Manufacturers of aeronautics and aerospace products fill demanding and diverse performance requirements
Sources remain mum on what it is about the fabric in Superman’s cape that allows him to fly faster than a speeding bullet. However, we know quite a lot about the Red Bull Stratos pressure suit that allowed Felix Baumgartner to survive his historic Mach 1.25 free fall from the edge of space last October. That critical piece of gear was made by David Clark Co., Worcester, Mass., using a middle layer of the company’s Link-Net material.
“That layer takes the structural loads of the internal pressure,” says Shane Jacobs, soft goods design manager at David Clark Co. “[Link-Net] is made in-house from high-strength, low-elongation cord. The cord can be made from nylon, Dacron®, Spectra®, Nomex®, Teflon®—a variety of materials, depending on the requirements for each mission.”
Granted, the number of potential customers who need or want to free fall from 127,852 feet above Earth’s surface is extremely limited, which is why David Clark Co. bases its business on pressure suits for Air Force pilots and based the Red Bull Stratos suit on that product. Baumgartner’s suit required customizing to handle the extreme temperatures.
“The biggest unique requirement was that it had to be designed to be used in the skydiving position,” Jacobs says, noting that suits for Air Force pilots are designed solely for the cockpit. “The Red Bull Stratos suit had to transition from seated position to standing on a ledge to jump off and then achieving the delta position. We had to redesign the shoulders, elbows and knees.”
On the light side
Wilbur and Orville Wright didn’t use proprietary or even sophisticated materials, but they understood the importance of fabric in aeronautics. They used unbleached muslin on their early-1900 gliders, unsealed to save weight. Today, the closest aircraft to the Wright brothers’ is the ultralight, defined as one seat and less than 254 pounds powered, or 155 pounds unpowered.
Jim Miller, president of Aircraft Technical Support Inc. in Orient, Ohio, says the fabric most used in ultralights is polyester with a coating that prevents airflow through it.
“The fabric is providing lift,” he explains. For combatting UV effects, he says, “The system we are using is aluminum powder in a liquid, so the fabric will last 25 to 40 years. We use different processes: Poly-Fiber and Ceconite. They seal the fabric and smooth it out airflowwise. And then there is a topcoat for looks.”
Also particularly focused on weight are companies that make aerostats, such as U.K.-based Lindstrand Technologies Ltd. of Shropshire.
“The primary specification for lighter-than-air fabric is to have low helium permeation,” says managing director Per Lindstrand. “Airships and aerostats experience high dynamic loading. Therefore, the tensile requirement is very important.
“Low-helium porosity is achieved by a multitude of passes with a good polyurethane compound,” he continues. “The very best [impenetrability] is achieved by using a barrier such as PVDC, but this can have a negative impact on the structure of the fabric. Aramids are rarely used in lighter-than-air technology because of their poor fatigue characteristics. However, with the arrival of Vectran®, we have a fabric with similar mechanical strength to Kevlar®, but with far superior fatigue properties.”
For UV protection, a barrier is either built into the fabric or lacquer is applied on the outside.
The business of customizing
One can readily see the use of fabric while admiring an ultralight in flight, but hard-body planes also rely on the flexibility of fabrics, particularly apparent in their interiors.
“We use a variety of materials,” says Alex Alequin, industrial designer for Cirrus Aircraft of Duluth, Minn. “More recently we have been attracted to suedes like Alcantara®, mostly by customer request. Customers are trying to tie their aircraft with performance cars and their personalization. We have customers who drive sports cars, and they bring a lot of that aesthetic to the customization program. With our new special-edition Vision Inspired aircraft, we are trying to tell a story of the materials we picked and their inherent value. It’s an opportunity to tell a story of materials used artistically, not just functionally.”
Cirrus sources carbon fiber for the fuselage and high-end leather for seats, control column, center console and cockpit dashboard.
“Our suppliers are always experimenting, particularly with making leather lightweight and more durable,” Alequin says. “We benefit from that research, but we don’t drive that. Weight, quality and customization would be our three biggest parameters when we are picking a material.”
No room for failure
Allied Materials & Equipment Co. Inc. of Kansas City, Mo., makes hood-and-mask assemblies to protect Air Force pilots from biological and chemical warfare agents.
“The Air Force will define the specifications of materials that are acceptable to them,” president Steve Pack says. Allied, which uses butyl rubber-coated nylon in its assemblies, contends with the effects of making a product that can never fail. Every component is serialized and tested with simulations of nerve and mustard gas exposure. And with products of such a critical nature, the Air Force is especially reluctant to make changes to a proven system, Pack says.
For Ehmke Manufacturing Co. Inc. of Philadelphia, Pa., which makes noise-dampening, thermal insulation blankets, the most significant development for the company has been the incorporation of complementary technologies in materials.
“We have to be able to incorporate innovation in design and innovation in related types of materials and be able to bring all those elements together to provide a solution,” CEO Bob Rosania says. “On some of our commercial applications, we have integrated composites into our design so it’s not just a soft-fabric solution.” The walls of an airplane cabin, for example, have rigid composite panels with upholstery, mixing hard and soft materials.
“When you are speaking about military aircraft, particularly rotorcraft, they are not pressurized and insulated like a commercial airliner,” he notes. The blankets are composed of a three-layer, quilted material: a fire-retardant facing of silicone-impregnated nylon, a middle layer usually of fiberglass insulation and a backing of protective film.
