Re: Split rear armament
- From: Eunometic <eunometic@xxxxxxxxxxxx>
- Date: Sun, 09 Sep 2007 07:50:46 -0700
On Sep 5, 8:44 pm, guy <guyswetten...@xxxxxxxxxxxxxx> wrote:
This refers specifically to guns in two separate locations operated
by one gunner simultaneously.
There wera a number of proposals toward the end of WW2 for rear
defence of British bombers e.g.the projected Vickers ultra heavy
designs to carry a pair of 20mm guns in the rear of each of 2 engine
nacelles, controled by a tail gunner in the conventional location.
What I do not understand the reasoning for it:-
That it would reduce the chances of all the rear armament being
knocked out by a single hit (guns in 2 locations so they cant all be
knocked out by one hit) (From Butler Secret projects 1935)
This does not make sense if you compare it with a conventional tail
turret (CT) as a hit in a split mounting will knock half the guns out
but with a CT a hit in the same place will knock no guns out (none
there)
A hit in the conventional tail turret will admitedly knock out all the
rear guns but it would also have the same effect with a split system
as the gunner and controls would be out of action.
So with both systems you have one chance of putting all the guns out
of action but with the split system you also have 2 chances of
disabling half the guns.
Was there another reason?
Guy
The advantages of remote controlled guns are manifold:
1 The turrets can be smaller and have less weight and drag.
2 They can be located in areas where a manned installation is
inpracticable or too performance robbing.
3 They simpify pressurisation of the aircraft. (An issue with the
Vickers bomber which was a high altitude aircraft)
3 They can be aimed by computer, something hard to do unless
the sighting mechanism and the gun are completelty detached
so that the necessary correction offset between gunsight and a
remotely driven turret. Gyro gun-sights are hard
to use since the aiming recticle moves to present the correct
ofset yet this very same moving recticle must track the target
and be enclosed around the wingspan of the target to guage its
range. I'd say this is the main reason the Vickers type used
this along with the tail gunners position being somewhat more
streamlined, armoured and clear. The system couldn't possibly
work without the use of a computer (probably based on electrical
transmission by synchro to a mechanical computer based
on cams, differtial gears and Faraday ball and disk integrators)
to compensate for the parrallex error between the nacelle
barbettes and the gunners position. Quite a few British computers
of the day were made out of mechano eg the plotters for mortar
finding radar based on GL3 radar sets.
It also clears the tail of hydraulics and ammunition and improve
gunner
view
Aircraft that carried remote controlled guns in service were:
-Messerscmitt Me 210 and 410 in cheaks attached to the
the left and right rear fueselage: they were aimed by 3 gunsights
left, right and middle to gain maximum vantage.
The mechanism was hydraulic (almost certainly electro hydraulic)
-Arado Ar 240 and 440. A slim dorsal and ventral turret was aimed by
an upper and lower duel periscope mechanism that automatically
switched between upper and lower views. It was found that special
wide angle optics needed to be developed for the periscope so that the
target, if approaching from below, could be acquired in time to make
the system usefull. Because the gunner was behined bullet proof glass
and because the german lens optics were excellent it was found that
the periscope offered superior night vision than looking directly
through glass. The system was hydraulic, earlier electric systems
failed to perform adaquetly.
-Junker Ju 388 (almost entered service) had single twing 13.2mm gun
tail turret, fully hydraulic, aimed by a similar split systems as on
the Ar 440. The actual turret postion was sent back from the tail to
the sight via highly geared multi-turn shafts to a precision spool
valve. The body of the valve was position by the feedback from the
turret via a rack and pinion while the spool was positioned by the
sight acting if there was a thus unless the valve body were aligned
perfectly fluid was supplied to hydraulic motors for elevation and
traverse. An electric synchro could be added for subsidiary turrets
if desired. The spool valve was designed to have a slight 30 micron
'leak' keep the hoses pressurised and stretched for quick aiming
response.
-Heinkel He 177: a single electro-hyraulic turret opperated by the
500Hz aircraft power supply, the sighting mechanism was electric but
the final drive was hydraulic control synchros provided seting and
feeback mechanisms. The sight was in a bubble on the top of the
aircraft. The more developed He 277 had multiple turrets in a B-29
style installation. The control system on the He 177 was by AEG and
known as the FA 10/1 and the turret was the FDL 131/Z. Other
companies such as Siemens were working on more advanced systems.
-Boeing B-29 had an all electric system with synchros in the gun sight
for accepting the setpoint, synchros in the turrets as the feedback
mechanism and differential transformers between the two in order to
allow an mechanical computer to insert the neccesaary ofset
corrections for air density, air speed, range, elevation, traverse and
required lead. The gun sight had a stedoscopic range finder whereby
the gunner adjusted a dial that enclosed the wing span of the aircaft
to give a reasonable range estimate for the computer. It took quite
a lot of practice to do this. The system was all electric, using
vacuum tube amplifiers and then final 'amplidyne' rotating generators
which drove the turret motors. (an amplidyne was a sort of motor
generator with the generator feeding back into its field winding to
create a lot of amplified power for driving the turret motors). The
USAAF prefered all electrics due to the reduced fire hazard.
( Climbing out of an slippery oily bomber eg a Lancaster at night was
a nightmare.) Despite this most advanced mechanism Curtiss LeMay
ordered fighters to fly ahead of his XX Bomber Airforce B-29's since
he found the semi-automatic sighting mechanism was only really
accurate for defending against rear based attacks. The USAF seems
to have lost interest in anthing but tail turrets after this, the
turrets being inadquet in Korea against MiGs yet again.
-Douglass A-26 Invader: mechanism similar to the B-29 using a twin
perisope mechanism: the pilots seat swivelled about the periscope.
-Piaggio P.108B the Italian B-17 saw service with a pair of hydraulic
12.7mm guns mounted in barbettes behined the outer engine nacells the
same split rear armament. Quite innovative.
-B-36 had retractable 20mm turrets. Unlike the B-29 the B-36
computers didn't have to compensate for the parrallax error created by
the gun sight being located quite far from the sighting bubble.
However as gun sight, computer and turret were closely placed together
the massive guns had a tendancy to 'knock out' the vacuum tube
amplifiers. Note in the German designs the use of perisopes or
gunsights placed near the turret tended to eliminate the parrallex
problem.
The British 4-engined bombers were built around the rear turrets and
there proably was no point to adding remote controlled guns to a
fueselage that was already so configured. There was a lot to be said
for stripping dorsal and frontal guns from British bombers as the
extra speed would proably have saved more bombers and crew members
than the extra armament. The British never bothered with an armed
bomber after the Mosquito again. Some remote engine nacelle
controlled guns were flight tested on Wellingtons. The General
direction of German armament seems to have been hightly streamlined
guns aimed by often by an elaborate periscope sited such that it was
clear of structures such as the tail fin.
Generally the German mechanisms were electro-hydrulic and steadfastly
avoided the use of vacuum tube amplifiers but used more reliable
magnetic amplifiers. The German mechanisms wen't to hydraulic for
their final stage of power amplification for some reason; probably
related to some of the early limitations of magnetic amplfiers. US
systems tended to be all electric: even for their ships.
Ultimetly the USAF went to magnetic ampliers for the B-47, the German
magnetic amplifier technology, which was core to making missiles such
as the Fi 103/V1 and EMW A4/V2 reliable caused a minor revolution in
power control till the mid 1950s.
My belief is that the Vickers bomber went to twin remote guns for the
following reason:
1 Clear sighting for the rear gunner, easier escape, lack of
hydraulics, ease of pressurisation.
2 Computer assisted aiming essential, remote control essential.
.
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