Editing Hawker Typhoon (section)

==Modifications 1941–1945==
[[File:Typhoonnew.jpg|thumb|''EK286'', "Fiji V" a brand-new aircraft, at [[Hucclecote]] airfield, April 1943 with the cockpit "car-door" open. The construction of the aircraft was sponsored by the Morris Hedstrom Fiji company]]
As was usual with many front line Second World War RAF aircraft, the Typhoon was modified and updated regularly, so that a 1945 production example looked quite different from one built in 1941. In the last months of the war, a number of older aircraft were taken out of storage and overhauled, sometimes seeing active service for the first time; for example, R7771 was from one of the first production batches, built in 1942 with the car-door canopy and other early production features. This Typhoon was delivered to, and served on the [[Fighter Interception Unit]] in 1942.<ref>Mason 1991, p. 558.</ref> In February 1945 ''R7771'' was listed as being in front line service on [[No. 182 Squadron RAF|182 Sqn.]]; by then it was fitted with a clear-view "bubble" hood, rocket rails and other late series features.{{refn|''R7771'' is listed as being shot down by [[Anti-aircraft warfare|flak]] on 28 February 1945. [[Warrant Officer|W/O]] F. W. Cuthbertson was killed.<ref>Thomas and Shores 1988, p. 209.</ref>|group=nb}}

===Carbon monoxide seepage===
The first problem encountered with the Typhoon after its entry into service was the seepage of [[carbon monoxide]] fumes into the cockpit. In an attempt to alleviate this, longer exhaust stubs were fitted in November 1941 ("Mod [modification] 239"), and at about the same time the port (left) cockpit doors were sealed. The Pilot's Notes for the Typhoon recommended that "Unless Mod. No. 239 has been embodied it is most important that oxygen be used ''at all times'' as a precaution against [[carbon monoxide poisoning]]."<ref>''Air Ministry'' 1943, p. 13.</ref> Despite the modifications, the problem was never entirely solved, and the standard procedure throughout the war was for Typhoon pilots to use oxygen from engine start-up to engine shut down.<ref>Thomas and Shores 1988, p. 30.</ref> In addition to carbon monoxide seepage, pilots were experiencing unpleasantly high cockpit temperatures; eventually a ventilation tube helped alleviate, but did not solve the problem. In addition two small, rear opening vents were added below the port side radio hatch, just below the canopy.{{refn| In April 1943, [[Flight Lieutenant|F/L]] A. O. Moffet of the [[Royal Aircraft Establishment|RAE Farnborough]] was attached to 486(NZ) Sqn in response to complaints about the overheated cockpits of the Typhoons. For a fortnight, "Moff" flew operationally with the unit. His tests showed that the cockpit temperatures could reach {{convert|135|F|C}}.<ref name ="Wheeler 1963">Wheeler 1963, pp. 80–86.</ref>|group=nb}}<ref name = "Sortehaug">Sortehaug 1998</ref>

===Tail===
A major problem, afflicting early production Typhoons in particular, was a series of structural failures leading to loss of the entire tail sections of some aircraft, mainly during high-speed dives. Eventually a combination of factors was identified, including harmonic vibration, which could quickly lead to metal fatigue, and a weak transport joint just forward of the horizontal tail unit. The loss of the tailplane of R7692 (having only 11 hours of flight recorded) on 11 August 1942, in the hands of an experienced test pilot (Seth-Smith), caused a major reassessment which concluded that the failure of the bracket holding the elevator mass balance [[Bellcrank|bell crank]] linkage had allowed unrestrained flutter which led to structural failure of the fuselage at the transport joint.{{Cn|date=March 2024}}

Starting in September 1942, a steel strap was fitted internally across the rear fuselage transport joint, although this was soon superseded by Mod 286 (modification number 286), in which 20 alloy "fishplates" were riveted externally across the rear fuselage transport joint, while internally some of the rear fuselage frames were strengthened. This was a permanent measure designed to stop rear fuselage structural failures and was introduced on the production line from the 820th aircraft; between December 1942 and March 1943, all Typhoons without Mod 286 were taken out of service and modified. Modified balance weight assemblies were fitted from May 1943. Finally the entire unit was replaced with a redesigned assembly from August 1944.<ref name="Thomas and Shores 1988, p. 20.">Thomas and Shores 1988, p. 20.</ref>

