Power levers on turbine helicopter

[baobab72]

Hi folks
I am curious about the engine controls on a turbine helicopter and i would love if any of you took the time to explain what those levers on the ovhd do? Together with those trim switches on the collective - i guess they are related!
And what the detailed start up procedure is - for the agusta 109,139 and/or for eurocopter/ecureil.

I can not even find a detailed picture of the ovhd!!

I am familiar with turbine engine and its ops but from an airplane standpoint.

Many thanks

Baobab

[Thomas coupling]

Same as FW.
Push the lever fwd and the ground gets bigger.
Pull lever back and the ground gets smaller.

[Savoia]

In the 109 the (overhead) throttles don't do much during the start:

CSpJQgLoylk

[HeliComparator]

In modern aircraft, of course there tend to be no throttles / levers, just switches that select off, idle, fly for the FADEC software.

In more traditional types the levers typically connect to the fuel control unit (FCU) on the engine. There is typically a shutoff position, that stops all fuel getting to the engine, an idle position that takes the engine to its minimum operating N1 (rotors probably less than flight speed on the ground) and is typically used for starting, and a flight position where, from the lever's point of view, maximum fuel flow is authorised, but of course the FCU then limits the fuel flow so as to maintain the rotor rpm at the correct value.

Imagine the lever as a tap at the inlet of the FCU - when its shut off, no fuel. When its at idle, a little fuel is allowed through for idle speed, and when its in the flight position the tap becomes fully open. So it may be possible to set the lever in an intermediate position between idle and flight - in the case of an FCU malfunction where the FCU is trying to give too much fuel, the pilot can set the power by partially closing this "tap" but then of course there is no rotor rpm governing.

Some types also allow fuel flow to be increased beyond the FCU demand, for the case where an FCU malfunction is not allowing sufficient fuel in. This may be a seperate lever, or may involve pushing the lever further forward than the flight position. Think of this as a tap bypassing the FCU and just letting fuel straight into the engine.

Beep switches are typically used to overcome the static droop of an analogue governing system, and to match engines in a twin engine setup. Static droop is the phenomenon whereby as the load is increased (raising the collective) the governor can't quite maintain the desired rotor rpm and it droops a bit. So for example at minimum collective pitch on the ground the rotor rpm would be more than when hovering at high pitch. The beep switches modify the governed datum a little, so that the pilot can set the rotor rpm to the optimum value at a given load (collective position). For twin engine aircraft, the beep switches can be used independantly to ensure that both engines are working equally hard and sharing the load.

Of course well designed helicopters, even of 1980s vintage, don't require beep switches!

[HeliComparator]

TC - don't you mean the other way round?

[baobab72]

Many thanks for the replies!

Just to clarify, when you start the first engine, do you have to advance he lever to the flight position prior to starting the other engine allowing the battery to recharge or you start the second engine with the other engine in idle?
When you start the engine do you select the idle position and then you let the fadec take care of the sequence while you monitor the engine for no light off, hung start, hot start, starter fail to disangage - those conditions stem from my jet flying background and i am not sure they apply to the helicopter as well! - or you start the engine with the lever in shutoff and then you advance it into the flight detent at a certain percentage of gas generator?
During normal flight as the tl's are advanced into the flight detent, i presume just prior to takeoff, does the fadec or fcu maintain a constant rrpm's by mean of a governor and correlator as the collective is changed, varying the load on the mrs, if so which instrument do you refer to to set the power? Probably you then back it up with the engine temperature
Do you have an APR postion - auxiliary power reserve - providing an uptrim either manually or automatically in case of an engine failure on the remaining engine? And if so, do you select it manually?

Many thanks and my apologies for the lengthy post

Baobab72

[SASless]

There is no telling "what" he means!:oh:

[Old Age Pilot]

TC - don't you mean the other way round?

That's what I thought.

To give such a silly answer of absolutely no benefit to anyone: at least get it the right way round :ok:

[Thomas coupling]

The throttle lever in a helo is the cyclic. Push it fwd to go faster - right?
Pull it back to slow down - right? Isn't that what throttles do?

The cyclic is connected to the Main AI (directly). Push it fwd and the AI shows descend and the helo goes down as well as fast. Pull the cyclic back, the AI shows climb, the helo slows down.

Where did I go wrong then? Have I missed something:{

[HeliComparator]

I can't answer specifically for the Augusta nor the squirrel but in general:
Many thanks for the replies!

