After the collaboration between the Technical High School Dresden (TH Dresden) and the local flying club, the Flugtechnischer Verein Dresden (F.V.D.), that led to the quite successful 1921 F.V.D. Stehaufchen wing warping biplane glider, the group designed and built a monoplane, the Doris. Originally known as the Dresden Doris or, in the UK at least, as the F.V.D. monoplane, it was later incorporated retrospectively into the Akaflieg Dresden's design list as the D-B2 Doris. Most notably, it had wings which could adjust their relative angles of attack independently both of each other and of the pilot.
The idea of such wings came from the poor understanding of slope soaring in the early 1920s and from observations of bird flight, where wings were seen to twist independently. It was hoped that such freedom could better capture the energy of the gusts that were thought to be the source of slope lift. An early glider of this type had been built by Erich Offermann before World War I and some theoretical work done by Albert Betz and, independently, R. Knoller, began to reach an understanding of how a plunging airfoil could generate thrust (the Knoller-Betz effect). By about 1920 Freidrich Harth was convinced this was essential for extended glider flight and the Harth-Messerschmitt designs were controlled in pitch by a variable angle of incidence wing and roll by wing warping. Its pilot had two levers, one for roll and the other for pitch. The 1921 Loessl Sb.1 Münchener, which won two first and one second prizes at the second Rhön (Wasserkuppe) gliding contest, extended the idea with wings that could be independently rotated with a single, conventional control column, doing away with the wing warping. Ten of the fifty-three competing aircraft at the third Rhön contest, held in 1922, had variable incidence wings but as slope soaring was better understood and the high control forces needed appreciated, rigid wings with ailerons for roll control became standard on gliders.
The Doris was a high-wing monoplane using a thick, highly cambered Göttingen 441 airfoil, braced from the lower fuselage on each side by a wide spread inverted V pair of struts connected to the wing at about 30% of the span, immediately below the single main wing spar on which the wing rotated. This was at about 40% chord, where the wing was thickest. The spars were mounted over the fuselage on a narrow central faired column. The wing was largely fabric covered but from the spar forward it was plywood skinned around the leading edge on the upper side, though the ply did not extend as far aft on the underside. The extreme tips were also ply covered.
The fuselage of the Doris had a wooden frame girder structure with a rectangular cross section, tapering aft to a horizontal wedge. Forward of the wing trailing edge it was ply covered, with fabric covering elsewhere. At the nose the sides curved round smoothly and there was also rounded decking immediately ahead of the open cockpit, which was under the leading edge with the vertical front face of the wing support column against the pilot's back. The rear edge of the column dropped gradually away from the trailing edge to the upper fuselage. The angles of incidence were adjusted from the control column via pushrods, sideways movement rotating the wings in opposite directions to roll. Fore and aft movement decreased and increased the angles of incidence together. The intention was that in level flight the pilot should largely allow the wings to follow their optimum setting by themselves. In addition there was a tailplane trim lever, originally fixed to the control column. The high aspect ratio, all-moving tailplane was nearly rectangular in plan apart from angled tips and was fabric covered behind its leading edge. The Doris was a short aircraft and its vertical tail was therefore large, with a quadrant shaped fin and a near rectangular rudder which had a small cut-away at its base for tailplane movement. The vertical tail surfaces were fabric covered. Like the Stehaufchen, the Doris had a pair of horizontal landing skids. These were fixed to the fuselage at the nose and mounted on the ends of a pair of transverse, arched ash brackets on rubber shock absorbers.
The idea of such wings came from the poor understanding of slope soaring in the early 1920s and from observations of bird flight, where wings were seen to twist independently. It was hoped that such freedom could better capture the energy of the gusts that were thought to be the source of slope lift. An early glider of this type had been built by Erich Offermann before World War I and some theoretical work done by Albert Betz and, independently, R. Knoller, began to reach an understanding of how a plunging airfoil could generate thrust (the Knoller-Betz effect). By about 1920 Freidrich Harth was convinced this was essential for extended glider flight and the Harth-Messerschmitt designs were controlled in pitch by a variable angle of incidence wing and roll by wing warping. Its pilot had two levers, one for roll and the other for pitch. The 1921 Loessl Sb.1 Münchener, which won two first and one second prizes at the second Rhön (Wasserkuppe) gliding contest, extended the idea with wings that could be independently rotated with a single, conventional control column, doing away with the wing warping. Ten of the fifty-three competing aircraft at the third Rhön contest, held in 1922, had variable incidence wings but as slope soaring was better understood and the high control forces needed appreciated, rigid wings with ailerons for roll control became standard on gliders.
The Doris was a high-wing monoplane using a thick, highly cambered Göttingen 441 airfoil, braced from the lower fuselage on each side by a wide spread inverted V pair of struts connected to the wing at about 30% of the span, immediately below the single main wing spar on which the wing rotated. This was at about 40% chord, where the wing was thickest. The spars were mounted over the fuselage on a narrow central faired column. The wing was largely fabric covered but from the spar forward it was plywood skinned around the leading edge on the upper side, though the ply did not extend as far aft on the underside. The extreme tips were also ply covered.
