Other flapping wing designs
When designing ornithopter models there are mainly two major tasks, the development of the drive technology and the development of the flapping wing. In general, the wide interest lies in the drive systems and components. But the main problem in the development of such aircrafts are the flapping wings. In this field of design desire differs very widely from reality.
Below, the attempt is being made, to give a rough overview about the physical characteristics of known flapping wings. But this collection is not exhaustive.
Contents:
- The bird wing, the ideal
- Membrane flapping wings
- 2.1 The sail as archetype
- 2.2 Simple membrane flapping wings
- 2.3 Simple membrane flapping wing with battens
- 2.4 Active twisting by spar rotation
- 2.5 Aeroelastically twisting by spar torsion
- 2.6 Flying wing ornithopter
- 2.7 In tandem
- 2.8 Thrust-wing
- 2.9 Thrust generation with an oscillating wing
- 2.10 Rotating wings
- 2.11 With non-twistable arm wing section
- Profiled flapping wings
- External links to other flapping wing designs
1. The bird wing, the ideal
Naturally, the great archetype for technical flapping wings is the living bird wing. His great effectiveness due to his manifold possibilities to move purposeful and to change the shape will certainly be unobtainable in aero modelling for a long time. This is also true for his weight distribution and his sensor technology.
In this drawing by K. Herzog the anatomic subdivision of the bird's wing in arm- and hand section is pictured. It can also to be used advantageously when describing technical flapping wings. The longitudinal parts of these wing sections are rather different depending on bird species (Please look at external link 1). Generally the bionics of the bird wing is very interesting (please look at external link 2).
2. Membrane flapping wings
Application range
Membrane flapping wings especially are changing the chamber direction in the hand wing section according to the flapping direction. This way, they can produce much thrust and achieve steep climbing flights (Flying with Thrust). But up to now they are less suited for gliding flights and for flying with lift.
2.1 The sail as archetype
A sail - though in other circumstances - has about the same function as a flapping wing. It shall generate as much thrust as possible under changing approach flow directions.
By material selection, layout, division into parts, sail trim and rig tuning the sail characteristics can vary in wide ranges. Battens give the sail more stability and an optimal shape. A lot of descriptions with sophisticated tips about the fabrication of the sail and its practical use can be found.
Indeed, a lot of membrane flapping wing systems have been developed, but detailed information about them is barely available (exception see at external link 3).
2.2 Simple membrane flapping wings
The pinion feather
by
Alexander Lippisch
(ca 1937) obviously was optimized for thrust generation. Therefore, he increased
the chord in the outer wing area. But this pinion feather was not intended
for generating lift at the same time. She's merely a propeller with changing
rotation direction.
Tim
was the first in
mass-produced rubber powered flapping wing model - with
simple membrane flapping wings - invented by Albertini
Prosper and de Ruymbecke Gérard (France 1969).
The membrane printing of Tim in the marginal picture was drafted by
K. Herzog.
Under the designation Tim Bird
this model is
available in trade till today.
2.3 Simple membrane flapping wing
with battens
Here a famous Membrane Flapping Wing, equipped with small battens
for stabilisation of the membran, developed by A. Pénaud
(France 1872).
(More informations at external
link 4)
2.4 Active twisting by spar rotation
Membrane flapping wing by Erich v. Holst (1943) with drive-controlled wing twisting in the arm wing section by spar rotation. Only the rib at the end of the arm wing (number 9) is fixed to the spar. It is linked with a crank drive which effects the stroke movement as well as the rotary movement of the spar.
The twisting in the hand wing section happens largely passively. In addition, a transition from cross to longitudinal battens can be seen. In spite of alternating profile chamber direction during a flapping cycle a relatively purposeful increase of wing twisting tipwards is made possible.
The bird models by K. Herzog (1963) follow this scheme, too.
2.5 Aeroelastically twisting by spar torsion
The flapping wing model of the Czech Cenek Chalupsky (1934) was flying steadily without a tail unit. Its achieved climb power is still considered remarkable today.
- weight
- wing span
- cane spar
- covering
- ceiling
- 3.1 kg
- 2 m
- linen
- 10-15m
- [109 oz]
- [79 in]
- [394-590 in]
Each flapping wing of this ornithopter has two spars. The straight, bending resistant spar (H1) transmits the power of the stroke motion. The bended torsion elastic spar (H2) determines the magnitude of the wing twisting.
