INVESTIGATIONS IN GERMANY
TANK ARMAMENT RESEARCH,
MINISTRY OF SUPPLY
SECTION D ARTILLERY RANGE METHODS AND EQUIPMENT
NOTE Artillery range methods in general were considered, as measurements of droop, jump, dispersion up to 1000 or 2000 metres, and muzzle-velocity etc are equally applicable to tank and S.P. guns.
- Dispersion of Shot
As the guns were set up in a special mount the normal service sight was not used to lay the gun. Instead, normal bore-sighting (cross?wires on muzzle and firing?pin hole) was used for each round. The tangent elevation appropriate to the range was then put on the gun by means of a clinometer placed on a plane on the breech ring. Dispersion was usually measured at a range of 1000 m, with checks being done at ranges up to 3000 m.
- Droop and Jump
Not measured at Unterluss The Heereswaffenamt probably measured jump with the gun mounted in a tank.
- Muzzle Velocity
In addition to the standard Boulenge chronograph, the following three methods were also used:
- Charged condenser equipment,
In this apparatus a charged condenser is discharged through a resistance for the period of the interval to be measured and the resultant tall of potential across the condenser measured with a valve voltmeter. An accuracy of 0.1% was claimed, and a report is being prepared under Dr. Braun for other investigators and is being forwarded through T force, Kiel.
- Coil pick-up equipment
This is very simple and consists of two coils of wire of rectangular section and each of 250 turns. The dimensions of each coil are 110 cm. by 90 cm The projectile is magnetised and as it passes through each coil it induces a pulse therein. Each coil is coupled to an electromagnetic oscillograph element through a transformer and a record is taken on a drum camera with a maximum peripheral velocity of 50 m/sec No amplification of any sort is used. The E.M. elements are mounted in oil in the usual way and have a natural frequency of about 5 Kc/s. The pick?up coils are normally placed between 12 and 20 metres apart according to convenience. and further variation can be effected by adjustment of the speed of rotation of the drum camera. The gun is electrically through a high speed solenoid relay by the drum camera to ensure that the first pulse shall fall correctly on the paper or film with which the drum camera is loaded. 'A report on this equipment is being prepared under Dr. Braun, and will be forwarded to TAR.
- The Cathodograph
This instrument was developed for checking the change of muzzle velocity due to wear in guns in flak towers and in the Navy, where more conventional apparatus could not be used. Two plugs are fitted in the. barrel of the gun and placed 60 cm. apart with the front plug 10 cm. from the muzzle of the gun. Each plug contains a pin surrounded by two coils one of which is energised by a12 volt battery As the shell passes either plug the pin is moved, inducing a pulse in the second coil. The pulses so derived are applied to?two pairs of deflector plates of a special cathode ray tube in which the plates are mounted in the same sense (i.e. both ‘X’ deflection). These tubes were manufactured by Leybold and A.E.G. Immediately on firing the gun, small pulses arrive at the first plug before the shell and these are used to switch on the cathode ray tube beam which is initially off. The switch circuit consists of an amplifier of gain 130 and a thyratron. The drum camera on which the record is taken has a maximum peripheral speed of 180 m/sec, the speed being controlled electrically. The signal for the control is derived from a comparison of the frequency of a small alternator directly coupled to the drum camera with a tuning fork. On the complete instrument tour cathode ray tubes are used so that several measurements can be taken simultaneously. The cathode ray tube spot is focussed upon the camera film or paper by an optical system (it is thought that the whole cathode ray tube housing and optical system were arranged to move steadily away from the camera during exposure to produce a spiral trace). On the trace, a length of 10 cm. Is roughly equivalent to one millisecond. A complete instrument has been despatched to London for other investigators via T Force, Kiel.
A flash?meter has beer! developed which uses a photocell in conjunction with a ballistic galvanometer. This could be used by day or by night. A report on the apparatus is being?prepared for other investigators and is being evacuated through T Force, Kiel.
Krupp, Essen (personnel evacuated to Kettwig)
Dr. Dihrberg said that the Heereswaffenamt used the normal tank sight when measuring dispersion of rounds from a gun mounted in a tank. The sight was adjusted so that its axis and that of the gun (bore-sighting) met at the target. This was checked for each round (10 rounds to a group). Movement of sight with respect to the gun was found during these trials (hence adjustment after each round), Dihrberg's remark on this particular point was –“naturlich”-, suggesting that some movement of the sight or of its bracket during firing was an accepted error.
Krupp’s Main Range, Meppen
Herr Weiss, head of the field measuring department gave the following information, with only occasional assistance from Haase, Uphus, Richter, Bornheim and Hirschmann.
Proof or all guns developed by Krupp were carried out at Meppen.
- Jump was measured by firing at vertical wooden targets at a range of 500 to 1000 m, and measuring time of flight. The latter as done with four microphones one at each corner of the wooden target, and connected by permanent cable to the measuring house. An oscillograph or a chronograph was used for recording the interval. The gun was layed by means of a muzzle telescope, which could be adapted to fit any gun. Parallelism of the optical axis of the, telescope and of the axis of the bore at the muzzle was checked by, rotating the telescope through 180degs. Jump was measured for one gun only of a given design, for it was known that there was no variation from gun to gun or from occasion to occasion for any one gun.
- Droop was neglected in all guns less than 10.5 cm. calibre. It was considered substantially constant for all guns, but Weiss had no information as to how much variation was introduced by manufacturing errors.
- Accuracy was measured in the same way as jump, but time of flight was not necessary.
- Muzzle-brake Efficiency was determined by measuring the velocity of recoil. This was done by using a fixed contact on the cradle and a series of contacts on a rod attached longitudinally on the gun. Records were obtained on an oscillograph, a tuning fork providing the time base. Pressure in the recoil cylinders was measured by means of piezo-gauges. In addition, a pointer and revolving drum method was used for recoil velocities, and a spring indicator apparatus for recoil cylinder pressures.
Piezo-gauges were used to measure blast pressure at the positions occupied by the crew of a gun.
- Flash wag measured at night by photographic or photocell methods. The interest here was entirely in connection with conspicuity of the flash, not its effect on the gunner's vision.
- Dust. No?one at Meppen had heard of any complaints due to dust, or of any work on its measurement or suppression.
- Muzzle Velocity measured normally by the Boulenge chronograph.
- Time of flight In A.A. work, a method was used which employed a photo-electric cell at the focus of a mirror 80 cm. diameter. A chronometer was started by a pulse from a membrane which was moved by the pressure wave close to the gun when it was fired. The chronometer was stopped by a pulse from the photo-cell caused by the light-flash from the shell burst falling on it. Due allowance was made for the interval between time of firing and the time at which the pressure wave fell on the membrane. This method could only be used in clear weather. No radio methods were employed.
- Other Measurements. The following measurements were also made at Meppen:
- Strength of carriages.(Using accelerometers railway type)
- Firing interval (contacts at muzzle and firing pin)
- Velocity of shell in bore (contacts arranged along bore)
- Temperature in bore (thermocouples)
- Vibration of barrel (piezo gauges)
- Fragment velocities (using wire screens)
- Moments of inertia of shell,.
- Measuring Apparatus. A large amount of measuring apparatus had been collected. Much of it had been designed by Herr Weiss. All had been removed from Meppen to the Flak Barracks, Oldenburg, where it was under the control of 63 Depot Control Company. R.A.O.C.