The fuselage of the Doris had a wooden frame girder structure with a rectangular cross section, tapering aft to a horizontal wedge. Forward of the wing trailing edge it was ply covered, with fabric covering elsewhere. At the nose the sides curved round smoothly and there was also rounded decking immediately ahead of the open cockpit, which was under the leading edge with the vertical front face of the wing support column against the pilot's back. The rear edge of the column dropped gradually away from the trailing edge to the upper fuselage. The angles of incidence were adjusted from the control column via pushrods, sideways movement rotating the wings in opposite directions to roll. Fore and aft movement decreased and increased the angles of incidence together. The intention was that in level flight the pilot should largely allow the wings to follow their optimum setting by themselves. In addition there was a tailplane trim lever, originally fixed to the control column. The high aspect ratio, all-moving tailplane was nearly rectangular in plan apart from angled tips and was fabric covered behind its leading edge. The Doris was a short aircraft and its vertical tail was therefore large, with a quadrant shaped fin and a near rectangular rudder which had a small cut-away at its base for tailplane movement. The vertical tail surfaces were fabric covered. Like the Stehaufchen, the Doris had a pair of horizontal landing skids. These were fixed to the fuselage at the nose and mounted on the ends of a pair of transverse, arched ash brackets on rubber shock absorbers.
| Type | Single seat glider |
| Dimensions | Length 5,30 m, wingspan 12,20 m, wing area 15,5 m2, aspect ratio 9,5 |
| Weights | Empty 118,5 kg, flying weight 195 kg, wing loading 12,6 kg/m2, wings 55,2 kg, fuselage 45,1 kg, stabilizer 8,2 kg |
| Performance | Max. glide ratio 14,5 |
| Type | Werk.Nr | Registration | History |
| The Doris took part in the 1922 Rhön contest, though Flight noted that it "does not appear to have accomplished very much". It remained on the Wasserkuppe after the competition but crashed, injuring Muttray. The accident, which badly damaged the Doris, was partially ascribed to the unfamiliar control column mounted tailplane trim lever, so when the glider was rebuilt this control was relocated further back in the cockpit. After the rebuild, completed in November 1922, the Doris flew from the Dresden club's airfield at Geising in the Erzgebirge. Some decent but unexceptional flights were made |
Monoplane 1922 of the Flugtechnische Verein Dresden.
By H. Muttray and R. Seiferth,
The discussion of the aircraft mainly comprises the following points: a) flight characteristics, b) workshop practice, c) operation.
a) Flight ownership. The aim was to improve flight characteristics with the help of rotating wings (adaptable wing decks). This idea is based on the
well-known Knoller-Betz theory.
The angle of attack of the wing deck can be changed with the help of the control stick. The position of the axis of rotation of the wing, taking into account the centre of gravity of the centre of
pressure, is chosen in such a way that no forces occur in the control stick during normal flight. As soon as the blowing
of the support deeks changes due to vertical wind direction fluctuations, forces occur in the control stick as a result of the migration of the center of pressure. The control stick thus forms a kind of gust indicator. The leader must
adjust the stick against the direction of force in such a way that the forces in the stick disappear. Then the wing decks have an
angle of attack compared to the respective blowing, at which the most favorable conditions of lift and drag prevail. When flight is somewhat depressed, a steady slight pull
forward occurs in the stick.
For the purpose of height control and torsion, the wing decks can be rotated in the same direction and in opposite directions.
') Since c;, is supposed to consist of 2 wires.
-) A thinner wire would also suffice for It. Plate 7, but for workshop reasons only two different wire thicknesses were carried out for the entire tensioning.
The type of wing control is the same as that used by von Lößl and Finsterwalder for the first time in 1921. The pivot points of the control linkage are
cardan-like. The slit created by the counter-rotation of the wings between them has been avoided by a middle piece belonging to the fuselage.
The rear horizontal damping surface is movable with the help of an adjustable lever located next to the driver's seat. However, it is not usually used for
height control, as the wing control is effective enough.
In the original version, in which the aircraft appeared at the Rhön Competition in 1922, it was intended to adjust the horizontal damping surface during flight
by means of a movable handle on the control stick. The simultaneous movement of the wings and the damping surface was intended to achieve further
adaptability of the fuselage and the tail surface to the air flow. For reasons that cannot be specified here, this order was provisionally waived after the Rhön Competition
in 1922. The idea of the simultaneous movement of the wings and the horizontal damping surface, which as far as we know was carried out for the first time on
our aircraft, has not been abandoned.
The altitude control by the wings alone has the advantage that the moment of inertia of the fuselage in relation to its transverse axis is switched off, because the fuselage constantly maintains
its position almost exactly. With the otherwise usual height control by the tail surface, a rotation of the fuselage around its
transverse axis occurs with each control deflection, which is calculated at the expense ofn the kinetic energy of the aircraft.
