Fuel burn: Are you doing it right?

Whether you are flying a light jet or an ultra-long-range jet, fuel consumption is something you want to cut down on – for more than one reason.

Fuel burn: are you doing it right?

Whether you are flying a light jet or an ultra-long-range jet, fuel consumption is something you want to cut down on – for more than one reason.

AS ALL businesses increasingly attract the steely gaze of environmentalists, it’s no surprise that the aviation industry is beginning to sharpen its sustainability act. It’s obviously a broad approach, but two of the more-promising areas for development are the use of sustainable aviation jet fuel (SAJF) and lowering aviation fuel burn – by way of aerodynamically clean aircraft and ceramic-based paints to coat aircraft exteriors. The introduction of SAJF has been intermittent for close to a decade. An increasing number of fuel providers, such as Neste and World Energy, are ramping up production of SAJF, which is a drop-in fuel, created from recycled household products such as plant oils, municipal waste and waste gases. SAJF is two to three times more expensive than regular Jet A-1, meaning that it is the least popular option amongst owners and operators.

But it can reduce as much as 80% of greenhouse gas emissions over its lifecycle compared with conventional jet fuel. Further, the current production of SAJF is a fraction of the total consumption of aviation fuel. Damian McLoughlin, at Neste, said the company would potentially produce only up to 1 million tonnes of SAJF per year. Compared with the 200 billion tonnes of fossil jet fuel consumed by aviation in the past 10 years however, it is not significant. McLoughlin said: "1 million versus 200 billion is a drop in the ocean. So, we are many, many miles away from carbon neutrality across aviation." This outlines one of the major problems with sustainable fuel at present; there is not enough of it. While electric aircraft are on the rise – whether all-electric or hybridelectric – eVTOLs cannot realistically fly people yet. Essentially, this means that aviation and fuel will continue to have a symbiotic relationship for the foreseeable future

SAJF supply chain

The International Air Transport Association’s (IATA) 2020 deadline for carbon-neutral growth across the air transport industry is fast approaching. And although there is a lack of product availability, fuel-distribution majors such as Air BP and Shell Aviation have begun to increase their commitments to helping meet this target.

In 2016, BP invested US$30 million in Fulcrum BioEnergy, a California-based company, to secure 50 million gallons of sustainable aviation fuel a year. In May 2018, this took a step forward with construction starting on a municipal solid-waste-to-fuel plant in Reno, Nevada, USA. Then, at the end of 2018, BP entered a partnership with Johnson Matthey – the science & technology company – to license its Fischer-Tropsch technology. This is helping support Fulcrum’s production of biofuel from municipal waste.

More recently, Neste and Air BP collaborated to deliver sustainable aviation fuel to airports and airlines in Sweden. Sweden has an ambitious target of being fossil fuel free by 2045. And it is doing so by proposing the introduction of a greenhouse gas

reduction mandate for aviation fuel within the country. The reduction levels are estimated to be equivalent of 1% (11,000 tonnes) sustainable aviation fuel in 2021, 5% (56,000 tonnes) in 2025 and 30% (340,000 tonnes) in 2030. According to Neste, this makes Sweden an undisputed leader in decarbonising aviation. From 2020, the Norwegian government will introduce a 0.5% biofuel blending mandate for aviation. Air BP has supplied sustainable aviation fuel in the Nordic countries since 2014 at around 10 airports, including most recently at Kalmar airport in Sweden and Oslo airport in Norway. The presence of an existing and functional supply chain for the fuel means the growth of SAJF has suitable conditions. Irene Lores, global sales & marketing director, Air BP, said: “Additionally, as part of our strategic collaboration with the on-demand private jet marketplace, Victor, we launched a carbon offset programme for private flying in April 2018. This programme allows participating aircraft operators to offer their customers carbonneutral flying when using Air BP fuel.”

“1 million versus 200 billion is a drop in the ocean”

In 2018, Shell Aviation announced a long-term partnership with SkyNRG, fuel supplier to commercial airlines, to ensure SAJF supply. Shell has also worked with KLM Royal Dutch Airlines, SAS - Scandinavian Airlines and Finnair to reduce carbon emissions at San Francisco International Airport (SFO), using SAJF. Shell is mostly working to cater for the commercial aviation and defence sectors. A spokesperson from Shell said: “The current supply accounts for less than 1% of the aviation industry’s total jet volume requirements. If the industry is to seize the benefits of a rapidly increasing demand, it is essential that business aviation companies and commercial airlines alike adopt a clear and comprehensive approach to carbon management beyond SAJF alone.”

