This document discusses the design and manufacturing development of a thick composite main rotor grip for Bell's 525 helicopter. Key points include: - The main rotor grip connects the rotor blade to the hub and experiences high loads. Its design considers structural attachments, clearances, aerodynamics, damage tolerance, and shape. - Manufacturing challenges include fiber distortion, thickness transitions, and complex tooling due to its twisted shape. Sub-scaled prototypes helped optimize the design and manufacturing process. - A full-scale test article was successfully fabricated using an automated layup process and underwent fatigue testing, proving the developed design and manufacturing process. Early consideration of both design and manufacturing were deemed critical to the program's success.

1. Design and Manufacturing Development
of
a Thick Composite Rotor Component
Pin Lin “Ben” Chiou and Mark Wiinikka
Engineer V
Manufacturing Research and Rotor Design

2. Overview
• Main Rotor Grip of Bell’s 525
• Design and Manufacturing Considerations
• Design and Sub-Scaled Article Development
• Full-Scaled Article Development
• Process Automation

3. 525’s Main Rotor Grip
The main rotor Grip is a highly loaded structure
connecting the rotor blade to the rotor hub
An U-channel with two arms
and a turn-around

4. Design Considerations
• Structural attachments of CF bearing, pitch horn, lead-lag damper,
flapping stops and rotor blades
• Clearance requirements (turn-around size)
• Aerodynamic drag (blade root size)
• Damage tolerance
• Twisted shape to simplify blade geometry
• Parallelism between two arms and
inside profile of turn-around
• Laminate quality and consistency (no fiber distortion)
• Weight (drop plies outside blade attachment area)

5. Manufacturing Considerations
• An U-channel structure is subjected to Spring-In
• Turn-around area is prone to out-of-plane fiber distortion
• Thickness transition area prone to out-of-plane fiber distortion
• Twisting or IML thickness taper adds complexity to layup and tooling
• Machined features on IML increase tooling complexity and difficulty
Tool angle 4.6°
Part angle 1.6°Part angle 1.9°
Out-of-plane fiber distortion

6. Sub-Scaled Article Development
• IML tool; utilized low cost tool
• Materials and forms – fiberglass or carbon; combine +/-, double thick
• Lay up sequence – ply pack or dispersed
• Lay up process – hand lay-up; pressure/tension in turn-around; automation
• Compaction cycles – bulk reduction required prior to cure
• Cauls – accommodate turn-around
• Thickness change; cure cycle; spring-in
• Preliminary testing; cured laminate characteristics; tool compensation factor

7. Design Evolution
Preliminary
• Glass or carbon construction
• Tapered IML and OML surfaces
• Ply pack lay up sequence
• Large areas of co-cured sacrificial
material for machining
In-line Twisted
Optimized
• All carbon construction
• Constant thickness
• Dispersed lay up sequence
• Secondary bond of small areas
for machining

8. Full Scaled Article Development
• Adjustable full scaled test tool
with a tool compensation factor
from sub-scaled development
• Vacuum compaction cycles
were time consuming
• Number of vacuum compaction
cycles needed depends on the
limited manual lay up pressure
applied

9. Full Scaled Article Development
• Finalized laminate thickness, ply orientation
• Finalized compaction cycles, cauls, cure cycle
• Finalized NDI development
• Double-wide blank for two parts at a time
• Detool fixture, machining fixture, bond assembly fixtures

10. Lay Up and Compaction Automation
• Hand lay up was the baseline process
• Automating the lay up and reducing vacuum compaction cycles will
significantly reduce the cycle time
• Conceived and designed a machine for automated lay up
Critical process parameters was the roller application
• Can be fully automated if desired

11. Lay Up and Compaction Automation

12. Full Scaled Fatigue Test Article
• Test article fabricated with imbedded
flaws in critical regions
• Fatigue tested to two life cycles
(25,000 hours each) of Ground-Air-
Ground loads
• Test article also subjected to impact
damage in critical areas
• Test article endured
The development of a thick composite rotor component was
successful considering both design and manufacturing

13. Conclusions
• Early consideration of both design and
manufacturing are critical
• Utilization of the sub-scaled test article
was efficient
• Design and manufacturing are both
critical to the success

14. Thank you!
Pin Lin “Ben” Chiou
Manufacturing Research
pchiou@bh.com