In order to keep the harmful resistance as low as possible, a good aspect ratio is chosen for the wing deck, which is almost cantilevered (about 1 : 9.6). The wing tips
are pointed to reduce the marginal vortex, and the wing cross-section turns into a drop filter with an angle of attack of 0° on the outside. The fuselage cross-section is kept as small as possible
(60 X 70 cm). Chassis struts have been avoided.
b) Workshop conditions. For the sake of quick and cheap execution, the simplest possible components were used in constant repetition. These were
mainly . Groove belts with glued-in plywood web and square rods, which, together with glued and nailed plywood strips, resulted in U-, T- and double-T cross-sections
. Stencil arrhythmia was widely used, e.g. for the ribs and fuselage frames (Fig. 2). Metal parts were only used for the fittings for
the suspension of the supporting deck.
c) Operation. The requirements of practical operation are the robust design of the parts stressed during landing (runners and front fuselage), grip of all parts
for transport and the simplest assembly and dismantling.
The front part of the fuselage, which is planked with plywood, is made of strong, multi-glued ash strips to protect the guide as much as possible in the event of a fall.
The runners lie just below the hull and are supported against it by two stirrups, which also serve to absorb lateral impacts. Runners and stirrups
are made of several layers of ash. The cushioning is provided by the elasticity of the ash runners
and rubber blocks. This design was already used in the 1921 biplane of the Flugtechnische Verein Dresden, where it proved itself excellently in the flights of the Rhön
Competition in 1921 and 1922 as well as in the school operation in Geising i. Erzgebirge in 1922 and 1923.
The construction of the aircraft is very simple: each wing, apart from the connection with the control stick, is suspended at two points under the spar
. After this connection has been loosened, the wings are removed and the strut triangles that hold the wings are folded onto the fuselage. This arrangement
at the same time achieves a permanent precise adjustment of the wings to the fuselage. For the first precise adjustment, the length of the struts, which are made of tubular steel, must be changed by
means of threads. The side damping surface and the side control are pulled out of the fuselage upwards (Figs. 6 and 7), the height control surface
is removed after removing the tubular steel axle (Fig. 8). The dismantling takes about 5 minutes, the assembly 10 minutes.Each
wing consists of two parts: an inner part of 4 m in length and an outer part of 2 m in length (Fig. 7), which, however, are only separated for rail transport
. The hull is the longest part with a length of 4.35 m. The aircraft can therefore be comfortably accommodated in a closed railway carriage.
The fuselage of the aircraft was arranged low, as in the case of the 1921 F. V. D. biplane, which was also designed by us. This arrangement allows the
omission of chassis struts and prevents infDue to the low center of gravity, the aircraft tilted after landing despite the small track width of the
chassis runners. For the monoplane (high-wing type), this fuselage arrangement also allows reliable attachment of the rotating wings. The hull superstructure behind the
leader's head replaces the tensioning tower. On both sides of this middle piece are the wings. (Figs. 3 and 8.)
The carrying deck spar is calculated for seven times safety. It is designed as a box spar with inner diagonal stiffener and recessed side walls. To achieve
torsional rigidity, the front half of the profile is planked with plywood. Profile 441 of the Göttingen investigations was chosen as the wing cross-section. It has the
advantage of high buoyancy values; so you can use high wing loading and therefore get by with a small wing
side S-l
. The curve Ca :'/cw- has a relatively high and, above all, wide maximum, and the rate of descent is therefore not very
variable within a large angle of attack range. The dimensions of the monoplane are shown in the drawing (Fig. 1). The weights are as follows: Two wings 55.2 kg, Eumpf 45.1 kg, vertical stabilizer
3.6 kg, elevator 4.ti kg, four steel tubes 10.0 kg, empty weight 118.5 kg.
With a wing of 15.0 in2, you get a wing load of 12.5 kg/m2 with a driver weight of 75 kg.
Since November 1922, the monoplane has been stationed at the F. V. D. airfield near Geising in the Ore Mountains. In a series of flights, which were carried out in different wind
By H. Muttray and R. Seiferth,
The discussion of the aircraft mainly comprises the following points: a) flight characteristics, b) workshop practice, c) operation.
a) Flight ownership. The aim was to improve flight characteristics with the help of rotating wings (adaptable wing decks). This idea is based on the
well-known Knoller-Betz theory.
The angle of attack of the wing deck can be changed with the help of the control stick. The position of the axis of rotation of the wing, taking into account the centre of gravity of the centre of
pressure, is chosen in such a way that no forces occur in the control stick during normal flight. As soon as the blowing
of the support deeks changes due to vertical wind direction fluctuations, forces occur in the control stick as a result of the migration of the center of pressure. The control stick thus forms a kind of gust indicator. The leader must
adjust the stick against the direction of force in such a way that the forces in the stick disappear. Then the wing decks have an
angle of attack compared to the respective blowing, at which the most favorable conditions of lift and drag prevail. When flight is somewhat depressed, a steady slight pull
forward occurs in the stick.
For the purpose of height control and torsion, the wing decks can be rotated in the same direction and in opposite directions.
') Since c;, is supposed to consist of 2 wires.
-) A thinner wire would also suffice for It. Plate 7, but for workshop reasons only two different wire thicknesses were carried out for the entire tensioning.
The type of wing control is the same as that used by von Lößl and Finsterwalder for the first time in 1921. The pivot points of the control linkage are
cardan-like. The slit created by the counter-rotation of the wings between them has been avoided by a middle piece belonging to the fuselage.
