Lightweight but safe aircraft seats?

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

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  1. Mar 29, 2016 #41

    henryk

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    inertia force in passive\static\ bumper or dampfer \kinetic enrgy conversion into potential\

    F=m*a=m*dV/dt

    in case of dynamical dampfer \kinetic energy conservation\ ,M*V^2=J*(omega)^2

    F=(1/i)*m*dV/dt

    i>1 ,in practice up to circa 10...

    m/i =effect of inertia mass decreasing.



    "a ball screw attached to a heavy disk "

    Kkin=0.5 J(omega)^2

    J=0.5 mr^2 \mass and radii\
    omega=2*3.14*n \revolution\

    =ligt flywheel with high rpm...
     
    Last edited: Mar 29, 2016
  2. Mar 29, 2016 #42

    choppergirl

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    Japanese Alpha Gel shown in the video, here is the Company that makes it (English) and their PDF catalog. You can probably buy it in the size you need from a third party distributor sold for some other application.

    If you search for things like "Sorbothane Seat Pad" or *Isolate-It!* or "Gel Pads"... stuff used for Orthopedic Back problems, rowing pads, motorcycle gel seats, etc... you may start barking up the right tree... Similar materials include polynorbornene, Noene, and Astro-sorb.

    Sheets / Pads

    Gel Pads (Warning, link not 100% work safe, as pics of breast implants on same page/site)


    After poking about the Inet for Sorbothane Seat Cusions and Isolation/Dampening Equipment Pads, they are a bit on the pricey side... for a 12x12x1inch square block... so I'm thinking, maybe a homebrew solution would be the way for us homebrew types to go.

    According to the theory on the wiki, its a polymere solid with liquidish properties a lot like "flesh"... which got me thinking... a lot of people make their own "homemade ballistic gel" on the cheap, with the same characteristics.

    I have never touched nor made any ballistic gel, so I may be up the wrong tree... but I think if you were to make it solid enough of the right consistency with close to your desired properties, and encase it some plastic seat cushion... perhaps... bingo... you've got a seat cushion you could add on top of any seat, that would increase substantially your comfort and survivabiility.

    From Isolate-It webpage: "More is not better. A large lightly loaded sheet will have a high spring rate and will not deflect enough to provide good isolation. Over compression will lead to short service life. The proper compression range is 3 to 20 per cent depending on the "Shape Factor." Shape factor is the ratio of contact surface (one side) divided by perimeter area. Geometry matters. Small circular pieces and rings "bulge" better than squares and rectangles. "Bulgeability" makes for better isolation. Use many small discs rather than a few large rectangles for best vibration isolation performance. Thickness matters. The thicker the sheet the lower the natural frequency. You need a sheet at least one-inch thick to get your natural frequency down to 10 Hertz. (10 Hertz is your target natural frequency for a 900 RPM motor.) "


    So think something super squishy and rubbery like pictured in the video, that will deform outward from your butt... (I'm visualizing a string balloon, how if you squeeze one end of it, it doesn't pop, but moves the pressure to the other end of it) and spread the force of the impact... and shock waves... outward and into the dampening material.

    Like sitting on two or three unfrozen large gel ice pack or a big Gummy Bear, or multiple little gummy bears in a bag, but with air space around the sides of whatever material to squish outward and deform. I like bags of little gummy bears, so after each flight I could eat my seat cushion which can be bought on Food Stamps. :) Just amortize it as a cost of flying. Any restoration chemical or part I can buy on FS for me is a win.

    You know if your spine was that egg and your brain that soda can in that video, you'd want it landing on that AlphaGel instead. CHOPPERGIRL for the Technical Win. And you guys thought you kept me around just for the pretty face. Pfft!

    Disclaimer: I'm just a amateur restorer and not an expert on anything other than being snarky :) Bonus points if you spotted the goldfish, newts, and gummy bears I slipped all innoculously into a thread about aircraft seating design.
     
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  3. Mar 30, 2016 #43

    BBerson

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    That alpha gel video is impressive.
    But absorbing a one ounce egg isn't the same as a 170 pound person.
    Would require some testing. Might need to be 6" thick?
     
  4. Mar 30, 2016 #44

    VAPORTRAIL

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    Quoting Cluttonfred,

    "My thought in terms of testing was to bolt a sample seat bottom to a some aluminum sheet on the ground and drop a 200 lb sack of something on the seat from an appropriate height to simulate a crash, film it and examine the seat afterwards. If folks have suggestions on how best to build this kind of seat, or other concepts for light but crashworthy seats, I'd love to hear them"

    My issue with your testing scenario is that it concentrates all the attention on the design and survivability of "the seat" rather than the "200 lb sack of something".

    I would rather secure the 200 lb pink bits to the seat/floor mockup for repeatable drop testing as unit, possibly adding some forward/angular component.

