New Propeller Innovation: Looking for Comment/Interested Parties

How do you make the propeller stay in neutral, without turning, if there are no clutches?

 

Oh OK I think I understand what you're saying- the engine start up is affected by the prop pitch that the engine stopped at?

So if the prop was left at fine pitch on shutdown then startup would give you a surge forward?

I'm wondering why the shutdown circuit just doesn't default to feather pitch which would provide no thrust at startup and ease the load on the starter motor.

But I may have got that all wrong.

 

You don't. The prop will turn at startup but by placing the prop at feather pitch it will generate no thrust and won't move the vessel.

Aircraft don't have a clutch. I agree that is not good from a safety perspective- especially say when running an engine in a tank to clean it after use.

It would be possible to design a clutch on the vertical drive shaft of the outboard in which a dog just lifts out of the shaft just as dogs disengage from forward/reverse gear. It would have the sole purpose of disengaging the shaft while in most designs it also engages the gears.

But at this stage we haven't made it a priority.

Thanks for your comment.

 

What an inconvenient question !

 

A dog clutch is pretty easy to implement on the vertical drive shaft.
Manufacturers don't tend to do it that way because they also want to engage gears as well as disengage the shaft. It would be splined of course with the
dog lifted and dropped on a bearing mounted collar.

We may put this higher on the list so thanks for highlighting it.

These forums (we're on several) are very proving very useful feedback and really helping to refine the design.

Thanks for your comments and encourage to contribute further.

 

You envisage no reduction gears, or do I misinterpret ?

 

You would need to be more specific in your question.

 

A prop will have no thrust , in a certain position at any RPM.

So neutral just mean no thrust , even though the prop is spinning.

The boats with a CPP are usually large enough to require a reduction gear to move the vessel with an efficient big slow turning prop.

This is why it must be shut down at the cold start RMP, to create "neutral" (no boat movement) on start up.

 

Why would anyone want a propeller diameter to decrease? I can't see this solving any problems a hybrid or diesel-electric system won't solve. Could create a hybrid system with combinatormode and it would still be less complicated and prone to errors.

 

Or a gearbox. Many Vee-drive ski boats use a car engine hooked up to a 3spd Automatic transmission (Ford C-4, etc). Supposed to help let the motor spin the prop at max power when the boat is starting from zero, to get the skier out of the water. Since water isn't rushing over the prop yet, it takes more power for given RPMs.

I guess a variable prop could do the same thing, but V-pitch would seem like the way to go.

Maybe decrease diameter for shallow water operation?

Like a sailboat "racing prop" that can fold to streamline it, just not fold all the way. Less power but less chance of grounding, and maybe less chance of fouling on lines or seaweed.

Maybe like shoes on a simple centrifugal clutch.

 

The two problems that jump out at me are; one, the aforementioned gap left by the expanding blade at the root - which may reduce or nullify the advantages of the larger diameter.

Two, I have seen no mention on how you handle the very large centripetal forces. There must be some form of mechanical balance so that you can retract the considerable mass and inertia of a spinning blade - or keep it from snapping to max diameter as soon as it starts spinning. I think you either have a very novel solution, or have overlooked this issue. Hydraulics could manage it, but not a manually operated linkage. IMO of course.

 

To operate efficiently over a wider speed range. As speed increases you need greater pitch, if diameter remains the same then the engine will not have enough power so a smaller diameter is needed. If the engine did have enough power at the higher pitch then it wasn't making max power at the lower pitch setting.

Varying pitch and diameter would enable the engine to operate at its most efficient power setting, and the propeller would be operating at its most efficient configuration. In theory.

Fixed pitch props are a compromise. Variable pitch props are also a compromise but a step up. Variable pitch/variable diameter props, if they work, would be another compromise but also another step up.

The next step up after that would be variable twist, then variable airfoil sections, then variable...

 

I think what you all neutral position is what others term "feather pitch" i.e. it imparts no thrust because the blades are at an angle that just makes them paddles moving no air.

I think the issue you refer to is identical in aircraft such that you can't leave the blades at an angle that imparts thrust otherwise the starter motor has too much load placed on it.

Hence there are mechanical links that push the prop into feather pitch as the prop spins down after shutdown.

The term feathering is also used on sailboats I think since they need the prop to provide least resistance when under sail.

My designs allow for any form of gearing either as the shaft leaves the crankcase, as it engages the prop shaft or as the prop shaft engages the prop.

 

Correct! Variable anything is good if justified by the extra complexity etc etc.

Morphing of airfoil sections is also on the cards as you suggest using smart materials.

 

As I understand it, a diesel-electric is just a different way of extracting/storing energy.

A propeller is a mechanism to apply that energy to the medium.

It is well known that large props are efficient at low speed. This is how human powered (i.e. leg powered) aircraft have flown given the small energy able to be delivered by the human body. Beyond a certain point a prop becomes a drag brake- a big disk pushing itself into the air/water. Paradoxically, reducing diameter will make the vehicle go faster - esp if coarse pitch is applied.

This has always been the theory but there has never been a way to vary diameter in practical terms. The centrifugal forces are enormous and your mechanism but be able to pull the prop in while also allowing it to expand WITH those forces and to maintain full blade retention at all times and all radius.