As a retro computing hobby project, I'm researching Helmut Hoeltzer's (Hölzer's) work on the Mischgerät analog guidance computer for the V2/A4 ballistic missile, with the goal of validating a schematic in PSPICE, and perhaps recreating the design using modern COTS components.

Thus far, I have dug up several publications which describe portions of the design, such as the control equation, implementation of signal integrators and DC/AC amplifiers1, and a high level block diagram2, 3, but nothing that spells the complete design out in detail.

Copies of Hoeltzer's two part dissertation4 based on his work on the Mischgerät and related analog simulation computer are in the stacks at the University of Minnesota, and I'm hoping it will provide the detail I seek.

As a hedge against not being able to obtain copies, is there a source for the complete Mischgerät schematic, or even a physical re-implementation?


  1. Ulmann, Bernd (Oct 26, 2008), "Von der Raketensteuerung zum Analogrechner Helmut Hoelzers Peenemünder Arbeiten und ihr Erbe". http://www.analogmuseum.org/library/hamburg_hoelzer.pdf

  2. Ernst, Wolfgang (2008), "Der Analogcomputer als Medium der Zeitmanipulation", Humboldt-Universität zu Berlin, Seminar für Medienwissenschaft, SoSe 2008 https://www.cdvandt.org/Busjahn_Analogcomputer.pdf

  3. Tomayko, James E. (July 1985). "Helmut Hoelzer's Fully Electronic Analog Computer". Annals of the History of Computing. 7 (3): 227–240. doi:10.1109/mahc.1985.10025. S2CID 15986944

  4. See UMN Elmer L. Andersen Library, Charles Babbage Institute, Helmut Hoelzer papers, "Anwendung elektrischer Netzwerke zur Lösung von Differentialgleichungen und zur Stabilisierung von Regelvorgängen", and appended "Gezeigt an der Stabilisierung des Fluges einer selbst-bezw ferngesteuerten Grossrakete".

  • 12
    perhaps recreating the design using modern COTS components Well, as long as you stop at the guidance system ...
    – dave
    Commented Feb 25, 2022 at 1:14
  • 2
    @another-dave Funny side note, the Canadian Arrow one of the hot candidates for the 2004 x-price, was essentially an updated A4 :))
    – Raffzahn
    Commented Feb 25, 2022 at 2:39
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    I've received a copy of Hoelzer's dissertation, 135 pages in German. Light reading, I'm sure.
    – cmholm
    Commented Mar 3, 2022 at 23:32
  • 1
    "Analog computer" might be on the verge of being a bit far-fetched for the Mischgerät, when it is in fact a control circuit. We don't tend to call capacitors "electrical integration calculators".
    – tofro
    Commented Mar 22, 2022 at 12:19

1 Answer 1


I've extracted a reasonably complete description and schematic from the document Das Gerät A4 Baureihe B Gerätbeschreibung (The A4 Device Series B Device Description) published by the Oberkommando des Heeres, Heereswaffenamt, Amtsgruppe für Entwicklung und Prüfung (Army High Command, Army Weapons Office, Office Group for Development and Testing), Berlin, 1 February 1945.

I'm quoting using OCR and machine translation from German, edited for typos and awkward translation of engineering jargon.

Cutting to the chase, the Mischgerät schematic I sought is Figure 79, below.

Also, as user @Forward Ed noted in SE Engineering, the digipeer.de site hosts a number of digitized copies of A4 design drawings, including the basic circuit diagram. While it would ideal to order copies, I haven't yet figured out how to do so on the Deutsches Museum site, so I've zoomed the on-line copy and stitched together a reasonably high resolution example. A low resolution example is at the bottom of this answer.

(Document cover)

A4 Device Description document cover

(from page 173, Section 18, "Device Control")

Similar to a projectile, the missile is held arrow-stable during its flight not by spin, but by fixed fins. However, since the device can be forced out of its flight position by external influences despite its arrow stability, which also results in a change in the direction of the drive in relation to its desired flight position, and because it has to fly through a curve in a certain direction during the flight, the device must [also] be controlled by additional control elements.

In the normal case, the control is carried out by a three-axis control system installed on board. For the special case with remote control, a guidance beam radio receiver is also available, which is connected to a guidance beam on the azimuth of the target during the propulsion part of the trajectory.

(from page 173, Section 181, "The Control System")

The task of the A4's control system (Fig 80) is to force the device to follow its prescribed path while it is being driven and to avoid oscillating and rolling movements. After motor burnout during the free flight path, control is switched off and the device flies on like a bullet.

