Powering the A400M was always going to be a challenge, requiring the development of the Western world’s biggest turboprop, the 11,000-shp TP400-D6, and integrating a host of highly complex systems and associated software. “The complexity of the integration task on the TP400 has been bigger than it was for the Airbus A380,” said Nick Durham, president of Europrop International (EPI).

The problems with the engine, centering mainly on the robustness of the high-pressure compressor, now appear to have been resolved, the TP400-D6 having notched a series of recent milestones on its way to its expected first flight not long after the Farnborough show.

In March, the last of the four engines that will power the flight test A400M went to the final assembly line in Seville, Spain. while on the test stand the TP400-D6 passed the 1,000-hour milestone. Two months later it passed the critical bird-strike test, maintaining more than 80 percent power after absorbing the impact of a four-pound bird. The test followed water ingestion and 150-hour cyclic endurance tests. Most recently, in early June, the TP400-D6 and its Ratier-Figeac propeller began the all-important ground runs aboard the C-130 Hercules flying test bed at Marshall Aerospace’s Cambridge, UK facility. Those will lead to the first flight later this month, the company estimates.

EPI technical director Steve Morgan said the program has progressed at full speed, the eight test engines having accumulated more than 1,500 hours of ground test between them. He said the engines are built to the same basic standard as those aboard the A400M, although they feature “various design enhancements, and there will be further optimization of the overall propulsion system as we get on with the flying test bed program,” he said.

“We’ve come a long way in the last nine months,” said Durham. “We’re working hard now on in-service support and a joined-up way of supporting the A400M customers.”

Durham said the strength of the TP400 program has centered on the level of cooperation between the four partners–ITP, MTU, Rolls-Royce and Snecma. He revealed, however, that “some personnel changes were made within the consortium” following the emergence of problems with the compressor. “We focused on the way the companies worked together and took leads on the strong and weak points of each.” As a result, he says EPI is “very pleased with the adherence to the design and manufacturing program for the new compressor.”

Changes to the design focused on improving the robustness of the compressor blades and refining the engine manufacturing route. Morgan points to the enormous task of integrating the software associated with the full-authority digital engine control system. “It’s a step beyond anything we’ve done before,” he said.
Meanwhile, Marshall Aerospace continues ground run trials leading up to the first flight of the C-130 Hercules test bed. Head of systems design, Mark Johnston, describes the TP400-D6 test effort as “one of the most challenging projects around. It’s been very beneficial to Marshall because it has used every single one of our capabilities to the full.”

The company has been responsible for integrating the modern technology, digitally-designed and controlled TP400-D6 with the 1950s analogue-technology Hercules, a task made easier by Marshall’s considerable experience with the type. Preparation for ground and flight testing has involved the development of a simulator program to enable test pilots to get used to the unusual characteristics of the re-engined aircraft long before it takes to the air. “We believe we’ve done a good job on modeling,” said Marshall’s chief test pilot, Iain Young. “We’ll get the first feedback on handling qualities during the low and high-speed taxi runs and we’ll feed in the data to check we’ve got it right.”

The TP400-D6 produces almost three times the power of the Hercules’ Allison T-56 turboprops, and because it is physically much bigger there is only 10.5 inches of clearance between the Ratier-Figeac propellers and the fuselage and 18 inches to the number one propeller. “This means we have to be very careful about things like acoustic fatigue to the fuselage and vibration levels inside the aircraft,” said Young.
Both propellers are heavily instrumented to check strain levels when running.
Mounting the engine itself has been “fairly innocuous,” added Johnston. “We had to strengthen the wing box and adapt the A400M pylon to the wing. On that level it’s all been quite routine.” 

By the time of the airshow Marshall expects to have built around 14 hours of the expected 30 hours of ground testing leading to flight clearance. At present the company plans about 60 hours of flight tests aboard the Hercules, following which the Western world’s biggest turboprop should be ready to power Europe’s military airlifter into the air.