compasses. a water temperature of60-75° C during flight. D. Engine Room and Flight Mechanics' Position-The single (or multiple) engine-rooms must be large enough and the engines installed in such a manner that they are accessible in liT. Internal Installations flight for service and repair of parts such as spark plugs, valve springs, exhaust flanges carburettors, oil gauges, oil check-valves and water pumps. The flight mechanics' positions A. Instruments-All instruments must be protected from vibration. A calibration chart shall be near the engines; all instruments and valves shall be mounted close together, easy shall be fastened beside each instrument. The revolutions of propellers and engines hall to operate and readily visible. be made known to the crew. The temperature of the cooling water of each engine and of E. Machine-gun Positions-The following guidelines must be observed: combined fire of the gear-box oil must be indicated to the pilots by electric thermometers and to the flight as many guns as possible in any direction, and the zone below the tail must be protected. mechanics by mercury thermometers. F. Bombardiers'Position-This position should be placed as near to the nose as possible. Communication between pilots and flight mechanics shall be kept as simple as possible. The bomb-release mechanism must be fitted so that it can be operated by the bombardier Repeating engine telegraph, high-voltage transmission and pneumatic tubes come into while aiming the bomb-sight. question. As a means for indicating course, a suitable device should be provided ~or the G. Bomb Bay-In order to save weight, the internal structure of the fuselage may be pilots and the bombardier in the bombardier's position. An alarm deVice for warnll1g the advantageously used to support the bomb racks. The bomb bay shall be equipped with crew shall be mounted in the commander's position. outward-opening, self-closing spring doors. The bomb-release mechanism shall enable Thefollowinginstrumentsmustbeinstalled in the pilot's position: two airspeed indicators, bombs to be dropped singly or in salvos. The bomb bay must be accessible during flight one variometerfor measuring altitude, one artificial horizon for longitudinal and transverse to permit checking of the release mechanism, to de-fuse the bombs and to release bombs altitude indication, two altitude recorders, one tachometer for each engine, one course by hand in an emergency. indicator, one drum compass, one clock, one electric thermometer commutator switch.. A bearing compass shall be installed at the commander's position so that vi ual beanngs can be taken in many directions. The floats in the fuel tanks shall be installed so that the 11. Engines fuel gauge reads correctly even when the aircraft is not in horizontal po ition. A. Engines and Transmission-The engines must be mounted in a manner so that they B. Wireless Equipment-The wireless equipment shall consist of: one 1·5 h.p. petrol can be installed or taken out a a whole. Hoisting and sliding devices must be provided enginedrivinga IOOO-watt(50-volt20-amperedirectcurrentor 150-volt,7-amperealtern~ting for thi purpose. Equipment must be installed to permit starting and stopping the engines current) generator, one R-transmitterfreceiver, condenser, aerial reels and associated in flight from the flight mechanics' position. Self-starting devices must be provided. equipment. The wireless generator shall also be connected to the lighting, he~ting a.nd Special care must be taken in mounting the engines. If the engine is geared, the gear electric bomb-release circuits. Itmay also serve as additional power for the electnc startll1g housing must be rigidly bolted to the engine housing or jointly supported on a common of the engines. An emergency lighting and bomb-release source must be installed in case engine bearer. When engines and gear-boxes are mounted separately, they shall be con of main generator failure. . nected by elastic couplings. Likewise, the transmission shaft between engine and propeller C. Other installalions-Cases containing oxygen apparatus, fire extingui hers, first-aid gear-box shall be equipped with ela tic or universal couplings. The revolutions ofpropeller equipment, repair supplies and tools shall be located at easily accessible places. The transmission shafts shall be kept low to avoid resonance oscillations. If several engines wireless and flight mechanics' positions shall be equipped with the necessary emergency are connected to one gear-box they must be equipped with clutches to permit starting or repair tools. In the commander's position a map table and seat shall be provided. 