A common surplus engine due to a large number of military units. This engine is a popular choice for ground based applications such as power boats and Tractor Pulling. One apparent problem with Gnomes is missing starters. The Gnome ECU (Engine Change Unit) does not include the starter motor, making ground use sometimes awkward.

A second problem with a Gnome is due to the hot section construction. The gas generator section of a Gnome/T58 makes a nice turbo jet unit of up to 1000 LBs thrust. Unfortunately the power turbine nozzle forms the end support for the gas generator rear bearing. The nozzle is a complex assembly which cannot be simply removed and replaced with a propelling jet nozzle. The Power turbine nozzle has to be expertly modified to locate and provide services to the rear bearing and to remove gas restrictions. A number of the nozzle guide vanes may be removed but some have to remain reducing the efficiency as a jet.

Bench running of this engine is possible but apart from the Wirlwind Version, most units do not carry a power turbine governor or reduction gearbox. Single engine uncoupled operation (To provide electrical and hydraulic Services) was adopted in the Wessex installation, engine operation at idle with an unloaded power turbine is therefore possible. The power turbine is equipped with a overspeed cut out mechanism which shuts the engine down in the event of a helicopter transmission failure, this prevents runaway and destruction of the turbine disc. At 60% the unloaded power turbine turns at approximately 60% also, at 75%, as power builds, the PT approaches 100%. Whilst ground running these engines with an unloaded PT, DO NOT RUN THE ENGINE FASTER THAN 75% or with the IGVs opening.

A British Gnome engine may be easily operated for ground use by manualy controlling the throttle and moving the power lever. The complex analogue computer used in the helicopter is not needed for ground operation. The engine is equipped with a useful electric fuel cock actuator for starting and stopping. A single power lever controls the fuel delivery to the engine.

The Gnome/T58 engine features variable inlet guide vanes and early stage variable stator vanes. A complex mechanical system of levers can be seen around the outside of the compressor section, driven by a hydraulic ram, these levers alter the angle of the vanes according to engine requirements. At high rpm, fuel pressure is used to operate the hydraulic ram which increases the flow of air into the engine. This arrangement is an alternative to operating a bleed valve which is common on other engines equipped with axial compressor sections. The ram deploys at around 75% gas generator speed, sticking or incorrect IGV position will result in the engine surging.

The most useful model of Gnome (H1000) to have is the original Wirlwind Helicopter unit, this is fitted with a reduction gearbox mounted at the rear. A reduction ratio of 3.26-1 provides a useful output shaft speed of around 6000 rpm. The Wessex Helicopter is fitted with a twin engine installation known as the "Coupled Gnome" (H1200). The coupling gearbox incorporates the primary reduction and is not part of an engine change unit (ECU). A Wessex Gnome has no on board reduction gearbox.