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SPACEFLICHT, Vol. 21, 2, 1979
1928-1929 FORERUNNERS OF THE SHUTTLE:
THE 'VON OPEL FLIGHTS'


By Frank H. Winter*

Introduction

On 11 June 1928, the tiny, cramped tailless sweptwing
sailplane named Ente ('Duck') with veteran glider instructor
Fritz Stamer in the cockpit leapt from Germany's Wasser-
kuppe mountains under the thrust of a pair of solid propel-
lant rockets and travelled just over three quarters of a mile
in about sixty seconds. The designers of the little 'Duck'
believed that this modest feat was but the first stage in their
own concept of a space shuttle. They envisioned, firstly,
terrestrially-bound rocket planes for either delivering        ?
passengers or mail from one continent to another in record
time; then, after the perfection of propulsion and life-
support systems, true spaceships capable of navigating to
other worlds. Their funds and science were not as grand as
their visions. The little craft and others like it saw a brief but
spectacular vogue until they disappeared both from the skys
and the Sunday supplements. Nonetheless, the story of this
dedicated group of enthusiasts has never been adequately
told.
If we discount the fantastic claims of the possibly legendary Chinese official Wan Hu, who is said to have lost his life in an attempt to propel himself by a kite-borne rocket chair in ca. 1500 A.D., and the story of a 1623 manned winged rocket flight by the Turk, Legari Hasan Tchelbi, who wished "to have a talk with the Prophet Jesus," we can safely assume that the first bonafide rocket plane flew in Germany , in 1928. It grew out of Fritz von Opel's rocket car stunts. \/
The idea also took shape in the mind of Antonius Raab, the 32 year old partner of the Raab-Katzenstein-Flugzeug-werk, GmbH, the aeroplane builders of Kassel, in the Spring of 1928. He was determined to fly the machine himself. On 29 April a contract was drawn up between the Opel Automobile Company of Russelsheim and the Raab-Katzenstein Flying Machine Works of Kassel "for the application of the 'rocket' principle to aircraft." Raab, with his partner Diploma Engineer Kurt Katzenstein would apply to their lightest aeroplane the solid-propellant Sander rockets that had proven themselves so well in Fritz von Opel's rocket cars. This machine was the 22 ft. 6 in. (6.85 metres) long, 552 Ib. (1,214 kg) Raab-Katzenstein R.K. 9 Grasmucke ('Warbler'). The two-seat cantilever biplane with a 29 ft. 5 in. (8.96 metre) span, was normally powered by one 40 h.p. Salmson radial engine fed by 42 litres (9 gallons) of fuel from a tank in the top wing. In its new role, the engine, the tank, and some anciliary equipment would be stripped out to accommodate the rockets and lighten the plane as much as possible.
Two batteries of Sander rockets of unspecified thrust and number were to be fitted on each side .of the fuselage between the wings, with electrical ignition from the cockpit, and cross-bracing and welded steel-tube structure of the R.K. 9 were to be specially strengthened "to withstand the high speed expected to be attained." Following Raab's consultations with his "scientific advisor," meteorologist Professor Ludwig Weickmann, Director of the Geophysical Institute at Leipzig University, both the pilot and the plane were to be equipped with parachutes and meteorological instruments also to be taken aboard. The latter included wind-temperature gauges, wind speed and pressure indicators manufactured to order by the famous Zeiss scientific instrument-makers of Jena. Should Raab find himself unable to breath or unable to withstand the cold during the climb towards the estimated maximum altitude of 32,800 ft. (10,000 metres) on the first run, he would bail out leaving
* Research Historian, Astronautics, National Air & Space . Museum, Washington, D.C.
f
SPACEFLIGHT, Vol. 21,2, Feb. 1979

Zeitschrift des Vereins ffir Raumschiffahrt E. V.

Da? erste bemannte Rafcetenfiugzeug.
Segelflugzeug ,,En!e" Ser Rhon-Rossitlengesellsdlaft.
Breslau, 15. Juli 1928        2, Jahrg.
