The US military is developing an aircraft that can fly without mechanical control surfaces such as ailerons, elevators and rudders, which most current planes use to manoeuvre. Experts say the technology could improve stealth aircraft, but it is unlikely to break into the risk-averse world of commercial aviation.
The one-off, experimental X-65 aircraft will replace moving control surfaces with jets of compressed air, a technology called active flow control (AFC). These won’t steer the aircraft directly, as spacecraft do with thrusters, but will instead change the way air flows over the wings and tail to alter aerodynamic forces.
The project has been launched by the US Defense Advanced Research Projects Agency (DARPA), which develops new technology for military applications and is also working on autonomous fighter jets and advanced drones. The organisation has said that eliminating external moving parts is expected to reduce weight and complexity and improve performance.
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at Swansea University in the UK, who isn’t involved in the project, says it could also drastically improve the stealth characteristics of an aircraft by removing the small gaps and changing geometry associated with moving control surfaces.
“The problem with radar signature is any relatively small chink [in the shape of an aircraft] is another potential thing that can be caught or detected,” he says. “So if the aircraft doesn’t change shape – it just blows jets – it’s not changing its radar signature and it’s staying that much harder to detect. There’s a huge advantage from a stealth point of view.”
The X-65 will weigh around 3200 kilograms, with a wingspan of just over 9 metres, and will be capable of speeds of up to 240 metres per second. Aurora Flight Sciences, a subsidiary of Boeing, has and will roll out a completed aircraft early in 2025. Aurora and DARPA declined to answer questions from 91av.
Shaw says commercial aircraft could also benefit from AFC technology by reducing drag, which increases fuel economy and therefore operating costs and range. But while flow devices could replace some control surfaces on commercial aircraft, flaps – which radically change the wings’ shape to boost lift and reduce the required speed for take-off and landing – would be too difficult to replace, he says.
In military aircraft, this can be overcome by taking off and landing at higher speeds and potentially deploying parachutes to slow down. But in commercial aviation, this would be impractical, says Shaw.
