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Author Topic: Surface Drive Props  (Read 2387 times)

Brigadair

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Surface Drive Props
« on: September 02, 2014, 08:46:16 PM »

Hi all


Just after opinions on surface drive props.


Could users of the new carbon fibre props advise if they recommend them?


I've see a few in action and they seem good? Good value, (4 for the equivalent metal ones)  light (unlikely to need working and balancing) , thin profile (efficient) , strong.


Downside, are they any good???? Fast?  cavitate? Etc.


Any bmprs members or any one else who runs carbon props - please advise me what you think of them,


Thanks.


Garry
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Time Bandit

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Re: Surface Drive Props
« Reply #1 on: September 02, 2014, 09:29:30 PM »

Depends on what kind of plastic props we are talking about.

Graupnerīs K-series -->  very good, much better than a lot of "self balanced" metal props. But efficiency decreases rapidly if the output power getīs too big (the blades are bending too much then).
I stop to use them if the diameter gets bigger than 48mm.

Never tried again any other plastic props since the K-series performance is way better than any other.

If you want to use very high powered motors or want to tease out the last 0.5 mph of a racing boat --> use metal props.


Btw:
Cavitation on surface props?  ok2

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Re: Surface Drive Props
« Reply #2 on: September 02, 2014, 11:03:47 PM »

Ive used them with some success but have found them to break easy when used on a high powered engine.they do bend abit under load which i found gives the boat a much better feel when powering on out of corners,BUT be aware that a snapped prop could mean not finishing the race, {:-{
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Brigadair

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Re: Surface Drive Props
« Reply #3 on: September 03, 2014, 08:57:14 PM »

Thanks to you both on the advice.


Just got my gas prop, a carbon one, which I confirm is the Graupner one.


Look forward to testing this and note the limitations you both advise.


(It's 78mm and big pitch!!!).   Help shatter lol!!!!!
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tmbc

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Re: Surface Drive Props
« Reply #4 on: September 04, 2014, 09:42:07 AM »

they tend to break on the dog drive area ! but good props
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Brigadair

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Re: Surface Drive Props
« Reply #5 on: September 04, 2014, 06:19:12 PM »

Thanks Mark. I did wonder how much to tighten the nut onto the prop? Too little might risk loosing it, to much might stress the prop and break it?

Will use a dollop of threadlock!


Briggy
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craig dickson

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Re: Surface Drive Props
« Reply #6 on: September 04, 2014, 07:26:10 PM »

Thanks Mark. I did wonder how much to tighten the nut onto the prop? Too little might risk loosing it, to much might stress the prop and break it?

Will use a dollop of threadlock!


Briggy


Personally Garry, I would never use thread lock on a prop retaining nut. But I realise that there was a single occasion when you had a prize expensive metal prop fall off after launch on a test run! So In understand why you may want to ensure that it never happens again! A lightweight prop that you have bought should in my opinion not need too much torque on the retaining nut. if you can source a slim profile nylon locker nut or a serrated flange nut, they should be fine.


Craig :-))
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Brigadair

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Re: Surface Drive Props
« Reply #7 on: September 04, 2014, 08:17:05 PM »

The nylon lock nut is my preferred choice. Don think think the  serrated flange nut will work on carbon/nylon?????


Thanks for the advice.

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ids987

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Re: Surface Drive Props
« Reply #8 on: September 05, 2014, 12:15:13 PM »

You shouldn't need to tighten down on any surface drive prop Garry. I often use a silicon sleeve between the nut and the prop; then screw the (nylock) nut so that the rear of the nut has just a couple of threads behind it. The only time I've ever known the nut to unscrew is if the dog comes loose; meaning that the prop spins the dog, which can spin the nut. Even then, under load / acceleration, it will tend to screw itself on, but when you throttle back, the inertia of the prop can spin the nut off. This is far less likely to happen with a carbon prop too, because they're not heavy enough. The silicon sleeve business makes it that much quicker / easier to change props (I position the dog such that the prop sits on the plain section of shaft - with the whole threaded section behind the prop), and I've never personally lost a prop that way.
I've had pretty good experiences with the Graupner carbon fibre props too, but only used them in small sizes. In the small sizes I've used (for .21 straight drive and electric), they seem to act at least one or two sizes smaller; in terms of loading, than Octura X series, so 42mm Graupner presents similar load to X437 or 438.


Just my 2p worth.


Ian
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Brigadair

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Re: Surface Drive Props
« Reply #9 on: September 05, 2014, 12:41:45 PM »

Thanks for that info Ian, appreciated.

Brigadair
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Brigadair

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Re: Surface Drive Props
« Reply #10 on: September 16, 2014, 08:44:29 PM »

Was going to run one at leicester but will wait till season over.


Interestingly, I inspected my 1919 alloy prop which was kindly balanced and sharpened by Craig Dickson after the last Nottingham race.


It was battered round the edges!!!




Weed must have done that! My bronze props were unmarked, but alloy is less forgiving on debris covered lakes, quite common late summer!




Advice is please check and re sharpen (or blunten!) alloy props for Leicester!!!


Garry
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Brigadair

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Re: Surface Drive Props
« Reply #11 on: September 26, 2014, 08:55:20 PM »

Several people lent me props at Leicester!!! Many thanks to those of you who did! Much appreciated!


Garry

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