How we’re going to return RL249 to flight
A UK-built Mosquito
Thanks to the wealth of technical data we hold on the de Havilland Mosquito, with more than 22,300 original drawings in our possession, we are able to build our Mosquito in the UK. To help us do that, we have contracted Retrotec Ltd, one of the world’s foremost historic aircraft restoration companies to help us deliver the first UK-build Mosquito in more than 75 years.
Under the expert guidance of Guy Black, Retrotec has established a reputation for delivering some of the most authentic aircraft restorations in the world over the past 30+ years. The business, which is fully accredited by the UK Civil Aviation Authority, offers services including design, parts manufacture and reconstruction of complete aircraft, all delivered by highly experienced engineers. This will be vital for an aircraft destined to fly in UK airspace.
The remains of RL249 were recovered in 2010 from a site near RAF Coltishall, where the aircraft crashed shortly after take-off in February 1949. Since then those remains have been stored in a shed in East Anglia. There is very little, if anything, that is in an airworthy state amongst those remains, but what we do have, importantly, is the identity of that aircraft.
The first thing we needed to do at the outset of this project, back in early 2012, was to formulate an engineering plan, and in July of that year we presented this to the Civil Aviation Authority in a “case conference’ with the Heads of Department of the Safety Regulation Group. Our plan was accepted by the CAA, which effectively gave us the go-ahead to proceed with the project, and the exchange of technical data between both parties is ongoing.
Prior to September 2012, there were no flying examples of the Mosquito anywhere in the world. Clues as to why that was the case lie in the trio of facts that the aircraft’s fuselage is constructed from a sandwich structure composite of three-ply birch and balsa bonded together with a milk protein-based glue called casein, and formed on mahogany or concrete moulds.
These moulds were destroyed – along with the main wing assembly jigs: many after the war, as production numbers fell, and the rest when production ceased in the early 1950’s. They were simply seen as surplus to requirement, and the result was no new Mosquitoes could be built.
The casein glue added its own issues to the longevity of the aircraft. After a time and under certain conditions the adhesive would fail, allowing the wood that formed the fuselage and wings to begin a delamination process – i.e. the ply would start to come apart. This is not ideal for an aircraft. This is compounded, as far as returning a Mosquito to the air, by the fact that it is very unlikely that 70 year old wooden structures could pass the CAA’s rigorous airworthiness tests, making it unfeasible to simply take a museum piece and return it to flight.
The CAA would not allow us to go ahead if that was our planned route. There is also the emotional side to the argument for returning a museum piece to flight: so much reconstructive work would need be carried out, that the result would be an essentially new build. This would be unacceptable as museum Mosquitos have their own histories and in many cases have actually seen action and for this reason alone are important airframes which anyone interested in conservation would be loath to dismantle.
The build will be carried out by our main contractor, Retrotec Ltd, here in the UK, supported by the proven expertise of engineering contractors in New Zealand. Many British companies will be involved in the work, and parts, sub-assemblies, engines and propellers.
There are many options regarding the type of Merlins which might be used in a Mosquito, and despite the fact that all Merlins look similar, they vary widely in power and rated altitude. We have decided to go with Packard-built 60 Series Merlins, as these have a little extra power, despite the fact that the second stage supercharging will not be used (the maximum permitted altitude allowed by the CAA will be 8,500 ft above mean sea level and a maximum speed no greater than 250 knots).
The tragic loss of the BAe Mosquito, RR299, at Barton, has been thoroughly studied by the Air Accidents Investigation Branch and a full report was issued. The People’s Mosquito has taken into account the conclusions of the AAIB, and will be fitting Bendix injection carburettors to the Merlins on RL249, which will preclude fuel starvation under certain flight conditions. Thus, our Mosquito will be inherently safer.
After a lot of research we have decided to go with a ‘late war’ build standard for the hubs and propellers, which means that RL249 will have ‘paddle bladed’ propellers similar to those used on the Avro Lancaster and Douglas Dakota, as spares are more readily available.
The speed with which we can get the aircraft built and flying is largely dictated by the speed with which we can raise the required funds, and also how successful we are at negotiating phased payments with our key suppliers.
Although every effort will be made to use authentic materials and construction techniques, inevitably, material sciences and metallurgy have moved on. There are modern equivalents for some of the original aluminium alloy sheet specifications used in the 1940s for example, but consultations with the CAA will allow for the most appropriate modern materials to be selected for each component, taking into consideration application, fatigue life, etc., the intention being to give RL249 a stronger, more durable structure, than its wartime predecessors. In essence, RL249 will have a much longer life than the original Mosquitoes.
Following consultation with Aerowood we have specially selected a two-part gap-filling, water-repellent epoxy adhesive, for which the manufacturer has guaranteed a service life of at least 50 years.
We will source our supply of Canadian Spruce from the same forest area that was used by de Havilland Canada to build their Mosquitoes during WW2. It is of the highest quality available. Other woods used will include birch, Ecuadorian balsa and ash.
RL249’s UK base
The People’s Mosquito will house, maintain and display the aircraft in Britain. The reason for building this Mosquito is to ensure that we have our own flying example right here, in the UK. We have had a number of offers from interested parties, but RL249’s permanent home once she is in the UK has yet to be determined, as many factors have to be considered. Not least of these is access for the general public to enjoy the Mosquito. One of our stated aims is the education of current and future generations, and we plan to allow as much access to RL249 as possible, where necessary maintenance activities allow of course. So this will be key in our choice of base. It is most likely at the moment that we will be basing the aircraft in either Lincolnshire or Cambridgeshire.
Budget and build time
We expect the budget to be in the region of £8m. The exact amount will depend upon the time taken to raise the required funds, as, the longer it takes, the greater the costs will become. At the present time, we estimate the cost of the fuselage and wings to be in the region of £1.1m, the engines and propellers (with one spare) to be in the region of £550k.
Fitting out and completing construction of the aircraft will cost in the region of £3.3m. The remainder of the budget will cover the costs of purchasing and selling merchandise to raise funds for the project, plus the running costs of the charity. Note that all those working for the charity are unpaid volunteers, so there are no salaries included in the budget.
After close consultation with Retrotec, and based on their extensive experience of building and restoring warbirds under UK regulatory requirements, we are working to a five year build build plan.
Once RL249 is in the air and based in the UK, we estimate annual costs in the region of £300K pa. That money will come from ongoing public donations, corporate sponsorship, donations in kind from companies, grants, sales of branded goods Club subscriptions and income from airshow participation. We will also be looking at Heritage Lottery Funding at some time in the near future.
If you would like to help us achieve our goal of returning RL249 to flight, please consider making a donation via our Donate page. Alternatively, have you considered joining our Club? As a Member you’ll have access to exclusive material, a quarterly newsletter and other benefits. See our Club site at www.peoplesmosquitoclub.org.uk.
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