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Posted 5 years 209 days ago ago by Admin

When it comes to helicopter operations there is actually no such thing as clean air. “Typically when you are in flight, you are in somewhat clean air, but most often it is not cruise flight that is the problem. Most of your damage occurs during takeoff and landing when you are kicking up the sand, grass, dust, or soot that is on the ground,” says Tony Bohm, director of business development at Aerometals. “Often it is not until an operator has a problem with an engine that they realize that their areas of operation are not as clean as they think they are. We had one operator who was trashing engines because they would cut the lawn every week next to the training area. They were constantly ingesting grass clippings into their engines and causing damage.”

Inlet barrier filters

While helicopter operations in pretty much any type of air can have negative consequences to the health of engines, some environments are indeed significantly more hostile than others. Helicopters operating in a marine environment can be subject to the erosive effects of beach sand and the corrosive effects of salt nuclei, while helicopters operating near wildfires can be impacted by erosion or foreign object debris (FOD) from landing in unimproved landing zones. Engine corrosion and fouling can occur from ingesting smoke. Operations into dirty air imply distinctive maintenance operations, but as inlet barrier filters (IBF) improve, the maintenance requirements associated with dirty air operations have the potential of becoming less burdensome. “Neither salt nor smoke imply any distinctive maintenance operations with an IBF installed. They are both contaminants that would increase condition maintenance if the length of exposure and concentration are severe though”, says Tom Newman, engineering director at Donaldson Aerospace and Defense. “As an example, aircraft operating in saltwater environments without barrier engine protection can require aggressive daily engine wash regiments, experience negative power trending due to hot section sulfidation, have limited hover time over saltwater, and increased overhaul and programmatic operational costs. Our IBFs with 99 percent separation efficiency capture everything that would have been ingested by the engine creating component wear and eventually extensive damage. Therefore, maintaining the IBF is critical to keep the filter dust holding capacity at optimal values while getting the maximum engine performance.”

IBFs are very similar to the ones installed on cars and they basically create a barrier between the outside environment and the inlet of the engine. “IBFs effectively clean the air used during the combustion process. The cleaner the air, the less damage will occur to the engine during combustion. On top of erosion, we also have the reduction of corrosion and fouling,” says Bohm. “Unlike particle separators, which only stop larger particles and FOD, IBFs also stop smaller particles & salt nuclei. In addition, IBFs are passive devices in that they create a barrier between the engine and the outside environment, whereas particle separators are active devices that require power to function.” 

Donaldson Aerospace and Defense IBF system installed on a Leonardo AW109. Photo Donaldson

Power Margin

Because they are essentially devices installed in front of engines, IBFs may contribute to power degradation, or ‘installation loss.’ Aerometals has been making use of the latest in computational fluid dynamic modeling software (CFD) to design new IBFs and reduce the installation losses. “In the past, the methodology of designing IBFs was very similar to what is done on automobiles: the more filter area you have the less impact the filter is going to have on the engine installation losses”, says John Holland, director of sales at Aerometals. “Through CFD we realized that it is much more complicated than that, and more filter area is not necessarily better. We found this on the H130’s IBF that recently got certified. We reduced the filter area quite dramatically and decreased the installation loss by about 50 percent. Without this engineering technology, we could not really see what was going on until the systems were installed and tested on the aircraft. In the past, we would just build a filtration system that was as light as possible and mount it in front of the engine as best we could. But with CFD, we have advanced by quantum leaps with respect to design early in the design process. We can really see all the things that impact the air and make adjustments to clean up the air flow. In the end, this helps us produce much better products for our customers.”

One common concern of operators is what happens if flight is undertaken through an extremely contaminated area that results in a high rate of contamination buildup on the filter. IBF Systems utilize pressure sensors to monitor blockage of the filter in realtime.  “The system will indicate to the pilot when it is time to open the bypass doors, prior to an unsafe condition occurring,” says Holland, “At that point, bypass airflow is provided to the engine resulting in power recovery to continue the mission. In contrast an unfiltered engine, which has degraded due to operating in an extremely contaminated area, has no means of power recovery.”

BEFORE: Older legacy design H130 IBF run through a computational fluid dynamics (CFD) simulation. Image Aerometals

AFTER: Nex-Gen H130 designed utilizing the latest generation computational fluid dynamics (CFD) modeling software shows a much more more efficient airflow. Image Aerometals

IBF Maintenance

While they contribute to a reduction in engine maintenance requirements, IBFs need dedicated maintenance to function effectively. “The best practice is to treat the maintenance of the IBF as you would your engine. It is the first line of protection from component wear, cost prevention, and unplanned downtime,” says Newman. “In extreme conditions, operators equipped with IBF watch their indicators more often to make sure they do not need to clean or replace their filter and are able to return to base and service the filters. Operators cannot afford to fly in extreme conditions without an IBF.”

The maintenance procedures of Donaldson Aerospace and Defense originated from the OH-58D Kiowa Warrior aircraft that were equipped with an IBF prior to its deployment in the 1990s. “We spent nearly 30 years building upon this knowledge to develop what are now industry standard practices. Each system developed contains the instructions for continued airworthiness (ICA) document or the operational maintenance manual (OMM),” says Newman. Routine cleanings are required when the filter maintenance aid (FMA) indicates the need or after 300 hours, whichever one comes first. The type of media, dry or wet, determines the cleaning regiment required. Many times, simply tapping out the debris will delay the need to clean the filter. When it is time to clean, a wet media filter will need to be washed and the oil replaced. A dry media may be tapped out, or rinsed, or replaced. Both need to be allowed to dry before reinstalling.

Fouling damage in a hollow shaft at 800 hours with no IBF system in place. Photo Aerometals

No fouling damage in a hollow shaft at 1500 hours with IBF system installed. Photo Aerometals

As more IBFs become available some misconception about IBFs remain in the helicopter community and much of the work of IBF manufacturers is in raising awareness as to the benefits IBFs provide. Indeed IBFs help improve operational performance and achieve cost efficiencies. “IBFs can eliminate the chance of a FOD event, which could cause serious damage and cause an aircraft to go off contract. With IBFs you can also reduce the chances of taking the aircraft out of service for unscheduled maintenance due to an engine not making power, which in turn reduces maintenance man-hours that will be spent working on the engine”, says Bohm. “The main idea is to keep the helicopter flying as much as possible. An operator may have a power-by-the-hour maintenance plan in which they do not worry about who is paying for an engine swap, because it is built into their maintenance plan, but that is not going to cover the cost of being off a contract for an unspecified period of time.”

“IBFs are passive filtration elements that capture 98-99 percent of contaminants. By eliminating the ingestion of contaminants, the engines can reach time between overhauls (TBO) even in austere environments. Once returned to the overhaul shop, costs are greatly reduced due to less engine wear and/or erosion, and the ability to reuse parts,” says Newman.

The case of helicopter operator Lider in Brazil is particularly noteworthy as to the benefits of having IBFs installed. “They were operating the S76 C+ (without IBF) and the S76C++ (with IBF) side by side. They realized after time went by, that their direct operating costs on their engines were much less on the C++ than on the unprotected C+,” says Holland. “So Lider asked Turbomeca what was the cause of this and Turbomeca did a study and issued a comparative report that showed the difference between near identical aircraft operating Ariel engines with and without IBF protection. This report showed the positive effects of operating IBF protection on the S76C++ in an environment where people typically think they do not need one.”

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