O.Thetford, P.Gray German Aircraft of the First World War (Putnam)

Gotha G IV and G V

   The Gotha was without doubt the most legendary twin-engined bomber of the First World War. The name came to be applied generically (and inaccurately) to all large enemy aircraft, in much the same way that "Handley Page" was applied to all and sundry Allied twin-engine machines. It was largely through the use of the Gotha in daylight raids on Great Britain that these aircraft became so widely publicized and were mentioned only with apprehension. The Gotha G.IV and G.V became the main production variants, having been developed from the earlier G 11 series of 1916, which were produced only in small numbers. The G.IV and G.V were manufactured by both the parent firm and sundry sub-contractors.
   Together with the Friedrichshafen G.III, the Gothas shared the brunt of the long-range bombing attacks from 1917 onwards. An outstanding feature of the G.IV and G.V was the "sting in the tail" whereby the rear gunner was able to fire not only upwards and backwards but downwards too, through a specially designed "tunnel" in the fuselage bottom. This firing position had been tried in the earlier Gotha G.III, but the gun had to be operated by the gunner adopting a prone position and firing through a trapdoor in the fuselage bottom. In the G.IV and G.V the plywood-lined tunnel was aligned with a V-shaped opening in the top decking so that the gun, on a normal mounting, could be sighted and fired through the fuselage, backwards and downwards, through an arc of 25 deg. laterally and 60 deg. vertically, although a prone position could also be adopted. Considerable toll was taken of Allied machines until effective evasive tactics had been evolved.
   Apart from this novel firing arrangement, the Gotha G.IV and G.V were quite conventional airframes, and the fuselage, unlike the contemporary Friedrichshafen G.III, was a one-piece wooden structure of spruce longerons and spacers. Although completely plywood-skinned, the basic structure was still braced in all bays with stranded steel cables. A gunner's cockpit was situated in the extreme nose, immediately aft of which sat the pilot on the port side of the fuselage. Beside him was arranged a folding seat for another crew member. Between the pilot's cockpit aft of the wings were located the main fuel tanks, which occupied the full width of the fuselage, preventing any interchange of crew positions in flight. Bulkheads were cut away extensively, however, which points to the fact that initially the design had intended inter-communication.
   Of three-bay layout, the upper wings were composed of two panels joined at the center with steel wedges securing interlocking rectangular staples. The lower wings had a center-section portion to which were attached the engine bearers, struts and undercarriage chassis, each side being an independent and separate unit. These sections were plywood-covered on both surfaces. Based on two spruce main-spars of channelled I-section, additionally walled with 4 mm. birch ply and fabric wrapped, the fabric covered wings were swept throughout their length at an angle of 4 deg. Ribs of ply, extensively fretted for lightening purposes, were flanged with solid timber and tacked to the spars. All interplane struts were of steel tube with three-ply fairings attached. Inboard the trailing edges of the wings were all cut back to allow airscrew clearance for the pusher-arranged twin 260 h.p. Mercedes D.IVa engines. Ailerons of welded steel tube were fitted to all four wingtips, those on the upper wing having a large horn balance. They were linked with a strut and actuated by a crank lever attached to the top ailerons.
   The complete empennage was fabricated from light-gauge steel tube and fabric covered. Only the rudder was balanced, and its size, compared with the fin, was considerable. Streamlined steel-tube struts rigidly braced the components to the fuselage.
   Each separate undercarriage chassis was fitted with two wheels which were attached to the main axle and sprung with long tension springs, unusually mounted inside the main struts. In the Gotha G.Vb a front pair of wheels was added to each chassis, forming an auxiliary attachment to facilitate night landings and prevent nosing over. An extremely rugged tailskid with steel reinforcing spine and shoe completed the undercarriage gear.
   Bombs were stowed externally on removable racks, and were arranged and fitted according to their size and the requirements of the operation.
   The emergence of the Gotha G.IV in the autumn of 1916 coincided with a realization of the Zeppelin airship's limitations as a raiding weapon, and it made the aeroplane bombing raids on England, for which the "Ostend Carrier-Pigeon" Squadron had been formed as early as November 1914, a practical possibility. Thirty Gotha G.IVs were issued to Heavy Bomber Squadron No. 3, commanded by Hauptmann Brandenburg, in the spring of 1917. They were based at St. Denis Westrem (Flights 13 and 14) and Gontrode (Flights 15 and 16). Two more flights (Nos. 17 and 18) were added in July 1917.
   In the daylight raids on England (25th May to 22nd August 1917) the Gothas achieved a remarkable degree of success with, initially, a surprisingly low casualty rate. The reason for this was two-fold. The Gotha's excellent 260 h.p. Mercedes engines enabled it to operate in the region of 15,000 ft. and, as the English defenses lacked adequate early warning facilities, was able to approach and release its bombs before Home defense aircraft could attain the same altitude. By the time such fighters as were then available (modified B.E., Sopwith Pups, Martinsydes, etc.) had laboriously clambered to their ceilings, the raiding aircraft were well on their way back across the North Sea. No significant material damage was achieved, but the effect on the public was such that the Government was forced to withdraw operational fighter squadrons from France, including the famous No. 56 Squadron, to combat the daylight raids. With the subsequent improvement of the warning system and the advent of the Bristol Fighter and Sopwith Camel defense units, daylight raids became impossible without disproportionate losses and the Gothas reverted to night raids from 3rd September 1917 onwards. The night attacks ended in May 1918. Altogether, the Gothas of Bombengeschwader 3 dropped 84,745 kg. of bombs on England in twenty-two raids. Twenty-four Gothas were destroyed by Allied defenses and a further thirty-seven lost in accidents.
   Capt. J. B. McCudden, V.C., had a brush with the daylight raiders while serving as an instructor at Joyce Green: strangely enough, it was on 5th July 1917, the day after No. 56 Squadron had returned to France. McCudden had his unarmed instructional Sopwith Pup fitted with a Lewis gun to fire over the airscrew and the under-surfaces of his aircraft painted blue to render it less visible should he be able to get above the Gothas to put in an attack. The warning came about 10 a.m., and McCudden immediately took off and climbed towards the south of the Thames, ultimately arriving over Southend at some 16,000 ft. Flying west along the estuary, attracted by A.A. bursts, he saw some twenty bombers in good formation returning east. Having altitude to spare, he waited for the formation to pass before diving on the rearmost machine firing a complete drum of forty-seven rounds. Misjudging the dive, McCudden had to pull out to avoid the Gotha so suddenly as to break his seat bearers. Pulling up for another attack, he dived to within 300 ft. on the Gotha's starboard quarter, then suddenly changed over to his port rear, closing to 150 ft. and finishing another drum before the enemy gunner could swing his gun to the opposite side. However, neither attack produced any visible effect. Putting on his third and last drum, McCudden again repeated the maneuver of changing from side to side to disconcert the gunner, and this time saw his tracers striking about the fuselage and wings, but was disappointed to achieve no more effect than for the Gotha to shove down his nose a little. Now out of ammunition, he could do no more than fly alongside the bomber at a discreet distance, screened from enemy fire by the Gotha's own wings, in the hope of distracting the attention of the gunners so that some of the other defense machines that had now appeared on the scene might perhaps get in an attack. After 25 minutes his vigilance relaxed, and one of the enemy gunners put a good burst through McCudden's Pup, one bullet smashing the windscreen.
  