Both spars cross approximately in the center of the half span. At the crosspoint they are movably interlinked. For the torsion elastic spar (H2) not to bent backward too much a string or an elastic thread is apparently tightened between the tips of the spars.
During downstroke of the wings the lifting forces are increased. The spar H2 and the wing are twisting. The magnitude of the twisting acts in accordance with the magnitude of the lift force and the stiffness of the spar. It therefore happens aeroelastically.
Additionally to the twisting the tip of the spar H2 bends upwards during downstroke. As a reaction it bends downwards at the other side of the crosspoint - thus, in the section of the arm wing. Thereby, the camber of the airfoil is increased a little. Thereby, an adaptation to the requirements of an effective stroke motion takes place.
Please look at
literature/Piskorsch
Adolf: Pressluft-Schwingenflugmodell Chalupsky
and the vidio of the
external link 5.
2.6 Flying wing ornithopter
Ornithopter without a tail unit, developed by Jean-Louis Solignac (France, 2000).
The flapping wing model has a very simple and light driving mechanism and is powered by a rubber drive. With a wing span of 15 cm (5.9 in) it has a weight of only 0.6 gramms (0.021 oz [US]). The airplane performances are amazingly good. (For the construction of the flapping wing model please also take a look at external link 6.)
The particular about this flapping wings is the down cambered airfoil shaped by battens. Thereby it flies in a stable attitude without a tail unit. This can theoretically be explained with the shifting of the pressure point of thin airfoils. It can be tested in the adjacent experiment with a paper airplane. The cross-section of this paper airplane equates to a down chambered airfoil.
2.7 In tandem
Ornithopter with two sets of flapping wings based on a dragonfly, developed by Erich von Holst (1943).
Here, for simplifying the mechanism both opposite halves of a wing are rigidly fixed to a unit. This way, the pressure point of the model is fixed between the two wing units.
In such tandem arrangements with wings flapping in opposite directions the vertical pendulousness of the fuselage should be avoided. This, however, bears the disadvantage that the backmost flapping wing is in the turbulence wake of the front one. Only for very small wings and at very small Reynold's numbers this may be beneficial.
Model by Horst Händler (1988).
2.8 Thrust-wing
By mechanisation of a dragonfly's flight principle Erich von Holst has developed his thrust-wing model with two in the opposite direction rotating three-blade wings (1940). The flapping angle in one stroke direction constitutes 180° and 360° for a complete flapping cycle respectively (Please take a look to the video at external link 7).
Three instead of two wing blades per rotor offer a constant supporting force (See also configuration of the rubber powered model ENTOID by Velko T. Velkov (2007) external link 8).
In contrast to a propeller a lift force perpendicular to the thrust is generated at the thrust-wing, too. One must only increase the "thrust-wing advance ratio" (v/u) - similar to a flapping wing - and fly with a positive angle of attack of the thrust-wing axis.
This is a fine example for an innovative transfer biological
principles of a flapping wing in engineering. But the specialism
bionics
did not exist at that time.
2.9 Thrust generation with an oscillating wing
Thrust also can be produced by raising and lowering a rigid wing in flight. But thereto the lift and the transverse force respectively during the upward motion must be smaller than during downward motion. The bigger the difference, the better for the thrust (please take a look to the principle of flight/vector diagram). Furthermore, a continual alignment of the angle of incidence is normally necessary.
Here a strikingly simple generation of an accordant oscillating motion of the wing by using an eccentrically pivoted rotating mass consisting of the mainspring and the gear. In this case the wing is aeroelastically twistable. The idea was coined by W. B. Mituritscha (probably from Russia, 1953).
Unfortunately, a forward and backward motion of the wing occurs along the way. However, this can be avoided by a second counterrotating mass.
There are diverse proposals to generate an oscillation motion of the wing by a pilot who is flying in a hang-glider or an other ultralight aircraft - for example by fast press-ups or knee-bends.
For new experiments with oscillating wings, please take a look at external link 9.
2.10 Rotating wings
To avoid the accelerating forces at the final stroke positions
flapping wings
rotating on a cone-shaped shell where
sometimes built whose apex lies at the wingroot.
Examples:
The Rotor Dragonfly
by Adolf Piskorsch
(1944 and 1989 respectively)
and
the flight model by Horst Händler (1989).
Both ends of the driveshaft are bended in Horst Händler's model. Thereon, the wings are attached freely twistable. The angles of incidence is guided by the upward pointing levers on the wings.
