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  1. D

    Moment of Inertia Formula

    Yes, if you are using metric, then the torque is mass in [kg] * 9.81 [m/s/s] * radius in [meters]. The first bit is just F=ma and gives you Newtons. In US units, we'd use T=weight in lbf * radius in inches or feet. The lbf is a force and has the gravity term baked in already. Careful with US...
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    Moment of Inertia Formula

    The authors left out a few common equations: The angle the system rotates thru is the length of the string divided by the radius it's wrapped around. This is from s=r*theta so theta=s/r where s is the arc length and r the radius The torque produced by the falling weight is constant...
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    Buying bulk fiberglass cloth and epoxy ? Any tips on cheapest suppliers ?

    Pro-Set Epoxy is headquartered in Michigan somewhere, and has distributors all over. Maybe one within driving distance of you? I think they're the same parent company as West Systems? https://www.prosetepoxy.com/contact/distributor-map/
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    NACA 6-series cusp

    NACA Standard Roughness for their 24" chord models was 0.011" tall grit over the leading 8%, 5-10% coverage per area. That grit height/density is very severe when scaled up to a vehicle in normal service. (well ok maybe if you never clean the bugs off) Again suggest finding another foil with...
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    NACA 6-series cusp

    What Reynolds number? Are you running free boundary layer transition, or tripping it to turbulent somewhere? Are you able to anchor your calculations against NACA data in Theory of Wing Sections/Report 824 (or Report 903 for the 6-series / no cusp "A" modification)? Reports available at...
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    RV-6 composite cowl repair materials

    Pics, please! Any idea what the source of the delam was? Impact damage, or entrapped water freezing? 8" sounds very large. Have you tapped it out to try to establish the delam boundary? If your cowl is no longer to contour can you take an OML splash off another aircraft to facilitate OML...
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    Composite design

    No, never figured out what was going on. We had decent agreement among all coupons tested at a given configuration, the coupons were sized to force a wrinkling failure mode, and visually appeared to be failing that way. The problem was the data points we collected did not seem to be behaving...
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    Composite design

    I haven't seen anything to indicate that the constant in the Hoff wrinkling equation is a knockdown, any more than the constant in a buckling formula is a knockdown vs. a physical fixity factor. Equations predict ultimate, how close you cut it (and how you report it) is then up to you. In the...
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    Composite design

    To clarify, are you analyzing fuselage sides loaded in shear, or a top/bottom skin loaded in compression (Fx) reacting the moment My created by the stabilizer load (Fz)? Your buckling-dominant failure mode matches my experience, and failure loads look like right order-of-magnitude. A 10' long...
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    General Design Questions for Project

    Have you seen http://corsair82.com/ ? Seems like a phone call to that builder could help influence your design.
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    Foam vs. honeycomb for carbon fiber sandwich

    When the time comes to detail out your spars, recognize that loads that act to open a curved lamination also induce inter-laminar tension forces that can be significant and lead to delaminations. So for your Corsair, negative g flight loads for instance could cause problems. One of a few...
  12. D

    High Density Foam for Hardpoints

    Spruce? Douglas Fir? (possibly as marine plywood rather than lumber) Alternatively, tooling board foam comes in that density range, although I don't know how its structural properties compare to the foam you're used to seeing. Sounds like you don't need much, see if a local shop will let...
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    Jet Contrail

    "Crow" (person's surname) type of wake vortex instability, made visible by contrail
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    Aerobatic Tandem Two-Seater

    How does your geometry compare against a T-34?
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    Advice on Engineering Degree

    When/if your career takes you outside the cockpit I'd expect you will have more luck building the next job off your flight experience vs. a dusty degree that hasn't been used. That said, an engineering degree or something else business/technical will look better on resumes than "underwater...
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    3D printing wing ribs?

    A few points to consider: Elevated- and low-temperature strength, with or without humidity effects, for the chosen material. Condition samples to 120F (or more) / moisture saturated and evaluate. This represents your bird baking in the sun on a muggy day. Hot-wet can be different than...
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    Nerd alert! Airfoil Comparison: Modified NASA 65018 vs Clark Y, and NACA 23000 series

    Re: Nerd alert! Airfoil Comparison: Modified NASA 65018 vs Clark Y, and NACA 23000 se The first attachment to the first post in the linked thread below by a well-respected (now deceased) member might be helpful: http://www.homebuiltairplanes.com/forums/showthread.php?t=10768 For your...
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    Too much stability???

    Yaw dampers are common (necessary even) on swept wing transport-category aircraft to suppress Dutch roll. The most likely problem I'd expect will be excess stability / poor agility/control harmony. Have you compared the numbers for your current design to other similar configurations? Can...
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    Easy CAD program

    I've used CATIA and Creo/ProE professionally, and they are in a vigorous competition for "tool that makes my life most miserable." Tough learning curve, non-intuitive behavior, cryptic errors, crashy ... please don't make the students use either of them! Solidworks would be my first...
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    6061 T6 Question

    In general, yes 6061-T6 bare drawn is suitable, if that's what the designer called out originally. If you want to get fancy, get the material certifications ("certs") when you order to prove it's really up to spec. But realize 6061-T6 vs. 2024-T3 is like comparing pine to oak -- same stuff to...
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