How fuel efficient is a commercial airliner? A Boeing 747 burns approximately five gallons of fuel per mile or a total of 30,000 gallons (98 tonnes) on a flight between London and Hong Kong. This is a significant cost for an airline. The honeycomb seal-ring is an extensively used component, which has been proven to optimise the fuel efficiency of aero-engines, but the measurement of these seals presents difficult engineering challenges. Now, HAESL (Hong Kong Aero Engine Services Ltd) believes that it has successfully solved this challenge by incorporating Renishaw's TONiC incremental linear and rotary (angle) encoders within its new optical Seal Ring Measurement System (SRMS).

Eric Lau, Senior Engineer, who has been working at HAESL for almost 20 years, and Engineer Raymond Siu explain: "SRMS is a joint development system by HAESL and The Hong Kong Polytechnic University (PolyU), which has transformed the way we inspect honeycomb. Before SRMS, we used vernier callipers to measure the rings manually which is time consuming and relies heavily on the skill and experience of the operator. This new system has changed all of that. SRMS is not only faster, which increases work efficiency by 50 percent, but also maintains the consistency of the results by eliminating human error."

Honeycomb seal-rings

Honeycomb seals are fitted into mounting rings that are juxtaposed to the blades of the turbine. They are used to seal the radial gap between the rotating blades and the turbine wall to optimise both the fuel consumption and service life of the aero-engine. Rotor blades expand, however, as the operating temperature increases. The honeycomb seal-ring, therefore, provides a sacrificial surface that allows the rotating blades to cut into the seal and preserve the integrity of both the blades and the turbine wall. Hexagonal cell size on the ring depends on the rotor blade dimensions; cell diameter typically varies from 0.8 mm to 3 mm, while depth is up to 13 mm.