Although these modifications reduced the numbers of Typhoons being lost due to tail assembly failure, towards the end of the Typhoon's life there were more tail failures, this time caused by a change to the undercarriage latch mechanism in late 1944; in high-speed flight the undercarriage fairings were pulled into the slipstream, creating an uneven airflow over the elevators and rudder resulting in tailplane and then rear fuselage structural failure.<ref name="Thomas and Shores 1988, p. 20."/> In total 25 aircraft were lost and 23 pilots killed due to tail failures.<ref name="Thomas and Shores 1988, p. 20."/>

===Canopy===
[[File:Hawker Typhoon 4 ExCC.jpg|thumb|Late model Typhoon of [[No. 440 Squadron RCAF|440 (RCAF) Squadron]]. Rows of five-gallon [[jerrycan]]s dominate the foreground]]
The Typhoon was first produced with forward-opening "car door" style<ref group=nb>Another aircraft with this sort of door was the [[Bell P-39 Airacobra]]</ref> cockpit doors (complete with wind-down windows), with a transparent "roof" hinged to open to the left. The first 162 Typhoons featured a built-up metal-skinned dorsal fairing behind the pilot's armoured headrest; the mast for the radio aerial protruded through the fairing.<ref>Thomas and Shores 1988, pp. 16, 29.</ref> From mid- to late 1941 the solid metal aft dorsal fairing was replaced with a transparent structure (later nicknamed "The Coffin Hood"),<ref name="Thomas and Shores 1988, p. 20."/> the pilot's head armour plate was modified to a triangular shape and the side cut-outs were fitted with armoured glass; the first production Typhoon to be fitted with this new structure was ''R7803''. All earlier aircraft were quickly withdrawn and modified. From early 1942 a rear-view mirror was mounted in a perspex blister moulded into the later "car-door" canopy roofs. This modification was not very successful, because the mirror was subject to vibration.<ref name="Thomas and Shores 1988, p. 21.">Thomas and Shores 1988, p. 21.</ref> Despite the new canopy structure, the pilot's visibility was still restricted by the heavy frames and the clutter of equipment under the rear canopy; from August 1943, as an interim measure, pending the introduction of the new [[Bubble canopy|"bubble" canopy]] and cut-down dorsal fairing, the aerial mast and its associated bracing was removed and replaced with a whip aerial further back on the rear fuselage.<ref>Thomas 2010, p. 10.</ref>

Starting in January 1943, ''R8809'' was used to test a new, clear, one piece sliding "bubble" canopy and its associated new windscreen structure which had slimmer frames which, together with the "cut-down" rear dorsal fairing, provided a far superior all-around field of view to the car-door type. From November 1943 all production aircraft, starting with ''JR333'', were to be so fitted.<ref name="Thomas and Shores 1988, p. 21."/><ref name="Bentley 1975, p. 542."/> However, the complex modifications required to the fuselage and a long lead time for new components to reach the production line meant that it took some time before the new canopy became standard. In order to have as many Typhoons of 2nd TAF fitted before "[[Operation Overlord]]" as possible, conversion kits were produced and used by Gloster, Hawker and Cunliffe-Owen to modify older Typhoons still fitted with the car-door canopy.<ref>Thomas 2009, pp. 10–11.</ref>{{refn|It is believed that the first modified Typhoon was ''R8843'' ''DJ-S'', flown by New Zealander [[Wing Commander (rank)|Wing Commander]] [[Desmond J. Scott]], C/O of the [[Tangmere]] Wing from September 1943.<ref>Thomas and Shores 1988, p. 52.</ref>|group=nb}}

