As just a few grams on an aircraft can have huge operational cost implications for airlines, they are constantly looking for ways to reduce weight – even down to the choice of drinks cup. Although much of the main structure and systems of an aircraft cannot be altered, one area where there is an element of design flexibility is the interior.
A prime example is seating where manufacturers and suppliers are continually striving to develop new designs that save weight but still give passengers the desired level of comfort.
This is the principal reason why composite development specialist Cecence was approached by a leading seat manufacturer to develop a new economy seatback for a national flag carrying airline.
The project not only had to provide a 15% weight saving for the seatback it also had to meet 16g Head Impact Criteria (HIC) industry standards, be Fire, Smoke and Toxicity (FST) compliant and importantly, be cost-effective for fast volume production.
Mike Orange, design and engineering director at Cecence begins: “We had demonstrated a cost-effective solution on a legacy seatback design of the customer’s by speeding up production, so we were then asked to work on a next generation unit. We had to remove the metallic sub-frames and deliver an all-composite seatback. Weight, safety standards and design flexibility considerations were all important.”
Fire resistant resin
Cecence chose to use a phenolic resin/carbon fibre composite for the seat, not only to meet the FST regulations, but also to enable faster production.
“We wanted to offer a seatback that had homogenous fire properties,” Orange explains. “There are techniques to use covers and foams as you can argue that certain areas of the seatback don’t have to fully comply as they are not exposed to flames, but this is risky in our opinion. We would rather start with material that passes FST regulations. At the time a phenolic resin was the only resin that easily passed these. We also tested epoxy and bio-resins but we couldn’t get the cycle times that were required, but we are working with our partners to develop these for future projects.”
An important factor was that phenolic resins offered the ability to develop a snap-cure process for the seatback. This was important for the customer as ease and speed of production was a key requirement on the project.
“We worked on the technology needed to cure phenolic in minutes rather than hours. Working with our supply partner we qualified new constituents that transformed this into a seven-minute snap cure process. I hesitate to use the term game-changing technology as it is banded about too frequently, but for us, unlocking this very quick turn-around time justified the investment in the process. We opted to utilise prepregs for accuracy and consistency and hot-in, hot-out press moulding for improved process time, surface finish and physical properties.”
With its suppliers Cecence had to develop new resin systems and fibre reinforcements from the ground up that could meet the stringent tests that aircraft seating is subjected to.
“A 16g seat with full in-flight entertainment and headrest package is a highly loaded scenario so we went back to fibre level. We lab tested a huge array of carbon tows. We checked the performance of the resin and sizing interaction, then scaled it up into woven cloths and made sure it was production ready. All production processes must allow for variance of results, but by static testing the units prior to committing to expensive external testing the customer satisfied themselves that our results were very consistent and we had predictable performance.
“Historically there have been issues with phenolic resin in terms of health and safety so we also worked with our prepreg supply partner to focus on improving this. The phenolic prepreg system is now formaldehyde free (the most contentious constituent) and this now makes it REACH compliant – the first REACH compliant phenolic prepreg that I’m aware of. This also means we can now offer this material to the whole aerospace market so others can see the benefit of snap-cure processing and the improved health and safety for the production team.
“At Cecence we offer support to engineer parts in composites or assist in setting up production lines so one of our goals is to support the aero interiors sector with a robust supply chain. If we can empower the industry with multiple sources with similar materials and processes then customers will gain confidence in the fact that there is price competition and this isn’t just ‘niche’ technology.”
Simulate to innovate
For this project, most of the design, testing and simulation was led by the customer but it was important that Cecence provided as much pre-testing information on the new composite as possible to help save costs.
“In the end, simulation can only take you so far, it can’t predict real life. There is a point were physical testing takes over and after observing in-house static testing results, we made recommendations and improvements based on our extensive composite knowledge and experience.
“You need to do this before you go for external crash testing because that is very expensive, added to the fact that you have to test rows of seats at a time and there are many issues that can spoil the test before you get to the required energy impact readings.”
Ultimately Cecence ended up delivering 2,500 seatbacks for the customer that are all now installed and being flown by the airline. The new material allowed the seat manufacturer’s design engineers to create shapes that would not have been possible in metal and to make space savings on the aircraft to allow for increased passenger comfort. With FST compliance built in to its core, this negated the need for fire proof dressing and the seatbacks came out of the mould with a good paint ready surface.
“Our finish was good enough to show, removing the need for expensive plastic shroud mouldings that would have added to the weight, but with no added structural performance. This also created more space for passengers.
“The seat design was extensively trialled for comfort prior to production and I’m told the airline reported excellent comfort levels. They are ‘in-flight’ and line-fit approved on A321neo and A320neo aircraft. Our customer has also added a dedicated exit row design variant that has also been tested to 16g HIC.”
JEC award recognition
The project achieved so many industry ‘firsts’, it was no surprise that it was selected for a JEC Show innovation award in Paris.
“The seat we made last year was apparently the first all composite 16g composite economy class seatback that was Airbus line-fit approved. We’re very proud of that and of being selected as finalists in the aerospace process category in the JEC Innovation awards. We were the only UK firm to win an award at the world’s premier composites trade fair. For us, it was a very fitting conclusion to what has been a fantastic programme and shows the strength of the UK aero interiors industry.
“It is also a testament to what can be achieved with real collaboration in ground-breaking innovation projects,” concludes Orange. “This is, in our opinion, an award that recognises all our partners within the process, and we hope to continue making tangible innovations through collaboration.”