Keeping a careful eye on the legislative process enabled DAF Trucks to be first to the market with an aerodynamic cab after the changes to weights and dimensions legislation.
But that came with risks, as DAF Trucks design director Bart van Lotringen reports. “We started design work in 2014, as we knew changes were coming that would give us a chance to replace the 95/XF cab that had served us so well since 1987. We had people keeping an eye on the proposed legislation, and using that information to refine the design.
“But there was a shock for us in 2017, when the dimensional envelope changed to specify a sloped, rather than vertical cab front. This was done to improve pedestrian safety: it would push people away from the vehicle rather than knocking them over. The problem was we were just two months away from the point where the design had to be fixed.”
A period of frantic activity followed, when virtual reality was used to produce a new, compliant and safer design. “After that we had to ‘industrialise’ the design, a process that takes about two years before the cab can go into production,” van Lotringen says.
But preparation for production of a larger cab had already begun. “We installed a new paintshop in our cab production plant, and although the dimensions of the new cab had not been finalised, the several dip baths had been sized to treat the entirety of a new larger cab although we didn’t know its exact shape at the time,” he notes.
RAISING THE BAR
The project had been driven by drawing up a top 10 of key improvements. While the full list of targets remains secret, van Lotringen reveals that one was a 20% improvement in aerodynamics, and another was no weight increase over the existing design despite the lager cab.
He continues: “We also aimed for better vision for the driver, and better ergonomics and driver environment too. It was easy to score a 10 for one target, then realise that the change made had dropped the score for another down to six. One of the pillars of the project was safety, and not just to meet current and anticipated legislation. We had to produce a cab that would be suitable for the next 30 years.
“Every legislative change has influence on the design of the ‘body in white’. It takes time for legislation to be clarified, and the political process is not always a straight line. The product has to be adjusted to suit. You have to be able to read the legislative map ahead.”
Van Lotringen pays tribute to DAF’s former global development director Ron Boorsboom for driving goals; he unfortunately passed away shortly after the launch of the new truck range.
“In drawing up the objectives, we hadn’t just looked at the legislation and what our competitors had done since the introduction of the 95, but other factors as well, including that humans themselves are getting taller, and that the next cab had to be ‘agnostic’ to the future drivelines that might be put beneath it.”
While design objectives may have been met, they still required refinement to keep them on target when they became reality. “We assess aerodynamics by using computational fluid dynamics, but they may not reflect reality in testing, and you then have to identify the problem, which may be a poor seal or something. You have to recover and keep the project on target,” van Lotringen says.
USER-DRIVEN
Changing legislation, some driven from London, meant that direct vision was now a priority, not just for distribution trucks, but for long-haul, too.
Van Lotringen says: “You can make the cab floor lower, but then find you have no space on the front firewall for all the items required. This might result in the loss of a few vital centimetres. Therefore, we called on the engineers to get inventive again. By maximising the ‘vision door’ with a kerb-view window, we recovered those centimetres and even went beyond.”
The most important influence was from potential users and five ‘customer councils’ were held every year.
“The height of the cab floor is defined by the height of the engine. Working within legislative parameters on the long-haul cab, we could have a flat floor with a four-step entry, or a small 50mm engine hump with a three-step entry. The consensus was that three steps were preferred, and the shallow engine hump was regarded as a flat floor,“ he says.
“It also had to be easy to convert the cab from workplace to rest area. Drivers wanted a minimum of fuss, which means a pull-out table and rotating seats.”
Other features were more difficult to settle. “We let the customers drive a vehicle with cameras instead of mirrors. Opinion was sharply split 50/50. In the end we offered both. Cameras are now standard for the UK, but the customer can specify mirrors if preferred.”
The first production date – ‘job one’ – was set in stone and the post-Covid disruption came at just the wrong time as DAF was ordering tooling for the new cab. Delays were inevitable, but the launch target was still met.
PATH TO EFFICIENCY
Anders Tenstam is a senior technology expert in aerodynamics at Volvo Trucks and says he was involved in developing concepts well ahead of the legislative reform that allowed manufacturers to stretch cab dimensions.
This work culminated in the reveal of the Volvo Concept Truck in 2016, which in turn inspired today’s FH Aero truck. He recalls the primary objective of the early work was to encourage legislators to relax the rules by showing the advantages that could result.
His colleague Mattias Hejdesten is a senior engineer expert specialising in aerodynamics, whose role includes taking concepts developed by Tenstam and developing them for production.
Hejdesten points out that while the Concept truck was designed as a clean sheet exercise, there are two paths to aerodynamic efficiency: one being the creation of an ideal shape, and the other the detail work that can either refine the clean-sheet design or improve the performance of an existing one.
“Attention to detail can generate a significant improvement by smoothing airflow through an existing design, then these refinements can be transferred over to the new product,” he says.
“We have seen a phased introduction of many of these features prior to the launch of the Aero,” Tenstam adds, saying that this work was done on the basis of making the easiest changes first. "Logically, you should start at the front but logistically it was easier to make the changes further back first,” he adds.
Tenstam explains that much of his work is in finding the ideal compromise between aerodynamics and other requirements.
“Aerodynamics is non-linear physics, with improvements being increasingly incremental. Aerodynamic improvements are always on a curve – you have to find the ‘golden egg’ where these are maximised without impacting on other factors too adversely.”
FINDING THE BALANCE
On the Aero truck, there was an inevitable weight penalty of around 70kg from the structure that supports the extended front-end, but the rounded corners of the ‘nose’ means that it does not impact on the turning circle.
Approach angles are unchanged, but a single large front step replaces the two-step design that enables windscreen cleaning on the standard FH: not good news for shorter drivers.
Developing a cab tilt mechanism that allowed full engine access while accommodating the extended nose was also a challenge, but there have been no complaints about this from operators now the truck is on the market.
The lower running speeds of trucks compared to cars mean that more attention must be paid to sidewinds. Tenstam says: “At typical truck speeds, drag can be 60-70% higher in a crosswind. There is a need to keep the airflow attached around the front of the truck. The two vertical corner-edges at the front of the truck are like wings and cannot be allowed to stall. The gentle radius of these corners maintains a smooth airflow which is efficient and aids stability. In developing the cab, we optimised the shape to suit models of the prevailing wind in Europe.”
Much of the development was done in simulation rather than in live testing, with many operators achieving the fuel savings of 5% estimated at the design’s launch in use. Tenstam cautions that transferring an aerodynamic improvement into an operational improvement also depends on other factors including terrain, load, speed and weather conditions.
Aerodynamic improvement also allows more effective use of other technology, such as sophisticated cruise control systems as the truck will freewheel for longer.
Tenstam and Hejdesten maintain the technology will really come into its own with battery-electric trucks. “With less drag, there is more scope for regenerative braking,” Tenstam says.
And Hejdesten adds the quieter driveline of an electric truck means other sounds, such as wind noise, are more intrusive. “And there is less wind noise in a more aerodynamic truck,” he notes.
For the moment, the (diesel) Aero truck is making up the majority of Volvo’s sales to operators in the long-haul market. “It’s certainly finding us customers in this segment,” Tenstam asserts.
