BRISTOL HERCULES 264by Terry Jones
When
it became clear that the Hercules 230 that I originally acquired could
not be got back into running order I decided to acquire another engine
but this time to be sure that it there was a high probability that the
engine could be got running. In the event a Hercules 264 was acquired
from Keith Smith. The Hercules 264, which has a two speed single stage
supercharger, was designed for and only fitted to the RAF's Varsity
training aircraft which was designed to fly at high altitudes for bomb
aimer training. This engine had been the property of Francis Machin of
Gamelow Manor who died in 2007 and whose significant collection of aero
engines, including a Merlin, had been put up for auction. During a pre
auction viewing it had been found possible to turn the engine by hand
directly on the hand turning shaft without the handle. Also acquired
from the auction was a cut down four bladed De Haviland propeller of the
type fitted to RAF Hastings aircraft and built under licence from
Hamilton Standard of the USA. Whilst the Varsity was normally fitted
with a Rotol propeller the De Haviland propeller is smaller and neater
and more appropriate for ground running.
Getting
the engine home via Chris Wilson's Jet Art establishment in Bradford
was quite an epic. The final stage of which involved dragging the
engine half a mile up the street from the engineering works were it had been
unloaded using a crane and a forklift combination from the trailer upon
which it had been brought from Bradford. Once home the airbox and part
of the cowling had to be removed before the engine would just fit into
my garage.
The propeller will need to be fitted with a different CSU (constant speed unit) if the pitch of the propeller is going to be controlled by the engine.
The basic structure of the trailer built for the engine. Fuel will be carried in the two longitudinal tubes and oil in the forward cross tube with a battery box in front of that. The two axles are rated at one tonne each.
The engine suspended ready for transfer to its trailer.
The engine partially secured to the trailer. The job of completing the securing to the trailer will take place once the propeller has been fitted and the overall balance of the trailer is known.
The airbox, which has been modified, fitted to the "carburettor". The modification, which only involved rearrangement of the existing components, has only one air inlet and ensures that the air inlet is firmly closed when the engine is shut down, a useful fire precaution, and is held open when it is intended to run the engine. To describe the arrangement of the fuel injection components as a "carburettor" is not strictly correct
The internal arrangement of the airbox, which is anodised black.
Undoing the four large bolts allowed the distributer cap of the magneto to be removed to reveal that the contact breaker and other components were in prisdine condition.
The label on the magneto indicates that it was maintained at No 30 Maintenance Unit, at RAF Sealand in July 1973.
The propeller fitted to the engine, the blades having been cropped and balanced. The pitch change mechanism was in generally good condition, but some corrosion on the inside of the dome had to removed in order that the piston could move freely.
The propeller was fitted at this stage in order to check the overall balance of the trailer and the clearance of the propeller. The balance has worked out quite well whilst the propeller clearance is adequate. If I were to build another trailer for a Hercules there are few minor changes to the detailed dimensions that I would make to further improve the balance and propeller clearance.
The propeller removed again to enable the engine mounting at the rear of the trailer to be completed.
Six pictures showing the fabrication and use of a socket spanner to tighten the propeller shaft nut to a torque of 500 lb.ft.
 
This picture shows one of two electrically
operated ex RAF 24 volt aircraft linear actuators used to raise and lower the
rear bumper. When lowered to the ground the system will take a few
hundred kilograms of weight off the trailer and will steady it
The auxiliary gearbox with dynamo and tacho-generator mounted.
These three pictures show how the exhaust system was modified to allow the engine to be mounted 100 mm lower on the trailer. The cabin air heater muff was removed from the exhaust system.
The lever for changing the supercharger gear.
Two levers for controlling the throttle and the engine speed controller. The longer lever is the throttle.
Two more levers are used to cut off the fuel and air supply to the engine.
When the engine is shut down it has been arranged that all the levers are down.
The completed instrument panel. On the top row rev counter, boost gauge, oil and fuel pressure. On the second row cylinder head, oil and input air temperature and an ammeter. The bottom row of switches are magneto, engine starter, fuel prime button, oil prime switch and bumper up down control.
The project September 2009
The battery box completely wired showing the two 12v batteries, and the oil priming pump, actually the propeller feathering pump from a RR Dart engine. Also shown the two relays controlling the starter motor and the oil pump and the cutout for the battery charging circuit. There is a space for tools.
A well used tool, aquired from the widow of a former Bristol engineer, used for tightening the terminal on the sparking plugs.
Dipstick for checking the level in the oil tank.
The engine starting up on 13th April 2010. The smoke is from the inhibiting oil burning off.
The instrument panel with the engine beginning to warm up at 1100 rpm.
Running steadily at 1600 rpm.
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