Turboprops????

[TotalBeginner]

Most of the turboprops that I have seen have power levers to control torque, and condition levers to control prop RPM.

Can anyone tell me why the King Air series of A/C have condition levers, propeller levers and power levers?

[Capt Claret]

From my T/P days:

Condition levers usually turn fuel on as one moves them forward, then they become pitch/rpm control levers. Conversely, when at feather, further aft movement of the condition lever, turns the fuel off, shutting down the engine.

Not being familiar with the new Kingair, I'd speculate that the condition levers are fuel on/off levers, and separate pitch & power levers are provided.

[arismount]

The turboprops you see with condition levers and throttles only have geared engines, i.e., mechanical connection between the engine (gas producer) and the prop drive shaft. These are "constant speed engines," i.e., the condition lever sets them at idle, and then further up, into a "flight" RPM that's unchanging.
Power is controlled by the throttles, or power levers as they're more properly called. Advance the power lever, the prop takes a bigger bite of air, and generates more thrust. This tends to slow the prop, the fuel control senses this and adds more fuel, maintaining RPM. This happens so fast you can't see any change. In a sense, the prop is governing the engine through the fuel control.
On P&W powered King Airs (all of them except the B100), you have a free-power turbine, i.e., no mechanical connection between the gas producer section of the engine and the separate power turbine. The Condition lever(s) serve only to introduce or shut off fuel to the engine, OR to change the idle speed. The prop levers set the prop governor to maintain prop RPM, and the power levers control power, as above, with the exception that when you push them up, the N1 (gas producer) speed increases...and vice-versa.
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"So many people have come and gone,
Their faces fade as the years go by.
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[TotalBeginner]

A ha, and is that why when you start them, the prop doesn't start turning until fuel is introduced?

[arismount]

...it just looks that way because the light off takes place pretty quick...it only takes about 3-4 seconds to get the N1 up to 12% where you can introduce fuel (with the condition lever), then it lights off a second or two later, and you look up and the prop's turning.

However...if you just motored the starter (you use a switch position called STARTER ONLY, which just turns the engine but doesn't energize the igniters), you'd push enough air through the gas producer to "blow" the power turbine wheel around...thus turning the prop. The prop wouldn't turn for a few seconds until the motored air flow was sufficient to overcome the inertia of the PT wheel/driveshaft/gearbox/prop combination. This is why it appears that the prop only turns after lightoff in a normal start.

Obviously the prop would turn immediately if you motored a geared engine such as a Garrett on an MU-2, or the Allison on the C-130...

[barit1]

The turboprops you see with condition levers and throttles only have geared engines, i.e., mechanical connection between the engine (gas producer) and the prop drive shaft. These are "constant speed engines," i.e., the condition lever sets them at idle, and then further up, into a "flight" RPM that's unchanging.
Power is controlled by the throttles, or power levers as they're more properly called. Advance the power lever, the prop takes a bigger bite of air, and generates more thrust. This tends to slow the prop, the fuel control senses this and adds more fuel, maintaining RPM. This happens so fast you can't see any change. In a sense, the prop is governing the engine through the fuel control.
That's called a "beta" control mode - the power lever sets the prop pitch and thus the load torque directly, and the FCU governor responds with the appropriate fuel flow.
On P&W powered King Airs (all of them except the B100), you have a free-power turbine, i.e., no mechanical connection between the gas producer section of the engine and the separate power turbine. The Condition lever(s) serve only to introduce or shut off fuel to the engine, OR to change the idle speed. The prop levers set the prop governor to maintain prop RPM, and the power levers control power, as above, with the exception that when you push them up, the N1 (gas producer) speed increases...and vice-versa.

Don't know the PT6 specifically, but the CT7 turboprop is also free-turbine, but has only two levers--a condition and power lever. The Condition lever sets the prop governor speed, as well as fuel shutoff. Power Lever sets the gas generator speed, effectively setting torque, and the prop governor responds to load up the prop blades. Thus the pilot can set max prop speed for TO, and slow it down for a quieter cruise. (IIRC, the condition lever also is used to select feathering)
One can always tell the difference between the two engine types by the prop blade angle when shut down. The single-shaft engine always has the blades at flat pitch (minimum drag) so it's easier to start. A free-turbine engine has the blades feathered when shut down (at least on types I'm familiar with), because the starter motor isn't directly coupled to the prop, and it doesn't care if the free turbine comes up to speed real quickly. :8

[zlakarma]

What is the reason of installed this two types - single shaft turbine and free turbine? I.e. in King Air you may manually change of propeller RPM, in Hercules is not necessary, why?

[ironbutt57]

A hercules pre "J" anyway is powered by a single-spool type gas turbine engine..that simply put is either "on" or "off" other than when being operated at low-speed ground idle mode (civilian version, not too sure about military engines) for taxiing about, this engine basically runs at one speed...twhen power is desired, pushing the power levers forward simply adds fuel...this would tend to cause an increase in rpm, but the propellor senses this, and increases it's blade angle "bite" causing increased thrust..and vice versa when the power lever is retarded...some fixed shaft engines TPE-331 for example are fixed shaft single spool as well, but are provided with an rpm lever to allow small changes in rpm for passenger comfort..by small 3-4% reduction...twin-spool turboprops as in pt-6 engines have a gas producer (n1) section that is controlled by the power lever, and a power-section (n2) that is connected through the reduction gear to the propellor..since the connection between the n1 and n2 is gaseous, and not mechanical, a bit of efficiency is lost...the fan section on all large hi-bypass fan engines on airliners are configured this way as well...since the fan is nothing more than a many-bladed propellor...so some turboprops have 3 controls...pt6 power...prop...condition (which turns on and off fuel for starting and shutting down, and adjusts idle speed), Garrett, honeywell whatever power, and (speed/ rpm lever which controls engine rpm using prop pitch during flight mode, and uses fuel to control rpm during ground ops(beta) and the good old t-56/allison501 early herc's cv580, l electra..which has one set of levers..power...anybody want to take a stab at the dart/tyne/kunetsov???:hmm:

[Clandestino]

ATR has three-spool turboprops and for sake of simplicity it has only power levers and condition levers. Function of condition levers is regulating prop rpm, feathering and fuel shut-off. Flight/ground idle is regulated via electro-mechanical idle gate attached to power levers.

