HydroComp, Inc. > Knowledgebase and software help desk > Knowledgebase

Search Knowledgebase:

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)


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.

Was this article helpful? yes / no

Related articles

Sizing for Gear ratio
Kaplan: blades and BAR
PropCad - Inserting sections, adding root fillets
Lofting a blade in Pro/ENGINEER

Article details

Article ID: 80
Category: PropExpert
Date added: 2015-07-02 15:53:52
Views: 419
Rating (Votes): Article rated 3.1/5.0 (19)

Copyright © 2019 HydroComp, Inc. All rights reserved. http://knowledgebase.hydrocompinc.com/

« Go back

Powered by Help Desk Software HESK, brought to you by SysAid