Control of flight speed
at the arnithopter model EV8
A flying model - especially an ornithopter in power flight - is flying optimally only in a relatively small speed range.
In gliding flight the elevator unit normally works as an automatic speed controller. Nevertheless in practice it comes to great speed fluctuations by radio-control comands and in powered flight (please look at Flight stability of ornithopters).
With the EV8 an electric controller should ensure the keeping of the optimal power flight speed. Then the slope angle will only be influenced by thrust resp. by the stroke speed. More or less thrust results in more or less climbing.
Controller of flight speed
A controller of flight speed for helicopters for combustive motors is used. Its properties to control have proofed quite useful in the control loop designed here.
Airspeed sensor
The vane sensor of a paragliders airspeed sensor works as a speedometer. It is designed for a wireless rotation speed transmission (type Skywatch, swiss made). A small magnet rotates with the vane.
The rotation of the magnet is scanned by the rpm sensor of the helicopter-speed controller, which otherwise detects the rotation speed of the rotor blades.
The desired rotation speed (resp. the nominal flight speed) can be predetermined by radio-control, and its influence can be activated and deactivated.
For testing, the van sensor can be brought to the desired rotation speed with a magnet which is mounted at the end of the motor shaft.
Mechanical mixer for the V-tail
Here, instead of the gas servo of the helicopter engine the controller steers the elevator servo.
A mechanical mixer had to be added to the V-tail linkage already existing in the EV8. A T-tail would have been better.
Phygoide
The slow oscillation of the airspeed almost accuring in every gliding flight
(re phygoide
please look at external
link 1) can be avoided with the electric regulation. The model
flies its angle of glide as controlled by rails.
Also miscarried hand launches with unfavorable angles of glide in the beginning are no problem anymore. The model directly passes into the angle of glide given by the desired speed.
However, landing should better be tried with switched off controller.
Becker Flap Rudder
For improving the elevator effect a linkage according to the principle of a Becker Rudder was applied to the EV8. Otherwise such a thing is used particularly on ships. It increases their capability of manoeuvre.
With the Becker Rudder control surface and deflection flap are moved synchronously with only one lever. The elevator changes its angle of attack and camber in the same tenor. In this way, the effect of the elevator is bigger as with only one of the two modifications.
Normaly small rudder throws are sufficient with an activated controller of flight speed. The advantage of the Becker Rudder is mainly obvious when the controller is switched off.
External link to this subject
- Simulation of the phygoide by Peter Rother:
http://www.aerodesign.de/peter/1998/phygosim.htm
To the Articulated flapping wing