The rear horizontal damping surface is movable with the help of an adjustable lever located next to the driver's seat. However, it is not usually used for
height control, as the wing control is effective enough.
In the original version, in which the aircraft appeared at the Rhön Competition in 1922, it was intended to adjust the horizontal damping surface during flight
by means of a movable handle on the control stick. The simultaneous movement of the wings and the damping surface was intended to achieve further
adaptability of the fuselage and the tail surface to the air flow. For reasons that cannot be specified here, this order was provisionally waived after the Rhön Competition
in 1922. The idea of the simultaneous movement of the wings and the horizontal damping surface, which as far as we know was carried out for the first time on
our aircraft, has not been abandoned.
The altitude control by the wings alone has the advantage that the moment of inertia of the fuselage in relation to its transverse axis is switched off, because the fuselage constantly maintains
its position almost exactly. With the otherwise usual height control by the tail surface, a rotation of the fuselage around its
transverse axis occurs with each control deflection, which is calculated at the expense ofn the kinetic energy of the aircraft.
In order to keep the harmful resistance as low as possible, a good aspect ratio is chosen for the wing deck, which is almost cantilevered (about 1 : 9.6). The wing tips
are pointed to reduce the marginal vortex, and the wing cross-section turns into a drop filter with an angle of attack of 0° on the outside. The fuselage cross-section is kept as small as possible
(60 X 70 cm). Chassis struts have been avoided.
b) Workshop conditions. For the sake of quick and cheap execution, the simplest possible components were used in constant repetition. These were
mainly . Groove belts with glued-in plywood web and square rods, which, together with glued and nailed plywood strips, resulted in U-, T- and double-T cross-sections
. Stencil arrhythmia was widely used, e.g. for the ribs and fuselage frames (Fig. 2). Metal parts were only used for the fittings for
the suspension of the supporting deck.
c) Operation. The requirements of practical operation are the robust design of the parts stressed during landing (runners and front fuselage), grip of all parts
for transport and the simplest assembly and dismantling.
The front part of the fuselage, which is planked with plywood, is made of strong, multi-glued ash strips to protect the guide as much as possible in the event of a fall.
The runners lie just below the hull and are supported against it by two stirrups, which also serve to absorb lateral impacts. Runners and stirrups
are made of several layers of ash. The cushioning is provided by the elasticity of the ash runners
and rubber blocks. This design was already used in the 1921 biplane of the Flugtechnische Verein Dresden, where it proved itself excellently in the flights of the Rhön
Competition in 1921 and 1922 as well as in the school operation in Geising i. Erzgebirge in 1922 and 1923.
The construction of the aircraft is very simple: each wing, apart from the connection with the control stick, is suspended at two points under the spar
. After this connection has been loosened, the wings are removed and the strut triangles that hold the wings are folded onto the fuselage. This arrangement
at the same time achieves a permanent precise adjustment of the wings to the fuselage. For the first precise adjustment, the length of the struts, which are made of tubular steel, must be changed by
means of threads. The side damping surface and the side control are pulled out of the fuselage upwards (Figs. 6 and 7), the height control surface
is removed after removing the tubular steel axle (Fig. 8). The dismantling takes about 5 minutes, the assembly 10 minutes.Each
wing consists of two parts: an inner part of 4 m in length and an outer part of 2 m in length (Fig. 7), which, however, are only separated for rail transport
. The hull is the longest part with a length of 4.35 m. The aircraft can therefore be comfortably accommodated in a closed railway carriage.
The fuselage of the aircraft was arranged low, as in the case of the 1921 F. V. D. biplane, which was also designed by us. This arrangement allows the
omission of chassis struts and prevents infDue to the low center of gravity, the aircraft tilted after landing despite the small track width of the
chassis runners. For the monoplane (high-wing type), this fuselage arrangement also allows reliable attachment of the rotating wings. The hull superstructure behind the
leader's head replaces the tensioning tower. On both sides of this middle piece are the wings. (Figs. 3 and 8.)
The carrying deck spar is calculated for seven times safety. It is designed as a box spar with inner diagonal stiffener and recessed side walls. To achieve
torsional rigidity, the front half of the profile is planked with plywood. Profile 441 of the Göttingen investigations was chosen as the wing cross-section. It has the
advantage of high buoyancy values; so you can use high wing loading and therefore get by with a small wing
side S-l
. The curve Ca :'/cw- has a relatively high and, above all, wide maximum, and the rate of descent is therefore not very
variable within a large angle of attack range. The dimensions of the monoplane are shown in the drawing (Fig. 1). The weights are as follows: Two wings 55.2 kg, Eumpf 45.1 kg, vertical stabilizer
3.6 kg, elevator 4.ti kg, four steel tubes 10.0 kg, empty weight 118.5 kg.
With a wing of 15.0 in2, you get a wing load of 12.5 kg/m2 with a driver weight of 75 kg.
