Improved Skua for FAA?

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My understanding is that the UK ordered a number of SBD early-war (pre-US entry?), but supply was slow to build up and the US would not release any in the time frame they were wanted. By the time enough SBD became available the SB2C was coming online - the FAA tested the SB2C-1 model but found them unsuitable for their use.
 
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Thumpalumpacus said:
For someone like me not so up on the details, were there recognizable advantages/disadvantages regarding electrically-powered/hydraulically-powered turrets?
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Oversimplifying and conveniently ignoring changes and developments in tech, but:

Hydraulic
+ ease of tracking/control
+ positive control at very low rates of movement
+ better at handling excessive torque loads
- much more vulnerable to damage
- much more servicing and reliability issues

Electric
+ better/more reliable performance over wide temperature ranges
+ tended to have higher speeds
- considerations re: capacity of aircraft's generators
 

If I'm reading this right, then, the electric turrets were too "snappy" and perhaps got away from the operators, while hydraulic turrets with slower speeds perhaps offered better gun-laying?

As for generators, wouldn't that also be an issue for engine-driven hydraulic pumps? After all, both are driven by engine PTOs, right?

Please forgive what may be ignorant questions, I've just never drilled into this.
 
That looks like a good summary.

Things did change a bit as the years went by.
Both camps were trying to improve their products.

Some were hybrids. That is a hydraulic pump powered by an electric motor close to the turret.

I don't know how some of the American planes were set up but some British 4 engine planes had different parts of the plane run by different engine generators. No cross over.
Like if the tail turret was powered by engine No 1 and you lost engine No 1 you also lost the tail turret but the turret and nose turret would still function. This was early in the war. Later they cross connected things and upsized the generators so that 2 generators out of three would carry the electrical load.
 
I knew the British bombers sometimes had dedicated engines for specific subsystems. Did this ever become an issue in combat? And did American bombers follow this practice?
 
Thumpalumpacus said:
Please forgive what may be ignorant questions, I've just never drilled into this.
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A lot of us haven't drilled into it as a subject on it's own.
Sometimes it's just snippets of things we have run across.

And just because a particular turret operated one way in 1941 doesn't mean it's replacement/later production version operated exactly the same in 1944.

A different variable is the ammo load. The British tail turrets would hold a huge amount of ammo in tracks that ran well forward into the waist of the fuselage.
I don't know how the American tail turrets/guns were set up. Some of the American dorsal turrets would only hold a certain amount of of ammo (which rotated with the turret) but their were extra boxes to reload with nearby. I have no idea how long it took to reload or change boxes? Early Martin turret in a B-26 would hold 200rpg. .50 cal ammo went about 30lbs per hundred so trying to move 200rounds with the box was not easy. Of course trying to move 200 rounds without the box was even harder unless you were a professional juggler
The turret may well have held 400rpg in the boxes but listed the extra 200rpg as "overload" and 200rpg per gun as 'standard load".
B-17s and B-24s often carried thousands of rounds in boxes inside the plane that had to be changed over in flight.
 
This might help if you can track down a copy.
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View: https://www.amazon.co.uk/dp/1852602236/
Volume 2 covered guns & gunsights.
Amazon product ASIN 1852604026
View: https://www.amazon.co.uk/dp/1852604026/
 
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I certainly can't elaborate on the differences between electrically driven and hydraulically driven turrets, but I can give an insight into the three main British turret manufacturers and their different systems. These were Boulton Paul, Bristol and Nash & Thompson.

We'll start with BP. Its turrets were all based on the same principles and workings of the de Boysson turret that was built under licence and first fitted to the Defiant. It was electro-hydraulic, which means that power for the hydraulic actuation was supplied by a 24 volt DC motor. This received motive power from slip rings in the turret rotating base. The DC motor was attached to and drove a hydraulic generator, which supplied hydraulic pressure to the pump, which drove the actuation of the turret in azimuth via a rotating cog and the guns in elevation via an actuator. The hydraulic working gear was supplied by Hele-Shaw Beecham, this name might be familiar to some of you as the company was affiliated with Gloster and in the 1920s built the world's first constant speed propeller.

In the BP turrets the controls were electrically actuated, as was the firing circuit. They were very simple and the turret was easy to operate. It had one joystick lever with a firing button on it, whose actuation in either direction rotated the turret and back and forth raised and lowered the guns. The seat also tilted slightly so the gunner's line of sight followed the guns. The one-handed operation enabled the gunner to cock the guns and un-jam them individually if need be while the others were still firing. The joystick was also a dead man's switch. The de Boysson turret was compact, but heavy. Visibility wasn't great, especially directly ahead, but other BP turrets solved this issue by bigger cupolas. BP turrets also had a boost function, which enabled rapid turret rotation in emergencies, but this wore out the hydraulic system and was not recommended for constant use. Boulton Paul Type C turret fitted to Hudsons and Halifaxes.

