Turbine Airtrainer Continues Flight Testing

One of the priorities was to strengthen the airframe which was originally designed for only +3. 8g to -1. 5. The prototype CT-4 was stressed to +69 to -3g and featured a hinged clear perspex canopy, side by side seating and a dual stick control in place of the single central mounted spade handle. This aircraft was first flown on 23 February 1972 as the AESL CT-4A Airtrainer.

The CT-4As are powered by a 210hp Teledyne Continental 1O-360-H flat six piston engine. It is designed for a maximum speed at sea level of 155kt (286km/h) and an endurance of more than four hours at 65% cruise. A maximum rate of climb at S/L of 1,350ft/min, with a service ceiling of 17,900ft and a maximum TIO weight of 1,090kg (2,400lbs). The first sales of the CT-4A were for 24 to the Royal Thai Air Force, the first aircraft commencing service in September 1973. A total of 51 CT-4As were delivered to the RAAF while the RNZAF acquired 13 aircraft, plus 6 attrition airframes in 1977. Today the RNZAF has 15 serviceable aircraft. These aircraft are actually designated CT-48 and have a higher all up maximum weight of an extra 22kg (48Ib) to accommodate the additional avionics the RNZAF required. The CT-48 replaced the Harvard with the first example entering service at Wigram in July 1976.

A total of 96 CT-4s have been built with at least 82 still flying with one being found on the NZ civil register. This is the original prototype, ZK-DGY, and is owned and operated by NZ Warbirds at Ardmore.

For several early years AESL had been looking at a turbine powered CT-4 but due to their looming receivership were unable to proceed any further than the project study stage. However in January 1982, Pacific Aerospace Corporation bought the assets off the receiver and set about rebuilding the ailing aircraft manufacturer. It was now time to have a serious look at a turbine powered Airtrainer PAC had no airframes available to perform tests on and consequently an airframe was sought from the RNZAF. In 1977 NZ1940 Serial No 088, a CT-48, failed to get airborne on a training flight out of Whitecliffs near Christchurch. This aircraft crashed and suffered substantial damage, being destined to be reduced to spares. However when zero-eight-eight was officially written off it was decided to loan the airframe to PAC. It was delivered on 24 January 1989 with the terms of the hire being to repair the damaged airframe in lieu of hire. PAC now had an airworthy, repaired airframe.

For some time Murray McGregor of PAC had been working on designs for a turbine powered CT-4, but no serious development had taken place. On 15 October 1990 John Hansen joined PAC as chief development engineer. John had spent 17 years with several aircraft maintenance companies and had also worked for himself as a contract aircraft welder. On joining PAC, John Hansen and Murray McGregor set about setting up a turbine conversion program. Using Murray’s designs, a construction program was drafted. By late 1990 these designs were taken up for consideration by PAC and a full conversion and flight test program was mapped out. The job was a full time task for four engineers to get the CT-4C constructed for a successful first engine run on 8 January this year.

The 420hp Allison 250-817 turbine was installed in late December and also featured a PAC designed and built fully inverted oil and fuel system so that the aircraft can be flown for up to 30 seconds inverted. The propeller is a three bladed variable pitch, Hartzell. Additional instruments for monitoring the gas turbine engine were also added to the existing panel.

The project finally became airborne, so to speak, when on 21 January this year a 20 minute test flight was flown by John Muir, company chief pilot and military contracts manager. This flight involved two circuits at Hamilton airport – essentially involving checking engine functions and general handling characteristics. Muir reported back that the aircraft performed “damn well, so nice to fly and very quiet with absolutely no lack of power. ”

As the flight test program proceeds, some of the flight testing is also being carried out by Ralph Etheredge, also a test pilot and the PAC senior inspector for quality control. The program was proceeding in such a trouble free manner that in less than one month after first flight the little CT-4C had logged 26 flights with a total of 14 flying hours. The engine was running at up to 300hp by April with full power probably being reached by the time these words are read. Prior to this the CT-4C had been run up to 420hp on a static ground test run with no problems.

At 300hp, Muir stated, “The aircraft is so quiet, with more noise actually coming from the slipstream rather than the engine. ” At 300hp the CT-4C cruises at 165kt (306km/h) and has an impressive 2,000ft/min climb rate at 165kt. It uses about 80 litres of air per hour, has a clean stall of 58kt (107km/h) and a full flap stall at only 48kt (89km/h) with 30 degree of flap.

John Hansen has had to perform very few minor modifications since the aircraft has been flying, and only really to the inverted oil venting system. Really other than that the CT-4C has operated trouble-free, he said.

So now it is largely up to PAC marketing manager Bob Geer. He says “prospects look encouraging for the long term future development of the turbine trainer. ” The concept of the CT-4C is the proof of this turbine development. Once market research has been finalised and assessed, the future of a production model will be decided. This could then lead onto the second stage of the CT-4C turbine family, the CT-4RC-having retractable under-carriage. This model will only go ahead after further extensive market research because of the design of a new wing to accommodate the retractable gear. PAC are looking at a market price of around $US3. 4 million for this model. So firm sales will first have to be won for this expensive capital investment to be made by a small company such as PAC.

Meanwhile, the future of PAC, which is 75% owned by Australia’s ASTA, looks encouraging with production taking place at this time of 12 CT-4Bs for the BAe-Ansett Flying College at Tam- worth, NSW. The first aircraft departed NZ in April and delivery is to be completed by September. To this PAC has also continued with its depot maintenance on the RNZAF Iroquois and Strike- masters in addition to building up a spares support package for the A-4K Skyhawk.

An unusual sideline for PAC is that it is one of two constructors of the rudders for the USMC and US Navy hovercrafts. Used successfully in the Gulf, each craft needs 4 rudders of about 4 metres in length. PAC have completed 44 to date and have current ongoing orders with the US DoD. PAC also has an annual $1m contract with Boeing, via ASTA, for 747 Kruger flaps plus a contract with Aermacchi for Dornier 328 fuselage components. From their small hangars neatly tucked away amongst the trees at the end of the main runway at rural Hamilton, we have hopefully the beginnings of yet another episode in a long success story that while being Australia’s loss, was certainly New Zealand’s gain.