Akaflieg Darmstadt D-40

Last updated
D-40
Role Experimental high performance sailplane
National origin Germany
Manufacturer Akaflieg Darmstadt
DesignerK. J. Heer and D. Teves [1]
First flight15 August 1986
Number built1

The Akaflieg Darmstadt D-40 is an experimental variable geometry single seat sailplane, fitted with almost full span, camber changing flaps for optimum aerodynamics in weak thermals and integrated into the wing so as to minimise flap tip drag. One flew successfully but the D-40, like other variable geometry sailplanes, was not commercialised.

Contents

Design and development

The Akademische Fliegergruppe of the Technical University of Darmstadt (Akaflieg Darmstadt) was first formed in 1921. It was, and is, a group of aeronautical students who design and construct aircraft as part of their studies and with the help and encouragement of their University. Design work on the variable wing geometry D-40 began in 1980 [2] but the first flight did not take place until 15 August 1986. [3]

As understanding of thermal soaring grew in the 1930s, glider pilots and designers became aware of two conflicting requirements for cross country flights. The aircraft needed good climb characteristics and low stalling speeds to enable tight turns within thermals but high speeds in the sinking air between them. These respectively called for low and high wing loadings on wings with high and low camber. [4] Several designs, e.g. the 1938 Akaflieg Hannover AFH-4 and the later LET L-13 Blaník and Beatty-Johl BJ-2, had added large area slotted Fowler flaps on the inner part of the wing to increase camber and add area when extended. These satisfactorily reduced stall speed and with it the turn radius, but disappointed hopes of improving climb rates because of vortex generation (induced drag) at the tips of the flaps, seriously decreasing the lift to drag ratio. A solution to this problem was to extend the whole trailing edge, including the ailerons, and this route was taken by both the disappointing, heavy and complicated Operation Sigma Sigma, the more successful but still heavy and complex Akaflieg München Mü27 and the World Championship winning 15 m class Akaflieg Braunschweig SB-11. [5] [6]

These last three designs changed the wing geometry by extending the wing rearwards at right angles to the trailing edge. Akaflieg Darmstadt took a different approach, pivoting the single piece flap near the tip and sliding it out from within the wing trailing edge, gaining the mechanism the nickname "penknife wing". As it is extended, a track in the fuselage side guides the thin flap into its high camber position at the wing root. The wing area is increased by 21% with the flaps extended. Although this arrangement avoids the vortexes at the flap tip, like any area increasing method used on a fixed span wing it results in a lower aspect ratio and hence a lower lift to drag ratio. [2]

The D-40 is constructed from a mixture of plastic-fibre composites, glass reinforced plastic (GRP), carbon fibre reinforced plastic (CRP) and aramid reinforced plastic (ARP) with some use of balsa wood. The shoulder mounted wing has a spar built from CRP rovings and GRP-balsa webs. The skin of both wing and flaps is an ARP/CRP/balsa sandwich; the flaps have CRP stringers. In plan the wings are straight tapered, with an increase in taper close to the tips; these outboard sections carry the short span ARP ailerons. The wing has 1° of dihedral and is swept forward at 2.3° at 25% chord. There are Schempp-Hirth upper surface airbrakes slightly forward of mid-chord near to mid-span. When the flaps, pivoted immediately inboard of the ailerons, are deployed the wing trailing edge becomes almost straight, making the plan almost triangular, and 12° of washout is generated by the now strongly cambered inner sections. This produces a lift distribution close to that of the ideal elliptical wing, with its minimum induced drag. [2] [3]

The D-40 uses the fuselage and empennage of the Rolladen-Schneider LS3. This is a GRP shell, slender aft of the wings and with a T-tail with straight tapered surfaces. The rather wide cockpit occupies most of the deeper forward fuselage and has a long, one piece, front hinged canopy. A retractable monowheel undercarriage was assisted by a tail bumper. [2] [3] [7]

Operational history

Initially the D-40 proved difficult for the relative novices of the Akaflieg to fly. In particular the short ailerons were lacking authority. The more experienced Helmut Reichmann did show, at one competition, that the D-40 outperformed the other sailplanes present under weak thermal conditions, as hoped for. The ailerons were redesigned and tall, narrow winglets added, which much improved the handling. [2] In the end nothing became of any of the variable geometry glider designs. They were too complex for club use and significantly increased the pilot's workload. [5]

Specifications

Data from Jane's All the World's Aircraft 1987/8 [3]

General characteristics

Performance

Related Research Articles

Glasflügel H-301 German single-seat glider, 1964

The Glasflügel H-301 Libelle is an early composite single-seat sailplane produced by Glasflügel from 1964 to 1969. The H-301 had camber-changing wing flaps so was required to compete in the Open Class because the Standard Class excluded wing flaps. It was often known as the Open Class Libelle.

The Sigma is an experimental glider developed in Britain from 1966 by a team led by Nicholas Goodhart. After disappointing performance during flight testing the Sigma was passed on to a Canadian group which carried out modifications, making the Sigma more competitive.

Akaflieg München Mü27 German prototype research glider, 1979

The Mü-27 is a research glider aircraft that designed and built in Germany in 1979. Only one example was constructed.

