v21-2

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
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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,
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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 wonderful feat is his 'Rocket Coat,' which has been preserved in memory of this perilous day" [6].
The flight of the Ente almost cost Stamer's life. The cost to von Opel, in cash, was 1,000 Reichmarks!
Papers picking up the news of the flights, such as the Berliner Tageblatt for 13 June 1928 and the Frankfurter Zeitung for 14 June 1928, generally confined their coverage only to Stamer's triumph [ 7 ]. The near fatal disaster is almost invariably never mentioned. Also unreported were the truly confidential experiments in 1928-1929 with a liquid fuel engine mounted on a tied-down airplane and conducted by Sander and others with von Opel's backing. Surely the liquid rocket-airplane combination was a "first" by any reckoning, even if it did not fly. It was all the more remarkable considering that by this time the liquid rocket was little more than an engineering concept. The press-shy Goddard kept silent upon the details of his own work and his successful 16 March 1926 shot remained unknown until a decade later.
Our knowledge of Sander's and von Opel's liquid-fuel phase comes from three sources: Max Valier's Rake ten fahrt, from long suppressed revelations made by von Opel himself in a paper presented before the Deutches Museum in Munich' on 3 April 1968, and from a hitherto mysterious photograph unearthed in the von Opel archives and published here, probably for the first time. There were in addition, contemporary hints that liquid fuel work was afoot. Von Opel could not contain himself entirely, especially after his own rocket flying experience on 30 September 1929.
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1928-1929 Forerunners of the Shuttle: 'The von Opel Flights'/contd.

$

This historic picture from the von Opel archives shows the static test of a benzol/nitrogen teroxide liquid propellant rocket engine mounted on a Mueller-Griesheim 1 two-seat high-wing monoplane, 1928, by Friedrich Sander (third man on right), Engineer Schaberger and Fritz von Opel. (Schaberger may be one of the other men shown in the photograph). The rocket developed a steady thrust of about 70 kgf (154 Ibf) and was intended by von Opel to power the Mueller-Griesheim plane across the English Channel. There was, according to von Opel, "lack of interest on the part of government and industry" and the project was never realised. The rocket plane, nonetheless, represents the earliest known liquid propellant rocket aircraft, even though it was never flown.
Adam OpelAG, Russelheim, Germany
As far away as Canada, for example, it was reported in the Canadian Air Review for December 1929 that: "The rockets in the flight were made of powder, but the German (von Opel) said experiments were going forward on a liquid to propel the plane." In a cabled exclusive to The New York Times on 30 September 1 929, von Opel is also quoted as saying: "Sander and I now want to transfer the liquid rocket from the laboratory to practical use. With the liquid rocket I hope to be the first man to thus fly across the English Channel. I will not rest until I have accomplished that."
In his speech at the Deutches Museum upon the occasion of the donation of a replica rocket car (a copy of his plane was intended but apparently never built because of space limitations), the immodest von Opel for the first time revealed the name and role of another of his co-workers. This was Engineer Schaberger, now identified as Josef Schaberger. "He belonged," von Opel said, "with the same enthusiasm as Sander to our small secret group, one of the tasks of which was to hide all the preparations from my father, because his paternal apprehensions led him to believe that I was cut out for something better than being a rocket researchist. Schaberger supervised all the details involved in construction and assembly (of rocket cars), and every time I sat behind the wheel with a few hundred pounds of ex-
plosives in my rear, and made the first contact, I did so with a feeling of total security." Then, after regaling his audience with both the glories and failures of his rocket cars and trains (one of which blew a hapless cat to smitherines), von Opel returned to Engineer Schaberger. "On this occasion, " he said, "I would like, for the first time, to reveal what I consider the crowning achievment of our work. As early as 1928, Mr. Schaberger and I developed a liquid rocket, which was definitely the first permanently operating rocket in which the explosive was injected into the combustion chamber and simultaneously cooled using pumps." No matter that Goddard began developing liquid fuel rocket pumps from 1921 (although resorting to pressure-feeding in his 1926 rocket). The claim of "permanently operating" is more justified. "We used benzol as the fuel," von Opel continued, "and nitrogen tetroxide as the oxidizer. This rocket was installed in a Mueller-Griessheim aircraft and developed a thrust of 70 kg (154 lb.)." Valier says that by May 1929, the Sander engine produced a thrust of 200 kg (440 lb.) "for longer than fifteen minutes and in July (1929) he was able to attain powered phases of more than thirty minutes for thrusts of 300 kg (660-lb.) at Opel's works in Riisselsheim. Moreover, Sander focused his attention to the constancy of performance. By using a by-product of the chemical industry as an oxidant, he succeeded in forcing
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I

1928-1929 Forerunners of the Shuttle: "The von Opel Flights'/contd.
