Mark,
This is my math nerd answer; some of the engineers on the list can probably
do a better job. The equation that we use to approximate a helical pitch is
Pitch =Diameter* 2PI * arctan(Blade Angle). Where the blade angle is a one
to one function of the diameter. Unlike a normal helix which continues to
revolve as it progresses through space, the helix given by the above
equation becomes asymptotic as it nears the bounds of the pitch. Its like
saying how do I use a y = x^2 curve to model y = 2x^2 +2. The only
difference is that in this case the parent function is Pitch = 2PI *
arctan(Blade Angle). Each shift or augmentation creates an new physical
representation of the function. Therefore, the equation that is used to
create a block is specific to the data points that the equation was solved
for. Moving the the prop blade on the block moves the prop to greater
diameter in the pitch that the block was. This is the same effect that using
as V/D prop generates. Thus, moving the prop blade on the block does not
change props pitch to anther helical pitch but to another shape. Essentially
making the prop block the same thing as a forming cylinder.
With that said, near as anyone can tell, the prop blades on most indoor
models deflect so much during flight that only during the last few minuets
of the flight are the blades working close to a perfect helical pitch. So
there is not that much lost by using a 25'' block to form a 27'' prop.
Hope that helps,
Nick
On Wed, Jul 2, 2008 at 5:57 PM, Mark <f1diddler_at_yahoo.com> wrote:
>
> Suppose I have a 26" pitch block, but preferred a 28" pitch. Suppose
> prop dia. is 14". How farther should I scoot the blade (tips)
> outboard of 7" radius to most closely approximate the angles or angle
> change rate of 28" pitch?
> thanks,
> Mark F1diddler
>
>
>
[Non-text portions of this message have been removed]
Received on Wed Jul 02 2008 - 16:00:59 CEST
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