206L question

[Canuck Guy]

Been flying a 206L around this summer and it's the first time I've ever gotten any real time in a Bell product. Noticed something it tends to do in flight that I don't ever remember hearing about, so not sure if it's just a given or if it means somethings maybe wrong with the machine.

I'll be in level cruise all fat dumb and happy with a good load of pax on. For no apparent reason the fuselage will sort of lurch forward once or twice in a few seconds, like it's being pushed from behind. Never does this with a light load though, only when heavy.

Not sure if it's just an odd reaction to a little turbulence, if maybe a tranny mount is a little sloppy (checks out fine on pre and post flight DI's). Any ideas?

Maybe I picked a bad week to stop sniffing glue.:confused:

[BlenderPilot]

I have considerable time in L models and I never noticed that? Weird?

But I know what you mean since I recently began flying the AS350B3 and it does that a lot, it's the fuel sloshing in the huge tank, and since it doesn't have any barriers, well. But never on a 206.

[Matari]

Canuck: It doesn't sound like a NodaMatic transmission problem; usually if you check the elastomerics carefully on DI and preflight you can catch problems before they get bad enough to cause inflight vibes.

You might take a close look at the "elevator" at the back of the horizontal stabilizer. There are small bearings at each end hinge point. Make sure these bearings are free, not sticking. I've seen them get hung up, then "let go" a bit causing the elevator to impart a (very slight) pitching moment in flight.

[SASless]

Same passengers every time?

[Choppersquad]

I fly a 206B3, it happens when someone moves back or forward in there seat .
i bet you do not feel it happening when you have dropped paxs.
choppersquad.

[sherpa]

I remember something similar and it that was caused by the bubble window. The vortices's created by the bubble window interfered with the horizontal stabilizer.

[407 too]

My guess is passengers re-arranging their butt, (pant tug to remove wedgie). Have noticed it on the 407 with full pax in the tight cabin.

[Canuck Guy]

At first I thought it was pax changing seats, but it's not... I start barking at them every time I hear a seat belt click open. This movement isn't nearly as pronounced as pax seat hopping. Could be some fatty shifting about though lol.

Never the same pax either, and I only ever notice the odd movement with pax on. So guessing it's either tied into a heavy load which made me worry about a crap tranny mount, or I'm stressing about nothing and you're right about someone shifting around picking out a wedgie.

Could it be fuel sloshing about in the forward tank under the middle seat row? Can't remember if that one has barriers to stop fuel from sloshing.

[Ascend Charlie]

Not fuel sloshing (like you get an the AS350) but probably passenger leaning forward to talk to friend sitting opposite, or grab a briefcase or sort the atomic wedgie. Pax are getting fatter these days.

Also, next time you are in smooth level flight, put the force trim on, then get the front seat pax to lean forward and watch the nose go down. A small weight shift like that can be noticeable.

[RVDT]

AC,

Cut the guy some slack, now you have got him real confused. Force Trim in an "L"?

Did you guys have one in your old "L Nothing"? Remember it was just a stretched Short Ranger.

[Gomer Pylot]

No, there has never been any force trim in any 206 model. I've flown pretty much all of them, from the OH-58, B2 & B3, and all the L models from the straight L on. No force trim, just cyclic friction.

I also think it's the pax moving around. They don't have to release their seat belts, just lean quickly. I've had a full load of pax start moving in unison, just to mess with me, and it can start lots of movement. I would just amplify the movement, and they would soon stop.

[helofixer]

The OH-58C that I maintain for the local Sheriffs office has a pseudo force trim system. It has a magnetic brake that the pilot can engage and disengage via cyclic grip switch to position and hold the cyclic in position. The control box/actuator is located under the copilots seat pan. And this aircraft is stock from US Army surplus sans a paintjob, a SX16 light and some mission equipment.As for slop in your xmsn mounts, it can hide in a few places. Ive seen the dogbones have seperation at the elastomers that wasnt visually apparent and went undetected till the suspect end was put in a vise and the bone was flexed. Another problematic area is the transmission restraint under the driveshaft. It has 2 bearings in the end that wear out constantly and can cause some shifting and the other end of the restraint has a sandwich of elastomer and metal that can debond, but that isnt as common as the bearings wearing.I have no idea if these could be a factor, just passing some knowledge along from 15 years of 206 series wrenching.

