Chapter 2

Solution Number One: The Siemens K4ü: Autopilot: The Ability to Fly on a Fixed Compass Bearing

The increasingly battered eighty-one-year-old fuselage of BF110 - VJ+OQ currently resides at the Imperial War Museum (IWM) Duxford in Cambridge, in the AirSpace hangar. (Turn left when exiting the ticketing hall.) It has been passed from pillar to post since its arrival from IWM Bedlam in London in 2012, and we are far from sure if the present curators understand the true significance of the absolute jewel that they are the custodians of. If they did it most likely would be in the British Museum (or, cynically, more likely be hidden away, its existence completely secreted) - not consigned to an inconspicuous corridor in a Cambridgeshire museum, complete with full public access.

Of particular note is, first, there is no auxiliary oil tank supply (being clearly tapped off by way of a substantial brass nut), which simply means that Hess could not have flown from Bavaria to Scotland - his engines would have been starved of oil (not fuel) and would most likely have seized somewhere over the North Sea. This revelation, which has been the subject of our previous books, has already been well covered and the implications explored and explained. It would be very unlikely indeed that a sensible Bf 110 pilot, anticipating such a long flight, would simply leave to chance that he would have enough oil to complete the journey. This could in extremis effectively amount to suicide. An auxiliary oil tank, or an en route landing, would be the only options, and we know for sure there was no auxiliary oil tank fitted. Please check the details for yourself.7

Secondly, and as far as we can ascertain, there are the major remnants of a Siemens K4ü in the forward section of the fuselage, though again badly damaged, demonstrating that Hess had the ability to fly on a set bearing. However, it is important to note that the machinery would not automatically fully adjust for the effect of wind drift. This problem has bedevilled the navigator since flight began, and most early aviators used 'dead reckoning' as the usual method of accounting for (or trying to account for) the effect of wind on a particular course. The method was and is always fraught, especially if trying to plan over a long distance, which is of course exactly what Hess was attempting to do, the main weakness being that wind drift had to be estimated from weather charts prior to the outset. In 1941, there were some rudimentary mechanical wind sights that allowed in-flight readings to be taken, but these were dependent upon the navigator literally protruding a telescopic device from the side of the aircraft mid-flight, and we have certainly seen no evidence that Hess had such machinery, or more pertinently the time or inclination to take such readings. He already had to contend with enough problems .

Figure 2.1. The remnants of the Siemens K4ü that still resides in the Bf 110 fuselage at IWM Duxford.

The Siemens' system relied on a sophisticated autogyro compass, one that was mounted in the central fuselage of the Bf 110. It is noticeable and relevant that the immediate pictures of the Hess fuselage in Eaglesham, post-crash, show the fuselage intact and no inspection plates removed. However, once taken to Carluke, the local RAF scrap yard, the inspection plate detailing the gyrocompass has clearly been removed. We show the progress by way of pictures to demonstrate the point.

We now know, thanks to Andrew Rosthorn, that Royal Aircraft Establishment (RAE) Farnborough had indeed sent one David Mitchell from Carluke to salvage the Bf 110 and the compass was most likely removed as part of this process.8 Thereafter the fuselage inspection panel is always shown as being removed. The compass was linked to the damper (see Figure 2.21), which then mechanically adjusted the rear rudders for the effect of drift and movement.

Figure 2.2. One of the first images of the crashed plane. Note the intact inspection hatch on the top right of the Balkenkreuz.

Figure 2.3. A second picture at Carluke also showing the still intact inspection hatch.

Figure 2.4. The location of the master compass and access hatch within the fuselage of the Bf110.

Figure 2.5. The plane on the Queen Mary trailer, in late May 1941, clearly showing the hole where the inspection hatch was later removed presumably by David Mitchell on behalf of RAE Farnborough.

Figure 2.6. The fuselage as can be seen at Duxford. (The wrapping plastic has also now been removed.

We hope the reader can now understand our pleasure at finding part of the early 'auto-pilot' in situ in the fuselage of the Hess plane, as clearly its use potentially eliminates all the problems of flying in a straight line while going up the North Sea. What is needed is to understand and learn how the device worked. In this connection we consider ourselves very fortunate to have been given permission to reproduce an excellent treatise on the operation of the Siemens' device, written by a true expert in its operation (who has a fully working example at his Normandy home). So, over to you, 'Funksammler' ('The radio collector').

General

One of the most widely used Kurssteuerungen used by the Luftwaffe was the K4ü system built by Siemens (Luftfahrt Geraete Werke Hakenfelde).

Siemens started the development of their K4 system from about 1936. The Luftwaffe required the system to be compatible with the Patin remote compass system. Together with some other lessons learned in early applications of the K4, this led to the development of the K4ü (the ü standing for 'überarbeitet', which means 'revised'). More than 50,000 examples of this autopilot were built from about 1938 to 1945 and were used in aircraft like the Messerschmitt Bf 110, Junkers Ju 88 and Heinkel He 111.

?Description of the K4ü autopilot

Figure 2.7. Overview of the K4ü installation.

Apart from the aforementioned Patin master and daughter compass, the K4ü consists of

• an LKu 4 Kurskreisel directional gyroscopean LKz 3 Kurszieger indicatoran Lrg 9 Richtungsgeber course adjustment switchan LKMm Kursmotor course adjustment motoran LRM 4ü Rudermaschine servo unitan LSch 4ü Hauptschalter main switchan Stützschalter compass coupling switchan LKW 1/4ü Wiederstandskasten resistor boxan LKW 3 Wiederstandskasten resistor box
• an Notauslöseknopf emergency release knob.

A number of variations of the K4ü system could be supplied, denoted by a number behind the name, for example K4ü-1 or K4ü-7. These versions differed mainly in the number and configuration of the control switches, so that the system could be tailored to different types of aircraft. For example, an additional Lrg 5 or Lrg 10 direction switch could be placed at the bomb aimer's position. With a special extension this switch could even be coupled to the Lotfe bombsight so that aircraft could be adjusted during the bomb run. For twin engine aircraft an LDS 10-2/4 Einmotorenflugschalter or single engine flight switch could be added, which automatically changed the balance of the autopilot to deal with the drag of a feathered propeller. Additional resistor boxes would be needed to tie these various optional switches into the K4ü autopilot.

?The Functioning of the K4ü autopilot

The principles of the autopilot

To understand the functioning of the autopilot, a little bit of control theory must be understood.

First, there needs to be a stable set point, a set course that the aircraft needs to fly towards. If the aircraft deviates to the left of the set course, the system needs to steer the aircraft back to the right, and vice versa.

The force generated by the measuring system is far too small to operate the rudder of the aircraft directly, so the second requirement is a large power amplification. As there is a time delay between the disturbance of the set course and the action of the rudder, this system tends to oscillate unless stabilised or 'dampened'. On slower aircraft the aerodynamics of the aircraft itself have a stabilising effect, but as aircraft got faster and 'slippier' another means of damping these oscillations was required.

Figure 2.8. Functional overview of the K4ü autopilot.

So thirdly a 'damping gyroscope' or 'Dämpfungskreisel' is required. This gyroscope measures the angular velocity of the aircraft. If this...