Cessna wing failures

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  • #20858
    AvatarJIM ASHBROOK
    Participant

    Hi Guys,

    I have snapped two wings between the fuselage and the strut connectors. One time was in a loop, but today I broke a wing in a gentle turn. Total losses of course 🙂

    I am using white Solutech PLA with standard settings on a Prusa MK2s. Any suggestions on strengthening the wings?

    Thanks for the help.

    Jim

    #20860
    Petr ŠťásekPetr Šťásek
    Keymaster

    Hi James,

    If you try to press the wing or fuselage with your nail, is it quite easy to separate the layers? If so, you’re probably printing with too low temperature (we’re printing at 230°C) and the layer adhesion is not enough even if the weight comes out ok and the part looks good in general. If printed properly, it shouldn’t fail, at least not under normal flight conditions.

    I wish I captured on video my todays hard landing with Edge. The plane stalled a bit too high, it bounced of the runway and caught a lump of grass with right wing. Guess what, it didn’t failed to my surprise, just a small crack in the fuselage, easily repairable in the field.

    #20877
    AvatarJIM ASHBROOK
    Participant

    Hi Petr,

    Adhesion seems ok (can’t separate the layers) and I am also printing at 230 degrees.

    I tried breaking a section of the wing that survived and had to break it over my knee, so it seemed pretty strong.

    I am thinking about increasing the extrusion multiplier rate from 1.02 to 1.05 on the fuselage section where the wing mounts and the middle sections of the wing and see if that helps.

    Thoughts?
    Thanks for the help.
    Jim
    PS…I have built six of these planes (four models other than the Cessna) and have not had this type of problem on any of them.

    #20893
    Stepan DokoupilStepan Dokoupil
    Keymaster

    Hello, hm, how about the struts connection to wing and fuselage, this should the common way as in the big plane (help with some wing moment)

    #20908
    AvatarJIM ASHBROOK
    Participant

    Hi Stepan,

    Both struts were not broken; it is hard to tell if the strut attachment on the wing was OK.

    I am thinking about three solutions:
    1. Raising the extrusion multiplier from 1.02 to 1.05 or highher on the center sections of the wing and the main parts of the fuselage.
    2. Changing to PETG filament for these parts. Do you know if CA works on gluing PETG to PETG and PETG to PLA?
    3. Adding fiberglas & epoxy to the top and bottom of the center wing sections and to the main fuselage attachments.

    Any thoughts on these ideas?

    Thanks for the help.
    Regards,
    Jim

    #20965
    Petr ŠťásekPetr Šťásek
    Keymaster

    Hi Jim, the easiest way how to reinforce any part of the print is to add some 2 perimeter processes to the exposed spots. Use the Split process feature in Simplify3d since v.4.0

    #20972
    AvatarJIM ASHBROOK
    Participant

    Hi Petr,
    Thanks for the suggestion. I have Simplify3d v4. I assume you mean to add another process to the existing processes. I tried this and it doubled the weight and time as I expected. Is this what you meant?
    Thanks, Jim

    #20979
    Petr ŠťásekPetr Šťásek
    Keymaster

    Yes, but set 2 perimeters just in some spots where it needs to be reinforced, i.e. where the struts meet the wing, if it is the spot where it failed. So for the wing part number 3 lets say from 10 – 30 mm of Z height. Then continue with 1 perimeter setting again. The feature is called Variable settings wizard in Tools menu. Select the process you want to split, then add some height points.

    I do this with the fuselage of the Edge to reinforce just the few cm with the landing gear slots. It can now survive even the hardest landings.

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    #21040
    AvatarJIM ASHBROOK
    Participant

    Hi Petr,

    Great explanation; I have been able to generate the stronger code for the strut area.

    Before I print it I had another question. Do you also increase the extrusion multiplier from 1.02 to a higher number as well?

    Thanks for the help.

    Regards. Jim

    #21046
    Petr ŠťásekPetr Šťásek
    Keymaster

    Hi Jim,

    tried that with the nose part of the Edge, where the motor mount fits. (Cessna is different here) 2 perimeters would be too much there and the motor mount wouldn’t fit. Value of 1.05 didn’t do much difference, next time I’ll try a bit more for this particular location.

    Maybe you would need to slow down a bit when raising the multiplier, so the extruder is able to feed enough plastic.

    #21050
    AvatarJIM ASHBROOK
    Participant

    Hi Petr,

    I have increased to 1.05 on the nose/motor mount for the Cessna as there is enough room. The extruder seem to work fine. I also printed it using PETG.

    I will experiment on raising the value around the strut mounts so the struts will still fit.

    Thanks again,
    Jim

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