Lightweight but safe aircraft seats?

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

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  1. Apr 2, 2016 #61

    choppergirl

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    The airbag inertia firing mechanism would probably have to be left alone, lest you accidentally set it off in your face while tinkering with it. I think they fire with an explosive charge and quickly deflate (unsure?) so you really wouldn't be able to time it right for impact with a thumb switch, you'd fire it too soon or too late and make the situation much worse. However, its designed to fire right at impact so you shouldn't have to change a thing.

    In a GA cockpit it probably would work ok, if you chose one to fit the size of your cockpit. In an ultralight I don't know how effective it would be, as there is nothing to the front or sides really to constrain it. It may work just fine anyway, who knows. I'd sacrifice a few test installed in my target application (if I could get them free) with a test dummy before flying hot with one installed, just to see what it did to the dummy.

    Speaking to people that have been in wrecks and had airbags deploy on them, having an airbag deploy on you is not a fun experience... it literally smacks you in the face/chest and hurts pretty bad... *but*.. its WAYYY better than eating the steering wheel or the glass with your face.... and in all cases, it worked as designed... saved their lives, and saved them from a lot worse injury.

    ~

    You could fill your soda/beer cans with Great Stuff (tm) of different densities, or packing peanuts? Brainstorming, have no idea if either is a bad or worthless idea. Experiment with a filler material, then smash em with a sledge hammer and see how they react.

    ~

    Thanks for the info on the helmet cable, I had the same idea but didn't know if anyone had done it before. I'll have to look into what race car drivers use, and what quick detach mechanism. I've been on rollercoasters that do multiple loops, and made the mistake of looking down before entering a LOOP... not a fun experience... the centrifugal force pins your head down and you can't lift it at all nor your arms and it don't feel good at all... downright painful and nauseating actually.
     
  2. Apr 2, 2016 #62

    don january

    don january

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    I guess you can never get the loading untill it's over
     
  3. Apr 2, 2016 #63

    BBerson

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    Beer cans are just to thin and even filled with foam won't help much either, I think.
    It might work to cut the ends off four cans and laminate them together to get .016" total. They are only .004" each.
    Probably best to roll your own tubes from 2024-t3 .016" sheet.
    I just did a column load test with .016" and it crumples very well.
     
  4. Apr 2, 2016 #64

    don january

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    Beer can's?? Have you ever looked a man in the face after a crash and the topic of seat came up? I found the condition of the craft was the only thing that came to mind. That and the hospital bill.
     
  5. Apr 2, 2016 #65

    rdj

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    Beer cans are problematic once the FAA shows up at the crash site and finds them strewn around. For certain, document that construction thoroughly in the build log :grin:
     
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  6. Apr 2, 2016 #66

    BJC

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  7. Apr 2, 2016 #67

    cluttonfred

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    Hmm, that whole document is very dense, but I think you're misreading the first part. The numbers in 6-3 refer to the structure maintaining a safe volume around the occupants -- the crash cage, if you will -- not the seat or it's ability to absorb deceleration. As you mentioned, the specifics on seats are in Chapter 7, here are some key highlights:

    So it looks to me like the ideal underseat decelerator would require about 1200 lb (550 kgf) to crush and maintain that resistance over about 6" (15 cm). Any ideas?
     
  8. Apr 2, 2016 #68

    henryk

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  9. Apr 2, 2016 #69

    choppergirl

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    If you've ever cut a soda/beer can with scissors or a paring knife or boxcutter , you will find what you end up with is a razor edge for a soda siding wall. I've saved and cut hundreds of them up with scissors to use as ad hoc roofing shingles.. and after cutting my first 300 in one or two days I stopped because I pinched a nerve in my hand and boy did that hurt for a long time.

    Crushed the corner points are sharp too. So at the risk of compressing your butt upon a ton of potential razor blades, I'd start cozying up to corregated cardboard or something else as my lifesaver instead. Not to say they are not without merit, but messing about experimenting with them, keep in mind an edge of that can is like a razor blade.
     
