Smith-Putnam Stressed Skin Blades and Bridge Construction Spar

By Paul Gipe

Included in the correspondence from Palmer Putnam to Herman Drees is a letter from Richard Heckscher who was involved in blade development on the Smith-Putnam project. (See Palmer Putnam to Herman Drees Letter Reveals Emphasis on Swept Area.) Hecksher had alerted Putnam to the work of Herman Drees in developing Drees’ Cycloturbine.

Two items in the letter are of interest to wind historians: reference to stressed-skin blade design, and the choice of blade spar.

Heckscher was apparently critical of the choice for the blade spar by chief designer Bud Wilbur and engineers at the S. Morgan Smith Company. He attributes the spar’s failure to this decision.

John (Bud) Wilbur, the project’s chief engineer, was the head of the Department of Civil Engineering at the Massachusetts Institute of Technology (MIT).

Carl Wilcox “was a civil engineer on loan to the S. Morgan Smith Company from the Budd Company” according to Kristian Nielsen [1]. He played a prominent role in the project.

It’s possible that Hecksher’s criticism was directed at Wilcox, as well as Wilbur and possibly others.

Hecksher’s letter was accompanied by several pages of black & white photos of the blades being assembled and installed on the turbine atop Granpa’s Knob. (See Palmer Putnam – Herman M. Drees Correspondence 1979.)

December 10, 1979

P. O. Box 7
Marstons Mills , MA 02648

attention: Mr. Drees and Engineering Staff


You may recall my dropping in to see your wind turbine installation in mid- October just before we returned to Devon from Cotuit. You were so cordial to me in touring your operation, that I should like to do something in return. AccordinglyI enclose prints of my complete set of photographs taken during the summer of 1941 in the Budd Company shops in Philadelphia and at Grandpa’s Knob, Vermont. At least so far as the blades are concerned, these are the only photographs extant of the project. The design of the blades represented the only application of state-of- the-art, skin- stressed aircraft design in the project. Had we been able to talk the S. Morgan Smith engineers and Bud Wilbur out of using the “brute force”, bridge construction type corten spar, no doubt we would have avoided the fatigue failure at the root of the spar, which terminated the project in its sixth year, after voluminous test results and nearly a year of power generation on the lines of the Central Vermont Public Service Company. I guess we were a generation too early!

If these pictures serve no other purpose, at least they will give you a historical perspective on the wind power generation field which you have set out in.


Richard Heckscher

1. Nielsen, Kristian H. “Technological Trajectories in the Making: Two Case Studies from the Contemporary History of Wind Power.” Centaurus 52, no. 3 (2010): 175–205.