Francis Marliere wrote:Gentlemen,
I wonder about modern AAA effectiveness and I'm looking about data to guesstimate it.
In 'Naval Antiaircraft Guns& Gunnery', Norman friedman states that
- A simple, optic director improves the effectiveness fo Bofors and Oerlikon by 50%.
- Late-war fire control and radar improve the effectiveness of 3" and 5" guns by a factor 2.
- Proximity fuzes triple the effectiveness of 3" and 5" guns.
If we accept the hypothesis that a late WWII fire control improves the effectiveness of a gun by a factor 2, how would a modern fire control would improve a similar gun ?
Thanks for any help,
The predictors used in heavy AAA could be quite sophisticated.
By simple optic sight Freidman must be referring to something like the USN Mark 14 which was mounted on the latter 20mm Oerlikon Guns. These sights used an angular rate method of computation. For instance, if the target was moving at 2 degrees per second and the impact point was estimated at about 2000 yards (about 3 seconds of flight time) then the lead was set to 6 degrees. This display was passed to the gunner by a mirror deflecting the illuminated reticule in the gunsight.
The process of aiming involved tracking the target, then smoothly keeping the reticule on the target as it deflected to the necessary lead of angle. A second operator estimated the range and mentally estimated the impact distance as the aircraft closed and dialled it into the range dial on the side of the sight. Obviously a simple range only radar or optical range finder would help.
http://www.ibiblio.org/hyperwar/USN/ref ... index.html
When the Mark 15 computing gunsight was used within the Mark 51 director for the 40mm Bofors gun the sight worked the same way only the guns were aimed remotely RPC (Remote Power Control). (If there was more than 1 barrel of a 40mm gun the blast, smoke and flash distracted the gunner too much.).
On the British Mark 1 40mm pom pom director the aiming was presented to the gun crew on dial indicators and they turned to pompom mount till it pointed in the correct directly. From the Mark 4 Pom Pom director the pompom was actually more sophisticated than the Mark 14 mark 51 gunsight mounted since the deflection was added to the gun rather than by offsetting the reticule. This director used a proper stereoscopic range finder and latter had Type 282 50cm range only radar added. (Repulse and Prince of Wales were likely sunk only because these radars had Brocken down)
https://en.wikipedia.org/wiki/Pom-Pom_d ... _A3651.jpg
Angular Rate Measuring Gyroscopes are used on ships but on land tachogenerators can be used to measure angular rate. The Prewar German C30 20mm gun actually had a wound clockwork driven gun sight but simpler methods were used until an electrical sight using a tachogenerator was added to the Quad 20mm C38 guns the Germans used on land.
These angular sights are primitive and the algorithm defective unless the target was flying directly toward the target or flying a perfect orbit. This probably doesn’t matter so much at short ranges such as 2000 yards since the aim was corrected by checking the tracer.
To get a mathematically correct solution Cartesian methods must be used.
It’s worth look at how a full FLAK or AAA director worked. Firstly, a word about mechanical computation. Numbers are represented as shaft turns, addition is performed by differential gears (as in a car) and multiplication division by using cam shaft to convert numbers into their logarithms, add/subtract and then find the antilog. Trigonometric and ballistic data such as superelevation and shell time of flight can also be machined onto a 3-dimensional cam.
This is how a FLAK predictor worked such as the Kommandogerate 58 or US Army M7 worked.
The target was tracked in bearing angle, elevation angle and range optically. These ‘spherical coordinates’ were converted to Cartesian coordinates by cams with trigonometric data. The result was the position of the aircraft in Cartesian coordinates (X,Y,Z) ie longitude, latitude, height which was presented on dials. Because of mechanical loading In early directors, such as the US M1, another set of 3 operators would match overlaying dial needles by adjusting small variable speed motors. This established the speed of the target in the three directions X’,Y’,Z’. By WW2 servo motors using synchro had eliminated these additional operators (I think no less than 9 huddled around the M1) plus the operators of the optics of the range finder. (It turned out to be better to use mechanical subtraction)
With these 6 parameters position of the target at any time in the future could now be predicted with these 3 equations:
These calculations were carried out mechanically, An officer would estimate shell flight to target eg 20 seconds and and an allowance time to load the gun after fuse setting 5 seconds i.e. from 25 seconds from now. The predicted position of the target was then converted from Cartesian back to spherical. A pair of 3 dimensional ballistics cams would then give the time of flight of the projectile (which also gave the fuse setting time) and also the superelevation of the gun.
