Blade Folding

[widgeon]

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 ?

 

[Heli]

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 😉

 

[Fully Articulated]

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.
============================================

BLADE AND PYLON FOLD/SPREAD SYSTEM

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 FOLDâ€￾ (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
connections.

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).

 

[Heli]

FA,

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?

 

[Fully Articulated]

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.