Boosting the power of the Sea King helicopter

Carson Helicopters Inc pioneered the first industrial use of helicopters in 1963. Over 40 years on, the US company uses its fleet of seven Sikorsky S-61 Sea King helicopters to deliver a range of services, but primarily fire fighting and transportation of personnel and equipment.

In 2003, Carson received Federal Aviation Administration (FAA) commercial certification for modified composite Sea King helicopter blades, which were developed to increase maximum lift load capacity to carry more water for its fire-fighting activities - a more attractive option economically than investing in new higher performance helicopters. The rotor blades use advanced aerofoil sections and a swept tip. The ‘Carson blades’ as they are known, claimed to increase maximum hover mass by 2,000lb at high altitude and to give the capability of increasing forward air speed by 15 knots for some aspects of flight.

The MOD Integrated Project Team (IPT) became aware of the capabilities of the Carson blades six years ago during a Sea King symposium and the Sea King IPT became interested in investigating the technology further but was prevented by funding and other operational commitments. However, some time later, the MOD looked at extending the life and capabilities of Sea King and Puma helicopters and Carson blades were again considered as a viable option, especially in view of its potential cost-effectiveness. The modified Sea King helicopter blades had only been certified in the United States for commercial use, so in December 2006, MOD declared the project an Urgent Operational Requirement (UOR). QinetiQ was selected as prime contractor with AgustaWestland to work on the tail rotor system.

A rigorous and intensive series of performance evaluation and flight testing was carried out on a QinetiQ-owned Sea King, which QinetiQ needed to fully instrument to collect the data required. The main rotor blades on the aircraft were replaced by modified Carson composite blades, manufactured by Carson Helicopters Inc, and the tail rotor was replaced by an AgustaWestland five-bladed tail rotor system. In a very short time frame, QinetiQ designed, manufactured and installed the instrumentation into the aircraft. The system was designed to allow onboard monitoring of all parameters in real time allowing trials to be carried out efficiently – monitoring of stress levels during flight gives more accurate results.

The main components of the instrumentation were numerous strain gauges to collect load survey data on the main blades, tail rotor blades and airframe structure, and airframe transducers to measure the vibration and stress, and other aircraft parameters. Most of the survey data was collected to make calculations on rotor blade fatigue. AgustaWestland used the same data for the rotor head and tail rotor analysis.

Staged testing
The first stage of the testing was held at Boscombe Down with the intention of proving instrumentation, and assurance that all aircraft systems were serviceable.

Subsequently, the aircraft was deployed via RAF C17 in Gunnison, Colorado, USA to continue the test programme. The location was chosen to carry out testing in a high-altitude and hot-temperature environment. The temperature and altitude are important factors in the testing as this influences the air density which in turn affects the forward speeds that can be achieved.

The intensive ‘high and hot’ flying programme lasted ten months and completed in October 2007. Both Carson Helicopters and AgustaWestland supported QinetiQ through both phases of the service modification. The project involved 230 hours of flight time and was completed within ten months.

The £5.25 million project, which started in January 2007, was completed when the independent safety advisors from QinetiQ managing the trial, submitted their final report to the Royal Navy and MOD for approval. The release was given to operate aircraft at new increased air speeds and lift capabilities in October 2007.

“The QinetiQ Carson blade test programme was carried out in partnership with the Ministry of Defence (MOD) Joint Test and Evaluation Group, known as ATEC, to determine whether the blades can provide a cost effective upgrade for Royal Navy helicopters to provide real performance improvement, benefiting them in their operations,” said Charles Ford, Project Manager of the Carson blades programme. “The result of the project was a resounding “yes” and the MOD is now bringing the blades into service quickly for use in operational theatres. The demanding trials programme was carried out by QinetiQ iX, Flight Engineering Services (FES) and Air Vehicle Concepts & Structures QinetiQ divisions and focused on delivery of specific capability enhancements to meet extremely tight timescales.”

A subsequent new programme started at Gunnison in January 2008, which set out to achieve higher forward speeds, which had been limited during the summer trials to prevent blade damage. The testing involved the fitting of additional instrumentation to collect a wider range of data. The environment for the new trials required low temperatures to test for higher speeds, which was the reason for testing during the winter months.

Much needed capability
The fitting of Carson blades to the Royal Navy’s helicopters has brought about significant improvements in performance. A conventional Sea King has a maximum lifting load capability, or hover performance, of 21,000 lb, which has now been increased by 2,000lb at high altitude with a significant increase in maximum forward speeds - up to 49 knots has been demonstrated. The service modification was made just in time to allow 846 Naval Squadron to conduct operational training in Cyprus with the newly modified aircraft. It has also enabled the Sea King HC Mk4 to be deployed in support of operation HERIC in Afghanistan – providing much needed capability in particularly extreme conditions of high temperature and high altitude where the air is thinner and increased power is required.

Lt Cdr Dave Maude of the Sea King IPT said about the project, “Within the MOD, the Carson blades programme is recognised as being demanding with regards to the short timescales involved and there has been a lot of admiration for the way that QinetiQ has tackled the programme and the amount of hours and effort that have been put in. Looking from the outside, the amount of work that individuals have given and their dedication is incredible.”

The relationship between QinetiQ and the other organisations was also praised by Lt Cdr Maud who said, “QinetiQ has attained a good working relationship with AgustaWestland and also the SK IPT, The Combined Helicopter Force (CHF) and Joint Helicopter Command (JHC) which have been involved in all aspects of the programme.”