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July 2, 2015


Simple estimate for blade area ratio



Is there a simple way to estimate the blade area ratio for a propeller using basic measurements? I have the root-to-tip blade length, the average width, number of blades, and diameter.

We can use a simple relationship between expanded area ratio (EAR) and mean width ratio (MWR) to develop the following formula.

EAR = MWR * Z / C

EAR = (ABW * Z) / (C * D)

EAR = (MBW * Z) / (C’ * D)

where,

EAR = expanded area ratio
MWR = mean width ratio (= average blade width / diameter)
Z = number of blades
D = propeller diameter
C = constant (typically 1.9)
ABW = average blade width
C’ = constant (different for each propeller model)
MBW = maximum blade width

Determining ABW is not always easy to calculate or estimate. One alternative approach is to use maximum blade width (MBW), which is typically easy to measure, and then used a larger C constant. Each propeller blade shape will have a unique value for C’ (a new MBW version of C), so you will have to do some calculating using known propeller data to determine appropriate values for different propeller models.

Of course, the precise way to estimate EAR is to use the Blade Scan Utility added to PropExpert in 2006.

 
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Article details

Article ID: 80
Category: PropExpert
Date added: 2015-07-02 16:53:52
Views: 398
Rating (Votes): Article rated 3.1/5.0 (17)

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