2.11 With non-twistable arm wing section
Membrane flapping wing with a non-twistable arm wing section and passive twisting at hand wing section.
The arm wing is triangle shaped and has a large wing depth at the wing root.
Arm- and hand wing membrane overlap in wing span direction. Obviously, the
hand wing spar could make a little flap movement at the wrist. Later the hand
wing depth was enlarged (Please also take a look at the
construction of the pinion feather
by Alexander Lippisch).
This daedalean flapping wing design of the Seagull
was developed by Percival H. Spencer (USA 1958)
(Please look at external link 10).
Today, this design principle of flapping wings with inserted battens is widely-used.
3. Profiled flapping wings
Application range
Profiled flapping wings respectively double-sided covered wings may work with a very high efficiency. With their mostly relatively low flapping frequency and the small operating range of lift coefficient of a simple airfoil not much thrust can be produced. Not, at least, if the full lift must be generated concurrently (flying with lift). Therefore, profiled flapping wings are suited especially for a level flight, the gently inclined climbing flight and of course for changing to gliding flight.
3.1 With artificial feathers
To ease the twisting, the closed airfoil can be faned out. So far, this is particularly used for large manned ornithopters.
Adjacent, a flapping wing with staggered wing tips of the manned
Schwan 1
, developed by Walther Filter (1956, at the
Hannover fair 1958). The angle of incidence deflection of the
feathers
designed as several wings was controllable.
Even for splay and straddle movement of the feathers
there are old design proposals. In contrast, with
EV7b
only with simple feather implementations experiments have been
made.
A further example for artificial feathers is the
Ikarus
by Emiel Hartman (England 1959).
More recent experiments with artificial feathers are to be seen
- at gliders with out-faned wing tips
by Johannes Huser, - at the
Birdman
Georges Fraise (France 2005) and - at the Ornithopter Project by Ryszard Szczepański (Poland 2002).
(Please look at external links 11, 12 and 13)
3.2 With inclined hinge of the hand wing
A special version of a flapping wing derives from K. Herzog (1963). With this wing, the rotation and the twist axis, respectively, is not standing vertical to the stroke axis.
The arm wing should perform a flapping motion and a twisting motion at the shoulder hinge. With rubber threads between arm- and handwing the latter was pulled down a little (aeroelastically wing).
This is also an early suggestion for an articulated flapping wing with an additional flap movement of the hand wing.
The kink of the profile between the arm and the hand wing lies approximately at the same location as on the above-mentioned membrane wing by P. H. Spencer.
3.3 Twisting by tilting the leading edge
of the wing
The feature of the pitch propeller
by John
Drake lies in the twisting of the leading edge, not the
trailing edge of the flapping wing (England, flight tests
in 1978).
3.4 With stepped twisting
An approximate wing twisting can also be achieved by a stepped rotation of relative non-twistable wing sections.
The model EV4 (1979) was also equipped with such a rotation of single wing sections. But in this case, the rotations was controlled by the wing drive.
A typical representative of a passive stepped twisted wing is
the Step-Twister
with his foam wings (Depron) by Karel
Pustka (2004). The developing gap between the wing sections is
covered with a membrane.
3.5 Twisting by stroke movement
of the auxiliary spar
Here, the wing twisting is generated by a phase-delayed stroke movement of the main and auxiliary spar - developed by Emile Räuber (France 1909).
This technology was also used at the EV2 (1976). In the margin, the wings with their two spars powered separately are to be seen.
The function is similar to the wing of a dragonfly. Here, too, the phase-delayed flapping movement of the main and auxiliary spar determines the amount of the wing twisting.
(dragonfly picture: 300 KB)
Furthermore, the dragonfly obviously works with a
strong spar at the leading edge. With the phase-delayed flapping
movement of three spars the camber of the airfoil can be
influenced, too. Supports or linkages of the three spars at the body
are clearly recognisable as dark partly cross over structures
at the back of the dragonfly.
(Please also take a look to
external link 14 and 15)
3.6 Servo controlled wing twisting
This is a lifelike and airworthy replica of a pterosaurs - a
Quetzalcoatlus Northropi (QN).
The aerodynamics of this ornithopter should fully equate
the original. The idea come from the creative genius Dr.
Paul MacCready (USA 1985).
The twisting of the wings was controlled by servos and the flight attitude was stabilized by backward and forward motions of the wing tips and nodding motions of the head.
