Welcome to the high-stakes world of aviation, where the pressure on aircraft builders is no less breathtaking than the prices. Whether flying in commercial passenger service, air cargo or military missions, aircraft are getting bigger, more powerful, more fuel efficient and more reliable. And the last of these, reliability, is no mere afterthought, says Steve Lee of QinetiQ. As the airline industry says, a non-flying aircraft is one that is not making revenue.

Thanks to increased demand for air travel and the need to replace older, inefficient equipment, aircraft buying is expected to surge for the next two decades. Boeing predicts the worlds airlines will need to buy more than 30,900 new jets by 2029, valued at $3.6 trillion. Over 7,000 of these, valued at $800 billion, will be bought by European airlines, it says, with over 95 percent of the European fleet turning over.

Airbus likewise sees demand taking off, but believes that concerns about airport congestion will lead airlines to put their money on bigger aircraft, thereby reducing seat-mile costs and assuring profit margins. It sees roughly 25,000 new jets seating over 100 being put into service by 2028, including of course hundreds of its own 525-passenger A380s . The top buyers will be Asia-Pacific-based airlines with 31 percent of the new buys, followed by airlines from Europe with 25 percent – particularly the United Kingdom with its mix of global, low-cost and charter airlines. North American airlines will snap up another 23 percent, Airbus forecasts.

While they may debate the most desirable scale for passenger jets, both aircraft builders agree that cost, efficiency, revenue and environmental issues are driving the development of all their equipment and components. And that includes lubricants, said Lee, principal scientist for fuels and lubricants at QinetiQ in Farnborough, U.K. QinetiQ, once part of the U.K. Ministry of Defense and now privatized, helps clients by evaluating materials and doing research, writing specifications and performing tests. Lee, who specializes in aviation lubes including gas turbine lubricants, spoke in late September to the ACI European Base Oils & Lubricants Forum in London. His paper, co-authored by Alun Williams of Airbus, offered an aviation industry perspective on the future of lubrication.

What does the aviation industry want? In a nutshell, they want reduced cost, increased revenue and increased efficiency, Lee explained. Also, an aircraft is a mass of vibration, and anything that a lubricant can do to help that is going to be seized on by aircraft operators.

The aviation industry is looking for reduced aircraft effect on the environment and, conversely, reduced environmental effects on the aircraft, he added. A good example was the cloud of volcanic ash which threatened air travel in Europe in April, and posed a major hazard for equipment. But more quotidian issues are harsh weather, dust, corrosive environments and temperature extremes.

Aircraft builders also want to be able to offer increased range, with greater ability to manage weight, power and fuel. Fuel costs are always important, Lee said, but the stability of fuel costs has also become essential to the airline industrys health, as proved by the crushing crude price hikes of 2008. Twenty-five airlines were bankrupted in 2008, he pointed out.

Higher power density is another critical demand. Operators want to get more power per kilogram of weight, so they can get more range for the same amount of fuel. Meanwhile, stabilizers and undercarriages keep increasing in size and weight, as do other onboard equipment. To offset these gains, the use of nonconventional, lighter weight materials, such as composites, carbon fibres and plastics, is expected to rise – but such moves always carry a risk of chemical incompatibilities, Lee said. In Singapore, one aircraft was fumigated, and the plane fell apart when some new materials unexpectedly dissolved. Similar issues with materials compatibility are likely to confront lubricants, he hinted.

When it comes to lubricants, airlines and builders alike want any oil to be proved before it reaches their aircraft, which can take years to accomplish, Lee stressed. They also want extra [performance] to be built into the fluids, so they can tap into it when theyre ready to extend drain intervals.

Another issue is the complexity and volume of lubricants that are required for each aircraft. There are a huge number of lube points, ports and parts that require attention, making lube inventories expensive to stock efficiently worldwide, as airlines must do. SAE Internationals E-34 Aviation Propulsion Lubricants Committee works on defining aviation lube performance, while the SAE AMS M Grease Committee has worked to streamline the selection of greases used in aviation components.

Other issues and challenges also include electricity supply for aircraft. The Boeing 787s air conditioning supply, for example, is not bleed air from the engines (as it was traditionally), but instead uses electric motors. The motor may not need lubrication, but what about the rest of the system, Lee mused.

Planes operating in the high outer atmosphere have their own set of issues, he continued. There may be problems with radiation, and the thin-air environment. Temperature and load ranges are much wider than in the lower atmosphere, too. Some lubrication systems appear to be in very vulnerable locations for outer atmosphere exposure.

The military, where QinetiQ got its start, has its own concerns. Military jets weigh less and tend to be more unstable than passenger jets, because they sacrifice stability for speed and maneuverability. They also demand more work from the engines, putting greater stresses on the lubricants. They must respond better to controls – meaning a higher-performing hydraulic system with exceptional fluid – and undergo more stress and fatigue.

Lee pointed out that the U.S. Air Force is having good success with less-flammable polyalphaolefin hydraulic fluids. Thats counter-intuitive, because PAO fluids indeed are flammable; however, theyre less likely to ignite under combat conditions, such as if a hot bullet pierces a hydraulic line. Commercial aircraft usually dont face the same fire-safety risks. However, USAF statistics show a marked decrease in financial losses due to fire, so apparently its working for them, he commented.

In all cases, no maintenance is the ultimate goal, said Lee, but this is highly unlikely to occur. Twenty-four months is the standard interval for engine maintenance, although some engine manufacturers are saying they can stay on-wing for 40,000 hours, he said, then wryly added, But can they do it without seeing coke deposits?

Fortunately, frequent top-ups are needed in aircraft engine oils, and that tends to replenish the additive part of the engine oil formulation, he continued. But less lubricant consumption is an-other goal of aircraft operators, which will reduce the need for top-up and diminish this oil-freshening effect. That means more robust additive systems could be needed.

Elsewhere, many aircraft have service points that are all but inaccessible, Lee noted. In such cases, longer-lived lubricants will help; he said it also suggests an opportunity for solid lubes, or ones that self-regenerate or even self-replenish. That would require some ability to purify the lubricant over its service life, he conceded, although the added weight of another oil reservoir and the purification system could be a deal-breaker.

For airlines, any maintenance breakdown is a cost, Lee said, and at the end of the day, what operators want most is guaranteed availability and up-time. They would like to reduce the need for redundancy and back-up systems.

QinetiQ has been assisting in these lube system needs by trying to discover how to improve oil life, through the use of computer modeling rather than impossibly costly field trials. Offering a preview of this research, Lee said the preliminary findings are that most engine oil life is used up in the most intense moments of flight: takeoff, early climb and reverse thrust (braking). Otherwise, the rest of the flight puts far less stress on the oil.

If this turns out to be true, and the oil is coasting along except for those energetic bursts of activity, can we ignore the rest of the flight plan in respect of its contribution to total fluid degradation? he wondered. Someday, he offered, maybe it will be possible to use an algorithmic approach to alert operators of remaining oil life, similar to the oil life monitors on many passenger cars. Now that would definitely change the stakes in the world of aviation lubricants.