SZD-40x Halny Polish two-seat glider, 1972

The SZD-40x Halny is an experimental two-seat glider designed and built in Poland in 1971.

Akaflieg Darmstadt is one of approximately twenty aviation groups attached to German universities. Akaflieg is an abbreviation for Akademische Fliegergruppe, an academic group of students and faculty from a German University.

The Marsden Gemini is a Canadian mid-wing, T-tailed, two-seats in side-by-side configuration, experimental research glider that was designed and constructed by David Marsden at the University of Alberta, first flying in 1973.

Akaflieg Darmstadt D-9 Konsul German single-seat glider, 1923

The Akaflieg Darmstadt D-9 Konsul, often shortened to Darmstadt D-9 Konsul, was a high performance, single seat, cantilever monoplane sailplane, designed and built by a German University student group in 1923 for hill soaring.

The Akaflieg Darmstadt D-17 Darmstadt, also called the Darmstadt D-17 and Darmstadt I, was a high performance, single seat, cantilever monoplane sailplane, designed and built by a German University student design group in 1927. It was followed in 1928 by the Akaflieg Darmstadt D-19 Darmstadt 2, a similar aircraft with a new profile, longer span wing.

The Akaflieg Darmstadt D-28 Windspiel was a single-seat, high-performance sailplane designed in Germany in the early 1930s. Intended to exploit a growing understanding of thermal soaring, it was small and manoeuvrable, with a 12 m span; silk-covered for lightness, it weighed less (empty) than its pilots. It held the world straight-line distance record for a time in 1934.

The Akaflieg Darmstadt D-30 Cirrus was an aerodynamically advanced single seat sailplane with a very high aspect ratio wing and a pod and boom fuselage. Built in Germany just before World War II, it was intended as a record breaker and duly set a new world out-and-return distance record in 1938.

The Akaflieg Darmstadt D-34 sailplanes were a series of experimental single seat sailplanes, designed at the University of Darmstadt in the 1950s and early 1960s to explore the structural and aerodynamic advantages of the then emerging plastics and composite materials.

Akaflieg Darmstadt D-36 Circe German single-seat glider, 1964

The Akaflieg Darmstadt D-36 Circe is a single seat, high performance sailplane designed and built in Germany in the mid-1960s, one of the early "glass ships". It was the winner at the German National Championships in 1964 and came second in the World Championships the following year.

The Akaflieg Darmstadt D-41 was a two-seat, side-by-side configuration sailplane designed to perform as well as tandem seaters. It was built in Germany in the 1990s and was used by Akaflieg Darmstadt students until it was lost in a crash.

The Akaflieg Braunschweig SB-11 is an experimental, single seat, variable geometry sailplane designed by aeronautical students in Germany. It won the 15 m span class at the World Gliding Championships of 1978 but its advances over the best, more conventional, opposition were not sufficient to lead to widespread imitation.

The FVA-20 F. B. Schmetz was a single seat, Standard Class sailplane, built as a one-off aircraft, to explore the application of glass fibre to glider construction. Built over a long period, it finally flew in late 1979.

The Beatty-Johl BJ-2 Assegai was a single seat, high performance competition glider built in South Africa in the early 1960s. Only one was built; it was optimised for South African conditions and performed well there, winning two nationals and setting several records, but was less successful under European conditions at the 1965 World Gliding Championships.

The Akaflieg Braunschweig SB-8 is an experimental, single-seat, high performance glider built in Germany in the 1960s, constructed largely from glass fibre skin over built up balsa wood structure. Two were built; the second of which was later fitted with a high aspect ratio (30:1) wing, becoming the Akaflieg Braunschweig SB-9 Stratus.

ISF Mistral-C German single-seat glider, 1976

The Mistral-C was one of the first gliders, designed in 1974 to the then new Club Class rules. It was based on the Strauber Mistral, a Standard Class glider flown a year earlier, but with a new wing and built from newer composite materials. Both types were designed and constructed in Germany. More than 75 Mistral-Cs were produced.

The Akaflieg Braunschweig SB-6 Nixope was an early (1961) GRP high performance single seat glider designed and built in Germany by aeronautical students from Brunswick University. It competed in the 1961 German National gliding competition, coming sixth, and led directly to two further GRP aircraft.

The Bertoni Altinger AB-1 Superalbatros,, is a high-performance sailplane designed and built in Argentina in the 1950s and 1960s.

References

  1. ↑ "Darmstadt D-40" . Retrieved 29 January 2012.
  2. 1 2 3 4 5 6 7 8 Simons, Martin (2005). Sailplanes 1965-2000 (2nd revised ed.). Königswinter: EQIP Werbung & Verlag GmbH. pp.  51–3. ISBN   3-9808838-1-7.
  3. 1 2 3 4 Taylor, John W. R. (1987). Jane's All the World's Aircraft 1987-1988 . London: Jane's Information Group. p.  747. ISBN   0-7106-0850-0.
  4. ↑ Simons, Martin (2006). Sailplanes 1945-1965 (2nd revised ed.). Königswinter: EQIP Werbung & Verlag GmbH. pp.  8–9. ISBN   3-9807977-4-0.
  5. 1 2 Simons (2005), p.58
  6. ↑ Simons (2005), p.21
  7. ↑ Simons (2005), p.129-130
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.