|Tony Neul's customised model of EE227 spent the summer of 2007 at Gloucester Folk Museum as part of a display to mark 90 years of the Gloster Aircraft Company and the centenary of the birth of Sir Frank Whittle. Click on picture for more details|
|THE FIRST OF THE TURBOPROPS|
|In February 1945 EE227 the 18th
production example of the Gloster Meteor F1 - the first
Allied jet fighter of World War II - went to Rolls Royce
at Hucknall, Nottinghamshire, for the installation of RB
50 Trent propeller turbines fitted with 7 11"
diameter Rotol propellers. EE227's first Trent powered
flight, with Eric Greenwood at the controls, took place
at Church Broughton on 20 September 1945.
This was the Worlds first flight by a propeller-turbine aircraft and EE227 is thus the ancestor of all the turboprop military and civil aircraft flying today. As will be seen in this article, many of these varied aircraft are still fitted with propellers built at Staverton. However, their technical development -and the development of the company that makes them - yields a story every bit as fascinating as the aircraft that they are attached to.
|Bristol Britannia 496 - formerly of RAF Transport Command - has been preserved at Kemble, Gloucestershire|
|DOWTY AND ROTOL|
|Dowty Aviation, named after its
founder and ex Gloster Aircraft
George Dowty, was set up in 1935 to build landing gear
systems and later branched out into aircraft hydraulics.
Then, in 1937, Rotol Airscrews was formed by Rolls Royce and Bristol Engines to take over both companies' individual propeller development programme - the market being too small to justify more than one business. The name of the new company was a contraction of ROlls-Royce and BrisTOL and the site near Staverton ( now Gloucestershire ) airport chosen as being part way between Bristol and Derby.
Rotol's propellers quickly gained an excellent reputation and equipped the Hawker Hurricane ( as built by the Gloster Aircraft Company ), Supermarine Spitfire and many other leading Allied aircraft of World War II.
As described above, the World's first turboprop flew with Rotol propellers in 1945 and the first scheduled turboprop airliner service - using Vickers Viscount aircraft - began in 1952. Indeed, the year that Queen Elizabeth II ascend the British throne also marked the first flight of the Gloucestershire built "whispering giant" - the four engined Bristol Britannia.
|A de Havilland Dove - similar to VP 952 preserved at RAF Cosford - was flown by Squadron Leader Neville Duke as the personal aircraft of Sir George Dowty. In the background is TG 511, a Bristol Hercules powered Handley Page Hastings similar to the Hastings stored outside by the Skyfame Museum at Staverton in the 1960s and 70s. Under the port wing of the Dove is a David Brown tractor also displayed in model form at Gloucester Folk Museum in 2007. Click on picture for more details.|
|Neighbours Rotol and Dowty merged
in 1960 to form the Dowty Rotol, later to be known as The
Dowty Group and in 1968 Dowty Rotol introduced the first
fibreglass propellers for hovercraft.
From 1960 to 1969 and again from 1970 to 1979 the twin engined personal aircraft of Sir George Dowty - a de Havilland Dove and later a Beech King Air - were piloted by Squadron Leader Neville Duke. Although most famous for setting a new World absolute air speed record of 727.63mph on 7 September 1953 at the controls of all-red Hawker Hunter WB188, Duke had an important and long standing connection to the early marks of Gloster Meteor.
A Hawker Siddeley Trident - as fitted with Smiths Autoland equipment - at RAF Cosford
|The sections of the Dowty Group
dealing with aircraft landing gear and hydraulics
collaborated with French opposite numbers Messier before
the two companies merged to form Messier Dowty, which
then split from the original Dowty Group.
The Dowty Group was taken over by the British Tube Investments (TI) Group in 1992, TI also owning a 50% share of Messier-Dowty, the other 50% being owned by French engine manufacturer SNECMA. SNECMA took over the TI shares in Messier-Dowty in 1998 and the TI Group merged with Smiths Aerospace in 2000.
Smiths was founded as a clockmaking company in 1851 and made airspeed indicators for aircraft as early as 1917. It was renamed Smiths Industries in 1966 and gained international recognition for its electrical engineering expertise when a Hawker Siddeley Trident test aircraft, equipped with a Smiths autopilot, became the first civil airliner to land in thick fog under fully automatic control.
Smiths Industries acquired BAe Systems' Marconi actuation systems division in 1999 and became Smiths Aerospace in 2001. The company employed more than 11 000 staff and had a $ 2.3 billion revenue in North America and Europe but by 2007 - seventy years after its foundation - what had started as Rotol Propellers had become part of the General Electric group. Further details can be found at
|Alenia C-27J Spartan MMCSX62127 of the Aeronautica Militare Italiana at the 2002 Royal International Air Tattoo at Fairford fitted with R391pattern Smiths Aerospace Dowty Propellers.|
|The erstwhile Smiths Aerospace
Dowty Propellers currently has two factory units at
Staverton: one producing new propellers and the other
involved in Maintenance, Repair and Overhaul (MRO) work.
