Re: Propeller camber [1 Attachment]

From: Nick Ray <lasray_at_gmail.com>
Date: Thu, 8 Apr 2010 01:32:13 -0400

Kang,
Camber may be added by sanding or shaping the desired airfoil into whatever
material you choose to make your prop block out of. Most people seem to like
balsa because its easy to work, and we seem to have a lot of it holding the
floor down in our shops. The ideal camber will vary between say 2% and 8%
depending on the ceiling hight that you will be flying. As with more wing
camber, you will increase drag and hopefully lift as you add camber. You
would have to play with your prop design a bit to see where the optimal
camber is for your design. I have always seen prop camber calculated the
same as wing camber and what you said is how I would like my props to come
out in an ideal world. In practice I've found that my form has more or less
consistent camber, so the fatter portion of the blades seem to get an 1-2%
or so.
 As far as forming props goes. Dr. Rash has done a very good job of
approximating helical pitch with his program. Helical pitch is considered by
most to be ideal for indoor props because unlike cylindrical pitch it is not
periodic.I.e if you tilt the blade enough on the form it will look like a
DNA helix rather than an aerodynamic helix. The formula for generating
helical pitch is pitch = 2*PI*radius of the prop*arctan(angle of the blade)
or P=2*pi*r*arctan(theta).
I don't fly any of the classes you asked for data on so hopefully someone
else can help out there.
Nick

On Wed, Apr 7, 2010 at 10:10 PM, Carl Bakay <carl.bakay_at_yahoo.com> wrote:

>
> [Attachment(s) <#127db388bcca382b_TopText> from Carl Bakay included
> below]
>
> Kang,
>
> Here is a page from Doc Martin's Hangar Pilot from 1994. Maybe some info
> you can use on can-formed props. Some people put down can-formed props, but
> the differences between them and molded propellers are too small to measure.
> Camber is taken care of by using the correct diameter can for molding.
>
> Fred Rash also has a computer program in the Articles/Files section.
>
> Carl Bakay
>
> ------------------------------
> *From:* ykleetx <ykleetx_at_gmail.com>
> *To:* Indoor_Construction_at_yahoogroups.com
> *Sent:* Wed, April 7, 2010 8:22:05 PM
> *Subject:* [Indoor_Construction] Propeller camber
>
>
>
> Hi,
>
> I've been making propellers by wrapping around oatmeal jars. I'm ready to
> graduate to making helically pitched props and will make the prop forms from
> styrofoam. After reading as much as I could, I think I'm almost ready.
>
> I would like to ask about the amount of camber in a propeller blade, and
> what is considered efficient. For example, one plan calls for 10% camber in
> the propeller blade. If I interprete this camber percentage in the same way
> as a wing airfoil camber, this means the camber thickness would not be the
> same across the length of the propeller.
>
> In Larry Corslick's Hobbyshopper article, he describes forming camber using
> a 3/32" sheet in the shape of the prop.
>
> First, what are some thoughts on the right way to specify camber -- by
> percentage (for example 10%) or by thickness (for example 3/32")?
>
> Second, for the way that you specify camber (in % or in inches) values are
> considered efficient for different model classes? For example, for an F1L or
> LPP, what are considered efficient camber values?
>
> Third, how do you put this specified camber into the propellers you make?
>
> I look forward to hearing your thoughts on propeller camber.
>
> -Kang
>
>
>
>
Received on Wed Apr 07 2010 - 22:32:20 CEST