  
Description: Twin-engined long-range bomber. Crew of three.
Manufacturers: Gothaer Waggonfabrik A.G. Gotha (Go.).
Sub-contractors: Luft Verkehrs G.m.b.H. (G. IV) (Lvg.)
   Siemens Schuckert Werke G.m.b.H. 80 a/c (G.IV) (Ssw.)
Power Plant: Two 260 h.p. Mercedes D. IVa 6 cylinder in-line water-cooled engines.
Dimensions:
   Span 23.7 m. (77 ft. 9 1/4 in.)
   Length 11.86 m. (38 ft. 11 in.)
   Height 4.3 m. (14 ft 1 1/4 in.)
   Area 89.5 sq.m. (966.6 sq.ft.)
Weights:
   Empty 2,400 kg. (5,280 lb.)
   Loaded 3,635 kg. (7,997 lb.)
Performance:
   Max speed 140 km.h. (87.5 m.p.h.) at 12,000 ft.
   Climb to 3,000 m. 28 min.
   Ceiling 6,500 m. (21,320 ft.) in 52.5 min.
   Range 305 miles.
Armament: Two manually operated Parabellum machine-guns in nose and rear cockpits.
   Bomb load varied from 300 to 500 kg. (660 lb. to 1,100 lb.) to suit operational requirements.
   Six 50-kg. (110 lb.) bombs were usually carried in the daylight raids on England.

