Loss of oil pressure - will it feather?

[italia458]

Regarding multi engine piston aircraft with fully feathering, single-acting prop governor systems, will losing all oil pressure move the blades to the feather position?

I've seen a number of articles that say the propeller will go all the way to feather and I've seen some that say that it will go to a coarse setting but will require manually selecting feather with the prop lever. Maybe they're both correct and it depends on manufacturer?

I would say I'm pretty familiar with the governor operation including when the prop is on the start locks, low pitch stops, high pitch stops (the IO-360 doesn't seem to have high pitch stops). I'm familiar with how the governor operates during overspeed, underspeed and on speed conditions. I'm familiar with governing range.

Say for example, the engine instantaneously dumped all oil. Assuming the engine was still making the same power, wouldn't the prop pitch remain the same since the oil is 'trapped' inside the hub? Obviously, the engine would seize eventually which would begin to slow the engine and prop governor and open the line for oil to go into the prop hub. Since there would be no pressure at this point in the line, as soon as the engine slowed a bit, I believe the propeller would actually dump all oil from the hub into the sump, and go to the feather position.

If anyone has some detailed diagrams with discriptions of the prop system I'd love to see them. I've gone through a number myself including Pelican's Perch and read a few excerpts from textbooks.

EDIT: I think it could also feather when it has low oil pressure vs zero oil pressure. As long as the pressure supplied to the prop pitch change piston, through the governor and its gear pump, is less than the force from the feathering spring and/or nitrogen on the opposite side - it would go to feather. Is that correct?

[barit1]

What a/c, what engine, what prop? :confused:

[Checkboard]

The designer can design a prop/counter weight/spring/air pressure combination to either run the prop fine or coarse on loss of oil pressure.

As I understood it, generally single engine aircraft run to fine (in order to provide an amount of useful power on failure) whilst multi-engine aircraft run to coarse (to aid feathering).

As a review, the constant-speed propellers on almost all single-engine airplanes are of the non-feathering, oil-pressure-to-increase-pitch design. In this design, increased oil pressure from the propeller governor drives the blade angle towards high pitch, low r.p.m.

In contrast, the constant-speed propellers installed on most multiengine airplanes are full feathering, counterweighted, oil-pressure-to-decrease-pitch designs. In this design, increased oil pressure from the propeller governor drives the blade angle towards low pitch, high r.p.m.—away from the feather blade angle. In effect, the only thing that keeps these propellers from feathering is a constant supply of high pressure engine oil. This is a necessity to enable propeller feathering in the event of a loss of oil pressure or a propeller governor failure.
Learn to fly Airplanes - Propellers (http://www.pilotoutlook.com/airplane_flying/propellers)

[blackhand]

Depends on whether it's into fine or inter course

[barit1]

As a review, the constant-speed propellers on almost all single-engine airplanes are of the non-feathering, oil-pressure-to-increase-pitch design. In this design, increased oil pressure from the propeller governor drives the blade angle towards high pitch, low r.p.m.

NOT AT ALL TRUE. The Hamilton Standard counterweight-type hub - models 2B20, 2D30, 12D40, 3D40 etc. (used on the BT-13, AT-6/SNJ/Texan/Harvard, Lockheed 10 & 12, Beech C-18, DHC-2 & -3, Norseman ...) will slew toward high pitch, low rpm when oil pressure is removed, because of the counterweights. In fact when used (sans governor) as a two-position installation, as on the BT-13 or the original L-10, this was the normal cruise mode - riding the high-pitch stops.

The Collier Trophy in 1933 (http://en.wikipedia.org/wiki/Collier_Trophy) went to the inventor of this propeller design.

Early Sensenich props worked the same way. While ferrying a PA-16 (http://en.wikipedia.org/wiki/Piper_PA-16_Clipper) with leaking prop seals, I once intentionally took off in high pitch just to attempt to keep the windshield clean. (light weight, long runway...) :*

[Checkboard]

"almost" :) For those of us not 70, and used to flying round engine aircraft :)


There are other exceptions as well, many aerobatic aircraft engines don't follow "the rule" so they don't overspeed under negative g etc.

[aerobat77]

hey ! a piston engine will not feather. you can see this on a normal shutdown where also oil pressure is gone finally. the prop will remain in low pitch wich is useful for low drag on next startup .
in general you can expect on a piston to force springs the prop in low pitch and oil pressure to high pitch- when oil pressure is gone the prop moves to low pitch.

cheers

[italia458]

barit1 - 1) Beech D95A, 2) Lycoming IO-360-B1B, 3) Hartzell HC-C2YK-2CUF/FC7666C(B)-4 propeller, 4) Woodward 210360 governor.

The prop specs: high pitch (feather) = 82 degrees, low pitch = 14 degrees, start locks = 19.5 degrees.

aerobat77 - hey ! a piston engine will not feather. you can see this on a normal shutdown where also oil pressure is gone finally. the prop will remain in low pitch wich is useful for low drag on next startup .
in general you can expect on a piston to force springs the prop in low pitch and oil pressure to high pitch- when oil pressure is gone the prop moves to low pitch.