For details - including the principle of the drive mechanism - please take a look to the articles (in German) about the project by Paul MacCready and for further informations via external link 16.
3.7 Shearflex principle
Here an aeroelastically twistable profiled flapping wing according to the Shearflex Principle. This system makes a relatively inelastic covering applicable. If the twisting along the wing is constant and not to excessive, the airfoil contour accuracy is therefore very good.
Here, the twist elasticity will mainly be determinated by
the spar designed as wing leading edge.
This system was invented by Professor
James
D. DeLaurier and Jeremy M. Harris (Canada 1994).
The ornithopter with its tripartition of the flapping wing is interesting, too. Jeremy M. Harris 1977 has applied it for patent.
On the adjacent photo James D. DeLaurier and Jeremy M. Harris can be seen with their remote-controlled model, 3 m in span and with combustion motor. A sustained flight was achieved 1991. A video is available (Please take a look at external link 17).
Here, a corresponding replica with an electrical drive system by Horst Händler (1994).
3.8 Shell wing
with active wing twisting by a drive controlled spar rotation, developed by Albert Kempf (France 1998). ( Please look at external link 18).
Apparently, the upper side of the wing consists of a cambered hard shell, which is shaped with foam on the lower side to a profiled airfoil wing.
A long thin plate with a cambered cross section may be twisted
easily and creaselessly. Also the aforesaid shearflexed wing is
using this property. This flapping wing category here is called
shell wing
.
The such equipped Truefly
is to be seen in the adjacent
picture - an ornithopter with a wonderful flying sight. It also
was the first ornithopter which achieved strong climbing flights
with profiled flapping wings.
In the essay
Flapping Wing Designs
(38 pages in German, version 2.3, PDF 1.8 MB)
additional information about these flapping wing designs can be
found.
In conjunction with the EV-models
developed flapping wings are to find on site:
Articulated flapping wings
4. External links
to other flapping wing designs
- Longitudinal part of the hand wing section of birds:
http://www.fen-net.de/oag-mittelfranken/hilfkipp.htm - Bionics, airfoils and wing cross sections of birds by Johannes Huser:
http://www.geier-segelflug.de/bionik.htm - Construction of Membrane Wings by Nathan Chronister:
http://www.ornithopter.org/how.wing.shtml - Alphonse Pénaud, (1850 - 1880):
http://www.ctie.monash.edu.au/hargrave/penaud.html - Video about a flapping wing model by Cenek Chalupsky:
http://ovirc.free.fr/Clips_video.php - Construction method of the flapping wing model by Jean-Louis Solignac:
http://ovirc1.free.fr/solignac-ornitho.htm - Video about flapping wing models by Erich von Holst:
http://www.ornithopter.org/video.shtml - Thrust-wing model ENTOID by Velko T. Velkov:
http://velkovelkov.blogspot.com/2009/09/entoid.html - The "Double flapping wing airplane" by Karl-Heinz Helling is flying:
http://www.modellbau-thiele.de/schlagfluegel.htm
http://www.mfc-rossendorf.de/fileadmin/Projekte/SchlagfluegelProjekt/SchlagfluegelProjekt.htm - Report about Percival H. Spencer:
http://www.seabee.info/spencer.htm - Gliders with out-faned wing tips by Johannes Huser:
http://www.geier-segelflug.de/flugmodelle.htm - Out-faned wings of the
Birdman
Georges Fraise:
http://ovirc.free.fr/GFraise.php - Out-faned wing tips at the Ornithopter Project by Ryszard Szczepański:
http://www.ornithopter.com.pl - Close-up view of an orange colored dragonfly:
http://www.grahamowengallery.com/photography/dragonfly_photography.html - Rubber-protein
Resilin
enables dragonfly wings for acrobatic flight:
http://www.springerlink.com/content/g5w5gq0l7lxhx202/ - Replicating of biological membranes, pterosaurs by Paul McCready,
http://pterosaur.stanford.edu/Proposals/ProjectDescription.pdf (0.4 MB)
http://ovirc.free.fr/McCready.php - Video of the proof-of-concept model for a manned ornithopter flight
by James D. DeLaurier:
http://www.ornithopter.net/MediaGallery/Videos/index_e.html - Ornithopter model
Truefly
by Albert Kempf:
http://truefly.chez.com/
To the workings by Erich von Holst and Karl Herzog