I was under the impression that if the button did not pop out that it would cause the motor for the aux feathering pump to burn out as it was continuing to try to operate the now feathered prop. I had not heard about the prop coming out of feather by itself in this scenario if the motor continued to run.
If you let the motor run long enough it may eventually experience some damage to exceeding a duty cycle, but so long as it runs, the prop will cycle in and out of feather repeatedly.
Perhaps our system was different because there was no way to push in that button on the Herc.
The C-130 uses the Hamilton Standard (now Sunstrand) 54H60 propeller, and does not use a hydromatic prop. It operates differently than the hydromatic,and uses it's own oil supply. In fact, the C-130 uses H-5606 fluid in a dedicated, pressurized resorvoir, for it's propeller, and doesn't use engine oil to control the prop. Operation of the propeller on the T-56 powerplant is similiar to operation of the propeller on the TPE-331 turboprop engines, except that the TPE-331 does use engine oil for the propeller. From a pilot perspective, they are very similiar. I mention this because while mostly only military will have experience with the T-56 (or those who flew the L100 or L382), many more have used Garretts (now Honeywell's), and will have a similar base of experience with a comparable engine type.
In all honesty, I was never 100% comfortable with my knowledge of the inner workings of that complicated prop and it seemed difficult to get answers sometimes, but going from memory, it seems to me that a propeller blade angle switch and a pressure switch in combination would stop the solenoid operating the motor on the pump.
James, I wouldn't feel too bad about an understanding of the Ham Standard on the Herc; it's the most complex propeller built, and the relationship between it and the engine is the most complex one in the land of turboprops. It's simply from an operators point of view, but if you want to dive into the technicalities of it, the entire combination of the prop and motor on the Herc and P-3/Electra is somewhat of a mechanical monster. One of the most complex turboprops built in common use is the TPE-331, and it has a lot in common, both in form and function with the T-56...but when put in concert with the propeller, the T-56 wins out in terms of complexity on several levels.
You said that, with increasing aircraft pitch, there's an altitude gain, and an airspeed reduction, so the propeller governor would increase blade angle to maintain an specific RPM; the opposite for an aircraft decreasing pitch.
Close, but not quite. When pitching up or decreasing airspeed, the tendency for a fixed-pitch propeller is to slow down in RPM. With a constant speed propeller, however, the individual blade angle is decreased (not increased)...this allows less drag on the blades and allows them to maintain their RPM.
The opposite is true in a dive; the propeller tends to spin faster in a dive with a fixed pitch installation. In a constant speed propeller, in order to prevent the RPM from increasing, propeller blade angle is increased in the dive.
So, my question is this: Do you have in the cockpit any way to check for the blade's angle of attack? Something like an AoA sensor gauge, or do the prop (or condition) levers move (not likely, me thinks, since the governor works on oil pressure, and the lever tells the governor which speed it wants via the weights, am I right?)?
Ocampo, there's no way to tell the blade angle from the cockpit (unless the propeller blade is actually stopped, and you can see it). From the cockpit perspective, the actual blade angle has little meaning. We're primarily concerned with it's effects, and those we know and understand from RPM and power settings.
In a piston airplane, we can determine our power from manifold pressure and RPM, and in turbopropeller airplanes, we can determine our power from RPM and either torque or horsepower/shaft horsepower (a few airplanes use horsepower gauges, rather than torque). What the blade angle is doing at any given time isn't really meaningful, as it's constantly changing with flight conditions to maintain a constant RPM. The constant RPM simplifies the use of the propeller from the cockpit, and simplifies power management, as well as serves to make the propeller more efficient and useful.
You are correct regarding the cockpit control of propeller RPM. When the pilot moves the propeller lever toward increase or decrease, he or she is controlling a spring in piston airplanes. That's it (except for feather and reverse operations, which vary with the propeller type, and may involve mechanical connections between the propeller control and other engine functions). Not actually moving anything else, the pilot is simply compressing or releasing compression on a "speeder spring." This spring acts against the flyweights in the propeller governor. The flyweights want to open a pilot valve, and the speeder spring wants to close it. At a given RPM for the flyweights in the governor assembly, the ability of the centripetal force on the flyweights to open the pilot valve is tempered by the resistance to moving the valve...and that's provided by the speeder spring, and the amount it's compressed, in turn, is determined by the pilot's use of the propeller control.
Does your PPRuNe handle mean you knew Statocruisers?
Actually, no, though I've been asked that before. It's a reference to the Sorrell SNS-2 Guppy, a small spruce and fabric reverse staggerwing single seat biplane I've had under construction for the last fifteen years or so (one of those projects that had dragged on far too long). When I originally began using the handle on the internet, I typed it in wrong, and I've been using it that way on a lot of sites ever since, for simplification.
I worked on C-97's, and was in line to fly them, but separated from that operation before I had the chance. I believe we flew the last operational working aircraft of that type...so I'll never get that chance again. It was an impressive airplane.