The Measurement of Lift and Drag

© 2002 Atkinsopht (03/02/09)
It seems unproductive to attempt the design of new blades without the means to determine their lift and drag coefficients at all angles of attack (preferably while rotating *).

Mechanical Solutions
I have worked out a schematic lift and drag measuring set-up. It does not, however, accommodate rotating blades. Anyone wishing to critique this with me (I am confident of, but not certain of the method) should get in touch with me.

* Rotating airfoils tend to exhibit advanced or retarded stall points when compared with static foils. An early experimental determination of the lift and drag coefficients of rotating oarblades was made at MIT in 1993. (see Ramsey, bibliography).

Computer Solutions
The capability exists, through solving the Navier-Stokes flow equations using finite difference or finite element techniques, to estimate the lift and drag coefficients of virtually any static and totally immersed three- dimensional planform at any angle of attack in any fluid at any fluid velocity. This capability extends to surface effects and partial immersions, etc. Blade designers could look into capabilities such as those offered by Fluent, Inc..

Predicting Oarblade Performance
Once good sets of coefficient data have been calculated or measured for promising blade designs they can be rigorously compared for performance and efficiency by entering the new data into a computer model where all variables but the ones of immediate interest can be controlled.