AK-4

AK-4

Data Acquisition System

The Idea…

In October 1982, Prof. Fiedler from the Meteorological Institute of the University of Karlsruhe expressed the wish to carry out climate measurements over the Upper Rhine Plain with a motorized aircraft. Due to the good contacts between this institute and the Akaflieg, the solution was to use our Bölkow for the measurement flights. We were also to procure and install the necessary measuring equipment.

After some measurements and their evaluation, the following requirements for the recording system emerged:

  • The entire system should be portable and independent of the mains supply
  • A total of 16 measurement inputs (channels) should be provided
  • The sampling sequence of the measured values should be independently selectable between ¼ sec and 32 sec for each channel
  • The measuring accuracy should be 0.25% of full scale
  • The acquired measurement data should be continuously recorded on magnetic tape cassettes
  • It should be possible to change cassettes without interrupting the measurement
  • The playback device should be included in the same device

…and its Realization

Due to the short construction time (limited to six months), we were forced to use ready-made components as far as possible. On the other hand, simple and safe operation had to be guaranteed despite the versatility of the applications. Our solution to these conflicting requirements was as follows:

  • We buy compact functional units available on the market (display unit, tape recorder, analog-digital converter)
  • We built further functional units ourselves that were not readily available for our specific case (control panel, coding switch for tape recording, mainframe interface)
  • A microprocessor centrally controls and links these units.

The mode of operation of the overall circuit is thus determined by a program that can be developed in parallel with the circuit. The flow of information can be taken from the overall data flow chart.

The entire system was finally housed in a shoebox-sized metal casing and weighs approx. 3.5 kg. The evaluation of the measurement flights for the meteorological institute led to satisfactory results. The most frequent source of error turned out to be the tape recording. By using higher quality material, we were able to reduce this factor to an acceptable level for all subsequent measurements.

Use of the AK-4 in a Glider

Once the goal of a fully functional data acquisition device had been achieved, this was also to be used for measurements in gliders. As a follow-up project, the development of an electronic variometer had been under discussion for some time. The idea was to use the AK-4 to test the suitability of all sensors that could be used for this variometer under real operating conditions.

By evaluating various thermal flights, we also wanted to find a framework for the glider pilot’s behavior in different events and situations. We hoped to gain insights into the constant control loop:

  • Instrument display and influences on the pilot
  • His control reactions
  • Changes in the flight status

At the Idaflieg summer meeting in Aalen Elchingen, recordings were made of the detection of thermals, pre-flight without cranks, the assessment of the control tuning of the glider and its dynamic flight behavior. The second goal, the use of the AK-4 in gliding, was thus also achieved.