down the price per kilogram of fuel mixture to 20 Pfenigs." Whether Schaberger or Stamer was the father of the von Opel liquid rocket remains an open question. Certainly both were very much involved and Valier's description of the fuel fits the hitherto "secret propellant" of benzol and nitrogen tetroxide. Presumably with this same mixture Sander was able to successfully launch a secret 50 kg (110 Ib.) thrust liquid fuel rocket on 10 April 1929, and another two days later, according to Valier. To confirm at least part of this, we have an occasional contemporary statement: e.g., Popular Mechanics for August 1929 reported that von Opel was constructing "a special ship... at Griesheim, Germany." Far more significantly, we have the photograph (p. 79). It clearly shows the chubby Friedrich Sander cheerfully and calmly standing beside two unidentified men (possibly one of them Schaberger) while a liquid fuel rocket motor blasts away at the rear of a grounded Gebrueder Mueller Griesheim G.M.G. I or II two-seat high-wing light monoplane. This aircraft was manufactured by the brothers Mueller at Gries-. heim bei Darmstadt from 1927 (see Jane's All the World's Aircraft for 1929, p. 176c). If pictures are worth a thousand words then this one gives full value. Sander and the other men stand astonishingly close to the rocket blast, their faces and postures altogether relaxed, indicated indeed that the static test was a very long and stable one. Admittedly, the performance figures quoted by Valier and von Opel are nothing short of phenomenal, especially for 1928-1929. Unfortunately we have no further details, nor do we have additional data on the gifted engineer Schaberger.
Why was the flight of the liquid-powered G.M.G. never
carried out? For the answer we must again return to von Opel's revelationary speech on 3 April 1968. In this presentation, entitled, "The Historical Development of Rockets and the Purpose and Limits of Technology," von Opel concludes that "In 1930 I wanted to fly across the English Channel in this craft, but this wish was never realized due to lack of interest on the part of the government and industry, and also because of my (automobile) activities in America. I can only say, thank God, because several famous pilots went down in the same type of aircraft one after another, because of a structural defect." Newspapers of the day confirm this.
By December, 1930, von Opel had completed a busy ten-month study of the manufacturing methods of General Motors at Detroit and Flint, Michigan. While in America with his new bride, he attempted but failed to interest the U.S. Navy in Washington in using solid rockets, "to prevent forced airplane landings."
In the interim, on 30 September 1929, von Opel made his "official" rocket plane flight which is too often claimed as being the first anywhere. Despite his well-earned reputation in the aeronautical world, Fritz Stamer never appears to have been particularly publicity-seeking. He did recount his adventures with rockets but never vigorously refuted von Opel's wide-reaching assertions that he (von Opel) had made the "first human rocket flight." As a postscript to Stamer's personal story, he continued to set national and world gliding records, to write, take out patents, and even to build his own light motor instructing airplane, the Stamer "Hummel" of 1934. One of the co-founders of the German

FRITZ VON OPEL at the controls of the Opel Sander Rak. 1 rocket plane. At left is Fritz Stamer who made the first rocket flight in an Ente. In the middle is pyrotechnist Friedrich Sander who supplied the solid propellant rocket motors. Photograph was taken on 30 September 19 29 at Frankfurt just before von Opel made his flight.
The Smithsonian Institution

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-<**
Aero Club and winner of the Federation Aeronautique Internationale (FAI)'s "Diplonle Tissandier," Stamer returned to rockets in 1939 when, with Lippisch, he also devised JATO's (see Flugsport, XXXI Jahrg, Band 31,18 January 1939, p. 59). Besides this, he also eye-witnessed Eugen Sanger's ram-jet test flown on a Dornier 217 in 1941. Dr. Irene Sanger-Bredt has told the author that as a vice-director of the successor to the RRG, the Deutsche Forschungsanstalt fur Segelflug (DFS) at Ainrung during the war, Stamer "tried to perform new applications of yet existing rockets in flight techniques, especially in soaring flight techniques." This unspecified work apparently translated into the JATO boosting of the huge DFS-230-A and possibly the Me 321 "Gigant" troop-carrying gliders. Stamer also contributed to the man-carrying Natter (Viper) rocket aircraft. "Thus," added Sanger-Bredt, "we never collaborated officially with Stamer on a rocket project, but my husband and Stamer became good friends. In his quality as a vice-director of DFS, Stamer procured us facilities for our experimental work as far as he could ? which was very important for us in that crazy time of total war. Eugen, on the other hand, furnished consulting advice from time to time to Stamer's experiments with rocket assisted take-off, rocket braking and so on." In his later years, Fritz Stamer was a vigorous advocate of space travel, becoming a member of the Deutschen Gesellschaft fur Luft? und Raumfahrt E.V. (German Society for Air and Spaceflight). On 20 December 1969, six months to the day man landed on the Moon, the world's first rocket pilot died.
Almost a year-and-a-half elapsed from the time Stamer made his flight until the next von Opel rocket plane took to the air. In the meantime, by the summer of 1928, another would-be rocket pilot appeared on the slopes of the Wasser-kuppe. His name was Julius Hatry, an obscure gliding enthusiast whose performance at the Rhon-Segelflug-Wette-werbes (Rhon Gliding Competition) early in August was not outstanding. Nonetheless, this young man, who has also been described as an engineering student from Mannheim, possessed boundless enthusiasm. After witnessing or hearing of the Stamer flights he approached Lippisch with his own plans. He wished to build his own rocket glider and fly it. At first Hatry favoured Eisfeld rockets, later changed to Sander units. According to Lippisch's recollections: "I (Lippisch) helped him with the design of his glider which was built in a small carpenter's shop in a nearby village. By some chance, Fritz von Opel got wind of the project and brought pressure to bear on young Hatry to sell him the glider so that he could gain the publicity of making the first official rocket propelled flight.