Since November 1922, the monoplane has been stationed at the F. V. D. airfield near Geising in the Ore Mountains. In a series of flights, which were carried out in different wind
Dresden D-B2 "Doris"
Motorless flight without loss of altitude was the very early and accurate definition of the desired gliding flight. It came from the physicist and co-founder of modern aerodynamics, Professor Ludwig Prandtl (1875-1953). He had already participated in the first Rhön competition as an observer, and subsequently elevated discussions about unpowered flight to the status of science at the Göttingen lectures. In his remarks on gliding, published as early as 1921, he was the first to speak of Design goals aspired to: High aspect ratio, strongly cambered airfoils with good lift coefficients, low form drag. These were accepted and implemented without reservation by the aspiring graduate engineers Horst Muttray (1898-?) and Reinhold Seiferth (1898- 1969) at the Dresden University of Technology.
Prandtl's simultaneous skepticism towards so-called "dynamic gliding" was, however, viewed more critically by them as by many of their colleagues and scientists. They all believed in the possibility of "motorless flight by utilizing the irregularities of the natural wind," which they considered The basis for gliding was considered. This theory was based on the scientific considerations of Dipl.-Ing. Albert Betz (1885-1968), the later director of the Aerodynamic Research Institute in Göttingen, who, interestingly, had become an employee of Prandtl in 1911. Since his Austrian colleague R. Knoller had a similar drawing logical conclusions, the phenomenon described by the two entered the literature as the Knoller-Betz effect.
At the first Rhön competition in 1920, the performance of the inadequate designs remained more than modest. An impression of how the glider could develop was given by Aachen students towards the end of the event when they arrived on the mountain with a cantilevered, thick-profile monoplane, which was called the Black Devil because of its dark covering. On its further development, the Blue Mouse, Wolfgang Klemperer had set a record – albeit only after the official end of the following year's competition. After launching from the west-facing slope, he overshot the take-off point and then flew in just over 13 minutes to the village of Gersfeld, five kilometers away. This was one of the first classic high-performance flights in slope lift. But nobody talked about that back then. Klemperer and the other pilots were convinced that a dynamic soaring flight had taken place, similar to that of seabirds over the surface of the open sea. Professor Prandtl, who pointed out that any large ocean wave deflects the wind upwards just like a slope, was (still) met with disbelief. But it wasn't Klemperer in the Blue Mouse who had become the winner in 1921, but Karl Koller in the Munich monoplane, with which he was able to achieve a better overall flight time and distance. And the success of this design was seen in its wing control system, with which the assumed wind currents could apparently be better controlled.
The wing control, that is, the rotatability of the individual wing halves around the lateral axis, was first practically tested by Erich Offermann (1885-1930) from Aachen.
The gliding pioneer, now hardly known, whose work—for example, with the introduction of a central skid—also influenced modern gliding,
built a 12-meter-high takeoff hill in the High Fens in 1908 and equipped it with a catapult launching system. He first experimented with biplane gliders of Wrightian design, then with monoplanes, in whose shaping he paid attention to minimizing harmful drag. The two halves of the high-aspect-ratio wing were designed to be rotatable, allowing the angle of incidence of both the overall surface and each wing half to be changed individually. This made it possible to control lift and the position around the longitudinal axis simultaneously or alternately. Offermann hoped this would allow him to react better to air currents.
Government building inspector Friedrich Harth (1880-1936) from Bamberg, another gliding pioneer Nier adopted such a wing control system for his prototypes and was successful with it. This spurred many other designers to choose adjustable wings instead of the normal control system with elevators and ailerons, including the two from Dresden. Their design, designated Dresden D-B2 and called Doris in the sequence, was a shoulder-wing aircraft. Each half-wing was rotatably attached to a neck that protruded from the otherwise square fuselage cross-section behind the pilot's seat. This simultaneously avoided the extreme slot formation that occurs when two oppositely rotating wing halves are attached to the fuselage. directly collide. For the fuselage and skid construction, Muttray and Seiferth drew on the positive experiences gained with the Stehaufchen: a low-slung fuselage that does not require long struts for the landing gear and whose center of gravity is so low that the aircraft remains level after landing, despite the small distance between the parallel skids, without any tendency to tip. For the structure of the plywood-covered front fuselage, they chose multi-layered ash wood strips to protect the pilot in the event of a crash landing, despite the added weight. The two skids and the components for their mountings were also made of the same material. Support brackets were required. This skid arrangement, for which rubber blocks were used for damping, proved to be very robust once again. Moreover, the construction as a whole proved to be exceptionally insensitive, since particular emphasis had been placed on grip strength for assembly and transport. In order to be able to transport the machine in an enclosed freight wagon, Muttray and Seiferth had designed each wing half to be divisible once again. The slender wing with an aspect ratio of almost 10 and tapered wingtips, to keep induced drag as low as possible, proved to be aerodynamically superior with the
chosen airfoil of high camber. This resulted in a relatively constant sink rate over a wide range of angles of attack.
It was designed, in an advanced Vampyr style, as a single spar with a torsionally rigid plywood leading edge, had a box spar reinforced with internal diagonal bracing and a safety factor of seven, and would certainly have contributed to a good grade for the overall design had it not been used by the designers also as a control element.
