RFC/RAF Gunsights

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Robert Hurst
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RFC/RAF Gunsights

Post by Robert Hurst » 05 Mar 2003 16:37

Hi

Early Gunsights - Pt 1

Vickers produced what was probably the first purpose-built gunsight, for the emplacement in the nose of their first Experimental Biplane No.2. This consisted of an elaborate parallel motion sight which was automatically raised when the gun was elevated , and lowered when thre gun was depressed. This was necessary as the gun was fitted to a conical mounting with a small slot through which the gunner could align the sight on the target.

The gate (frame) sight

The Fokker E monoplanes were among the first to use the frame gunsight, a smaller version of a naval sight for use on quick-firing warships guns. It consisted of an elongated rectangular wire frame which could be easily aligned onto a target crossing the gunner's line of fire. Additional upright wires were fixed at intervals along the frame, giving the gunner graduations for estimating deflection. The aerial version was soon adopted by Allied and German airmen. It was found that if the upright wires were made adjustable, they could be used for estimating both deflection and the range of the target. When the two upright wires were set to correspond to the wingtips of an aircraft at maximum range, the pilot could avoid wasting ammuntion.

The British model came to be known as the gate sight. It was fixed on the cowling just in front of the windscreen, and lined up with a small ring element further forward on the engine cowling. The RNAS version used on Sopwith Pups used a wider rectangle than that used on RFC aircraft. German pilots preferred to mount the sight at the end of the barrel housing, using it as a foresight which was aligned with a post or small ring. The pilot of a fixed-gun fighter had no great need for an elevated gunsight; his marksmanship depended on his ability to out fly his opponent, and when he was in a position to open fire his point of aim was relatively stable.

The text and photos were taken from "British Aircraft Armament Vol 2: Guns and Gunsights", by R Wallace Clarke.

If anyone would like to comment about anything in this section, please feel free to do so.

Regards

Bob
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Post by Robert Hurst » 06 Mar 2003 12:33

Hi

Early Gunsights - Pt 2

The ring and bead

The frame sight had shown that a rudimentary allowance could be made for 'aiming off' or deflection by placing the target on the edge of the frame before firing. However, it could be used in this way only if the target was moving across the line of sight horizontally. It was soon realised that, if the rectangular frame was changed to a circular shape, it would enable a pilot or gunner to engage an opponent flying at any angle across his line of flight, while some idea of range could be given by comparing the size of the ring to the enemy aircraft. The ring backsight was aligned with a small red bead mounted on a pylon at the muzzle end of the gun, and the system became known as the 'ring and bead'.

An observer manipulating a free-mounted gun had to be prepared to meet an attack from any angle, and his gun was if possible mounted in such a way as to cover the maximum field of fire. It was also essential that his sight gave him a quick sight line whenever a target came into view. By early 1916 the ring and bead had been adopted for free guns.There is no record of the first use of this sight; like so many other inventions, several people probably realised its logic at about the same time.

The dimensions of the ring and bead varied with its distance from the eye. Typical distances were 584 mm (23 in) for a 76.2mm (3 in) ring, 965 mm (38 in) for a 127 mm (5 in) ring, and 914 mm (36 in) for a 114 mm (4 1/2 in) ring fitted to free-mounted Lewis guns. These measurements were calculated to give a full angle of deflection in an average combat situation. Typical parameters for a fixed gun were: own speed - 161 km/hr (100 mph), target crossing speed - 161 km/hr (100 mph 90 degrees across the pilot's line of sight), range 183 m (200 yds). In this situation the bullet would take 0.254 sec to reach the target, which would have travelled 11.5 m (37.7 ft). The aimimg procedure was to keep the red bead in the small ring in the centre of the ring element, and the target on the edge of the outer ring, flying towards the centre of the ring element. In an ideal situation this would give the correct deflection angle, and the target would be hit. The parameters for a free gun were slightly different, and of course the actual angles, range and speed varied for every engagement, but ring elements gave fair allowance for an average encounter.

The ring was usually made of steel strip, with four radial wires supporting a central ring of 12.7 mm to 25 mm (0.5 in to 1 in) diameter, observer's rings often having only one supporting wire. The stem was hollow, fitted on a fixed post secured with a pin or screw. Observers removed the fragile rings after a sortie, handing the gun and ring to squadron armourers. The bead element was mounted on a shaped pylon; its distance from the ring was not critical, being used to align the ring with the centre-line of the gun or flight-line of the aircraft.

