feathering prop

I suspect it's similar to what's used on airplanes

although the power to shift the blades may be an electric or hydraulic motor rather than a hydraulic piston. A constant-speed aircraft prop needs to change pitch quickly to respond to changes in manifold pressure. I doubt that a boat prop needs such sophistication.

-- Bob (Chief Pilot, White Knuckle Airways)

I don't have to like Bush and Cheney (Or Kerry, for that matter) to love America

Feathering (blades passively feather to reduce drag when sailing) or variable pitch? I've seen two types of feathering props.

In the simplest, which I've only seen as 2-blade, the blades are hinged at their bases on pins perpendicular to the prop shaft. Drag causes them to fold up, their own thrust forces them open. The two blades are linked together by sector gears centered on the hinge pins, presumably to avoid imbalance if one blade gets stuck. These are very inefficient and will not drive the boat in reverse--things can get exciting if you're docking a boat equipped with one and forget until you try to reverse at the dock. Here's one...

Bevel gears in the other type take advantage of shaft torque to overcome torque and pivot each blade about a radial axis. This type will drive in reverse.

Ned Simmons

The term "constant speed" indicates the pitch is varied to maintain the selected engine speed.

While manifold pressure is part of the power equation the propeller governor does not in any way sense or respond to manifold pressure.

Rick

That's true, but if you change manifold pressure (which indicates engine power) by changing the throttle setting, the prop governor senses the changing engine speed that results and must quickly alter the prop pitch to keep the engine speed constant. I shortcutted the whole cycle for brevity. Sorry for the confusion.

-- Bob (Chief Pilot, White Knuckle Airways)

I d> > A constant-speed aircraft prop needs to change pitch

No confusion here. Manifold pressure is the least significant factor within the constant speed range. Aircraft attitude and airspeed change far more often than throttle settings during cruise and will rapidly influence rpm.

It is called a constant speed prop for a good reason and implying that manifold pressure is the controlling factor is very much in error.

Rick

There is/was a constant speed prop. that balanced thrust and RPM by way of weights and special blades that moved for and aft as they rotated. They adjusted the constant speed by changing the weights (on the ground).

Don't know any more about them.

Bill K7NOM

Im interested in the pitch actuating linkage of a reversing prop which will change pitch from the cockpit while under way.

You might be thinking about the Hamilton Standard Hydromatic prop. It evolved into the first cs prop after HS incorporated the newly invented Woodward propeller governor around 1930.

The counterweights were there to return the blades to fine pitch (the high rpm position.) In operation the pilot would adjust the admission of engine oil pressure to a cylinder in the propeller dome to increase pitch (low rpm.) Selecting a high rpm setting allowed oil pressure to bleed off the cylinder and centrifugal force on the counterweights twisted the blades to fine pitch.

Later models, including the feathering version, used oil pressure modulated by the governor to move the blades both directions, eliminating the need for large counterweights.

Rick

I've only seen Beach 18's apart , they look very complicated. If it wasn't for my dad's A&P using every trick to keep me form learning anything I could tell you more. I was told they use oil pressure , but never could figure out how. If you find some really good pictures , please post them.

"I've only seen Beach 18's apart , they look very complicated. If it wasn't for my dad's A&P using every trick to keep me form learning anything I could tell you more. I was told they use oil pressure , but never could figure out how. If you find some really good pictures , please post them."

I give up whats a beach 18? also what would your dads A&P be?

(C-45%2FAT-11%2FJRB%2FSNB)&distinct_entry=true A&P = Airframe and Powerplant mechanic.

-- Bob (Chief Pilot, White Knuckle Airways)

I don't have to like Bush and Cheney (Or Kerry, for that matter) to love America

Bob got the A&P for ya.

Hmmm, they seem to be hard to find on the web. Its about 3/5 the size of a DC-3 with a wide horizontal stabilizer with a vertical stabilizer on each end. Two P&W radial engines , tail dragger, and a longer nose than the DC-3. Can't recall a different name for them , Beach Craft-18. Made somewhere around WWII and probably for brass transport and "light" hauling.

Maybe searching the patent office would get you better pictures of how the props are adjusted. You should forget the aircraft if you want it for a boat.

Sorry, the URL I tried to send didn't wrap properly, but if you click on the fragment, you'll get a Beech 18 (called a C-45 in the military) in the top picture and the fifth picture down.

-- Bob (Chief Pilot, White Knuckle Airways)

I don't have to like Bush and Cheney (Or Kerry, for that matter) to love America

On my Sabb-Diesel boat engine with original propeller linkage, prop pitch is adjusted by sliding the driveshaft/prop axle back and forth. At the engine end is a splined driveshaft that allows longitudinal movement, and a control lever for adjusting pitch. The propeller runs on a thrust bearing attached to the stern of the boat, and is turned by a splined drive on the axle so that the axle can slide back and forth while the propeller hub remains static in the lenghtwise direction. Turned grooves on the axle engage gear teeth on the prop blades to adjust pitch, and the blades have about equal area on both sides of their pitch axis so there is little torque on them.

Hopeless explanation I know, but I coldn't find any good pictures. It's really simple when you see it.

-- Aamund Breivik

I forgot to mention that here in Norway, at least, such controlled-picth propellers are more or less standard on small fishing vessels etc. Ours is on a 20-foot wooden boat powered by a 30 year old

8hp engine. A controlled-picth propeller is in most respects vastly superior to fixed-pitch ones, at least on relatively slow boats that don't plane. You have infinitely variable pitch from full ahead thru neutral to full astern; some models made for sailing will feather as well. There is no reverse gear on the engine; all maneuvering (sp?)is done with the pitch control lever.

For some reason these seem to be uncommon on the other side of the pond, and there is much misinformation about them. One article I saw claimed that controlled-pitch props were only really suitable for mounting on large boats, like 60' up.

-- Aamund Breivik

On my Sabb-Diesel boat engine with original propeller linkage, prop pitch is adjusted by sliding the driveshaft/prop axle back and forth. At the engine end is a splined driveshaft that allows longitudinal movement, and a control lever for adjusting pitch. The propeller runs on a thrust bearing attached to the stern of the boat, and is turned by a splined drive on the axle so that the axle can slide back and forth while the propeller hub remains static in the lenghtwise direction. Turned grooves on the axle engage gear teeth on the prop blades to adjust pitch, and the blades have about equal area on both sides of their pitch axis so there is little torque on them. "

I recently had the pleasure to check out the sabb diesel prop system. It appears to me that this prop was actuated not by bevel gears on this particular unit, but something more like a pitman arm allowing it to only twist the blades into forward & reverse but not into a total feather. I think I need at least

135 degrees of rotation on the prop blades to accomplish this.

That's it. I had to put Beach Craft & C-45 in to get this one.

They will be easier to find if you look for a Beech 18 (Beach makes nice enough tool boxes, though)

:-)

Cheers Trevor Jones

No, you'd need less than 90. The leading edge of the blade goes forward in feather, and it's already forward of neutral when it's in thrust position. Many aircraft props use link rods inside or outside the hub to control prop pitch, and they'll go full feather and some will even go into reverse pitch. It might be interesting to try a hollow prop shaft with an internal rod that is moved fore and aft to control a small linkage at the rear of the prop, similar to the mechanism used to adjust tail rotor pitch on some helicopters. A shaft directly connected to the engine would preclude this design, but the vee-drive layout would allow it. Dirt would be the biggest enemy of any exposed mechanism. Dan