Sunday, 13 November 2011

External Tanks

External Fuel Tanks

As stated previously, newly purchased Voyageurs differed visually from Labradors in that they had four extra glass panels in the nose and lacked the large external fuel tanks. The lack of external tanks on the Voyageur was reflected in dissimilar fuel capacities of the two types, which resulted in significant flight time and range differences. Voyageurs carried about 1,438 litres in the rear sponsons, giving it a flight time of about, two hours, whereas the Labrador could typically stay aloft for about four hours. When equipped with one internal fuel bladder the range of a Voyageur was extended to about three hours.  The need to carry an internal bladder to conduct SAR missions, meant some differences in the internal configuration of Voyageurs, chief among these was the relocation of spotter seats from the forward search blister to the window in the middle of the fuselage. The reduced range meant a reduced operationally capability not favoured by seasoned SAR crews.

For the modeler intent on modeling a Voyageur, it is worth noting that later model American CH-46s; E models I believe had larger sponsons, shaped like those of the Voyageur, but with an almost doubled fuel capacity.  Since the shape of the sponson was retained but the size enlarged, modelers need to be wary of this difference when selecting a kit to build a Canadian variant.

When the Canadian aircraft were purchased, it is possible that neither was equipped to dump fuel in an emergency or when necessary to loose weight for improved flight, and in particular when in the hover. Pictures of the Labrador, still wearing American civilian registration clearly show the tanks devoid of a fuel dump system as pictured below, however dump tubes are noticeable on the tanks after the aircraft is decked out in RCAF markings, the most notable being the CEPE cold weather trials logo. What is interesting about the dump tubes is that they are located on the bottom outside of the tanks and not on the rear end. This finding suggests, but cannot conclusively confirm, that the Labrador was delivered to the RCAF without a fuel dump system in place. Shortly after delivery, Labradors were modified with a fuel dump system characterized by tubes sticking out of the back end of each tank. One unanswered question is, “was 401 the only aircraft fitted with the early fuel dump system?” Voyageurs lacked this capability in any form until Speedline modifications.

Starting in 1979/80 as part of the Speedline modifications, Voyageurs received the larger Labrador style tanks purchased from Kawasaki in Japan.  Whereas Labrador tanks carried 3,408 litres of jet fuel, the new Kawasaki tanks carried 3,786 litres.  This gave both the Labrador and the modified Voyageurs an endurance of around four hours.  The Kawasaki tanks were also equipped with a fuel dump system.

Even when modified with Kawasaki tanks, Voyageurs and Labradors when parked side-by-side, were virtually impossible to tell apart simply by looking at the tanks, for all but those familiar with the helicopter variants.  There were, however two ways to differentiate the tanks: first by looking at the tank braces and secondly by looking at the grounding point on the tank. Like their Swedish cousins, Labradors were initially fitted, during acceptance testing by CEPE, with only one tank brace per side. Photographic evidence shows that Labradors may even have been purchased with the large tanks without braces. At any rate, while being trialed by CEPE, they had but one brace. The single brace also lacked end covers. While it is purely supposition by the time the tandem rotor marvel went operational, they did so with two braces per side. Labrador tank braces were flat with end covers while the braces on the Voyageur’s Kawasaki tanks were round bars.  Additionally, the covers over the brace attachment points on the Kawasaki tanks were larger.  As for the grounding points, it is located more to the center of the tank on the Labrador while on the Kawasaki tanks the grounding point is noticeably nearer to the fuel tank filler cap.  A small point to be sure, but a difference none-the-less.

As an aside, 442 Squadron fitted a single Labrador with wheel skirts intended to keep water out of the main wheel wells. The trial carried out before the summer of 1980 was intended to address problems of water in the wheel wells weighing the helicopter down as it tried to lift off the water.  The addition of the skirts however just compounded the problem so the trial was short-lived. The skirts were attached to the tank on either side of the main wheels. By simply looking at the tank around the wheel, it can be seen where the skirts would have been attached. Note that the red of the tank comes to an abrupt end and is replaced by yellow zinc chromate. !

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