40 Years and Counting: Honeywell’s B757 Test Bed Just Keeps Flying!

by James Careless | Aug 29, 2023 | Innovation

June 1982: That is when Honeywell Aerospace’s 757-200 test bed aircraft (now registered as N757HW) rolled off the line at Boeing’s plant in Renton, Washington. It was the fifth 757 ever produced, entering service with Eastern Airlines from February 1983 to January 1991. This ‘Flying Pencil’ (as 757s were nicknamed) then flew with Airtours International Airways starting in March 1995, according to planespotters.net, followed by MyTravel Airways starting in May 2002.

Honeywell acquired this 757 in 2005 to serve as its engine and instrument test bed, which explains the engine pylon jutting out of this aircraft’s upper forward starboard side. The company spent three years modifying it as a flying test bed with 25 seats, lots of onboard power, and room for all kinds of swappable equipment test stations inside. N757HW started flying test missions in 2008, and has been flying them ever since.

Although B757HW’s age is technically 40 years and counting, “we’ve made so many modifications and changes to this 757 over time that the only thing actually this old is its airframe,” said Captain Joe Duval, Honeywell Aerospace’s director of flight test operations. “It is configured to serve as a ‘generic flying test bed’. This means we can modify this 757 to test basically any aerospace product that we may be developing and have interest in, whether for pure research or certification.” According to Honeywell, their 757 is likely the only one in existence that has flown to more than 30 countries across five continents, conducted more than 800 flight tests, and logged more than 3,000 flight test hours.

Perfect for Testing Engines

The main reason Honeywell wanted this 757 was to have an aircraft large enough to mount and test its engines on. “This has traditionally meant turbojet and turbofan engines, but now it includes electric engines as well,” said Captain Duval. “The safest way to do this, when we’re making engines for business jets and general aviation, is to put them on an airplane that doesn’t require the propulsion from the engine under test. A 757 has two much larger engines for propulsion, which allows us to do whatever we need to do with the test engine mounted on the pylon without affecting the flying qualities or the performance of this aircraft.”

To date, N757HW has been used to test Honeywell’s HTF7000 jet engine series, which are used on business aircraft such as the Embraer Legacy 450/500. It has also been used to test the company’s TFE731 and TPE 331 turboprop engines, which are used on corporate and military aircraft.

Also Good for Aircraft Systems Testing

“Airborne weather radar, satellite communications, Controller Pilot Data Link Communications (CPDLC), equipment, flight management systems, navigation and other communication systems might be something you might think of as being simple as voice radio,” Captain Duval said. “But these things do need to be taken airborne to make sure they’re robust and safe for operation before we put them out there for the flying public. Fortunately, the uncluttered interior of the 757 makes it ideal for testing these systems, even though it’s not what people generally think of when they see that pylon sticking out of its fuselage.”

To date, the systems tested on N757NW include Honeywell’s IntuVue RDR-4000 and IntuVue RDR-7000 3D Weather Radar, next-generation flight management systems, JetWave and JetWave MCX in-flight Wi-Fi systems, and Aspire 350/400 satellite communication suites. More will be put through their paces in this test bed in the years to come.

The reason this 757 is able to test these and other systems so thoroughly has to do with its highly sophisticated data acquisition system. “It’s modular and generic, so that we’re always able to record Airplane State Data,” said Captain Duval. “This includes the air speed, altitude, bank and pitch angles, all synchronized with time of day. We can combine this information with data from any of the units/systems that we’re testing, whether that be an airborne weather radar, communication system, an engine, or what have you. We have a very capable data acquisition infrastructure system that is adaptable to whatever kind of unit/system we have on board, plus the real estate to house all of the computers and test stations we need inside this 757.”

The Honeywell Boeing 757 is equipped with a robust data acquisition infrastructure system that is adaptable to whatever kind of unit/system being tested as well as the space to house all of the computers and test stations needed.

A Beefed Up Aircraft

The stock version of the 757-200 was never intended to have a third engine attached to its fuselage adding weight and stress when activated in flight, let alone a cargo door inserted into it as well.

