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Twin boom-mounted cannons?

riggerrob

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Many designers have proposed mounting machine guns or cannons in the front of twin booms, but few have entered production.
Why?
Is it merely the hassle of aligning wing-mounted guns?

An early example was the (mockup) Focke-Wulf Flitzer, twin-boom, jet fighter. The Flitzer mockup had a cannon in the front of each tail boom, plus nose armament that resembled the production DH Vampire with a pair of cannons on the underside of the nose
The last know operational use was the Rhodesian conversion of Reims-Cessna 337s with Browning .30 calibre machine-guns mounted on top of the booms. They were primarily used by "Fire Force" against fleeing, light infantry guerillas. The Rhodesian War ended in 1980. Cessna 337 has a rare push-me-pull-you configuration with propellers in both front and rear of the centre passenger cabin. The front propeller prevents installing guns on the nose centre-line. I have never heard of anyone developing synchronization gear for post-WW2, horizontally-opposed, air-cooled engines (current production standard made by Continental, Franklin, Lycoming and Rotax).
 
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_Del_

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The last know operational use was the Rhodesian conversion Cessna 337s with Browning .30 calibre machine-guns mounted on top f the booms
I don't think this is accurate. They were fuselage mounted. The booms on a 337 don't extend through the wing, for starters.
 

Apophenia

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True. The guns on the Rhodesian Cessna were mounted above the wings - much closer to their roots than to the booms.
 

1635yankee

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I can't think of any piston single fighter with twin booms, except the J.21; in general, there are few single-engine aircraft with twin booms, mostly because the twin configuration has a) more wetted area, so more drag, and b) the twin booms complicate the design of the wing structure. I don't know where the guns were mounted on the (unbuilt) Bell XP-52.

Basically, if the nose is available, it's easiest to put the guns there, as the nose is likely to have more room than the wing.
 

MihoshiK

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I can't think of any piston single fighter with twin booms, except the J.21; in general, there are few single-engine aircraft with twin booms, mostly because the twin configuration has a) more wetted area, so more drag, and b) the twin booms complicate the design of the wing structure. I don't know where the guns were mounted on the (unbuilt) Bell XP-52.

Basically, if the nose is available, it's easiest to put the guns there, as the nose is likely to have more room than the wing.
Less problems with aligning the guns into a preset killbox at a specific range too. Just align the guns parallel to each other, and you're good to go.
 

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My favourite example - Tupolev I-12 / ANT-23. Twin-engined (push-pull) heavy fighter with two wing-mounted 76mm APK-4 recoilless guns that also served as tail booms (they actually were inside those booms, but it looket that way).
 

Arjen

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Single seat yes, but the D.23 had two engines. De Schelde S.21 was single seat, single engine but that prototype never flew. Nose-mounted armament BTW.
 
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riggerrob

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True. The guns on the Rhodesian Cessna were mounted above the wings - much closer to their roots than to the booms.

Yes dear Apophenia,
I reviewed Rhodesian Air Force photos and concluded that those machineguns were bolted to the wing root/fuselage junction. That put them just high enough and just wide enough to clear the front propeller.
 

riggerrob

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De Schelde S.21 was quite the revolutionary airplane with twin-booms, tricycle landing gear, a machine gun firing aft through the propeller shaft, forward-firing cannon, etc.
The attachment was miss-labelled by an American, WW2-vintage air model magazine. There were also ads for FW 189 balsa flying models. We wonder if WALLIES understood S.21's true identity until after the war.
De Schelde S-21 is also mentioned in Justo Miranda's book "Enemy at the Gates, Panic fighters of WW2." Miranda's book includes 1/72 scale drawings that include the forward-firing cannon.
 

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Justo Miranda

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The lack of indigenous aircraft engines was the main limitation of the Dutch aeronautical industry. When Fokker started the design of the successor of the D.XXI at the end of 1937, he made it taking into account that, in any future European war, it would be difficult to access the powerful 1,000 hp engines that were already being manufactured in Germany, France and Great Britain.

It was decided that the Fokker D.XXIII would be powered by two 500-700 hp engines, allowing to increase the CAP range using only one of them. A twin tail booms airframe, with short wingspan and tandem engines, was then chosen to obtain a fast aircraft. This configuration neutralised the gyroscopic coupling of the propellers and the power plants torque effect, giving the D.XXIII superior manoeuvrability compared to the Bf 110 and Potez 63 conventional twin-engine fighters. The D.XXIII could indistinctly use air-cooled engines of the types Walter Sagitta I.S.R. (528 hp), Isotta-Fraschini Delta (700 hp), Gnôme-Rhône 14 M-4 (700 hp) or liquid-cooled Rolls-Royce Kestrel V (755 hp), Hispano-Suiza H.S.12 Xcrs (690 hp) and Junkers Jumo 210 Ga (745 hp).
The project Ontwerp 156 was also considered. It was a version of the D.XXIII propelled by two 1,030 hp Rolls-Royce Merlin II which would have been the fastest fighter of its time.
The D.XXIII prototype flew for the first time in May 1937, surpassing the 500 kph and 9,000 m ceiling, propelled by two Walter Sagitta. Hit by a bomb on 10 May 1940, it never flew again.
The construction system of the airframe was the same than that of the D.XXI, but the idea was to use a wing entirely built of metal for the production version. It was armed with two 7.9 mm (synchronized) machine guns in the fuselage and two 13.2 mm FN/Browning heavy machine guns in the tail booms.


