Freewheeling propellers: the chopper theory

[bill2]

methinks in the spirit of fairness to all contributors a small experiment ( to dispel any discrepancies in prior articles - full versus fin keel versus deadwood versus fixed versus folding versus flat versus pitched versus three bladed ad nauseum ) to be made thusly -

a> a tank ( fixed amount ) of water is passed through a tube ( column ) into which first a locked prop then a freewheeling prop is located

and

b> for a fixed period of time a steady supply of water is slowly injected in the tube ( column ) with a fixed prop and then a freewheeling prop

The water passing the prop is saved in a graduated tank and the amount of water and the time required are recorded. The winner of course will be the one that takes less time/passes more water respectively.

IMHO - my trans requires cooling when the prop is turning ( spell that running the engine ) and I find it cheaper to add sail to get to hull speed ( at hull speed does it not matter whether the prop is free wheeled or locked ? ) than freewheeling the prop - but I am certainly not an engineer and don't even know how to spell flewid dynamics.

BTW - I certainly put a great deal of stock in those old PS articles but as was pointed out earlier - this thread is defined as strictly addressing the question of drag only and a test known to only address drag would seem to satisfy all here.

and Happy New Year to all - regardless of whether we all agree or not

In the interest of surpassing 10K posts I hereby theorize that it generates less drag to repost existing posts - greatly expediting our passage thru these pages . . .

and

as to the above quote ( of myself in part so as not to offend any disinterested party ) I propose to supply the water for the above tests ( which , since designed by a self defined sailor, are, by nature, frugal ) and wonder who else among ye will partake in "Faire Des Expériences" ?

Of course these tests are self evident and all parties may ( not ) agree with the findings - howsoever fair they may seem . . .

[darmoose]

If you lock the rotors of a helicopter in flight, the airfoils will stall and the whole aircraft will fall like a brick.

But if you allow the rotors to freewheel, they will generate enough air resistance to stop the helicopter falling and allow a safe landing.

There is no question of that being wrong. It's fact.

Now, if you just think of a boat as being a helicopter . . .

Cheers,

John V.

Dear John,

your analogies, as i have explained many times, are ludicrous on the very surface.

of course, what you say above about a helicopter gliding to a safe landing is true. we all know that part.

but, if you think a Cape Dory of just about any size (except maybe the Typhoon) can be dropped from, say 1000 ft., and glide to a safe landing just because you let the propeller freewheel, you should be writing fiction.

and about visualizing a helicopter on its side as a boat.... i dont think the thing will even float, let alone fly, and it certainly wont sail very well.

speaking for absolutely everyone, i think we have had enough of your silliness.

GO BEARS!
anonamous writer

[Neil Gordon]

speaking for absolutely everyone, i think we have had enough of your silliness.

Speaking for me, I'm looking forward to even more silliness, from John or otherwise.

[Neil Gordon]

Our Volvo MD-7A manual says to lock the gearbox in reverse,

The Sept 1976 manual states, "During saiing the control should be in the Neutral or Reverse position, if a folding propeller is used. the control should be in the Neutral position if a fixed propeller is fitted."

[John Vigor]

if you think a Cape Dory of just about any size (except maybe the Typhoon) can be dropped from, say 1000 ft., and glide to a safe landing just because you let the propeller freewheel, you should be writing fiction.

My dear Darmoose, calm, yourself. You really mustn't get your knickers in a knot like this. Only posters with unknotted knickers have any credibility on this board.

The last time I tried dropping my CD27 from 1,000 feet, it did in fact glide to a safe landing because, as any smart sailor would in such dangerous circumstances, I deployed my parachute drogue.

Oh, and I hate to point this out, but you're a bit behind the times. I have already written fiction--and not only on this board. I've had three children's adventure novels published, all about sailing. Those young readers are really smart. They all know for sure that a screw that's allowed to freewheel will create greater drag, just like a helicopter's. And they're only 12 years old.

Cheers,

John V.

[Derek Matheson]

Extract from the 1980 Volvo MD7A manual . . .

Folding propeller, S-drive: When switching from engine
operated running to sailing the propeller rotation is stopped by
engaging reverse gear. When sailing maintain the control
lever in the reverse position.
Fixed propeller: When sailing the control lever should be in
the neutral or reverse position. During long sailing trips with
the lever in the neutral position, the engine should be run for
some time every tenth hour in order to ensure lubrication in
the drive or reverse gear.

Essentially, the Volvo folks say that lubrication will be inadequate when free-wheeling.

[Cathy Monaghan]

This has been a great and truly interesting topic. But for the sake of leaving enough room on the forum's main view page for other topics, it's probably a good idea that we put this one to rest, so I've put a lock on it. If you want to continue this discussion, just click on the "new topic" button to start a new message thread.

Thanks everyone for your comments and good humor.


Cathy
CDSOA Webmaster