Title page of Die Rakete 15 July 1928 depicting the flight of the rocketpropelled glider Ente.
Photo: F. I. Ordway Collection

FRITZ STAMER (1897-1969), believed to have been the world's first pilot of a rocket-propelled plane. He flew the Ente glider (above) from the Wasserkuppe Mountains, Germany, on 11 June 1928.
The Smithsonian Institution
75

1928-1929 Forerunners of the Shuttle: The Von Opel Fljghts'/contd.
the Grasmiicke to continue until its fuel was exhausted. S3iuttle-like,the Grasmiicke was to glide gently back to Earth.
The initial flight or flights were to be made with the small Salmson engine. If Raab confirmed the theory expressed by Weickmann and his colleagues that neither fogs nor storms are found above 8,000 metres (26,248 ft.), then the question of a regular trans-Atlantic air service by rocket plane (it was believed) would be practically solved.
Professor Weickmann, who later co-edited an account of the 1931 Polar voyage of the Graf Zeppelin in which he participated, also held the theory that the Earth is surrounded by a stream of ozone and that the temperature there is about like that on the Earth's surface instead of being unbearably cold. He based his theories on tests made with sound waves, a kind of pre-radar scan of the upper atmosphere. While much hope was thus entertained upon the success and findings of the Grasmucke flights, the practicalities were still essentially Earth-based. Even the most sanguine believed that a "journey into space beyond the atmosphere is still far in the future."
Rocket propulsive methods were crude, and von Opel shopped around to four or five of Germany's leading pyrotechnicists before engaging the services of Friedrich Wilhelm Sander. Sander was the genial, rotund general manager of the old Cordes firm at Wesermunde, near the port of Bremen, where he supplied ships with his large gunpowder lifesaving rockets and rocket signals as Cordes had been doing for 60 years.
A shrewed businessman, von Opel arranged a lucrative partnership between himself and Sander so that both would profit. Probably in his mind, though never overtly expressed, was the enormous amount 01 publicity he would reap upon himself and his Opel Car Company. He signed an exclusive contract with Sander. The "research" was to be paid partly out of his own pocket and partly by his company. Von Opel also built for Cordes a special hydraulic rocket press. In return for these considerations the motor magnate had" the option of buying Cordes' majority.
The research programme was outlined as follows: ground vehicles with rockets, model airplanes with rockets, and manned aircraft with rocket propulsion. Then came the development of liquid-fuel systems, likewise applied to manned flights. The third party in this contract was Max Valier, then one of the world's leading exponents of rocketry and space travel. The agreement was consummated on 8 December 1927.
In large measure, this ambitious programme was actually carried out ? including the liquids. Typical solid fuel Sander steel-cased rockets for von Opel's projects were 650 mm (26 in.) long minus the 150 mm (5.9 in.) long nozzle. Outside diameters were 125 mm (5 in.) and 70 mm (2.7 in.) at the flare of the nozzle. Other models were also available.
There were two basic types: rockets with bored charges, or conical cavities called "seelen," or souls, and end-burning grains like cigarettes and called "branders." The former possessed greater burning area about the orfice and therefore produced greater thrusts for shorter periods of time. The seelen rockets thus served as boosters and the branders as steadier, long-duration, low thrust sustainers. A wide variety of performances were available, typical figures for the boosters being 180 kg (396 lb.)/3 seconds and 20 kg (44 lb.)/30 seconds for the sustainers. An average rocket weighed about 6 kg (13.2 lb.), 4 kg (8.8 Ib.) of which consisted of the powder. By "mixing" the batteries or clusters of these rockets, the experimenters hoped to achieve something approaching controlled thrust ? boost phases for fast starts and get-aways followed by lower but steadier impulses for sustained performance.