In opposition to the 'low tech' policy of Fokker, the De Schelde firm decided to enter the market of the fighters in 1938 with the S.21, a sophisticated twin tail booms design built entirely of metal, spanning 8.5 m, and incorporating a number of innovatory features. It would have been powered by a 1,050 hp DB 600 Ga, 12-cylinder inverted-Vee German engine driving a three bladed VDM, controllable-pitch, pusher propeller.
The armament would have consisted of one 7.9 mm MG 17 machine gun rear-firing through the propeller hub, for deterrent purposes, four 7.9 mm FN/Browning forward-firing machine guns and one flexibly mounted 20 mm Solothurn Tankbüsche S18-350 anti-tank cannon. During low-level attack, an automatic stabilising system controlling the ailerons and elevator, the pilot just had to operate the rudder to aim the cannon, which could be set in two positions: horizontal and 25 degrees downwards. The pilot used a retractable periscope to aim the MG 17. The propeller could be detached using explosive bolts when the pilot had to bail out.
The S.21 was expected to have excellent manoeuvrability and flight stability, due to the use of fixed wing slots and the position of the engine, installed over the CG. It was decided to change the engine to a 1,360 hp DB 601 Aa, with turbocharger, in March 1940, to improve performance at high altitude. The prototype c/n 58 was captured by the Wehrmacht in May. The production version, with DB 601 Aa, would have had an estimated maximum speed of 590 kph and 10,000 m ceiling.

Bibliography​



Books

  • Green, W., Warplanes of the Second World War -Fighters, Volume Three, MacDonald 1962.
Publications

  • Hazewinkel, H., “De Schelde S.21”, Air International, February 1974.
  • Hazewinkel, H., “Fokker D.XXIII”, Le Fanatique de l’Aviation Nº 60.
 

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Justo Miranda

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In February 1942, the U.S. Government placed an order for 1,600 Boeing B-29 superbombers, able to fly at 595 kph and 9,700 m of altitude. In April, the Koku Hombu Technical Branch issued a specification calling for a high-altitude interceptor with 800 kph max speed, 13,000 m service ceiling and 3,000 km range, armed with four 30 mm cannons. The specification was so demanding that most Japanese aircraft manufacturers decided not to submit projects.

The exhaust-driven turbo-superchargers were larger, involved extra piping and increasing an aircraft size, weight, complexity and cost. It is not possible to install them in a conventional single engined fighter and it use requires airplanes specially designed, with enough room for installation of the turbo, the intercooler and the heavy tubing system.

In the summer of 1942, the Tachikawa firm began the design of the Ki.94-I, a twin booms heavy fighter powered by two 2,000 hp Ha-211 Ru air-cooled radial engines (mounted in push-pull configuration) driving two VDM constant-speed propellers with 3.32 m of diameter. With the use of the new Ru-302 mechanically-driven superchargers, a service ceiling of 14,000 m was expected. In October 1943, the mock-up was presented to Koku Hombu, but IA experts decided that the plane was too heavy and with an overly complex propulsion system. The project was dropped.

Ki.94-I technical data

Wingspan: 15 m, lenght: 13.05 m, height: 3.85 m, wing area: 37 sqm, max speed: 780 kph, max weight: 9,400 kg, ceiling: 14,000 m, range: 4,520 km. Proposed armament: 2x37 mm Ho-203 and 2x30 mm Ho-105 cannons.
 

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Tony Williams

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In opposition to the 'low tech' policy of Fokker, the De Schelde firm decided to enter the market of the fighters in 1938 with the S.21, a sophisticated twin tail booms design built entirely of metal, spanning 8.5 m, and incorporating a number of innovatory features. It would have been powered by a 1,050 hp DB 600 Ga, 12-cylinder inverted-Vee German engine driving a three bladed VDM, controllable-pitch, pusher propeller.
The armament would have consisted of one 7.9 mm MG 17 machine gun rear-firing through the propeller hub, for deterrent purposes, four 7.9 mm FN/Browning forward-firing machine guns and one flexibly mounted 20 mm Solothurn Tankbüsche S18-350 anti-tank cannon.
The S18-350 would have been pretty well useless in aerial combat: as the name indicates, it was an anti-tank rifle, firing one shot at a time, from a 10-round magazine which presumably would have to be changed by the pilot (while still flying his aircraft in combat!). This gun actually saw service in a few Fokker TV bombers (IIRC) but at least in that installation it had its own gunner to aim and fire the gun and change the magazines. Still of little use, though.

It is instructive to realise that in c.1937 the Luftwaffe had a prototype He 112 fighter which was combat-tested in the Spanish civil war. This was armed with an MG C/30L 20 mm cannon which had a firing rate of 5 to 6 rounds per second from a 100-round drum magazine and, for a bonus, had a higher muzzle velocity than the S18-350 - yet it was considered unsatisfactory for aerial combat because of the low rate of fire!
 

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