Pilots and observers who survived long enough soon found how to vary the allowance for range and bullet drop, and the ring and bead was the first effective gunsight used in air warfare. The first sights were made in squadron workshops, but these were soon repaced by factory-made units, easily detached from free guns when not in use. The ring and bead was eventually adopted by both sides, and remained in use until it was replaced by the reflector sight in the late 1930s.

The above text and photos was taken from "British Aircraft Armament Vol.2: Guns and Gunsights", by R Wallace Clarke.

Regards

Bob
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Post by Robert Hurst » 06 Mar 2003 13:30

Hi

Early Gunsights - Pt 3

The 'own speed ' factor

As the ring and bead came into widespread use, observers reported that, even though they had a target coming in from the beam and had made the necessary adjustment to their aim, a long burst seemed to have no effect. When experimental batches of Woolwich tracer ammunition became available in 1915 it was found that, when fired to the beam, bullets seemed to curve to the rear. This was due to the bullets losing the forward speed of the host aircraft, and became known as the 'own speed' factor.

The Norman vane sight

Lt. G.H. Norman, Workshop Officer of No.18 Sqn RFC, listened to the 'own speed' factor being discussed in the Mess. He came up with an idea that was to be adopted by every major air force: the vane sight, which all but solved the 'own speed' factor. It consisted of a swivelling vane foresight, similar to a weathercock on a church steeple. The 'cock's tail' of the sight was a vane which was free to swivel in the slipstream. A small red bead was mounted at the cock's beak end. When the gunner aligned the bead with his ring backsight, the barrel always pointed to a position lagging behind the line of flight. The amount of lag was at its maximum when the target was at 90 degrees (exactly to the beam); in any other position the sight automatically gave the correct amount of allowance.

The first sight was made in the squadron workshops by Sgt. Steel and Cpl. Horsley, working under instructions from Lt. Norman. The fitters devised several improvements in the design, and many alterations were needed before the dimensions were found to be correct. The vane was used with a ring backsight 114 mm (4 1/2 in) in diameter, the two elements being 457 mm (18 in) apart. Lt. Norman was sent back to supervise production in London. From early 1916 the sight became standard issue for free guns. The design of the vanes varied with the manufacturer, some being of sheet steel, others aluminium castings. The two elements of the sight were mounted on moving arms which, when the vane was reacting to the slipstream, rose into a horizontal position, allowing the elements to assume a position parallel to the line of flight. The effect of gravity on the bullet was not taken into consideration in the sight design: a Mark VII bullet would fall 365 mm (14.4 in) in 183 m (200 yds) and 1,701 mm (67 in) in 366 m (400 yds). Although this appears to be large, it was the centre of a cone of fire, and was reduced for any angle above or below horizontal. The bead element was a rod 152 mm (6 in) in length, the stem being threaded for 76.2 mm (3 in). It tapered from the base to a ball-shaped bead of 9 mm (.35 in) diameter painted a brilliant red. As aircraft speeds increased, the connecting arms were lengthened, the speed allowance being stamped on the upper surface of one of the wind vane arms. A modified design was produced in 1932 in which the speed setting was adjustable, but this was not adopted for squadron service. When the US 8th Army Air Force became concerned at the inaccurate fire of waist gunners of B17 and B24 aircraft, a vane sight based on Norman's was designed by Capt. John Driscoll of the 389th Bomb Group, USAAF, based at Grafton Underwood.

The above text and photos were taken from "British Aircraft Amament Vol 2: Guns and Gunsights", by R Wallace Clarke.

