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 | | From: | John T Lowry | | Subject: | Computing performance increase due to CG shift? | | Date: | Thu, 16 Dec 2004 08:45:13 -0800 |
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> My club has a Piper Arrow with an aftermarket 3-blade prop. We're
> thinking of putting the original 2-blade prop back on. The 2-blade
> prop
> weighs 11 lbs less than the 3-blade one.
>
> Ignoring for the moment the aerodynamic attributes of the prop change,
> and the gross weight change, is there any easy way to calculate the
> performance increase due to the aft CG shift? Moving the CG aft means
> less down-force on the horizontal stabilizer. I'm guessing 11 lbs on
> the nose means 3-4 lbs on the tail to balance it out.
>
> The proponents of the prop swap claim it will improve performance
> because of the aft CG. My guess is that while the change will
> certainly
> be an improvement, the magnitude of the effect will be so small as to
> be
> insignificant. I'd love to work some numbers and see how it comes
> out.
>
You'll find easy versions of the relevant formulas in Chapter 4 of
Performance of Light Aircraft, around page 112.
John Lowry
Flight Physics
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