[Canuck Guy]

Cool thanks a bunch guys, helped calm my nerves.No kidding too about the pax getting bigger every year. Yesterday had 4 pax (2 kids 2 adults) and just barely got off the ground in my L3 with only 400 lbs of gas in the thing... 95% torque before the skids left the ground. Unreal!

[Ascend Charlie]

RVDT: Hey Giovanni, you re-surfaced!

Yeah, sorry about the force trim - my current steed (B412, serial number ONE!!) has it and my old-dog-new-tricks brain is overloaded.

Sorry:eek::8

[jemax]

I recently flew an L1 with a 2 axis autopilot including force trim. The fact is that because of this it has it's almost 600lbs heavier than a basic L1 as a result of all the inverters/gyro's etc it needs to support the suto pilot and therefore it's virtually useless as a Longranger. It also has floats for good measure.

The amazing thing is that it all still worked too, minus a couple of buttons.

[Paul Cantrell]

We have force trim in our SPIFR -L3...

[helonorth]

I third (or forth) the opinion it's passengers moving around. Doesn't
take much and it freaked me out the first few times it happened until
I figured it out. I now regularly fly a guy over three hundred and he
gets the 407 moving, too.

[helicopter-redeye]

No, there has never been any force trim in any 206 model. ...... No force trim, just cyclic friction.


Yes there is on the machines fitted and approved for IFR flight. The unusually named L1 Longranger II (thats what it said on the side anyway..).

[Furia]

I had aroud 1000 hours in the L series and I never had such movement.
Not even when transporting firefighters that they use to be moving all the time. You can feel how the move of course but it is not like the kind of "movement" you described above.
Is this movement associated to any kind of noise? How many degrees nose down are we talking?
Do you have any "untied load" on the baggage compartment?
Have you talked about this to any certified mechanic?

[Jack Carson]

Take a close look at the Horizontal Stabilizer system. We had an L4 with an improperly installed horizontal stabilizer. There is a set pin that attaches the right and left side assemblies in the tail cone. This pin was loose. As a result one side was moving slightly with respect to the other side. Grab one side of the stabilizer and see if there is any play with respect to the other side. I do not believe that any play is allowed. We felt a similar lurching in our airframe when fully loaded at level max cruise speed. Once we rebuilt the assembly the problem went away. :ok:

[Canuck Guy]

Is this movement associated to any kind of noise? How many degrees nose down are we talking?
Do you have any "untied load" on the baggage compartment?
Have you talked about this to any certified mechanic?


Nope, no noise at all. And the movement didn't really produce any nose down I could tell. Was just like the machine was on it's ground wheels and given a push forward. Like a lurching motion if that makes any sense? No unsecure loads in the cargo bay either, everything strapped down tight.

Didn't go anywhere today and it was the only thing in the hangar, chief engineer went over every nut and bolt and she's all good. Guessing it has to be pax shifting about, but still not letting my guard down.

I'll have a carefull look at the stab too Jack. Thanks for that.

[helofixer]

Does this aircraft have dual control capability? Does it happen with the copilot seat occupied? Do you feel uncommanded movement in your cyclic? I have heard of aircraft with the dual control provisions having the copilot cyclic cover plastic piece missing or loose enough that a person riding in the co-pilot seat can inadvertently kick or nudge the cyclic socket where the copilot controls would be installed causing some control movement that can scare the PIC. Just throwing stuff out there.

[Heli-Jock]

I've had a lot of time in the 206L over the last 2 years and have noticed this on a few occassions. However, i have always thot it was a cramped pax, in the back pulling him/herself up on the seat to try and get a better seating position. It gets cramped in back when 5 pax in there. Unless theyre all midgets of course or 5 supermodels, you get the picture.
People moving around is my guess, just like Helonorth describes.

Cant say ive ever felt the fuel sloshing around enuf to bump the aircraft forward or aft?


HJ

[Canuck Guy]

Yeah I tracked it down to pax just shifting about. Had one big fella in and asked him to shift around "with feeling" and sure enough it replicated the motion I was feeling.

Simple enough explanation for sure, but thanks for all who put forward their thoughts. :ok:

[CGWRA]

I was flying a 206B on one of my early revenue flights and I had two big water bottles on the two window seats in the back. I seatbelted them in with shoulder straps and everything but imagine the look on my 100hr face when one of the jugs fell off the seat and banged into the ground. It was a very loud bang the machine lurched quite good haha. I almost bottomed the poll before clueing in to what happened.

[GeorgeMandes]

From a BH friend:

Its the L model shuffle. Track it. Most likely the hub is out of center.