Less is more

While SAJF is being used in small measure by OEMs and operators – who fly to trade shows or summits using it – to increase awareness in the industry, its incorporation into full-time commercial operations is highly likely to be some years away. At present, however, owneroperators, OEMs and aftermarket paint providers have outlined that there are significant other ways to reduce fuel burn. And with these come the benefits of reducing operational costs and a sound moral compass – in line with corporate social responsibility.

Austrian operator, GlobeAir, is one of the companies using ceramic-based nanotechnology to coat its fleet of Cessna Citation Mustangs. GlobeAir has committed 20 Cessna Citation Mustangs to a partnership with aftermarket products company Aerocoat. Aerocoat, based in the UK, uses its nanotechnology to coat aircraft, reducing the drag coefficient and, in turn, lowering the fuel burn.

GlobeAir’s CEO, Bernhard Fragner said: “When it comes to achieving both high aesthetics and cost effectiveness, it’s essential for us to rely on the market leaders within the industry. The Aerocoat process is a good alternative to repaint to achieve both aesthetic appeal and higher performances for the most enjoyable experiences on board.”

Dirt gathered across the engine nacelle of a Citation Mustang.

One of GlobeAir’s aircraft after the Aerocoat treatment.

Some of the aircraft in GlobeAir’s fleet of Mustangs have been in service close to 10 years. Meaning that their exterior coats have been slowly worn down by exposure to sunlight and atmospheric pollutants. Typically, as aircraft age, they consume more fuel as a result of surface drag, airflow and dirt adhesion.

Aerocoat’s nanotechnology refines the surface of aircraft on an atomic level, to ensure the smoothest coating of the exterior of an aircraft. A Mustang uses no more than two Coca-Cola tins of the ceramic coating – which Paul Stansfield, operations manager at Aerocoat, explained is basically glass: “The first layer will last around five years, burning off 10-12 per cent every year. The second is the UV layer, which works with the first layer to preserve the colour of the aircraft. Effectively, it will look vibrant for another five years.”

What products like Aerocoat also ensure is that aircraft do not get taken out of service for very long, as they would if they were going to be traditionally re-painted. Stansfield added that a Citation Mustang takes about three to four days to complete from the time it arrives. He said Aerocoat “works on the aircraft when it is in for its longest scheduled maintenance”. “We return the aircraft to factory performance and with some aircraft, we have found that the fuel consumption can go back to what it was 14-15 years previous,” added Stansfield.

Richard Jowitt, former Airbus pilot who now flies a Rockwell Commander 114B, found a marked enhancement in performance of his aircraft after the application of the ceramic coat.

“The Commander now offers 1-2 gallons per hour saving and has become extremely easy to clean,” said Jowitt.

Stansfield added that a saving of even 1% in fuel burn means “thousands of billions of tonnes of aviation fuel not dumped into the atmosphere”, because the aircraft is performing at initial efficiency. However, aftermarket applications are yet to take off in a big way for business aviation. The majority of current users opt for the technology to enhance the cosmetic appearance of their fleet – for potential buyers and customers. But, in general, aftermarket applications and their benefits do not seem to make the list of priorities in the business aviation industry. GlobeAir’s head of maintenance, Patrick Marchant, said: “It lists as an unnecessary expenditure for many people, but the nanotechnology undoubtedly has commercial, environmental and maintenance benefits.”

OEM speak

An article on the BBC website some years ago said the costs of fuel incurred by low-cost carrier easyJet were 40% – approximately £730m – of its annual costs. So, easyJet decided to coat some of its fleet with polymerbased nanotechnology provided by TripleO Solutions, in an effort to reduce costs. The company said it could lower easyJet’s fuel consumption by 2% and that the coat would add only 4oz (113g) to the weight of the jet. The nanotechnology was not only meant to help reduce fuel consumption and its costs, but also to reduce the weight of the aircraft. The BBC noted the industry had used lightweight composite materials, lighter drinks trolleys and thinner carpets. A study by Boeing stated that decorative paint schemes could add between 50-250 kgs onto the weight of their jets. But, the polymer-based technology has been used on US military aircraft for years to help avoid this.

