As an aside, another deHavilland of Canada product - the Twin Otter - is also build on a variety of concrete molds. If you taxi past the Viking hangar at Victoria International Airport, you will see a wide variety of concrete molds sitting on shelves. Those concrete molds are used to make the dozens of small aluminum fairings, etc. on Twin Otters. Though I suspect that many of the non-structural fairings on Viking-built Twin Otters are now made of fiberglass. Remember that Viking production of new Twin Otters grew out of an extensive network of overhauls and PMA (Parts Manufacturing Authority) until the weight of new components eventually out-weighed the original components in major overhauls and major repairs.
IOW Viking did not need to learn how to build many new parts by the time they started building all-new Twin Otters.
The moulds are referred to as
form blocks and are also commonly made of dense stable hardwoods
like "rock maple", phenolic composite, MDF, epoxy etc. depending on what's being made, complexity
of the shape and how much force is required in the forming process.
Something to remember about the "concrete" used to make a fuselage mould, male or female, is that it
ain't the same as what you use to pour a patio slab, sidewalk or even the floor in a multi-story building.
The mix would be quite different and the engineering of the form would take shrinkage into consideration.
Also the male mould used to build the Mosquito fuselages didn't require tolerances of a few thousandths
of an inch because of the nature of the airframe construction techniques, which fall under the classification
of
cold-moulding. A boat-building term that indicates that no heat source, steam or direct, was used to form
the wood used to construct the hull.
Frankly I'm also skeptical about the story that the wooden moulds used by DH in the UK actually changed
any noticeable amount with changes in temperature and humidity, properly seasoned timber used in the
methods used to construct the forms isn't going to change by any great amount with the change in seasons.
It's more likely that they went to concrete moulds at DH Canada because they could and it enabled them to
produce the required number more quickly.
There is a lot of mythology around the Mosquito one of the biggest being the tropical climate failures, which
Geoffrey De Havilland et al were quick to blame on the glue, despite an official investigation that determined
the majority of the failures were due to poor quality control during construction.
The fuselage of the Northrop designed Lockheed "Stars", Vega etc., was built up by layering the plys into heavy
concrete female moulds, a rubber bladder and fitted cover were bolted down and the bladder was pressurized
to press the layers of ply and glue together. Only one shape of mould was required because the fuselage was
symmetrical on all axes. Which was a clever decision in terms of simplifying the process of manufacture, almost
the exact opposite of the methods used to construct the Mosquito.
