Thoughts from Dan O'Grady

Here is some background information on balsa stiffness testing: The Euler method for calculating balsa stiffness and density was first described by Hewitt Phillips in an article in the NFFS Digest in May, 1987.

The method has been used by Jack McGillivray since that time, and I have used it for about 5 years. Fairly recently Jack has simplified the calculations with the use of a programmable Casio calculator. The Euler method, and Jack's calculator program for the method were fully described in an article by Jack in the Jan 1997 issue of'SAM 86 Speaks' - editor Dan O'Grady.

In Jan 1997 John Barker presented a paper at the British Model Flying Association (BFMA) Free Flight Forum at London, England, on balsa quality and testing. This paper was co-authored by Bernard Hunt and John Taylor and described a measurement method for determining balsa stiffness (Youngs modulus) by measuring deflection caused by loading a balsa sheet with a weight.

This 1997 paper (subsequently published in the Feb 1997 issue of the English indoor newsletter 'Norwind News') was the fourth in a series of papers on the measurement of stiffness using a defection/weight system and is the culmination of their experience to that date.

A similar system for measuring Youngs modulus was described by Joe Maxwell (the Scottish custom balsa component supplier) in the European indoor newsletter'Indoor News' in their Nov 1995 issue.

The Hunt/Taylor method is innovative in that the authors develop a 'stiffness coefficient' as a standard against which to evaluate samples irrespective of their density. The method requires the fabrication of jigs and weights and the measurement process is more involved than the Euler method.

In either method, if a lot of measurements are to be made the calculations can be quite tedious, and a programmable calculator or a computer is highly desirable.

Although I've seen Bernie's papers on the deflection/weight method of stiffness testing, I haven't seen his paper on the Euler method in any of the modeling literature. I look forward to seeing any developments or improvements of the method originally described in the a/n NFFS Digest (1987) and SAM 86 Speaks (1997).
Dan O'Grady

Euler Method Page | concerns for accuracy

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