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  1. SuperStress

    Prying (Heel-Toe) Calculations

    James, The answer to your question depends very much upon the stiffness of your tension clip. If it is very stiff,like a thick fitting, I would assume a linear deflection from the end of the clip all the way to the applied load. This would give you a linear relationship such that you could...
  2. SuperStress

    Reduction in Fbru for 7075-T6 Sheet as of MMPDS-05

    Thanks SparWeb.... lol. I suspect the chances of getting the Air Force to order anything that isn't currently in the depot would be slim, but I'll pass those suggestions on to the responsible engineer. SuperStress
  3. SuperStress

    Reduction in Fbru for 7075-T6 Sheet as of MMPDS-05

    Thanks Aerodesign. I contacted Battelle and your suspicion was spot-on. The data were examined to see if the legacy (1950s) data reduction methods and production lot release data met current standards, and they did not. The updated allowables reflect the change to current methods. The MMPDS...
  4. SuperStress

    Reduction in Fbru for 7075-T6 Sheet as of MMPDS-05

    In MMPDS-04 (and previous) the allowable for 7075-T6 bare sheet per QQ-A-250/12 is Fbru=156ksi (0.040"<t<0.125", e/D=2.0, A-basis, Table 3.7.7.0(b1)). In MMPDS-05 (and on) the allowable is Fbru=146ksi (same parameters, Table 3.7.8.0(b1)). The table says that it was last revised in Apr 2010 per...
  5. SuperStress

    &quot;Dry Pin&quot; Bearing Allowables

    A colleague of mine mentioned that his company does not use a knock-down factor on the MMPDS-given allowable bearing stresses (Fbru and Fbry), and this concerned him. MMPDS is pretty clear that such knock-down factors should be used if all of the "dry-pin" conditions do not exist in your...
  6. SuperStress

    Fatigue Critical Baseline Strucure

    "Safe Life" and "Damage Tolerant" are merely two aircraft lifing paradigms. Safe life designed aircraft (especially older ones) were analyzed using stress-life fatigue analyses. Some newer planes have used strain-life methods. The idea in either case is that some design service goal is...
  7. SuperStress

    2 spar differential bending

    You've asked a very complex question to which there are no simple answers. Load follows the stiffest path, plain and simple. Finding the stiffest path is not always obvious. It has to do not only with the geometry of your spars, but also the stiffness of their attachments to the fuselage...
  8. SuperStress

    Bruhn lug curve descriptions - thickness - Machined or stock material thickness?

    My understanding is that the lug curves are for final machined thicknesses. Lug performance is dependent on the final geometry and grain orientation more than stock thickness. SuperStress
  9. SuperStress

    Acrylic Canopy / Windows Bolted Joint

    Since canopies and windows are often critical for bird strike conditions, I would be surprised if you could qualify any installation purely analytically. SuperStress
  10. SuperStress

    Material Variability Factor for Composites

    Irek, I have not seen A- or B-basis calculations applied to joint allowables in the way you describe, only to material property or fastener strengths. For single load path structure, A-basis numbers should be used. B-Basis should only be used for redundant structure or repairs/doublers, etc...
  11. SuperStress

    Solid Rivet Installations - &quot;Butt Driving&quot;

    Wil, Here's what I know... 1/4" MS20470D (BM8) rivets. Temper: driven hard. Hole prep: Good hole prep and quality control per standard shop practices. The primary concern is about gapping and consistent residual clamp-up. Hole fill on the manufactured head side is generally constrained...
  12. SuperStress

    Solid Rivet Installations - &quot;Butt Driving&quot;

    Hi folks; I haven't been around for a while... life just gets too busy. Wil - this might be one for you. The folks I represent are in the process of procuring a major piece of replacement structure for an aging airframe. The supplier wants to "butt drive" solid rivets (D-rivets) in the...
  13. SuperStress

    Blind Bolt Bending Analysis

    Bolt bending is not a function of hole fit, but of joint eccentricity as SWComposites infers. Blind bolts are not preferred for large-eccentricity joints. They lack the clamp-up capability of a traditional threaded fastener, and will fail prematurely in that usage. That's why you can't find...
  14. SuperStress

    NASGRO 3.0

    The NASGRO consortium is now managed by Southwest Research Institute. http://www.swri.org/4org/d18/mateng/matint/NASGRO/default.htm A single seat license costs $3000 (US). SuperStress
  15. SuperStress

    McCombs Publications Source

    A coworker recently pointed me to the following location where all three publications authored by Bill McCombs are available: http://www.thattechnicalbookstore.com/results.asp?o=d&au=William+F.+McCombs The three titles are: "Introduction to the Stress Analysis of Lightweight Aerospace...
  16. SuperStress

    Good questions for stress engineers

    737eng, I assume they are referring to "Intermediate Diagonal Tension"... beams designed such that the web buckles (by design) at a load below limit load. See p. 483 (and on) in Niu for an explanation of shear resistant, pure diagonal tension, and intermediate diagonal tension beams. As for...
  17. SuperStress

    Good questions for stress engineers

    Back when I used to work interior structures, I used to show applicants an inboard-facing open-faced cabinet and ask them to freebody the reactions for 9g-forward crash loads. It was a good way to see if they understood shear center. Now, I'm happy if I can find anybody that can give me a...
  18. SuperStress

    Training New Hires

    aerodog, While I don't have any special insight to the Eclipse program, I would agree that if the press release is correct, having an airplane with no detrimental permanent deformation at ultimate load is indeed overkill. Boeing would call this "growth potential", but I doubt that's what the...
  19. SuperStress

    Training New Hires

    I think the reason manufacturers miss their empty weight projections is because they are made by the Marketing department, not Engineering. SuperStress
  20. SuperStress

    Training New Hires

    Crackman makes an excellent point about strain gage correlations. Stress engineers tend to want to locate strain gages for the static test right on the "hot spots": areas of very high strain and very high strain gradient. Gages in these location do a lousy job of providing data for a...

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