Rainbow Flying Service Spar Stress Testing

[@johnenglish5077]

Great destructive testing sequence to witness, thanks for sharing Ron.

[@jimmyboy163]

Good use of safety glasses @9:00, watch out for them splinters!

[@louisvanrijn3964]

At 6:56 you see a compressive fracture in the wood occurring just above the top-larger hole in the right of the screen. The next the spar wants to buckle away sidewards, which it intends to do. Shortly after that a shear failure in the wood occurs, probably initiated by the side wards buckling. At 7:47 again a shear faulure in the (probably?) not +/-45 plywood covered spar. At 12:14 again a shear failure, causing a compression failure above the most outward bolt. Conclusion: lack of shear carrying capabilty cause premature failures. +/-45 birch-ply added on the spar on both sides, only 1.2 mm or 0.05 inch thick, will make it , say, twice as strong. This configuration is general in wooden (-glider) wings. General comment: good that you load test everything. Well done .

[@Love2FlyKAP]

What did all that prove? The root end of the spar should be secured too.

[@slipstream5542]

looks like an aeromatic propeller over the entry way :)

[@louisvanrijn3964]

Hi. This video gives comparative results, using the same test method and testing machine. A is better than B so to say. If it is however a braced wing-spar with fuselage and strut bracket, the wing spar has to be tested using both the support points. Does Rainbow understand that the bending moment changes sign from root to tip? Ask your DAR.

[@bishopcedric4395]

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[@phillipmitchell2969]

@Bishop Cedric Instablaster ;)

[@bishopcedric4395]

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[@bishopcedric4395]

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[@phillipmitchell2969]

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[@louisvanrijn3964]

Second comment: Norwegian Fir wood can take 5 Mpa in shear, but 50 Mpa in compression. And 80 in tension. Density 0.54 kg/dm3 So shear-fracture is always you Achilles heel. You will have to convert these values to PSI's etc.

[@BetterAircraftFabric]

Hi, an interesting video, but some more explanations on the why and what would sure help us that have planes with these wooden spars. ... Thanks for posting & Regards from Alaska.