The control system consists of the following parts:

Equipment section

  1. 1 gyroscope D
  2. 1 gyroscope EA
  3. 1 command control battery
  4. 1 mixer
  5. 4 power steering engines


  1. 2 rudder drive motors (together called rudder drive or also trim rudder spreader)
  2. 4 graphite vanes, 2 of which (vanes I and III) with a potentiometer arrangement for actuating the rudder drive motors
  3. 4 rudders (2 roll rudders and 2 trim rudders)
  4. 4 rudder trim pots

(Figure 80)

A4 Control System Schematic

Every steering action on the A4 device causes a turning movement around the center of gravity. All possible rotational movements can be represented by rotations around three mutually perpendicular axes. These are named as follows on the A4 (Fig. 84):

A - axis or roll axis is the longitudinal axis of the device.

E - axis or yaw axis is the straight line running parallel to the axis of rudders I and III through the center of gravity.

D - axis or pitch axis is the straight line running parallel to the rudder axis II and IV through the center of gravity. It is also perpendicular to A and E.

The task of the control system is to prevent any unwanted rotation around the A (roll) axis and around the E (yaw) and D (pitch) axes.

(Figure 84)

Missile axes and fin numbers

(from page 181, Sub-section 8, "The Mixer Device", Figure 79)

Mixer Device

(The active stabilization problem:)

In addition to the command voltages of the A and E potentiometers, the pressure pieces of fins I and III also have to react to the voltages of the [radio] beacon device if necessary. Mixing these 3 command voltages into 2 control currents is one task of the mixer.

However, the main task of the mixer is as follows:

If the command voltages of the D [pitch], E [yaw] and A [roll] potentiometers corresponding to the incorrect angular position of the device were given directly to the steering gear as control currents, the following picture would result (Fig. 82, case a).

As long as the tip is on the left when the unit oscillates, the steering gear receives a command current that is proportional to this right position. The steering gear then runs to the right at more or less high running speed in order to bring the unit back into the target position via the pressure piece (ie. a graphite vane or fin rudder). The unit also reacts to this pressure piece movement that has meanwhile taken place and returns to its zero position.

During the entire time that the tip of the unit was to the left of the zero position, however, the steering gear constantly received a command to continue coasting. The unit has now probably returned to its zero position, but the thrust pads are still on the right. The consequence of this is that the unit now not only swings over the zero position to the other side as a result of its momentum, but is even supported in it by the pressure pieces that have run out.

During the first period, in which the tip is now on the right, the pressure pads are on the wrong side for a long time, as long as the steering gear needs to pull the pressure pads back and turn to the other side as a result of the new command. In this way, the deflection of the tip increases with every change of direction, and the oscillation builds up. Care must now be taken to ensure that the pressure pieces return to the zero position before the unit tip returns to this position.

(The active stabilization solution:)

It must now be ensured that the pressure pieces [control actuators] return to the zero position before the unit [missile] tip returns to it. The steering gear must therefore receive the command to run back some time beforehand. Since these are oscillations, i.e. sinusoidal processes, the required lead of the rudder current before the unit oscillation is called a leading phase shift (Fig. 82, case b).

The advance of the rudder current is generated by sending the command picked off at the direction indicator through an electrical network of resistors and capacitors. An amplifier picks up the new command obtained in this way and sends it amplified to the steering machine. The processes taking place in the network of resistors and capacitors are also referred to as double electrical differentiation of the command currents.

It is therefore necessary to measure not only the misalignment, but also the angular velocity and the angular acceleration with which the device rotates from the target shot direction into the misalignment. The capacitors are used to measure this angular velocity. A capacitor consists of two mutually insulated conductive layers.

As long as the resistance shown in the picture is not changed, the voltmeter on the right will not show any voltage. But as soon as the voltage is changed on the left, the voltmeter deflects on the right, which is a function of this voltage. In the mixing device (in a simplified representation) the command voltage from a straightener is located on the left-hand covering.

If this voltage changes, ie. the angle changes continuously, ie. if there is an angular velocity, a voltage corresponding to the angular velocity is generated on the right-hand pad, which is used for damping. This procedure is called 'Electrical Differentiation'. In the mixing device, the voltages generated from the angular velocity are differentiated again by a further capacitor circuit and the angular acceleration is also used for damping.

(Figure 82)

Damped oscillation

(Basic Circuit Diagram)

enter image description here


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