This is one of those unashamedly ‘what-if’ scenario blog entries – so apologies in advance to those hoping to find hard news about the U.S. Air Force reversing its decision not to equip its new Boeing KC-46A tankers with winglets.
Despite the demonstrated fuel burn savings of winglets and the remorseless spread of both retrofit upgrades and forward-fit winglets on virtually all active and new-build air transport programs, the Air Force evidently elected to forgo the feature for its 767 tanker variant. Read a blog by my colleague Amy Butler for a great discussion about the whys and wherefores of this.
But what if things change? What if fuel costs continue to spiral upwards? In fact, what are the chances they won’t? Virtually nil is the short answer. What if large-scale winglet designs improve to the point where they reduce outboard wing loading (and hence structural complexity for retrofit) to a negligible degree? What if new structural concepts appear that dramatically cut installed weight and manufacturing cost?
You don’t have to be a rocket scientist to imagine all of this happening because it already is. Well before the first KC-46A even comes together, the seeds are being sown that could one day lead to a fleet-wide retrofit which would ultimately save the Air Force millions of gallons of fuel. According to the Air Force’s Alternative Aviation Fuel Initiative, the military is the largest single consumer of petroleum products in the U.S. and the Air Force alone uses more than two billion gallons of aviation fuel each year. The service’s annual energy bill is around $6.7 billion, of which over 80% is spent on jet fuel. Staggering numbers at a time of vicious budget cuts.
So what about these advances? Not surprisingly for a world in which commercial and business aviation is increasingly pushing technology ahead of the military (a reversal of the historic trend), they were on display at this year’s National Business Aviation Association show in Las Vegas, Nevada.
GKN's winglet technology demonstrator (Guy Norris)
UK-based aerostructures company GKN aims to change the manufacturing paradigm for winglet technology by developing a one-piece, integrated composite structure offering significant weight and cost savings over current built-up designs. Unveiling its development technology demonstrator winglet structure at the show, GKN says the co-cured unit will undergo loads tests later this year before further evaluation.
Interior winglet structure exposed at root (GKN)
Interior structure without skin (GKN)
Current GKN-built winglet for comparison (GKN)
The design incorporates co-bonded skins and webs which form integral trapezoidal spars and forms a radical departure from conventional winglet structures. Interestingly GKN builds Aviation Partner Boeing winglets for the 767, with the 767-300/BCF converted freighter due to become the latest variant to use the devices from February 2012.
In the same exhibit hall, Aviation Partners displayed a blended split-tip scimitar winglet which is an evolution of the baseline blended winglet with a downward canted element to counter vortices generated by interactions between the wing tip and the lower wing surface. The new design is expected to provide additional drag reduction without generating so much of an increase in bending moment and weight penalty. Aviation Partners CEO Joe Clark says computational fluid analysis of the design indicates potential drag reductions of up to 9.5% over an unmodified wing, producing a cruise performance gain of over 40% above the original blended winglet configuration.
So with these promising advances in the wings, perhaps winglets will eventually earn their way onto the KC-46A one day after all.Aviation Partner's radical blended split-tip scimitar concept (Guy Norris)