The glider was then transported to a small repair shop at Frankfurt airport where it was promptly pronounced unsafe for flying without overhaul, and Hatry did not get the money that Opel had promised him." Lippisch cut off and jumps to the von Opel flight of this machine on 30 September 1929. Obviously, the plane was suitably remade and procured by von Opel. By the time it did fly it boldly bore the name "Opel-Sander Rak. 1 " on its tail surfaces and in smaller letters, "Hatry Flugzeug" ("Hatry Airplane"). Typically, von Opel's vanity prevented him making it known that Hatry himself had test-flown the Rak. 1 in private before he himself took the controls for the "official" flight. Thus, Julius Hatry technically became the second man to fly in a rocket plane and von Opel the third ? or fourth. But "flight" is a loosely used term here as these glider hops were barely controlled. Moreover, they too were hardly qualified successes. Harty's attempt, apparently made early in September 1929, ended in a crash landing.
What of the machine itself? The so-called Opel-Sander Rak. 1 was a high-wing braced monoplane with a abbreviated nacelle of wood, aluminium, and fabric. The tail assembly consisted of dual-booms which raised the elevators and two
fins clear of the rocket exhaust which emanated from the rocket units imbeded in the rear of the nacelle. The wings were parasol type, flat, with no dihedral. The cockpit was cramped enough and even more so with asbestos padding. Controls were at the left hand side of the pilot. The motor assembly comprised a bank of sixteen open steel tubes which contained Sander cartridges of 76 mm (3 in.) diameter and 457 mm (18 in.) length. Standard references say that each unit produced 50 kg (110 Ib.) of thrust for 25-28 seconds for a total thrust of 900 kg (1,980 Ib.) or almost a ton. However, von Opel himself provided quite different figures in a rare account published in The Journal of the Royal Air Force College for Spring, 1930 (Vol. X, No. 1, p. 38): "I used Sander's continuous firing (brander) rockets which gave a continuous propelling effort of 23 kilograms (50 Ib.) for 25 seconds. The aeroplane was fitted with 11 continuous firing rockets and, for landing purposes, with 5 short-firing rockets." Thus, the total sustaining thrust was 550 Ib. (247.5 kg). The landing rockets fitted into the five remaining tubes of the rocket bank and were meant for manoeuvring in the last few seconds [8]. All units were fired electrically from the cockpit. The empty plane weighed 180 kg (396 Ib.), the loaded rockets 90 kg (198 Ib.) and the allowance for the pilot was 80 kg (176 Ib.) All-up weight of the plane was 770 Ib. (350 kg), including boosters. Again following von Opel's description, "For propelling (boosting) purposes 3 rockets, each of 300 kilos. (6 cwt.) propelling effort, have been used. The propelling effort can be reduced in accordance with the length of the starting run. The acceleration is quite endurable for the pilot at a starting run's length of 8 metres (26 ft.) and at the required final speed of 120 kilometres (75 miles) an hour. The average speed during the flight was about 170 kilometres (106 miles) an hour." The total boost thrust was therefore 900 kg (1,980 Ib.) thus accounting for the believed sustaining force of all the rockets. The firing time for the boost was 1.5 seconds. Few other specifications have been published. Based upon the given wing span of 39 ft. (11.8 metres), the overall length of the Opel-Sander Rak 1 is estimated at 24.5 ft. (7.5 metres) and the wing area approximately 215ft2 (19.9 metres2).
Dare-devil racing driver, speedboat pilot Fritz von Opel felt the need to brush up on flying for this wholly new experience which lay ahead [9]. His instructor was the director of the Frankfurt Airport, Hellmuth Walter Wolfgang Felmy, then also a Major in the Infantry and who afterwards became a Luftwaffe General in the Second World War. This same Felmy (whom von Opel inaccurately remembered as a Captain) was to play an even greater role in the success of von Opel's flight. In the meantime, with von Opel's mechanics August Becker and Karl Treber assisting him, and perhaps Josef Schaberger too, the Sander-Rak. 1 Hatry Flugzeug and its attendant launcher were set up at the Reb-stock Airport at Frankfurt for rehearsals. The unloaded airplane was first released several times from the catapult in a dry run without the rockets. Then, on 10 September 1929, von Opel himself climbed in and had the Rak 1 hooked up to "a powerful jface-car," no doubt an Opel machine. As Robert Esnault-Pelterie had done 25 years earlier in testing his 1904 glider, the plane was automobile-towed and cut loose when sufficient lift was attained. Rak 1 's minimum flying speed proved to be 60 mph (96.6 km/h) unaided by rockets and without benefit of the catapult. The catapult and booster rockets, von Opel assumed, would easily double this speed and more than gain enough altitude and time for sustainer ignition once cleared of the launcher. At this point von Opel set the launch date. He gave himself twenty days. The route was mapped and the press informed.