To cope with these challenges, “the aircraft’s metal is a little thicker because of the cargo door,” Captain Duval said. “Honeywell also added a pretty extensive crescent frame inside that strengthens the fuselage from above that cargo door up through that where the pylon sits. There are some really big, heavy attachment points for the test engine mounting that the pylon covers aerodynamically to make it look a little nicer. Those big attachment points are where the load is carried from the thrust and the weight of the engine and then distributed through the fuselage, so it’s not a problem.”

In order to minimize the third engine’s impact on the 757’s flight stability, Honeywell placed the third engine mounts as close to the center of the airplane. This keeps it from affecting the aircraft’s yaw axis and reducing its flyability.

“We had a goal of making sure that we didn’t reduce the operating envelope of the airplane, meaning we could still go as fast or as slow or as high as this 757 was originally designed to do,” said Captain Duval. “We needed and wanted to have that kind of performance envelope and we achieved that with all the design and effort that went into the installation. As well, there’s some pass-throughs that are built into the fuselage, just holes that we cap and we can use just depending on what we might be testing. And there’s lots of cabinets inside the aircraft that take all the instrumentation that might be going out to the engine, along with scanners and other things that are part of that data acquisition system.”

In order for this data acquisition system to work properly, N757HW needs to move massive amounts of data around; both on board and from the aircraft to the ground. “So we’ve made a lot of efforts in the last seven or eight years to enable high-speed bandwidth connectivity to the aircraft, using a few different SATCOM systems,” Captain Duval said. “After all, we make the terminal, the antenna, and the other SATCOM components that go into the airplane. We’re not making the satellites that we connect to, but we provide all the equipment such that if you have a wireless device inside the plane, you’re connected by Wi-Fi to the systems that we provide.

In a commercial airliner, this high-speed bandwidth would be used to support passenger internet access and in-flight entertainment. On N757HW, the purpose is to collect testing data and get it from the aircraft to the ground.

Not only is this connectivity useful for Honeywell’s testing procedures, but it could be something that enhances commercial aircraft availability going forward. “If you have a system that can describe the type of braking that was just used on a landing, and continually gather that data with the airplane being connected, then you could have a better way of doing predictive or preventive maintenance by changing a brake assembly when it needs it,” said Captain Duval. “This capability could also be connected to engines and other kinds of components on the airplane.”

Tough Test Conditions

Even though Honeywell’s 757 test bed is going on 41 years old, the company baby it. That’s because a flying test bed has to put the equipment being tested through extreme flying conditions to spot problems and remedy them back on the ground.

A case in point: “One important and exotic thing that we do with the airplane is wind shear testing,” Captain Duval said. “Our airborne weather radar has a predictive wind shear capability, which is important for safety when there are thunderstorms and things in the area that cause this wind shear phenomenon. So when we put this in an airplane, we need to certify it. We need to make sure that what the system is predicting is actual and true, so we have to go fly through wind shear events to develop a system that helps pilots avoid that.”

Because wind shear is dangerous to fly through, Honeywell does what it can to minimize the risks to its 757 crew and aircraft however it can. “We try to de-risk the activity as much as we can,” said Captain Duval. “We plan for a flight test area that’s not mountainous and doesn’t have other features or problems. This is vital for safety, because we have to go down to about a thousand feet above the ground and fly near or maybe even sometimes underneath heavy thunderstorms that are producing this wind shear phenomena to test the equipment. And so we’ll do that: We’ll fly through and see that the system’s predicting wind shear in a certain area and then, using that data acquisition system, gather all the data being generated as the aircraft flies through that wind shear event.”

“Again, this is something that pilots would normally be absolutely avoiding,” he noted. “But we are able to do that using a lower risk method because we’ve done all the work ahead of time to make sure we’re doing it safely.”

N757NW has also played a role in proving the viability of ad hoc wide area communications support for troops by taking part in Exercise Northern Edge. It was a multinational training exercise that brought together the United States Air Force, Navy, Marine Corps, the United Kingdom Royal Air Force (RAF), and the Royal Australian Air Force (RAAF).

