Torque Fluctuations 206BIII

[Red Borun]

I have been recently flying the Bell 206BIII and notice massive (40%) torque fluctuations when moving in and out of wind without moving the collective; there are rudder inputs of course, in hover IGE close to Sea Level. Could someone throw some light on this as well as compare it with experience in other manufacturers like Eurocopter, which dont have such torque limitations?

[Gomer Pylot]

Large pedal movements will cause torque fluctuations, especially with a quartering tailwind. It's nothing unusual. You have to be really careful when landing or taking off with a wind on your right, because the 206 will weathervane enthusiastically, and the large, rapid left pedal inputs that result can easily result in an overtorque. If the wind is on the left, right pedal will be required, and not cause the torque spikes.

[arismount]

I can't let this one go by. Maybe you meant "4%" torque, not "40%" torque.

If you meant "40%" torque, and it takes you 70% to hover (not unusual)...then, you're saying you have "fluctuations" up to 110% !! That's an overtorque!

"+/- 4%" is a "fluctuation." But +/- 40% torque without moving the collective ain't a "fluctuation" (regardless of wind change effects!) and it sure ain't normal.

Can't believe no one either caught this or cared to respond. If this is in fact what you are seeing on this aircraft, DON'T FLY IT ANY MORE UNTIL YOU BRING THE PROBLEM TO THE ATTENTION OF A QUALIFIED MECHANIC.

Yes, I am shouting.

Have a nice day.

[Choppie]

If you meant "40%" torque, and it takes you 70% to hover (not unusual)...then, you're saying you have "fluctuations" up to 110% !! That's an overtorque!



I think he was saying a total fluctuation of 40%. That could mean from 60% to 100%. Not 40% either side. I think if he had a 4% fluctuation I don't even think he would have asked the question here.

And if I could remember correctly (haven't been flying 206's for a while), then you can pull (not intentionally) upto 110% for 10 seconds... or is it 5? Either way I don't think that's an overtorque.

And yes you could have quite big fluctuations in torque when doing pedal turns like Gomer Pylot said.

[K48]

RedB,

This is exactly the same symptom as described to me on a B3 close to home. Fluctuating torque. I cannot remember the specific problem, I will make some enquiries. As far as I remember it was something like the freewheel unit or maybe something off the accessory gearbox (e.g Starter/ Gen) that caused the fluctuations. It was potentially very serious so I also suggest no more flight until resolved. I will post more if/when I find out some facts for you.

[K48]

OKay I got that info on the incident of torque fluctuations that I mentioned.

I quote the reply given to me by a man who knows...:8 :

"These were large fluctuations (torque), due to loose engine mounts, very unusual. The fluctuations were due to drive shaft going in and out of alignment with the Main Gear Box.
It's an oil pressure system, so otherwise leakage/blockage/low oil px.
"

Hope that helps in your search for the cause.. let us know what you find.

[The Nr Fairy]

IIRC, unintentional overtorques in a 206BIII up to 110% require no intervention.

110% to 120% require visual inspection. 120% requires disassembly. Anything over those limits also requires a dose of pilot integrity.

[thelynxeffect]

The Nr Fairy


I think that youll find that even intentional overtorques in a 206BIII up to 110% require no intervention.

:}

[Lioncopter]

I had a Torque fluctuation in a 206B2 while in flight, made a precautionary landing turned out to be a fairly major oil leak.

[heliski22]

Not current on the 206 these days but did a lot of aerial work and other "fun" stuff in them some years ago, much of it in "yanking and banking" type situations.

I don't remember anything like that degree of torque fluctuation, even in extremis and would, therefore, suggest a call to maintenance pretty much straight away.

[Red Borun]

I spoke with a Test Pilot about this and his response was:
1. Quartering Tail wind causing large rudder inputs making variations in torque requirements upto 15-20%.
2. Coupled with a free turbine and a hydromechanical fuel delivery system based on torque requirements. The lag in demand and supply of fuel on such a varied torque requirement from the tail rotor causing the fuel system to go into resonance with the varying power demand. Like an undamped system in resonance the catalyst being the aircraft doing a pedal turn in quartering wind conditions.

I tend to agree, having seen other larger aircraft with free turbines easily tending to go into undamped oscillations of Free Turbine RPM with a little PIO of the collective even in straight and level flight. Maybe, these issues are catered for by more responsive FADEC based fule delivery systems, or by aircraft which do not have a propensity for tail rotor induced torque problems like the two bladed T/Rs like the Bell. I wonder what a Dauphin or a Fenestron based aircraft would behave in similar conditions. I believe, they are less prone to LTE and if I am not mistaken do not even have a torque gauge in the cockpit! Which is why they (Like the bumble bee) can hover in a 70 knot crosswind!

[bogey@6]

Red Brown, just my 2 cents..

Any engine wth automatic governing system (piston or turbine) will show fluctuations due to governing itself-- that's normal. As you mentioned, you are in hover-- so, there would naturally be pedal inputs. These inputs adds more to the governing action, You may or may not have overtorqued the engine. From experience I have seen several overtorques to have the pilots complaining losing Tq indication afterwards. This is due to the Tach Gen shaft severance. Can't hide that from the tech guys! On the Bell, if I remember it right there is a torque tube on the overhead compartment. This tube's got serrations (slits) along its axis. Overtorques twist these slits.

Now, if your 40% fluctuation is happening while on cruise-- man, that aint fluctuation! That's surging either due to Bleed Valve sticking close or a faulty FCU. I've seen surges due to FCU contamination (on the AS350) and the machine fies (on the way down) like a Cobra swinging its head left and right.

[rotormatic]

"On the Bell, if I remember it right there is a torque tube on the overhead compartment. This tube's got serrations (slits) along its axis. Overtorques twist these slits."
That torque tube on the 206 is part of the engine governor control linkage, which is connected to the collective control.
The puropose of the serrations (slits) is to allow the collective to be raised or lowered if the governor control system jams. When the system jams, this torque tube twists, allowing collective movement.

[kflexer]

Ive never seen a 206LIII with rudder pedals! or with a rudder for that matter ha ha :}

[The Nr Fairy]

thelynxeffect:

You are indeed right. The torque gauge doesn't know whether it's indicating an intentional or unintentional exceedance. The only thing in the loop which does is the one with the hand on the lever.