The sight of an aircraft crashing and burning is for most engineers the stuff of nightmares. But, for engineers developing a new class of unmanned air vehicles (UAVs) called attritable aircraft, such destruction is not likely to elicit more than a shoulder shrug.
Attritable aircraft are designed to be thrown out – eventually.
The US Air Force (USAF) believes that by designing and building military UAVs cheap enough it can gain an edge over its adversaries in a war of attrition (hence the name “attritable”). Essentially it wants UAVs that it can afford to lose.
The service says it is seeking UAVs priced between $2 million and $20 million each to accomplish a range of missions, including intelligence, surveillance and reconnaissance, air strikes, air-to-air combat and electronic warfare. Exactly what price point offers the best balance of affordability and military performance is debated by the aircraft manufacturers that are vying to build the USAF’s fleets of attritable aircraft in programmes such as Skyborg and MQ-Next.
“The philosophy behind an attritable aircraft is really around design for cost,” says Andrew Glynn, programme manager for the Boeing Airpower Teaming System, an attritable UAV. “It’s about trying to get a good enough product at the right price.”
Building a “good enough product” is a change in mindset for the aerospace industry, which is usually doggedly focused on high levels of safety and reliability. However, with attritable UAVs there is no pilot to keep alive. And, by design, the equipment is so cheap that combatant commanders – and the US Congress – will not mind the loss.
Manufacturers say model-based systems engineering – a common set of digital designs for engineering, manufacturing and maintenance, as well as flight simulations – is at the core of making attritable aircraft work. Model-based systems engineering software tools allow aircraft builders to create a digital twin of a UAV and then explore its total lifetime cost in various simulations. Such in-depth analysis is vital for making cost-cutting trade-offs.
“When you have a digital twin that goes all the way from the product through the production system into the operating environment, we can very rapidly model the impacts of any change as it goes through the whole process,” says Glynn.
Using those model-based systems engineering tools, US manufacturers aim to spot how small tweaks might increase or decrease the cost of an aircraft.
“It could be really detailed-level decisions around informing how you transport parts around the factory, or what enables lean flow through the production system,” says Glynn. “Any number of those small decisions all cumulatively add up to making a big difference to the overall cost base.”
Getting different types of engineers on the same (digital) page is critical, but that is just the beginning, says Steve Fendley, president of the unmanned systems division of Kratos Defense and Security Solutions, maker of the XQ-58A Valkyrie, another attritable UAV. Manufacturers must also adopt a different mindset about quality and reliability, he says.
That might mean building on the cheap. Fendley explains, in an exaggerated example, that a fuel valve part that might cost $500,000 and is guaranteed to work for 5,000h could be replaced by three $50 valves each guaranteed to work for 1,000h.
“When you run the reliability analysis, it’s terrible for the cheaper component,” says Fendley. But “we’re now going to build redundancy. We’re going to put in three parallel paths… all we need is any one of the three working and the system will keep operating.”
Sourcing parts and components from the commercial aviation sector is helpful.
“Stay away from bleeding-edge technology,” says Fendley. “Don’t try to incorporate the very latest technology that still has risk associated with it [and] probably has additional costs associated with it.”
Kratos and Boeing also have selected commercial business jet engines to power their aircraft. Boeing declines to identify the manufacturer of the powerplant for the Airpower Teaming System. Kratos says its engine is made by Williams International, though it declines to name the model.
“We need to have an engine that’s super reliable, that’s super predictable,” says Fendley. “We understand the performance, it can be maintained, [and] it is a reasonable cost. And, it all fits within the system. That’s why we went to something in that [business jet] class.”
Fendley says in the future there might be an opportunity to find ways to customise business jet engines for attritable applications – that is, cut costs – by changing materials or manufacturing parts with 3D printing.
Another method for saving money is going without, Fendley says. That might mean fewer control surfaces. “If your attritable [aircraft] gets shot and you lose a control surface, you’re probably going to decide to ditch and not try to bring it back,” he says.