Although nanotechnologies such as ceramic coatings and polymer-based technology are known to be frequently used on commercial airliners, the principles of reducing drag, carbon footprint, fuel consumption and the costs therein apply across aviation – something from which more owners and operators can benefit. According to a study conducted by Boeing’s aerodynamics engineers,most of the drag characteristics of an aircraft are set during the initial design. The key characteristics that affect drag are wingspan, exposed surface area, aerodynamic shapes, and numerous design details. Drag can also be controlled by laminar flow, surface roughness and dirt adhesion (excrescence).

Laminar flow

Boeing’s study examines surface coatings as one of the paths to the promotion of laminar flow, hence reducing skin friction. Laminar flow is defined as the state of the boundary layer, the thin layer of air next to the airplane skin where the effects of friction would be observed. It found that surface coatings may reduce the local irregularities, therefore reducing drag by a small amount. However, Boeing and, indeed, other manufacturers do not necessarily believe that surface coatings are more effective than aircraft that are designed to be aerodynamically clean. Manufacturer Aerion Corporation is designing its supersonic business jet AS2 in collaboration with Boeing and GE Aviation, using reimagined laminar flow wing design from the onset to reduce drag. Aerion’s thin wing and horizontal stabiliser, with moderately swept leading edges, allow for laminar flow on these surfaces. Richard Tracy, co-founder and chief technology officer (CTO), Aerion, said: “Skin friction using this laminar flow design for one square foot, for example, can be reduced by 10% compared to what it would be with turbulent boundary layer.” The company is calling the concept supersonic natural laminar flow (SNLF), something its predecessor, the Concorde, lacked due to its delta wing. For supersonic flight, drag increases at Mach 1.0 but decreases again after the transition. The 12-passenger AS2 is expected to fly at a speed of Mach 1.4 over water and speeds approaching Mach 1.2, where permitted, over land.


Excrescence is another way to reduce drag. It represents 7% of the total drag of an aircraft. Excrescence represents discrete items, mismatches and gaps, internal airflow and surface roughness on the aircraft. Bruce R. Plendl, senior aerodynamics engineer and author of the Boeing study, said: “Aerosmoothness, or excrescence drag, can also be reduced through detailed design of the fit and fair of external surfaces, through better seals around movable surfaces such as landing gear doors and control surfaces, and through clean-up of other external protuberances.” Jowitt added that his aircraft was slowed down by insect and dirt adhesion collected over time.

Retrofitted elements

Further, it is understood that aerodynamic drag can still be improved after initial design. For example, span can be increased, or winglets can be added to reduce induced drag, or drag due to lift. Boeing’s aircraft have used winglets on its different product lines – primarily airliners – to the effect of improving their aerodynamics. While Airbus has used its own version of the same, calling them sharklets, it also employs sharkskins or riblets – inspired by ridgelike structures found in sharks. These riblets are retrofitted microscopic ridges or structures that are carefully applied to external surfaces and tailored to the local flow behaviour of a given part of the aircraft. They are often applied as part of the painting process or via large adhesive patches. Airbus’ head of aerodynamics, Simon Galpin, said: “Riblets are well researched, physical devices that can reduce drag. They achieve a reduction in skin-friction drag by reducing the small-scale turbulence very close to the aircraft skin.”

Even though the texture reduces drag by small amounts, the savings in operational costs per year for Lufthansa – which uses Airbus’ riblet technology on some of its fleet – would be close to $60 million dollars. It also said its fleet would reduce carbon dioxide emissions by 200,000 tonnes annually. The media might have lashed out at Prince Harry and Meghan Markle’s carbon emissions related to business jet travel. But whether aircraft save more fuel through aerodynamic design, retrofitted elements or aftermarket paint products, the benefits to reducing fuel consumption are substantial. The average fuel burn for a light jet is 77 to 239 gallons per hour. While the same for a long-range jet is 358 to 672 gallons per hour. Fuel burn efficiencies vary greatly (as can be seen in the table below) due to factors affecting fuel consumption. But if you own or operate a Cessna Citation X+ in North America for an average 200 hours annually, at 336 gallons/per hour with a per gallon price of 181.96 cents, you know how much your fuel consumption is costing you.

Yuvan Kumar, Reporter, Corporate Jet Investor