In this exercise, the aircraft connected military forces with each other and the outside world through its multiple onboard SATCOM systems.

The Challenges of Age

The fact that Honeywell has done extensive modifications and constant servicing of its 757 test bed does not change the reality that this is a four-decades-old airframe. This makes finding parts a challenge, given that Boeing stopped manufacturing the 757 in 2004 after building 1,050 of them.

“I would say this: As long as there’s plenty of 757s flying around in other forms with other airlines and such, it’s less of a challenge right now,” said Captain Duval. “But as they get older and there’s less of them and there’s less parts available, people just don’t have the interest to keep these aircraft in service. When this happens, that will be even more of a challenge from its age.”

This being said, Honeywell’s 757 has proven itself to be a very, very reliable aircraft with lots of availability time. “We have a great group of mechanics and staff here that keep it up to date and keep the airplane operating,” Captain Duval said. “There’s also the fact that we only put a couple of hundred hours a year on it, when the 757 was built to fly in an airline and get many more hours flown on it in a year. We’re not inducing that same wear and tear on the aircraft, and updating it is — at least from the avionics perspective — actually easy for us because we’re using Honeywell equipment for the flight management system, the weather radar, Datalink, and anything else that might be a new kind of communication or navigation tool.”

As for the day when Honeywell needs to replace its 757 test bed? Given how well maintained this airframe is, plus the fact that B52 bombers made in the 1960s remain in service — as do some DC-3s built three decades earlier — it seems reasonable to assume that N757HW has lots of life left in it yet.

“We’re not looking for a replacement,” said Captain Duval. “We don’t feel like this is necessary yet. It will take us a few years to get through the analysis and figure out what we would want to replace it with, but we haven’t done that yet because we feel like we’ll be able to operate this airplane for quite a long time.”

Meanwhile, Captain Duval and his team are looking ahead to N757HW’s future missions. “In the foreseeable future, I expect to be testing Honeywell’s electrical propulsion systems using fuel cells, batteries, or other power generation capabilities that Honeywell is involved in creating,” he said. “So, we’re adapting the plane to support those activities. As well, there’s continued work with all the satellite communications systems being launched, and the terminals that access them.”

The bottom line: Honeywell’s 757 test bed has proven itself to be a reliable, flexible, and robust testing platform for the last 15 years, and its future looks just as promising.

Sharks in the Sky: Lufthansa Technik’s AeroSHARK Coating Reduces CO2 Emissions

by Ian Harbison | Aug 29, 2023 | Innovation

Biomimetics is the science (or art) of engineering natural phenomena. Sharks are known to be extremely efficient swimmers and this is helped, in part, by their skin, which is covered in denticles, or small riblets. These smooth the flow of water and reduce drag. As the science of hydrodynamics and that of aerodynamics are similar, this has been of interest to aviation for some time but has taken on a new lease of life with the increased push towards the reduction of CO2 emissions.

Lufthansa Technik has been playing with the idea for a number of years. In 2011, along with Fraunhofer Institute for Manufacturing Technology and Advanced Materials (IFAM) and Airbus, it started the three-year Multifunctional Coating project funded by the German Federal Ministry for Economic Affairs and Energy. This involved embossing a riblet pattern into a coating, the process also curing the coating to give rigidity. Small patches were then attached to the fuselage and the upper surface of the wing of various Lufthansa aircraft to test the longevity and durability of the coating in regular aircraft operations.

With additional funding by the Federal Ministry for Economic Affairs and Energy, 2014 saw the three partners joined by bwm, a specialist machine tool manufacturer, in the FAMOS project, which set out to develop a method of automatic application of the riblets. This was achieved in 2017 in a demonstration at the ZAL Center for Applied Aeronautical Research in Hamburg. However, the conclusion was that embossing was too complex.