The initial scheme was a course from Frankfurt to Russel-sheim, site of the Opel Automobile Works and about 10 miles (16 km) due southwest. He envisioned a huge publicity
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1928-1929 Forerunners of the Shuttle: 'The von Opel Flights'/contd.
coup, both for himself and his company. But at the last minute the Government intervened in the name of safety. There was fear that he might crash into a village or railroad station. He was thus obliged to confine the flight to the immediate environs of the Rebstock Airport, set in an otherwise uninhabited forest glade. As for the press and public, von Opel this time sincerely wished to keep them within limits, "to avoid any possible trouble with the unruly crowds." Perhaps he was alluding to past difficulties attending his other stunts. He had invited only a few papers and granted exclusive American rights to The New York Times and Fox Movietone for filming.
When the great day came, on 30 September 1929, it looked as if the flight was never going to be made. At 9 a.m., the air tense with excitement, von Opel shoved himself snugly into his little machine and prepared for liftoff. He waited a few moments for a favourable headwind. Just then, Major Hell-muth Felmy came up, trying to look as calm as possible despite the message he bore with the Air Police and everyone else looking on. He whispered in von Opel's ear: "A telegram just came from the Oberpraesidium in Kassel. All flight tests are forbidden. Take off quick! I haven't had the telegram yet!" [ 10]. "Felmy's willingness to risk his position to protect my first rocket flight from bureaucratic prohibitions," commented von Opel years later, "is something I will never forget." Yet even Major Felmy's magnaminity was not potent enough to halt all technical flaws. The order for the catapult release was given. At first, it was a grand display. Fire and smoke leapt out of the big boosters. But the sus-tainers failed to ignite. Gracefully, the Opel-Sander Rak. 1 Hatry Flugzeug glided back to Earth at only 50 metres (164 ft.). At 11 a.m. they were ready again. By now, impatience and lunchtime hunger pangs had gotten the better of the spectators and many of them had disappeared. Von Opel once more girded himself for liftoff. The signal was given with similar results except that this time one of the boosters also burst, the yellow hair on the back on von Opel's head being slightly singed.
Not until 3:30 or 4:00 in the afternoon was another attempt made. By now only the most fervent of aviation enthusiasts, von Opel's supporters and friends, and some of the newsmen were present. Fritz Stamer, Friedrich Sander and Frau Sellnik, von Opel's fiancee, were there. Herself a pilot and one of Germany's six aviatrixes, Frau Sellnik had been another of von Opel's professional advisors on aviation for the previous several months. After the flight (following one account) she had been the first to run up and congratulate him. Ten minutes after the flight, and still bubbling over with excitement, von Opel wrote down his impressions which he afterwards dispatched to The New York Times as his exclusive. "My first rocket flight!," he began. "...For today's flight I have trained for a year... For an hour before this morning's start I inspected the course and personally went over every detail of the plane ? cables, fittings and rockets... Finally I draw a deep breath and then ignite. Tremendous pressure! I feel the machine racing forward. It tries to rear like a horse. Thus I race into space as in a dream, without any feeling for space or time. The machine practically flies itself. I scarcely need to touch the wheel. I only feel the boundless intoxicating joy of making a flight such ashman has never made before... The force of the rockets has expired. Visions cease; actuality calls. I must return to EartlL.. Gliding with terrible bumps along the ground, the plane comes to a halt."
The Opel-Sander Rak. 1 came down in a cloud of black smoke badly battered, pilot intact. Partly because of his exuberance, von Opel had neglected to say how close he had come to being seriously injured and possibly killed. Exact measurements of the flight were impossible. After he had levelled off to about 100 ft. (30.5 metres) the ground crew attempted to time the flight. It was determined that he was
then going at 90 mph (145 km/h). In a few moments, according to Heinz Gartmann, "a downward gust of wind, coinciding with the edge of the landing ground, caused him to make a forced landing after only using up five rockets. At a speed of 80 mph (129 km/h) this was a difficult feat, and Opel hit the ground with a crash as the landing-skid broke and the cockpit floor was shaved away, leaving him hanging by his safety-belt with an inch to spare." Officially, von Opel had been aloft for an estimated 75 seconds, attaining a maximum velocity of 95 mph (153 km/h) and had traversed a distance of nearly 5,000 ft. (1,525 metres), or 1.4 miles.
In his speech at the Deutches Museum in 1968, with the widow of Friedrich Sander in the audience, von Opel painted another picture of the events which followed the landing. "After my successful rocket flight in Frankfurt," he said, "I had to land outside the airport grounds on a potato patch, unfortunately with a tail wind and with several thrust rockets still hot. The flight speed was approximately 110 km/h (68 mph) and was too high to remain on the ground after landing, but too low to clear a raised crossroad at the end of the field. Upon impact, the landing skids, the entire cabin and a part of a wing were ripped away, but I had drawn up my legs and hung completely uninjured from the totally intact rocket frame by my safety belt. A flock of cars stampeded across the airfield with the world champion glider pilot leading the way. Stamer gathered me up, sat me on his shoulders and jumped around like a madman. While joy was reigning supreme, (mechanic Karl) Treber appeared, still shaking from what he thought had been an accident, planted himself in front of me in a rage and bellowed: "You'd think you earned a living by pulling these stunts!..." The joy that everything had gone well did not last long. Capt. (Major) Felmy rushed up with the news that the enormous air pressure during the launch had knocked over a spectator standing 100 metres (328 ft.) away and had broken her arm. Her husband was on his way to pick up the casualty. I have to admit that I would have ten times more preferred to repeat the flight than to meet the raging husband. But before I could offer my apologies to the woman, her husband jumped out of a taxi and said to her in Frankfurt dialect the most comforting words I have ever heard: "Serves you right you stupid ass. Next time stay home with the kids."
