Wing twisting

At the EV7a again was used aeroelastic twisting along the whole wing. At rest the wing takes the twist position of the upstroke (look also at the preceding picture).

While gliding

the wing twisting was OK.

Wing root fairing

No inclination of the the stroke plane applied. Therefore, a bend results in the trailing edge at the transition between the rotational symmetric wing adapta roller and the airfoil of the wing (please see handbook, chapter 8.8).

EV7 -drive mechanism

The pneumatic spring to store the aerodynamic upstroke energy and balance the lift forces is good to be seen. A pressure vessel with the valve of a bicycle, is like the drive mechanism of the EV4. Also visible is the small cover for the steel spring at the final wing stroke positions.

For the flow of energy in the springs, please look at the handbook, chapter 1.5, 1.6 and 2.5, also 5.2 and 5.3.

The wing stroke was controlled by linkages over the 55 mm long lever arms of the wing adapter rollers.

There are also some drawings of the drive mechanism.

Flapping wing drive unit of the EV7

Here a part of the rack and pinion drive system is to be seen in front view (please look at the picture in the report).

Inflating the air spring

By the pressure you may control the flapping time comparison between the upstroke and downstroke. At the EV-models mostly was aimed for ratio 1:1.

High start

With the EV7a ornithopter high starts with a rubber cord were carried out for the first time. A hight of about 10 meters was enough. To do this the mechanism must be locked in glide position.
In the picture for the report one can see the servo (facing the motor) for locking the mechanism.

Wing twisting at downstroke

On the inner arm wing the twisting is approximately correct. But from today's view it is inadequate near the wing tips. Refer to the following:

Wing twisting at upstroke

- as above -

Overshoot of the angle of attack

(Annotation like picture before last of EV6 )
At the end of the strokes in the hand wing the twisting increases too much. This is mainly caused by the inertia of the trailing edge when slowing down the stroke motion and when accelerating in the opposite direction.

When the wing comes to a standstill at the end of the stroke, in the interest of lift and thrust the angle of attack should be like gliding. But there are also small advantages to the overshooting (see handbook, chapter 6.8 and 6.9).

Flight stability of ornithopters

On basis of the pictures of a circle flight the problems of the flight stability appears.

Long distance flight

This is one of the original photos whose display details with the model was composed to a strip. All display details was composed in correct positional arrangement by land marks.

flight pictures in large size (136 KB)

Wings with feathers

To enlarge the wing twisting near the wing tips experiments with feathers have been made.

The feathers were not designed to decrease the induced drag, because that would be too difficult.

EV7b at gliding flight

The connection line of the feather tips corresponded to the ideas of the designer. The feather tips continued the camber and twisting of the hand wing.

In powered flight (in direction of down stroke) the bending of the feathers was often quite variable as seen in the following fly by of an ornithopter.
Usually it is quite useful in gliding. Also the wing twisting was alright.

A 3 meter bird at approach

- an aero modelers highlight -

You can have a look at a picture series of this.