J.Herris Gotha Aircraft of WWI (A Centennial Perspective on Great War Airplanes 6)

Gotha G.IV

   By late 1916 it was apparent to the German Army that the strategic bombing campaign against Britain using Zeppelins was not a success, and furthermore the Zeppelins were too costly and vulnerable. The Army was planning to abandon airships in favor of cheaper, more effective heavy bombers. The operation to attack London and other strategic targets with bombers was called Turkenkreuz (Turk's Cross).
   Of course, the plan required bombers with sufficient range and payload for the task, and the Gotha's performance made it the obvious choice. On 16 August 1916 Idflieg ordered 52 Gotha-built bombers of an improved type, the G.IV, making the G.IV the first Gotha design to be ordered in substantial numbers. So many of the new Gotha G.IV bombers were wanted that two other manufacturers, LVG and SSW, were given contracts to build the G.IV under license.
   The G.IV was simply a refinement of the G.III. Powered by the same 260 hp Mercedes D.IVa engine used in the G.III, the G.IV featured ailerons on both upper and lower wings connected by an actuating strut for improved controllability. The G.IV also introduced the patented Gotha tunnel, a hollowed-out opening in the rear fuselage that enabled the gunner to depress his gun through the tunnel to fire at aircraft below, or to mount a ventral gun at floor level for a wider field of fire. To retain torsional rigidity despite the cut-out in the bottom of the fuselage, the fuselage was covered in plywood instead of fabric.


Gotha G.IV(LVG)

   LVG received an order for 150 Gotha G.IV(LVG) bombers in December 1916. The type test for the initial 50 aircraft was completed on 25 June 1917, after the Gotha-built aircraft had already bombed London. One aircraft was fitted with two 245 hp Maybach Mb.IVa engines in an attempt to raise the bombers' operational altitude, but inability to find a suitable propeller thwarted the attempt. Another aircraft tested Flettner servo tabs starting in October 1917.
   LVG built an additional 40 G.IV bombers to an Austro-Hungarian order. These were modified to take 230 hp Hiero engines built in Austria. The squadrons received these aircraft in March-April 1918. Weak engine bearers and unsuitable propellers led to excessive engine vibration that caused piping leaks and structural damage, limiting their usefulness, and by September 1918 the G.IV(LVG) bombers were essentially grounded.


Gotha G.IV(SSW)

   Idflieg ordered 80 Gotha G.IV(SSW) bombers from SSW at the same time the LVG machines were ordered. The first batch of 40 were delivered between July 1917 and February 1918; about 30 went to operational units and the rest went to training and replacement units. The second production batch, ordered in May 1917, was delivered to training units between December 1917 and August 1918. The twin-wheel Stossfahrgestell (shock landing gear) designed by Siemens was fitted to all aircraft from G.217/17, and many machines were also fitted with the Flettner servo tabs. Instead of the normal 260 hp Mercedes D.IVa engines, some aircraft had 185 hp NAG C.III or 180 hp Argus As.III engines for training use.


