> 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.


Thanks Joe,
that's useful information, I've got a lot of researh to do before I
embark on this project.

Brian Trubee

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