“Depending on the application, if it’s primarily for acoustic protection or thermal protection, those materials are interchangeable with other proprietary fabrics,” Rosania says.
David Clarks Co.’s pressure suits also use a variety of fabrics. “There are a lot of different requirements that must be addressed by different layers,” Jacobs says. The outer layer needs to be fire retardant, abrasion resistant and offer protection from punctures and tears, while the inner layer must be completely airtight to create a human-shaped envelope that maintains a pressurized atmosphere.
Baumgartner’s historic freefall was “a chance to prove out and expand performance for the equipment that is currently being worn by pilots,” Jacobs says, noting that David Clark constantly tries out new fabrics and tests new designs. “I have companies from IFAI Expo sending a variety of samples.”
The pressure suit helmets use phase-change materials—materials that absorb and release heat by changing phase (i.e., liquid to gas)—for thermal comfort.
“That’s been a recent breakthrough,” Jacobs says. “Another significant advance in pressure-suit technology is the use of breathable, airtight materials for the innermost layer. These materials are impermeable to oxygen and nitrogen, but allow for transmission of water vapor. In years past, we used rubberized fabric like urethane-coated nylon, but heat builds up. These new breathable materials significantly reduce the thermal burden.
“One thing that is changing for our industry now is we are entering into commercial space flight,” he adds. “We are getting into this interesting area of how will these commercial provider systems get regulated? How will they get ‘man rated?’ There are people at NASA and the FAA working to figure that out, and we are working with them on the suit side to understand what it’s going to take.”
Really out there
Orbiting more than 200 miles above Earth, the International Space Station is exposed to extreme hot and cold. But, notes Brent Anderson, “Satellites like to operate at room temperature.”
Anderson is engineering manager for Aerospace Fabrication & Materials LLC of Farmington, Minn., which makes thermal-barrier blankets for satellites, including the International Space Station.
“They’re there basically to keep the satellite from getting too hot if it’s exposed to the sun or losing too much heat if it’s facing deep space,” he says. “They’re very thin, in the 1/8- to 1/4-inch range. The outside will be upwards of 300 degrees and the inside room temperature. Other blankets that will protect around rocket nozzles can be 1,000 degrees facing the nozzle and 100 degrees inside.”
Additionally, the space environment is harsh because of atomic oxygen. “What we see is that the degradation of materials is quite dramatic,” Anderson says. “There are tests going on at the International Space Station to determine what materials work best in lower Earth orbit. … They constantly look at ways to improve the coatings and types of materials used in space to mitigate the effects.”
The weight the blankets add to a satellite also must be considered. AFM uses low-conducting fabrics that separate the layers. One of the least expensive is polyester based.
“It’s like a bridal veil,” Anderson says. “It’s a Dacron® material. We also use Nomex® and Kevlar® versions. Another type of spacer material is spunbonded.”
The company is working with suppliers of new materials that show promise for improved thermal blankets. However, Anderson says, “When a material has been tested in space and deemed to be a good fit for its particular use, if another material comes along that shows some improvement, it takes longer for that new material to break into the [aerospace] market, just because the market tends to stay with what works.”
A recent modification of export control laws has eased restrictions. “The parts we make have for a long time been deemed rocket parts and so are restricted for sale outside the U.S.,” Anderson says. “That’s just been changed [to satellite parts] and we, along with a lot of other companies, will now be able to sell commercial satellite parts around the world easier than in the past.”
Few and far between
A common concern among manufacturers involved in aeronautics and aerospace markets is that there’s is a scarcity of fabrics for the products. According to Per Lindstrand of Lindstrand Technologies Ltd., a shortage of qualified lighter-than-air fabric has resulted from top fabricators switching their manufacturing focus to the more-profitable electronics industry.
Allied Materials & Equipment Co. Inc. finds it difficult to source butyl rubber-coated nylon for its hood-and-mask assembly.
“There’s only one source as far as we know, and they are not located in the United States,” Steve Pack says. “I think there are only one or two sources for a similar item that the military uses for ground troops.”
Similarly, Ehmke Manufacturing Co. Inc. finds sourcing fabrics for its insulation blankets a challenge. “Often our customer demands a certain type of supplier that has specific process and quality standards,” Bob Rosania says. “So they not only have to meet Ehmke’s requirements, but also often the requirements of the U.S. government and Boeing Co., which is our largest customer.” Ehmke is a silver-rated supplier to Boeing. “There are only 500 companies globally that are either silver- or gold-rated suppliers,” Rosania says. “Boeing has made it a requirement that their suppliers achieve AS9100C certification, a quality standard for the aeronautic and aerospace industry that is a step above ISO 9000.”
“A lot of materials we find are not qualified, but there are techniques you can use to pass the test,” says Alex Alequin of Cirrus Aircraft. “You can add a chemical back coating or different backing to get a fabric to pass the required burn test.” But even with those measures, a fabric still may not pass.
According to Shane Jacobs of David Clark Co., the extreme requirements of pressure suits make it difficult to find qualified materials. “Typically, we are using very specialized, highly engineered fabrics,” he says. “We constantly try out new fabrics and test new designs. We are always searching for new ways that we can improve our products.”