Gotha G.IV Operations

   The G.IV was the aircraft that made Gotha a household name. Built in much greater numbers than earlier models - 232 were built by Gotha, LVG, and SSW - it was intended by the German Army to replace the expensive, vulnerable Zeppelins as Germany's long-range bomber of choice. Although the first G.IVs were delivered in November 1916, a number of problems had to be resolved before the G.IVs were ready to bomb London, their intended target, delaying their first attack on England to 25 May 1917. This attack by Kagohl 3 did not reach London, nor did the second. But on 13 June the third attack did reach London, causing the most severe casualties of any bombing raid of the war. Together with the heavy casualties, the spectacle of Gothas leisurely bombing targets in London in broad daylight shocked the British public, with a significant ramification being the creation of the RAF from the RFC and RNAS on 1 April 1918 to provide a more coordinated and effective air defense capability. In the interim, the war cabinet agreed to double the size of both the RFC and RNAS as a direct result of these raids.
   Initial Gotha G.IV losses during the daylight attacks were light, but rapidly improving defenses caused a shift to night bombing starting the night of 3/4 September after eight daylight raids.
   The Gotha bombers were stable when fully loaded but only marginally stable when lightly loaded, as was normal during landing. Photos of loaded Gothas show bombs mounted under the front gunner's cockpit, far ahead of the center of gravity. Small, 12.5-kg bombs were also carried in bomb racks in the bombardier's cockpit. After release of these bombs the center of gravity moved aft significantly, making the Gothas much less stable in pitch. Accordingly, most operational losses were due to crashes during landing, when the lightly loaded bombers were least stable. And the night landings now required in its new role as night bomber emphasized the Gotha's handling problems during approach and landing; landing accidents causing 76% of all Gotha losses.


Gotha G.IV Specifications
Engines: 2 x 260 hp Mercedes D.IVa
Wing: Span Upper 23.70 m
Span Lower 21.90 m
Area 89.5 m2
Chord Upper 2.30 m
Chord Lower 2.30 m
Gap 2.22 m
Sweepback 1.16°
General: Length 12.40 m
Height 4.30 m
Empty Weight 2413 kg
Loaded Weight 3648 kg
Maximum Speed: 140 km/h
Climb: 1000m 3 min
2000m 9 min
3000m 16.5 min
4000m 25 min
Range: 700 km

  
  
Gotha G.IV Test Aircraft
G.210/17: Had Maybach Mb.IVa engines, tractor propellers, and a 24.94 m wing span. Later re-engined with NAG C.III engines and pusher propellers.
G.211/17: Had Mercedes D.IVa engines and four-bladed tractor propellers.
G.212/17: Had a span of 28.20 m.
G.213/17: Had Flettner servo-controls on all control surfaces.
G.220/17: Had Flettner servo-controls on all control surfaces.
G.227/17: Was powered by 260 hp Mercedes D.IVa engines supercharged with an SSW compressor.


Gotha G-Type Bomber Production Summary
Order Date Type Qty Serials Notes
Aug. 4, 1916 G.IV 12 401-412/16
Oct. 19, 1916 G.IV 25 600-624/16
Nov. 23, 1916 G.IV 15 649-663/16
Dec. 4, 1916 G.IV(LVG) 50 980-1029/16
Dec. 18, 1916 G.IV(SSW) 40 1055-1094/16 Delivered July 1917-February 1918
May 1917 G.IV(SSW) 40 200-239/17 Delivered Dec. 1917-Aug. 1918
Aug. 1917 G.IV(LVG) 50 100-149/17
In addition to these aircraft delivered to Idflieg orders, LVG built an additional 40 G.IV bombers that were delivered to an Austro-Hungarian order and used 230 Hiero engines built in Austria. The squadrons received these aircraft, Austro-Hungarian serials 08.01-08.40, in March-April 1918.

