Props without pressure ?

[Unregistered]

Hi Gang,

this is about propellers after engine-failures.

As far as I understand, September Fury´s Prop was
put into sailing-position (right words ?) after the engine
collapsed. Like prop-lever full backward or even farther.
This helped to add much less drag compared to a faster
turning windmilling prop with the blades in flat pitch.

I think in 2002 Miss-A´s Prop went flat, which made a
awful big airbrake. Red Baron`s contra-rotating
Props after her last race were even worse...

Has September Fury a special system to turn the blades
intro (ultra) high pitch when the oil-pressure is lost ?
How does it work ? Maybe seperated oil-system or a
pneumatic system ?

Which other planes have that ? Maybe Voodoo ?
After her engine let go this year, she was parked on the
ramp with the prop-blades in very high pitch.

Hopefully somebody can explain that and maybe tell
about the differences between the airplanes/types.


Jan

https://www.airrace.de

[Ron101502]

FYI Bob Hoover said, in his visit at the Checkered Flag Club, that the most dangerous race plane in an engine failure is one with a contra-rotating prop.

Ron Henning

[Race5]

I don't know for sure, but I would guess they use an acumulator assembly. In other words, a pressurised tank ( pneumatically charged or spring/diaphram type) is used to hold oil routed directly to the prop governor. When the engine quits, the contents of the acumulator can be released by the pilot through a solenoid valve of some type, to force and hold the blades in the feathered position. I don't know of any warbird that had such an assembly stock, and the only racers I know for sure that have something similar are Sept Fury and Precious Metal. As far as the contra props being the most dangerous, I would guess that is simply because they have close to twice as much frontal area when in flat pitch because they have twice the number of blades as compared to a three blade prop. I would have to guess the Bear would be a major b**ch with those huge blades flat to the wind too. Just my .02. I'm sure someone who knows for sure will be along shortly to shoot down my ideas.

Jason

[Leo]

flat pitch

A constant speed prop adjusts the pitch to compensate for power applications. ie a courser pitch for more trottle to maintain prop speed. I know the C-130's system only runs at basically one speed. More power, more pitch to "slow" the prop. That's why there is so much twist to the blades, and why it makes so much noise on the ground. The engines are going full RPM while the prop is operating in both positive and flat or reverse pitch.
Anyone who remembers th RB crash remembers the awful howl it made when the prop flattened after oil loss. And in 82 when Jeannie's prop went flat on a quali run the noise was incredible.
That big P-3 prop on th Bear must have one heck of a bite!


Leo

[Unregistered]

props

September fury uses an Aero Products prop as opposed to a Ham Standard.This prop is self contained with its own pump,resivour,regulator etc. Because of this as long as the prop is rotating its is controllable,assuming its is functioning.The down side to this is it uses its own fluid which must be maintained.A Ham Standard will also continue to be controllable as long as the engine has oil pressure and the govenor is functioning.Aero Products were used on skyraiders.bearcats certain mustangs amoung others.

[Howard]

Feathering props

So far as I know (Cessna 310), props on all multi-engine aircraft can be feathered to reduce drag on a dead engine. Most twins can't maintain alitude unless dead engine prop is feathered. This must be accomplished before rotation stops because there is provisions to keep the blades near flat (normal) pitch on shut down. If you don't get it feathered before rotation stops, it can't be done. Oil pressure is required to keep or get most props out of feathered position. Some aircraft have an accumulator to provide the oil pressure to get the prop out of feathered position. If not, the engine must be cranked with the starter until oil prssure comes up.... and believe me, when an engine starts with a feathered prop, it does not like it much...
Did I get it right this time Wayne?
Howard.

[T. Adams]

Sept. Fury's prop

Not the greatest autofocus job here, but here is a picture of Sept. Fury being towed in after the cylinder blew.

[Ron101502]

It's my understanding that the Bear uses a DC-7 prop hub, and I don't know if it's Hamilton-Standard or Aeroproducts.

