The USAF has been exploring ways of lowering its fuel consumption and discovered that when two of its largest cargo aircraft fly in trail, there's a 10 per cent drop produced.
The pair of USAF C-17 Globemaster III strategic airlifters have been flying in line astern formation, one behind the other. This allowed the rear aircraft to exploit the vortex surfing effect.
Vortex surfing involves the turbulent swirls produced by aircraft's wingtips as they cut through the air. Because these air swirls are associated with drag, many modern aircraft including commercial airliners feature upturned wingtips (winglets) as a means of countering the effect. Now, quite the opposite's taking place, with the USAF actively drawing on the positive side of these vortices to actually create drag and, so, reduce fuel consumption and associated greenhouse gas emissions to boot.
Surfing Aircraft Vortices for Energy
The USAF's $AVE (Surfing Aircraft Vortices for Energy) programme got underway in September and the flight trials have been continuing into this month, too. The C-17 Globemaster IIIs have been launching regularly from Edwards Air Force Base - the USAF's key test centre - before getting into position and discovering the optimum vortex exploitation technique.
While a 10 per cent fuel saving might not sound like a huge amount, the USAF points out that its Air Mobility Command (AMC) carries out no less than 80,000 yearly flights. So, scaled up across the fleet as a whole, this 10 per cent drop would likely save millions of dollars annually.
USAF $AVE Flights
The USAF's $AVE flights have yielded a raft of useful data, which scientists at the Air Force Research Laboratory are now exploring in-depth. Based on what they find, it's expected that vortex surfing could then be carried out by other USAF aircraft types.
"AMC has done really well with fuel efficiency at the operational level", Air Mobility Command's chief scientist, Doctor Donald Erbschloe, explained in a recent USAF press release. "The command has worked to gain efficiencies from the 'low-hanging fruit' such as optimizing flight routing, reducing weight where possible, and by not carrying excess fuel. $AVE offers significant efficiency gains, if employed in concert with these initiatives."
C-17 vortex image copyright USAF - Courtesy Wikimedia Commons