My dear friend im just a bell-412 engineer and dont know about policy.
Thank you

Reach out to your local Bell Field Service Representative, I'm sure he'll be happy to assist.

Thanks to everybody problem solved.a

It's on the Bell website mybell.com Providing you have access of course...

DAFCS, you don't have enough posts (10 required) to use the messaging/email function here. If you like to put up your email I could contact you and may be able to help you out.

megan, email sent

Bell 412 with AHRS Mast Torque fluctuations
 

Good morning all,

I'm a B2 (avionic engineer) working on four Bell 412EPs, for the past seventeen years, fitted with AHRS gyros and 4 axis SPZ7600 DAFCS.
The aircraft have always had an underlying tendency towards a two second oscillation similar to Dutch Roll which the autopilot seems to enhance rather than dampen out especially in Rad Alt hold probably as it's a demanding mode driving through the collective actuator. FDR traces of Mast Torque, Nf, Ng, all show this two second fluctuation which I assume to be the natural governing cycle of the old mechanical governors and AFCUs. It can affect the aircraft in SAS or ATTD. In Rad Alt hold we can see 20% Mast Torque fluctuations on the FDR with controls, N1s, Nfs, Hdg all showing FDR traces with a two second fluctuation. BUT rolling back either engine reduces the oscillation sometimes to zero.
Soon after the laser gyros (AHRS) replaced the old Tarsyn (spinning wheel) gyros, Bell came out with Tech Bulletin TB180 which changed the yaw rate output to the DAFCS from the AHRS due to problems with it's sensitivity particularly in relation to differing frictions within the Tail Rotor hub!
Some customers who carried out this TB then complained about Mast Torque fluctuations so Bell gave permission to revert back to pre-TB180 to see if it would help with affected aircraft.
We did, and it helped, BUT whenever we have to change Nf governors / AFCUs this problem can reappear as we are experiencing this past month.
The engine governing system seems to be suited to the old Tarsyn / analogue AFCS but since the AHRS / DAFCS were introduced the engine governing system has to be operating ultra-perfectly which can be a challenge at times. We seem to changing too many governors and AFCUs on these aircraft.
I could go on but my main question is.....has anybody else out there with Bell 412 / AHRS configs experienced anything similar?


Dave Ed

EP's are notorious for fluctuating tq's at low power settings in cooler weather/cool nights when they are rigged to generally fly in warm/hot weather , fly during the day (average 25-30 oC day) no problem , fly the same machine at night do a low power decent to an airport or low speed/power search for example and you will have massive tq fluctuations of up to 10 % , nothing to do with Auto Pilot , it just makes it worse, if you engines are rigged for the general climate they operate in , being Cyprus average day 25oC , machines run fat dumb and happy in the warm climate all the time but because the 3D has the bleed valve at P2.8 air unlike the old 3B at P2.5 air it has a greater impact to the P3 air to the engine controls, as less power is needed and the air is cooler the bleed valve flutters as it is right on the open/close threshold and causes spikes in the P3 air as the engines start hunting one chases the other, easiest just split the tq about 4% , one engine bleed valve is definitely closed and the other definitely open , when the pilot pulls power again to normal levels match the engines again,
I have worked on EMS/SAR EP's for years in hot climates and the big Tq fluctuations always happen when the weather gets cooler or at night , I just got my pilots to get used to splitting tq's as soon as big fluctuations start and problem goes away.

Let the pilot switch off the AP and SAS, then test fly it.

While doing it, switch on one ap back on at a time.


Often they have issues with the AP, resulting in one of them overacting on engine control.

​​

Our 412s in Cyprus normally only need an adjustment to torque matching as we transition from Summer to Winter and back.
When we do get a set of engines / governors / AFCUs / control frictions / DAFCS set up and behaving, they are normally fairly stable day or night but we dread having to change a governor / AFCU as that one change can lead to weeks of pain. We can go through three or four governors until we get one that is well suited to that particular aircraft. Get a bit tired of loading and removing ballast weights!!

We have done endless test flights over the years with all combinations of SAS ATT FD, on various aircraft at various airspeeds and flight regimes. This exact problem has shown itself on all four of our aircraft so I still think there is an inherent problem with the AHRS / DAFCS and the way it doesn't suppress the oscillations, probably related to the yaw channel as highlighted by TB180 and then the option to change back to pre TB-180 if it improved things. The option to revert to pre TB-180 was after other customers were complaining of cases of Mast Torque fluctuations but Bell gave no details of who they were and what configuration these aircraft were in.

"Torque-oscillation" on the 412 can have many reasons....SAS/ATT FD are only one....

Tail rotor balance issues, Hydraulic issues, FT issues, pilot input, Throttle feathering, Mast mount issues and many more are just a few things to start looking at.


I know this is not an issue with most companies-but thats one advantage of a company having a properly trained maintenance test pilot working closely with very experienced engineers-those crews are most times able to detect and solve smaller issues before they result in something bigger (or-let alone-catastrophic...)...

I think you guys have covered all the bases, but would still like to offer two areas to look into:

1) Governor to AFCU matching: Pratt came out with a bulletin about 15 years ago (sorry, do not have the number) which specifies governor P/N that is tuned to the latest AFCUs and helps reduce oscillations on the -3D. You may have done this already.

