http://www.aniprop.de/dlrhp/index.html (you are here)

The DLR provides an electronic library catalogue. Please, visit "ELIB". A new system is in operation since November 1st, 2005, in which a large number of publications still is missing. Unfortunately, there is no English version presently available.

Abstract. The mutual influence of two profiles is studied in subsonic and transonic 2D viscous flow. The profiles are arranged such that the second one is located downstream of the first one similar to the configuration of  a tail plane behind a wing. The physical effect is that of a gust generator. The unsteady wake of the leading profile encounters the trailing profile and effects a load change. A first simplified attempt has been made using a rigid grid where both profiles execute a synchronous heaving motion. The Fourier analysis of the load history shows the load spectrum. The accuracy of the computation is investigated using inherent physical properties.

W. Send, Flapping-Wing Thrust in Compressible Flow, 25th International Congress of Aeronautical Sciences (ICAS), Hamburg (Germany), September 3-8, 2006: icas06_send_paper_3.10.4.pdf (1.4 MByte). English website related to this paper.
Abstract. The phenomenon of thrust generation by a coupled bending and torsional motion is surveyed ranging from incompressible flow to the transonic region. 2D wing sections and 3D planforms are studied. The paper also touches on the question, whether flapping-wing thrust for larger airplanes is physically possible.

W. Send, Der Traum vom Fliegen (Dreaming about Flying), Naturwissenschaftliche Rundschau 2/2003, 76-73). The paper is not available on the web. The reader is kindly referred to the journal.
At the beginning,  the article substantiates the fact that human beings are 'not made for flying' with flapping wings. Can the gap be closed between the maximum power output, which the world's best trained athlets are capable of, and the mininum mechanical power input required for a human flapper? Based on some rational estimates (Microsoft Excel data sheet including the famous 2D analytical solutions for the plunging and pitching plate by H.G. Küssner, 1936, and Th. Theodorsen, 1935) the answer is, for the time being: 'Well, it might work'. The article emphasizes the urgent need of progress in the techniques of coupling fluid and structure for large amplitudes in viscous flow for a final answer.
The author keeps on dreaming: "Advanced Adaptive Airplane Technologies A³T" (500 kByte) shows the author's recent initiative to promote the study of flapping flight by emphasizing the potential technical spin-offs for drag reduction and enhanced wake decay.

W. Send, Physik des Fliegens (The Physics of Flying), Physikalische Blaetter 6/2001, 51-58 (since 2002 renamed to Physik Journal).
Among others, the article pursues educational goals, and promotes the teaching of the Physics of Flying in junior courses at universities as well as in senior classes at the German high schools. The subject is treated on a broad basis, reaching from our present knowledge of animal thrust production to perceiving the vortex structures behind lifting surfaces with modern flow-analysis tools (like particle image velocimetry PIV). A prominent contention is raised once again: Where does the lift come from? Based on Ludwig Prandtl's concept of what the author names the infinitely thin boundary layer, the roles of Bernoulli's equation and of the boundary condition for the flow are clarified with respect to the computation of lift and drag.
Data sheets and formulas for the examples given in the paper may be found in the internet pages, which accompany the publication. A forum for discussion is open for German speaking readers.

W. Send, Coupling of Fluid and Structure for Transport Aircraft Wings, International Forum on Aeroelasticity and Structural Dynamics, Williamsburg, Virginia (USA), June 22-25, 1999: ceas-aiaa_va99.pdf (670 kByte).
This paper focusses on the data exchange between the two meshes on one and the same wing surface: the CFD mesh for the fluid and the FE mesh for the structural analysis (ANSYS FE model). A mathematical procedure is developed which accomplishes the mappings in both directions by means of a documented 2D B-spline algorithm (subroutines taken from the IMSL)and an iterative solution for the respective locations of the nodes.
Explanation: The figure shows a converged solution (the structural side) in steady flow for a windtunnel model in a former French/German project named the Aeroelastic Model Program (AMP). The figure relates to the pressure distribution (the aerodynamic side) obtained from the same computation (not shown here). The odd torsion spring pursues a scientific goal. Its purpose is to reduce the - normally much higher - torsional stiffness to a first torsion mode with a natural frequency slightly above the first bending mode. Thereby the configuration yields a flutter case slightly above that Mach number Ma = 0.82. For more details, please, see the paper.

W. Send, Subsidiäre Schuberzeugung mit gekoppelten Biege- und Torsionsschwingungen in transsonischer Strömung (Subsidiary thrust production with coupled bending and torsional motion in transonic flow), Deutscher Luft- und Raumfahrtkongress 1999, Berlin 27.-30. September 1999: dglr_jt99_086.pdf (530  kByte).
The paper gives an introduction into the basic mechanisms of coupled bending and torsional motion. The reader is invited to study the from scratch derivation of the basic formulas for thrust production and its location on the wing surface. A tentative estimate is made of the benefits applying the mechanism of subsidiary thrust production to a modern transport aircraft.

The paper given 1996 at the anual congress of the German Society of Aeronautics and Astronautics (DGLR) on the occasion of the 100. anniversary  of  Otto Lilienthal's  death  addresses the  early development  of  flapping  flight. W. Send, Otto Lilienthal und der Mechanismus des Schwingenflugs (Otto Lilienthal and the mechanism of flapping flight), Deutscher Luft- und Raumfahrtkongress 1996, Dresden 24.-27. September 1996: dglr_jt96_030_send.pdf (3.6  MByte).

