B206 Torque

[skippers]

Any ideas why the torque on a 206 would be sitting at around 40% at flat pitch and at flight idle on the ground? I would expect it to at least 10% lower at this setting.
Once flying torque figures seem pretty standard with other 206's ive flown.
Cheers

[the coyote]

Check the auto RPM.

[Aesir]

Only time it happened to me was after incorrect rigging after Rotor installation! I would be careful of flying it like this?

[skippers]

I had suspected it could be to do with the auto RPM setting. I have only flown this particular machine a couple of times and am unware as to how long it has been doing it.
I do no that nothing has been changed recently in regards to rotor heads so hopefully no dramas with installation.

[FH1100 Pilot]

Define "flight idle."

[Gomer Pylot]

What's the N1 and N2 at idle? What is the autorotation Nr? Is the airspeed at 80% torque about right, or a little slow?

[skippers]

Thanks for the replys so far.
Flight Idle being collective at flat pitch and throttle fully open.
The airspeed at 80% torque seems about right for a jetranger. Cant remember of the top of my head n1 at flight idle, but n2 was at 100%. Havent done an auto in it yet but will try soon.

[puntosaurus]

Erm. You might want to check with an engineer before doing an auto. I'm absolutely not an expert, but if it takes a lot of power from the engine to turn the blades with the collective all the way down, then it seems to me that the autorotative airflow will also struggle with the same task, and you may well have rpm problems.

[Gomer Pylot]

The engineer will just have you do an autorotation RPM check anyway. The 206 is about as benign a helicopter as you can find in autorotation, and a prudent pilot would get plenty of altitude before entering anyway, and pay attention to the RPM and start a power recovery before the RPM gets out of the green. I've never seen the Nr in a 206 dangerously low with the collective full down, and they have lots of blade inertia.

[skippers]

I will speak with the engineer tomorrow and as everyone has said I suspect the auto RPM will be a bit low.
Hopefully it will be a quick fix by adjusting the lower pitch setting with collective all the way down.

[Semi Rigid]

Umm are you sure you don't mean 'flight rpm'? with club down & presumably flat pitch with the throttle wide open? to me that would be flight rpm as opposed to 'ground idle' club down throttle back to detent possie.

[chuckolamofola]

Semi Rigid:
On the 206,
Nr/N2 at 100%, collective at min pitch = Flight Idle
N1 at 58% to 62%, collective at min pitch = Ground Idle
A couple of things could be the culprit, either Tq. gage is incorrect or Autorotoation RPM is too low or a combination of both. Since he said his cruise speed at 80% Tq looked about right, my hunch is low auto rev's. An easy flight check for auto rev's would be the first place to look followed by testing the tq gage with a dead wt. tester.
I would also suspect the aircraft felt light on the ground and took a lot less of collective travel to get it light on the skids.
Chuck

[skippers]

Semi Rigid.
I agree with chuckolamofola. And if you like at my previous post I defined flight idle as "Flight Idle being collective at flat pitch and throttle fully open"
I didnt notice needing less collective to get machine light on skids than normal but it could well have been.
Cheers

[Hiller]

:ok: This is my first post, so be gentle. As your question was about torque on the 206 I suggest you do this. Do not fly it. On a ground run do your normal start and when you increase the rotor speed over the N2 yellow caution band bring the twist grip back to the Idle Detent. Your N2 NR needles should be above the N2 yellow caution band. If it is not then you probably will not be able to autorotate, well not for long. An engineer should be able to sort this out, ie if you are below the yellow band the pitch links should be shortened. The other check would be to check your engine oil pressure is in tolerance. Torque is measured by a modulated engine oil pressure, so if the engine oil pressure is high so the torque reading will be high, and vice versa.
Hope this helps
Hiller

[Hiller]

One thing I missed out, do not trust the engine oil pressure guage, Test it with a dead weight tester.

[jeffrey1]

The torque reading is directly proportional to the engine oil pressure being produced at the N1 rpm.
Look at your oil pressure and torque readings and run up slowly while watching engine oil pressure.
Torque readings are only accurate while engine oil pressure is in the double green band of the gauge.

[RVDT]

jeffrey1 - really? Where did you get that information?

The only reason an A250 has such high oil pressure is to make the Q meter work. The lube side does not need high pressure but is subsequently designed to operate with it. In other words low oil pressure is a problem for the lube system as it is designed. I am not saying that low oil pressure is not an issue. The oil pressure is regulated in the engine and only needs to be adjusted to higher than the demands of the Q meter system.

The following probably sums it up quite neatly.

United States Patent 4690614

A torque meter is provided for use in conjunction with a layshaft having a forward and rear end and which is rotatably mounted in a housing. The layshaft is axially movable with respect to the housing between a forward and a retracted position while a gearing arrangement in mesh with the layshaft urges the layshaft towards its forward position with a force proportional to the shaft torque due to the helical cut of the gears. The torque meter comprises a body secured to the housing adjacent the front end of the layshaft which forms a chamber open to the front end of the layshaft while a piston is axially slidably mounted within the chamber. The chamber is pressurized with a fluid, such as oil, which urges the piston against the front end of the layshaft with a force proportional to the pressure so that the piston balances the layshaft against the axial force imposed by the engine. A fluid pressure gauge determines the pressure within the chamber which varies proportionately with the layshaft torque. In addition, a piston ring on the piston opens the fluid chamber to an opening in the body and a passageway in the housing when the layshaft moves to its rearward position, indicative of a negative shaft torque condition, whereupon fluid discharges from the chamber, through the passageway.