The Imitators
Following in the footsteps of Stamer and von Opel were several imitators. In 1929 Gottlob Espenlaub flew a rocket glider which had been towed into the air by a light aircraft. This arrangement worked well on several occasions but the rocketplane finally crashed.
In 1932 there were reports of a rocket-powered bicycle with wings which the inventor launched from a German rooftop.
More practical work took place in America and Italy. On 1 June 1931 William G. Swan flew his 'Steel Pier Rocket Plane' over the summer resort town of Atlantic City, New Jersey, thus becoming America's first rocket pilot.
At the end of June 1931 the Italian aeronautical engineer, Dr. Ettore Cattaneo, produced his well-designed R.R.I rocket glider which made at least four brief but successful flights at Milan's Taliedo Airport 111].
Crude as these machines were by our standards, they represented valiant if modest steps in the history of the rocket plane in this 'Century of the Shuttle.'
NOTES
In a letter to the author dated 7 April 1975, Alexander Lippisch said that: "Raab and Katzenstein had some trouble
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1928-1929 Forerunners of the Shuttle: 'The yon Opel Flights'/contd.
coup, both for himself and his company. But at the last minute the Government intervened in the name of safety. There was fear that he might crash into a village or railroad station. He was thus obliged to confine the flight to the immediate environs of the Rebstock Airport, set in an otherwise uninhabited forest glade. As for the press and public, von Opel this time sincerely wished to keep them within limits, "to avoid any possible trouble with the unruly crowds." Perhaps he was alluding to past difficulties attending his other stunts. He had invited only a few papers and granted exclusive American rights to The New York Times and Fox Movietone for filming.
When the great day came, on 30 September 1929, it looked as if the flight was never going to be made. At 9 a.m., the air tense with excitement, von Opel shoved himself snugly into his little machine and prepared for liftoff. He waited a few moments for a favourable headwind. Just then, Major Hell-muth Felmy came up, trying to look as calm as possible despite the message he bore with the Air Police and everyone else looking on. He whispered in von Opel's ear: "A telegram just came from the Oberpraesidium in Kassel. All flight tests are forbidden. Take off quick! I haven't had the telegram yet!" [ 10]. "Felmy's willingness to risk his position to protect my first rocket flight from bureaucratic prohibitions," commented von Opel years later, "is something I will never forget." Yet even Major Felmy's magnaminity was not potent enough to halt all technical flaws. The order for the catapult release was given. At first, it was a grand display. Fire and smoke leapt out of the big boosters. But the sus-tainers failed to ignite. Gracefully, the Opel-Sander Rak. 1 Hatry Flugzeug glided back to Earth at only 50 metres (164 ft.). At 11 a.m. they were ready again. By now, impatience and lunchtime hunger pangs had gotten the better of the spectators and many of them had disappeared. Von Opel once more girded himself for liftoff. The signal was given with similar results except that this time one of the boosters also burst, the yellow hair on the back on von Opel's head being slightly singed.
Not until 3:30 or 4:00 in the afternoon was another attempt made. By now only the most fervent of aviation enthusiasts, von Opel's supporters and friends, and some of the newsmen were present. Fritz Stamer, Friedrich Sander and Frau Sellnik, von Opel's fiancee, were there. Herself a pilot and one of Germany's six aviatrixes, Frau Sellnik had been another of von Opel's professional advisors on aviation for the previous several months. After the flight (following one account) she had been the first to run up and congratulate him. Ten minutes after the flight, and still bubbling over with excitement, von Opel wrote down his impressions which he afterwards dispatched to The New York Times as his exclusive. "My first rocket flight!," he began. "...For today's flight I have trained for a year... For an hour before this morning's start I inspected the course and personally went over every detail of the plane ? cables, fittings and rockets... Finally I draw a deep breath and then ignite. Tremendous pressure! I feel the machine racing forward. It tries to rear like a horse. Thus I race into space as in a dream, without any feeling for space or time. The machine practically flies itself. I scarcely need to touch the wheel. I only feel the boundless intoxicating joy of making a flight such ashman has never made before... The force of the rockets has expired. Visions cease; actuality calls. I must return to Earthi.. Gliding with terrible bumps along the ground, the plane conies to a halt."