This technique was fully proven in a spectacular run of von Opel's Rak III car on the Avus Speedway near Berlin
76
on 23 May 1928 before an invited crowd of 2,000 including high government officials and ranking members of the Reichwehr (the Army) and Navy. Von Opel himself had been at the wheel, a fitting image of the man of action and of the future with his goggles and blond hair streaming in the wind. All two dozen rockets worked perfectly, the car reaching a maximum velocity of some 125 mph (201 km/h). Afterwards he spoke to the crowd via a public-address system, extolling the vast potential of the rocket. But he was, curiously silent about his ongoing rocket plane project with Antonius Raab. Instead, the audience heard prophesies of how the conquest of the stratosphere and of space itself was only a matter of time. Von Opel was saving the spotlight for himself.
While awaiting the much promised flight of Raab's Grasmucke, the world air-minded public was confronted with suspense enough, with the saga of Umberto Nobile's flight of the 'Italia' dirigible over the North Pole. The airwoman, Amelia Earhart, was reported to be preparing for her Atlantic crossing. As for Raab's intended feat, the German, American, and presumably other papers published occasional reports but they were neither clear nor consistent. The New York Times for 4 May 1928, for example, announced that the flight day would be within three weeks, "probably immediately after Whitsunday." Three batteries of rockets were to be installed, the story went on, two under the wings for "an almost vertical ascent" and a third battery in the rear for level flight. The Times and the Berliner Morgenpost for 6 May moved up the schedule to two weeks and also revealed the original planned launching site as the Leipzig-Mockau flying field. The place was changed, the papers said, because the field near Berlin offered better facilities. The Times for 25 May and the Morgenpost for 26 May now said the flight would be in the middle of June. Von Opel, Valier, Sander, and "a commission of experts" were expected to visit the Raab-Katzenstein works at Kassel within ten days to examine the machine prior to lift-off. The 8 June edition of the Times introduced an entirely new configuration. The tailess duck-shaped Ente gave way to the biplane canard. The maiden trip also had an expanded route from Berlin to Paris and propulsion was to be derived by short spurts from a conventional reciprocating engine, presumably assisted in flight by the rockets. If everything went well the rockets would fully supersede the piston motor. Garbled as they were, these stories contained elements of both fact and fiction.
When the Berliner Tageblatt, the Morgen Post and other papers around the globe finally reported the flight, the man at the helm was not Antonius Raab but Fritz Stamer. What had happened? This fifty year old puzzle has been only partly solved by a follow-up item in the Times of 16 June 1928, The Times of London for 19 June and other newspapers. Stories were datelined to at least 15 June. They told of a rift between von Opel and Raab. It was a "row" that lead to von Opel's cancellation of his contract with Raab and a law suit for recovering damages reportedly amounting to several hundred thousand marks. Von Opel accused Raab of violating the agreement by unauthorizedly leaking plans to the press. Von Opel also stated that the Raab-Katzenstein airplane "of the duck type" was unstable and incapable of high speed. Raab denied these accusations, declaring that he would continue his own experiments "without Herr Opel and I will make the first flight in a fortnight" [ 1 ]. In fact this was the last public mention of Antonius Raab's rocket machine. Willy Ley, inhis Rockets, Missiles, and Space Travel, alludes to some supposed later experiments and adds that they were discontinued because "the Army intervened." We have found no other source to corroborate this account.
Always conscious of the power of the Press and eager to insure the permanent entry of his own name into both
SPACEFLIGHT, Vol. 21, 2, Feb. 1979
iii

1928-1929 Forerunners of the Shuttle: "The von Opel Flights'/contd.
aeronautical and automotive history, von Opel has left us only with a one-sided and cloudy view of what really happened. With his death in 1971 we must turn to other ? sources.
