# Kuhn's Diagonal Tension Factor

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#### imamac96

##### Active Member
Chris Heintz's book makes many references to Kuhn's Diagonal Tension Factor. I understand that Kuhn wrote an entire structures textbook. I'm trying to dig through to find any curves that match the one on page 185 in the 3rd edition of Heintz's book. Can anyone tell me where I can locate this formula? I have found the NACA report (https://ntrs.nasa.gov/api/citations/19930082135/downloads/19930082135.pdf) on curved webs (Chris used it for flat webs, e.g. the spar). I have also searched the site and have found many references to Kuhn's book but no direct discussion of the formula. At the moment, I'm interpolating using regression to get me "close enough" for spreadsheet calculations.

#### plncraze

##### Well-Known Member
Supporting Member
Heintz sometimes changes formulas for his book. He did the redesign of the Robin wing when it went to metal construction. The H in the HR prefix on Robin aircraft was for him. So sometimes he will have his own formula for structures. I tried looking for the same chart or something close to it in Bruhn and Niu but could not find it. His book title is below.

### Stresses in Aircraft and Shell Structures​

#### plncraze

##### Well-Known Member
Supporting Member
This is from Niles and Newell book "Airplane Structures" from 1938

#### plncraze

##### Well-Known Member
Supporting Member
Here is a graph using this formula from another book. I always try to double-check some of these formulas with an engineering text but Heintz is the only book that tries to get it all in one place.

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#### imamac96

##### Active Member
plncraze,
Thanks for looking. I really appreciate it. Yes, Heintz rounds... a lot. It can be really hard to follow him because he constantly changes between units (and uses weird ones too sometimes to meet his approximation formulas). These graphs look pretty similar but not quite. I'm looking at inverses, but it's still not lining up. I have an approximation with a log right now, so that's sufficing as an approximation of an approximation at the moment.

#### SpruceForest

##### Well-Known Member
Kuhn and Griffith TN 1481 (Diagonal Tension in Curved Webs) was published in Nov 1947, while Kuhn, Peterson, and Levin TN 2661 (A Summary of Diagonal Tension - Part 1: Methods of Analysis) followed in May 1952. A quick pass through 2661 looks like both plane and curved webs are presented with numerical examples for each.

#### plncraze

##### Well-Known Member
Supporting Member
Check out figure 7.

#### plncraze

##### Well-Known Member
Supporting Member
I wrote a question on Heintz's website for this book when he was alive but there was no reply. I figured it out but I would have like to have used this in a class where he was the teacher so he could explain some of this. I can tell you it is nice to have all of the steps in one book. It is a neck of a lot better than P. E. Bird's book from the early 80's.

#### imamac96

##### Active Member
Figure 7 of report 1364 was what I was looking for. Thanks! Now, I need to read the whole report.

Yes, it’s a cluttered book, but it’s really a nice, comprehensive coverage.

#### imamac96

##### Active Member
In case anyone else is curious: it’s Equation 5 in the text.

$$k = \tanh(0.5 \log_{10}(\tau/\tau_{CR}))$$

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