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Blade Folding

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after you land a sea king , how is the head turned to get the blades into the correct position for folding ? , is the starter used for this purpose ?. I noticed on the EH101 site that it has electric blade fold , is the pylon fold electrical of hydraulic ? , anyone got any info on how it works , will the H92 have hydraulic blade fold ?

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Looong time since I flew the truck (29 years!!), but the blade fold (for the Westland SK) works when the #1 engine is in Accessory Drive, and #2 shut down. Rotor brake off, the MGB is turned via hydraulic (IIRC) power, until the slip ring reaches a blank segment, indicating to the system that the primary (non folding) blade is over the tail. Rotor brake "on" then sequences the blade fold into action, hydraulically folding #2 & #5 blades horizontally aft alongside #1, and #3 & #4 blades sweep aft and down, to rest alongside the tail boom.


Acropyphal tale was of a Sikorsky (USN) ship where the slip ring was faulty, and the #1 blade was straight ahead when the sequencing allowed blade folding. As all the blades then folded forward, the CoG took control and tipped the lot over. Sounds a good story, but I'd give it the urban myth category ;)

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Urban Myth for sure. I have seen it folded out the front and there was no tip over. Perhaps that is due to the ledgendary aft C oo G on the Can SK. Who knows. Aparently the slip ring assembly was installed 180 deg out with the 1 deg segment on the wrong side. Oops.


I had a piccie of it like that once, but cannot locate.


AFAIK the H-92 will be electric too. It is tricky (but not impossible) to put hydraulics into the rotating head through a rotary coupling.





Automatic Blade and Pylon Fold System

21. The automatic blade and pylon fold system

automatically positions and folds the main rotor blades

and folds the pylon. Power for system operation is

provided by the utility hydraulic system and the

system is electrically controlled. System controls are

grouped on a panel marked “MAIN BLADE AND

PYLON FOLD” (Figure 1-8-6) located on the overhead

switch panel. Whenever the rotor blades or pylon are

not fully locked in the flight position, the SAFETY

VALVE switch is open, or the MASTER switch is ON,

the CHECK BLADE FOLD light on the advisory panel

will be illuminated.


22. The blades and the pylon may be folded or

spread in sequence or separately. If both the blades

and the pylon are to be folded, the blades shall be

folded first. Incorrect operation is prevented by

sequencing controls which prevent blade movement if

the pylon is unlocked. During the spread operation the

pylon shall be in the flight position and locked before

the blades can be spread. The operation may be

halted at any stage of the folding or spreading cycle

and reversed, if desired. Electrical and hydraulic

power for the folding and spreading operations are

normally supplied by operating No.1 engine at 104 per

cent Nf with the accessory drive switch in the ACCESS

DR position. It is possible to operate the system using

the external hydraulic and electrical power connected

into the external hydraulic and electrical power



23. The pylon can be folded utilizing hydraulic

pressure only by closing the pylon fold bypass valve

and depressing the appropriate button provided on

either end of the selector valve which is located on the

cabin wall above the cargo door. Due to the proximity

to, and similarity of, this selector valve and the rescue

hoist manual override valve, inadvertent use is

prevented by a quick-release guard over the entire

valve (Figure 1-8-13).

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Obviously a number of differences with the Westland machine. Our tail fold is manual, with a ratchet jack on the port side to insert/retract the locking pins, and the hinge on the stbd side. Frantically looking through old notes (even watched the RAN SK video!), but no recollection of whether the blade fold positioning was elelctrical or hydraulic. The hydraulics are going up to the head anyway (your comment re the 92) to fold the blades, but the drive to the slip ring is where I'm a bit hazy: since we had to check hydraulic pressure 1500psi before and after blade fold operation, ISTM that we woudl have been utilising the hydraulics to turn the gearbox?

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The positioner is hydraulic. It decides which direction to go based oh which side of the 1 Deg segment the slip ring pick-offs are. The positioner is a small hydraulic motor that engages a set of gear teeth that are on the outside of the rotor brake disk. Once it hits the 1 deg segment, the automatic rotor brake comes on and the positioner disengages.

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