Hants and Sussex STAD LP Starter Mk12

Hants and Sussex (H & S) STAD 250 LP Starter MK12A-

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H&S Auto Diesels STAD 250 Specification MK12A
Output....................................250 Air Horsepower (2.2 Lbs/s @ 42 PSI)
RPM(Full)...................................….…………………………….................25,000

RPM (Idle)……………………………………………………………………………………………..15,000
Compressor..............................................Oversize Centrifugal Impeller
Combustion Chamber.....................................2 Reverse Flow Can Units
Turbine.............................................................Radial Inflow Impeller
Layout..........................................Single Spool with Accessory Gearbox
Starting.............................................….…………………..........Electric Motor
Ignition.............................................................2 High Energy Igniters
Fuel System...............................Mechanical Pump with Electronic Control
Lubrication..................................….………………………................Wet Sump
Accessories....................................….…………………............24V Alternator
Application............................……………….....LP Starting Cart MK12A and L


H & S LP Starter MK12

A wonderfully piece of quirky British Air Ministry engineering the Hants and Sussex STAD 250 sold by Auto Diesels Braby  known as the LP Starter MK12A and MK12L. A heavy duty stationary gas turbine engine developing the equivalent of 250 air horsepower. The gas turbine was trailer mounted and towed around the airfield to the awaiting aircraft to be started. A large hose conveyed the compressed air to the aircraft at a rate of around 120Lbs per minute at a pressure of some 40 PSI.

The STAD 250 engine consisted of an oversize centrifugal compressor driven by a large radial inflow turbine. The turbine was fed by two apposing combustor cans through a wrap around volute. A large casing enclosed the burner cans and was fitted with an air bled port and a regulating valve. The single over-size compressor was quite highly loaded in order to provide the required mass flow and pressure. If miss handled the engine could be prone to surging so a regulating valve was fitted to ensure the compressor operating conditions were not exceeded.

The engine was fitted with two duplex burners and some flow dividing valve work, the engine would initially light off on a moderate fuel flow and then accelerate under greater flow accompanied by a characteristic “howl” from the combustors! The control system on early units was fully hydro-mechanical with a gear type fuel pump and a servo air system to operate various valves and the centrifugal governor. Engines were also fitted with a thermostatically controlled exhaust temperature limiter similar to Garrett engines. Later versions were fitted an electronic governing system and incorporated an electrically operated spill valve.

The engine could be considered a rival to the Palouste air starter and also the American MA1A starting carts that were fitted with the Garrett GTC85.

An apparent weakness with these engines is the starter. A big heavy duty Lucas lorry-type CAV pre-engaged type unit makes hard work of the big high inertia compressor and turbine rotor. Another problem inherent with LP start carts is the environment in which they operate. The units were mostly stored out side that leads to the inevitable corrosion and contamination of  the fuel system leading to malfunctions. Also the simple relay controlled electrics could suffer too. The mechanically governed engines were fitted with a number of electrical pressure switches and relays to automatically sequence the start cycle.

The Mk12A unit featured a long trailer assembly with the engine stood in the middle and an exhaust silencer at the back and a fuel tank and control panel at the front. A MK12L unit featured the engine mounted at an angle to reduce space the silencer omitted.

H and S LP Starter MK12A LP Starter MK12A Instructions Exploded view gas turbine MK12A Sectioned view gas turbine engine MK12A trolley Auto Diesels Gas Turbine Air Starter Advert

Thanks to www.aviationancestry.co.uk for the Auto Diesels Ad

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