The following paper receives still some interest, and has been made available now:
W. Send, R. Voß, W. Wegner, Das aeroelastische System "Flügel mit Triebwerken" als Funktion der aerodynamischen Modellbildung (The aeroelastic system "wing with engines" as a function of the aerodynamic modeling), Deutscher Luft- und Raumfahrtkongress 1994, Erlangen 4.-7. Oktober1994: send_dglr94.pdf (630 kByte).
The paper deals with the process of modeling the 3D unsteady kinematics entering an aerodynamic calculation in the frequency domain. It is shown that proper kinematics yields surprisingly good results also for unsteady airloads obtained from the 2D thin plate approximation being corrected for the Mach number. The data are compared with transonic doublet lattice computations and an Euler solution. The corresponding equations for aeroelastic stability are derived.

Within the DLR HighPerFLEX project (2004 - 2006), one work package refers to the effects of  coupled bending and torsional motion (CBT) on drag reduction and wake decay, which are investigated by the author.  The well known  mechanism of thrust  production  in nature  happens to occur also during flight tests of transport aircraft with marginal effects just while activating the exciters for flutter tests. The basic relationships were discussed in an earlier papger cited above ( dglr_jt99_086.pdf - 530  kByte). The investigation is planned to be accompanied by experiments to verify theoretical predictions of the CBT effects on a flexible structure and to develop appropriate actuators. A  tip model with 1.5 m span  is deformed by bending and torsional motion. The preliminary tests will take place in a rotary test stand similar the development ANIPROP RL3 depicted below. Unfortunately, the construction, which is almost completely designed, is currently protracted due to changes in the institute's management.
 

Overall view	Hub	Boom	Bearing	Eigenmode, Deformation

 The preceding drawings show some parts of the test stand. The excellent design work was done by the student Birk Wollenhaupt supervised by the DLR engineering office, site Göttingen.

In 2007 a new DLR project named iGREEN was launched, which deals, among others, with the gust problem and the influence of wings on each other (like the main wing on the horizontal tail plane). The contour plots give an impression of  a numerical study in the course of  the research programme. Two synchronously heaving profiles affect each other by vorticity shed downstream and sound waves travelling upstream (see also the recent 2008 paper cited above).

Vorticity shed downstream	Deviation from dq/dt = 0 (Adiabatic condition)	Sound waves travelling upstream

The corresponding movies may be found on  http://www.aniprop.de/dglr08/ 

Movie Touch SM1 (1.3 MByte), Siemens Forum - Bionik Exhibition, München, Berlin 1999

The lasting commitment to animal flight led to the development of a unique test stand, which demonstrates and measures all basic phenomena of the Physics of Flying like lift, drag, animal propulsion and aeroelastic flutter of a wing. The RL3 acts like a carusel. The artificial bird produces its own thrust to fly with a speed of about 3-4 m/s. The diameter of the circular course is 6 m. The picture below shows the test stand ANIPROP RL3, which has been manufactured by Send's partner in the company ANIPROP GbR, Felix Scharstein.  At present, the next copy is planned to be delivered in March 2004 for the TU Hamburg-Harburg.

Another copy of the test stand ANIPROP RL3 was acquired by the DLR for the DLR_School_Lab Initiative in Göttingen (despite the fashionable complaint in Germany to name everything in English, this website is written in German only). The laboratory is the DLR's contribution to the EXPO 2000 and beyond within the frame of a local science-related EXPO project in Göttingen.The description of Experiment #5 (340kByte) shows on page three the excited motion of a lifting surface above a specific speed limit, the phenomenon which is called flutter.

Experiments with the test stand ANIPROP RL3:
Movie Bird flight (0.7 Mbyte) Educational TV Quarks&Co, WDR 1999
Movie Wing flutter (0.2 MByte)
Movie Lifting surface (1.3 MByte)

The experimental lecture The Physics of Flying was selected by an international jury as one of the two German plenary lectures (named presentations) contributing to the Physics-on-Stage Festival in Geneve, November 2000 (see also the current activities following  the initial event). Most recently, we were invited to contribute to the 2002 event Highlights in Physics of the German Physical Society and other institutions .

Since the winter term 2000/2001, a new experimental  lecture Der Tierflug with the RL3 was held at the Zoological Institute of the University of Goettingen together with Wolfram Zarnack, Send's long-standing partner in the field of Experimental Biology. These activities terminated at the end of the winter term 2002/2003 due to Wolfram Zarnack's retirement in March 2003.  Copies of the former lecture Aerodynamik des Tierflugs held since 1990/1991 are still available on demand. 

Photos courtesy of Christina Hinzmann.

On June 23rd 2004, the stroke-wing engine (our English term for Hubflügelgenerator) ANIPROP HFG3 was launched in the city of Augsburg in Bavaria. The technology demonstrator extracts energy from the small, fast flowing channel Mittlerer Lech bypassing the river Lech through the picturesque Old Town. The private development pursues the goal of gaining renewable energy directly from the kinetic energy in the flow. The basic physical concept rests on the well known aerodynamic properties of a coupled pitching and plunging motion, which also drives the mechanism of airplane flutter. However, the mechanism is substantially improved by introducing a "partially linear" motion instead of the common sinusoidal pitch and plunge, for which a patent is pending. The tests are planned to last until June 2006. Meanwhile, several options are considered to bring the concept onto the market.
The engine was constructed and built by Felix Scharstein,  Send's partner in the company ANIPROP GbR. The nominal power is 1kW. The left picture shows the HFG3 at night, almost idling to comfort its neighbours. For more pictures and videos, please visit  ANIPROP HFG3 .

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