Such papers as Sander may have had were probably seized by the Gestapo upon his arrest in 1934 when he was accused of treasonably selling his lifesaving rockets to the Italians [2]. For his part, Valier remained diplomatically silent. In his Raketenfahrt (1930), he briefly dismisses the entire affair, saying cryptically that: "At the beginning of May there entered an unexpected development, a temporary partnership with the Raab-Katzenstein Works, in which an Ente-type 'Grasmiicke' was to be modified into a rocket plane. Finally, there was a separation of the author [Valier] with von Opel and Sander and at the beginning of June the experiments were transferred to the Wasserkuppe, not to Kassel."Of Valier's own falling out with von Opel, the science fiction writer Otto Willi Gail, who knew them both well, says that after the Rak HI car run of 23 May and excited private discussions about rocket planes, Valier came into heated disagreement with von Opel over their approaches. "These differences were basically insignificant," Gail observed, "but obstinancy on both sides made every attempt at settlement hopeless." The headstrong yon Opel, still in union with the unflappable and faithful Sander, thus pursued his own course. He was to have his way. As for the rocketry ''career" of Antonius Raab, like a meteor it flickered out almost as soon as it had appeared. The Raab-Katzenstein Works, by mergings and purchases, became the Gerhard Fiesler Werke GmbH that produced the infamous V-l and other missiles of World War II. Raab himself conducted his aircraft business in several places. The German aeronautical journals reported his presence in Finland, then in Tallin, Estonia, then Athens, and so on. Otherwise, the would-be first rocket pilot in the world who once astonishingly proved the manoeuvrability of his light planes by landing one in downtown Berlin on Unter den Linden, never again became engaged with rocket aircraft [3].
Other missing pieces of the story are supplied by the protagonists themselves. Enter Dr. Alexander M. Lippisch, a brilliant young aerodynamicist. His favourite swept-wing delta configuration was to streak through German skies during World War II as the first all-rocket fighter Me-163.
In late 1925, when he was 31, Lippisch had been put in charge of the technical department for aerodynamic research and glider design at the Forschungsinstitut (Research Institute) of the Rhon-Rossitten-Gesellschaft (RRG) on the Wasserkuppe in the Rhon Mountains of Thuringen, southeast of Kassel. Together with the chief gliding instructor Fritz Stamer, Lippisch gained invaluable experience designing ever advanced shapes and having them test flown as gliders.
From at least 1927 both Lippisch and Stamer began to collaborate on booklets teaching the construction of flight models and gliding for beginners. These works became classics of their field, one of them being translated into Spanish in 1941 and several others into English. Lippisch's partnership with Stamer became permanently sealed, as it were, when in 1926 he married Kate, Fritz's sister. By 1928 Lippisch completed his experimental tail-first planes the Storch ('Stork') and Ente ('Duck') which "by chance" in his own words, "were to provide my first contact with rocket propulsion." Historically, however, the tail-first design did not originate with Lippisch. It may be found long before World War I, notably in the designs of the Englishman Lieutenant John W. Dunne of the Royal Engineers [4].
In May, 1928, Lippisch recalled ? unfortunately we do not have the exact date to place it in context with von Opel's 23 May rocket automobile run and his falling out with Antonius Raab ? he (Lippisch) was visited at the Wasserkuppe by two men eagerly looking for a tailess airplane
suitable for testing a "new type of engine." These gentlemen, Lippisch later learned, were Fritz von Opel and Friedrich Stamer. "I showed them the Storch and the Ente, and when Fritz Stamer and I eventually found out that they were really interested in rocket propulsion, we promptly proposed the use of the Ente since this aircraft had good longitudinal stability and control, and we suspected that the rocket thrust would affect the longitudinal stability. However, when Opel and Sander again visited the Wasserkuppe ijji the following month, we first tried models of the Storch with Alexander (sic) Sander's powder rocket between the wings, launching the 'boosted glider' from short wooden rails." Perhaps Antonius Raab really did begin to progress from the cantilever Grasmucke biplane? with its inherent drag and stability problems to the tailess pattern. Nikolai A. Rynin, the Soviet astronautical encyclopaedist and "clearing house" for the astronautical and rocketry literature of the world at that time, wrote in Volume IV of his famous Interplanetary Flight encyclopaedia (published in 1929) that the Grasmucke was being converted into "a 'Canary' with elevator in front, and installation of the rockets was proposed at the rear." Indeed, a drawing of this arrangement of the Grasmucke is found in the respected German aeronautical journal Der Plug for May, 1928 (10 Jahrg., Erstes Maiheft, 1928, p. 164). If there was any truth in this, von Opel still did not find the design satisfactory and desired an entirely new plane. One of the principal features of the Lippisch configuration was the elimination of any danger of backburning by the rockets; the Grasmucke was originally to have had a specially protective steel plate in front of its tail and in the general path of the exhaust. The Ente obviated this necessity. Flames from the Sander units reached one metre (3 ft.) from their nozzles. It was the inferior aerodynamics of the ill-chosen Grasmucke which must have upset von Opel most of all.
