The first flying electric bird

(Elektro Vogel No. 1)

The inner (arm) portion of the wing was actively pitched and twisted. The outer (hand) portion of the wing twisted aeroelasticly.

EV1 at powered flight

EV1 at gliding flight

EV1 with wings at the upper final stroke positon.

The twisting along the whole span unfortunately was too small for powered flight. It was made harder by the large rigid trailing edge.

Wing twisting at downstroke

Fuselage of the EV1

Length 1.6 m, outer diameter 147 mm, fuselage side approx 10 mm, made of rigid foam rings, covered with polyester-glass laminate.

Open fuselage and wing attachment

EV1 was working with a wing root pitching.
Inside of each wing tongue a mechanism was installed. The wing wrists in the center of the wing halfspan were pitched with it additionally.

Electrical equipment in the front part of the fuselage

Left:

The drive motor and the servos to control the model.

Right:

Microswitches to reverse the motor and the resistance for a smooth starting.

Flapping mechanism

In the adjacent picture there are to be seen:

Left:

The fitting for fixing the cord of the pulley of the rubber compensation spring in the rear part of the fuselage (next picture).

Steel wires between the pulley and the angled lever which presses the main scotch yoke up and the wings down, respectively.

Centre:

Fixing for leading the scotch yoke.

Right:

Rods with spherical bearings to pitch the wing root.

Underneath one can see a bit of the drive unit and right of this the blue micro switch for the gliding position.

The spherical bearings of the main scotch yoke are pivoted inside the tube ends of the main spar.

Technical drawing

with a longitudinal section through the fuselage and the drive mechanism of the ornithopter EV1.

Pulley of the rubber spring to balance the lift forces.

Planetary gear drive unit for ornithopters

This special planetary gear mechanism converts the rotary motion of the electric motor into a straight line reciprocating motion of the crank pin (cardan gear mechanism). A scotch yoke was only used to switch between gliding and powered flight.

Glide is obtained by orienting the path line
of the main crank pin horizontally.

Powered flight is obtained by orienting the
path line of the main crank pin vertically.

The 2 mm stagger between the main and the control crank pin is visible in the photograph.

On the top there are two triggers for two settings of glide to stop the motor at the dead center of the crank. In this way the glide position was locked.

This drive unit was used in the ornithopters EV1 to EV6.

For further details and technical data, please see Report,
my patent DE 26 28 846, application 1976
and the

Plans of the single parts (PDF 1.4 MB)
18 pencil drawings, in German

You also can see an animation of this cardan gear mechanism with two crank pins.

The active twisting of the wings resulted from the separate controlling of the main and auxiliary spars in stroke direction.

The spreading of the tubular spars was necessary for a relatively small twisting at the wingtip by a given stagger of the crank pins and a given distance between the main and auxiliary spars at the wing root.

There was no trailing edge. The ornithopter did not sustain flight, but good engineering progress was made (please take a look at the report).

For covering the wing the elastic foil type Platilon U 04 was used for the first time, thickness 0.03 and 0.05 mm (for data sheet please take a look at the external links of the Articulated flapping wings).

EV1 in comparison with EV2, top view

Fuselage opened

The main and the auxiliary spars was separately controlled by two steel wing levers.

In front one can see the micro switches to reverse between gliding and powered flight.

The fuselage was divided. The rear part was detachable to change the batteries.

Wing twisting

The servos to modify the wing twisting are inside the front wing adapter rollers.

EV2 drive mechanism

To the rear one can see the accumulators and the cover of the steel spring used for lift force compensation.

View from below to the drive mechanism

Single parts of the mechanism
Data of the steel spring: d = 4 mm, D = 44 mm,
k = 3.26 N/mm, F_max = 536 N, W = 184 g [6.5 oz]

Drawing (longitudinal section) of the drive mechanism

The EV3 did not get past the phase of design.
Only plans exist (terminated 1978).

Run tests

Arm and hand wing sections was actively pitch controlled at the relevant section root. The arm wings were rigid. The hand wings should be twisted aeroelasticly. The twisting of the hand wing was appropriate for gliding.

Drive mechanism of the EV4

There is a picture series about the details of the mechanism. They reveal the design and function of the system.

Technical drawing

with a longitudinal section through the drive mechanism in the fuselage.

EV4 with stepped wing twisting

During powered flight, the twisting of the hand wings has been to small. During the downstroke, especially near the wing tips, the angle of incidence was not enough negative. But at that time, definite theoretical instruction about the distribution of this angle along the span was missing (e.g. handbook, 2001, chapter 6.5 to 6.7).

Adjusting works

The pitch of the hand wing could be modified in a small range.

At the wing root fairing one can see the high camber of the like bird airfoil.

EV4 with his wings at the lower final stroke positon.