YAM 62

Out of the three types, the Bristol turrets were the simplest and lightest. They were plumbed into the aircraft's hydraulic system and driven by the EDP. Their controls comprised the gunner sitting on a bike seat that was attached to a central stork, which had a handle bar that the gunner held and turning it in either direction moved the turret in azimuth. Elevation was achieved by twisting movement of the handles, the seat moved with the guns, enabling line of sight. The left hand handle had a trigger to open the hydraulic system and the right hand handle had the firing trigger attached to it. The problem some Bristol turrets faced was that they didn't have enough motive power in times of high slipstream or forces acting on the guns and some of the turrets refused to turn in flight against the slipstream. This didn't happen to all their turrets, but was problematic for the ones it happened to, including the B.11, which was fitted to (two) de Havilland Mosquitoes and was intended for Douglas Bostons, but because it failed at high speeds it was not put into production. Bristol B.1 turret cupola as fitted to a Bolingbroke. The gun was offset to enable the gunner to fire directly aft and not hit the fin.

DSC_1101

The N&T turrets, like the Bristol ones were hydraulic and relied on the aircraft's system to work. The advantages of this was that the turret was light, but that if the hydraulic system suffered a failure, like in combat, the turrets stopped working. N&T and BP turrets had a wee hand operated handle that could rotate the turret if it had no power. It took about 10 to 15 seconds to turn the handle around enough times to turn the turret 360 degrees. The N&T turrets were actuated by two handles canted at an angle outward in line with the guns and although they had individual firing triggers on each handle, the turret would not turn unless both handles were twisted in the direction the gunner wanted the turret to go. This meant that the guns had to be cocked before they could be turned and if there was a stoppage, the gunner had to release one hand to clear the stoppage, which stopped the turret from rotating. He could continue to fire the other gun/s not blocked though. Nash & Thompson FN.20 rear turret fitted to Avro Lancasters. The yellow turret behind is an unpowered Armstrong Whitworth turret as fitted to Avro Ansons and Airspeed Oxfords.

YAM 60

So, in summary, the BP turrets benefitted from ease of operation and the fact that the entire workings of the turret, e.g. its hydraulic system was entirely self-contained. The slip rings ensured that the turret could still work if there was an electrical failure and not relying on the aircraft's hydraulic system could also fully function in the event of hydraulic system failure. The down side was that the BP turrets were heavier because they were self contained and they were more sophisticated, bringing higher maintenance. The other types were lighter, but relying on the aircraft's hydraulics meant that failures of that meant the turrets could only work manually. They also relied on messy moveable hydraulic joints in the hydraulic lines that leaked and provided a mess for the mechanics to clean up and at worst caught fire if ignited. Obviously, none of the turrets were particularly easy to get in and out of and the Defiant and its early A.1 turret got a reputation as a gunner killer. There was supposed to be a hatch in the bottom of the aircraft below the turret, but the gunner would have had to dismember himself to get through it because it was so small. Defiant gunners wore a special flying suit that had their parachute packed into it, called the Rhino-suit and ingress and egress was best made by turning the turret to one side and climbing in and out of externally. Boulton Paul Type A.1 turret as fitted to a Defiant.

DSC_0056

The Bristol turrets were easy to get into and out of from below (correction) and there was less clutter in them, but the gunners couldn't carry their parachutes in the turrets with them as the bike seat they sat on was too small. N&T turret gunners could sit on theirs, as pilots did. Access for those was obvious, through the doors in rear turrets or up from underneath for mid upper and front turrets, both easily achieved. Getting out was always the difficult bit, although rear gunners could turn the turrets to one side and open the turret's doors and fall out backwards. All this illustrates that being a gunner was not the most comforting occupation on board an aircraft.
 
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The GE Amplidyne control system allowed electric turrets to be as precise as hydraulic. The Martin upper turret used this system and was extraordinarily successful being utilized on a multitude of types (B-26, B-24, A-20, Baltimore, Ventura, Neptune, B-32) and continuing on to the post war.

In fact, late production Lancasters used it in lieu of the FN 50 hydraulic turret.
As you note the hydraulic lines were more vulnerable to damage and worse, presented a fire hazard if the lines were breached. I recall a note stating that a surprising number of Lancasters were lost due to hydraulic fires. The Bolton Paul turrets obviated that problem by using local pumps for the hydraulics. The BP turrets were one of the few advantages that the Halifax had over the Lancaster and when the Lincoln replaced the Lancaster it used BP nose and rear turrets in conjunction with the Martin upper turret which together eliminated the long hydraulic lines.
The attached document from which the above snippet was taken provides an overview of the extraordinarily complicated American development of a bewildering variety of turrets to perform the same basic functions, some doing it much better than others. It's ironic that the Americans, who pride themselves on mass production and standardization, produced such a chaotic program.
 