Hence, the confused newspaper accounts. Unhappy with the design and aggrevated by the distorted reports, von Opel apparently sought out Lippisch in secret to investigate other pdssibilities and severed his relations with Raab at his own convenience.
Fritz von Opel was not a man to linger once he had set his mind on a specific goal. Throughout 9-11 June 1928, he personally financed and witnessed rocket model tests of a scale Storch glider at the Wasserkuppe. The complete, illustrated report by Lippisch and Stamer appears in the Zeitschrift fur Flugtechnik und Motorluftschiffahrt, 19 Jahrg. 1928, 12 Heft, pp. 270-274. It is, however, incorrect to say that these were the fkst rocket model tests with the ultimate goal of manned flight. In August, 1903, for example, the prolific German-born inventor of the Berliner helicopter, Emile Berliner, successfully shot off a "flying machine" at Washington, D. C. to 50 ft. (15.2 m) with two 2 Ib. (0.9 kg) skyrockets. And in his own quest for suitable motive power for a heavier-than-air flying machine, the Scottish-born creator of the telephone, Alexander Graham Bell, tried out a series of small rocket-propelled model planes, including one with delta wings, in 1892 in Novia Scotia, Canada. To fully internationalize these experiments we also may add the names of the Italian dirigible pioneer, Enrico Forlanini, and the Rumanian man of many inventions, Henri Coanda. About 1885 Forlanini sent his own miniature rocket airplanes along a stretched line to investigate their behaviour at closer range. As a preliminary step towards his supposed "turbo-propulseur" jet aircraft of 1910, Henri Coanda also claimed to have resorted to skyrocket-powered model flying machines, in 1907 [5].
Such efforts preclude strictly recreational winged model rockets. These may be traced back to at least the last century and have been thoroughly surveyed in the paper, "A Century of Rocket-Propelled Model Aircraft" by Frank H. Winter, George S. James and Gregory P. Kennedy and presented at the 26th International Astronautical Congress,
77
SPACEFLIGHT, Vol. 21, 2, Feb. 1979


1928-1929 Forerunners of the Shuttle: 'The von Opel Flights'/contd.
Lisbon, 21-27 September 1975.
The von Opel-Sander-Stamer-Lippisch tests were elevated to a full-scale airplane immediately after the model flights ; in effect, this was to be the first manned rocket flight.
The Rhon-Rossitten-Gesellschaft's Ente was brought out. Sander supplied 360 kg (790 lb.)/3 second thrust bored rockets and branders of 20 kg (44 Ib.) which burned for 30 seconds. Von Opel had insisted upon this powerful but unpredictable combination but fortunately for the cautious and experienced pilot, Stamer, this foolhardiness was over-riden.
Lippisch and Stamer both humorously recount the incident. In his memoirs, ZwolfJahre Wasserkuppe (Twelve Years on the Wasserkuppe'), published in 1933, Stamer recalled that: "Von Opel had hidden a group of itinerant musicians ("Wandermusikanten"), who happened to be crossing the Wasserkuppe, behind the hangar. As we were setting out to start the proceedings, he himself directed the 'Stamer-Lippisch-12-Kilogram March' to the (funereal) tune of Immer langsam voran ("Always Slowly at the Head"). This was then followed by the Opel-360-Kilogram March' to the melody of the 'Radetzky March.' "As might have been expected," Lippisch adds, "the atmosphere became a little tense." But the cautious Stamer-Lippisch team won out. The manned Ente was fitted with the more reasonable 12, 15, and 20 kg (26.4, 33, and 44 Ib.) 30 second units (this is contrary to the supposed 25 kg or 55 Ib. motors often reported, even by Lippisch). The best accounts of these first . flights are found in the official report by Fritz Stamer as his part of the joint article with his brother-in-law Lippisch, "Versuche mit neartigen Flugzeugtypen" ("Experiments ; with New Airplane Types"), in the Zeitschrift fur Flug-technik und Motorluftschiffahrt cited above and in Stamer's more popularly written ZwolfJahre (pp. 96-100). (A shorter Stamer account is also found in Flugsport, 20 June 1929, pp. 232-233).
