Design and development of standalone fuel quantity digital display system

for ALH on ground

Synopsis:

The advanced technology has made the Helicopter division of HAL to build series of

Advanced Light Helicopter (ALH) in 2000-2001.Example of such ALHs are Dhruv and

Rudra. The ALH is a multi-role, multi-mission helicopter in 5.5 tonne class, fully designed

and developed by HAL.ALH is designed to meet the requirement of both military and civil

operators. ALH is designed to perform both utility and attack roles. With a twin-engine

configuration, ALH allows continued flight virtually throughout the flight envelope. ALH

incorporates a number of advanced technologies; Integrated Dynamic System (IDS), Anti-

resonance Isolation System (ARIS), Full Authority Digital Electronic Control (FADEC),

Hingeless Main Rotor, Bearingless Tail Rotor, and Automatic Flight Control System.

Fuel system allows to pump, manage, and deliver fuel to the propulsion system of

ALH.The purpose of ALH fuel system is to ensure continuous supply of fuel to both engines

under all operating conditions. The fuel is contained in five flexible fuel cells/tanks which are

located, under cabin floor boards. There are five fuel tanks and two expansion space cells.An

additional auxiliary fuel tank of 250 litre capacity can be mounted in the cabin when required.

Fuel tanks are made of flexible light weight hycalite material. The cells are manufactured by

a process of high frequency welding. One gravity refuelling point and one pressure refuelling

point are provided in undercarriage version and only one gravity refuelling point is provided

in skid/wheel version. These points are provided in front main tank on starboard side of

fuselage. The five different fuel tanks are:FMT(Front Main Tank),MMT(Middle Main

Tank),RMT(Rear Main Tank),ST1(Supply Tank 1),ST2(Supply Tank 2).Fuel is stored in

three main tanks and two supply tanks. The tanks are flexible and crashworthy type having

550% elongation so that during crash these tanks can take the shape of structural

deformation. In addition, the supply tanks are provided with self sealing protection. When

bullet is piercing these tanks, the self sealing layer comes in contact with fuel and forms foam

thereby closing the hole created by bullet heat.

Fuel gauging probes is installed in each tank to sense the fuel quantity. The probes are

of capacitance type. Probes are provided with weak/fragile section so that during crash the

probes will break and the broken piece will remain inside the tank without piercing the tank.

The probes sends signal to the fuel gauge in cockpit which displays the fuel quantity in digital

formats. Fuel low level sensors are integrated on the probes installed in supply tanks. These

are mechanically integrated with supply tank probes but they are electrically independent.

The fuel low level indicator comes on, when the fuel quantity in supply tank comes down to

40kg.

Fuel probes are installed in each tank to sense the fuel quantity. The probe is a

cylindrical capacitor and works on capacitor principle. This project deals with development

of logic to determine and display the quantity of the fuel for intermediate and undefined fuel

levels in the probe. The frequency output of the probe is fed to the cpu, where the logic is

performed and the quantity of the fuel is digitally displayed. The calibrated values of the fuel

level are stored in the memory of the cpu.

Fig: