> After seeing Perry's prop, and having to wait for the funds to buy a
> prop, I've been mulling over the idea of building my own prop. I could
> go with a two bladed or three. I'm assuming a top speed of around 210
> mph, 190 hp, 72 inch diameter prop 2.85/1 redrive turning up to 7000
> rpm. I'm working out the pitch angles on the blade with 77inches pitch
> at the tip. If I do this, I want to make the blades in a monolithic
> pour, rather than making the blades first and then fixing them into a
> hub. I have acess to a metal lathe, so I could turn inserts for prop
> bolt bushings. Still in the thinking stage-
>
> what type of planform for the blades- rectangular, or eliptical? How
> wide should the cord be on the blades? Thickness?
>
> should I go with a 2 or 3 bladed prop? I want to be able to have a nice
> cruise speed, but still be able to get into reasonably short airstrips.
> Emphasis on speed over stol capabliities.
>
> Where do I get carbon fiber "yarn"? I know where to get fabric, but not
> yarn.
>
> Anyone have the exact measurements of an SAE 2 hub?
>
> Any input about pitch?
>
> Any and all input is welcome. I'm trying to conceptuallize a molding
> device that I can build that would enable me to make a monlithic layup
> and force resin uniformly throughout the mold. I like the idea of
> winding carbon fiber throughout the mold and around the prop bolt
> bushings to make the strongest possible prop.
>
> Brian Trubee
> RV-4/13 BREW
>
>
Brian -
Here are some helpful links to other "Prop builder's" web pages:
http://www.maddyhome.com/canardpages/pages/alwick/prop.html
http://k0lee.com/propfab.html
http://mywebpages.comcast.net/unick3/Nicks%20Website/PropIndex.htm
You can see on a couple of sites that S-Glass strands are used as a "spar"
that connects blades to hub. Also attached is a simple spreadsheet that
goes
through the calculation of prop forces as against the strength of
fiberglass. Carbon fiber is OK - but not necessary for prop making unless
you want to really skimp on weight and blade thickness - in which case you
better have an engineer work out the calculations for you - there be
dragons
there!
SAE2 Flange Info:
Hub Bore - 2.255"
Bolt Circle - 4.75"
No. of Holes- 6
Hole Dia. - .375"
Hub Thickness: varies by Manufacture from 3.38" to 5.38" with 3.50" being
most common(?).
Spinners for props are generally either 10" or 12" in Diameter - so your
hub
diameter should be at least a few bolt-hole sizes bigger than the bolt
circle and less than the spinner size you choose.
That's some of the info I have gathered - give me a shout if you want
more!
Joe Hull
Cozy Mk-IV (45 hrs - Rotary 13B NA)
Redmond (Seattle), Washington
----------------------------
An advantage of a thicker hub is you get a better angle of
attack near the root. Thinner blades near the tip translate
to delayed drag rise and a more efficient prop.
The big advantage of carbon fiber is stiffness.
Carbon is three or four times stiffer than glass
for a given weight.
Paul Lamar ...No rotor no motor.
The stiffness of Carbon Fiber is a two-edged sword. Rather than stretch to
meet a sudden rise in force (e.g. a bird strike), Carbon Fiber will fail
rather spectacularly with a giant cracking sound like a rifle shot.
I'm a big fan of Carbon Fiber - just not sure I want it where impact may be
an issue (remember I'm a pusher - got to think about things that fall off
and go through the prop!).
Joe Hull
Cozy Mk-IV (45 hrs - Rotary 13B NA)
Redmond (Seattle), Washington
Joe, Isn't the prop the last thing on a pusher <grin>
Chance are the prop would come out better than the bird if
it were made from carbon fiber. Much stronger than wood.
Lots of wood props out there and you rarely hear of a bird
taking out a wood prop.
The stiffness problem is out near
the tip where you want the blade VERY thin due to transonic
conditions. That is why aluminum props still dominates at Reno. Glass
is way too flexible. If you are concerned about shattering
you can mix carbon and Kevlar like the Indy and Formula One
chassis builders do. Kevlar is also stiffer than glass.
Klaus is about the only guy that I know of that goes
well at Reno with out an aluminum prop and he has a carbon prop.
Then there is the guy running Paul Lipp's prop made with carbon.
Paul Lamar ...No rotor no motor.
The Rotary Engine NewsLetter. Powered by Linux.
ACRE NL web site.
http://www.rotaryeng.net
Copyright 1998-2006 All world wide rights reserved.