===Long-range fighter and fighter-bomber===
[[File:Hawker Typhoon 3 ExCC.jpg|thumb|Early production Typhoon with 45-gallon drop tanks and unfaired cannon; the shallow gull shape of the wing can be seen in this view.]]
From early 1943 the wings were plumbed and adapted to carry cylindrical {{convert|45|impgal|adj=on|abbr=on}} [[drop tank]]s,{{refn|These same drop tanks used by the Hurricane from 1940.|group=nb}} increasing the Typhoon's range from {{convert|690|nmi|km}} to up to {{convert|1,090|nmi|km}}. This enabled Typhoons to range deep into France, the Netherlands and Belgium. Some units, such as 609 Squadron and [[No. 198 Squadron RAF|198 Squadron]], were able to achieve notable success in air combat and ground attack operations using these long-range Typhoons.<ref name="Thomas and Shores 1988, p. 25.">Thomas and Shores 1988, p. 25.</ref>

As production continued, the Typhoon's role changed from a low-level interceptor fighter to a fighter bomber. Racks capable of carrying {{convert|500|lb|adj=on}} bombs were fitted to the wings from October 1942 and were first used operationally by [[No. 181 Squadron RAF|181 Squadron]]. By mid-1943, all Typhoons off the production line were capable of carrying bombs. Bigger, solid rubber, grooved "anti-shimmy" tail wheel tyres were introduced in March 1943 on all Typhoons from the 1,001st production aircraft, ''EK238''. The new tyres helped to make heavier, bomb-laden Typhoons more manageable during ground manoeuvres. With the introduction of the bomb racks, small extensions were added to the cannon shell case ejector slots. These allowed the casings to drop clear of bombs or drop tanks suspended from the wing racks.<ref name="Thomas and Shores 1988, p. 23">Thomas and Shores 1988, p. 23.</ref> Because of the vulnerability of the Typhoon's [[Water cooling|liquid-cooled engine]] cooling system to ground fire, some {{convert|780|lb}} of armour was added, lining the sides and bottom of the cockpit and engine compartments, as well as the [[radiator (engine cooling)|radiator]] bath.<ref>Thomas 2010, p. 11.</ref>

With the added weight of the bombs and armour, bigger [[disc brake|brake discs]] were fitted to the main wheels. At first this only applied to "Bombphoons", but eventually all Typhoons used these brakes. After tests conducted in 1943, it was determined that the Typhoon was capable of carrying a {{convert|1000|lb|adj=on}} bomb under each wing. With the increased load, it was decided that the extra take-off performance conferred by a four-bladed propeller was an advantage. This led to the adoption of a four-bladed propeller unit (de Havilland or [[Rotol]]) from early 1944. Coinciding with the new propeller, it was also decided that the larger tailplanes of the [[Hawker Tempest]] were to be fitted when tests showed that they improved the handling characteristics of the Typhoon when carrying {{convert|1000|lb|adj=on}} bombs.<ref name="Bentley 1975, p. 542.">Bentley 1975, p. 542.</ref><ref>Thomas and Shores 1988, pp. 23, 24.</ref> Problems were experienced with oil seal leaks from the new propeller unit and a growing number of Typhoons were held in Maintenance Units (MUs) awaiting the arrival of new seals from the U.S. Some 200 Typhoons were manufactured with the new Tempest tails and the three-bladed propeller. A modification programme was inaugurated but it took several months before a majority of operational Typhoons had the four-bladed propeller and enlarged tailplane.<ref>Thomas 2010, p. 15.</ref>{{refn|Early in its service life, the Typhoon airframe was prone to a high-frequency vibration while in flight, such that pilots reported that touching the cockpit walls was akin to receiving a mild electric shock.<ref>Thomas and Shores 1988, pp. 21, 23.</ref> Although not dangerous, it was uncomfortable, and a specially sprung seat was designed and fitted. With the introduction of the four-bladed propeller and larger tailplane it was found that not only was the performance and handling of the Typhoon enhanced, the vibration was much reduced.<ref name="Thos0912">Thomas 2010, p. 12.</ref>|group=nb}}

