John Heeboell Posted November 23, 2012 Report Share Posted November 23, 2012 Here is one for the engineers: I need information that allows me to calculate stress load in the area just in front of the intersection between fuselage and tail. (Induced by a hanger towing system).I have not been able to obtain data from Grob on skin thickness, materials data (like glass type, woven or rovings etc.), max permitted stress load in skin. Can any reader of this thread provide any data on this. I would be happy even to get just the skin thickness in the intersection area. Quote Link to comment Share on other sites More sharing options...
John Heeboell Posted November 23, 2012 Author Report Share Posted November 23, 2012 Here is one for the engineers: I need information that allows me to calculate stress load in the area just in front of the intersection between fuselage and tail. (Induced by a hanger towing system).I have not been able to obtain data from Grob on skin thickness, materials data (like glass type, woven or rovings etc.), max permitted stress load in skin. Can any reader of this thread provide any data on this. I would be happy even to get just the skin thickness in the intersection area. Quote Link to comment Share on other sites More sharing options...
StuOstrander Posted November 25, 2012 Report Share Posted November 25, 2012 Hi John, The Grob Maintenance Manual, Repair Instructions, describes the construction of the stressed skin, both thickness and materials. The fuselage is constructed of : 1 layer Double Twill 161 g 1 layer Chain Reinforced 433 g 3 layers Double Twill 390 g However, before attempting to optimize the calculation’s accuracy, it is possible a conservative estimate of the variables involved will serve to give you comfort that your handling equipment imposed stresses will be well within reasonable values. For instance, Wikipedia lists values such as: Tension (ksi) Compression (ksi) Polyester and Woven Rovings Laminate 45% E-glass 36.3 21.8 Polyester and Satin Weave Cloth Laminate 55% E-glass 43.5 36.3 Polyester and Continuous Rovings Laminate 70% E-glass 116 50.8 It is reasonable that inspection of the Grob specs will indicate values in the range of the 50%, or 43,500 psi in tension. Assuming a lower value of 36,000 psi (and 22,000 psi in compression) is reasonable for your analysis. Likewise, I might initially assume that the skin thickness is 0.1 inch from which both the section modulus and the unit stresses can be calculated. If one assumes the section ahead of the vertical stabilizer is a rectangular shape, 12” high and 10” wide, and 0.1” thick, the section modulus on the two major axis would be : 16 in3 15 in3 Can you take it from there? Stu Quote Link to comment Share on other sites More sharing options...
StuOstrander Posted November 25, 2012 Report Share Posted November 25, 2012 Hi John, The Grob Maintenance Manual, Repair Instructions, describes the construction of the stressed skin, both thickness and materials. The fuselage is constructed of : 1 layer Double Twill 161 g 1 layer Chain Reinforced 433 g 3 layers Double Twill 390 g However, before attempting to optimize the calculation’s accuracy, it is possible a conservative estimate of the variables involved will serve to give you comfort that your handling equipment imposed stresses will be well within reasonable values. For instance, Wikipedia lists values such as: Tension (ksi) Compression (ksi) Polyester and Woven Rovings Laminate 45% E-glass 36.3 21.8 Polyester and Satin Weave Cloth Laminate 55% E-glass 43.5 36.3 Polyester and Continuous Rovings Laminate 70% E-glass 116 50.8 It is reasonable that inspection of the Grob specs will indicate values in the range of the 50%, or 43,500 psi in tension. Assuming a lower value of 36,000 psi (and 22,000 psi in compression) is reasonable for your analysis. Likewise, I might initially assume that the skin thickness is 0.1 inch from which both the section modulus and the unit stresses can be calculated. If one assumes the section ahead of the vertical stabilizer is a rectangular shape, 12” high and 10” wide, and 0.1” thick, the section modulus on the two major axis would be : 16 in3 15 in3 Can you take it from there? Stu Quote Link to comment Share on other sites More sharing options...
John Heeboell Posted November 25, 2012 Author Report Share Posted November 25, 2012 Thanks Stu, this is just what I needed. May I contact you for a sanity check on my calculations? I'm on jh<att>catsys.dkAll bestJohn Quote Link to comment Share on other sites More sharing options...
John Heeboell Posted November 25, 2012 Author Report Share Posted November 25, 2012 Thanks Stu, this is just what I needed. May I contact you for a sanity check on my calculations? I'm on jh<att>catsys.dkAll bestJohn Quote Link to comment Share on other sites More sharing options...
StuOstrander Posted November 26, 2012 Report Share Posted November 26, 2012 John, My email is: stu.ostrander@gmail.com. Quote Link to comment Share on other sites More sharing options...
StuOstrander Posted November 26, 2012 Report Share Posted November 26, 2012 John, My email is: stu.ostrander@gmail.com. Quote Link to comment Share on other sites More sharing options...
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