Friday, January 20, 2017

Mosquito: Background information

As an old car mechanic, my first step on getting my hands on something obscure to (re)build is to get hold of suitable manuals. (A mechanic of old cars, or an old mechanic? No comment). In the absence of actual period manuals for the Mossie and the Merlin, I turned, as I often have in the past, to the aftermarket.

While these Haynes manuals are a little short on actual specs, such as cylinder head bolt torques or big end clearances, they do give a very nice overview of the subjects.

The Merlin is well known but its level of advancement is perhaps less so. With lots of aluminum castings and 4-valve SOHC heads, the Merlin presages modern automotive applications. In particular the bore:stroke ratio is decidedly modern at 0.90, compared to the classic Jaguar 3.4 at 0.78. (The Jag 4.2 got its added displacement from a bore increase, bringing the ratio to 0.87). One wonders why the British were so resistant to oversquare motors when Ferrari had been building the classic 3-litre at a ratio of 1.24, and beating the C and D-Types mercilessly as a result. The run of Jag successes at Le Mans in the 1950's was mainly due to Enzo being leery of disc brakes, because the Jags certainly couldn't keep up with the Ferrari 250s on the straights. And once Enzo adopted IRS and discs, it was pretty much all over for Jag.

Now that I have ticked off all the Jag fans out there, on to the Mosquito and the revolutionary plywood construction methods involved.

I haven't digested the whole thing yet, but some initial impressions are revealing.

The fuselage was built in two long halves, of balsa wood sandwiched between two layers of Canadian birch. Glues were similar to the ones still in use today, namely urea formaldehyde formulations. Total wall thickness was only 7/16"! Of course load bearing points were reinforced, and it seems the internal bulkheads were aluminum. The construction method allowed all the wiring, hydraulics and control bits to be put in before the two halves were glued and screwed together.

Wings and tail were also wood, with wooden spars covered with a plywood sheet. The wing was built as a single big piece, and is modeled this way in the Airfix kit. The completed fuselage was lowered onto the wing, the two pieces glued and screwed together, and the whole thing covered with fabric and airplane dope to seal it.

One big advantage of this approach was that precious reserves of aluminum were stretched, but another was that a large number of British furniture makers and coach builders could make the basic structure, freeing up existing metalworking industries for other war-time uses. Although I don't have numbers at the moment, presumably the power to weight ratio was better than similar all-metal planes, contributing to the Mossie's reputation for speed and manoeuverability.

Stay tuned, there is more to come, starting with the actual first gluing of parts.

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