The Welkin was essentially an evolution of the Whirlwind built to Air Ministry Specification F.4/40. The most obvious feature was the enormous high aspect ratio wing, with a span of 70 feet (21.3 metres). For comparison, the Avro Lancaster four-engined heavy bomber spanned 102 feet (31.1 metres) or the Supermarine Spitfire Mk.VB single-engined fighter had 36.8 feet (11.2 metres). The Whirlwind's troublesome Rolls-Royce Peregrine engines were replaced by the Rolls Royce Merlin Mk.76 / 77. However, the most important feature was a pressurised cockpit. The last item required the majority of the effort in designing the Welkin. After extensive development a new cockpit was developed that was built out of heavy-gauge duraluminum bolted directly to the front of the main spar. The cockpit hood used an internal layer of thick perspex to hold the pressure, and an outer thin layer to form a smooth line. Heated air was blown between the two to keep the canopy clear of frost.

The pressurisation system was driven by a Rotol supercharger attached to the left-hand engine (this was the difference between the Merlin 76 and 77), providing a constant pressure of 3.5 lb/in² (24 kPa) over the exterior pressure. This resulted in an apparent altitude of 24,000 ft (7,300 m) when the plane was operating at its design altitude of 45,000 ft (13,700 m). This apparent altitude is still too high for normal breathing, so the pilot still had to wear an oxygen mask during flight. A rubber gasket filled with the pressurized air sealed the canopy when the system was turned on, and a valve ensured the pressure was controlled automatically. The pilot still had to wear a high-altitude suit, however, as he may have required to bail out at altitude.

The Welkin required a sophisticated electrical system. This was to minimise the number of seals and points of entry in the cockpit for the controls and instrumentation. It took an electrician experienced in the features of the Welkin four hours to undertake a pre-flight check of this system. The wings were so large that the high lift Fowler flaps of the Whirlwind weren't needed, and were replaced by a simple split flap. The extra wing area also required more stability, so the tail was lengthened to provide a longer moment arm. The armament was the same as the Whirlwind - four Hispano 20 mm cannon - but these were relocated to a tray in the belly, which facilitated loading and was less likely to dazzle the pilot from barrel flash.

By the time the plane was complete and rolling off the line, it was apparent that the Germans had lost interest in the high-altitude mission, due largely to successful interceptions by specially modified Supermarine Spitfires. In the end, only 75 complete Welkins were produced, plus a further 26 as engine-less airframes. Two Welkins served with the Fighter Interception Unit based at RAF Wittering from May to November 1944, where they were used to gain experience and formulate tactics for high-altitude fighter operations. A two-seat, night fighter version known as the Welkin NF Mk II for specification F.9/43 was developed but only two were produced as the design was not ordered into production.

The Welkin was seriously handicapped by compressibility problems exacerbated by its long but thick wings, causing the flyable speed range between high-incidence stall and shock-stall to become very small at high altitudes - any decrease in airspeed causing a "normal" stall, any increase causing a shock-stall due to the aircraft's limiting critical Mach number. This reduction of the speed envelope is a problem common to all subsonic, high-altitude designs and also occurred with the later Lockheed U-2. When W.E.W. Petter came to design his next aircraft, the English Electric Canberra, it was distinguished by noticeably short wings.

Planet Models has built up a reputation for producing fine resin kit and this one is no exception. Packaged in a sturdy cardboard box with lots of foam peanuts, the parts are in those compartmentalized bags that one so often sees. Now you'll probably be mad at me, but until I'm ready to actually start construction, I'll leave this one in its bags. You can see that the large parts are generally no more than one or two parts per segment, while the smaller bits are packaged together.

I gave all the bits a good going over and could only find a total of three pinholes on all the parts. One was on the rudder, one on a lower engine intake and a third was an incomplete mold of the 'spade' handgrip on the control column. While the one on the hand grip might be difficult, the others will be quite easy to repair. This kit also has reinforced landing gear to help bear the considerable weight of the kit. The wings are totally warp free with big honking alignment tabs, but one still has to wonder how well something that long and unsupported will hold up over the years in terms of sagging.

The kit includes a photo etched fret that contains some interior bits (like belts, rudder pedals and harness) along with inside canopy bracing, aerials, and engine intake screens. The interior has good detail in the sidewall and floor area and should be rather easily seen through the well formed vacuformed canopy, of which two are supplied. Probably the most difficult part of the build will be the wheel wells as the strut arrangement in there is rather complex. One thing I cannot tell is if the props were handed or not. No indication in the instruction to this regard.

Instructions are photo type that are becoming more popular in that they show where the bits are situated once the area is complete. It works fairly well here as the images are well printed and easy to see. Markings are provided for three aircraft. One is in the Dark Green/Ocean Grey over Medium Sea Grey scheme of the very early planes (no unit). The other two are both in Medium Sea Grey over PRU Blue with the FIU in May/July 1944 (the two mentioned in the historical background piece). Decals are by Aviprint so should provide no problems and are very nicely printed.

Perhaps not everyone's cup of tea, but you are most unlikely to find a better molded kit of it than this one. And that is a good thing as Planet Kits have always shown themselves to be superb builds. I think you'll find this one fits right into your collection as well.

http://en.wikipedia.org

May 2007

If you want one of these beauties, you can get it from www.coopersmodels.com