Regards

Bob
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Post by Robert Hurst » 07 Mar 2003 12:07

Hi

Early Gunsights - Pt 4

Tracer ammunition

When the first batches of RL and Buckingham tracer reached front-line squadrons in France it was thought that the answer had been found to many of the problems of air-to-air gunnery. How could a gunner or pilot fail to miss when the trajectory of his bullets was visible? Experience proved that when the spark like bullets seemed to be hitting the target they were often missing it by a large margin. One problem was that the tracer chemical often burned out prematurely, another that the trajectory differed from that of ball ammunition. Gunnery schools eventually stressed that, although tracer could be an aid, accurate shooting could be achieved only by the correct use of the gunsights. Nevertheless, tracer was in widespread use in both fixed and free-mounted guns, sometimes as many as one round in three being requested by pilots and gunners. The reason was not entirely a quest for accurate shooting; it was an acknowledge fact that enemy pilots often broke off an attack when streams of tracer began to fly towards them. Tracer was not popular with armourers, the heavy barrel fouling meaning hours of extra work after operations.

The above text and photos were taken from "British Aircraft Armament Vol 2: Guns and Gunsights", by R Wallace Clarke.

Regards

Bob
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Post by Robert Hurst » 07 Mar 2003 12:22

Hi

Early Gunsights - Pt 5

Night Sighting

The Hutton Sight

The first night sights were ring and bead elements treated with luminous paint, but these were found to be either too bright or too dim. The first practical night sight was invented by an armourer serving with No.39 Sqn based at Hainault Farm. Sgt. Albert Hutton had been responsible for major improvements to gun mountings and ammunition feeds. He devised an illuminated sight which could be used on both fixed and free-mounted guns. It was simple, but, when tested at Martlesham Heath, trials' pilots preferred it to the more elaborate sights designed by scientists.

It consisted of a tubular foresight containing a red bulb. At the top of the domed tube was a 0.5 mm (0.02 in) hole through which showed a minute point of red light. The backsight was similar, but had a hollow vee-shaped tube at the top. At the base of the two arms of the vee were holes which, when a green bulb was switched on inside the tube, showed as three green spots in the shape of a vee. The gunner simply aligned the red spot in the centre of the vee and on the target. The bulbs suffered severe vibration when the guns were fired, but they usually lasted long enough for what were often very short engagements. The bulbs were usually fed by batteries taped to the gun body.

The caption to the bottom photo should read as follows: An Avro 504 night fighter of No.77 Sqn RFC. A Hutton sight is fixed to the Foster mounted Lewis gun, which could be drawn down for drum changing and upward firing. On the engine cowling is an illuminated Neame sight. The 47-round drum was used to save weight.

The above text and photos were taken from "British Aircraft Armament Vol.2: Guns and Gunsights", by R Wallace Clarke.

Regards

Bob
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Post by Robert Hurst » 07 Mar 2003 15:47

Hi

Early Gunsights - Pt 6

The Neame Sight

Unaware of Hutton's work, the Technical Directorate of the War Office had instructed their design department to devise a night sight. The project design leader was Engineer Lt. H.B. Neame. Several designs were produced, leading eventually to an illuminated backsight. It took the form of a hollow domed tube with a slot cut into the top, surrounded by a strip metal ring. A bulb inside the tube projected a dim light onto the inside of the ring, which was used to align a red point of light (similar to the Hutton foresight) onto the target. The sight was tested at Martlesham and accepted after minor modifcations.

The diameter of the ring varied the smallest being a 51 mm (2 in) No.2 ring used on the Scarff compensating sight, the largest the 115 mm (4.5 in) No.1, which corresponded with the wingspan of a Gotha bomber at 91.4 m (100 yds). For fixed guns the sight was fitted directly in front of the pilot's windscreen. As pilots gained experience it was found that the ideal attack was from below, when one's machine merged with the land mass and the target was silouetted against the night sky. The first special night armament was a Lewis installed to fire upwards at an angle of 45 degrees. W/O Scarff, one of the foremost RFC armament experts, produced a 45 degree Neame sight consisting of an 457 mm (18 in) bar carrying the two elements. The Neame was produced by Purdy and Co., the famous London gunsmiths. They were used mainly on single-seat fighters, although some Bristol Fighters were fitted with upward-firing guns, sighted by the pilot and fired by the gunner in the rear cockpit.

A typical engagement using a Neame sight took place on the night of 20 May 1918. Lt. Edward Turner of No. 61 Sqn., flying a Bristol Fighter reported:

It was my fourth night sortie with Sgt. Barwise. After an hour in the air we saw an aircraft which we soon recognised as a Gotha. After several attempts we managed to get into position below and behind, where the huge wings filled the illuminated ring of the Neame sight. On my signal Barwise fired, hitting the port engine with his first burst. After receiving the contents of two 97-round drums, the Gotha put its nose down and went into a flat turn. We followed until it dived into the ground with a tremendous explosion.