The Opel-Sander Rak. 1 came down in a cloud of black smoke badly battered, pilot intact. Partly because of his exuberance, von Opel had neglected to say how close he had come to being seriously injured and possibly killed. Exact measurements of the flight were impossible. After he had levelled off to about 100 ft. (30.5 metres) the ground crew attempted to time the flight. It was determined that he was
then going at 90 mph (145 km/h). In a few moments, according to Heinz Gartmann, "a downward gust of wind, coinciding with the edge of the landing ground, caused him to make a forced landing after only using up five rockets. At a speed of 80 mph (129 km/h) this was a difficult feat, and Opel hit the ground with a crash as the landing-skid broke and the cockpit floor was shaved away, leaving him hanging by his safety-belt with an inch to spare." Officially, von Opel had been aloft for an estimated 75 seconds, attaining a maximum velocity of 95 mph (153 km/h) and had traversed a distance of nearly 5,000 ft. (1,525 metres), or 1.4 miles.
In his speech at the Deutches Museum in 1968, with the widow of Friedrich Sander in the audience, von Opel painted another picture of the events which followed the landing. "After my successful rocket flight in Frankfurt," he said, "I had to land outside the airport grounds on a potato patch, unfortunately with a tail wind and with several thrust rockets still hot. The flight speed was approximately 110 km/h (68 mph) and was too high to remain on the ground after landing, but too low to clear a raised crossroad at the end of the field. Upon impact, the landing skids, the entire cabin and a part of a wing were ripped away, but I had drawn up my legs and hung completely uninjured from the totally intact rocket frame by my safety belt. A flock of cars stampeded across the airfield with the world champion glider pilot leading the way. Stamer gathered me up, sat me on his shoulders and jumped around like a madman. While joy was reigning supreme, (mechanic Karl) Treber appeared, still shaking from what he thought had been an accident, planted himself in front of me in a rage and bellowed: "You'd think you earned a living by pulling these stunts!..." The joy that everything had gone well did not last long. Capt. (Major) Felmy rushed up with the news that the enormous air pressure during the launch had knocked over a spectator standing 100 metres (328 ft.) away and had broken her arm. Her husband was on his way to pick up the casualty. I have to admit that I would have ten times more preferred to repeat the flight than to meet the raging husband. But before I could offer my apologies to the woman, her husband jumped out of a taxi and said to her in Frankfurt dialect the most comforting words I have ever heard: "Serves you right you stupid ass. Next time stay home with the kids."
The Irriitators
Following in the footsteps of Stamer and von Opel were several imitators. In 1929 Gottlob Espenlaub flew a rocket glider which had been towed into the air by a light aircraft. This arrangement worked well on several occasions but the rocketplane finally crashed.
In 1932 there were reports of a rocket-powered bicycle with wings which the inventor launched from a German rooftop.
More practical work took place in America and Italy. On 1 June 1931 William G. Swan flew his 'Steel Pier Rocket Plane' over the summer resort town of Atlantic City, New Jersey, thus becoming America's first rocket pilot.
At the end of June 1931 the Italian aeronautical engineer, Dr. Ettore Cattaneo, produced his well-designed R.R.I rocket glider which made at least four brief but successful flights at Milan's Taliedo Airport [ 11].
Crude as these machines were by our standards, they represented valiant if modest steps in the history of the rocket plane in this 'Century of the Shuttle.'
NOTES
In a letter to the author dated 7 April 1975, Alexander Lippisch said that: "Raab and Katzenstein had some trouble
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1928-1929 Forerunners of the Shuttle: 'The yon Opel Flights'/contd.
coup, both for himself and his company. But at the last minute the Government intervened in the name of safety. There was fear that he might crash into a village or railroad station. He was thus obliged to confine the flight to the immediate environs of the Rebstock Airport, set in an otherwise uninhabited forest glade. As for the press and public, von Opel this time sincerely wished to keep them within limits, "to avoid any possible trouble with the unruly crowds." Perhaps he was alluding to past difficulties attending his other stunts. He had invited only a few papers and granted exclusive American rights to The New York Times and Fox Movietone for filming.
When the great day came, on 30 September 1929, it looked as if the flight was never going to be made. At 9 a.m., the air tense with excitement, von Opel shoved himself snugly into his little machine and prepared for liftoff. He waited a few moments for a favourable headwind. Just then, Major Hell-muth Felmy came up, trying to look as calm as possible despite the message he bore with the Air Police and everyone else looking on. He whispered in von Opel's ear: "A telegram just came from the Oberpraesidium in Kassel. All flight tests are forbidden. Take off quick! I haven't had the telegram yet!" [ 10]. "Felmy's willingness to risk his position to protect my first rocket flight from bureaucratic prohibitions," commented von Opel years later, "is something I will never forget." Yet even Major Felmy's magnaminity was not potent enough to halt all technical flaws. The order for the catapult release was given. At first, it was a grand display. Fire and smoke leapt out of the big boosters. But the sus-tainers failed to ignite. Gracefully, the Opel-Sander Rak. 1 Ha try Flugzeug glided back to Earth at only 50 metres (164 ft.). At 11 a.m. they were ready again. By now, impatience and lunchtime hunger pangs had gotten the better of the spectators and many of them had disappeared. Von Opel once more girded himself for liftoff. The signal was given with similar results except that this time one of the boosters also burst, the yellow hair on the back on von Opel's head being slightly singed.
