Articulated flapping wings
Description
of flapping wing constructions
which have been developed together with the den EV-models
Contents:
1. Requirements
The design layout demands on a technical flapping wing-among other things-results from the theoretical distribution of lift based on Robert T. Jones USA 1950, 1980) and the therefore necessary angle of incidence along the halfspan of the wing.
Here, for example, the relevant, extensively optimised functional distributions for a gently inclined flight of a rectangular flapping wing with the all-round airfoil CLARK-Y are shown (principles please see Handbook). In this case, the angle of incidence at the wing root remains constant. The distributions of the downwash angle along the span are straight-lined in all three cases.
In the flapping wing design the momenta of inertia round the stroke axis and the rotating axis of the flapping wing are also important.
2. Aeroelastically controlled
articulated flapping wing
Basic spar framework of a profiled flapping wing with an articulation for an additional flap motion of the hand wing spar. This is pulled down by a spring (spring device here not shown).
- While gliding flight with its medium lift force, the hand wing takes over the stretched center position.
- At downstroke in the hand wing area the lift forces distinct increase and the hand wing strokes up against the spring force.
- If at upstroke the lift forces decrease the spring force pulls down the hand wing.
The small, on aerodynamic forces dependent and thereby aeroelastic stroke movement of the hand wing will be used by levers (brown for arm wing, green for hand wing) to control the twisting along the whole wing. In this way an articulated flapping wing with aeroelastically controlled twisting has been developed. Its mode of operation resembles a little that of a bird's wing.
Exept for the wing root rib all ribs are put freely rotating on
the spars. For the covering of the flapping wing the highly elastic
polyurethane film Platilon U 04
is planed
(Please take a look at
external link 1).
The principle of this aeroelastically controlled articulated flapping wing was developed in connection with the flapping wing model EV6 (1983) and was also always used again for my subsequent models.
3. With expanding wing twisting
This is the functional model of a
stroke amplitude expanding wing spar
in short form called shift spar
.
This mechanism can be used at main and at auxiliary spars of flapping wings.
linkage above:
shift linkage dismounted
linkage below:
Shift linkage mounted.
The left hinge here provide as basis.
At a stroke moving of the middle shift linkage - here downward
- the outer right spar section implements an expanded stroke
amplitude.
Technical drawing
for a shift spar in a coaxal tube-in-tube construction
Joints of the shift spar
with different centre distances for transmitting the flapping motion (1:1.5).
Complete coaxial shift spars
Adjacent, the spar framework of a profiled flapping wing for active wing twisting at the arm wing section by main spar rotation.
There a stroke amplitude expanding auxiliary wing spar
is used. In doing so the twisting at the hand wing section is
increased. The spar shift linkage is hereby mounted coaxially.
The rib at the wrist is fixed firmly to the main spar and the auxiliary spar hinges fixed firmly to the wing root rib. All the other ribs are stuck on the spars rotating freely. The covering is done with an elastic foil.
For a passive or aeroelastic twisting the rib at wrist should to be pivoted on the main spar.
4. Flapping wing with
adjustable twisting moment
By splitting the flapping and twisting tasks of a flapping wing on a main and an auxiliary spar its twisting moment can be designed adjustable.
Adjacent, the framework configuration of an aeroelastically twistable flapping wing with an adjustable twisting moment becomes obvious. The adjustment is effected by the torsion arm at the wing root.
The rest of the other ribs not shown here are fixed to the spars rotating freely. The covering is done with an elastic foil or according to the shearflex principle. Also shell and foam wings can be designed adjustable this way.
If you apply this system on a non flapping aerofoil, a propeller blade or a wind turbine blade, their twisting can be controlled by the auxiliary spar respectively.
Generally, the different types of wing systems can be combined together in many ways.
In the adjacent picture for example, the auxiliary spar of the armwing with its torsional moment is used as a spring device for the small flap moving of the spar of the hand wing of an aeroelastically controlled articulated flapping wing.
The arm wing torsion linkage AT and the arm wing auxiliary spar AHi are hereby fixed firmly together. This way, the auxiliary spar-torsional moment will be transformed into a torque of the torsion linkage AT. This is pivoted at the front and presses down the spar of the hand wing in the indicated rotary direction. The pressure will be adjusted with the inlying lever InH at the wing root.
The profiled arm part of this articulated flapping wing can also be combined with a membrane hand wing. This is possible a useful design for medial climbing and gliding flights.
Adjacent, the wing mechanism near the fuselage with the setting mechanism of the turning moment of the auxiliary spar, the damper of the wing twisting at the upper final wing stroke position and the servo to keep the wing twisting in glide position.
5. Aeroelastically controlled
articulated flapping wing
with adjustable twisting moment and expanding wing twisting at the wing tip
Wing framework of the model EV8
(2004), designed as an aeroelastically controlled articulated flapping wing,
combined with a stroke amplitude expanding auxiliary spar of the hand
wing
at the wing tip section.
- The twisting elasticity of this flapping wing can be adjusted by the torsion of the auxiliary spar of the arm wing at the wing root.
- The downstroke twisting is slowed down by a dashpot.
- The twisting when gliding can be fixed by a radio-controlled servo.
The downstroke twisting here corresponds with the theoretical guidelines almost to the wing tip (please also look at the picture which shows the upstroke twisting). But still disturbing is the high mass moment of inertia of this flapping wing round its axis of flapping and twisting.
Maximum intended wing twisting (click on picture)
In flight practice the articulated flapping wing has a big advantage. The bending of the hand wing in comparison to the arm wing depends on lift of the hand wing. At the same time it determines the distribution of the angle of incidence along the wing span. If the amplitude of the bending is estimable on flight pictures, the lift forces of the hand wing in comparison to the gliding flight can be estimated. Furthermore, the distribution of the angle of incidence the moment of the picture was taken can easily be suggested (please take a look at EV6 and EV7). With these both informations selective adjustments of the twisting moment of the flapping wing, the driving power and the cycle time ratio are possible. Especialy flight pictures taken approximately in the middle of up- and downstroke are informative.
Here you can find some further details about the
Articulated flapping wings
(version 1.1, in German, PDF 1.3 MB)
6. Covering of flapping wings
As well as for the other EV-models a 0.050 mm thick elastic polyurethane-foil was used as cover for the aforesaid wing .
Double-sided adhesive tape was used to adhere the foil to the wing framework (here still covered with release paper).
Version of a trailing edge for flapping wings
composed of a fishing line at the end of the airfoil
wrapped with an adhesive tape.
Here the description of the manufacturing processes of the
Covering of a flapping wing with an elastic film
(version 1.1, in German, PDF 360 KB)
External link
- Data sheet for the highly elastic film
Platilon U
:
http://www.epurex.com/fileadmin/downloads/WaPlaU_e_2006-10.pdf (PDF 0.6 MB)
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