Overspeeding Prop.

[SNS3Guppy]

If those that operated the Hydromatic prop think it's complicated and unreliable, you should have seen the complexity of the CurtisElectric design.

The hydromatic propeller was a simple and reliable system.

[Big Pistons Forever]

OCAMPO

All light pistons twins have very poor performance on one engine. This is why engine failures right after takeoff when the aircraft has little or no excess airspeed or altitude, are so dangerous. If the prop were to overspeed on takeoff on an aircraft I am flying I know it will still produce quite a bit of usable thrust and the magnitude of the overspeed will by definition be limited by the relatively low airspeed (compared to cruise flight). Therefore I will climb to a safe altitude before securing the engine. If this results in ruining the engine than that is just too bad.

[411A]

The hydromatic propeller was a simple and reliable system.

This would seem to be at odds to your prevoius comments, thus...

A common problem with the hydromatic prop was that the button wouldn't pop out. The solenoid would hold the button in, and the propeller would feather, then with the pump running, continue to drive itself out of feather again.

.

That 'solenoid' was properly called a 'holding coil' and its operation was very straightforward.

[Ocampo]

Thanks Big Pistons

I see your point; but actually by "structural damage" I was referring to something a bit more..."drastic", something like a big prop overspeed (I take your point however, the overspeed will be "small") that forces the blade out of its design limits, let's say, by centrifugal force. Can a blade be destroyed (or at least that the blade comes off the blade hub) by an excessive centrifugal force caused by an overspeed?.

My concern is that, if it can come off the hub, it could hit the fuselage and make some serious damage. Is that a posibility?

[SNS3Guppy]

This would seem to be at odds to your prevoius comments, thus...

Again, I said NOTHING about the system being unreliable, or complex.

Yes, the feather button frequently failed to pop out. You can call it a holding coil if you like; as an electrical switch being held in place by an electric field, it was a coil; it was also called a feather button, and was named as much in the aircraft flight manal and the maintenance publications I used. This is irrelevant. That the buttons do tend to stick in and should be guarded when feathering the aircraft is a fact and good practice.

Given your proclivity toward declaring anything that isn't an L-1011 to be unworthy, one might presume that you deem all else to be complex and unreliable.

Personally, I never found the ham standard to be complex, and unreliable. I've flown them into places that most could scarcely imagine, I've had them apart and overhauled them in the darkest of places in the dad of night over 55 gallon drums, and have installed them and removed them countless times...and really can't say I ever considered them either complicated, or unreliable. If you find them to be so, so be it.

[Big Pistons Forever]

OCAMPO

The only instances of a prop shedding parts due to an overspeed I have ever seen documented occured on large displacement Radial engines. However these props are huge and weigh hundreds of pounds. When the prop departs the aircraft on light aircraft engines it is almost invariably a result of a catastrophic crank shaft failure and is unrelated to an overspeed condition.

[411A]

Yes, the feather button frequently failed to pop out. You can call it a holding coil if you like; as an electrical switch being held in place by an electric field, it was a coil; it was also called a feather button, and was named as much in the aircraft flight manal and the maintenance publications I used.

Now, now, Guppy, don't go getting all bent outa shape.

The feather button assembly also contained a holding coil inside, which held the feather button in (electrically), and when the propellor reached feather, the holding coil was de-energized, and the feather button released.
A simple and quite reliable system, seemingly contrary to your previous comments...
I have plenty of hours in DC-6's, Constellations, and a few hours in Stratocruisers, and never had any problem whatsoever with the feather button assembly.

[SNS3Guppy]

There's nothing wrong with the holding assembly. In order for it to release, it needs a signal telling it that the blade and reached the feather position. It's not uncommon in aircraft using the hydromatic propeller to have the button fail to pop out, and accordingly the feather pump continues to run and the prop can drive back our of feather.

This is not complex. Neither is it unreliable.

One puts one's fingers behind the button and is ready to pop it out in case it doesn't pop out on it's own. This is why a cutout is made around the button guard on aircraft equipped with them...for that very reason.

Guarding the feather button isn't rocket science. Just good procedure.

[GotTheTshirt]

The feather button holding coil was activated by an oil pressure switch.

We did have occasional failures on DC3 and 4's and the procedure was just to pull it out manually.

The main point of misunderstanding runaways was the fact that the although the pitch lever was fully fine the propellor on DC3/4 started to fine off before full throttle and was constant speeding for take off and hi power.
In fact the max rpm for the engine is set by adjusting the CSU and not the engine.
On DC3/4 if the prop went into overspeed ( on the ones I was involved with it was metal contamination from CSU internal failures) the feather pump does not have sufficient pressure to overcome the CTM of a prop above its normal max RPM. Additonally in flight there is the effect of airflow.

Some of our pilot handing notes had a section on prop runaways and the procedure ( as noted by previous contributer) was the low and slow technique to reduce airspeed (airflow) and low to increase density altitude.
On some aircraft that had oil shut off cocks there was a final pcedcure to shut of the engine oil cock to sieze the engine and have the porp shear off !! The notes said to fly in a circle so that the departing propellor went away from the aircraft

The propellor/ engine relationship is different between the big piston engines and the turbine engines.

In the days before CAA a typical ARB P & W 1830/2000 written question ( No multi guess ) was to draw the CSU and explain the controlling forces

[stevef]

Feathering Button.

The report into the loss of the DDA's Dakota makes interesting (and sober) reading.
dda

[411A]

On some aircraft that had oil shut off cocks there was a final pcedcure to shut of the engine oil cock to sieze the engine and have the porp shear off !!

The Stratocruiser had such a procedure...pull the engine fire handle (fuel, oil, hydraulics flow stopped) and hoped the engine seized, before the propellor went bye bye.