Wingco57 Posted October 20, 2013 Share Posted October 20, 2013 Mk 21 (type 356) By early 1942, it was evident that Spitfires powered by the new two-stage supercharged Griffon 61 engine would need a much stronger airframe and wings. The proposed new design was designated the Mk 21. At first the Mk 21 displayed poor flight qualities that damaged the otherwise excellent Spitfire reputation. The wings were completely redesigned with a new structure and using thicker-gauge light alloy skinning. The new wing was torsionally 47% stiffer, allowing an increased theoretical aileron reversal speed of 825 mph (1,328 km/h). The ailerons were 5% larger, and were no longer of the Frise balanced type, instead being attached by continuous piano-hinges. They were extended by eight inches, meaning that with a straighter trailing edge, the wings were not the same elliptical shape as in previous Spitfires. The Mk 21 armament was standardised as four 20mm Hispano II cannon with 150 rpg and no machine guns. The Griffon engine drove an 11 ft (3.35 m) diameter five-bladed propeller, some 7 inches (17.8 cm) larger than that fitted to the Mk XIV. To ensure sufficient ground clearance for the new propeller, the undercarriage legs were lengthened by 4.5". The undercarriage legs also had a 7.75 inch (19.7 cm) wider track to help improve ground handling. The designers then devised a system of levers to shorten the undercarriage legs by about eight inches as they retracted, because the longer legs did not have enough space in which to retract. These same levers extended the legs as they came down. The larger diameter four spoke mainwheels were strengthened to cope with the greater weights; post-war these were replaced by wider, reinforced three spoke wheels to allow Spitfires to operate from hard concrete or asphalt runways. When retracted the wheels were now fully enclosed by triangular doors which were hinged to the outer edge of the wheelwells. In other respects, the first production Mk 21s used the same basic airframe as the Mk XIV. The first true Mk 21 prototype, PP139 first flew in July 1943, with the first production aircraft LA187 flying on 15 March 1944. However the modifications over the Mk XIV made the Mk 21 sensitive to trim changes. LA201's poor flight control qualities, during trials in late 1944 and early 1945, led to a damning report from the Air Fighting Development Unit: "...it must be emphasised that although the Spitfire 21 is not a dangerous aircraft to fly, pilots must be warned...in its present state it is not likely to prove a satisfactory fighter. No further attempts should be made to perpetuate the Spitfire family." Supermarine were seriously concerned because Castle Bromwich had been converted to produce Mk 21s, and more were coming off the production lines daily. Jeffrey Quill commented that "The AFDU were quite right to criticise the handling of the Mark 21...Where they went terribly wrong was to recommend that all further development of the Spitfire family should cease. They were quite unqualified to make such a judgement and later events would prove them totally wrong." Spitfire F Mk 21 of 91 Squadron. After intensive test flying the most serious problems were solved by changing the gearing to the trim tabs and other subtle control modifications, such that the Mk 21 was cleared for instrument flying and low level flight during trials in March 1945. An AFDU report on LA215 issued that month noted that the Spitfire 21 was now much easier to fly; General Handling The modifications carried out to this aircraft have resulted in an improvement of the general handling characteristics at all heights...Conclusions The critical trimming characteristics reported on the production Spitfire 21 have been largely eliminated by the modifications carried out to this aircraft. Its handling qualities have benefitted to a corresponding extent and it is now considered suitable both for instrument flying and low flying. It is considered that the modifications to the Spitfire 21 make it a satisfactory combat aircraft for the average pilot.[44 ] Spitfire 21s finally became operational on 91 Squadron in January 1945. 91 Squadron had little opportunity to engage the enemy before the war ended, but scored a rare success on 26 April 1945, when two Spitfire Mk 21s shot up and claimed to have sunk a German midget submarine which they caught on the surface. With the end of the war most orders for the Mk 21 were cancelled and only 120 were completed. In 1946 40 Spitfire 21s were delivered to Shoeburyness; once there their leading edges were removed and destroyed in "lethality" tests. Some aircraft had less than five hours flying time. Mk 22 (type 356) The Mk 22 was identical to the Mk 21 in all respects except for the cut-back rear fuselage, with the tear-drop canopy, and a more powerful 24 volt electrical system in place of the 12 volt system of all earlier Spitfires. Most of the Mk 22s were built with enlarged tail surfaces, similar to those of the Supermarine Spiteful. A total of 287 Mk 22s were built: 260 at Castle Bromwich and 27 by Supermarine at South Marston. The Mk 22 was used by only one regular RAF unit, 73 Squadron based on Malta. However 12 squadrons of the Royal Auxiliary Air Force used the variant and continued to do so until March 1951. The Mk 22 was also used at Flying refresher schools. In May 1955 the remaining F.22s were declared obsolete for all RAF purposes and many were sold back to Vickers-Armstrongs for refurbishment and were then sold to the Southern Rhodesian, Egyptian and Syrian Air Forces. Well, I'm not Edgar, but if the above from Wikipedia is correct, I'd conclude that the Mk.21 used the original horizontal tailplane from the earlier marks with the enlarged mass balances. Edit: I have included the information provided by Erik here for completeness. Cees Here's the start of an attempt to create something that's not available in our scale.The Spitfire 21 was the first version of the Spitfire with a new wing. By combiningThe Revell / Matchbox Spitfire 22/24 ( thanks Dave) wings with a PCM Spitfire XIV fuselage.I started with the most difficult part, the wings.The original Spitfire 22/24 was made by Matchbox in the seventies, i remember buildingIt in 1977 and I was very impressed. However, the detail is now ancient but the wingsCan be used as a base to start from.The wheelbays need work as there isn't any detail. The kit walls were snipped off and sandedsmooth, the detail is represented with Plastic strip. The pics show the current state of progressCees 2 Link to comment Share on other sites More sharing options...
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