On Tue, 05 Apr 2005 03:19:57 GMT, "LCT Paintball"
wrote:
I was interested in the discussion concerning the weight of different prop
materials. Has anybody tried to make a hollow aluminum prop? What about
titanium? Carbon fiber?
I am not a prop expert and don't play one on TV either, but like you
I've been hanging around here for a while (quite a long while
actually) and have learned a thing or two. I also spoke with a
Hamilton Standard engineer about a prop they built for the Lexus V-8
engine conversion. Hollow aluminum props are not uncommon. Don't
know about titanium. Carbon fiber props are made all the time by a
number of manufacturers, many are certified. Googling "carbon fiber
propeller" brings many hits including Warp Drive, Ivo and Sensenich,
to name a few.
What kind of testing needs to be done on a home built prop?
Are there prop styles that can be copied without patent infringements?
Be aware, props live in an EXTREMELY harsh environment. They are
subject to twisting loads, bending loads, centrifical forces and
engine power pulses. In addition they suffer abrasion from sand, dust
and gravel to rain and hail.
The one material I'm pretty sure you can use without much worry about
having one half of it disappear in flight is wood. Wood props dampen
vibration, metal and some composites can accelerate vibration if
encountered at the right frequency. The engineer I mentioned warned
me that in his opinion, many of the non certified prop makers were
making props that scared the absolute bejeesus out of him. Very few
did the kind of comprehensive vibration testing that they (the makers
of certified props) had to do, nor did they do long term systematic
test runs. He thought that people should be extremely careful about
what they use for a prop.
Has anybody tried making a flexible prop? My thinking is that it might be
possible to create a prop with a low angle of attack for high power take
offs, then have it flex to a higher angle of attack as the load decreases.
Could something like that give the performance of a constant speed prop
without the complexity and added weight?
Yes, a company did attempt to create a fixed pitch prop that varied
it's pitch by being flexible fairly recently. They called it the
Quasi Constant Speed Prop. It was computer designed using very
special composite materials oriented in specific patterns and thread
direction. They were scimitar shaped. They also incorporated
different airfoils for different parts of the prop because the prop
itself sees different airspeeds at different locations from the hub to
the tip. Many props use a Clark Y airfoil, which seems counter
intuitive when you realise that out at the tip, most props are going
some 400 to 500 mph.
Unfortunately, during vibration testing they discovered that the prop
had some problems and the last time I checked they'd given up
attempting to make an actual fixed yet variable pitch prop.
If I were to play around with different prop designs, is there somebody
around here with the knowledge and time that might be willing to test them
for me?
--
There are several on-line programs that allow you to design a prop.
The problem is prop design is inherently complicated due to the many
factors that go into their design. You have to factor in airplane
weight, wingspan, how fast the airplane is supposed to go, altitude it
will fly, air density, drag of the airframe, engine speed, prop
diameter, pitch, material to be used, air foil design, planform. I
mean it's almost hopelessly endless.
The formulas used to determine various aspects of prop design look
like nighmarish versions of greek. And that's if you're a
mathematician. :-)
There are also proprietary software designs that allow you to design
your own prop. These aren't cheap but they will allow you to create
your own prop and design virtually all aspects of it including the
planform. All the formulas are built into the program. You have to
plug in the particulars of your airplane.
To me, prop making is such a black art that I gave up attempting to
design my own and bought an Ivo.
Corky Scott
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