I do know that the Convair 580, which has the same engine/prop setup as the Electra (L-188) and P-3 (The C-130 is similar only "upside down"), although with all four blades and not clipped like on the Bear's 3 blades, ran at a constant rpm of 1020 at the prop and 13820 or so at the compressor, and as power (fuel flow) was increased the blade angle increased to maintain these RPMs. (This is in normal flight mode where the power levers controlled fuel flow. When the power required was less than would normally be required to keep the N1 at 13820 the power lever directly controlled prop pitch which is call Beta mode which inlcude taxiing and idle reverse. There was a gound idle mode activated by a button that lowered rpm for ground ops and again the power lever controlled blade angle while the underspeed governor kept engine rpm at whatever ground idle was).

The interesting thing is that there were 2 systems to keep from exceeding too high a pitch to try and prevent a runaway prop and a "de-coupler" that would prevent negative torque, i.e. the prop would not turn the engine. They explained that the hot section of the engine actually produced 10,000 hoursepower but that running the compressor actually used 6000 hp, leaving 4000 at the prop (about the same as the Bear). If the engine were to fail and the prop failed to feather then it would turn the compressor which would be the same as having 6000 hp in REVERSE, obviously catastrophic. So the de-coupler would physically disconnect the prop from the engine under these circumstances. You would end up with the prop windmilling at 1020 rpm and engine rpm at 0. Obviously a lot of drag but manageable.

The 2 observations I make from this is that, since the prop is designed to make 4000 hp at 1020 rpm, that explains the "slow nose" case described in other threads on the Bear, and also the high pitch/feather mechanism is probably the same as whatever was on the DC-7.

Ron Henning

[Reever]

Question

So here's my question.

What kind of prop RPM are we looking at with a C-130 or a P-3C taxing on the ground?

[Peashooter]

Originally posted by Ron101502
It's my understanding that the Bear uses a DC-7 prop hub,

DC-7s used 4-blade props. Isn't the Bear hub from the 1649 Connie, which also used the slow nose case, turbo-compound R-3350? Peas

[Unregistered]

Types of props

There are (according to Hartzell and MT) 3 kinds of variable pitch props for the purposes we are discussing here.

1. Variable pitch (or constant speed), no counterweights, oil pressure regulated. This type is common to most general aviation aircraft and uses an engine driven governor to supply oil pressure which moves a piston in the hub. This piston controls the blade pitch. The disadvantage of the system is that the prop goes flat (max RPM, max drag) when oil pressure is lost.

An additional disadvantage that wrecked one of the fastest Sport racers a few years back is that the prop can only be moved to a coarser pitch as fast as the governor can supply pressure. So when this racer ran up the throttle on the start, the engine HP exceeded the rate the prop could absorb it. The result was a 4000+ RPM runaway and many expensive scattered parts.

2. Variable pitch (or constant speed), counterweighted, oil pressure regulated. This type is common to most high performance piston and turbine general aviation aircraft and uses an engine driven governor to supply oil pressure which moves a piston in the hub. This piston controls the blade pitch. The counterweights force the blades towards feather (min RPM, low drag) and the governor supplies oil pressure to take the prop out of feather.

The obvious advantages are that any oil pressure failure will feather the prop and that the prop can go to a coarser pitch faster than any throttle up.

3. Hydraulic, double acting. Common to most of the big iron. A separate hydraulic system is maintained and supplies pressure to move the prop pitch in any direction. The disadvantage is that it takes pressure to do anything. So in the event of system failure, the prop stays where it is (theoretically). The problem here is that air loads tend to drive the pitch flat in the absence of hydraulic pressure. Also, any failure on approach leaves the prop in a high drag configuration and unlikely to make the runway.

MA2 used a separate accumulator to provide emergency feather control to the pilot. While far from auto-feather, it was a big step up from the other Unlimiteds.

It is my (far less than humble) opinion that counterweighted, or otherwise auto-feathering, props should be madatory for all air racers not using fixed pitch. The number of prop runaways and the danger of a failed engine on flat pitch would seem to make this obvious.