2) M/R servo input lever friction: as Bell went to "D" seals (D shaped O rings to help reduce oil leaks) in lieu of O Rings in the hydraulic servos, this drove to input lever friction above the desired value. This value is very low, around 1.5 Lbs if I remember correctly. This causes overshoots as the AFCS system pushes the lever until it finally moves and then moves too much. This was especially apparent during coupled ILS approaches, in very still air. Going back to plain O rings has helped reduce the friction.

Hope this helps.

Fly Safe, Always :ok:

Mmmmm ......

One of the many issues the years have thrown at the 412EP .... have you investigated the matching of the M/R Elastomerics ... and at what Nr you balance the M/R in cruise ... in the past we (?) have noted that depending on the age that they can cause issues especially when lifting HEAVY loads (especially heavy sling loads) ... if the RPMs are not beeped to say 101-102 the coning angle can allow for a sort of 'Hooks joint effect' oscillation which the engines then try to catch ... the engines the have a fight with the Yaw SAS and you can end up with an O'torque which spoils all your fun .... turning OFF the Yaw Ch. reduces it .... also putting the T/R into clear air when lifting also helps (but brings you into conflict with the RFM re: wind from the right etc etc) ..... compromise maybe the key (as Bell did with the design of that M/R head) ... *sigh

Cheers

Spinny

Thanks all.....keep them coming...………...with so many variables it's no wonder the DAFCS struggles to keep things under control!
If you could specify whether your machines are AHRS or Tarsyn equipped that would be appreciated.
Anyone out there with specific experience of that original AHARs yaw rate output change in TB180 that we were then given the option to reverse depending on Tail Rotor bits friction.
We have been measuring servo input lever frictions again only last week plus tail rotor pedal breakout forces with the aircraft running!! at the request of Bell.

Where are you located?

Dave Ed,

My comments/suggestions were for an AHARS machine. Old day Tarsyns did not seem to get into these oscillation issues.

Good fix would be going to the EPi :D. The T-9 engine is much better at keeping things steady (has been since the RSAF & TCG days!).

Fly Safe, Always :ok:

My terms and conditions would not allow me to specify location.
Worked on Tarsyn equippped 212 / 412s on and off since 1979 with SCAS / SFENA / Sperry Helipilot with no memorable issues that weren't permanently mitigated. All old technology working well together.

Hello Every body,
I have a question, is there anyone who can give me the reference of the plug which can be connected to the 28VDC power auxilary socket which is on the left side control panel of the B412 (left pedestal)???
It look like this below but not sure, 97-3107A-16-11P.

https://cimg3.ibsrv.net/gimg/pprune....1e09d99a5e.png

If looking for the correct P/N: MS3106A16-11P along with backshell P/N: MS3057-8A. Most commercial electrical suppliers will carry these. Just mind the polarity of the equipment you wish to connect.

Very important point! Standard for most equipment is B+, A- on these plugs (Spectrolab, Cineflex). There are outliers (Shotover) that use A+ polarity, so a reversing/polarity flipping cable is needed for that equipment.

Hello,

Thank you very much for the P/N and the polarity.

JMP

Bell 412 stl by any chance?
 

Hi there,
a little bit of topic- or not, cause its about Bell 412
I became friends with a few model builders, which needed dimensions for building a scale BK117, which I flew at that time.
Through that connection I came in contact with 3D printing, which is as addictive as some other things in life 🤪
So now to my question- anybody else around and by any chance, has a stl (3D printing file) of a Bell 412?

Hi just be aware that plug is a solder connection.

for the murkins amongst us, that would be “sodder” :}

I need a solder plug that's perfect.

JMP

Hi not called sodder any where east of mid atlantic as far as i know.

Thanks "gulliBell" for your useful reply. Of course there will be inflation $% wise over the last 20 years and a huge inflation in red tape.

Morphed into a interesting thread and stay active for 17 years. Didn't see that comming.

I am loathe to be the grammar police....but is not the correct usage "soldered connection"?

Thus one can be a solderer if using Solder to solder a connection and the process being called "soldering".

Quote:

---

solder

---

PT6T-3DF Hot section Damages
 

Assalamualikum. Can someone interpret what could have caused Fuel Nozzle sheath damage, fuel boss damage on combustion liner, ignitor damage on PT6T-3DF.

Hi all

I'm looking for a weight and balance sheet in excel format for a 412EP, I saw this post from megan awhile back. Hopefully you or someone can help.

Thanks a lot

My English friend was in hysterics while I was talking about my electronics hobby and how I used "sodder" and a "soddering iron".

Mitch, Send me an email at babrahamATnetspace.net.au and I'll send the Exel file. Off to hospital for a few days come the 22nd of the month by way of explaining any tardiness in reply.

Hi everyone,

Looking for some advice on fuel consumption from seasoned pilots.

412EP with 3DF engines.

Temperature around 25°C at sea level.

What would the fuel consumption be at 5000ft and 10000ft with torque at 55% 65% and 75%? And what airspeed will the aircraft be able to maintain at those respective torque settings?

Thanks all