M.Dusing German Aviation Industry in WWI. Volume 1 (A Centennial Perspective on Great War Airplanes 84)

Luftverkehrsgesellschaft mbH, Berlin-Johannisthal, (LVG)

<...>
  In accordance with the wishes of the Inspektion der Fliegertruppen, LVG decided in September 1916 to resume construction of large fighter aircraft. This led to the start of series production of Gotha G.IV large fighters in early 1917. Further efforts to build its own large fighter did not bring any significant success.
<...>

P.Grosz, G.Haddow, P.Shiemer Austro-Hungarian Army Aircraft of World War One (Flying Machines)

Gotha G.IV(LVG) Series 08

  In lieu of the Friedrichshafen G.III bomber which was not released for export, on 23 December 1917 the LFT purchased six Gotha G.IV(LVG) bombers powered by 230 hp Hiero engines, followed by 14 in February and 20 in April 1918. The serial numbers assigned were 08.01 to 08.40, but only 39 were delivered as one bomber was demolished in a "typical landing accident" by an LVG factory pilot.
  The bombing squadrons, Flik 101/G, 102/G, and 103/G, received the new bombers in March-April 1918. Technicians labored long to correct the excessive engine vibration, caused by weak engine bearers and unsuitable propellers, which led to piping leaks, instrument and structural failure. In the summer of 1918, the Gotha bombers began limited night attacks against Italian cities and tactical targets such as troop concentrations, river crossings, and Caproni bomber airfields far behind the lines. Difficult to fly under any condition owing to a center of gravity shift after the bombs were dropped, pilots considered the Hiero-engined version even more demanding since the carburetor characteristics made it virtually impossible to synchronize engine revolutions to maintain a straight course. Records show that only a handful of the 37 bombers in frontline inventory on 1 August 1918 were fully serviceable. Similar to German experience, operational accidents (11) caused the greatest attrition, primarily due to engine failure. A further two were shot down, two damaged in an Italian bombing raid, and five demolished by a tornado-like storm. As the war progressed, bombing squadrons increasingly turned to the reliable, single-engined Brandenburg C.I(U) series 169 and 369 bombers. By late September 1918, the Gotha G.IV was virtually grounded, performing only sporadic training flights, as work to correct the engine problems continued.

Gotha G.IV(LVG) Series 08
Engine: 2 x 240 hp Hiero
Wing: Span Upper 23.70 m (77.75 ft)
Span Lower 21.90 m (71.85 ft)
Dihedral Upper 6 deg
Dihedral Lower 6 deg
Sweepback Upper 2.1 deg
Sweepback Lower 2.1 deg
Gap 2.22 m (7.28 ft)
Total Wing Area 89.5 sq m (963 sq ft)
General: Length 12.44 m (40.81 ft)
Height 3.90 m (12.80 ft)
Empty Weight 2265 kg (4994 lb)
Loaded Weight 3500 kg (7718 lb)
Maximum Speed: 140 km/hr (87 mph)
Climb: 1000m (3,281 ft) in 8 min 1 sec
2000m (6,562 ft) in 18 min 6 sec
3000m (9,843 ft) in 33 min 6 sec

E.Hauke, W.Schroeder, B.Totschinger Die Flugzeuge der k.u.k. Luftfahrtruppe und Seeflieger 1914-1918

01. — 010. Flugzeuge ausländischer Produktion (Самолеты иностранного производства)
08.01 — 08.40 Gotha G.IV (L.V.G.) 2 x FI 230

Журнал Flight

Flight, July 12, 1917.

SOME 1917 TYPE GERMAN AEROPLANES.

TWIN-ENGINE MACHINES, TYPE G. I AND G. II.

The Twin-Engine Gotha Three-seater, 520 h.p.