We're talking about a piston multi-engine airplane. A single will normally go to low pitch with a loss of oil pressure. Start locks prevent the prop feathering on shutdown with a multi engine airplane. As you can see above, the start locks are greater than the low pitch stops. When running the engine above ~1000RPM, the engine will be at the low pitch stops. When you shut down, the RPM decreases to ~700-800RPM at which time the start locks will slide in and stop the prop from moving beyond the start lock pitch. You'll notice that the engine doesn't really lose oil pressure until you're below ~500 which will then allow the props to go towards high pitch but will be stopped at the start lock pitch.

Back to my question at the beginning - I'm basically looking for someone who has some maintenance diagrams/schematics with detailed descriptions about the operation of specific governor and propeller models.

[italia458]

I think I found my answer! I found the Hartzell owner's manual which clearly states that the propeller will feather with a loss of oil pressure. In the case of this particular propeller, the air charge, spring and blade counterweights are then free to increase blade pitch to the feathering (high pitch) stop.

[Tinstaafl]

As I understand it, typically a light multi will feather with loss of oil pressure as long as the RPM is greater than that needed to cause the anti-feather latch pins to engage. If the RPM happens to be lower than the latch pin RPM threshold then the prop will be prevented from feathering because the latch pins will have engaged.

One of the checks I taught with twins during the initial failure actions (where there was a choice to try to fix the failure or feather eg in cruise) was to check if the RPM was reducing towards the anti-feather latch pin critical RPM. If RPM was reducing then skip trying to fix the failure & go straight to feather before the ability disappears.

[Oktas8]

Interesting exception Tinstaafl. The DA42 with Thielert engines has start latches designed to lock the propeller just a few degrees away from full fine. If an engine malfunction occurred in flight with the blades in the intermediate pitch range (that is, already "beyond" the start latch position), they could feather from any RPM at all.

This happened to me when the propeller control valve failed, so blades oscillated between full coarse and fine, with associated RPM oscillation. At low RPM the blades were at full coarse with start latches unable to engage.

[italia458]

Tinstaafl - that's my understanding as well.

Oktas8 - I'm not totally familiar with the DA42 but I believe you're describing the same system as Tinstaafl. Once above 800RPM (according to my propeller owners manual; it usually varies between 700-950RPM on most multi engine pistons) the start locks will be disengaged. When they are disengaged, you have nothing impeding the range from the low pitch stops all the way to feather. Basically, as long as you're above the start lock RPM, you will be able to feather the prop regardless of its current pitch - assuming normal operation of the prop and governor.

[Exaviator]

If my memory serves me correctly the DC-3 fitted with the P&W 1830 and Hamilton Standard Propeller, a loss of total oil pressure will cause the propeller to become uncontrollable at the low pitch stop (18 degrees). It requires positive pressure backed up by the feather pump to feather the prop.

In this condition there is a danger of an over speed and the propeller should be feathered. Note: The oil tank has a reserve of approx 2.8 gallons specifically for the feather pump.

An additional safety feature is a balance spring in the governor system that will stabilize the engine at approximately 2050 RPM if the control cable or governor pulley shaft fails. The prop governor has a range of 18 to 23 degrees, with high pitch (full-feathered) set at 88 degrees. :ok:

[barit1]

Exaviator - That's because the HS Hydromatic hub has no springs and no counterweights. Left to its own devices, a prop blade will migrate toward low pitch simply because of centrifugal force on each molecule in the blade; and once this starts, rpm increases, which in turn increases the centrifugal force. That's the very definition of a runaway prop.

Related accidents:
CV-580 (http://www.ntsb.gov/aviationquery/brief.aspx?ev_id=21426&key=0)

EMB120 (http://www.ntsb.gov/aviationquery/brief.aspx?ev_id=20001212X16773&key=1)

[Check Airman]

I know a fellow who had an engine fail on the takeoff roll on the seneca due to a busted oil line. he said it feathered pretty quickly. Lycoming engines with Hertzell (sp?) props.

[barit1]

The Hartzell prop has both counterweights and spring(s) for actuation. Per their service manual:

Operation is such that the counterweights provide only sufficient force to neutralize blade twisting moment. Governor oil pressure rotates the blades into low pitch (high RPM) and reverse blade angles, while springs contained within the hub assembly rotates the blades towards high pitch (low RPM) position.

Thus to feather, just remove oil pressure, and the spring force feathers the prop. And their reputation is that feathering is pretty quick!

[whiskey1]

Rag left in the sump following engine overhaul in a BE76 Dutchess.
Prop "auto feathered" on takeoff when said rag blocked oil screen causing a loss of oil pressure.
Look on the Maintenance organisations face when rag was discovered priceless!