From memory on a 20 series the pressure equates to 1 PSI = 4HP at 100% N2. Any difference in N2 and these numbers will change.

As to the Jetbox high Q at flat pitch - most obvious is too much pitch.

If the passageway (bleed) is blocked or restricted your Q meter will read engine oil pressure or be slow to indicate less Q as appropriate.

[ShyTorque]

Has the aircraft rigging actually been disturbed? When was this problem first noticed?

Something worries me about this - this might be so obvious that it has (hopefully) already been taken into consideration. A failing gearbox bearing would require more torque to turn it.

Has someone checked that the main rotor gearbox turns without undue resistance or noise? Does it slow down to "stop" after engine shutdown in a normal manner and period of time?

I was once flying an aircraft with a failing main gearbox. We had no real symtoms or indications in the cockpit except for a tiny bit of extra vibration (we had no torque gauge on that type, we only had a collective pitch gauge). On our return, we spoke to the engineers, who pulled an oil sample. The mag plug had a piece of ferrous metal stuck on it that was so big it wouldn't come out of the plug hole.

So take care!

[jeffrey1]

I received that information from the Bell factory school in which I just returned from last week.
They explained in detail about the torque system and the double green lines on the engine oil pressure gauge.

[skippers]

Thanks for all the replys so far.
ShyTorque. The blades slow down and start up at the same speed as on any jetranger I have seen.
jeffrey1. Very usual information.

I did some autos in the machine yesterday to check auto RPM and it was fine. 100% with collective down so no dramas there.

I have been told that the problem could be something as simple as a small object lodged somewere in the actual line running to the torque gauge. And apparently to retreive the "object" you have to pull the whole accessory gearbox apart. Any views on this?

[BlenderPilot]

I have been told that the problem could be something as simple as a small object lodged somewere in the actual line running to the torque gauge. And apparently to retreive the "object" you have to pull the whole accessory gearbox apart. Any views on this?
This is absolutely right, but to add a little, that small "object" is very likely to be loose carbon, and the place where it would be lodged is in the calibrated orifice to the TQ meter, and this is very common on old JR's that don't have an AF facet filter installed, as it was optional equipment to them, although now standard.

Also if I remember correctly the accessory gearbox is an "on condition" item, and most of the time when they pull those apart there are usually a few items in there that will need reparing, so be ready to pay a large bill after that.

[the coyote]

I did some autos in the machine yesterday to check auto RPM and it was fine. 100% with collective down so no dramas there.

How did you conduct the auto RPM check? Get the engineer/s and check the auto RPM IAW the maintenance manual, not a pilot only "seems OK to me" check as it seems you have done. What was your gross weight and DA at the time you had "no dramas"? Can the aircraft achieve acceptable auto RPM at all gross weight/DA's for operation?

It may well be fine, and only some minor indication thing, but it may also be combined with a more sinister flight control/power train problem that rears its ugly head at a particular DA and gross weight while the engine is silent, for example.

What do the engineers think? You must categorically eliminate a potential cause using published methods or you risk multiple contributing factors that may one day negate the hope in "hopefully no dramas there".

[FH1100 Pilot]

100% with the collective full down...wh, whaaaa? Were you at max gross weight at sea level?

A 206B with the auto rpm correctly set is a little disconcerting. Lightly loaded, the auto rpm will actually be quite low; it increases as does the AUW. With two guys (pilot and mechanic) and a moderate load of fuel (45-50 gallons) the rpm could still be something *less* than 100%.

Those of us raised up in Bell 47's like to see 100% with the pole fully down, but that's not always correct. Helicopters that have a big difference between "very light" and "max gross" will have a larger range of acceptable auto rpm. 100% at a very light weight means an overspeeding rotor at max gross. If you have to pull collective to keep the rpm in check in the auto, then that's that much less pitch available at the bottom.

Elementary, I know, but needs to be said?

Still, if the torque on the ground at full throttle/flat pitch is *high*, then I would expect the auto rpm to be *low*, not high. Something's fishy.

This is why we do trend checks. Have they been done and logged in that machine? We need to establish baselines so we can tell when stuff is changing. I fly the same ship every time, and when I set cruise torque, I note the OAT, N1 and TOT. I fly in a very corrosive, salty environment and so far, 100-hours down the road, the parameters are still the same. Thankfully. If they change, I will know it.

A B3 with a C-20B engine should be runnning...what, 710 or so and 96% at 80% torque (sea level, 20 degrees C or so)? Man, it's been a long time since I flew B-models. Whatever. They're all pretty much the same. Can you compare yours with another B3 with a C-20B?

Bell publishes (or used to publish) a very good and thorough guide to doing "ops check flights." Maybe you could get a copy of it, go out and fly and see what's up with that machine.