   This machine will probably be found the most interesting of those included in this series, as it played such a prominent part in last Saturday's raid on London. In view of this fact we have given the drawings illustrating it rather more prominence than those of the other machines.
   Although by far the largest of the German biplanes, the Gotha is not quite so large as our own Handley-Page biplanes, the sample of which, duly delivered to them at Lille, has undoubtedly provided the Germans with valuable data for their Gotha three-seater. As distinct from the Handley-Page, however, the Gotha has its propellers at the rear of the wings, and a considerable backward slope to the main planes. Also, the tail is of the monoplane type. The top plane is built up in two halves, attached to a central cabane, while the bottom plane is in three sections, one of which runs from the inner side of one engine housing under the fuselage to the inner side of the other engine housing. The main spars are of I section with three-ply flanges. Structurally the ribs are of little interest, but as they are at right angles to the spars they form an angle with the line of flight. This disposition also has the effect of offsetting the inter-plane struts, the front and rear ones of which are not in line. This is not shown in the sketch.
   The shape of the tail surfaces can be seen from the illustrations, and they are chiefly remarkable from the fact that they are, as already pointed out, of the monoplane type. Their area is, therefore, very small as compared with that of the tail surfaces of the Handley-Page.
   The long enclosed body is of rectangular section, and is covered with three-ply in front and with fabric at the rear. It is built up of four ash longerons and ash struts. The placing of the .three occupants is rather peculiar, being unsymmetrical. If the gunner in the front cockpit is seated centrally in the body, the pilot is placed on the left-hand side with his controls, leaving an open space between him and the starboard wall of the fuselage. This space is, as a matter of fact, provided to form a passage from the front to the rear gunner. Behind the pilot are two bomb racks, while further back still is the cockpit for the second gunner. Two guns are within reach from this seat, one is placed above the body, while the other fires down through a tunnel sloping backwards and downwards from the cockpit, permitting of firing in that direction.
   The undercarriage consists, briefly speaking, of two separate Vee chassis, one under each engine, and is, needless to say, built of streamline steel tubes. The engines themselves are housed in roomy nacelles resting on the bottom planes. They are 6-cyl. vertical Mercedes motors, each developing 260 h.p. at 1 400 r.p.m. The cylinders, which are 160-bore by 180-stroke, are in two groups of three each. There are four overhead valves and two sparking plugs to each cylinder, and the usual overhead camshaft is employed. The radiators are mounted in the nose of the engine housing, and under them are placed the oil tanks. The main petrol tanks are situated below the engines.
   The armament consists of three machine guns, one in front, capable of being fired in any direction within the hemisphere limited to the rear by the wings. A second is mounted on a transverse rail almost touching the top of the fuselage, while a third can be fired downwards and backwards through a tunnel in the body. In addition, there are several bomb racks carrying a total of 14 bombs.


Flight, December 27, 1917.

THE GOTHA TWIN-ENGINED BOMBING BIPLANE.

