Lancaster Turret

[k9kiwi]

From the original source.

The Boulton Paul Type D Tail Turret
After four years of indecision the Air Staff finally issued production orders for turrets armed with heavy-calibre guns. Both Parnall and Boulton Paul had previously submitted designs for such turrets, but circumstances had prevented their adoption. Boulton Paul designers decided to embark on a completely new design which proved to be extremely roomy and efficient. The new turret was armed with 12.7 mm (0.5 in) Browning guns mounted low and to each side of the seated gunner. The turret had a fabricated structure, most of which was above mounting ring level, the guns being mounted upright in cradles. The ammunition supply was located in the centre fuselage well forward of the turret, thus placing the heavy boxes 255 kg (560 lb) when loaded near the centre of gravity. The structure of the turret consisted of two outboard members carrying the outer bearings of the gun cradle, and two inner sections supporting the inner bearings. The gun mountings were quite substantial, being strengthened Type T turret mountings. The turret was designed for the Mk.IC gyro sight, but this was replaced by the improved Mk.IIC gyro. The sight was mounted on a horizontal tube supported by two levers which were connected to the torque tube to move in harmony with the gun cradles.

The power system was the usual electro-hydraulic unit, with one modification - the elevation mechanism was changed from a hydraulic ram to a hydraulic motor, which was found to be more accurate in control at slow speeds. The gunner sat at his control table with the well-proven controllers to his front, while his central sighting panel was supported in channels which permitted it to slide downwards, leaving an open aperture when conditions were such that sighting through the panel was difficult. Two side panels were also arranged to slide open if needed. The turret doors were mounted on tracks, the two doors meeting in the centre and locking automatically when the outer edges were pushed outwards. There was provision for hand turning the turret in the event of power failure. The 'Free' and 'Engaged' lever was set to the 'Free' position, which automatically broke the gun-firing circuit and disengaged the drive. If the gunner was incapacitated, the turret could be turned by pressing a switch in the fuselage outside the turret, which enabled the dome to be turned until the doors could be opened and the gunner taken out.

The heavy ammuntion belts were stored in boxes in the rear fuselage, and the feed mechanism worked as follows: when the firing button was pressed, an electrical relay was energised which switched on powered sprockets which pulled the belts out of the boxes, feeding them through ducting to the 90 degrees bends at the turret base. Ammunition feed assisters then hoisted the belts into the guns, which were controlled by clutches which engaged when the belts reached a preset tension, ensuring an even feed. The guns were fired by Dunlop Maxifort solenoids, and cocked by hand lever chargers of BP design. The gun barrels were aligned with the sight by lock nuts on the rear support mounting, the guns being usually set to converge at 549 m (600 yds). The electrical load of the turret was considerable, a load of 130 amps was needed, and the maximum load of the main drive motor was 330 amps during the start sequence, though the average was 45 amps. Gun heater, feed assisters, and firing solenoids all needed considerable power, and after problems with the circuit breakers on full load, arrangements were made to cut off the gun and the AGLT scanner heaters (see below), when the guns were fired. An accumulator charged by the aircraft generator supplied the 24 volt power, all fuses and circuit breakers being in easy reach of the seated gunner.

As mentioned above, the guns were sighted by the Mk.IIC gyro sight, the range control of the sight being operated by the gunner's right foot. The selector dimmer and height and airspeed control boxes were fixed on the right hand gun chassis support tube. The sight switch and fire/safe switches were fitted to the top right of the control table. If a Mk.IIIA reflector sight was used, the graticule illumination was controlled by the rheostat on the sight. The Type D was the first to be fitted with the AGLT (airborne gun-laying turret) blind tracking radar system, codenamed Village Inn. The control panel for this was behind the gunner's right shoulder, the spot cut-off switch being fitted on the control table. A system of IFF (identification friend or foe) was devised, using an infra-red detector which would identify any friendly aircraft approaching from the rear fitted with an infra red lamp in the nose. The receiver, which used a 10,000 volt detector, was fitted to a bracket mounted to the left of the gunsight, the control box for the system being mounted between the gunner's legs. Gunners were not altogether happy with the mechanism, as they could imagine themselves being electrocuted in the event of battle damage or a loose connection.

The prototype turrets were manufactured at the company's Pendeford Lane works, where most of the development took place. The main production was undertaken by Joseph Lucas, where most Boulton Paul turrets were made. The first squadron aircraft to be fitted with the new turret was the Handley Page Halifax VII, which used the Type D in operations in the last months of the war. The turret was the contemporary of the Parnall FN.82 which was designed for the same specification, but after its successful use in the Halifax it was the Type D which was chosen for the Avro Lincoln heavy bomber, which served for many years after the war.

Several Type D turrets still exist, many having been rebuilt by enthusiasts. A prime example can be seen at the Royal Air Force Museum at Hendon, where it is exhibited on a stand.