Just to clarify, when you start the first engine, do you have to advance he lever to the flight position prior to starting the other engine allowing the battery to recharge or you start the second engine with the other engine in idle? Normally you would go to flight position, as you say so that alternators come on line etc
When you start the engine do you select the idle position and then you let the fadec take care of the sequence while you monitor the engine for no light off, hung start, hot start, starter fail to disangage - those conditions stem from my jet flying background and i am not sure they apply to the helicopter as well! - or you start the engine with the lever in shutoff and then you advance it into the flight detent at a certain percentage of gas generator? Depends on type but on reasonably recent designs, you put the lever into idle. Earlier designs you typically left it in shutoff until a certain N1 was reached
During normal flight as the tl's are advanced into the flight detent, i presume just prior to takeoff, does the fadec or fcu maintain a constant rrpm's by mean of a governor and correlator as the collective is changed, varying the load on the mrs, if so which instrument do you refer to to set the power? Yes, although there can be static droop on some poorer designs as I previously mentioned. Power can be set by looking at torque, N1 or on some types, collective position. Whether torque or N1 depends on which parameter is the limiting one, which varies according to density altitude. Probably you then back it up with the engine temperature You need to check you are not above a limit, but on most types you should top out on torque or N1 first. Decent modern types have a "First Limit Indicator" that tells the pilot how far he can raise the collective before hitting the first limit, whether it be TOT, Torque or N1.
Do you have an APR postion - auxiliary power reserve - providing an uptrim either manually or automatically in case of an engine failure on the remaining engine? And if so, do you select it manually? Not APR as such, but on some old types yes, to counter the static droop at max OEI power you might beep the Nr up to a high value for takeoff and landing, so that the inevitable droop when OEI max power doesnt reduce the rotor rpm too much. Modern types dont suffer from static droop - the FADEC typically limits you to AEO power until an engine failure is detected, then it arms OEI power automatically.

Many thanks and my apologies for the lengthy post

Baobab72

[HeliComparator]

TC yes, OP was talking about heli engine fuel flow controls. For a FW throttle you push forward to climb, pull back to descend. Fuel control levers on helis the same, pull it back, you are going to be descending!

The cyclic is connected to the Main AI (directly). Push it fwd and the AI shows descend and the helo goes down as well as fast. Pull the cyclic back, the AI shows climb,

Must try that in the hover sometime!

[Anthony Supplebottom]

Whatever TC's drinking - I want some!

[Thomas coupling]

Helocombatulator: Thanks for that. It's cleared matters up now. Didn't realise I'd got it back to front.....:uhoh:

PS: It's Agusta....not augusta :oh:
And Squirrels don't have fadec (except the 355N).

I read it from a book.

[SASless]

TC.....You really must be looking in a mirror or something!

Cyclic controls attitude only.

The Collective (Power) determines speed.....think not....leave it on the floor and see how fast you go.....as no matter how fast you can get the helicopter up to...it will ultimately reset to ZERO.

(This explanation is just as accurate as HC's and TC's as a few minor variables are left out in all of them.)

[170']

'And Squirrels don't have fadec (except the 355N).'

Ermm....Might want to re-think that!

AS350 B3
High-performance version, is powered by an Arriel 2B engine equipped with a single channel (DECU) Digital Engine Control Unit with a mechanical backup system. This helicopter is the first ever to land on Mount Everest. AS350 B3/2B1 variant introduces enhanced engine with dual channel (FADEC) Full Authority Digital Engine Control, dual hydraulics and a 2,370 kg (5,225 lb) Maximum Take Off Weight. AS350 B3e (introduced late 2011) equipped with the Arriel 2D engine.

[Thomas coupling]

SASless: What??? Please translate the transmission.

170: Ooops u r correct, I meant the twin squirrels, sorry. (355f's).:ouch:

On startrek, if you push the throttles fwd, the universe gets larger and magnifies. If you throttle back to impulse power, it decreases in size and looks smaller.....isn't this the same as my theory?;)

[Coconutty]

On startrek, if you ....

:8 :ugh:

http://i34.photobucket.com/albums/d129/coconut11/Coconutty.jpg

[heli1]

So if I rotate one hand on my stomach and one on my head as fast as possible do I go forward,up or down ?:ugh:

[baobab72]

Any other hints on the ops of the power levers?

With reference to any helicopter you are familiar with?

Many tks

Baobab

[Sailor Vee]

All I can say, "upside-down tree", is the further back you go, the more usage the 'power/speed-select (for main rotor rpm)/'throttles', got.

On a modern helicopter, such as the EC225 LP, the engine control switches have 3 positions - Off/Idle/Flight, speed of the main rotor is controlled completely by the FADEC, dependent on collective position, no manual reversion as per the AS332,mentioned elsewhere.

I also think TC had been on the hooch before posting!

