| |
|
|
|
|
|
|
BRISTOL HERCULES 230
The completion of the Welland project created the opportunity to consider what to do next. It was decided not to undertake a Merlin restoration as there are already a number of ground running Merlins in existence and a further number in progress. The decision to undertake a project based on the Hercules was based on the fact that this engine was the second most important British engine, after the Merlin, in WW2 and that as far as is known there is no Hercules restoration project currently in progress in the UK, although there are two such projects ongoing in Sweden.
There are a number of issues both positive and negative concerning the Hercules. There are a number of post war Hercules engines available at reasonable prices in the UK, they are very much cheaper than Merlins. However, the best of these engines, ones that have been “inhibited” and can be “turned over” often do not have complete exhaust systems. The second class of engine are those that have not been “inhibited”, have been stored for a long time, often in the open, and do not turn over. An opportunity arose to acquire one of the latter class with a complete exhaust system, at a very reasonable price including delivery, so the decision made itself. The challenge of getting the engine turning over being all part of the fun with the added benefit of delaying a future decision about what to do next.
The engine was acquired form Bill Fern a member of Doncaster Aeroventure where the engine was displayed. It is Hercules 230 which was originally fitted to the Vickers Valletta C2 VX577 which was destroyed by vandals at the North East Aviation Museum in 1997. It would appear that it has not been run since 1969, almost 40 years, so it is not surprising that it is reluctant to turn. Early indications are that it has not had a lot of use, the oil in the sump was very clean and the starter motor has seen little use. The biggest problem will be the cylinders and the sleeves and the separating thereof a problem that one of the Swedish groups have successfully tackled.
|
UPDATE AUGUST 2008 |
Unfortunately the Hercules 230 has proved to be unrestorable with the resources we have available. The engine has therefore been placed in Solway Aviation Museum where it will be prepared as a static exhibit, something the museum are very good at. However, some very useful lessons have been learnt and some very useful parts for the next step towards getting a ground running Hercules have been acquired. |
It is now appreciated that available Hercules engines fall into three broad categories, not just two, the first category are engines that were switched off and just left after the last flight of the aircraft in which they were fitted. The aircraft being stored in the open for many years before being broken up and the engines becoming available. The second category are engines that were removed from aircraft with “hours” still remaining and were then inhibited with a view to further use and than stored under cover. The third category of engine are those engines that were overhauled, most likely by Hawker Siddeley Engines, well inhibited, stored undercover and never used. There are a number of Hercules engines that are available or might become available in the future in all three categories in the UK. |
The problem with the first category engines is that the sleeves and cylinders of the topmost cylinders will be so badly corroded that they cannot be taken apart without destroying the sleeves, which are quite fragile, and the pistons. A number of the lower cylinders will probably be able to be dismantled and the pistons, sleeves and cylinders reused. In order therefore to get a single ground running engine from this source one needs at least two engines to start with and lots of time. There is a project in Denmark that is taking this approach. An advantage of this category of engine is that it will probably come with a complete exhaust system, starter motor, sparking plugs and other components and maybe even a propeller. These engines generally have part or all of the engine mounting struts remaining. |
It has been shown that engines in the second category of engine, those removed from an aircraft with “hours” left and then inhibited, can be got turning and therefore have potential to become ground runners. A Swedish project has tackled an engine in this category and after removing a number of the topmost cylinders managed to get the engine to turn over. |
The engines with the greatest potential are those that have retained their “inhibitions” since having been manufactured or after overhaul. These can be recognised by by the presence of waxed paper covering the outlet from the exhaust pipes, the paper being secured by string going from one exhaust pipe to the next. These engines can come in two forms, either as bare engines on simple wheeled wooden or steel frames or as “power plants” on a “power unit transit stand”. These steel stands are 8ft 8in long and 4 ft wide. “Power plants” have all of the engine mounting struts and most of the ancillary components and part of the cowling structure present. |
Other ancillaries that will be needed to get an engine running include a fuel and oil priming pumps, instrumentation and switches, a boost coil and perhaps an ancillary gearbox and dynamo, as well as batteries for the starter motor, fuel and oil tanks and a propeller. |
The Hercules is a very underrated engine in the UK unlike in the Scandinavian countries where its qualities are more appreciated. In the UK it is possible to obtain an early post war, overhauled and pristine Hercules engine for the same price, about £2000, as one might have to pay for the remains of a crashed Merlin engine that has been dug out of the ground. Claims are often made of their being a pristine Merlins, still in its box, in a remote barn or sometimes in a cellar. These are the Holy Grail of the aero engine world. The value of a Holy Grail Merlin would be many tens of thousands of pounds, so a quest might be justified. They are highly valued because they are used in an ever increasing number of airworthy WW2 aircraft, whilst there are very few if any Hercules engines still flying. There can be fewer bargains, in terms of the shear mass of engineering skill and technology, than an overhauled Hercules. There were about 75 thousand Hercules engines manufactured, all “Made in England”, half the total number of Merlins. Nonetheless the Hercules was a very significant WW2 engine used in many front line RAF aircraft from the Lancaster to the Beaufighter, the Wellington and the Sunderland. After the war the Hercules was the most successful British piston aero engine far more successful than the Merlin in this role. The sleeve valve was used by Bristol in a range of aero engines, but predominately in the Hercules. The Hercules is an example of a unique type of engine which has a unique sound and is well worth preserving. The only present day manufacturer of sleeve valve engines, that the author is aware of, are RCV Engines who make a range of engines, in a very simple form, for model aircraft, see www.rcvengines.com. |
|
A vain attempt to separate the sleeve from the piston! |
|
|
|
|
|
|
|
|
|
|
