Loads calculations for an SAE Aero aircraft

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  • เผยแพร่เมื่อ 27 พ.ย. 2024

ความคิดเห็น • 9

  • @SoloRenegade
    @SoloRenegade 3 ปีที่แล้ว +3

    Thanks for sharing the excel spreadsheet as an example. Very few people explain these aspects of designing an aircraft.

  • @thawdartechnology9042
    @thawdartechnology9042 2 ปีที่แล้ว +1

    Thanks for sharing

  • @mohammadkaramzadeh1686
    @mohammadkaramzadeh1686 11 หลายเดือนก่อน

    Thank you bro

  • @0623kaboom
    @0623kaboom 2 ปีที่แล้ว +1

    ok so you are saying that span wise surface structures wont transfer bending loads ... so the top wont be in compression when the wing bends up and the bottom wont be in tension as well .... that seems extremely wrong ... and stringers from my understanding do NOT go full span they only go a framer or two to resist loading in that specific zone ... while longerons go span wise of full length or as close to it to balance the loading across the complete frame and not just in point areas ... and yes longerons are NOT stringers and stringers are not longerons ... like a 45 automatic is not a snub nose 38 ... one is a workhorse the other is a pea shooter ...

    • @0623kaboom
      @0623kaboom 2 ปีที่แล้ว

      so the tail doesnt apply a downward force ... hmm kind of wrong that assumption ... even it's weight will be a factor ... and it also incorporates a torsion moment on the plane in NON level flight ...

    • @AeroDesignCADTutorials
      @AeroDesignCADTutorials  2 ปีที่แล้ว

      @@0623kaboom hello, the way I did the loads on the fuselage was to take account of all the masses/inertial loads in the fuselage on its own (mass properties section) separately from the wings and hstab. They are isolated as we could do in a freebody diagram. I included the vfin in the fuselage as a static mass for the purposes of the vertical balance, since it doesn't contribute any vertical forces. The wings and hstab reactions section shows both inertial loads and applied loads from wings and hstab (hstab at 38:50). Of course we have to pay attention to the sign of the force from the fuselage to the hstab which is opposite when we consider the freebody of forces from the hstab to the fuselage. So effectively there are 3 freebody diagrams in the analysis, and you're correct that the hstab is not lumped in with the fuselage freebody, I separated them for the purpose of keeping track of the forces transferred between the fuselage and wings / fuselage and hstab via their spars.

    • @AeroDesignCADTutorials
      @AeroDesignCADTutorials  2 ปีที่แล้ว

      Good question. I talked about this a bit in the video, since I am planning to make a video on exactly this. You are correct that in most large airplanes, the portion of the wing skin between the spars is a part of the structural wing box. The spars (longeron in French) often go full wing depth, their webs join the top skin with the bottom skin. In that case, the stringers/stiffeners spanwise structural members are indeed in compression on the top skin and tension on the bottom skin (for +ve G's). This is the most common configuration for full size aircraft so that's what we see in stress courses.
      However, the structural layout common to SAE Aero Design and D/B/F aircraft often has spars/wing boxes that do not go full depth. Teams often use square or circular extrusions for the spars/wing boxes, or in this example a pyramidal sheet metal built-up beam that does not go full-depth. When we consider the load paths, clearly yes the top skin of the pyramidal beam is in compression, and the bottom skin of the pyramidal beam is in tension, since the side skins (webs) can transfer shear. So the neutral axis of the built-up beam is somewhere in the middle plane of the shear webs (side skins). BUT... the balsa wood stiffeners do not have shear webs connecting them from the top skin to the bottom skin all that directly... Let's imagine there was no monokote or thin vaccuum formed plastic outer surface skin. The stringers then only contact the ribs, which mostly resist shear in the fwd/aft direction, not spanwise. When the wing bends upwards, yes, each stringer will bend upwards along with the central built-up beam. But since there is no shear web connecting top stringers to bottom stringers, each stringer has its own neutral axis through its center plane. Yes they are providing resistance to bending, but not with I=1/12 bh^3 + parallel axis. Only with their own 1/12 bh^3. Also, we have to take into account the material stiffnesses. The metal box beam is quite deep and stiff, so the deflection is limited by that. The balsa stringers will only deflect a bit due to that, and because they are so very un-stiff, they contribute little to the bending resistance. In my experience in SAE teams this discussion always comes up (i.e. how much do the balsa stringers and ribs contribute to bending resistance?) After some industry experience, what I would do now in a stress analysis here would be to consider the composite beam of the built-up box beam along with all the wood stringers as if they were laid out side-to-side, i.e., if we imagine them glued to the box-beam, we can imagine them all glued side-to-side at the neutral axis of the box beam. Then we analyze as a composite beam with 2 material stiffnesses. That's even less of an effect than if they were glued to the top and bottom wing box skins. And the stringers contributing the most to the bending resistance would be the ones where the wing is thin since there the stringers are rotated (if they are rectangular). If you want to be conservative, you can ignore them. I'm not sure how much of an effect you'd get if you don't ignore them, but I would guess it's quite small. There would be more of an effect with thin wings... since the central box beam will be less stiff due to lower depth... but I would still imagine it's very low overall. If anyone wants to crunch the numbers we could see. Does that make sense? Yes it's true the monokote wing skin and the intermittent 1/4 inch of spanwise ribs can shear a little bit spanwise, but imagine the load path to go from the top skin to the bottom skin (around the leading or trailing edge for the monokote/plastic skin, and how stiff is that stuff compared to metal?).

  • @ihsanullah5673
    @ihsanullah5673 3 ปีที่แล้ว

    sir this is aeronutical engineer design answer me soon

    • @AeroDesignCADTutorials
      @AeroDesignCADTutorials  3 ปีที่แล้ว

      Hi thanks for watching. Do you mean if it was done by an aeronautical engineer? I did these designs - I have worked in aerospace companies, although where I’m living , in the field of loads and stress , we are doing engineering yes but there is a relatively small proportion of people who are responsible for signing off on analyses and designs and therefore are required to get their professional engineering designation - I don’t have mine at least not yet