December 23rd 2020 (revised January 8th 2021) Robinson Helicopter Company issued a Safety Alert: R44 & R66 Hydraulic Controls Pre-Takeoff Check.
Robinson had received a report of a helicopter’s hydraulic controls becoming stiff in flight. Examination of the system found one of the servos with excessive internal wear, which caused the servo to move too slowly in one direction.
The safety alert describes a new pre-takeoff control check (in addition to the normal hydraulic check) to confirm all three servos are able to move rapidly in both directions:
…With helicopter at governed flight RPM and collective down, position cyclic approximately 1 inch aft of neutral. Move cyclic rapidly forward approximately 2 inches, then rapidly aft approximately 2 inches. There should be no feel of resistance…
RHC Safety Alert: R44 & R66 Hydraulic Controls Pre-Takeoff Check
If any resistance is felt (similar feeling to the resistance felt when hydraulics are turned off) – DO NOT FLY & contact maintenance.
Video Demonstration
Robinson have released a video showing the pre-takeoff check:
Why only cyclic forward and aft?
Now at first thought you maybe wondering how only pushing the cyclic forward and aft tests all three servos and why is there no left and right movement of the cyclic or any movement of the collective. To answer that have a look at the R44 hydraulic servos:
In this diagram from the R44 Mx Manual you can see two servos at the front and one at the back. Pushing forward and back with the cyclic activates all three.
In this photo you can see the servos from below the top of the fuselage (now front facing left). The collective up and down also moves all three at the same time. But that is not a smart way to test the servos on the ground…Unless you want to replace the skids/tailboom…
In this photo you can see the servos from above the top of the fuselage (with the mast cover panel removed).
In this photo you can see the push rods connecting with the lower swashplate (with the mast cover panel removed). Cyclic left and right activates the front two push rods and servos only.
More Info
Check out all the other Robinson Helicopter Safety Alerts