[jjj2]

King Air PT6 as far as I remember has the option for high or low idle. Low idle for normal use and high for improved reverse thrust operation when runway limited. Other manufacturers seem content with just one idle thus only two levers (Power&Condition/Pitch).

jjj2

[ironbutt57]

the condition lever on some FAR25 aircraft Shorts for example was required to be set high during flight for engine spool up requirements

the "speed lever" associated with most garrett installations performs this same function during ground ops it is connected to both the underspeed governor(idle fuel flow) and the propellor governor for selecting rpm (flight mode), as the engine fuel valve is electronic not mechanical on the tpe-331, no cockpit lever is needed to open and close it, except in the emergency feather scenario stop/feather knob

[rigpiggy]

The RR dart is a single spool 2 radial compressor engine. the HP cock ie Hi pressure cutoff is a mechanical lever that also will disable the AFX on the other side. The power is controlled by a single lever which controls engine RPM between around 7200-15000 RPM cruise normally set at 14,200 with fuel datum trimmers set to control temps/fuel flow, as i remember you could control the FF+/- 7% of total set by the FCU. some guys I used to fly with wanted the torques matched others fuel flow others temps

[barit1]

some guys I used to fly with wanted the torques matched others fuel flow others temps

That's really interesting - on a t-prop the only thing that makes sense to the airplane is to match torques, so there's no rudder trim required. I can't understand why a pilot wants to match ff or temps - can you shed any light on that?

BTW, on a ride I once had in a Falcon 20, the pilot liked to match fan speeds for the same reason you sync the prop rpms - to zero out the "beat" or difference frequency between the L & R fans.

[rigpiggy]

The Dart has different torque figures for each individual engine due to machining tolerances etc.. there is no correction factor available. your torques for t/o must meet a minimum figure as set by an extensive test run after you change any of the parameters. new prop do the runs, new engine do the runs etc... Different torque mins based on temperature, whether you use W/M etc. RR has a circular slide rule where you set the WAT, and it gives a fuel datum figure for the trimmers. After t/o you pull the power levers to set 14,200 and set the trimmers for climb temps, shut off the W/M and do your after T/O's. All from memory haven't flown a Dart in nearly ten years so forgive any mistakes.

[Micky]

blades at flat pitch (minimum drag) so it's easier to start. A free-turbine engine has the blades feathered when shut down (at least on types I'm familiar with

Sorry for being a pain but I think you ment Flat pitch = fully fine = Max Drag and feathered = min Drag...:rolleyes:

[ironbutt57]

flat pitch is min drag when starting the engine, as opposed to max drag when windmilling try starting a fixed-shaft engine in the 'min drag for flight feathered' position and see what happens:rolleyes:

[barit1]

Well, now that would cook out the hot end pretty well - :eek:

I presume the controls are interlocked to prevent a Dilbert from attempting same??

But then - how does one go about performing a "buddy start" when the starter is defunct?

[Micky]

Thank you Ironbutt, I stand corrected!:8 I confuesed what barit said sorry:ok:

[zlakarma]

power lever, and a power-section (n2) that is connected through the reduction gear to the propellor..since the connection between the n1 and n2 is gaseous, and not mechanical, a bit of efficiency is :

Okay, I know how it work, there are single spool and double spool turborop engines. But I ask WHY?
Which of them is best?

brgds

[Daysleeper]

on a t-prop the only thing that makes sense to the airplane is to match torques, so there's no rudder trim required. I can't understand why a pilot wants to match ff or temps - can you shed any light on that?

Yup, going a long way in the electra, great FF gauges, rubbish fuel Quantity gauges, fly a constant fuel flow and thus multiply FF by 4 to get burn (or more likely multiply by 3 on the electra :{ )

Or more normally,

set a constant turbine inlet temperature (TIT) as that means each engine is performing to a known datum (well theory anyhow)
IFAIR 971C for T/O , 932, Reduced temp TO, 895 climb. As the temp is the most important limit it made sense to be focusing more on that when we were likely to bust it.

[barit1]

OK that makes sense for TO & initial climb - but cruise?

[ironbutt57]

just set TIT for cruise...847c if i recall correctly..rpm no need for change...cant do it in flight anyway...propellor automatically reduces it's own blade angle to accomodate power changes and maintain it's "on-speed" rpm..when flight idle is selected, the fuel control maintains a minimum fuel flow to prevent the propellor from driving the engine...prop rpm when on-speed is 1020rpm..the flight deck gauges read engine spool rpm of 13,820..but it's all connected directly..so doesnt matter which side of the gearbox you take the reading from...without getting too specific, certain bleed valve configurations on the engine could change if the prop were to malfunction and cause the rpm to decay, (droop is the term) and the results would be very undesireable...so the engine spool rpm is the one monitored by the flt crew...:ok:

[Daysleeper]

Thats it 847.

My old brain isn't working quite like it used to.