  10. Apr 2, 2016 #70

    Swampyankee

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    The Sikorsky S-70 uses honeycomb; crash survivability was one of the requirements for both the H-60 from Sikorsky and the H-61 from Boeing; this requirement was included because survivable H-1 crashes tended to leave few survivors. Nomex honeycomb is great at the energy absorbing needed for crashworthiness. Composite structures, per se, are not very good for this, as they don't plastically deform, while metal structures do. You need something that converts energy to heat in a controlled manner: honeycomb will do it by controlled crushing; something like corrugated cardboard may, too. Plastically deforming metal definitely will work.
     
  11. Apr 2, 2016 #71

    henryk

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    Finertia=m*a

    for constant deceleration\optimal\ a=V^2/2s

    in auer experiment with dynamic bumper=

    m=10 kg , V=2 m/s s=0.04 m \stroke\

    we can expect= a=4/0.08=50 m/s^2 \ 5.1 "g"\, F=500 N

    -but we have \oscillogramma\=

    View attachment NewFile2.bmp

    a\overload\ max=4.5 "g", s=0.036, a\overload\ everage=1.5 "g"

    1.5/ 5.1 <0.3 \ 30 %\ !!!
     
    Last edited: Apr 2, 2016
  12. Apr 2, 2016 #72

    cluttonfred

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    Choppergirl, I hear you on the sharp edges of the cans, but that seems like something that could be easily mitigated, say with a light composite bottom panel matched to the cans and their various heights. If not cans, then I agree that some simple sheet metal shapes might work well. Just for the sake of discussion, an ordinary aluminum beverage can, empty, supports about 110 lb before collapsing, so it would take an awful lot of cans to manage 1500 lb over 6". It would be very interesting to see if cans used as containers for liquid or spray expanding foam would do the job.
     
  13. Apr 2, 2016 #73

    Topaz

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    One of the key points throughout the report is that the entire system should be designed to the same set of design impact loadings. There's no point in designing the "safe volume" crash-cage to a higher or lower loading than the seat or some other part of the system. This is one of their key criticisms of FAR 23 and EASA CS 22. So the loadings on that page explictly refer to the overall design loadings, too.

    The AGATE report is saying that a minimally-adequate decelerator can be designed with as little as 2" thickness, but that 4-6" is much more desirable since it provides a lower g-loading during stroke. Take that as you will.

    Something I found recently that was disappointing is that we see a substantial reduction in the crushing strength of our vertebrae as we get older. 20-25 year-olds can absorb as much as 1500 lbs before their vertebrae start to crush. By 60 years of age, that value has reduced to just under 700 lbs. I not only don't think it's ethical to only design for "the young", but at 51 years of age, I'm already at the point where I need to reduce the loadings in my design in order to keep myself safe.

    I think a full 6" deep decelerator is pretty darned big compared to most small-airplane cockpits, but even a 1200 lb loading is too high for older pilots. Coming up with the right balance is going to be a significant challenge. I don't think beer cans or similar solutions are going to be predictable enough to have confidence of safe outcomes.

    And through it all, weight is the enemy. You can build a airplane that's as safe as safe can be, using every known technology to the maximum. It'll probably be too heavy to fly, which is the safest airplane of all.
     
  14. Apr 2, 2016 #74

    Hot Wings

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  15. Apr 3, 2016 #75

    dcstrng

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    I saw your reference to the BlackMax seats and was hoping that someone might have experience with them, or at least be able to visually guestimate how they might muddle through in this dialogue before if flitted off into the ethereal mists. From what I read the so-called "NASA foam" is supposed to be the best of the best (certainly one of the best at separating cash from pocketbook) and recently I ran across a "foam" website where they'd looked at impact absorption both from catapult launching and ejections standpoints as well as for helicopter (I I assume for the auto-rotations that spread the skids...)