This was reflected in a relatively constant sink rate over a wide range of angles of attack. It was designed, in an advanced Vampyr style, as a single spar with a torsionally rigid plywood leading edge, had it had been reinforced with internal diagonal bracing, and had a box spar with a safety factor of seven, and would certainly have contributed to a good grade for the overall design, had it not also been used by the designers as a control element. Muttray and Seiferth cited improved flight characteristics as the reason for choosing the wing control system – which they called "adaptable wingtips". Undoubtedly, during normal flight, the wingtips rotate
Motorless flight without loss of altitude was the very early and accurate definition of the desired gliding flight. It came from the physicist and co-founder of modern aerodynamics, Professor Ludwig Prandtl (1875-1953). He had already participated in the first Rhön competition as an observer, and subsequently elevated discussions about unpowered flight to the status of science at the Göttingen lectures. In his remarks on gliding, published as early as 1921, he was the first to speak of Design goals aspired to: High aspect ratio, strongly cambered airfoils with good lift coefficients, low form drag. These were accepted and implemented without reservation by the aspiring graduate engineers Horst Muttray (1898-?) and Reinhold Seiferth (1898- 1969) at the Dresden University of Technology.
Prandtl's simultaneous skepticism towards so-called "dynamic gliding" was, however, viewed more critically by them as by many of their colleagues and scientists. They all believed in the possibility of "motorless flight by utilizing the irregularities of the natural wind," which they considered The basis for gliding was considered. This theory was based on the scientific considerations of Dipl.-Ing. Albert Betz (1885-1968), the later director of the Aerodynamic Research Institute in Göttingen, who, interestingly, had become an employee of Prandtl in 1911. Since his Austrian colleague R. Knoller had a similar drawing logical conclusions, the phenomenon described by the two entered the literature as the Knoller-Betz effect.
At the first Rhön competition in 1920, the performance of the inadequate designs remained more than modest. An impression of how the glider could develop was given by Aachen students towards the end of the event when they arrived on the mountain with a cantilevered, thick-profile monoplane, which was called the Black Devil because of its dark covering. On its further development, the Blue Mouse, Wolfgang Klemperer had set a record – albeit only after the official end of the following year's competition. After launching from the west-facing slope, he overshot the take-off point and then flew in just over 13 minutes to the village of Gersfeld, five kilometers away. This was one of the first classic high-performance flights in slope lift. But nobody talked about that back then. Klemperer and the other pilots were convinced that a dynamic soaring flight had taken place, similar to that of seabirds over the surface of the open sea. Professor Prandtl, who pointed out that any large ocean wave deflects the wind upwards just like a slope, was (still) met with disbelief. But it wasn't Klemperer in the Blue Mouse who had become the winner in 1921, but Karl Koller in the Munich monoplane, with which he was able to achieve a better overall flight time and distance. And the success of this design was seen in its wing control system, with which the assumed wind currents could apparently be better controlled.
The wing control, that is, the rotatability of the individual wing halves around the lateral axis, was first practically tested by Erich Offermann (1885-1930) from Aachen.
The gliding pioneer, now hardly known, whose work—for example, with the introduction of a central skid—also influenced modern gliding,
built a 12-meter-high takeoff hill in the High Fens in 1908 and equipped it with a catapult launching system. He first experimented with biplane gliders of Wrightian design, then with monoplanes, in whose shaping he paid attention to minimizing harmful drag. The two halves of the high-aspect-ratio wing were designed to be rotatable, allowing the angle of incidence of both the overall surface and each wing half to be changed individually. This made it possible to control lift and the position around the longitudinal axis simultaneously or alternately. Offermann hoped this would allow him to react better to air currents.
Government building inspector Friedrich Harth (1880-1936) from Bamberg, another gliding pioneer Nier adopted such a wing control system for his prototypes and was successful with it. This spurred many other designers to choose adjustable wings instead of the normal control system with elevators and ailerons, including the two from Dresden. Their design, designated Dresden D-B2 and called Doris in the sequence, was a shoulder-wing aircraft. Each half-wing was rotatably attached to a neck that protruded from the otherwise square fuselage cross-section behind the pilot's seat. This simultaneously avoided the extreme slot formation that occurs when two oppositely rotating wing halves are attached to the fuselage. directly collide. For the fuselage and skid construction, Muttray and Seiferth drew on the positive experiences gained with the Stehaufchen: a low-slung fuselage that does not require long struts for the landing gear and whose center of gravity is so low that the aircraft remains level after landing, despite the small distance between the parallel skids, without any tendency to tip. For the structure of the plywood-covered front fuselage, they chose multi-layered ash wood strips to protect the pilot in the event of a crash landing, despite the added weight. The two skids and the components for their mountings were also made of the same material. Support brackets were required. This skid arrangement, for which rubber blocks were used for damping, proved to be very robust once again. Moreover, the construction as a whole proved to be exceptionally insensitive, since particular emphasis had been placed on grip strength for assembly and transport. In order to be able to transport the machine in an enclosed freight wagon, Muttray and Seiferth had designed each wing half to be divisible once again. The slender wing with an aspect ratio of almost 10 and tapered wingtips, to keep induced drag as low as possible, proved to be aerodynamically superior with the
chosen airfoil of high camber. This resulted in a relatively constant sink rate over a wide range of angles of attack.
