Nor is it even clear that an entirely fresh approach to the problem is what is needed. Richard Hallion, a former senior advisor to the US Air Force and aerospace historian says there have been improvements in established technology over the years - composite materials, fly-by-wire flight controls, and better propulsion - which may make past VTOL concepts now feasible. “Many of those are waiting to be rediscovered or mined,” he says. “Frankly the history of aerospace technology is one of constant reinvention, reinterpretation, and to a certain degree, rediscovery. That’s not a bad thing.”
No one denies that the road to VTOL aircraft is littered with the corpses of past aircraft, including several Darpa programs, but proponents argue that that’s the whole point of the new initiative. Mark Moore, a Nasa engineer who has specialized in VTOL aircraft for three decades, says he’s excited about Darpa’s plans, but cautions that the example included in a graphic announcing the programme, showing a fan-in-wing design, is not likely the solution. “I would be very surprised if the resulting concepts ended up being fan-in-wing concepts as shown in this graphic,” he says. “Fan-in-Wing were pretty much the least successful of all the VTOL approaches attempted by Nasa and the [Department of Defence] over the past 60 years; they have fundamental transition problems [between take-off and forward flight] that the new technologies available do not solve.”
Instead, Moore suggests that advances in electric propulsion and automation will ultimately lead to entirely new concepts.
Mike Hirschberg, executive director of the American Helicopter Society International, is also optimistic. A new X-plane program, like the one Darpa has started, offers a real opportunity – and money - to tackle an age-old problem, says Hirschberg, who previously served as a consultant to Darpa for over a decade.
Hirschberg, who tracks VTOL aircraft design, and updated the famous “wheel,” disagrees that it is in fact a “wheel of misfortune” (that nickname came about years after the original wheel was developed). It’s true that of the dozens of VTOL concepts, only three have been fielded, but that doesn’t mean the idea is futile, he says.
One could use the same wheel to depict ideas for conventional takeoff and landing aircraft, and perhaps come to a similarly bleak picture. “I don’t know if it is as bleak, but it’s probably not that much better,” he says.
Darpa’s project, while high-risk, is not without a solid base: internal studies done by the agency demonstrate that a VTOL aircraft is feasible. That challenge is simply identifying a design that will make it work practically.
“If you start with a clean sheet and ask: what is the art of the possible, and throw open the door to unconventional approaches, you get a lot more creative ideas, and a lot more innovative ideas,” says Hirschberg. “A lot of them, after full analysis may not work, or may not have a compelling capability that outweighs the cost, or penalties, but maybe there will be a breakthrough, maybe you’ll be able to do something. “
There is, he acknowledged, a great deal of disbelief from people about the Darpa project, and some aviation experts may wonder if the agency is crazy. “Maybe it is, but maybe someone is crazy enough out there to come up with a new idea or a new approach to an old concept.”