The Secretan sight

When night operations by German bombers increased in 1917, other ideas on night sighting were tried out. One of these was the subject of a patent taken out in 1917 by Major Secretan, RFC. This worked on the principle that, even on the darkest night, everything appears as various shades of grey. Secretan's sight consisted of a large ring backsight with two parallel cross wires, made of wood and coated with a black velvet substance. The foresight was a smaller ring of similar construction. Records show that the arrangement was tested at Martlesham and found to be reasonably successful, but showed no improvement over the existing night sights.
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Post by Robert Hurst » 07 Mar 2003 16:21

Hi

Early Gunsights - Pt 7

The Aldis Sight - Pt 1

One of the drawbacks of the ring and bead was the need to align the two elements with the target. Whilst this was easy enough with a pivoted gun, a pilot with only a split second to fire in in a dogfight needed something which would give him an immediate point of aim.

In 1915 Martlesham Heath tested an optical sight submitted by the Aldis Brothers of Sparkhill, Birmingham. It consisted of a 559 mm (22 in) metal tube containing lenses giving a magnification of x 3 and a cross-hair aiming mark. The new sight was mounted on the cowling of a Be.2c with a Lewis gun on the upper wing, and firing tests were carried out at ground targets. The sight proved more accurate than the ring and bead, though on one occasion the pilot nearly flew into the ground whilst looking through it! The sight was then tested in air fighting manoeuvres. Magnification of the field of view often made it difficult to locate the target quickly. Another problem was that the front lens was prone to fouling by oil from the engine, and it was also no longer possible to estimate target range by comparing the wingspan with the ring diameter. Hugh Aldis was therefore asked to submit a sight without magnification, but with a circular graticule which could be used for range-finding, and possibly, deflection. A spring-loaded oil flap was fitted, and leather-lined adjustable clamps mounted on short sturdy brackets were supplied.

The modified sight received the highest praise after testing under all conditions of temperature (inert gas had been sealed into the tube) and combat manoeuvres. Martlesham recommended that the Aldis should be the RFC's standard fixed gunsight. As air activity over the front intensified, casualties were reaching serious proportions. The ascendency of the Fokker monopane had been broken, but new German types were being encountered, and if the new sight could give the pilots any advantage, it was decided to rush it into production. An initial order for 200 sights was issued, and the company was told to prepare for further substantial production.

The sight tube contained four hermetically sealed collimating lenses, with a graticule in the form of two concentric circles engraved on a plain glass screen. The outer circle gave the deflection needed for a target plane crossing at 161 km/hr (100 mph), and a small circle gave the gun alignment point. On some later models the outer ring was modified to indicate the wingspan of a Gotha bomber at 183 m (200 yds), and with practice pilots found how to use the circle for other aircraft. The lens system gave unity (no) magnification, and ensured that the ring was always centred on the axis of the sight no matter where the eye was placed. The ideal eye distance from the rubber eyepiece was 127 mm (5 in), which gave a FOV (field of view) of 20 degrees. The anti-oil flap was operated by a cable to the cockpit, where a ring was hooked to a small bracket; when unhooked, the shutter sprang open, giving a clear view. If the shutter was left open, oil fouling would occur, so it became standard practice to fit both Aldis and ring and bead sights. In the first installations the windscreen was cut away in the top right-hand corner, but factory-installed sights passed through a hole drilled in the screen.

The above text and photos were taken from "British Aircraft Armament Vol 2: Guns and Gunsights", R Wallace Clarke.

Regards

Bob
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Post by Robert Hurst » 08 Mar 2003 11:01

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Early Gunsights - Pt 8

The Aldis Sight - Pt 2

Production Aldis sights were issued to selected front-line squadrons for operational trials in mid-1916. Pilots found the Aldis superior to the ring and bead, and news of a secret new gunsight soon spread to other squadrons. The Aldis was said to possess almost magical powers, and at a time of high casualties the authorities did nothing to dispel these rumours.

