C130K Propeller Blade Angle

[splitbrain]

Gentlemen of the C130 operators world,

I am conducting a bit of research into propeller control and operation from the sanctuary that is the West Midlands training base; the subject has not long been re-introduced into technician training. I worked on the C130K fleet (as a techy obviously) in the late 90's so my memory has faded somewhat.
I am trying to understand what happens to propeller blade angle as a C130 accelerates down the runway on its takeoff run, climbs to altitude and then establishes itself in the cruise.
Conventional wisdom with, say, a two pitch propeller tells us that the crew would select fine pitch for takeoff to give good acceleration, and then coarse pitch in flight.
A constant speed propeller is of course governed to a certain RPM, however I can see that there are two different flavours of constant speed prop. The DH Dash 8 condition lever allows the crew to select a high propeller RPM for takeoff (fine pitch?) and then decrease the RPM during climb and cruise, presumably increasing blade pitch and torque.
The C130K condition lever only has one flight position 'run' (thats correct isn't it?). So, when you power up at the start of the takeoff run, blade angle increases to absorb the engine power and keep the engine RPM more or less constant ergo it seems you are starting the takeoff run with a fully coarse pitch, the effective pitch then decreases as airspeed increases. Is that right? Or have I missed something obvious.
Many thanks for your help.

[Top Bunk Tester]

It's been a few years, but this is what I remember from memory :}


The aircraft is powered by four Allison T56-A-15 turboprop engines. The basic engine consists of two major assemblies - a power section and a reduction gear assembly - that are attached to each other by an extension shaft assembly and two supporting struts. The engine is provided with fuel, oil, starting, ignition, and control systems. The engine operates at a constant speed; therefore, engine power is related to TIT that varies according to the rate of fuel flow. An increase in fuel flow causes an increase in TIT and a corresponding increase in energy available at the turbine. The turbine then absorbs more energy and transmits it to the propeller in the form of torque. In order to absorb the increased torque, the propeller increases blade angle to maintain constant engine rpm. A decrease in torque results in a decrease in propeller blade angle to maintain engine speed. Thrust is obtained from the propeller, and a small amount of additional thrust (approximately 10 percent at takeoff) is created by the tailpipe exhaust.

ENGINE CONTROLS AND CONTROL SYSTEMS
Throttles
The throttles are quadrant mounted on the flight control pedestal. Throttle movements are transmitted through mechanical linkage to an engine-mounted coordinator. The coordinator transmits the movements through mechanical linkage to the propeller and to the engine fuel control, and it also actuates switches and a potentiometer which affect electronic temperature datum control system operation. Each throttle has two distinct ranges of movement, taxi and flight, which are separated by a stop. Both ranges are used for ground operation, but the taxi range must not be used in flight. In the taxi range, the throttle position selects a propeller blade angle and a corresponding rate of fuel flow. In the flight (governing) range, throttle position selects a rate of fuel flow, and the propeller governor controls propeller blade angle. The throttles have four placarded positions as follows:
1. MAXIMUM REVERSE - (0° travel) gives maximum reverse thrust with engine power approximately 40 percent of take-off power.
2. GROUND IDLE - (Approximately 18 ° travel) is a detent position. This is the ground starting position at which blade angle is set for minimum thrust.
Note
Throttles must not be moved out of GROUND IDLE detent during ground starting because the resultant increase in propeller blade angle might overload the starter, reducing the rate of engine acceleration.
3. FLIGHT IDLE - (34° travel) is the transition point between the taxi and flight (governing) ranges. A step in the quadrant limits aft travel of the throttle at this position until the throttle is lifted.
4. TAKE-OFF - (90° travel) is the maximum power position.

The throttle quadrant is also divided into two unmarked ranges with respect to control of the electronic temperature datum control system. The crossover point is at 65° throttle travel, at which point the switches in the coordinator are actuated. Below this point, the electronic temperature datum control system is limiting turbine inlet temperature. Above this point, it is controlling turbine inlet temperature if the TD valve switches are in the AUTO position.

