"William Donzelli" wrote in message
om...
"Emmanuel Gustin" wrote in
message ...

It was technically quite difficult to provide a smooth control
that had a more or less natural 'feel' for the gunner, was capable
of
high speeds of rotation but also of accurate slow tracking, and
had
no dead spots anywhere where movement wasn't linked correctly
to control input -- for example when passing the 0 degree line
from
left to right, where the forces working on the turret reversed.

This I do not understand. The radar antennas of the era often used
synchro feedback systems - synchros do not have dead spots, they
provide a rotational signal from 0 to 360 with no interruptions when
making the 359 to 0 transition. What was the problem with the
control systems in the turrets?

Very hard. The electronics of the period used numerous
vacuum tubes which had a short lifetime.

Only hard working transmitter and radar tubes had short lifespans
(often just 50 hours). The tubes found in just about everything else
were quite hardy - most outlasted the war and are still good today.
Many small signal tubes often clocked lives well past 10,000
operating
hours.

William Donzelli



The tubes involved were special power amplifier tubes with heavy anode
cathode currents that must have been erosive. I do not believe they
had nearly 10,000 hours life. Amplifying DC was not possible because
directly unlike today when complimentary npn and pnp transistors are
available only valves were available and they had very particular
biasing requirements.

The technique of the day was to use an AC signal of 50,60 or 400Hz to
chop up the DC signal (called modulation) via a high speed relay known
as a vibrator. Typical life of these was 2000 hours. After being
chopped up the signal was transformer coupled to amplifier valves and
then demodulated by another relay similar to the first one and
operating in phase. This phase sensitive demodulation then restored
the chopped up signal to DC. Both relays chopped at the same time.
The phase sensitive modulation and demodulation could also be carried
out by a 4 valve ring modulator and ring demodulator. For reasons of
noise and power the modulation was carried out by a vibrator relay and
the phase sensitive demodulation by a valve based ring demodulator.

Its sounds crude but was quite accurate. A full serve system would
involved resistors for position sensing that were amplified in DC,
amplidynes which operated in AC to generate mathematical functions
such as sine, cos etc (amplidyne is a sort of rotary transformer in
which the overlap of the poles of the two secondary windings are
added/subtracted from each other. The area of he poles can be used to
generate voltages that are functions of shaft position.

The noble prize winner William Schokley who's team invented the
transistor was I believe funded in part to provide replacements for
valve gear in B29 barrettes.

During the Korean war the electromechanical computers of the B29 could
not compute for the closing rates of the MiG 15s. I don't see how
they would have coped with an Me 262 in that case.

I guess that Aiming consisted of tracking the target while enclosing
the wingspan of the aircraft in a "ring" in the gun sight to estimate
range. The "rate" and range determined lead and elevation.