Zachern
Zachern is a method named after Hans Zacher for determining the flight characteristics of gliders .
This systematic examination of the flight characteristics takes place in two steps:
- In thermal weather , slow flight behavior , rudder effect, maneuverability , lateral stability, rudder adjustment ... are examined.
- Experiments on the static and dynamic behavior of the aircraft follow. These can be located in calm air at about 1300 meters altitude drag and examines the elevator paths and forces at different speeds (static behavior). Then the orbital oscillation ( phygoids ) is flown: To do this, slow down from the trimmed state and let go of the control stick . The oscillation that now begins is documented by measuring the period duration and by describing the aircraft behavior. A distinction is made here:
- stable : oscillation subsides after less than 6 periods
- unstable : airplane swings up (amplitude increases)
- indifferent : execution of 6 oscillations of the same amplitude possible
Zaching is carried out with a few and simple aids using the Zacher protocol. The following are used: stopwatch, tape measure, hand dynamometer and a transparent protractor called a phipsitheta , which is attached to the cockpit canopy in the direction of the pilot. The phipsitheta is used to estimate the angle between the aircraft fixed and the geodetic coordinate system , and thus to determine the aircraft movement: φ (Phi) is the angle between the aircraft's longitudinal axis and a fixed point on the horizon, θ (theta) in the transverse axis and Psi (ψ ) in the aircraft vertical axis .
Not to be confused with flight characteristics determinations with flight performance measurements of gliders, which are also regularly carried out by Idaflieg at the annual summer meeting at the Aalen-Heidenheim airfield .