FDC/Aerofilter manufactures this PMA filter for the Bell 206L-1, L-3 and L-4. Image courtesy of FDC/Aerofilter
Protecting the power plant from the worst effects of the ingestion of particles has always been a problem. But when United States military helicopter forces began operating in the dusty environments of Iraq, and then the even worse and oft quoted “talcum powder” environment experienced in Afghanistan, renewed energy was channeled into improving existing filtering technology.
Particle ingestion not only causes a decrease in engine performance, but it results in damage and wear, which inevitably leads to an increased frequency of overhauls. Not an expense that any operator wants to face. This is not only a cost factor in terms of the extra labor time associated with more frequent inspections, but also adds to the bottom-line running costs as parts need to be replaced more frequently.
Rotor & Wing asked some of the industry’s filter specialists how the lessons learned from military operations in harsh climates had helped to advance the industry’s development of better filtration type products. Had the experience led to any breakthrough technologies?
Donaldson, founded in 1915, is one of the leading providers of air intake filters for the rotorcraft industry. Business development director Bob Stenberg and engineering director Tom Newman said that the major areas to have been advanced were in dry media and systems that reduced the impact on overall aircraft/engine performance. The experience of the U.S. military during opera-tions revealed that the cleaning of filters had been very time consuming and was considered a major maintenance burden.
The older model UH-60A had its performance limited by the kit that was already in place. “We have subsequently qualified a dry media filter on the Black Hawk and a newer generation kit is on the drawing board,” said Newman. “This kit is lighter, more aerodynamic, and will have less of an impact on performance which is, of course, critical for a military aircraft, particularly when they need to fly at higher altitudes, such as in Afghanistan.”
There is also the question of whether helicopter OEMs can further assist in engine protection through the design of how each helicopter receives its air into the engine.
Said Newman: “The aircraft inlets can be oriented such that the airflow enters from the side of the aircraft into a plenum and not directly into the engine. This makes the performance loss less and also makes the certification requirements easier to meet, as it positively effects the prob-lems connected to icing and bird ingestion, among others.”
He added that when a system is planned into the design of an aircraft, such as in the case of the Bell 429 and 525, then it will naturally be more successful in its operation than had it not been planned for, and then fitted as a retrograde step fixing it into the space available.
“Planning for a filter in the early stage of an aircraft’s development is critical in how well it performs and how it will be accepted by the customer,” stated Newman.
An inlet filter for a Sikorsky S-76A-C. Image courtesy of FDC/Aerofilter
As with anything, filters take their fair share of criticism from operators, but sometimes unfairly. “Filters can last much longer in a severely erosive environment than people think,” said Stenberg. “In the earlier days of barrier filters, it was anticipated that cleaning would have to occur after a very short period of operation. But we have shown that in the worst of environments, barrier filters can operate in the vicinity of 200 hours between cleanings.”
“The inlet barrier filter (IBF) systems have a very low pressure drop when the filters are clean. Even when fully loaded, some systems can pass basic inlet power assurance checks (PAC). In other words, you hardly notice the filters are installed while at the same time they are protecting your en-gines,” said Newman. He added that while very fine sand may not impact and damage the engine compressor, it does damage to the hot section components and increases overhaul costs. “Basically, you really need to keep all sand out of the engine,” he stated.
Looking forward, Donaldson is currently working on systems that can fly in all types of environments, including known icing conditions. “We are looking at the interface between our pressure transducer and the engine control to provide real time performance information to the pilot,” revealed Newman.
With similar problems extending across the mechanical world, he added that the company was also “looking at technology we have today for ground vehicles that provide the ability to self-clean the filters.”
He said that there was excellent and widespread industry enthusiasm for any improvement to filter technology, with the U.S. military and Bell Helicopter among the most interested in what Donaldson was working on.
“We have been selected to provide inlet filtration on all of Bell’s new aircraft development programs and are working on several new military programs,” said Stenberg, adding that announcements could be expected in the near future.
Filtration products for the AS350 and AW109 manufactured by Donaldson Filtration Systems. Image courtesy of Donaldson
Among customers for Donaldson’s inlet barrier filters are air medical operators, some of who were present at the recent Air Medical Transport Conference in Nashville, Tenn. (Sept. 22-24).
Jon Wilson, director of maintenance for EagleMed, said that protecting the intake provides another layer of safety in that it keeps damaging contaminants from entering the engine. Among its fleet of fixed and rotary wing aircraft, EagleMed, a subsidiary of Air Medical Group, operates 28 Airbus Helicopters AS350s across 10 states in the Midwest and Eastern U.S.
Back in February, EagleMed ordered 11 Donaldson IBF system kits for installation on its AS350B2, B3, and B3e aircraft. The kits will be fitted as the helicopters enter their major scheduled maint-nance period. Wilson said there was no power penalty with Donaldson’s IBFs, a statement with which Mihir Mirajkar, director of maintenance for Summit Air Ambulance, was in agreement.
Summit Air Ambulance actually worked with Donaldson while it was trying to gain the FAA Supplemental Type Certification (STC) for the IBF system for use on Summit’s AgustaWestland AW109Es, which will be based in the different climactic conditions found at the two bases in Mon-tana and two in Nevada.