Details of the Type D Turret

Position: Tail
Motive power: BP electro-hydraulic
Power source: Accumolators charged by aircraft generator
Operating voltage: 24 v
Armament: Two 12.7 mm (0.5 in) Browning No.2 Mk.II guns
Ammunition: 1,515 rounds per gun
Belt feed assisters: BP booster units, Dunmore motors
Firing system: Dunlop Magnovox solenoids Type 14 D.I:G:S
Gun chargers: Hand levers, BP design
Armoured shielding: 9 mm (0.354 in) plate. front aspect
Gunsighting: GGS Mk.IIC gyro sight, or Mk.IIIA reflector sight. Light models AGLT Blind Tracking Radar
Weight of turret:
Empty: 200 kg (440 lb)
Armed: 249 kg (548 lb)
Weight of guns: 33 kg (72 1/2 lb)
Weight of ammunition: 415 kg (914 lb)
Operating limits:
Traverse: 90 degrees either side
Elevation: 45 degrees above horizontal
Depression: 45 degrees below horizontal
Speed of operation:
Traverse: 35 degrees/sec
Elevation: 35 degrees/sec

The following aircraft were fitted with the Boulton Paul Type D Turret

Aircraft type: Handley Page Halifax B.Mk.VII; Avro Lincoln B.Mk.I & II
Type & Mark: D.Mk.II
Position: Tail
Guns: 2 x 12.7 mm (0.5 in) Browning No.2 Mk.II
Traverse: 180 degrees
Elevation: 45 degrees
Depression: 45 degrees
Status: Series production

[Hot Space]

Thanks for that. An excellent read

[FLYBOYJ]

Very Cool!!!

[Des Brinn]

Dear members
This may have been answered before. Is there anyone who can tell me where I might find turret manuals
Regards

Des Brinn

[Glider]

I think its also worth mentioning that the AGLT Blind tracking Radar was very accurate. So much so that British bombers were fitted with a sensor to show up on the gunners sight.
There was more than one case of the Gunner firing at and hitting other allied aircraft that had strayed into the arc of fire. Officially the bombers never actually fired but did track targets but then again, no one ever explained how some damaged Halifax's and Lancasters were hit by .50 bullets either.

[Maharg]

Thank you very much Kiwi I have minimal data on Lancaster turrets, thanks mate.

[Bf109_g]

Thanks for that Kiwi! A cannon-equipped mid-upper turret on a Lancaster would have been absolutely awesome to handle!

[k9kiwi]

Turret manuals are about as scarce as hens teeth.

For some reason everyone gets wet pants over pilot instruction manuals, which are about as usefull as breasts on a bull when it comes to the actual construction of the airframe.

I am doing some serious digging into this and will update this thread with anything I get.

[Micdrow]

Originally Posted by k9kiwi

Turret manuals are about as scarce as hens teeth.

For some reason everyone gets wet pants over pilot instruction manuals, which are about as usefull as breasts on a bull when it comes to the actual construction of the airframe.

I am doing some serious digging into this and will update this thread with anything I get.

Hi Kiwi, I believe I have The nose and tail turrent diagrams around here some where very simular to the one top turrent of a lancaster that I posted here if you are interested I will look for them.

http://www.ww2aircraft.net/forum/wea...rent-8234.html (FN 50 Center Turrent)

[genkideskan]

High,

Tony Williams write some outstanding books about Turets, aircraft guns ect.

CANNON, MACHINE GUNS AND AMMUNITION

[k9kiwi]

Micdrow

I think I have them, but others will be interested.

Somewhere around here I have details pertaining to the ammunition loading for the turrets as well to dig up, may take a while as 9 weeks later we have not finished unpacking everything from our house move.

[Micdrow]

Here is the two that I have.

[k9kiwi]

Right have found out the appropriate Air Publications, they are

AP 1659A VOL III PT I SECT 14. FRASER NASH GUN TURRET FN 5 SCHED OF PARTS.

AP 2799Q VOL III PT I. FRASER NASH GUN TURRET FN 82 LANC TAIL S.O.PARTS

AP 2799F VOL III PT I. FRASER NASH GUN TURRET FN 121 SRS 1 MK 1. S.O.PARTS

AP 1659A VOL III PT I. FRASER NASH GUN TURRET FN 5. MANCHESTER NOSE. S.O.PARTS.

AP2799H VOL III PT I. FRASER NASH GUN TURRET FN 150 MK.I LANC MID UPPER. S.O.PARTS

AP 2799F & G VOL III PT 1. FRASER NASH GUN TURR- ET FN121 SRS. 1 S.O.PARTS


Apparently they are available for copy at Hendon.

[Micdrow]

Originally Posted by k9kiwi

UPPER. S.O.PARTS

Apparently they are available for copy at Hendon.

Its amazing whats out there that you can find on the net. It just finding it when you need it.

[propellerhead BF-109]

hi there.
any ideas on:
what hydraulic fluid type did they use in those FN-20 turrets?
what kind of pressure?
all i can find out is that they run on individual pumps on a 24 volt system.
any technical pics would be appreciated.
I'm dying to find out....
cheers lads.