Engine Condition Levers
Four pedestal-mounted, condition levers are primarily controls for engine starting and stopping and propeller feathering and unfeathering. They actuate both mechanical linkages and switches that provide electrical control. Each lever has four placarded positions as follows:
1. RUN is a detent position. At this position, the lever closes a switch that places engine fuel and ignition systems under control of the speed-sensitive control.
2. AIR START is a position attained by holding the lever forward against spring tension. In this position, the lever closes the same switch closed by placing the lever at RUN, and in addition closes a switch that causes the propeller feathering pump to operate.
3. GROUND STOP is a detent position. In this position, the lever actuates a switch that causes the electrical fuel shutoff valve on the engine fuel control to close only if the landing gear touchdown switches are closed. The switch also closes the nacelle preheat control circuit making this system operable.
4. FEATHER - A detent position. When the lever is pulled toward this position, mechanical linkages transmit the motion to the engine-mounted coordinator and from the coordinator to the propeller and the shutoff valve on the engine fuel control. Switches are also actuated by the lever as it is pulled aft. The results of moving the lever to FEATHER are the following:
a. The propeller receives a feather signal and mechanically and electrically energizes the feather solenoid valve.
b. The fuel shutoff valve on the engine fuel control is closed both mechanically and electrically.
c. The propeller feathering pump is turned on.
d. The nacelle preheat system remains operable only when the aircraft is on the ground (if installed).

CAUTION
When pulling a condition lever to FEATHER, pull it all the way to the detent to assure that the propeller is fully fathered when the engine fuel is shut off. If the lever is left at midposition, and the NTS is inoperative, an engine decoupling is possible.

PROPELLER SPEED CONTROL SYSTEM
The speed of the propeller is controlled by the propeller governing system and the synchrophasing system.

PROPELLER GOVERNING SYSTEM
The principal function of the propeller governing system is to maintain constant engine operating rpm. Propeller governing is accomplished by the action of the flyweight speed-sensing pilot valve.

SYNCHROPHASING SYSTEM
The synchrophasing system is an electronic system for controlling the blade position relation between all four engines.

ELECTRONIC PROPELLER GOVERNING
The synchrophaser electronic unit provides circuits for the following governing functions: speed stabilization (derivative), throttle anticipation, and synchrophasing. The propeller mechanical governor will hold a constant speed in the flight range but throttle changes will cause the governor to overspeed or underspeed while trying to compensate for the change in power.

NTS LOCKOUT SYSTEM
The propeller is equipped with a lockout system to deactivate the NTS system for throttle settings below flight idle. When the throttle is moved below flight idle, a cam moves the actuator away from the NTS plunger and renders the system inoperative. This is necessary to prevent a propeller from receiving a possible negative torque signal at high landing speeds when the throttles are moved toward reverse, with resultant asymmetrical power problems.

PROPELLER CONTROLS

Throttles
Each throttle is mechanically linked through the engine coordinator to an input shaft on the propeller control assembly. When the throttle is in the governing range, between FLIGHT IDLE and TAKE-OFF positions, the input shaft rotates with throttle movement but has no effect on propeller speed. When the throttle is in the range below FLIGHT IDLE, any movement of the throttle is transmitted to the speed sensing pilot valve to increase or decrease blade angle. The maximum negative blade angle is obtained when the throttle is at MAXIMUM REVERSE. Approximate minimum thrust angle is obtained when the throttle is at GROUND IDLE. When the throttle is moved below FLIGHT IDLE, a cam locks out tie NTS system and a switch interrupts synchrophaser signals to the propeller.

