Originally Posted by
60FltMech
JohnDix,
When I wrote the post opening this thread I had two questions in mind that I wanted to ask: first was about fly by wire and the second question, which is regarding flight control hydraulic systems.
It seems that if you could develop a rugged fly by wire system you would be well on your way to simplifying your flight control hydraulic systems.
Regarding V-280, I assume Bell will use what they have learned on their 525 FBW and hydraulic systems. But as you pointed out the standards for such systems for VTOL aircraft aren’t fully established, so how does it all come together in the end?
I just can’t see an aircraft with a mass of push pull tubes, mixers, bellcranks and Hydraulic lines being the future of Army Aviation(or VTOL in general), someone has to crack the code on simplifying these systems, while also keeping redundancy for battle damage or other emergencies.
FltMech
60FltMech,
First, thanks for starting this thread, this site has become dry of new topics of late.
Many people don’t realize that the FAA FARs are only the equivalent of a cover page. Interpretation of FARs correctly is impossible without referencing the
advisory circulars (ACs). ACs provide guidance and describe acceptable methods for demonstrating compliance to the FARs.
Where the rotorcraft ACs fall short, are for new and novel technologies, like FBW. But FBW is only new on commercial rotorcraft (Part 27 and 29). For Part 25, Transport aircraft, FBW is well established. So using Part 25 ACs to provide guidance for Part 27 and 29 FBW has been the path for the AW609 and Bell 525.
This path drives FBW rotorcraft to be designed to many of the same requirements as a large Transport aircraft like a Boeing 777 or Airbus 350 airliners. So cost and weight become a major factors. This is why eVTOL developers are trying to circumvent this path to certification. Like you, I fear this will result in the loss of many lives if it is allowed to happen.
The only three production FBW rotorcraft, the V-22, NH90, and CH-148 were built to military or company standards, and don’t meet FAA certification requirements. Sikorsky attempted to get FAA certification for the CH-148 FBW system, but design’s architecture was inadequate.
The AW609 and Bell 525 will be the first civil certified FBW rotorcraft, and both have the same FBW system design. Their FBW systems build on the lessons learned from the V-22, but are very different in design. Bell realized 25 years ago that a V-22 FBW architecture could not be FAA certified. Additionally, cost, reliability, and maintainability aspects of the V-22 architecture were incompatible with a commercial customer. So Bell started from scratch, designing a FBW design based on the KISS principle (as simple as a FBW system can be). Because of the long delays in AW609 and 525 certification, Bell (and Leonardo) engineers have had decades to develop these FBW systems.
When the FAA eventually publishes ACs providing guidance on FBW for rotorcraft, it will be based on the standards set by AW609 and 525.
The Bell V-280 FLRAA and 360 FARA FBW systems are based on the 609 and 525 architectures. Since the US Army is now requiring FAA levels of critical failure reliability for these platforms, Bell was well prepared with an FBW system solution.