Eric Ahlstrom

[Ron101502]

Nor sure about the C-130 or P-3 but I got my old CV-580 manual out. That eninge is an Allison 501-D13D driving an Aeroproducts A6441FN-606A prop. Engine rpm in flight was 13820 plus or minus 140 and the prop was driven at 1020 rpm or 13.54:1. Low speed ground idle was 10,000 for the engine which would be 738 rpm (the engine tach only gives engine rpm, not prop rpm. Rmember this engine is controlled with a single power lever, there are no condition levers).

I stand corrected-I think the "slow nose case" on the Bear came from the L-1649 Connie.

And I also agree that some sort of autofeather device as described on MA should be mandatory. The inability to feather a prop is what killed Rick Brickert in the Pond racer (Dick Rutan said that with a windmilling failed engine the Vmc was 160KIAS and the rate of descent with full power on the good engine would be 1600 fpm, which explains why Rick had to go to idle on the good engine and land in the sand. The picture of the wreckage in the Reno Gazette-Journal clearly shows the failed engine prop in flat pitch-I have the picture).

Ron Henning

[Unregistered]

Re: Props without pressure ?

Originally posted by Unregistered
Hi Gang,

this is about propellers after engine-failures.

As far as I understand, September Fury´s Prop was
put into sailing-position (right words ?) after the engine
collapsed.


Jan
www.airrace.de

Its called "Feathering" the prop.


I'm by no means an expert, but I do remember reading a few articles on the subject.

For one thing, all the aircraft that use Skyriader props (made by Aeroproducts) have a system independent of the engine oiling system that manages prop pitch. As long as the prop is rotating, even if the engine is just a shredded pile of garbage, the prop can be brought into feathered condition to minimize drag. That is what I assume Mike Brown did with September Fury. Other aircraft that use that prop system include all the Wright 3350 powered Sea Furies, Rare Bear with the 4-bladed prop (currently on loan to Critical Mass, IIRC), and (I'm pretty sure) Voodoo, if she's still running the custom prop with T-28 blaces on an aeroproducts hub.

Merlin and Griffon Mustangs with either the contra-prop or Hamilton Standard propellors control prop pitch with the engine's oil pressure. A major engine failure that breaches the oiling system, such as a broken crank, will drop the oil pressure to zero even if things are still rotating. It is possible to plumb in an "accumulator" that is pressurized by the engine, but will hold pressure if the engine fails and allow one final feathering of the prop. Miss Ashley reportedly had such a system exactly because of what happened to the Red Baron. I couldn't tell you which Mustangs are so equipped right now, but one would hope that they all are. Note that this wouldn't help in the situation Bob Hannah had with Voodoo the year she had the Thorne pink Merlin (I think someone called that motor "Victoria Mouse" :-) ) and the prop control line blew out. When that happens, nothing is going to keep the blades from going flat except yet another different type propellor that auto-feathers when all pressure is lost. But those have their own problems too.

A completely different set of circumstances are at work on, for example, P-38s with their Curtiss Electric propellors. As long as the props have electric power, they're controllable. The down side is that Curtis Electrics in the P-38 have a habit of popping circuit breakers at the most inopportune moments (whether or not the engine has failed) but the pilot can manually hold the breakers in for long enough to feather the props.... but that takes one hand away just at the time the pilot needs about 5 extra hands.


-Steve L.

[Unregistered]

Sorry guys, you are not looking at picture of a feathered prop, but of one that´s taking the bite required.

If you think about it, how much pitch would it take to absorb that much HP?

[Howard]

Prop pitch...

that is a interesting question... I went back to the photo and it sure looks feathered to me.... within the limits of the twist in the blade... hard to see how it could take that big a bite, but maybe it is possible. Most constant speed props I have seen have only a very small angle change from flat to full bite... then, ofcourse, a very large change when going to feathered. Using the speed of sound as an approximate limit for the tip speed, then the aircraft is moving forward at perhaps .75 MACH??? Yes, that would need a big bite allright.