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Fuel Flow Transmitter

Technical Information

Catalogue No: C0176
Category: Fuel Systems
Object Type: Sensor/Transducer
Object Name: Fuel Flow Transmitter
Part No: 270SK 3326?
Serial No: -
Manufacturer: Marconi Avionics
Division: Instrument Systems [ISD]
Platform(s): Tornado
Year of Manufacture: circa 1980
Dimensions: Width (mm): 76
Height (mm): 105
Depth (mm): 190
Weight (g): 1,381
Location: Rack RAA02 [Main Store]

No inscriptions on the main body but the two end plates are stamped with:
"270SK3326" plus "O/L" on one and "I/L" on the other.


This unit has an in-line rotor which suggests that it is more recent than C0780 or C1074.
The 270 Divisional Code was Servo and Electrical Instruments Division which probably became Instrument Systems Division.

The Marconi-Elliott Avionic Systems Limited fuel flowmeter system fitted to the Tornado comprises two engine-mounted true mass transmitters and a twin channel computer/indicator, which displays left and right engine flow rates on concentric pointers.

The transmitters apply measurement techniques similar to the Marconi-Elliott Avionic system supplied for the VC10, Phantom and Harrier aircraft. For the Tornado, however, a turbine is used as the driving element in place of the conventional electric rotor. Turbine speed is controlled by a spring-operated valve, which allows some fuel to by-pass the turbine at high flow rates.

This new design feature improved transmitter reliability, significantly reduced transmitter size and weight, eliminated the need for an electrical power supply and, allied with improvements to the pulse pick-off, has allowed the transmitter harness to be reduced to three wires in an enveloping screen.

System development was conducted by Marconi-Elliott Avionic Systems Limited at Rochester. In production the system was also manufactured by Teldix of Germany and OMI of Italy under the work sharing agreement.

Tornado has one Fuel Flow Indicator with two pointers, marked ‘L’ and ‘R’ for the two engines. The legend is kg/min up to 60kg/min. This pattern of Indicator is  installed in the Tornado GR1,GR4 (and other variants) with the range increased to 75kg/min. However a single pointer Fuel Flow Indicator appears to have been used on the same variants and this needs to be clarified.

'The published climb speed was 450 knots but, unless the pilot maintained a good instrument scan, the aircraft would inevitably go supersonic between 15,000 and 20,000 feet. That exercise also helped to generate great awareness of fuel consumption, the fuel flow meters being against the top stops.'

Instruments for the measurement of fuel tank capacity and flow seem to have been made by a number of companies such as Simmonds Aerocessories of London who advertised the product in 1952 and in that year, they acquired Firth Cleveland Instruments and as that became the overall company name from 1953 onwards they are found under the  Firth Cleveland Instruments name. Elliott Bros purchased Firth Cleveland Instruments in 1961 and the Aircraft Engine Instruments Division of Elliotts continued the brand from the Treforest works. This site produced fuel flow equipment such as the ‘Pacitor’ system of Fuel Tank Gauges and Fuel Flow Transmitters. Elliott (Treforest) Ltd also made portable testers for Pacitor capacitance gauging systems and Elliott fuel-flow meters. The former are used with the Beverley, Belvedere, Argosy 660 and long-range Britannia, while the latter are for fuel-flow systems in the refuelling portion of the Valiant tanker and in the Javelin, Buccaneer, Scimitar, Sea Vixen and Sea Venom. 

The business later transferred to Rochester where new types of fuel measurement and indication equipment was made.

The Transmitter is a transducer that measures the rate of fuel flowing through it and converts this to an electrical signal to drive a remote meter.There are a number of different measuring techniques:

Differential Pressure Flow meters
The Company made a range of Differential Pressure Flow meters for civil and military aircraft based on the principle of an orifice plate. The fluid flow is measured through the difference in pressure from the upstream side to the downstream side of a partially obstructed pipe. The plate obstructing the flow offers a precisely measured obstruction that narrows the pipe and forces the flowing fluid to constrict.  The accuracy however is poor at low flow rates.  A unit, Type 7801-11000, was designed for direct engine mounting to the Rolls-Royce Spey on the Trident. It had an accuracy of ±1.0% of actual flow rate over the cruise band. Variants of this type use Venturi tubes or flow nozzles but the principle is similar.

Velocity Flow meters
In a velocity flowmeter the flow is calculated by measuring the speed in one or more points in the flow, and integrating the flow speed over the flow area. The Company has produced Turbine Flowmeter which in general operate on the simple principle that if a fluid moves through a pipe and acts on the vanes of a turbine, the turbine will start to spin and rotate. The rate of spin is measured to calculate the flow.