[diginagain]

I think I was taught 'control speed with attitude, height with power', but that was in 1988.

[HeliComparator]

I think I was taught 'control speed with attitude, height with power', but that was in 1988.

You probably were, but it was never taught very well IMO! In reality it's as you say at low speed, but when you are fast cruising it has to be the other way round.

[Lonewolf_50]

baobab72:
An example of using a turboshaft eneine to provide power to a helicopter.

In the Sikorsky S-70 series of Helicopters, the power control levers levers, (PCLs) are situated on the overhead/ceiling of the cockpit. They are connected directly to the HMU (part of the fuel control/governor, which is finely controlled by the ECU or DECU (ecu = electronic control unit, another governor), and then fuel is metered in gross terms by the Load Demand Spindle. (see below) Engine speed signal is feed back into the HMU and ECU as a part of this design. (And IIRC, so is Nr, but memory is a bit sketchy here).

What you typically do is start the engines, make sure all is running OK, and then move the power levers into a "fly" detent with the idea being that you will keep the Nr at 100% rated speed by use of the governor in the HMU and the ECU/DECU. (D for digital)

This means that you rarely, if ever, touch the power control levers in flight. You instead increase or decrease demand for engine power to the transmission and rotor system by moving the collective up and down, which is where the Load Demand Spindle comes in. Pull up, earth gets smaller, lower and earth gets larger. TC, are you still with us? :}

If I pull the collective up, the HMUs fuel metering valve changes position to allow more fuel to flow to the engines, though the the ECU fine tunes the fuel flow to keep the Nr as close to 100% (258 RPM in a Blackhawk or Seahawk, and I suspect most S-70s) as it can. It's quicker than the HMU.

If I lose electrical power, my ECU or DECU can't fine tune the fuel flow, so that Nr will vary a bit as I change power demand with the collective. The HMU slowly catches up in its governing functions to keep Nr at 100%. This leads to operator manuals usually advising to move collective slowly when in more or less 'manual' fuel mode, to avoid surges in NR and engine speed.

If your ECU or DECU begins to go wrong, you can lock it out and revert to 'manual" power control (which is actually just using a gross governor rather than a fine governor) which will again be driven by collective position and the HMU's gross governing function.

In other turbine engine helicopters I have flow, there is a fine tuning "beep" button for the ECU to fine tune or control the fuel flow depending upon demand, or in a case where the fuel control malfunctions and you need to adjust Nr as you fly to avoid overspeed or underspeed of Nr or engines.

Each helicopter manufacturer who installs turboshaft engines will adopt a particular combination of controls so that governing of engine power in flight is mostly done without the pilot constantly having to adjust fuel flow manually.

There are a lot of good design reasons to do this, which inclue overspeed and overtemp protection.

I hope that helps.

[diginagain]

You probably were, but it was never taught very well IMO! In reality it's as you say at low speed, but when you are fast cruising it has to be the other way round. Bloke was doing his best to keep it simple. Experimentation came later. Most of my time was spent flogging-around at low-level with TOW launchers fitted after that.

[baobab72]

Dear all
Many thanks for the time you took to share your knowledge!!

One additional question: in the jet world, at least based upon my personal experience, the ECU is driven by a permanent magnet alternator or PMA driven by the engine through the accessory gear box, is it the same in the helicopter world?

When you start up the engine, do you start it with the power levers in cutoff or idle?

Is there any helicopter where the power lever and its detents are mounted on the collective cos i saw a picture that showed a collective with a twist grip that seemed having a FLY detent together with some other figures?

Are the fadec power levers always mounted on the ovhd? Cos i have never seen any ovhd panel with a single power lever.

Many thanks

Baobab

[HeliComparator]

Dear all

One additional question: in the jet world, at least based upon my personal experience, the ECU is driven by a permanent magnet alternator or PMA driven by the engine through the accessory gear box, is it the same in the helicopter world?

Depends, for example the EC225 has separate small engine driven alternators just for the FADECs, whilst the earlier variants (AS332L and L2) relied on airframe electrical power. Most older types are the latter I suspect.

When you start up the engine, do you start it with the power levers in cutoff or idle?

Depends on type as I mentioned before

Is there any helicopter where the power lever and its detents are mounted on the collective cos i saw a picture that showed a collective with a twist grip that seemed having a FLY detent together with some other figures?

Yes, Bell seem to like this setup.

Are the fadec power levers always mounted on the ovhd? Cos i have never seen any ovhd panel with a single power lever.

Overhead or collective (although someone will come up, with an exception). Tends to be on collective for singles and single-pilot twins, and overhead for multi pilot types (generalisation)

Many thanks

Baobab