2 3 IY. Acceptance Flights accessible in flight so that they could be serviced or repaired if the need arose. This in turn required The senior officer ofthe acceptance commission and the manufacturer shall choose a day large engine-rooms or spacious nacelles and large aircraft to permit a mechanic to move freely and time for the acceptance flights. The first flight shall consist of an endurance and while attending the engines. maximum load flight. The greatest horizontal speed shall be recorded at the prescribed A second characteristic of the R-plane, implied but not detailed in the specifications, was its great altitude, and bombs shall be released during this flight. The second flight shall determine load-carrying ability. To lift bombs and fuel and to furnish reserve power in case ofengine failure, maximum altitudeand climbing speed underfull load. Both flights may becombined as one. all R-planes were by necessity equipped with three or more engines. The principle ofin-flight accessi The aircraft shall be flown by a company pilot, and the acceptance commission shall bility and multi-engined power were instrumental in saving a number ofR-planes which might other take positions ofits own choosing. The commission shall weigh carefully all loads, deter wise have been lost. Here are several instances quoted from combat reports: mine the quantity offuel and install its own altitude measuring instruments. Staaken R.Vl(Av) 33/16 reported that during an attack on London both engines in the port nacelle began to fail, the front engine finally stopping altogether. The cause was traced back to oil Y. Final Acceptance of the Aircraft by the Arm)' congealed by low temperature. By cutting open the oil tank and filling the engine by hand. it was After completion of successful acceptance flights, the commission will provisionally possible to prevent a forced landing in the Channel (16/17 February 1918). accept the aircraft from the manufacturer. Final acceptance by the Army shall take place Staaken R.Yl 25/16 reported that the port rear engine lost coolingwater because ofa broken hose after theacceptance and inspection records have been signed by the Chiefofthe Air Service: clamp. It was possible to repair the leak and the engine continued running at reduced r.p.m. A when all supplemental and reserve parts have been delivered and modifications ordered by short while later the engine lost several exhaust headers and the exhaust flames caused the oil tank the commission have been executed. covering to catch fire. The fire was extinguished, but the engine had to be stopped. The R.25 returned safely. Staaken R.Y 13/15 reported a broken valve spring and that the valve was lifted by hand during the return flight so that the engine again ran smoothly. Staaken R.Yl 31j16 reported that the port rear engine stopped on approaching the target owing to faulty lubrication, but the flight over the target was nevertheless completed. Staaken R.IY 12/15 reported that the port nacelle gear-box broke and caught fire, which was extinguished in flight. A perfect landing was made in spite ofstopped port engines. During a IO-hour endurance flight the valve rocker arm ofa Navy Staaken seaplane was replaced. Although the principles of in-flight accessibility and multi-engine power were common to all R-planes, their designers were divided into two schools regarding which engine and airframe con figuration was the optimum. One group believed in the superiority ofdecentralized power units for R-planes while the other favoured centrally or internally powered machines. The wide range of R-planes, proposed or built, is proofthat R-plane design was in a constant state offlux and that the ultimate configuration had still not been found by the end ofthe war. Decentrally-powered R-planes were characterized by one or two engines mounted in port and Staaken R.VI(Av) 33/16 being inspected by an Idflieg acceptance team at Leipzig. There is· one requirement in the BLVR which put the R-plane in a class by itself, apart from all other German aircraft, and which, to a great extent, determined the size and configuration of the R-plane. This unique requirement specified thatan R-plane'senginesmust befully accessible, service able and capable of being repaired inflight. It can be shown that virtually all other BLYR specifica tions could apply to aircraft of other classes (i.e., duplicate controls, wireless equipment, geared engines. etc.). but the in-flight accessibility provision was an exclusive feature ofthe R-plane. and was the primary characteristic by which an R-plane's classification was determined. From the outset the R-plane was intended as a long-range bombercapableofcarryingheavy bomb loads and large quantities offuel. To perform its long-range mission successfully an infallible power plant that would operate for many hours without failure was imperative. Contemporary aircraft engines were not sufficiently reliable to meet this demanding endurance requirement. As a solution to their problem, R-plane designers followed the example set by airships; they made the engines AEG R.1. A centrally-powered machine with four 260 h.p. Mercedes D.IVa engines. 4 5