Fill ‘er up, Sir!
I want you to visualize this scene. Imagine you had to fill up your car while you are traveling at 300mph, and the pump is also moving, and also the hose is moving around the pump?
You can’t just roll down the window and grab the nozzle with your hand, you have to drive your car — a car which is more like a truck — and align the filler with the nozzle just so.
And now let’s add wind and turbulence to randomly perturb the motion of your car, the pump, and the hose of course.
Oh! And now let there be complete darkness, on a dark night with a new moon and rainy weather.
And the most important thing for you to consider is that you don’t have plenty of time to fill up your car, you are running out of gas!
It seems like a very difficult task to carry out, doesn’t it?
This is exactly what every fighter pilot faces during an Air-to-Air Refuelling (AAR) operation, one of the most challenging tasks by far in long-endurance missions.
It takes months of training for fighter pilots and Air Refueling Operators (ARO) to master this complicated “dance in mid-air”. These highly trained experts must have a steady hand and nerves in order to complete this remarkable and crucial task so the air force can successfully complete all of its missions.
But this situation might change in the near term. With millions of dollars spent in Research & Development programs, the defense industry is investing in new technologies that could help to increase the autonomy of these operations and reduce the complexity of these operations.
The industry’s objective is to diminish the tremendous workload associated with Aerial Refuelling operations, improve safety, and optimize the rate of air-to-air refueling transfer in operational conditions — not every attempt ends up in a satisfactory wet contact.
New cutting edge technologies could provide the air forces with an unprecedented capability that would maximize air superiority, the Fully Autonomous Air-to-Air Refuelling (FA3R).
Get the Hands-off the Stick and Let the System Do the Hard Job
Here goes the technical definition: Fully Autonomous Air-to-Air Refuelling defines an automatic operation involving coordinated interactions between a set of dissimilar manned and/or unmanned aircraft flying in close formation — before, during, and after the fuel transfer.
Going back to the cars’ analogy, a FA3R operation would be like trying to fill up your car at 300mph, but this time on a highway among other cars, which just like you, are also trying to refuel before running out of gas.
In this case, some of those other cars would be Tesla models, driven automatically by their autopilot, without human intervention at all. Well, and to be fair, you would be also driving a Tesla — that’s the cool point.
But there is a big handicap in this imaginary analogy, Tesla’s autopilot does not incorporate an automatic refueling operation mode — and it never will of course — so you would still need to do the hard work by yourself.
At this point, wouldn’t it be great to have a refueling autopilot to let you relax, take your hand-off the wheel-drive, and let the autonomous system do the hard job for you? This is when the FA3R concept comes into hand.
That’s why the aerospace industry has started to do the maths, imagining the concept of future autonomous operations, and flight testing new technologies that will shape forever the refueling operations in the near future.
Indeed, during the last fifteen years, there have been major breakthroughs in the field of one-to-one A3R, with flight test demonstrations of image recognition and control technologies implemented in the receiver aircraft side, like the Northrop Grumman X-47B, and in the tanker aircraft side, like the A310 MRTT.
Autonomy Levels in Air-to-Air Refuelling Operations with a Flying Boom
In essence, during an actual A3R operation with a flying boom system, all or part of human pilots’ responsibilities are delegated to the Flight Control System (FCS) of the tanker and/or the receiver aircraft. Accordingly, autonomy levels of A3R operations are defined by the tasks assigned to the computers.
Top-Down Autonomy Levels
- Fully Autonomous Air-to-Air Refuelling (FA3R)
- Automatic Air-to-Air Refuelling (A3R)
- Semi-Automatic Air-to-Air Refuelling
Semi-Automatic Air-to-Air Refuelling
In the lower part of the autonomy scale, we find the Semi-Automatic Air-to-Air Refuelling, in which the Air Refuelling Operator (ARO) is responsible only for the extension or retraction of the telescopic beam, and the flight control computer is in charge of the tracking of the receiver’s receptacle.
During semi-automatic operations, the tanker’s flight control system flies the boom, meanwhile, the ARO just needs to extend the telescopic beam and make the contact with the receiver aircraft.
Automatic Air-to-Air Refuelling (A3R)
The next step in autonomy is the Automatic Air-to-Air Refuelling (A3R). In these operations, the A3R flies the boom automatically and keeps the alignment between the boom tip and the receiver receptacle with an accuracy of a couple of centimeters.