On smaller ground, based guns such as the German FLAK 37 88mm bearing and elevation was transmitted to the crew by dials and the gun then hand cranked to position though the fuse setting machine could take the data in directly.
Bigger guns had power drive in some cases with direct Remote Power Control. On German guns this was done by a electrohydraulic system in which a variable displacement reversible swash plate pump controlled speed. For early German ships the elevation was controlled directly form the predictor presumably with a small electric motor adjust the swash plate pitch through a threaded rod drive. For traverse manual adjustment was used.
US systems used electrical control because of a rotating amplifier called an amplidyne.
Computations for surface fire were done the same way as for AAA/FLAK predictors. Likewise, computations for aiming a torpedo and also for dropping a bomb from a bomber on a moving target while under the influence of cross winds.
The Cartesian system also allowed relatively easy correction for parallax errors caused by differences in gun and director position. Ships motion could be compensated ie changes in speed and direction as well as cross winds and even the Coriolis effect of the shells change in altitude while the earth spun.
These corrections could all be transmitted by synchro servo systems and added in by differential gears from elect mechanical units mounted in racks.
Mechanical computations are fast and accurate.
The system used for USS Missouri’s guns in the 1980s was considered for replacement with a digital system but it was found that no improvement in accuracy or reliability was to be expected. Remember that the sensors that measure gun and sight position also are inaccurate.
The advantage of modern fire control is
1 Digital Computer is extremely small and elaborate algorithms reserved for cruisers and battleships could be included cheaply.
2 Although 75mm guns can easily carry a proximity fuse for systems using 35mm shells and up a muzzle velocity sensor measures projectile velocity and then programs a digital timer (more accurate than the 0.6% typical in mecanjical timers of WW2). I think 57mm guns tend to use a muzzle velocity sensor, they set a timer to explode the shell ahead of the target and disperse tungsten fragments.
3 in other words systems use for Heavy AA and Main guns on Battleships could be applied to smaller guns down to 20mm.
Note that at the end of the war the Germans were developing the 5.5cm gun using a full Cartesian director and going for a hit to kill (ie no proximity fuse) know as Geraet 58 (implemented as the soviet 57mm system)
Radar provided two advantages:
1 Early radar could crudely locate the target but generally range it accurately. Optics still needed to be used for bearing and elevation but range could be accurately tracked.
2 Full blind fire. In the attack on the Bismarck the Swordfish hid in clouds. Assuming the Bismarck’s radars were working they would have known their bearing within a degree or two (beam width was 6 degrees) and range to within 70m but not known height. This was inadequate for blind fire. Latter German radars had blind fire. The Swordfish themselves had radar and could track the Bismarck’s rough bearing and range. Likewise the Prince of Wales was sunk by Japanese bombers carefully using clouds to hide to the last minute.
The best German radar in range measurement was the FuSE 64 Manheim Issue 2 which had auto track on the range gate and could track range to within 6m. (Auto track was important) but the earlier Wurzburg D was limited to a 25m. Since the destruct effect of a shell was likely less this ((say 10m) was not likely to burst the shell correctly. A proximity fuse would tend to explode the shell at its closest point to target.
Wurzburg D which featured conical scan, tracking accuracy to 0.3 degrees and the ability to transmit to a predictor director was available in the autumn of 1941 (ie late 1941) and I suspect one could have replaced the rear most 4m optical range finder for the 10.5cm guns but it was maybe 6 months too late for Wurzburg. The earlier Wurzburg A as available but it lacked conical scan (accuracy only 2 degrees), accurate range (about 100m) and the synchro transmitters.
The very accurate USA army SCR-584 was post war added to the USS Iowa class they seemed to offer unheard of accuracies.