Lightweight but safe aircraft seats?

Discussion in 'Workshop Tips and Secrets / Tools' started by cluttonfred, Mar 26, 2016.

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  1. Apr 6, 2016 #81

    cluttonfred

    cluttonfred

    cluttonfred

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    Here is a very slick design for a lightweight but strong beach chair, now out of production, but I think the principle would work well for an aircraft seat: rectangular nylon sling with a thin foam cushion hung between two horizontal bars with a separate lightweight cloth-and-aluminum headrest for comfort. Yes, the nylon sling would stretch in a severe vertical deceleration but you could still have 4-6" of safety foam underneath.

    New Picture.jpg New Picture (1).jpg

    SLING-LIGHT®
     
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  2. Apr 11, 2016 #82

    cluttonfred

    cluttonfred

    cluttonfred

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    OK, I received some free foam samples from the Sunmate folks -- Dynamic Systems, Inc. - SunMate, Pudgee & FIPS Orthopedic Cushion Materials -- and I am trying to do the math on crushable foam energy absorption. According to their site, "T50E, our firmest SunMate formulation, is often used as a crash protection or energy absorption layer in ejection seats." So, that seems like a good place to start.

    Elsewhere on the site, there is this graph that shows that the T50E cushion can absorb about 6 ft-lb per cubic inch at room temperature, more when it gets cooler, less when it gets hot. So for energy absorption it would likely work better if not in direct contact with your rear end so it stays cooler. Unless you're in New Orleans in August, when your bum would be cooler.

    2013-impact-chart_164ceabe-09df-4dce-b22b-1fe50ea5bd36_large.jpg

    So, if we take a 8" wide x 8" deep x 6" high block of foam and put it under your rear end under a light seat expected to give out in a severe deceleration, how much energy would it take to bottom out? Let's imagine that we've put a little aluminum or fiberglass tray over the top of the foam so you have to crush the whole block more or less uniformly. So I get 12 X 8 X 6 = 576 cubic inches of foam x 6 = 3456 ft-lb of energy, but since we've only got 6" that's 6912 lb over .5 ft.

    That seems much too hard, but wait a sec. The site also provides this graph of support pressure, which, if I understand correctly, suggests that the hardest T50E foam begins to compress at 2.8 PSI.

    green-application-chart_b4acb95a-ff44-4ac4-ab10-862fffdfe646_large.jpg

    Since our foam block only has a surface area of 96 sq in, then the foam will start to compress at just 268 lb. So now I am just confused and it's been, ahem, about 30 years since I last sat in a math class. Can anyone help me figure out what size and type of foam would be required to provide, say about 1,000 lb of resistance over 6"? Or maybe I am barking up the wrong tree because the foam only provides progressively increasing resistance?
     
  3. Jun 15, 2017 #83

    Derswede

    Derswede

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    Chatted with my neighbor about this subject yesterday. He used to work for Fairchild (Now Jepson Burns?) designing aircraft seats. He said he would see if he had any data that would be of interest. Most of what they did was encapsulated foams...he said that it was basically memory foam, and that little was done on crush structures or zones, but he will look and I will post anything of interest.

    Derswede
     
  4. Jun 16, 2017 #84

    wsimpso1

    wsimpso1

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    The amazing work done by Oregon Aero on this topic works nicely on sturdy composite base and Conforfoam (or its brother foams). The other stuff did not work as well because other systems have elastic rebound after the plastic deformation that actually raises the peak G's and raises the energy dose.

    That is what I am building. It is also what Oregon Aero builds and sells to Cirrus and others...

    Billski
     
  5. Jun 18, 2017 #85

    cluttonfred

    cluttonfred

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