In 2007, new propellers were being made by Smiths Aerospace Dowty Propellers for the in-production Alenia C-27J Spartan, Bombardier Dash 8-Q400, Lockheed C-130J Hercules and the Japanese Shin Maywa US-1A Kai flying boat. Smiths Aerospace Dowty Propellers have also made propulsion units for the LCAC (Landing Craft Air Cushioned ) hovercraft used by the US Navy.
Replacement propellers are also being made for the now out-of-production Swedish Saab 340 and Saab 2000 regional feeder aircraft and for the re-engined Chinese Shaanxi Y-8F600. The MRO side of the business meanwhile has a contract to refurbish the metal propellers of the Royal Air Force's C-130K fleet.
The CT7 powered Saab-Fairchild 340 was certificated as the World's first carbon reinforced all-composite bladed turboprop aircraft in 1984. The Saab-Fairchild 340 used R320 propellers, with each blade comprising a carbon fibre spar with a glass fibre shell filled with polyurethane foam and covered with an anti-erosion polyurethane coating. The shank incorporated an annular wedge trapped between an inner and light alloy sleeve. The R320 reduced drag to below that of a feathered propeller by windmilling at the optimum angle.
1993 meanwhile saw the Saab 2000 certificated with the first full FADEC ( Full Authority Digital Engine Control ) integrated electronic propeller control system. The first electronic constant speed and synchrophase control system was certificated on the Fokker 50 aircraft while the six bladed all-composite propeller system for the Lockheed C-130J was certificated in 1997 and on the Alenia C-27J Spartan in 2001. Bombardier's Dash 8-Q400 saw certification of the lightweight, single removable blade propeller system in 1999.
In the late 1990s, the future for propeller driven airliners looked bleak as the increasing popularity of regional jets meant few new turboprops were being built. However, in the last few years, the increasing cost of aviation fuel has meant that turboprops are becoming more and more popular and economical - especially on shorter sectors - and now it is the turn of the smaller regional jets ( up to 50 seats ) to suffer a decline in orders. Modern turboprop airliners can also offer reduced noise footprints for near-jet speeds.
|Royal Air Force C-130J Hercules C5 ZH884 of the Lyneham Transport Wing at the 2002 Royal International Air Tattoo at Fairford fitted with R391pattern Smiths Aerospace Dowty Propellers.|
|MAKING THE BLADES|
|The three or four layers of carbon
composite / fibreglass mixture on each propeller blade
take three or four minutes to be assembled on a machine
that looks like a cross between a weaving loom and a
spiders web. There are different numbers of layers on
different parts of the blade, which has a fibreglass
trailing edge and a lighning conductor braid through the
middle to minimise possible damage from electrical
storms. Resin is then added to the composite material in
the mould and the whole blade is then cured in an oven
before detailed imperfection analysis and possible
Contrary to popular belief, the outer parts of composite propeller blades can be easily repaired and in any case can have enhanced damage protection designed in to them. For example, each one of the four six-bladed R391 pattern propellers for the Lockheed C-130J military transport need to be more resistant to damage than the R408 equivalents on Bombardier's Dash 8-Q400 civilian passenger aircraft. Similarly, the C-130J needs ice resistant aluminium central propeller spinners while the Dash 8 can use lighter composite spinners.
A typical propeller will last around five years and 7 500 flying hours ( depending on environment ) although the Time Between Overhaul (TBO) on the Dash 8 is as much as 10 000 flying hours. In addition to the hundreds of staff employed at Staverton, Smiths Aerospace Dowty Propellers also has highly qualified service engineers permanently based around the World to repair aircraft on the ground at remote locations - thus minimising expensive downtime for the owners.
|No less than six of the older versions of the Lockheed C-130 Hercules represented a variety of air forces at the Royal International Air Tattoo at Fairford in 2002. Many of them were fitted with Dowty built metal propellers.|
|MAINTENANCE, REPAIR AND OVERHAUL|
|The one time Smiths Aerospace
Dowty Propellers MRO facility handles metal blades and
composites and also has a special cell for the care of
C-130 propellers - either four bladed types on the K or
six bladed types on the J variant. Each propeller takes
around 100 hours - during a ten day period - to dismantle
and rebuild. Firstly, all components are cleaned - either
with hot water or kerosene - and then analysed for
possible faults using non destructive X ray techniques.
Modern propellers may have only seven major "bits" - the blades and hub - but older examples can have ten times that number! Metal blades have large tolerances for balancing purposes that allow them to be skimmed to eliminate surface cracks. Composite propellers however - although able to have damaged material cut out and directly replaced - have such precise balancing tolerances that they have to be balanced in an enclosed and almost totally still-air environment.