Not until 3:30 or 4:00 in the afternoon was another attempt made. By now only the most fervent of aviation enthusiasts, von Opel's supporters and friends, and some of the newsmen were present. Fritz Stamer, Friedrich Sander and Frau Sellnik, von Opel's fiancee, were there. Herself a pilot and one of Germany's six aviatrixes, Frau Sellnik had been another of von Opel's professional advisors on aviation for the previous several months. After the flight (following one account) she had been the first to run up and congratulate him. Ten minutes after the flight, and still bubbling over with excitement, von Opel wrote down his impressions which he afterwards dispatched to The New York Times as his exclusive. "My first rocket flight!," he began. "...For today's flight I have trained for a year... For an hour before this morning's start I inspected the course and personally went over every detail of the plane ? cables, fittings and rockets... Finally I draw a deep breath and then ignite. Tremendous pressure! I feel the machine racing forward. It tries to rear like a horse. Thus I race into space as in a dream, without any feeling for space or time. The machine practically flies itself. I scarcely need to touch the wheel. I only feel the boundless intoxicating joy of making a flight such asjman has never made before... The force of the rockets has expired. Visions cease; actuality calls. I must return to EartlL.. Gliding with terrible bumps along the ground, the plane comes to a halt."
The Opel-Sander Rak. 1 came down in a cloud of black smoke badly battered, pilot intact. Partly because of his exuberance, von Opel had neglected to say how close he had come to being seriously injured and possibly killed. Exact measurements of the flight were impossible. After he had levelled off to about 100 ft. (30.5 metres) the ground crew attempted to time the flight. It was determined that he was
then going at 90 mph (145 km/h). In a few moments, according to Heinz Gartmann, "a downward gust of wind, coinciding with the edge of the landing ground, caused him to make a forced landing after only using up five rockets. At a speed of 80 mph (129 km/h) this was a difficult feat, and Opel hit the ground with a crash as the landing-skid broke and the cockpit floor was shaved away, leaving him hanging by his safety-belt with an inch to spare." Officially, von Opel had been aloft for an estimated 75 seconds, attaining a maximum velocity of 95 mph (153 km/h) and had traversed a distance of nearly 5,000 ft. (1,525 metres), or 1.4 miles.
In his speech at the Deutches Museum in 1968, with the widow of Friedrich Sander in the audience, von Opel painted another picture of the events which followed the landing. "After my successful rocket flight in Frankfurt," he said, "I had to land outside the airport grounds on a potato patch, unfortunately with a tail wind and with several thrust rockets still hot. The flight speed was approximately 110 km/h (68 mph) and was too high to remain on the ground after landing, but too low to clear a raised crossroad at the end of the field. Upon impact, the landing skids, the entire cabin and a part of a wing were ripped away, but I had drawn up my legs and hung completely uninjured from the totally intact rocket frame by my safety belt. A flock of cars stampeded across the airfield with the world champion glider pilot leading the way. Stamer gathered me up, sat me on his shoulders and jumped around like a madman. While joy was reigning supreme, (mechanic Karl) Treber appeared, still shaking from what he thought had been an accident, planted himself in front of me in a rage and bellowed: "You'd think you earned a living by pulling these stunts!..." The joy that everything had gone well did not last long. Capt. (Major) Felmy rushed up with the news that the enormous air pressure during the launch had knocked over a spectator standing 100 metres (328 ft.) away and had broken her arm. Her husband was on his way to pick up the casualty. I have to admit that I would have ten times more preferred to repeat the flight than to meet the raging husband. But before I could offer my apologies to the woman, her husband jumped out of a taxi and said to her in Frankfurt dialect the most comforting words I have ever heard: "Serves you right you stupid ass. Next time stay home with the kids."
The Iiriitators
Following in the footsteps of Stamer and von Opel were several imitators. In 1929 Gottlob Espenlaub flew a rocket glider which had been towed into the air by a light aircraft. This arrangement worked well on several occasions but the rocketplane finally crashed.
In 1932 there were reports of a rocket-powered bicycle with wings which the inventor launched from a German rooftop.
More practical work took place in America and Italy. On 1 June 1931 William G. Swan flew his 'Steel Pier Rocket Plane' over the summer resort town of Atlantic City, New Jersey, thus becoming America's first rocket pilot.
At the end of June 1931 the Italian aeronautical engineer, Dr. Ettore Cattaneo, produced his well-designed R.R. 1 rocket glider which made at least four brief but successful flights at Milan's Taliedo Airport 111].
Crude as these machines were by our standards, they represented valiant if modest steps in the history of the rocket plane in this 'Century of the Shuttle.'
NOTES
1, In a letter to the author dated 7 April 1975, Alexander
Lippisch said that: "Raab and Katzenstein had some trouble
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1928-1929 Forerunners of the Shuttle: 'The von Opel Flights'/contd.

Rocket glider of the German aircraft builder Gottlob Espenlaub gets airborne at Dusseldorf in October 1930. Speed attained was 90 kmh (55.9 mph). Aircraft weighed 220 kg (485 Ib) including 70 kg (154 Ib) for the rockets. Total length about 2 metres (6.56 ft), wing span 12 metres (39.4 ft).