In June 1943, Hawker fitted a Typhoon with four steel "Mark I" rocket rails under each wing. Trials at the [[Aeroplane and Armament Experimental Establishment]] (A & AEE) and [[Air Fighting Development Unit]] (AFDU) showed that the combination of the [[RP-3]] rocket and the stable, high-speed platform of the Typhoon was promising. Carrying the eight rails and rockets, it was found that the top speed was reduced by {{convert|38|mph|abbr=on}}, with no adverse handling effects. As a result, the Mk I rails and RP-3s were first fitted to production aircraft of [[No. 181 Squadron RAF|181 Squadron]] in October 1943.<ref>Thomas 2010, pp. 13, 46.</ref> At first attempts were made to arm Typhoons with either bombs or rockets depending on requirements but it was soon decided that squadrons would specialise. By [[D-Day]], the 2nd TAF was able to field 11 RP ("Rockphoon") Typhoon squadrons and seven "Bombphoon" squadrons.<ref>Thomas 2010, pp. 16, 58, 88–90.</ref>

Later in 1944, attempts were made to increase the firepower by "double banking" rockets on each rail, enabling the Typhoon to carry 16 rockets. The problems involved in operating Typhoons from 2nd TAF airstrips meant that this was not much used, although some Typhoons did fly operationally with 12 rockets, using double-banked rockets on the inner rails.<ref>Thomas 2000, p. 25.</ref> When extra range was required, Typhoons could also operate carrying a drop tank and two rockets outboard of the tank under each wing. From December 1944, aluminium "Mark III" rails, which weighed {{convert|240|lb}} per set, replaced the steel Mk Is, which weighed {{convert|480|lb}}.<ref name="Thomas and Shores 1988, pp. 25-26.">Thomas and Shores 1988, pp. 25–26.</ref>{{refn|Starting in June 1944, new production Typhoons had the landing light in the leading edge of the port wing, although most units of 2 TAF omitted this feature and faired over the opening with a metal panel, giving the appearance that all production Typhoons were manufactured without the lights.<ref>Thomas 2010, p. 20.</ref>|group=nb}}

In late 1943, Mk III IFF replaced the Mk I and the tailplane tip to fuselage [[Identification friend or foe]] (IFF) aerials were replaced by a "[[bayonet]]" aerial under the wing's centre section. A [[Beam Approach Beacon System]] (''Rebecca'') transponder unit was fitted in 1944, with the associated aerial appearing under the centre section.{{Cn|date=March 2024}}

Once Typhoons started operating from forward landing grounds in Normandy, it was found that the dust clouds stirred up by propeller wash consisted of over 80 percent of hard, abrasive material which was damaging the Sabre engines. The [[sleeve valve]]s in particular were subject to excessive wear and it was calculated that engines would last for three take-offs. As a result, a "dome deflector" was designed and manufactured at great speed by Napier, and within a week most Typhoons had been fitted with it. In operational service these mushroom-shaped [[air filter]]s, which became red hot, had a propensity for being blown off the air intake at high speed whenever a Sabre engine backfired. They were soon replaced by drum-shaped filters designed by the [[Royal Aircraft Establishment|RAE]] and Vokes. These had "[[cuckoo clock]]" doors in front, which swung open with the pressure changes caused by engine backfires. This standardised filter became Typhoon Mod.420.<ref name="Shores and Thomas 2008, p.602.">Shores and Thomas 2008, p. 602.</ref>

At the end of June 1944, a decision was taken to fit tropical air filters as standard, similar to those fitted to the three Typhoons which had been sent to North Africa in 1943. One thousand sets of the filters were to be manufactured and fitted to front line Typhoons as Mod. 421. It was estimated that these could be fitted to all Typhoons on the production lines by the end of September. Research shows that late Typhoons starting in the ''RB---'' series were fitted with the filters, as were some rebuilt aircraft from earlier production batches. Mod. 421 appeared as a streamlined rectangular "hump", just behind the main radiator fairing and between the inner wheel doors, where the [[carburetor|updraught carburettor]] intake was located.<ref name="Shores and Thomas 2008, p.602."/>

A small, elongated oval [[Pitot-static system|static port]] appeared on the rear starboard fuselage in late 1944. This was apparently used to more accurately measure the aircraft's altitude.

