Re: [PSUBS-MAILIST] Props

[Gregc02@ibm.net]

You can probably build a composite prop that would work well but I don't see any advantage over 
bronze. If you look at any of the comercial boat, ship or tug operators, none that I know of are 
using composite props.
The Cessna Caravans that I fly for a living, originally had composite props. They were advertised 
as being field repairable (just fill the big nick in the leading edge and off you go) but nobody 
mentioned that they had a stainless leading edge, and that if you dinged the prop enough to 
have to fix it, that the stainless leading edge was also trashed. When the Caravan started being 
built with a 675hp turbine instead of the 600hp version Cessna went with a normal aluminum 
prop. We got a large performance boost and figured that it was mostly the larger engine. When 
we started replacing composite props on the 600hp versions with the aluminum version, as the 
old ones ran out of time, we got about half of the performance boost that we'd gotten with the 
larger engine and the aluminum prop. The aluminum prop just provides more thrust and also 
more drag when you reduce power on final, both good things. 
We can buy three of the aluminum props for the price of one composite ones ($13,000 for the 
aluminum one vs $34,000 for the composite the last time I checked).
The aluminum prop also deiced better in flight because it conducted heat better.
In our fleet of 39 Caravans there is only one or two that still have the composite props and they'll 
be gone as soon as their time expires.
The only advantage of the composite prop was that we had about 2 inchs more ground clearance 
compared with the aluminum and we get a bit more blade erosion from sand and such with the 
aluminum prop. All that happened with the composite prop, was that sand erosion just took the 
paint off the stainless leading edge. In our fleet this doesn't make any difference, because we 
operate from major airports. If someone needs more clearance in the bush, Cessna makes a 
longer nosewheel fork to give you that clearance.
I know that this is a little far afield from PSubs but thats my real world experience with 
composite props.
Hopefully, we won't have to worry about better prop deicing in a sub. :)

Greg

From:           	"Chris Crouch" <eccrouch@cpol.net>
To:             	<personal_submersibles@psubs.org>
Subject:        	Re: [PSUBS-MAILIST] Props
Date sent:      	Mon, 26 Feb 2001 09:27:36 -0600
Send reply to:  	personal_submersibles@psubs.org

> I disagree. We manufactured a composite prop for one of the US Aircraft
> carriers. It just has to be made correctly. However a cheap true plastic
> prop (even Polycarbonate or Nylon) isn't enough.
> Chris
> ----- Original Message -----
> From: <VBra676539@aol.com>
> To: <personal_submersibles@psubs.org>
> Sent: Sunday, February 25, 2001 6:56 PM
> Subject: Re: [PSUBS-MAILIST] Props
> 
> 
> > Dan,
> >
> > My sub has bronze props. Nix the plastic idea. Too fragile.
> >
> > Vance
>