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Lug Analysis Spreadsheets

We have updated the lug methods for our engineering textbook and one of the best explained and best laid out classic lug analysis comes from the US Airforce Stress Manual, AFFDL-TR-69-42. We has used this as the basis for our lug analysis spreadsheets. All of the curves are fully digitized. There is a spreadsheet for each of the individual failure modes :

AA-SM-009-001 Lug Analysis – Shear Bearing Strength.xlsx

AA-SM-009-002 Lug Analysis – Axial Strength.xlsx

AA-SM-009-003 Lug Analysis – Transverse Strength.xlsx

and there is a fully automated sheet that does all of the calculations and calculates the interaction:

AA-SM-009-005 Lug Analysis – Compact Oblique.xlsx

There is also a spreadsheet that calculates the complex pin bending effect.

AA-SM-009-004 Lug Analysis – Pin Bending.xlsx

Enjoy!


Membrane Analysis Spreadsheets

AA-SM-013-053It has been a few weeks since we posted any new analysis spreadsheets. We have been busy getting the check version of the engineering textbook ready for the mailing list subscribers which was finally released in the June newsletter.

Along the way we did manage to create some analysis spreadsheets of the membrane analysis methods in AFFDL-TR-69-42 .

AA-SM-013-051 Circular Membranes.xlsx

AA-SM-013-052 Long Rectangular Membranes.xlsx

AA-SM-013-053 Short Rectangular Membranes.xlsx

Enjoy!

 


Landing Gear – Rational Spin-Up and Spring-Back Loads – Update

 

This is an update to a previous post here. During further background reading I came across this reference ARC-RM-2588 which gives a more detailed method for developing spin-up loads for aircraft landing gear. When I get time I will see if it is worth adding as an alternative spreadsheet method to the library and run some comparisons to the NACA method (NACA-TN-863).


Disk Springs/Belleville Washers – Sizing and Analysis

AA-SM-0042-001We had to design a set of belleville washers for a client last year so we had to go and find a useful design criteria. NASA came to the rescue this time. In (NASA TM X-73305, 1975) there is a simple method for sizing and behaviour of disc springs.

The behaviour of disk springs is non linear and this can clearly be seen from the graph in the analysis spreadsheet here.

Note that for large deflections the stress prediction may not be accurate – this is explained in the referenced text.

Enjoy!


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Landing Gear – Rational Spin-Up and Spring-Back Loads

AA-SM-517There is a relatively simple method in the FAR part 23 appendix for calculating rational landing gear spin-up and spring-back loads. This method is referenced to and better explained in NACA-TN-863 which also has some other very interesting and useful data.

This Spreadsheet has a method for calculating the rational horizontal loads for the part 23 basket of cases. Note that the  braked roll horizontal loads is calculated using the arbitrary 0.8 coefficient of friction from the regulations.

This method can provide a significant load saving and weight saving over the simple method. However! As always there are caveats; this method assumes that the aircraft is landing on a well prepared runway, therefore the loads generated by the method are likely to under-predict loads for rough field landings.  If you are designing an aircraft intended for rough field use it is recommended that a rational approach is used to assess the load generated by rough ground or that the arbitrary horizontal loads from the regulation are used.


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Plate Compression Buckling Coefficients – Derivation Spreadsheet

AA-SM-007-092Again, NACA provides a the solution to another problem. The theoretical derivation of plate compression buckling coefficients. I had a simple derivation, which uses this equation for the simply supported  plate buckling coefficient

Compression Buckling Equation simple

NACA-Report-733 has the expression that give the general curve for any edge restraint condition:

Compression Buckling Equation

The free spreadsheet is available here and has the simple expression in the first tab and the expression for the general curve in the second tab.

All thanks and credit is due to NACA. Enjoy!

 


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The Microsoftization of Google

A note on Google. We love Google – we use Google as the backbone for our company communications and Google hangouts makes a lot of what we do possible. But since we moved from Canada to the Cayman Islands we have had trouble getting our Google maps entry to update correctly. First we were not able to update our Google+ company page and map entry to our new location.

We Google Errordeleted the old one and created a new one from scratch. We went through the verification for our new Google+ page for our new location and map entry and all was good. Google then automatically created a Google+ page and a map entry for the defunct business in Canada and I had to go through the process of shutting that page down – twice.

We still had the Google maps entry at our old address in Canada – finally, in mid-may, 9 months after our move, I got Google to remove it. All good, right?….Wrong! Google has created a Google maps entry for Abbott Aerospace in an obscure part of Canada and defaults Google search to show that location. We flagged it as being ‘closed down’ in the hope that it would remove the entry from Google maps. Now Google shows Abbott Aerospace as a closed down business that used to exist in a small hamlet, M’Chigeeng, on Manotoulin Island. Hmmmmmm.

We are trying to resolve this issue but it looks like most of the maps entries are automatically generated and updated. We have to send Google specific information that we think will allow the algorithm they are using to give us the correct Google maps result…..without knowing how the algorithm works.

As we are not a retail business this will not harm us directly, it is disruptive to our overall on-line presence and certainly confusing for people trying to find out about our business.

In this age of geographical mobility and international outlook it is surprising that Google , of all organizations,  seem unable to accommodate a simple business move. It looks like Google is slowly turning into Microsoft – large, unresponsive, unwieldy, time consuming but still essential.


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Flange Buckling Coefficients – Derivation Spreadsheet

AA-SM-007-093 Mathematical Derivation of Flange Compression Buckling CoefficientsYet again NACA shows what a remarkable set of work it really is. I am going through the buckling of isotropic design features for our Stress Analysis book. Almost every time I need a derivation from first principles or the mathematical basis for a set of design curves NACA does not disappoint.

In this case I was looking for flange buckling coefficients, in NACA-Report-734 the following expression is given as the derived expression for the required coefficient: Mathematical Derivation of Flange Compression Buckling Coefficients

After a few hours of removing my own errors from implementing this complex expression in a spreadsheet I had created the tool that I wanted. This spreadsheet also compares the comprehensive approach with two approximate methods.

The 2nd tab in the spreadsheets gives the ‘textbook’ curves and allows you to create a specific curve over the top to find a particular value of k. This will be followed by the complete set of flange buckling spreadsheet tools – now that I have a derivation of ‘k’ that is unimpeachable…….

 


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Aluminum Material Data, Free Spreadsheet – Full range Curves and Plastic Buckling

One of the basic building blocks of any stress analysis is material data. It is one of the 3 basic parameters of material, geometry and loads that are required for a stress analysis. I wrote the first version of the spreadsheet 15 years ago and it has been updated and improved over time. It automatically calculates the following from built in aluminum material data that can be accessed from a drop-down box.

AA-SM-000-001 Aluminum Material Data Basic Full Curves and Data

  • Shear Yield stress
  • Shape factor for Shear
  • Intercept stress for Cozzone plastic bending allowable
  • Plastic bending allowable stresses for rectangular and circular sections
  • Full range stress-strain curves for longitudinal and longitudinal-transverse direction
  • Plastic Correction for Shear Buckling
  • Plastic Correction for Plate Compression Buckling
  • Plastic Correction for Flange Compression Buckling
  • Plastic Correction for Inter-rivet and Column Buckling

It can be down loaded here

 


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