Mike Atwood, senior director for advanced programmes at General Atomics Aeronautical Systems, agrees.
“An attritable [aircraft] doesn’t need to survive decades of use and abuse – many will likely be only one-time use, no different from firing a missile – so the need for redundant systems is diminished compared with an aircraft that is designed for a 40,000-hour service life,” he says.
Allowing for less precision in manufacturing will also be helpful, says Fendley.
“The tighter tolerances are going to drive cost. It’s going to drive the failure rates up, drive the number of things that don’t make it out of the factory, that end up being rejected,” he says. Accommodating looser tolerances is also helpful if the aircraft sustains damage in flight or on landing, as repairs do not need to be as precise.
Generally, manufacturers say attritable aircraft must be simpler than their peers. That means designs that are modular and have an open architecture, two ways to plug-and-play new hardware or software.
“It really does almost become a kit perspective, like more of an Ikea furniture kind of mindset,” says Renee Pasman, director of integrated systems within Lockheed Martin’s Advanced Development Programs unit, known popularly as Skunk Works.
Using various manufacturing technologies, including 3D printing, but also traditional CNC machining, attritable designs ought to have simple shapes that can be assembled quickly, even within a couple of hours, she says.
Boeing uses reconfigurable and modular assembly jigs to build the Airpower Teaming System, says Glynn. That includes “a common base that can be easily reconfigurable to accept different types of major structure components, for example the fuselage or wing,” he says.
And because Boeing is simultaneously designing the UAV’s production system using digital engineering software, the first prototype was built with high levels of automation and is production representative, Glynn says,
“We start by designing the full-rate [system] and we work backwards or we tune it from there,” he says.
Atwood says General Atomics is looking toward commercial manufacturing processes, including 3D printing.
“One of the key technologies is additive manufacturing of thermoplastics. Using tool-less part manufacturing enables minimised development cost,” he says. “In addition, this technology reduces overall part count, which reduces touch labour and integration costs.”
Artificial intelligence and big-data analytics will also play a big role in identifying areas of operational inefficiency, which could help reduce costs, he adds.
Manufacturers say there might be roles for several types of materials, although composites seem to have a leading application.
“The strength-to-weight ratio, the basic strength characteristics, the damage tolerance characteristics, the ability to evaluate a potential flaw in manufacturing, or for failure or a soon-to-be failure in the field, carbonfibre is just fantastic,” says Fendley. Carbonfibre structures also tend to have fewer parts, unlike those fabricated from aluminium which are typically held together with rivets, he says.
“Composites lend themselves to complex shapes,” says Atwood. “But for small attritables, we might get away with high-strength, injection-moulded or additive-manufactured composites or plastics. Carbonfibre is a material of choice – due to strength versus weight benefits – but carbon composites are more expensive than fiberglass composites.”
Low-cost, resin infusion composites have advantages, but material qualities are not the only important consideration for Boeing, says Glynn. “It’s not just the material costs or the fabrication time, it’s understanding how those materials and processes help to support lean, single piece flow through a factory,” he says.
Ultimately, the price of attritable aircraft has to include the cost of sustaining them throughout their lifecycles, say manufacturers.
“Keeping touch points and maintenance to a minimum, and parts count and redundancy low, can make attritables affordable,” says Atwood.
That might mean forgoing maintenance access panels on aircraft, says Pasman. In such a scenario broken or damaged UAVs might just be thrown away, instead of repaired. “If you can get the price point right that actually starts making some amount of sense,” she says.
To achieve the mass of attritable aircraft needed to overwhelm an adversary, without breaking the bank, Lockheed argues that UAVs need to be even cheaper than the USAF’s $2 million floor, and certainly nowhere near the $20 million price ceiling.
“In order to really get that very large mass of small, low-cost vehicles, you really have to get to a cost point that you don’t necessarily care if they come back,” she says. “$20 million airplanes, are we really not going to care that they don’t come back?”