Why do the giant drive fans in wind tunnels sometimes...?

Question

have wooden blades? Wouldn't metal (carbon, titanium, etc.) be a superior material?http://www.boeing.com/news/frontiers/archive/2005/december/ts_sf06.html

Answer 1

Its cheaper to build, much much much cheaper
metal on the other hand is expensive by the weight and the bending of metal takes complex machines which also need to be built to build the blades- where as to shape wood, all you need is a hammer and a chizzle

this is due to the fact the wind tunnel is most likely in America- where capitalism rules

its also probably has a little do due with safety also. A giant wind tunnel requires large blades which spin at relatively high speeds. If for instant one of the blades where to break off; would you rather have a super strong metal blade hurled at you (able to stick into a tank) or a chunk of wood which will most likely be stopped by the first wall?

Answer 2

I was under the impression that wind tunnel blades were made from composite materials (i.e. fiberglass, etc.)
Attached is a recent article:
STW will create a finite element analysis of the blades and use its proven composite design techniques to ensure the blades meet the dynamic environment of the BTWT. The 18-inch-wide by 40-inch-long blades will be manufactured by a manual lay-up process using fiberglass/epoxy prepreg from one of several qualified suppliers. The blades' skins will be laid up over a structural foam core from General Plastics. Precise, aerodynamic, geometric tolerances will be met using graphite epoxy composite tooling, also produced by STW.

Bill Wailes, STW president commented, "Our objective is to produce the blades with the same basic design and shape as the original blades. The existing composite blades have been in service since 1953. They have done their job well for more than 40 years. We plan to capitalize on this history -- avoiding radical design changes, yet offering the improvements afforded by current aerospace-grade materials and advanced manufacturing techniques."

Ref: http://composite.about.com/library/PR/2000/blscaled2.htm

Answer 3

Yes metal, titanium, carbon fiber would be superior but would very expensive in so many ways - manufacturing, shipping, installation.

Wood is inexpensive and easy to work with.

For the application, precise high-strength, high-temperature materials aren't needed so why spend the money?

Answer 4

yes...but it's a matter of costs. Wood, properly made as blades, will accomplish the same at a fraction of the price. The weight is the only issue which is made up by a slightly larger voltage on the motor.