After discovering some teams in the Red Bull Air Race were successfully using sharkskin film to boost the performance of their aircraft, it was decided that this was the better solution. Two Austrian concerns had developed the sharkskin film. Bionic Surface Technology, a small high-tech start-up specializing in high-fidelity flow simulations, had used a self-developed code to design the optimal size for the microstructures, while Joanneum Research, a material sciences research institute, could print the microstructures on a very thin adhesive film.

Although Joanneum Research was able to develop the riblet film and produce enough for testing and certification, it would be unable to do this on an industrial scale, so chemical giant BASF became involved as it had already started to work on a process to produce films with microstructures for various applications and had developed and lab-tested a prototype aviation-grade riblet film for Lufthansa Technik, the first version of AeroSHARK. The next steps were to resume testing with more than 100 small patches again being fitted to aircraft in service to monitor durability and to test application and removal methods on a Boeing 737-500 used as an apprentice training tool in Hamburg.

AeroSHARK has riblets measuring around 50 µm in size and a maximum weight of 180 g/m2.

In October 2019, during a C-check, almost the entire lower fuselage of a Lufthansa Boeing 747-400 was covered in 500 m2 of the film, the first large-scale application made to a commercial aircraft. With the modification certified by EASA, the aircraft has remained in service and has accumulated more than 6,500 flight hours, demonstrating that emissions were reduced by up to 0.8%.

The first 777 application was to a SWISS 777-300ER in August 2022. A total of 12 Boeing 777-300ERs will be fitted with AEROshark by SWISS

Jens-Uwe Mueller, manager AeroSHARK, says the main reason for selecting the Boeing 747-400 back then was to promote the benefits of retrofit to customers while taking advantage of many years of experience with the aircraft to accelerate the testing and certification process. He adds that 0.8% may not sound much but, combined with other emission reduction measures, it plays a small but important part in making aviation cleaner. It also means that the technology is mainly aimed at long-range, widebody aircraft, which spend the greatest part of each flight in cruise.

In October 2019, during a C-check, almost the entire lower fuselage of a Lufthansa Boeing 747-400 was covered in 500 m2 of the film, the first and largest application made to a commercial aircraft.

Unfortunately, plans to retrofit the entire Lufthansa 747-400 fleet were cancelled by the pandemic but, encouraged by the test results, the partners designed a new, and even larger, AeroSHARK modification that uses the same adhesive films with riblets measuring around 50 µm in size and a maximum weight of 180 g/m2.

Having looked at possible alternative platforms to the 747-400, the Boeing 777 was selected, not just because there are plenty of aircraft in service (about 1,100, or 25% of the world widebody fleet) but also because they are operated by two Lufthansa Group airlines: Swiss International Air Lines (SWISS) flies the 777-300ER, carrying passengers, and Lufthansa Cargo has the 777F freighter.

The AeroSHARK film is able to withstand strong UV radiation as well as temperature and pressure fluctuations at high altitudes. Resilience against cleaning procedures and icing and flammability were also tested. One result was that dry washes are not yet permitted for AeroSHARK-equipped aircraft.

The film comes in standard panels measuring 100 cm x 50 cm, which are cut to size and currently applied to about 40% of the overall surface area of the aircraft, covering large parts of the fuselage and the engine nacelles. For the 777 modification, this involves more than 2,000 individually trimmed parts. The shapes and riblet pattern are determined using a 3D model of the aircraft developed from very precise laser scanning and CFD computation to establish the airflow around the aircraft. To include the wing bending geometry in the 3D model, Fraunhofer IOSB carried out a photogrammetric procedure on a SWISS flight from Zurich to San Francisco in the summer of 2021. A single camera looking through a cabin window took a photo every few minutes, mapping the positions of special markings on the wing to provide a 3D model of the wing flex. The accuracy of Lufthansa Technik’s CFD simulations was validated, in August 2021, with a series of tests in the low speed wind tunnel at the Deutschen Zentrum für Luft- und Raumfahrt (DLR) in Brunswick, using a scale model of the cancelled Dornier 728 regional jet.

