SINGAPORE - One month into his new role as president of Pratt & Whitney, Bob Leduc is determined to “set the record straight” with airlines over plans to improve start times on the company’s PW1100G flagship geared turbofan on the Airbus A320neo.
Fixing the start time issue, which pushed back first deliveries of the A320neo into January, is the “biggest concern we have got,” Leduc told Aviation Week on the eve of the Singapore Airshow. At the heart of the matter is a condition known as ‘rotor bow’ which impacts virtually all gas turbines to some degree and, in the case of the PW1100G, has led Pratt to impose a more conservative start time to ensure the blade tips of the compressor rotors do not rub against the walls on start up.
Pratt’s plan will cut engine start time to those similar to today’s IAE V2500 by the end of 2016. Leduc says his priority now is to get the message out to geared fan customers, and to those airlines still weighing the PW1100G against CFM’s competing Leap-1A. “We call it setting the record straight. We’re going to show them everything we’ve found in flight test, everything we have seen and what we have done to fix it. I have nothing to hide here. You go to Lufthansa or Indigo and they’ll tell you the same thing. I describe it as the least number of issues I’ve seen on a new engine and I’ve done a lot. I’m going out to every airline in the world and saying ‘listen, I’m tired of those GE guys sliming me’ – we’re basically going to every airline in the world and saying ‘here is the truth.’”
Rotor bow, or thermal bowing, is normally due to asymmetrical cooling after shut-down on the previous flight. Differences in temperature across the shaft section supporting the rotor lead to different thermal deformation of the shaft material, causing the rotor axis to bend. This results in an offset between the center of gravity of the bowed rotor and the bearing axis, causing a slight imbalance and potentially reducing the tight clearance between the rotor blade tips and the compressor wall. Maintaining this clearance as closely as possible is critical to engine efficiency. Slower starting allows more even heating, eliminating differential thermal deformation.
“On an A320 it takes about 150 to 160 seconds to start both engines, and those are (IAE) V2500 kind of numbers,” says Leduc. “The initial PW1100G engines we put into service on Lufthansa take about 350 seconds. All engines have a bit of rotor bow. The V2500 had it, the PW2000, PW4000 and the CFM(56) had it, there’s not an engine built that doesn’t have a certain amount of rotor bow. We have taken an incredibly conservative approach here. We basically have dictated start times to ensure ourselves we will never rub a rotor out,” says Leduc.
Pratt is adopting a two-pronged attack on the issue. All production standard engines now feature a damper on the third and fourth shaft bearings to help stiffen the shaft. “The engines we are building in the factory today are to this bill of material and the first 20 engines we built were not. With these 20 we have a plan with the customers to go back and modify them as needed,” says Leduc.
The second prong is to collect data from engines in service and under accelerated testing, and to gradually reduce the start time based on real experience. “We are basically going to be able to match rotor clearance, engine by engine. And we are going to do it with an algorithm that will have greater and greater fidelity over time. By the time we get to June, it will be down to 200 seconds for start time and by the time we get to December we will be down to 150 seconds for start time. It’s all about how much data we accumulate and the level of fidelity in the algorithm,” he adds.
Leduc, who succeeded Paul Adams as president in January, says an abundance of caution is needed because “we have got a compressor that’s got lots of surge margin and you know our history of compressors has not been the best. I don’t want to sully the reputation of this compressor by doing something silly. I’ll be honest with you, the early operators like Lufthansa, are not thrilled about it. But they understand it, and they knew it when they bought it, and they understand the plan and they have great confidence in it. Lufthansa engineers have scrubbed it, and so have Airbus.”
The result will be start times that are “consistent with historical operations,” says Leduc. “CFM said they were down to 50 seconds start time. Number one, that’s only for one engine, not two. They’re probably at around 100 seconds. I don’t know whether they are at that or not, but I’m going to believe what they said. Can we get below 150? Probably – but to be honest I’m not sure the operator cares. 150 is normal airport operations.” As for crew reaction, Leduc says Lufthansa’s pilots said “they love the engine, just fix the start time. That’s not bad for something that’s revolutionary.”
Pratt also says the PW1100G is the only one of the family that has exhibited the issue. “It’s kind of curious, and I’m not going to say it is the cause, but it is certainly an indicator. This is the only engine we had to core mount to the pylon. All the other engines we could fan mount,” says Leduc.
Start time is not the only watch item on Leduc’s list. The new president also faces the critical challenge of steering Pratt’s production system through the largest ramp-up in its peacetime history. This will see deliveries of the PW1000G geared turbofan family go from around 20 in 2015 to 200 or more in 2016 and close to 1,400 by 2020. Deliveries of military engines are also set to triple to 300 over the same period while Pratt & Whitney Canada will see turbine deliveries climb to around 3,600 by 2020.
To bolster support for the PW1100G ramp-up Pratt has spent $1 billion on infrastructure and signed $22 billion worth of long term agreements with suppliers under contract. “We’re doing five programs simultaneously. We’ve never done that in the history of the company and now that big development bubble is going to get swallowed by manufacturing to produce. Then that bubble gets swallowed by customer support as the new product goes into service,” says Leduc. “Since I got back I added 180 people to the supply chain and will probably add 50 to 100 field reps because I think it is light. You have just got to scale it up but you have to be ready for it.”