Engine Condition Levers
The engine condition levers serve primarily as feathering and unfeathering controls. Each lever is mechanically linked to the engine coordinator, which transmits the motion of the lever to the propeller linkage only when it is moved to the FEATHER position. When pulled to FEATHER, the condition lever also actuates switches to turn on the electrically driven auxiliary pump in the propeller control assembly, and the propeller blades are moved to the feather angle, For unfeathering, the engine condition lever is held in the AIR START position. A switch is actuated to turn on the propeller auxiliary pump, and the pump continues to operate as long as the lever is held in this position, When the engine condition lever is in the AIR-START position and the auxiliary pump is operating, fluid is routed to the aft side of the dome assembly piston to move the blades to low-pitch angle. When the condition lever is in GROUND STOP or RUN positions, the propeller is controlled normally and the lever has no effect on its operation.

[billynospares]

not fully coarse on take off roll as that would be feather :ok: You should see if there is a copy of prop-a-gander on line anywhere that will help you out. I have a copy here but not sure i can scan it all

[Herc-u-lease]

I'm amazed the training notes for this are no longer available. I had to do a whole oral board on C130K prop control when i went through there in '98. Needless to say my notes are no longer in my posession. Incredible that aspect had been dropped from the syllabus.

Stupid Q i know but I'm assuming you tried the guys at the school at the secret wiltshire training base?

Glad to hear it's back in and good luck

[SirPeterHardingsLovechild]

I wonder if anyone can do it in a couple of sentences...

Erm,

As you toddle orf down the runway, the power plant is temperature limited, unless its a cold day you might be torque limited, so as you gain speed, the relative airflow angle to the blade decreases, so the torque would decrease, but it doesn't because the blade coarsens.

[isaneng]

Ok, in basic terms, and ignoring the electronic refinement systems.....

At the end of the runway, as you push the throttles up, the increase in energy from the engine is sensed as an increase in speed by the hydro-mechanical governor system in the prop assembly. This allows hydraulic pressure to the coarse selection that moves the blades to absorb this extra speed/energy, thus maintaining a constant(ish) rpm, but delivering more power. The higher blade angle is moving more air mass, but as the rpm is constant, unlike a 'standard' jet, the measurement of power produced is torque, measured at the input to the gearbox that drives the prop.

Obviously a reduction in power setting works vice verca.

The propellor is designed to work at a set angle of attack to the oncoming airflow. As the TAS increases with altitude, the relative angle of the airflow will change, and this will also be sensed as a change in rpm by the same governor system (also corrects for IAS (and thus TAS) changes).

Accelerating down the runway, the increasing IAS (and therefore TAS) would increase the relative angle of the airflow. As the blades would therefore have less bite into the airflow, they would tend to overspeed, and once again the governor will coarsen them off to maintain the rpm.

The only time full coarse is selected is when the propellor is told to 'feather'.

Their is always a little bit of coarse pressure holding the propellor against its tendency to fine off due to the CTM/ATM battle. This tendency to want to fine off is enough to allow 'fine' or lower power settings in most cases, although full px is available to the fine line to allow the propellor to come out of the latches that hold it in feather, or to enter the ground range when the throttles are so selected.

Hope that helps.

[isaneng]

SPHC, nice to see you're still alive you old bigger. Big 'Do' on Friday I believe?

[Aerials]

Hey Splitbrain, is there something you are not knowing? I saw 2 powerplants with props attached on the back of a wagon leaving the Secret West Midlands Training Base at lunchtime today!

[SirPeterHardingsLovechild]

Interesting sub-plot here

Air Engineers making it really complicated to justify their (non) existance :ok:

Ground Engineers keeping it simple 'cos they have to fix it :rolleyes:

Yes, isaneng, sewing a button on my favourite fighting shirt, right now :}

[Mal Drop]

Just popped on to the RAF website to have a look at the Herc specs (wanted to check that my recollection of the powerplant being a T56-A-15 was correct) and noticed some interesting information.