The first starts were failures. The Ente's 12 and a 15 kg rocket were to be ignited electrically one after the other from the cockpit. A built-in override system prevented the rockets from igniting simultaneously. With the initial push provided by the bungy cord the rockets were to have switched on once the plane was free of the rope. Yet when the switch was thrown the thrust was found to be pitifully feeble. "Even the 12 kg rocket could not lift..." For the next attempt the rockets were slightly upgraded to 15 and 20 kg. These too proved inadequate. The plane "could not maintain horizontal flight and it had to land after about 200 metres (656 ft.), without the 20 kg rocket being used." In the third attempt, made with two 20 kg rockets fired in succession automatically, Stamer became not only fully airborne but also successfully, albeit briefly, rocket propelled. Quoting from Stamer's official report: "The airplane left the ground very well with the starting cable aided by the rocket. After a straight flight of about 200 metres (656 ft.) during which there was a slight ascent of the machine, I made a curve to the right of about 45њ and again flew straight for about 300 metres (984 ft.). Then a curve to the right of about 45њ was made again. The first rocket was burned out immediately after this curve and the second rocket was ign|ted, which immediately made further flight possible. This time I flew about 500 metres (1,640 ft.) in a straight line, then in a 30њ curve to the right and after about 200 metres in the new direction the machine was landed on gently rising ground just before the second rocket burned ofit. The total flight, including all curves, was about 1,300-1,500 metres (4,264-4,920 ft.). The total flying time was 60-80 seconds."
Attempt No. 4 did not fare so well. The Ente was to soar over a higher slope and, as before, it was fitted with two 20 kg thrust Sander cartridges. From Stamer's ZwolfJahre, we have the information that: "The takeoff went without a
hitch. The first rocket was burning and I had really become accustomed to the very loud hissing of the jet flame spurting out of the nozzle, when about 3 seconds after ignition there was an ear-splitting explosion... the entire aircraft was burning away merrily, and judging by the violence of the explosion, a few things contributing to its stability must have suffered some damage too. I was particularly concerned about the wing suspension. I decided not to force the burning bird down vertically, although in doing so the flames would be pushed back to the rear, but to let it glide down carefully so as not to break up in the air. I was further comforted by the thought that the second rocket was there behind me in the fire, likely to go off, one way or another, at any moment.
"Moreover, under my seat it was becoming first pleasantly, but then obtrusively warm. Fist-sized chunks of powder from the exploded rocket had come flying in all directions into the machine and had set fire to it. One such chunk was now appropriately situated under the thin plywood seat. At last I grounded the machine. I made the finest landing and thereby possibly coming into closer contact with the second rocket. This was likely to go off at any moment as it was, and things would be in a bad way if I happened to crash right onto it. No sooner had the machine stopped than I had already climbed out of it: I saw the ignition wire burning on the iron rocket casing and I tried to tear it away. But it was already too late. The second rocket ignited, but it fortunately burned out in the proper manner, despite the intense heating of the steel jacket. If it, too, had exploded, my prospects would certainly have not been very bright. Now I wriggled about in the wet grass in order to extinguish and cool my smouldering posterior. After the second rocket had burned out I was then able to extinguish the burning ship with the helpers who had arrived in the meantime. My need to fly with powder rockets was temporarily satisfied..."
Fellow glider pilot Robert Kronfied supplied this postscript: "Herr Stamer went into a dive to extricate himself from the flames, and landed in the nick of time with two large holes burnt in the back of his coat. Thus ended the first attempts to pilot a machine propelled by a rocket. The experiments were carried on in all secrecy, so that the only modest record of Herr Stamer's