M.Simons The World's Vintage Sailplanes 1908-45

THE VAMPYR

  The Vampyr was a product of the Akaflieg of Hannover Technical University. Working to a basic design by Dr Georg Madelung, the students Martens, Hentzen and Blume tackled the detailed work for part of their diplomas. Madelung chose ДальшеMore>>> a high wing layout to free the upper surface from flow disturbances, and devised an ingenious tricycle landing gear of three spherical footballs, pivoted on axles. Two large wingtip protecting pads were provided. The fuselage nose section was covered by plywood to make a box enclosing the cockpit. Aft of the wing the ply skins extended to the tail on the sides of the fuselage but the upper and lower surfaces were fabric. The rear end was wedge-shaped, carrying the tailplane clear of the ground for take-off and landings, the pilot being seated upright under the leading edge of the wing.
  The wing structure was unique in its day and set a fashion that was to persist for more than forty years in advanced sailplane design. It was also frequently adopted for powered aircraft. Madelung called for a near-cantilever monoplane with a high aspect ratio. A single short strut was used near the wing root to relieve the highest stresses. There was only one spar, a deep, 'I'-sectioned beam, flanges of fir with a web of plywood fretted out to reduce weight. This took all the bending loads and was placed at the deepest point of the Goettingen 441 aerofoil section. Normally, whilst such a member could carry simple vertical loads, it would twist and break as the centre of pressure on the wing moved back and forth at changing airspeeds. Previous designers had added complex wire bracings or heavy internal cross members to stiffen such wings, or had abandoned the monoplane layout in favor of biplanes or even triplanes. The Vampyr obtained its torsional stiffness from its skin; one of the first known applications of stressed skin in aircraft design. A thin plywood sheet was glued to the top of the mainspar, bent and carried round to the lower flange of the spar over the light nose ribs and token leading edge member. This created a tube of 'D’-shaped cross section, of great strength and stiffness. Probably almost as important, the plywood skin over the entire front third of the wing chord ensured that the wing profile was accurate, a very great advantage. Behind the spar it reverted to fabric over ribs in the interest of lightness. The arrangement was immediately copied by almost every other sailplane designer and became standard practice.
  The Wasserkuppe meeting in 1921 was something of a disappointment until Klemperer on 30th August managed at last to exceed the Wright Brothers’ time with a duration of 13 minutes. A few days later Martens in the Vampyr followed his example and set a new record at 15 minutes and 7.5 km distance.
  During the interval between contests, Harth’s soaring flight of 21 minutes took place and some attractive prizes were offered for the 1922 Rhoen meeting, especially one for a duration of 40 minutes. Martens and Hentzen worked over the Vampyr. They rebuilt the wingtips, replacing the ailerons with wing warping for lateral control and removing the clumsy tip pads.
  On 18th August 1922, announcing his intention of trying for the 40 minutes prize, Martens was launched and, tacking to and fro above the slope, he soon rose to 100 metres above his take-off point. For almost everyone there it was the first time that true soaring, under full control, had been demonstrated. The Vampyr, with its white, semi-transparent fabric covering and dark brown, varnished plywood, rose smoothly upward and seemed well set for the duration record. It was a great moment. Martens hovered above the crowd happily, and was able to call down from time to time to learn his duration. At last signals from the ground told him he had achieved 40 minutes. Martens turned away from the hill to fly out over the valley, leaving the zone of the upcurrent and gliding down to the meadows far below. Only after 50 minutes did it dawn on him that he might be able to stay up for a whole hour. This he managed to do, flying carefully, until he turned to land in a field from the ample height of 150 metres. His time was 1 hour 6 minutes, and he had covered a distance from launch to landing of 8.9 km. His best height above take-off was 108 metres.
  Next day it was Hentzen’s turn. He broke all the records again with a great flight of two hours, a height gain of 200 metres, and a distance of 9 km. Again on 24th August he did 3 hours 6 minutes. This was the great breakthrough.
  In 1923 the Vampyr, slightly modified again and with a larger, aerodynamically balanced rudder, competed again but was badly damaged by an inexperienced pilot. It was then taken to the Deutsches Museum in Munich and preserved there until, during the Second World War, the museum was destroyed in the bombing. The wreckage of the Vampyr was saved by Heinz Cordes, who, as an apprentice, had helped build it in Hannover. He restored it and it remains on display in the rebuilt museum today.

