Rolls-Royce has begun ground tests of a modified Trent 1000 in which both the fan blades and fan case are made from composite material, marking a key step toward development of the company’s next-generation geared UltraFan engine family.
The fully integrated tests mark the finale of the Advanced Low-Pressure System (ALPS) technology demonstration program that until now has separately validated the carbon/titanium (CTi) fan and composite fan case. The move to adopt lighter composite materials is imperative for the bigger UltraFan-family variants, which will have larger diameter fan sizes than current engines for the same relative thrust, and a very high bypass ratio of 15:1 or more.
The fan diameter of the UltraFan demonstrator is expected to be larger than the 118-in. dia. fan of the Trent XWB, currently the biggest engine in the company’s inventory. Senior Rolls officials have previously said fan diameters for the big new engine could be as large as 140 in. For comparison, the General Electric GE9X, currently the world’s largest engine dimensionally, has a 134-in. fan dia. On a large twin, Rolls estimates ALPS technology will save more than 1,500 lb. in weight per shipset.
“It’s all about bringing the composite fan and case together as a system,” says Phil Curnock, chief engineer for Civil Aerospace Future Programs. “We’ve been testing the fan system, but now we want to see how it works with the composite case as a total system, how it moves and reacts.” The evaluation, which began in mid-February at Rolls’ Derby, England, facility, includes composite annulus fillers in the sections between the roots of the blades, and will cover performance and operability testing.
“We will also get an understanding of the complexity of things like flutter and vibration modes, because there could be something different in the interaction between the blade and the case. We shall also be looking at tip clearance and how it changes with varying temperatures and speeds,” Curnock says. The performance of the baseline CTi fan was evaluated in 2014 on the company’s Tucson, Arizona-based flying testbed, using a Trent 1000 with a conventional titanium fan case.
The validation tests, which are expected to take around one month, will also include runs with blades already damaged by simulated bird impact during whirl rig tests of individual blades. “Rather than do a whole bird-strike test, we will take some of those damaged blades, slot them in and run the engine to see how they perform in a fan set,” says Curnock.
“One of the most difficult things about a bird strike is that some blades are damaged and some are not. As a result, there isn’t a uniform flow and you have imbalance. So we need to understand how that works in a system. Often the most challenging aspect of a bird strike is not the actual impact, it is running the fan down and running it afterward,” he adds.
Results from ALPS will feed directly into the UltraFan demonstrator fan, the design of which will be guided using aerodynamic data collected over a series of subscale low-speed fan rig tests conducted at the Anecom AeroTest facility in Wildau, Germany. “We tend to hold the [fan blade] tip speed the same, which means sonic/transonic. So, if you increase the diameter but hold the same tip speed, the rotational speed goes down,” says Curnock.
“A slower fan speed means different aerodynamics. So one of the things we are doing is low-speed fan testing, and we [recently] completed evaluation of the fifth generation of this fan design on a subscale rig. The results [appear to be as] predicted, which is what we want because it is calibrating the model,” says Curnock. Conducted on a 35-in. dia metallic fan stage with blades shaped like the composite design, the testing included evaluation of flutter, aerodynamic performance and operability margins of various fan configurations.