Flying a vortex surfing formation

[RRTrentSymphony]

At night, our widebodies are usually sent out in major packs to international destinations and those flying to the same region of a continent usually end up in one of the two main airways that lead in that direction. Company aircraft launching from other places in the country also end up on the same airways around the same time so we meet them at altitude and are sometimes unable to obtain our optimal flight level for ATC separation purposes.

I look up at the contrails of a company jet flying slightly ahead, 2000 feet above and wonder if we could be flying in tight formation at the same flight level and make use of their wingtip vortexes to augment our lift and save some fuel burn. I asked the captain, he said its a good idea but he's never heard of it. When we're back at the operations center at our hub a few days later, we had a long discussion with the flight crews and they say its been proposed before but spacing regulations in our neighboring country's airspace (& international airspace) forbid the concept was dumped. (domestic flights usually don't meet up that often in my country so we don't bother using it for domestic operations)

Is anyone out there using this concept at the moment? I would suspect large countries like the US would benefit trying this due to long range of some domestic flights and their urge to test new technology (like NexGen + continuous descent approach...) If so, are there any software mods to keep the planes an ideal spacing apart (matching speeds seem to be a disaster waiting to happen, one plane might drift into the other if the A/P doesn't take the location of the other jet into account).

[underfire]

It was tested by NASA and the US Air Force.

Using the station keeping mode in the fms, they were able to offset fly on autopilot. (Station keeping is how bombers fly in configuration, and dont hit each other with the ordinance being dropped)

It worked very well for fuel consumption purposes, but the aircraft offsets to effectivly 'ride' the uplift part of the vortex are on the order of 10 aircraft lengths by one wingspan offset each side of the leading aircraft centerline.

It was quite amazing, with the lead aircraft on a coded centerline, the trailing aircraft would offset 10 by one in the FMS from the associated leader, hence forming a perfect 'V' formation. In addition to the trailing length, the systems has the capability to offset by ticks, the H and V from the leader.

They did this with 9 C-17 aircraft from Edwards AFB to Charleston, SC, alternating the offset configuration along the flight, to optimize the configuration.

While the concept worked, there is no way you would have commercial aircraft in that tight of an offset enroute.

Formation flight system keeps C-17s in line (http://www.edwards.af.mil/news/story.asp?id=123223228)

http://upload.wikimedia.org/wikipedia/commons/thumb/2/27/US_Air_Force_C-17_Globemaster_III_formation.jpg/800px-US_Air_Force_C-17_Globemaster_III_formation.jpg

[Dash8driver1312]

I only change aircraft configuration with flaps and landing gear...

Formation, on the other hand...

[Tu.114]

Consider a mechanical malfunction like an engine failure on the leading aircraft in climb (with high power setting and low airspeed). This will induce a bit of drift and a reduction in speed, which will reduce the already marginal separation between the two aircraft quite rapidly; quite possibly to a point where it becomes zero.

Of course, one could think of hooking these two aircrafts flight warning systems up via datalink (or so) so that the following aircraft can be called to automatically start an evasion manoeuver by the leader aircraft systems. With military aircraft that allow their small crew the silk way out in case of need, this may be practicable. But would You want to try this with unharnessed passengers or worse with cabin crew walking the aisle with their heavy trollies? I really do not.

[gums]

Great idea, but think not very practical for the heavies, especially in weather or night.

Our "lights" did it on the wing of a tanker crossing the pond. Don't get too close to the heavy's centerline, however, or you'll roll into him.

So one day I fell behind a bit on purpose and maintained nose-tail clearance, then moved in. Wow! took lotta aileron and such, but I could feel the "surfing" aspect easily. My fuel flow went down about 25%.

And just look at the migrating geese and cranes!

[underfire]

The station keeping, or now FFS I guess, was really quite interesting. One the screen, you have a grid box with dots. There is the centerline which is the lead aircraft. You select the dot and the aircraft maintains that position, over up, over down, etc. Was really quite interesting, and entirely automated.
As gums noted, they did realize quite the fuel savings by staying in the uplift part of the vortex.

I am not sure of the disconnect capability if something goes wrong with the lead aircraft...

EDIT: The Autonomous Formation Flight system marries an extremely robust flight control and guidance system with a close-coupled GPS/IMU placed on the aircraft. Inter-ship communication allows the multiple GPS/IMU systems to share state data and through and extended Kalman filter technique, they yield a differential carrier phase solution. They resolve the relative position accuracy between the aircraft in formation to less than 10 cm.

Through shared state data, the guidance systems aboard the aircraft resolve coordinated trajectories that permit the aircraft to maintain formation. The trailing aircraft is thus capable of maintaining its position within the lead aircraft’s wing tip vortex with extremely high accuracy.