By 1917 the Aldis had become the standard British sight for fixed guns. It was usually mounted on the right side of the engine cowling, with the ring and bead on the left. A smaller version was used on large guns such as the Davis and COW, and a version for anti-aircraft guns had a prism which could be clipped into the field of view, giving a set deflection of 30 degrees. In 1918 the French Aviation Militaire introduced a similar sight manufactured by Chretien, and the German Oigee company produced a very similar optical sight for use on both fixed and free guns. Aldis sights were much sought after by German pilots, who took them from the wreckage of crashed Allied aircraft.

The above text and photos were taken from "British Aircraft Armament Vol.2: Guns and Gunsights", by R Wallace Clarke.

Regards

Bob
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Post by Robert Hurst » 08 Mar 2003 11:57

Hi

Early Gunsights - Pt 9

The Scarff Compensating Sight

In late 1915 an elaborate free-gun sight was designed by Lt. Scarff, RNAS. It was based on the fact that the deflection required was at a maximum when the target was at 90 degrees to the line of flight, and progressively decreased as the angle narrowed. The sight was in effect a gun mounting fitted to a purpose-made gun ring, on which a pillar supported speed cranks which automatically offset the sight line. The Lewis gun was fitted to a framework which was linked to a bar, on which was an aperture and bead sight. The gunner selected target range on a calibrated knob which elevated the gun and sight line. He then set his own and estimated target speed on knurled dials. As the gun was traversed towards 90 degrees the speed cranks moved the sight bar progressively behind the gun line, giving 'own speed' allowance. The cranks also made allowance for deflection when this was needed. If all settings were accurate the correct sight line would be obtained, though in practice it was far too involved for a gunner in the heart-thumping situation of engaging aN enemy fighter.

The mechanism was used on two free gun mountings. The first was the gun ring which was to be used in place of the normal Scarff ring; the second was known as the 'gallows' mounting and was designed for use on flying-boats or large aircraft. It comprised an upright tube on which was pivoted a second tube supporting a bracket holding a spiggot into which a gun was fitted. The sight was mounted on the compensating mechanism, the sight line being offset according to the setting on the dials. The foresight was a 76 mm (3 in) ring mounted high over the barrel; the backsight consisted of a peep-sight aperture behind a glass screen engraved with four small arrows pointing towards the centre, protected by a rubber eyepiece. For night sighting the peep-hole could be drilled out larger and used with an illuminated ring foresight.

The installation of both versions was very involved, needing careful setting up, but like all Scarff's inventions the system was well designed. The RNAS tested the ring mounting in a Sopwith 1 1/2 Strutter, and the 'gallows' in an F.5 flying-boat, but judged the ingenious mechanism to be no improvement over the more practical Norman vane sight. A similar compensating sight was developed 20 years later by Messrs Barr & Stroud, and a compensating sight, the VE, used by Luftwaffe gunners, surprised many over-confident fighter pilots in the Second World War.

The DPG

In 1925 Martlesham evaluated a new version of the Aldis sight which was intended to upgrade it for faster aircraft. Lens sealing was improved and minor modifications made, but the main change was due to a requirement for long-range firing with heavy calibre guns. Adjustable optics gave a magnification of x 2.5, achieved by a shaft rotated up to 270 degrees by a flexible cable operated from a handle in the cockpit. A dimming screen could also be swung into place for use against white cloud or glare from the sun or water. This 'double purpose' gunsight was evaluated alongside a standard Aldis on a Sopwith Snipe. F/Lt. Pynches reported:

The DPG is satisfactory in general principle for long-range work. The DPG is considered superior to the Aldis for short-range firing. For ranges of 366 to 549 m (400 to 600 yds), greater or less magnification than 2.5 times would not serve any advantage. On a steady aircraft a line can be maintained on an objective with a steady magnification of 2.5. During moderately quick movements, however, it is extremely difficult to keep a line on an objective, and unity magnification is preferable. It has a distinct advantage that on long-range attacks the DPG mists up considerably less than an Aldis, especially on long steep dives from high altitudes. The present shade of sun screen is a definite advantage when sighting into the Sun, although it is considered that a slightly larger screen would be an advantage. (Report M/ARM/55).

The above text and photos were taken from "British Aircraft Armament Vol.2: Guns and Gunsights", by R Wallace Clarke.

Regards

Bob
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