Technical data:
  Vampyr: Span. 12.60 m. Wing area 16.0 sq m. Aspect ratio 9.95. Empty weight 120 kg. Flying weight. 195 kg. Wing loading 12.0 kg/sq m. Aerofoil section. Goettingen 441. Minimum sinking speed (calculated), 0.8 m sec at 50 km h. Best glide ratio 1:17.

Flight, August 1922

THE HANNOVER GLIDER

   IT is no exaggeration to say that world-wide admiration has been aroused by the splendid flights made in the Rhon mountains during the recent German gliding competition. First the news came that Herr Martens had remained aloft for one hour on a Hannover glider. The next day it was announced that a college fellow of Martens, Herr Hentzen, had kept in the air for two hours. This performance, excellent as it was, did not long remain a world's record. A few days later Herr Hentzen increased the duration to 3 hours 10 minutes. How long this record will be allowed to stand there is no way of telling. It may be, however, that exceptionally favourable weather conditions helped materially in enabling this performance to be attained, and that it will be some time before the four-hours mark is reached. On the other hand, if a glider will remain aloft for three hours there is apparently no reason why it should not remain up for any length of time, provided the pilot is physically and mentally capable of sustaining the strain which must of necessity accompany the constant alertness required to take advantage of every gust of wind. However that may be, we congratulate Herr Hentzen on his remarkable feat, and trust to have the pleasure of seeing him in this country, either in connection with this year's Daily Mail competition, or at some future date. In the meantime, a few notes dealing with the glider on which the flights were made may not be without interest.
   Generally speaking, the machine used by Martens and Hentzen in the Rhon competition this year is similar to last year's model. Certain modifications have been made, such as a reduction of the wing span, which is obviously somewhat large, and certain other minor alterations. The accompanying general arrangement drawings show last year's model, and it should be kept in mind that certain changes have taken place. However, even last year flights of long duration were made; for instance, one of 15 minutes 40 seconds, during which Herr Martens covered a distance of 4 1/2 miles. It is understood that, in spite of the reduction in wing span, the wing area has been slightly increased. This would mean that the chord has been increased, and the aspect ratio reduced to more normal proportions.
   Fundamentally, the Hannover glider consists of a cantilever monoplane wing of thick, high-lift section and large aspect ratio, mounted en parasol above a rectangular section fuselage. The wing is built in three sections, the central one of which measures approximately 22 ft. in span, with two end sections (tapered) attached to it. The wing section employed is one of the Gottingen sections, and the wing construction is somewhat unusual inasmuch as there is only one main wing spar.
   This spar is of I-section, with the web built up of a series of lattices in order to save weight. The spar is located approximately one-third of the chord from the leading edge. As a single spar, although capable of resisting the bending moments, could not be expected to resist torsion, the wing has been built up in the form of a tube of three-ply wood. This three-ply extends from the top of the spar, around the leading edge, and back over the lower surface as far as the lower edge of the spar. The tube thus formed, although being quite light, is very stiff against torsion, while at the same time having the advantage that it retains the shape of the leading edge of the wing better than could the usual rib construction. The main ribs are spaced about 18 ins. apart, but in the front portion false nose ribs are placed in the intervals between main ribs, thus supporting the three-ply at short intervals. The rear portion of the wing is covered with fabric in the usual way.
   The fuselage, which is of rectangular section, has four longerons, and is a girder of the usual type, with struts and cross-members, and braced with wire. The wing is attached to the fuselage by three bolts, one through the main spar in the centre, which engages with a fitting on the top longerons (which meet at this point), and two through special reinforced ribs over the full-width edge of the body. In order to reduce the bending moments somewhat, single struts slope out some distance and are attached to the single, spar.
   A notable feature of the Hannover glider, which, by the way, was designed by Dr. Madelung, is the undercarriage, which consists of three footballs, two side by side under the deepest part of the fuselage, and one under the nose. Two similar, but smaller, air-filled spheres are housed in the wing tips. In practice this undercarriage is stated to have worked very well, and certainly it would be difficult to imagine anything lighter and simpler. The machine was built for some of the members of the flying club of the Hannover Technical High School by the Hannover Coach and Carriage Works.

