Can an airplane
operate without elevators, flaps and rudders for flight control?
The U.S. Defense Advanced Research Projects Agency
(DARPA) says ‘Yes’ and it has homed in on a potential alternative system.
DARPA's new X-plane concept will remove moving external control
surfaces, shifting from a century of standard aviation design practices.
DARPA has moved into the next phase of its Control of Revolutionary Aircraft with Novel
Effectors program, or CRANE. The project is centered on an experimental uncrewed aircraft,
which Aurora Flight Sciences, a subsidiary of Boeing, is developing.
In this video Defense Updates analyzes how DARPA's new X-plane concept would change the way US Air
Force goes to future wars? Let’s get started
Moving aircraft parts has been a necessary evil for more than a century.
On the one hand, control surfaces create aerodynamic drag and reduce fuel efficiency,
on the other hand, they are needed to safely move the airplane in flight.
Importantly, elevators, flaps, and rudders have been tried, tested, and improved for decades.
DARPA’s effort is focused on removing these moving parts altogether with a new more efficient
system - AFC or Active Flow Control along with some other tech like thrust vectoring.
AFC uses a variety of methods such as jets of air or even electric discharges
to shape or sculpt the flow of air over the aircraft thereby controlling its movement.
Elimination of so moving parts also means fewer things that can break, improving safety and
reliability. This would do away with various maintenance and logistics requirements too.
When it comes to military domain, the new system could be used to develop
super stealthy aircraft with very low radar cross-section (RCS) since no moving parts
mean lesser gaps and edges that affect the Low Observable (LO) profile of the aircraft.
CRANE program has moved to Phase 2 and DARPA has issued
a press release regarding the latest developments.
DARPA stated,
"Phase 2 will focus on detailed design and development of flight software and controls,
culminating in a critical design review of an X-plane demonstrator that can fly
without traditional moving flight controls on the exterior of the wings and tail"
Aurora Flight Sciences received a Phase 2 contract to continue
work on this project back on December 12, 2022. Aurora has already done significant wind tunnel
testing of subscale models with representative AFC components as part of CRANE's Phase 1.
It was earlier stated, "Using a 25% scale model,
Aurora conducted tests over four weeks at a wind tunnel facility in San Diego, California.
In addition to 11 movable conventional control surfaces, the model featured 14 AFC banks with
eight fully independent controllable AFC air supply channels. Over 14,000 data points were
collected, including 8,860 AFC control power points, forming the foundation
for a flight-quality aerodynamic database to enable rapid execution in future program phases."
DARPA has also added, "The contract includes a Phase 3 option in
which DARPA intends to fly a 7,000-pound X-plane that addresses the two primary technical hurdles
of incorporation of AFC into a full-scale aircraft and reliance on it for controlled flight."
So technically, if DARPA proceeds into Phase 3 of the CRANE program, Aurora will then build the full
7,000-pound prototype, which the company also says is expected to have a 30-foot wingspan
and be able to reach speeds of up to Mach 0.7. Flight testing could begin as early as 2025.
Aurora’s public release issued in December 2022, states,
“Aurora’s X-plane candidate uses active flow control (AFC) for multiple effects, including
flight control at tactical speeds and performance enhancement across the flight envelope.
The experimental, purpose-designed aircraft is designed around an AFC
system that supplies pressurized air to AFC effectors embedded in all flying surfaces.
The vehicle configuration provides AFC testing for multiple wing sweeps using
nozzle arrays located at the upper surface of each wing. Aurora continues to collaborate
closely with its parent company, Boeing, on the design of the aircraft and its AFC system.”
It was further noted, “The aircraft is configured
to be a modular testbed featuring replaceable outboard wings and swappable AFC effectors.
The modular design allows for testing of not only Aurora’s AFC effectors but also AFC effectors
of various other designs. By expanding testing capabilities beyond Aurora-designed components,
the program further advances its goal to provide the confidence needed for
future aircraft requirements, both military and commercial, to include AFC-enabled capabilities.”
The United States has been at the forefront of stealth technology.
F-22 Raptor is the stealthiest fighter ever built & has a very low RCS of only 0.0001 m2.
It achieves this due to its structural design
as well as the use of Radar Absorbing Materials (RAM).
As per some analysis, Russian Su-57 has an RCS of 0.05 m2 which makes it around 500
times larger on the radar when compared to F-22 and at least 10 times when compared to F-35.
B-2 Spirit is the only operational stealth bomber
in the world and US Air Force will soon get its hand on B-21 Raider.
A ‘cat and mouse’ game is ongoing when it comes to aircraft design and radar technology.
New radar tech is challenging current stealth
aircraft which are handicapped to an extent due to external moving parts.
If the CRANE X-plane design proves viable and turns into an actual airworthy aircraft,
it could power the new set of stealth aircraft that would be even lower observable.
The ability to eliminate the need for moving control surfaces could lead to
fundamental changes, in how US Air Force plans logistics and carry out missions.