[[File:Hawker Typhoon ExCC.jpg|thumb|A late production Typhoon with full RP-3 armament, a mix of SAP/HE 60 lb warheads and HE fragmentation head.<ref>Thomas 2010, pp. 13–14.</ref>]]

One Typhoon, ''R8694'', was used by [[D. Napier & Son|Napier]] for trials with the more powerful Sabre IV, cooled using an annular radiator and driving a four-bladed propeller. The new engine and radiator arrangement required substantial modifications to the forward fuselage and engine bearer structures. Although a maximum speed of {{convert|452|mph|km/h|abbr=on}} was claimed by Napier, it was decided that the modifications would not be worthwhile, mainly because of the promising development of the Tempest, and because the disruption to Typhoon production would not be sufficiently outweighed by any benefit achieved.<ref>Thomas and Shores 1988, pp. 20–21.</ref><ref>[http://www.napierheritage.org.uk/spip.php?article100438 "Napier Power Heritage."] {{webarchive|url=https://web.archive.org/web/20090212123126/http://www.napierheritage.org.uk/spip.php?article100438 |date=12 February 2009 }} ''napierheritage.org.'' Retrieved: 31 July 2011.</ref>

===Sub-variants===
In 1943, one Typhoon, ''R7881'' was converted to a prototype night fighter (N.F. Mk. IB), fitted with [[aircraft interception radar]]  (A.I.) equipment, a special night-flying cockpit and other modifications.
Also in 1943, five Typhoons<ref group="nb">''R8889'', ''R8891'', ''R8925'', ''DN323'' and ''EJ906''</ref> were modified to "Tropical" standard by fitting of an air filter in a fairing behind the main radiator housing. Three<ref group="nb">''R8891'', ''DN323'' and ''EJ906''</ref> underwent trials in Egypt with [[No. 451 Squadron RAAF]], during 1943.<ref name="Thomas and Shores 1988"/>

The Typhoon FR IB was developed in early 1944 and was used as a tactical reconnaissance fighter. In this version the port inner cannon was removed and three (one forward-facing {{convert|14|in|mm|adj=on}} and two vertical five-inch) [[F24 camera]]s were carried in its place.{{refn|Pilots soon discovered that the aircraft yawed to the left when the cannon were fired because the recoil of the two cannon on the starboard wing was not properly balanced by the single cannon to port; as a result the starboard inner cannon was also removed from some aircraft.|group=nb}} Few FR IBs were built, and most served with [[No. 268 Squadron RAF|268 Squadron]], starting in July 1944. The aircraft was never popular with the pilots, who preferred the older [[North American P-51 Mustang|Mustang Is and IAs]], and the inherent engine and airframe vibrations meant that photos were invariably blurred. As a consequence of these problems, the FR IB was phased out in January 1945..{{Cn|date=March 2024}}

===Naval designs===
In 1941, as Blackburn's [[List of Air Ministry Specifications#1930-1939|specification N.11/40]] high performance base defence fighter (that was carrier transportable) was delayed, the Admiralty looked at navalised version of the Typhoon as an alternative. The Hawker P.1009 design modified for the purpose had a new centre section, extending the wingspan to over {{convert|45|ft|m|abbr=on}}, and thus increasing the wing area; the wings themselves were to be [[Folding wing|folding units]], which swung and folded parallel to the fuselage, with the leading edges pointing upwards, much as did the [[Grumman F6F Hellcat]]. The rear fuselage was to be longer and a v-style [[Tailhook|arrestor hook]] and associated [[Aircraft catapult|catapult-launching]] gear was to be fitted. However it was not thought that the redesign and production would be any faster than proceeding with the N.11/40 and the Hawker "Sea Typhoon" submission was not taken up. The N.11/40, after changes to its role and Centaurus engine replacing the Sabre entered service postwar as the [[Blackburn Firebrand]].<ref>Buttler 2004 p. 173-175.</ref>

A Typhoon (''DW419'') was later allocated for carrier trials when the idea for using Typhoons (or Tempests) as carrier aircraft due to their stronger construction over the Seafires then in use came up in November 1942. ''DW419'' crashed in February 1943; by December the view was that the Typhoon was not suited to carrier use due to long take-off run and high stall speed.<ref>Buttler 2004 p. 175.</ref>