The proper alignment and the receiver stability is checked in real-time to keep a safe distance between the boom and the receiver and also to determine the optimum moment to extend the telescopic beam and to achieve the connection with the receiver.
At this point, the fuel transfer is initiated to fill up the receiver aircraft. Once completed, the disconnection is commanded, and the boom is cleared away from the receiver by automatically retracting the telescopic beam, and flying the boom away to keep a safe separation distance.
During this process, the ARO is still in the loop but simply monitoring the operation.
Fully Autonomous Air-to-Air Refuelling (FA3R)
At the opposite end of the autonomy level spectrum, we find the Fully Autonomous Air to Air Refuelling, where the whole operation is performed without requiring any human intervention, neither by the ARO nor by the manned receiver’s pilot or the UAV’s operator.
With such an autonomy level, even the tanker aircraft could be an unmanned platform, as the tanker’s aircrew would no longer be indispensable for aerial refueling operations.
The Tanker: The Main Actor in FA3R Operations
In the Fully Autonomous Air-to-Air Refueling operation envisioned by Airbus Defence and Space, the tanker would play a key role in the refueling operation, acting as a mothership that transmits through a secure data-link the guidance, coordination, and collision avoidance commands to the receiver aircraft’s autopilots.
Maybe this concept sounds familiar to you. Do you remember when in the Independence Day movie, Will Smith’s was towed by the alien mothership until the docking?
Well, this is exactly the representation of the “tanker-centralized” concept in FA3R operations.
If you were a fighter pilot, you would just need to engage the FA3R-autopilot, then take your hands off the flight control stick, and let the tanker do the job, just like in the Independence Day movie.
At this point, you might be wondering what are the advantages of this “tanker-centralized” concept with respect to a distributed architecture. Could a distributed architecture — where the responsibilities lie in the receiver’s flight control system side — be more appropriate?
Well, the answer is that one of the biggest advantages of the “tanker-centralized” control architecture is that it maximizes the compatibility with any type of friendly receiver aircraft, either manned or unmanned.
In contrast with a “receiver-distributed” control architecture, the “tanker-centralized” architecture would not require any specific hardware on the receiver aircraft, and neither any modifications of its flight control software, just the capability to receive external commands from the tanker to the receiver aircraft’s autopilot.
Thus the “tanker-centralized” architecture would allow the air forces to save millions of dollars in retrofits and compatibility upgrades to their fighters and bombers fleet. The only major modification or upgrade required to perform FA3R operations would be located on the tanker’s side.
The Future of Air-to-Air Refueling
In the near term, it is expected that the Automatic Air-to-Air Refueling capability will become a reality for some of the most advanced air forces in the world.
Indeed, at the beginning of this year, the Government of Singapore’s Air Force declared that one of its six A330 MRTTs is taking part in the ongoing development, flight test campaign, and final certification program for the new automated aerial-refueling capabilities that are being developed by Airbus.
Thus it is expected that the small southeast Asian island will be the first nation in the world to add the automatic refueling capability to its tanker fleet, with the incorporation of the new A330 Smart MRTT later this year.
The United States’ Air Force is willing to incorporate to its tanker fleet the automatic refueling capability as well, with future development versions of the remote vision system of the Boeing’s KC-46 tanker. In recent declarations, Will Roper, Air Force acquisition executive reported:
“A proper Remote Vision System like that (the one of the KC-46) is right on the doorstep to autonomy. All you have to do is take that data that tells the world inside the jet the reality of geometries between the airplane and the boom outside the jet. Once you have that, you simply need to translate it into algorithms that allow the tanker to tank itself.”
After the last flight-test demonstrations of A3R technologies performed by the leading companies in the aerospace industry during the last years, it is becoming more evident that it will take no longer than a decade or so to see the first demonstration of a Fully Autonomous Air-to-Air refueling operation between several unmanned platforms.
It is clear that the journey towards fully autonomous capabilities will face many technological challenges, but today, the aerospace industry and the airworthiness authorities are working together to bring the autonomous aerial refueling technology to the tankers of the next decade, providing new drone refueling capabilities, increased safety, and cheaper operation costs.
Maybe one day, one of the most complex tasks in the aviation world, will be just like playing a video-game.
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Rodney Rodríguez Robles is an aerospace engineer, cyclist, blogger, and cutting edge technology advocate, living a dream in the aerospace industry he only dreamed of as a kid. He talks about coding, the history of aeronautics, rocket science, and all the technology that is making your day by day easier.