Pylon Rock

[Over-Talk]

I've read through all the replies......all excellent, but I still had my own thoughts....then Skids Up pretty much mirrored my ideas........

 

Is this a strong, increasing-amplitude vertical bounce, (collective bounce) or more of a fore and aft shuffle that seems to whip from the masthead to the bottom of the long-line (pylon rock) ???????

 

For collective bounce, tighten the pre-set friction etc. etc. (very scary stuff, often resulting in punching-off the load to save the ship).

 

Pylon rock.....here's what I know.

It usually happens in a heavily loaded ship on a slow approach (or possibly departure), the disc is fully-loaded and the pilot moves the cyclic forward or back to slightly change airspeed, then a fore/aft rock or whip starts.

It can happen with just a heavy passenger load, but is more commonly seen with a sling load, more so on a long-line.

 

Tests....is the collective bouncing from floor to ceiling ?? If yes, see above. If not, continue...

next....if it's a rock/slow-hump/shuffle/whip, try not to punch-off, fly around a bit, gain airspeed, change power settings etc. If it goes away.....it is probably pylon rock.

 

Causes....many factors as mentioned above....but usually xmsn mounts/rubbers/dampers/stuff getting worn. I believe they are an on-condition article and are hard to check (other than sending them to Lord for factory testing). One of the best ways the engineers access their 'condition' is whether several pilots complain of pylon rock !

Some pilot's personal techniques may show this problem before others, but something worth noting is still going on up there.

 

Remedies....Tighten the pilot's cyclic friction a little......**** hard to do from the left seat !! Depending on the ship and mounts, this may be all that's needed.

 

Depending on location and job, try a different approach, i.e. steeper, flatter, out-of-wind/more left pedal, etc. This sounds like a tough job Vibe, especially to try something new. Good luck. Fly safe.

 

Climb on the roof and shake the mast HARD while your engineer checks the mounts/dampers etc........as mentioned above.

 

Hope that helps with the diagnosis.

OT

[carholme]

Reference skullcaps post above:

Check the 212 Flight Manual and I am sure you will find that there is a CAUTION re shutting both hydraulic systems off at the same time.

 

Regards

carholme

[Over-Talk]

Yes, section 2-6-G., (it is a WARNING)

 

That is the pre-takeoff section.

 

Skullcap's copied memos seem to suggest to do this in the air.........YOWZA.

 

....yes, we know it can be done (despite what the manual warns), but.......it could get exciting.

[VERTICAL REF]

Vibrator, if you don't get it figured out PM me! Will see if we can send you down the right path.

[skullcap]

My recollection of 212 with sans hydraulics is that you should not lower collective as you can't get it back up(like sex with twins). Otherwise is like 204 cyclic without hyd. Yes bell says no no and they also say that dual hyd failure is impossible(ya right). This is a momentary off then on shortly after, no big deal, check hyd off on ground before hand to ensure no surprises.

[cap]

HV ------some questions:

 

(1) what's the nature and make-up of your slinging gear and hook-ups?

 

(2) does it happen with ALL loads, no matter what their shape or weight?

 

(3) Does it always start about the same A/S and disappear again at about the same A/S?

 

(4) While this is going on, has the wind always been from the same direction or from varied directions off the nose?

 

(5) do you have any indication of this at all, OTHER than when you have something on the hook, no matter how minor? If so, does that occur while mt/lite or with some weight internal?

 

(6) considering where you are, I'd ask you if you have dual hydraulics or single. If dual let me know....if not e-mail me. Oh and "yes Virginia" there are Bell 212's with single hydraulics.

[Blackmac]

HV; Take the panel off the access to the hydraulic, sit the engineer in front of it on the rear facing seat, make sure all your frictions are properly set on cyclic and collective, then find a big field and go "barn dancing" with all inputs to the left, using left pedal and left cyclic.

 

You will find out with the help of the engineer if you have soft mounts or loose huck bolts holding the lift link, they are all inter connected.

 

As you stated this only happens when fully loaded, the hook is attached to the lift link and then the xmsn.

 

Neeless to say an actual "expert" in this field is Rick MacDonald.

 

The barn dancing requires inputs from every control on the helicopter.

 

Cheers, Don

[4961]

This may have been said already.

 

Add cyclic friction, trust me.

 

[sharkbait]

Bad experience has taught me that a foward cyclic movement of an inch or so followed by a small looping backward movement kinda in the shape of an upside down J will induce it easily if the aircraft has bad mounts. ( usually cause - a slight forward over-rotation followed by a backwards correction on takeoff ) A slight turn and added power will help in recovery.

New guys on the a/c tend to get it more often. I hector them about it constantly.

A little friction and small cyclic movements help avoid it.

[cap]

To those who have had an experience with severe "collective bounce", it is not something they will forget and when they find out what the cause was, they then realize why the pre-set friction is supposed to be there. In my experience, it came quickly and a pull-up on collective made the a/c go down VERY quickly......the resultant immediate push-down cause the a/c to go up real quick. I had about 5 of those in a row until my brain clicked-in and I had enough height to gain A/S without "punching" the load.......but the finger was milli-seconds away from doing so. Thereafter and to this day, the friction gets a scale put on it by the engineer and corrected to the factory settings or there's a whole mess of collective friction turned on. It's an area of flight that I have no intention of entering again.

 

This could all be the result of not enough friction, but until I hear otherwise, I'll give HV the benefit of the doubt. I do know that all the Mediums have a "right and left personality" and strongly prefer one side or the other depending on the desired function.....if you listen to them when they 'talk to you". My questions to HV were all probing that area.