Attachments

  • Turrets.pdf
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Lincoln first prototype PW925 flew with the Martin turret in the dorsal position. But the second and third prototypes and all production Lincolns used a Bristol B.17 turret fitted with 2x20mm Hispano cannon in the dorsal position. Postwar they were removed from many aircraft.

Bristol B.17 mid-upper turret with twin 20 mm Hispano cannon | World War Photos

Bristol B.17 mid-upper turret with twin 20 mm Hispano (Mk IV or V) cannons
www.worldwarphotos.info
 
Interesting snippet about the Amplidyne system, which was also applied on the Bendix Type A top turret fitted to the B-25. I can't say I know the history of US turret design and manufacture (thanks Reluctant Poster for the attachment), but I do know that US gun turret manufacturers benefitted enormously from a technology exchange with Britain in 1941. Examples of Boulton Paul and Nash & Thompson turrets were sent to Wright Field and manufacturers were quick to adopt British technology into their turrets, which by that stage had yet to yield anything that was suitable for service use. The biggest problem that turret designers had with their turrets was weight (!) and getting the actuation system right. The Bendix B-25 turret and the Martin Type 250 CE turret, one of the widest applied top turrets of the war and which saw installation in Canadian built Lancasters and was going to be fitted to Handley Page Halifaxes, took advantage of the Nash & Thompson design of hand controls redesigned by General Electric and adapted to suit the electrical control system via the amplidyne unit. The successful Martin 250 CE top turret showing its GE control yoke, Amplidyne control box and N-8 GGS.

DSC_0221

Consolidated and Emerson applied the N&T control system to its B-24 end turrets, despite the Emerson ones being electrically driven, although the Consolidated turrets were hydraulically powered through ther aircraft's hydraulic system, like the N&T turrets. The Sperry Gyroscope Company took full advantage of the British technology, particularly the Boulton Paul Type T turret that was sent to the USA and the Sperry Type A-1 top turret fitted to B-17Es and Fs had a more than passing resemblance to the BP Type T turret and used its electro-hydraulic working gear. Sperry also applied this system of using a DC motor to drive the hydraulic system to power the turret in the Briggs-Sperry Ball Turret applied to B-17s and B-24s. Like the BP turrets, the ball turret was entirely self contained and didn't rely on the aircraft's hydraulic system. A Boulton Paul, sorry, Briggs-Sperry ball turret.

DSC_0469

Its interesting to note that the first US bombers fitted with power operated turrets of the war were RAF LB-30s and Liberator Mk.IIs, the latter of which was specially built for the British, although the USAAF received Mk.IIs and designated them LB-30s. The Mk.II had a Boulton Paul Type A turret (as fitted to the Defiant and Halifax) aft of the wing spar and a Boulton Paul Type E tail turret, also fitted to the Halifax. The Type E turret also remained in use on some RAF Coastal Command Liberator GR variants, which, once US turrets became available generally replaced the British turrets on RAF B-24s, but not all. It was decided (by the Air Ministry?) that foreign types in RAF service would be fitted with Boulton Paul turrets, which included the Lockheed Hudsons and their distinctive BP top turrets, but also the Liberators and Douglas Bostons, which were also going to be fitted with BP turrets, but different types were trialled, including a Rose turret. The Bristol B.11 turret, which was originally designed for the not proceeded with Beaumont bomber, was intended on being fitted to Bostons, but might not have ever been fitted to one. To my knowledge the only fitting of this turret to an aircraft was the two prototype de Havilland Mosquito turret fighters. These British built turrets were originally intended for installation in Boston IIIs, but the Boston IV was delivered with the standard Martin 250 CE turret, and RAF Boston IIIs never went to war with power turrets.
 
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I should note that as much as I'd like to, I can't provide a list of source info for what I've written here, as most of it comes from stuff I've read or copied over the years from a multitude of books and magazines. I have photocopied pages from various books and magazine articles, including the British Aircraft Armament books, but also books on Boulton Paul and manuals for the BP electro-hydraulic system. I copied a lot of stuff when I worked in museums in the UK and, I'd imagine like you guys, I have boxes full of clippings that will probably one day end up on the rubbish tip...
 
The study I posted on US turrets gives much credit to the Brtish leading the wy in turret design





 
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