With the CFD model verified, work turned to where the panels might be applied. No-go areas included sensors, heated areas and doors as well as where they might be at risk from ice build-up or foreign object damage or could disrupt laminar flow. In addition, some panels required holes to be cut so that they could fit round access panels. Preferred areas were those that were easy to certify and, thanks to CFD, where drag reduction would be greatest. This is a complex exercise, as the airflow alters direction along the aircraft, which is also, typically, in a 4° nose up attitude in cruise. That means the direction of the riblets must subtly change from panel to panel. The panels are applied in such a way that they do not overlap. This means, in the unlikely event that a panel detaches, it will not take other panels with it.

AeroSHARK comes in standard panels measuring 100 cm x 50 cm which are cut to size and applied to about 40% of the overall surface area of the aircraft, including large parts of the fuselage and the engine nacelles. For the 777 modification, this involves more than 2,000 individually trimmed, parts.

Having said that careful alignment is needed for maximum results, the effect of not being aligned in climb and descent is negligible. Similarly, the weight penalty can be offset after a couple of hours in cruise. For the 777-300ER, the basic saving is 80 kg of jet fuel per hour, which means a little less fuel can be loaded, making the aircraft lighter. Taking a 10 hour flight as an example, that means a saving of 800 kg. This is reduced to 640 kg by the deadweight of 160 kg for AeroSHARK. However, the lighter aircraft weight realizes additional fuel savings of 180 kg for that flight, giving a total reduction of 980 kg.

Application on the first Lufthansa Cargo Boeing 777F.

Annual savings for the same aircraft are expected to be around 400 tons of kerosene and more than 1,200 tons of CO2, while the Boeing 777F will save around 370 tons of fuel and 1,170 tons of CO2 each year. The differences arise from the routes, world regions and utilization for each airline. As SWISS and Lufthansa Cargo have twelve 777-300ERs and eleven 777Fs respectively, these are meaningful reductions, more than 25,000 tons of CO2 annually.

In the future, Lufthansa Technik plans to use a software algorithm in its AVIATAR system to calculate the savings by using consumption data from the fuel flow rate sensors on the engines. Currently, the company uses a different method based on full flight data. This delivers precise measurements to within +/– 0.1%.

The first 777 application was to a SWISS 777-300ER in August last year, with successful test flights in early September resulting in a temporary Permit To Fly from the Swiss Federal Office of Civil Aviation (FOCA) for that particular aircraft, which entered revenue service in October. The test flights were followed by several weeks of evaluation of the collected data and other documents, such as measured values from flow simulations. After completing its review of all submitted documents, EASA granted the STC for both types in December, allowing fleet modifications to begin. The first 777F was fitted with AeroSHARK in February in Frankfurt during a scheduled maintenance layover. The FAA STC was received in April. Incidentally, although the two types have different fuselage lengths, they share many aspects relevant for the design and certification process, for example the same wing geometry and structure, so each STC covers the 777-300ER and the 777F.

To date, ten 777-300ERs of SWISS have been modified so far, with completion of remaining two expected in late summer/early fall this year. This is because the airline is very keen to advance their sustainability efforts and willing to take aircraft out of service just to receive the modification. In contrast, Lufthansa Cargo is integrating the AeroSHARK modification into the standard scheduled base maintenance layovers of their 777Fs, with the second aircraft planned for July and completion of the remaining nine aircraft not expected before 2026. However, experience has brought about a reduction in downtime for the modification to about five days (less than usually needed for a C-check on this aircraft type). The eleven 777s currently modified with AeroSHARK have also already accumulated several thousand flight hours in recent months.

The plan is to expand coverage, for example, to the Airbus A330 and A350 and Boeing 787. There is also an exception to the widebody application and that is the Airbus A321XLR, with its 4,700 nm range making AeroSHARK a viable option. Of course, each of these would require a new CFD model and a separate STC.

Finally, Mueller says the reaction from the industry has been very positive, with airlines showing interest in the 777 having more than 250 of these aircraft in their fleets. He also notes that the interest is now coming from airline personnel involved in sustainability, not engineering.