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.
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