S61 Collective Friction

[moo747]

Afternoon Gents, I'm having some maintenance issues with the collective friction lock.
Does anyone know how tight it should be with friction fully applied and how loose with friction off?
One of our pilots seems to think it should be impossible to move with full friction on with hyds running and it should rise up on it's own with fully off with hyds still running.

Any help would be appreciated.

Cheers

[Buzz Control]

Collective Friction

A while since I worked on these on the military side. I dont know if the friction assembly was the same on the S61, but with the collets correctly inserted the guard fitted & the securing screws wire locked. IAW maintenance manual you should apply hydraulics & carry out a pull off check with a spring balance & friction applied at max to the stop in the guard. Exact figures I cannot remember but 27lbs rings a bell.

[victor papa]

Also remember a check like that. The collective friction is critical on the S61. Saw one once get a "collective bounce" on landing and it was not a pretty sight nor where the tail wheel schock in a good state aftewards. Normally with collective friction off the collective's tendency should be to creep upwards and not drop down for obvious reasons. There has been a few issues with the 61 friction and can remember at least 2 SB's after North Sea(I think) incidences. I know one was with the lock interfering during flight. I will check with some friends tomorrow if you want who are stil active and has 30 years experience on the 61 and will give you feedback.

[JohnDixson]

Collective Friction

My recollection is that for any SA model incorporating adjustable collective friction, with the friction full on the pilot must be able to move the collective ( hydraulics on ). There may have been some maximum force measurements, but I can't recall them. For some models, e.g., the S-70, a minimum friction is specified, like 3.5 lbs. The S-61 AFCS collective channel was made to function with near zero friction and the minimum levels there are like a pound or less.

All of that info should be in your maintenance manual, and also incorporated in the maintenance test flight procedure.

Thanks,
John Dixson

[moo747]

Thanks for your help Guys

[3D CAM]

Moo
If memory serves me correctly, force required to overcome the collective friction when fully on to the stop is 8lbs, or was it 15lbs.
I am more than happy to be corrected because the Maintenance Manual is more useful than memory.
3D

[VTA]

8lbs "friction on" rings my bells, and neutral collective position with "no friction" rings the other set of bells...

VTA

[sycamore]

The last thing anyone needs on landing/flying is for the collective to rise if the friction lock is `off`-think about it !
The collective friction `off` should hold the collective in that condition,fully up/down,or have a `tendency` to fall towards min pitch.Probably a friction `pull-off` of about 1-2 lbs; if it`s any lighter and you don`t have friction/hand on collective,in turbulence you will get a PIO on the collective which can damage the head very quickly.
Any collective friction applied should be `smooth` from fully up to fully down with no `lumpiness/unevenness`,and a smooth single twist ideally from fully `on` to `off`. Can`t recall actual figures,rather `personal criteria` applied to Wessex and S-K as MTP for 4Yrs and TP for 8. Isn`t there a `collective` balance spring in there somewhere ? Syc...

[Night Watchman]

I remember landing on a rig many years ago and we had to borrow a wrench from the helideck crew to get the collective friction off so we could depart!

[flyer43]

Although discussions can be quite helpful in helping to locate answers, I'm quite concerned that moo747 might actually pick one of the many ideas proffered in this thread, rather than taken some advice hinted at by 3D CAM and look up the correct procedure and settings in the Maintenance Manual.

[toolguy]

Check the maintenance manual chapter 65-42, adjustment test of the collective friction, which states the stick must move with 15 pounds of pull on a spring scale. There is a lot of room for adjustment with the collet and stops, so you should not have too much trouble.

[unstable load]

I have had occasion in the years to have to remove the blocks and clean the inside of the faces due to pilots holding the shaft rather than the handle and dirt collecting from their handprints and gumming up the works, so that would affect final figures.

I can't recall the figure (RFB) but it should move without binding under hydraulic power when fully on.

[Ikoyian]

Cleaning the blocks

UL Got there before me, I was about to mention the same. Did this quite a number of times as well as its normally a good fix.

Ikoyian

[Sikorskyfan]

I have to agree with Toolguy, read the manual and all shall be revealed.

[Phil Kemp]

Afternoon Gents, I'm having some maintenance issues with the collective friction lock.
Does anyone know how tight it should be with friction fully applied and how loose with friction off?
One of our pilots seems to think it should be impossible to move with full friction on with hyds running and it should rise up on it's own with fully off with hyds still running.

The maintenance manual contains some explicit warnings regarding setting maximum friction, and there have been some pretty close calls when the max stop is not adjusted correctly and the friction actually stops the use of the collective - hence the variety of emergency release mechanisms (pip pins) installed on various operators aircraft. Glazing of the friction face is the major cause of inadequate friction, but also worn chrome on the collective, or bent collectives cause some of the more unusual irregular friction problems.

The collective should be neutral and neither raise or lower by itself. The basic rigging process will address the the adjustment of the collective balance spring; but if the rigging is correct, then a collective open loop adjustment on the aux pack will remedy the situation.

Any good S61 engineer or mechanic will know this, and as always the manual details precisely how to accomplish this task - and of course will be referenced in the appropriate maintenance entry.

We always did dual inspections on any adjustment or maintnenance activity on the collective friction - a good plan based on some of the things I have seen people do to them!