Flight, September 1922

The Hannover "Vampyr." - A scale drawing of the Hannover monoplane on which first Martens and later Hentzen made such remarkable flights was published in our issue of August 31, 1922. This drawing represented the machine in the form in which it was used in 1921. It was pointed out that alterations had been made, and from the photograph published on p. 534 in our last issue (this photograph was taken almost directly from below the machine) it was apparent that the chief alteration was the addition of triangular pieces to the trailing edge of the wing tips. In its earlier form the machine had tapered wings, but the alteration made turned this taper into swept-back tips and also slightly increased the area. One result of the change would appear to be a slight shifting to the rear of the centre of pressure, and it may be assumed that in its original form the machine was slightly tail-heavy. It seems reasonable to suppose that a glider should have its centre of gravity fairly far forward and its tail set at a negative angle, and this was probably done in the "Vampyr." The constructional features were dealt with in our description of the machine on August 31, and it will therefore suffice to recall that the fuselage is three-ply covered, with flat sides. The wing has but a single spar, and the necessary torsional stiffness is obtained by covering the entire leading edge with thin three-ply wood, which, with the spar, forms a D-section tube of light weight, as well as having the advantage of retaining the correct shape of the front part of the wing section. Footballs are used as "wheels," two being mounted under the deepest portion of the fuselage, one under the nose and one under each wing tip.

   The Hannover "Greif." - In addition to the "Vampyr" two other monoplanes were entered by the students of the Hannover High School. One of these, known as the "Mucki" ("Sulky") seems to have lived up to its name, as we have been unable to discover that it made any noteworthy flights. The other is a very pretty little machine called the "Greif" (Condor), of which photographs are published herewith. This machine is a refinement of the "Vampyr," having a carefully streamlined fuselage and tapered cantilever wings. The machine is said to be less pleasant to fly than the "Vampyr," possibly because it has not yet been so thoroughly flown-in ("eingeflogen," the Germans call it) as the older model. Several very good flights were, however, made with the "Greif," and when perfected as regards trim, etc., by extensive trials and alterations should prove a very fine little machine. It is somewhat smaller in span and area than the "Vampyr," and probably the wing loading is slightly greater, but, on the other hand, the drag of the complete machine is probably considerably lower, owing to the better streamlining. The "Greif" appears to have but a single football "wheel" under the centre line of the fuselage, and when on the ground one wing tip is always touching. Possibly this fact may be in part responsible for the relatively small use that was made of this machine, as there would appear to be considerable risk of damage to the wing tips in landing.

Flight, June 1924

   THE second German glider meeting at Rossitten, near Koenigsberg, was held in the middle of May, and was chiefly remarkable for the fact that the world's duration record for gliders was beaten by the German school teacher Schulz, who succeeded, on May 11, in remaining up for 8 hours 42 minutes 9 seconds.
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   ANOTHER feature of the meeting was Martens flying on the “Strolch." Although he did not come anywhere near equaling Schulz's performance, Arthur Martens made many excellent flights, and the opportunity was taken to ascertain, by scientific measurements, the characteristics of his machine. The rate of descent was ascertained to be 0-5-metre (1-64 ft.) per second, which is an extraordinarily good figure. The gliding angle of the "Strolch" was found to be 1 in 20, so that the efficiency of this machine appears to have been amply demonstrated
   ON another glider, Mr. Martens made several flights. This machine, the "Max," was fitted with an Ilo engine of about 5 h.p., and as long as the wind gave a certain amount of assistance the machine could remain aloft. If, however, the wind dropped, the machine usually had to come down, the power developed by the engine being, apparently, insufficient for flight. In one of the accompanying photographs the "Max" is seen being catapulted off the top of a hill. We understand that Herr Martens intends to fit the machine with one of the Blackburne "Tomtit" engines, when a vastly improved performance is to be looked for.