[Hiller]

100% with the collective fully down! Where was your twist grip position, hopefully at idle. If not then you were not autorotating and I guess that your N1 speed was a great deal higher than ground idle, i.e. the engine was still driving. Please be careful as I had this problem many years ago. The next time you do an autorotation check is to have plenty of height, lower the collective fully and check that the N1 speed is at Ground Idle. If it is not, which means that you cannot autorotate, and if you are happy, SLOWLY rotate the twistgrip towards idle monitoring the Rotor Speed.My gut feeling is that you will see a decay in Rotor Speed, and if you do, do not snap open the throttle too quickly, but smoothly. I hope I am coming across as not trying to teach Granny to suck eggs, but just trying to help.
Take Care!!

[Hiller]

Skippers. Are you still with us? If so, what was the problem and how was it fixed? I am concerned.

[skippers]

Hey there Hiller.

Still here just been a bit busy lately!
The problem has been fixed. What the engineers did was fix the line running from the back of the torque gauge. As soon as they did that, started up as normal. Up to flight idle, and torque was sitting right were it should be.
Thanks for your concern but problem is all fixed now.

[rotors88]

Morning Gents

May I have a simple explanation of how to conduct the trend checks in both a B206 & B206L4. Cheers

[Jack Carson]

A high torque reading can be an indication of the collective pitch being adjusted either too high or too low. If the flat pitch is set too low you may experience excessive bounce on the ground because the rotor is actually pushing the aircraft down. This is more prevalent on a 206L series with the nodal beam system.

I have seen a similar case before. You need to go through the entire collective control system. In one instance we had, a mis-rigged collective servo corrected for by mis-adjusting the PCLs to achieve the correct flat pitch rotor speed in an autorotation. We replaced that servo when it developed a leak with a correctly rigged unit. At this time we noted that the flight idle torque reading was high. We also noted on preflight inspection that too many threads showing on the PCLs. At this point we went back to square one and re-rigged the collect control system. All turned out well.
Jack:ok:

[Arm out the window]

rotors, the trend checks we do in the 206B and L3 are:
fly at 500ft on QNH 1013
set 85% tq and let everything stabilise
note OAT
note eng & transmission temp and pressure
note Ng and TOT

Then the figures get recorded in an Excel spreadsheet. The Ng and TOT figures are adjusted for temperature as per a table derived from the engine documentation so that they can be compared over time.
Not sure if these are a widely used standard or just something the company came up with to keep tabs on how the engines were travelling.

[busidriver]

The checklist for the B206 which I'm flying (I know no other) states a torque limit of 40% for the first acceleration of the rotor disc from idle, and of 30% for the second (following the idle check).

Given that, so far as I can see, there is no mechanical difference (in terms of loads, stresses, and so on), between the two accelerations, why the different limits?

(I ask because it's practically impossible to accelerate the rotor disc without exceeding 30%, and I feel bad when I do so...)

[busidriver]

Oh well, just one of those flight manual limits that have to be exceeded, then...

[tomstheword]

28% - 30% torque at flight idle flat pitch is about normal in a jetranger so your not far out.

[busidriver]

That wasn't really my question...

Why are the two limits for acceleration different, and is it usual that the 30% limit has to be exceeded in order to achieve acceleration to 100% NR?

[206 jock]

I suspect the 30% was inserted by your fuel farm!

I always stick to 40%,my instructor told me that this limit was only there to stop the aircraft spinning on the skids (overcoming the friction).

[busidriver]

Found some good answers today.

Not here, of course...

[Shawn Coyle]

The checklist 'limitation' is not a limitation at all. If it's not in the limitations section of the FM, then it's something somebody dreamed up.
I've heard of this before- 'don't exceed 40% torque on wind up' - and when I asked where this came from, there never was a satisfactory answer.
Could be someone was a bit too ginger winding up on a slippery surface, and so some military chap wrote another 'rule'.
But there is no limitation.

[LeakyLucy]

Pretty sure its a POH caution in the BIII Shawn. I'll take a look tomorrow.

[vaqueroaero]

The torque limit on acceleration is not found anywhere in the limitations section of the flight manual.

It came about from military days and has been passed down in to the civilian world. The reasoning behind it was that when a 206 was parked on PSP and you exceeded about 40% torque there was a risk of the nose spinning to the right. That's all.

If you open the throttle fast enough even parked on smooth concrete or asphalt the same thing can happen.

It is a good rule of thumb to follow, but as stated previously doesn't appear anywhere in the flight manual.

[LeakyLucy]

yep, you're right it aint in the FM,just read it in so many places.

[krobar]

Glad to hear the problem was easily fixed.

[RVDT]

In fact.....................

A good test for the condition of your Allison engine is to wind that throttle open as fast as you like without exceeding limitations and the limits of the surface friction of course.

This will let you know if you have problems that may give you compressor stall............................ bad compressor plastic, bad rich FCU etc.

Call it a slam accell, opposite to the slam decell that everybody still does to check their FCU - yeh right.

Talk to your RR Allison Tech rep.