    See: High-Performance Cushions for Aircraft Seating Applications &mdash; Dynamic Systems, Inc.

    Although this morphed into an interesting discussion, other than the beer-can solutions :para: I wonder how functional the posed remedies are outside the lofty realm of the technical elite, and given that most of us will be building to long-established plans (with our own pet mods of course), assembling kits by-the-numbers (for speed if nothing else) or refurbishing older designs in the acceptable manner (whatever that means), I wonder what may improve our lot (or at least be useful) down here in reality-land.
     
  16. Apr 3, 2016 #76

    cluttonfred

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    Thanks, Larry, that's a neat site with some useful info and the foam seems cheaper than the stuff Aircraft Spruce sells. It did jump out at me that a 16" x 16" x 4" block of SunMate weighs 4 lb. So building up a 6" cushion under each of two seats would add 12 lb to the plane.

    For the application we've been discussing here -- something to put under the seat(s) for one-time use in crash -- I would hope we could find a lighter and maybe cheaper solution. The design guide that I linked to mentioned a deformable seat as one energy-absorbing solution, here is the illustration:

    deformable seat.jpg

    I would think that we could come up with something like that, in say a 12" x 12" package, 4-6" high, to pop under the seats of existing aircraft.
     
  17. Apr 4, 2016 #77

    Twodeaddogs

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    Im not familiar with crashworthy seats but aren't they one-shot items. I'm guessing that that's what you are aiming for here. What about a stack of Belleville washers, like older suspension systems used?
     
  18. Apr 4, 2016 #78

    Topaz

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    If you can also include something to absorb energy, that's fine. The washers alone function as springs and, by themselves, rebound is an issue.
     
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  19. Apr 4, 2016 #79

    Topaz

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    If you can also include something to absorb energy, that's fine. The washers alone function as springs and, by themselves, rebound is an issue.
     
  20. Apr 5, 2016 #80

    BobbyZ

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    I've felt crash safety of airplanes has been way behind the times.It essentially has been we're not going to crash so don't worry because no matter what you're dead if you do.

    I really feel that we have the technology to design a very safe aircraft that could survive a lot more than most think.If you look at how far race car crash technology has come I think you'll agree with me.

    For this thread I really think that a base designed to deform on impact like recently posted is going to be a good fit for most aircraft.As long as the mounts are secured to a strong enough bulkhead.

    As far as the low slung cockpits go.Their best bet is going to be a carbon shell and absorbing foam solution like was previously mentioned.It isnt easy for me to explain but if you looked at a F-1 seat design you'll see what I mean.The foam used isnt your average home depot foam,it is more along the lines of bike helmets and the great thing about it is that you can add different densities in order to adjust the rate of absorption.

    Last but not least,not even 10 years ago a accelerometer was not easily within reach for the hobbyist.So no matter what we designed it was a guess at best,unless you were a real engineer.Therefore people just went along with the plans as it was the best choice at the time.Thankfully that has changed and in the grand scheme of things they are dirt cheap.So it is quite easy to design a safer option and have the data to prove it.

    This here is a decent introduction for those not familiar with them https://learn.sparkfun.com/tutorials/accelerometer-basics and while it is very basic it should get you pointed in the right direction.

    I dont know about you guys but destructive testing can be quite fun :D As long as its done safely what's not to like about tossing things from a high distance lol.

    This is another interesting thing and I'm sure there are better ones out there,it should give you a ballpark idea on G forces for those of us who didn't take physics ;) Deceleration Calculator Granted it isnt for calculating things that your life depends on it will still give a rough estimate and it's fun to tinker with.

    With the information and tools available these days I think people shouldnt be as afraid to experiment in some areas more.I know that 9 out of 10 times the mantra of following the plans is the way to go.But when the equipment needed to design and test things is at your fingertips to make a safer plane I dont think people should be so afraid to experiment with a experimental airplane again ;)
     
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