It seems that the K has a crew of six (I am standing by to be recalled for a large number of boards of enquiry for getting airborne with insufficient crew). I was also heartened to find out the 70 Sqn are still operating it (so the LXX farewell bash I attended last year was probably just a practice) and best news of all is that the C1/C3 are " receiving an ongoing avionics, electrical and structural upgrade, which will enable them to remain the workhorse of the AT fleet into the next decade."

Pip-pip for the RAF Corporate Comms folk and their well-earned salaries!

[billynospares]

I have a copy of prop a gander which is a nice simplified explanation of the k prop and control system on pdf now if you want it

[splitbrain]

Billynospares:

Absolutely, yes please :ok:

Thanks for the replies gents, its much appreciated, to kind of wrap the observations made up in one reply....

Propellers has come back as a C&G requirement essentially, had that not existed in the spec for the qualification our course is accredited to then I doubt it would have returned. In the intervening decade or so we have been subjected to the process of cleansing known as Lean or Continuous Improvement. I leave it to your imaginations to figure out what happened when several lockers full of years worth of corporate knowledge, obsolete APs, industry notes, course notes etc etc on subjects that were 'obviously never going to be taught again', were discovered by the various clipboard wielding teams as they toured our real estate. <sigh> What notes we have left have gaps in them that would be filled by the instructor, but nobody is left who previously taught the subject so we are having to restock our lockers full of knowledge based on what we have and who we can talk to.
Yes, our favourite school of propeller driven machinery has been contacted, but you have to know what the right questions are to ask as your starting point and we need to go back there when we know what questions to ask. I come over quite critical perhaps, but its not as easy as it seems trying to reload a dormant subject into the training syllabus especially where all of your personel bar one are from fast jet and helicopter backgrounds.

Isanang:

Thanks thats the kind of thing I was looking for.

Sirpeterhardingslovechild:

Again, that works for me, although we try to skirt round talking about engine limits.
{Edit - Hmm, apologies, thats the bit I was missing isn't it? Whilst the engine is temp limited prop blade angle will be constrained to a comparatively fine angle to maintain engine RPM.}

Top Bunk Tester:

Thats a nice summary overview of the system, I might nick that!

Aerials:

Those two old Dart engines heading off are victims of our, erm, budget constraints. One of them has a control box that allows the prop to be run through its full range of movement, but it broke and theres no cash to fix it.

[TheChitterneFlyer]

Distant memories of 242 OCU... Derrick Jeans; Pete Fryer (he's still there!); Tom Osbourne and many others. I still have my (1977) groundschool notes and I reckon that I could still teach aircrew prop and engine theory.

98 to 102; torques within a thousand! Flight Idle (reducing); 98.5 - 100.5; torque-rise noted (stops engaged)!

Those big gauges were much better than those small (digital) thingies of today.

Fond memories.

LXX long retired...

TCF

[Old Fella]

Just a couple of points. The T56/HS prop combo is essentially a Constant Speed installation. The temp limiting mentioned will always (0-90 degrees throttle angle) be active whenever the Temperature Datum Control is not in the Null position. This allows the TD Valve to "take" fuel to limit TIT (Turbine Inlet Temperature). Above Cross-over (above 65 degrees of throttle angle) the TD system can "take" or "put" fuel to Control TIT to that selected by throttle position. As for the propeller blade angle, it will change to maintain 98-102% RPM in the flight range. When Take off thrust is set, blade angle increases to absorb the power and maintain RPM within the limits 98-102%. As the aircraft accelerates the blade angle will increase as required to maintain RPM (This is evidenced by the increase in torque as the aircraft speed increases) Some where it was stated "unless it is a cold day, you may be torque limited". Maybe it is just the way it was written, but the colder the day the more likely to reach the Max permissable torque of 19600 " lbs. I am presuming that what was meant was that, unless it is a cold day, the Max torque may well not be able to be achieved. PS. TCF, you certainly are correct, those big dials are much easier to read and monitor.

[billynospares]

Does anyone know how to post a pdf on here ?