It was designed, in an advanced Vampyr style, as a single spar with a torsionally rigid plywood leading edge, had a box spar reinforced with internal diagonal bracing and a safety factor of seven, and would certainly have contributed to a good grade for the overall design had it not been used by the designers also as a control element.
This was reflected in a relatively constant sink rate over a wide range of angles of attack. It was designed, in an advanced Vampyr style, as a single spar with a torsionally rigid plywood leading edge, had it had been reinforced with internal diagonal bracing, and had a box spar with a safety factor of seven, and would certainly have contributed to a good grade for the overall design, had it not also been used by the designers as a control element. Muttray and Seiferth cited improved flight characteristics as the reason for choosing the wing control system – which they called "adaptable wingtips". Undoubtedly, during normal flight, the wingtips rotate
When the fuselage is turned around its transverse axis, this comes at the expense of the aircraft's kinetic energy. And this disadvantage is undoubtedly eliminated with wing control, because the fuselage generally does not change its horizontal position. However, since wing control can be static and present problems in terms of controllability, very specific reasons must have been the deciding factor in choosing it.
The designers stated this verbatim: "The angle of attack of the wing is variable with the help of the control knob" (Author's note: In reality, the wing control functioned like the Munich monoplane of 1921, via cardan-like pivot points on the control linkage).
The position of the wing's axis of rotation is chosen, taking into account the wing's center of gravity and the center of pressure, so that no forces are exerted on the control stick during normal flight.
This occurs. As soon as the airflow over the wings changes due to vertical wind direction fluctuations, forces occur at the control stick as a result of the movement of the center of pressure. The control stick thus acts as a kind of gust indicator.
The pilot must adjust the stick against the direction of the force so that the forces on the control stick disappear.
Then the wings have an angle of attack relative to the respective airflow at which the most favorable lift-to-drag ratios prevail. In slightly compressed flight, a steady, slight forward pull occurs at the control stick. Paradoxically, Muttray and Seiferth went a step further by providing an additional adjustment of the horizontal damping surface at the stern via a movable handle on the control stick – a design innovation whose novelty the designers particularly emphasized. But this is precisely what led to disaster.
The Doris was transported to the Wasserkuppe immediately after its completion, where it successfully had its airworthiness certified by the Technical Commission, and subsequently completed its first test flight under Horst Muttray on the western slope. This ended – probably due to the unfamiliar controls – with a crash, during which Muttray was injured. The Doris was rebuilt after the competition and flew again from November. In 1922, at the club's own airfield near Geising in the Ore Mountains, the only structural change made during the repair was the relocation of the adjustment lever for the rear damping surface away from the control stick to a safer location in the cockpit. It was never used again, although the two designers steadfastly defended their theory of combining wing control and movable damping. With the otherwise meticulously engineered prototype, several satisfactory flights were still possible.
However, no outstanding performances were achieved. as soon as the airflow over the wings changes due to vertical wind direction fluctuations, forces occur at the control stick as a result of the movement of the center of pressure. The control stick thus acts as a kind of gust indicator. The pilot must adjust the stick against the direction of the force so that the forces on the control stick disappear.
Then the wings have an angle of attack relative to the respective airflow at which the most favorable lift-to-drag ratios prevail. In slightly compressed flight, a steady, slight forward pull occurs at the control stick. Paradoxically, Muttray and Seiferth went a step further by providing an additional adjustment of the horizontal damping surface at the stern via a movable handle on the control stick – a design innovation whose novelty the designers particularly emphasized. But this is precisely what led to disaster.
The Doris was transported to the Wasserkuppe immediately after its completion, where it successfully had its airworthiness certified by the Technical Commission, and subsequently completed its first test flight under Horst Muttray on the western slope. This ended – probably due to the unfamiliar controls – with a crash, during which Muttray was injured. The Doris was rebuilt after the competition and flew again from November.
In 1922, at the club's own airfield near Geising in the Ore Mountains, the only structural change made during the repair was the relocation of the adjustment lever for the rear damping surface away from the control stick to a safer location in the cockpit. It was never used again, although the two designers steadfastly defended their theory of combining wing control and movable damping. With the otherwise meticulously engineered prototype, several satisfactory flights were still possible.
However, no outstanding performances were achieved.
The 1922 Rhön competition featured no fewer than ten wing-controlled designs. But wing control had its price, as two significant reasons spoke against it. Firstly, the arrangement of the rotating elements at the most stressed points of the structure could lead to static deficiencies; secondly, unfavorable leverage ratios posed the risk of overtaxing the pilot's physical strength. With the progressive exploration and mastery of slope soaring, wing control was quickly forgotten by designers.
Technical Description
Wing: Four-section wing in single-spar wooden construction with box spar and torsionally rigid plywood leading edge, otherwise fabric-covered. Each wing half is supported by an inverted V-strut towards the fuselage lower chords and directly below the spar axis within the setting angle range by means of pushrods, directly via the control stick. Chord in the center section 1,350 mm. Airfoil in the center section Göttingen 441, tapered symmetrically towards the wingtips.
Fuselage: Truss construction in wood, fuselage front section to the wing trailing edge plywood-planked, otherwise fabric-covered; Fuselage width 600 mm.