Positive Displacement Flow meters
The positive displacement flow meter measures process fluid flow by precision-fitted rotors as flow measuring elements. Known and fixed volumes are displaced between the rotors. The rotation of the rotors are proportional to the volume of the fluid being displaced. The number of rotations of the rotor is counted by an integral electronic pulse transmitter and converted to volume and flow rate.

The earliest versions of this type have a 'paddlewheel rather than an in-line rotor but only seem to have been experimental.

The Company made gear meters having rotating gears with synchronized, close fitting teeth. A fixed quantity of liquid passes through the meter for each revolution. Shaft rotation can be monitored to obtain specific flow rates.

Another type in our Collection are rotary vane meters consists of equally divided, rotating impellers, two or more compartments, inside the meter's housings. The impellers are in continuous contact with the casing. A fixed volume of liquid is swept to the meter's outlet from each compartment as the impeller rotates. The revolutions of the impeller are counted and registered in volumetric units. Under high pressure a spring loaded disc is pushed open to allow a direct flow through.

Mass Flow meters
Mass meters measure the mass flow rate directly and have two main technologies; the Thermal Flowmeter and the Coriolis Mass Flowmeter

The thermal mass flowmeter operates independent of density, pressure, and viscosity. Thermal meters use a heated sensing element isolated from the fluid flow path where the flow stream conducts heat from the sensing element. The conducted heat is directly proportional to the mass flow rate and the temperature difference is calculated to mass flow.

Coriolis Mass Flowmeter uses the Coriolis effect to measure the amount of mass moving through the element. The fluid to be measured runs through a U-shaped tube that is caused to vibrate in an angular harmonic oscillation. Due to the Coriolis forces, the tubes will deform and an additional vibration component will be added to the oscillation. This additional component causes a phase shift on some places of the tubes which can be measured with sensors. The Coriolis flow meters are in general very accurate, better than +/-0,1% .

Vibrating Vane
The Company Research Lab FARL developed a novel Fuel Flow Transmitter  that used a vibrating metal vane rather than a rotor to measure the rate of fuel flow. The rate of vibration would be modified by the fuel flowing across it in a ratio proportional to the flow of fuel, and the varying vibration frequency was sensed and converted to a signal that could be used in further real time calculations and indications. The item proved to be either unsuitable, unreliable or not viable for full scale production.

See Engineering Toolbox

The Fuel flow business was important to Elliotts and a new fuel-flow test laboratory—the most advanced in Europe, if not in the world—was opened at Elliott-Automation's Rochester factory on November 20 1964 by Mr Neil Marten, Parliamentary Secretary to the MoA.

Enclosed in a blast-absorbing concrete emplacement, it was designed to test fuel flow equipment for the new generation of supersonic aircraft where fuel temperature of 150°C or higher would be encountered, and units would be required to operate at rigid standards of accuracy under extreme conditions of temperature (up to 200°C ambient) and in areas of extreme vibration.All controls and observers are in a separate building and several closed-circuit TV cameras give a view of critical parts of the system. Hot water and freon are used respectively as heating and cooling media. The laboratory is suitable for developing flow-measurement systems for supersonic airliners or VTOL aircraft. 

The Laboratory can achieve gravimetric calibration accuracy within an error band of ±0.1% of flow rate under the following conditions:

1. Flow rates from 50 to 120,000 lb/hr through three different bores of pipe.

2. Fuel temperatures from -55°C to +180°C.

3. Ambient temperatures from -60°C to +200°C.

There is also a Vibrator capable of producing a maximum thrust of 500 pounds with frequencies of up to 3,000 c.p.s. for resonance searches.

Mass-flow test measurement is effected by weighing the fuel as it accumulates in a tank mounted on a weighing balance, the whole unit being housed in a sealed container filled with nitrogen.

Fuel measurement systems such as Tank capacity, Fuel Flow rate, Fuel Remaining, Fuel Consumed were all big business for Elliott Bros (and subsequent names) and a snapshot of the platforms to which these were fitted can be gained from one of the Company databases:

AV8B, Buccaneer, Concorde, Dominie, EFA, Fiat Rig, Hawk, HS125, HS146 (BAe146), Javelin, Sea Venom, Sea Vixen, Valiant, Scimitar, P1127, Phantom, Phoenix, Trident, Transall C160, MRCA (Tornado), Finnish Hawk, G222, VC10, RB211 and RJ500 engines.........

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