From: Friedrich Wilhelm Radenbach,
'Gottlob Espenlaub ? Ein Fliegerleben,'
(Stuggart: K. Thienmanns Verlag, 1943).

Gottlob Espenlaub inspecting the burnt rudder after his first rocket glider flight 23 October 1929, at the Lohausen-Dusseldorf Flying Field. The plane crashed but Espenlaub escaped without injury. The rocket motors were made by Friedrich Sander who had previously made them for Fritz von Opel's rocket gliders.

William G. Swan, born 1902, American parachutist, stunt flier, rocket pioneer, at the controls of his 'Steel Pier Rocket Plane," Atlantic City, New Jersey, 5 June 1931, prior to making his second flight in the aircraft. The full thrust of the plane's 12 powder rockets was applied in the flight and the 200 Ib (90.7 kg) glider rose to a height of some 200 ft (61 metres) and remained aloft eight minutes.
Times Wide World Photos (from 'Mid-Week Pictorial', 20 June 1931, p. 5).
with von Opel. They got across (sic) each other, but this is a long story which I probably will tell in my memoirs." Lippisch never completed his memoirs. He died in 1976.

Sander published almost nothing, except a rare, generalized article in Ley's Die Moglichkeit der Weltraumfahrt (Leipzig, 1928).
According to the long-time German glider pilot Peter Riedel, Raab left the country to escape the Hitler persecutions and went to Greece; Katzenstein went to South Africa.
See Aeronautics (London) 3, 6, June 1910, pp. 33-34; and Aeronautics (New York), 8, 3, March 1911, pp. 81-83.

5. It has not been satisfactorily proven that the Coanda
"propulseur" was really a jet. It may merely have been a large ducted air intake fan fitted around a conventional piston Clerget engine, the exhaust gases of the Clerget being injected rather than gasoline or other fuel as in a true jet.

Elsewhere in his book, Kronfield speaks highly of the promise of rockets for the future of soaring. Besides being an ideal "auxiliary motor force," he says, the rocket could also dispense with ground launching crews.
The Tageblatt story was datelined Fulda, the largest town close to the Wasserkruppe. The Zeitung issue of 14 June also carried an account of a Max Valier lecture entitled, "From Rocket Plane Flight to Spaceship." An overall report of Stamer's flight also appeared in the Zeitung for 15 June and a lengthy article by Heinrich von Sewall, "Rocket Flight and Altitude Investigation," is carried in the 17 June number. Stamer lived at Gerfeld, a village also close to the Wasser-kuppe,then Germany's gliding centre.
Some accounts, as The Times (London) for 1 October 1929, state that the "braking rockets" were set in the reverse direction and meant for slowing down the plane for landings, much like retro-rockets on Apollo L"EM's for landing on the Moon. However, this description does not conform to von Opel's account of the flight given above. Moreover, all available photographs of the aircraft do not show any reverse rockets, at least not on the exterior. The number of rocket holes in the rocket band, 16 in rows of four, also fits the pattern for all on-board rockets facing forward.
At least one reference, a biographical cartoon depicting von Opel's various feats and appearing in von Opel's Die Geschichte der Raketenentwicklung, indicates that he served in the (German) Air Corps during World War I and was stationed in Belgium, perhaps as a flier.
It is not known what time this telegram was received and its message "conveyed" to von Opel.
An account of the Espenlaub, Swan, Cattaneo and other rocket planes will be given by the author in a later article.
BIBLIOGRAPHY The following represents the major sources used in this article.

The Aeroplane, 34, 20 June 1928, p. 860. Air Enthusiast, 2, March 1972, pp. 149-150. "Die erste Raketenflug mit Besatzung," Die Rakete, 2,15 July 1928, pp. 198-100.
"Erster Raketenflug gegluckt," Berliner Tageblatt, 13 June 1928. "Erster Versuch mit einem Raketenflugzeug" Frankfurter Zeitung, 14 June 1928.
Essers, I., Max Valier, A Pioneer of Space Travel (National Aeronautics and Space Administration, Washington, D.C., 1976) NASA TT F-664.
[Continued on page 92
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1928-1929 FORERUNNERS OF THE SHUTTLE: 'THE VON OPEL FLIGHTS'/ Continued from page 83J
DerFlug, 10, May 1928,164, pp. 182-183.
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Popular Mechanics, 50, September 1928, pp. 356-357. Polular Mechanics, 52, August 1929, p. 282. "Raketen-Flugzeug imBau," Berliner Morgenpost, 26 May 1928. "Reich Rocket Fliers Break After Row," Atew York Herald Times, 30 September 1928.
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"2,000 Miles an Hour is Forecast," New York Sun, 30 November 1928. Valier, Max, Raketenfahrt, R. Oldenbourg: Munich, 1930. "Die Versuche mit einem Raketenflugzeug auf der Wasserkuppe," Frankfurter Zeitung, 15 June 1928.
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"Von Opel, Rocket Flier, Weds Woman Pilot Who Advised Him," New York Times, 30 Octoberl 929.
Von Opel, Fritz, "Rocket Plane Soars in Uncanny Flight; Wrecked in Landing," New York Times, 1 October 1929.
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