“We were convinced that filters were the way to go,” said Mirajkar. After witnessing the damage that could occur when engines were unprotected, such as during seismic surveys and firefighting missions where both compressors and turbines had been damaged, he made the decision to go with IBFs. “I think putting the IBFs on our aircraft is one of the best things we’ve done,” he said, adding that Summit’s two new AW119Kx helicopters will also be delivered with Donaldson’s IBFs.
The PUREair PA100 dry barrier filter. Photo courtesy of DART Aerospace and Pall Aerospace
Rex Kamphefner, the owner of Aerometals and subsidiary FDC/Aerofilter, both located in Califor-nia, pointed out that in many R&D developments it was the military that usually led the way as they often have the budget (sequestration aside). “The more outwardly aberrant conditions realized in military operations can be worse than those seen in civil operations…and require more frequent filter cleanings and/or replacement with previously cleaned elements.” He added that the usual urgency the military had to fulfill readiness and deliver missions to a schedule has provided the impetus for industry to keep filter maintenance times as low as possible.
Examining the military’s experience of “brownout,” when a helicopter is descending into sand or dust that is blown into the air by the rotor’s downwash, he explained that the orientation or size of the engine air inlet has no impact on particle ingestion. “Once the particles are air-borne, particularly in hover brownout, they are generally omnipresent in all directions,” said Kamphefner.
Kamphefner acquired FDC/Aerofilter in 2010, a company recognized for its expertise in developing inlet barrier filtration technologies. Aerometals has long been associated with providing components to the helicopter industry. It holds over 300 PMAs (Parts Manufacturer Approval) – and the new company fit into the overall strategy.
According to Kamphefner, there have only been a few “small advances” in different types of media filter “such as in foam or even dry element media.” However, he said that they did not improve the overall performance of the filter systems. “The biggest advance that FDC has undertaken concerns the ease of installation, limiting the amount of down time for the aircraft. Our next system that is going to flight test ing incorporates more of a ‘plug-and- play’ approach by incorporating the filter kit into a new cowling door, thereby allowing for minimal alterations to the aircraft,” he explained.
In terms of working with industry on the design of inlet barrier filters, Kamphefner said that their relatively recent introduction meant that OEMs were not yet accounting for them in the development of new aircraft, although this company was trying to keep them involved and updated on new IBF designs. “In fact it is more the engine OEMs that can have a positive effect on IBF development through the sharing of information. FDC has a good relationship with several of the engine OEMs, and their willingness to share information has been extremely helpful,” he added.
Air filters can make a difference to the bottom line, a factor that operators who do not use any kind of system sometimes fail take account of. Kamphefner said, “Most understand that the system will clean the air, but they can’t relate that simple fact to all the effects of the clean air. In a tactile sense, they don’t understand how much better the engine looks using an IBF until they do their first engine tear-down.”
The cleaner the engine, the better the efficiency is how he describes it. “Many of our customers can directly relate the decrease in their cost of maintenance to the installation of the filter. The IBF will pay for itself in a short period of time.”
Looking to the future, FDC is working on two more IBFs for Sikorsky’s S-92 and AgustaWestland’s AW139, and both OEMs are “extremely enthusiastic” about the development. “It is the customers that operate larger fleets in sandy environments such as in the Middle East and Africa that will particularly benefit,” said Kamphefner. “These two aircraft are used for oil operations – it is not as obvious, but salt is very damaging to the engine and IBFs can provide a tremendous benefit in reducing that damage,” he concluded.
Pall Corporation recently introduced its PB110D PUREair dry barrier filters at Helitech International in Amsterdam. These filters are FAA-PMA direct-fit replacements for oil-wetted filters.
The PUREair dry barrier filters are cleaned with water and are claimed by the company to signifi-cantly reduce any maintenance associated with the more conventional oil-wetted barrier filters.
Todd Barrett, VP of marketing at Pall Aerospace commented, “‘DO NOT OIL’ is not only an instructional placard on the product, but represents a new level of engine protection. We have been investing in the development of our advanced synthetic dry media for many years and we’re proud to see our first commercial application certified.”
Pall Aerospace also revealed a further three PUREair dry barrier filters at the event that are still awaiting certification, although this is predicted to be complete by the end of the year. According to the company, “these are direct-fit replacements for Bell 206L/407 and Airbus Helicopter AS350 barrier filter installations.”
“This is an important expansion of the PUREair product portfolio that we are working on with Pall Aerospace that will eventually allow us to cover any requirement for engine protection,” said Mike O’Reilly, president of DART Aerospace.
In the summer DART Aerospace announced that the South African-based Ultimate Heli will install the PA100 PUREair engine protection system on its AS350 helicopter. Co-developed by Pall Aerospace and DART, the PA100 is now a “redesigned, reengineered, and retested engine air pro-tection system that takes the capabilities of its EAPS predecessors to the next level,” claimed the company. It is claimed to be self-cleaning with low maintenance.
“We are excited about the opportunity to fly the PA100 and work with DART,” said Chris Cornwell, director of maintenance at Ultimate Heli. He reports a two percent gain in power over conventional inlet barrier filters.”