Tail structure : Cantilevered wooden structure with fabric covering;
One-piece horizontal stabilizer wing with a depth of 600 mm and a wingspan of 3.30 m, adjustable by a lever in the pilot's seat; semi-circular vertical stabilizer with a depth of 850 mm and a height of 1,000 mm, rudder also 1,000 mm high, but 650 mm deep.
Landing gear: Two parallel ash wood skids, supported at the fuselage by two ash wood struts and dampened by rubber blocks.
Paintwork: Plywood skinning and natural-colored impregnated muslin covering.
The designers stated this verbatim: "The angle of attack of the wing is variable with the help of the control knob" (Author's note: In reality, the wing control functioned like the Munich monoplane of 1921, via cardan-like pivot points on the control linkage).
The position of the wing's axis of rotation is chosen, taking into account the wing's center of gravity and the center of pressure, so that no forces are exerted on the control stick during normal flight.
This occurs. As soon as the airflow over the wings changes due to vertical wind direction fluctuations, forces occur at the control stick as a result of the movement of the center of pressure. The control stick thus acts as a kind of gust indicator.
The pilot must adjust the stick against the direction of the force so that the forces on the control stick disappear.
Then the wings have an angle of attack relative to the respective airflow at which the most favorable lift-to-drag ratios prevail. In slightly compressed flight, a steady, slight forward pull occurs at the control stick. Paradoxically, Muttray and Seiferth went a step further by providing an additional adjustment of the horizontal damping surface at the stern via a movable handle on the control stick – a design innovation whose novelty the designers particularly emphasized. But this is precisely what led to disaster.
The Doris was transported to the Wasserkuppe immediately after its completion, where it successfully had its airworthiness certified by the Technical Commission, and subsequently completed its first test flight under Horst Muttray on the western slope. This ended – probably due to the unfamiliar controls – with a crash, during which Muttray was injured. The Doris was rebuilt after the competition and flew again from November. In 1922, at the club's own airfield near Geising in the Ore Mountains, the only structural change made during the repair was the relocation of the adjustment lever for the rear damping surface away from the control stick to a safer location in the cockpit. It was never used again, although the two designers steadfastly defended their theory of combining wing control and movable damping. With the otherwise meticulously engineered prototype, several satisfactory flights were still possible.
However, no outstanding performances were achieved. as soon as the airflow over the wings changes due to vertical wind direction fluctuations, forces occur at the control stick as a result of the movement of the center of pressure. The control stick thus acts as a kind of gust indicator. The pilot must adjust the stick against the direction of the force so that the forces on the control stick disappear.
Then the wings have an angle of attack relative to the respective airflow at which the most favorable lift-to-drag ratios prevail. In slightly compressed flight, a steady, slight forward pull occurs at the control stick. Paradoxically, Muttray and Seiferth went a step further by providing an additional adjustment of the horizontal damping surface at the stern via a movable handle on the control stick – a design innovation whose novelty the designers particularly emphasized. But this is precisely what led to disaster.
The Doris was transported to the Wasserkuppe immediately after its completion, where it successfully had its airworthiness certified by the Technical Commission, and subsequently completed its first test flight under Horst Muttray on the western slope. This ended – probably due to the unfamiliar controls – with a crash, during which Muttray was injured. The Doris was rebuilt after the competition and flew again from November.
In 1922, at the club's own airfield near Geising in the Ore Mountains, the only structural change made during the repair was the relocation of the adjustment lever for the rear damping surface away from the control stick to a safer location in the cockpit. It was never used again, although the two designers steadfastly defended their theory of combining wing control and movable damping. With the otherwise meticulously engineered prototype, several satisfactory flights were still possible.
However, no outstanding performances were achieved.
The 1922 Rhön competition featured no fewer than ten wing-controlled designs. But wing control had its price, as two significant reasons spoke against it. Firstly, the arrangement of the rotating elements at the most stressed points of the structure could lead to static deficiencies; secondly, unfavorable leverage ratios posed the risk of overtaxing the pilot's physical strength. With the progressive exploration and mastery of slope soaring, wing control was quickly forgotten by designers.
Technical Description
Wing: Four-section wing in single-spar wooden construction with box spar and torsionally rigid plywood leading edge, otherwise fabric-covered. Each wing half is supported by an inverted V-strut towards the fuselage lower chords and directly below the spar axis within the setting angle range by means of pushrods, directly via the control stick. Chord in the center section 1,350 mm. Airfoil in the center section Göttingen 441, tapered symmetrically towards the wingtips.
Fuselage: Truss construction in wood, fuselage front section to the wing trailing edge plywood-planked, otherwise fabric-covered; Fuselage width 600 mm.
Tail structure : Cantilevered wooden structure with fabric covering;
One-piece horizontal stabilizer wing with a depth of 600 mm and a wingspan of 3.30 m, adjustable by a lever in the pilot's seat; semi-circular vertical stabilizer with a depth of 850 mm and a height of 1,000 mm, rudder also 1,000 mm high, but 650 mm deep.
Landing gear: Two parallel ash wood skids, supported at the fuselage by two ash wood struts and dampened by rubber blocks.
Paintwork: Plywood skinning and natural-colored impregnated muslin covering.