   WE are able this week to give our readers some further particulars and illustrations of the Gotha bombing-type biplane. From the various samples that have fallen into the hands of the Allies, it would appear that the Gotha bomber has been altered in design, as regards certain details, from time to time. The accompanying scale drawings, therefore, should be looked on as being approximately correct as regards the general design of the Gotha machine.
   The total span of the top plane is 78 ft. and that of the lower plane 72 ft. It will be noticed that the top plane, which is in two sections, is given a sweep-back from centre to tips, whilst the lower plane is similarly swept back only from the engine nacelles to the tips, the central plane section between the nacelles being "straight." The amount of sweep-back appears to vary according to type, but 5 # may be taken as being about correct. It will be further noticed that the ribs are at right angles to the spars, and the interplane struts are not, therefore, in line when viewed from the front as is general practice. The only advantage one can see in such an arrangement would be cheapness and ease in construction, but it is doubtful if this is really "worth the candle," when one considers the loss in efficiency that must arise therefrom, especially due to the resistance offered by the ribs should the fabric become a bit slack.
   The top plane sections are connected by steel tongues or plates on the inverted V cabanes supporting the plane above the fuselage - these tongues being inserted into clips on the wing spars.
   The main spars of the top plane are of I section ash with three-ply glued over the spindled-out portions on each side and wrapped with fabric, giving the equivalent of a rectangular section. The ribs are built up of three-ply webs, cut out for lightness and pine flanges. At each pair of interplane struts, and also between each pair, are tubular steel compression struts. These are held in sockets bolted on the spars, and each bay - which is practically square - is braced with single-strand cable. The spars of the lower plane are of similar construction to the top ones, except that pine is employed instead of ash.
   Some models are piovided with ailerons on both top and bottom planes, upper and lower ailerons being connected by steel struts. The ailerons on the top plane are balanced by a small portion extending beyond the wing tip as shown, and are hinged to the rear spars by strap hinges. They are built up of steel tubing, and are operated by a crank arm curving over the rear main spar with its end projecting in a slot formed in the plane - a practice common on German machines.
   Top and bottom planes are separated by three pairs of interplane struts a side. These are of steel tubing, streamlined by means of wood fairings and bound with fabric. The interplane struts are attached to semi-spherical fittings mounted on the main spars, and, as may be seen from one of the accompanying sketches, the wire bracing attachment is somewhat novel. The bracing cable is passed through a hole in a cigar-shaped steel fitting and spliced: a bolt on the spar fitting screws into the end of the cigar-shaped fitting, which is locked by a piece of wire. Adjustment is apparently made by screwing the cigar-shaped fitting by means of a tommy bar inserted in another hole drilled at the pointed end of the fitting. Portions of the trailing edges of both top and bottom planes are cut away to give clearance for the propellers.
   All the tail planes, stabiliser, fin, elevators, and rudder, are constructed of steel tubing, the various members being welded together. No wire bracing is, however, employed. The rudder and elevators are, like the ailerons, hinged with strap hinges, and the two elevators are coupled together to work in unison. The stabilising plane is braced top and bottom by steel tubes. The Dep. type of control is employed, the wheel column being mounted on a tubular steel rocking shaft supported in bearings on the lower fuselage longerons. The elevator control cables are attached to quadrants mounted above and below the rocking shaft. The aileron control cables are attached to the ends of a chain on a sprocket wheel mounted on the control wheel shaft. The cables pass over pulleys at the bottom of the control column, through the rocking shaft, and inside the lower plane to the ailerons. The rudder is operated by a pressed steel bar fitted with neat stirrups for the pilot's feet. The engine control is situated at the pilot's left hand.
   The fuselage is of almost square section, tapering to a vertical knife edge at the rear and a rounded point at the front. The maximum depth and width is about 3 ft. 6 ins. and the length is 39 ft. It is built up of four longerons, which are of laminated ash in front and pine at the rear, and cross struts, cable and wire braced.
   The longerons are spindled out in places, and where spindled have a covering of three-ply. The longerons gradually taper in section from the centre, and, on the whole, are not particularly striking as regards strength. The covering of the fuselage is of three-ply, tacked to the longerons and cross struts. Behind the rear cockpit the bottom of the fuselage is tunneled out so as to enable the gunner to fire rearwards and downwards - there are, therefore, no cross struts bracing the lower longerons at this part, which is indicated by a dotted line in the side elevation in the scale drawings.
   The arrangement of the cockpits is as follows :- In the nose is a circular cock-pit for the forward gunner, the gun being mounted on a semi-circular rail. Behind the front cockpit, and just forward of the main planes, is the pilot's compartment. The seat is a little to the starboard side, there being a gangway on the port side, leading from the front cockpit to the pilot's and after gunner's compartments. The latter compartment is situated at the trailing edge of the planes, and is provided with a gun mounting on the top of the fuselage, as well as the tunnel gun previously mentioned.
   The engines are each 260 h.p. 6-cyl. Mercedes, mounted some 15 ft. apart, and completely enclosed within housings of three-ply and sheet aluminium. A honeycomb radiator is mounted in front of the engine on extensions of the bearers, and below the engine are located the fuel tanks. The engines are supported on stout spruce bearers connected by tubular struts to the lower plane sections the whole of this engine frame is wire braced.
   Below each engine nacelle is a two-wheeled undercarriage, consisting of a pair of tubular steel V members, streamlined with wood fairings and fabric bound, carrying a tubular axle, which is, we believe, also streamlined by a fairing. The front members of the V's are connected at their lower ends by a tubular tie-rod, the anchorage for the cross-bracing being at the attachment of the tie-rod, as shown in one of the accompanying sketches. The shock absorbing system is of particular interest, in that rubber is not employed. Instead, two lengths of cable attached to the axle pass under pulleys mounted in the axle box, formed by the apex of the V, and up each of the chassis tubes to a long steel compression spring within the latter. This arrangement is shown diagrammatically in one of our sketches.