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Ornithopter models EV5 and EV6

Ornithopter model EV5

flapping wing model EV5
  • first flight
  • wing span
  • weight
  • aspect ratio
  • airfoil
  • 1981
  • 2.70 m
  • 5.2 kg
  • 7.3
  • like bird
  •  
  • [106 in]
  • [183 oz]

The fuselage and driving the mechanism of the EV4 were used again in the EV5. The fuselage was extended and a T-tail unit was added like the EV1. The inner (arm) wing was actively twisted and the twisting of the hand wing was aeroelasticly.

configuration of the wing spars
Wing design

The EV5 arm wing was actively twisted by the forward spar. (For the pivot point, please look at the next picture and at the picture series of the EV4 drive mechanism.)

The back main spar of the hand wing was hinged. This facilitated the aeroelastically twisting of the hand wing.

control of the wing twisting
Active wing twisting

In the wing root fairing of the EV5 one can see the mechanism to pitch the main spar.

Karl Herzog
Karl Herzog

as an advisor during flight experiments with the EV5

cardan gear mechanism with two crank pins
Altered cardan gear mechanism

Switching between gliding and power flight at EV5 and EV6 was no longer effected by reversing the direction of rotation, but by a servo controlled step switching system of the internal gear in the cardan gear mechanism.

 

Ornithopter model EV6

ev6 ornithopter at gliding flight
  • first flight
  • wing span
  • weight
  • aspect ratio
  • airfoil
  • 1983
  • 2.90 m
  • 5.2 kg
  • 7.4
  • CLARK Y (11,7)
  •  
  • [114 in]
  • [183 oz]

Here the EV6 with the fuselage and the tail unit of the EV5 but with new wings and a new pivot point of the wing. The twisting along the whole wing comes aeroelasticly.

First the angle of attack along the span must be adjusted.

wing twisting at gliding
Wing twist in gliding flight

One can estimate the twisting of the wing based on the trailing edge.
In this picture it is alright.

Fly by of the ornithopter
Fly by of an ornithopter
EV6 at upstroke
wing twisting at upstroke
EV6 at upstroke

with relatively constant twisting along the whole wing. Thus, the angle of incidence grows lineary towards the wing tip.

wing twisting at upstroke
twisting at upstroke of the wing
EV6 at downstroke

There is also a constant twisting along the whole wing.
Even at that time, by first results of calculations, for an optimized distribution of lift in the center of the up- and downstrokes the increase of the twisting out to the wing tips was missing.

There is also a video of this flight.

A view to the trailing edge.
With exception of the wing tips, the twisting looks very good.

final wing stroke position
Overshoot of the angle of attack

In the range of the upper final wing stroke position the twisting of the hand wing increases too much. This is caused by inertia of the trailing edge at braking the movement of the upstroke and accelerating in the opposite direction. The increasing lift at the end of the upstroke supported this mistake.

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 advantages to the overshooting (please see handbook, chapter 6.8 and 6.9).

ornithopter model with articulated wings
Articulated flapping wing

EV6 with his articulated flapping wings without a rigid trailing edge. Because of missing lifting forces the hand wings are bent down.