    The filming idea is great, think SLOW MO GO PRO.
     
  5. Mar 30, 2016 #45

    Norman

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    Exactly. Eggs have all the hard material curve in a nice arch. All you have to do to keep it from breaking is avoid point loads. Spreading the load out evenly across the surface of your behind is a start but it won't protect your spine. A good seat harness will hold you in the seat thus keeping most of your spine from folding but high G loads will break it anyway. Of course that floppy part at the top of the spine will be broken too so the compression fractures in your lower back may be a moot point. What you need to protect the spine, and particularly the neck, is to spread the load out over time not area. That means you need something that will collapse slowly over a distance of several inches. It would also be nice if it didn't weigh anything and had an indefinite shelf life because, hopefully, it's going to be along for the ride for a long time before you need it. I don't see a gel pad doing that, especially not home made ballistics gel made from water and protein. An air bag probably wouldn't be adequate either because crashes often involve more than one impact and once the balloon is popped it's all over.
     
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  6. Mar 30, 2016 #46

    Norman

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    [video=youtube;Bi7kF2RkN5c]https://www.youtube.com/watch?v=Bi7kF2RkN5c[/video]
     
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  7. Mar 30, 2016 #47

    BBerson

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    Yes. At the end of video (slow motion) I see a shock wave that ripples across the pad. It might require a rather large mass to absorb a small load.
     
  8. Mar 30, 2016 #48

    nucleus

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    This is true for most RV's, but the there is buckling structure beneath the floor. Your butt is behind the spar.

    On the RV-10, due to the spar location, they specify Part 23 compliant front seats from Oregon Aero.

    Page 9 of their catalog discusses the testing they do:

    http://www.oregonaero.com/images/OAcatalog_0312.pdf
     
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  9. Mar 30, 2016 #49

    choppergirl

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    Collapsing over large distances is not feasible in something like an ultralight though. At most I've got maybe a few inches to play with. And your shockwave could be transmitted on into the frame. A gel pad could be something retro fitted into just about any plane simply by 'sitting on it', rather than reengineer an entire seat. Its a start. The idea being, make it more survivable than what your current seat may be at, which may be nothing at all but a foamy seat cushion. In my own case, the seat is missing from my plane, so ... what to put in there.

    I think your neck is going to snap before you spine goes if you are thrown forward (most likely), and you may bite your tongue off in the process, and then your hit your head again in the back when your body springs back. May not be a bad idea to fly with one of those football player mouth piece thingees, and maybe some way to also keep your head from getting thrown forward in the event of a crash. Your head is pretty heavy with a lot of intertia, and if one is wearing a helmet (like I would be apt to do in an ultralight) or headset gear, that's only additional weight.

    Yes, there may be a crash force downward that will compress your spine, like pancaking from a flat spin?, but I think the most likely crash scenario is being thrown forward by coming to an abrupt stop. You can impact other ways (like from the side or top or back) but in those cases, you're really out of control and probably not going to survive anyway except through random luck of the draw. So most of my safety strategy would be on dampening that 'thrown forward' impact like passengers experience like crash test dummies hitting walls in cars and smashing their faces on the dash or steering wheel or windshield.

    You want to spread the force out over a large area, and slow it down across a long travel area, but some of these other ideas and materials (like the intertia dampener and gel) take a different approach, transferring the energy into a new medium or expending it in some other force vector.

    I've fallen out of trees before and landed absolutely flat on my back and suffered no injury other than that annoying pine cone in the small of my back. Usually if I fall or jump out of a tree or fall off a ladder and have to impact, its feet first, so I try to angle my feet into springs at a 45 or shallow degree angle so they bounce me from a vertical drop in to a horizontal roll vector which is has a lot more travel area to expend its energy than a dead stop into the ground. I dread the day when I may have to take a low dive off a moving motorbike into a ditch or get thrown over the handlebars from one (high side, very bad).

    My sister has been in a car accident and broken her leg because she was stomping the brake during impact. The car crumple zone crumpled, but because she was stomping the brake, she broke her leg.

    I think an airbag would be fairly good system even if it is one shot/one impact deployable, as the first impact will probably be the worst, but can you imagine flying up in the air and accidentally have it go off (not that that happens). LOL. Where is the steering wheel, I can't even see out the windows, and you're wrestling with the thing to get it deflated and out of the way. On the plus side, and a big argument in their favor, is availability... you should be able to get auto air bag systems out of junkyards for next to... nothing... on the down low. You can't say the same for say a.. BRS parachute.... or a highly engineered 747 passenger seat... or jet fighter ejection seat.
     
    Last edited: Mar 30, 2016
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  10. Mar 30, 2016 #50

    BBerson

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    Maybe the harness should loop under the pilots armpits and attach above to help suspend the pilot in tension to relieve vertical compression.
    The harness should be attached above and behind to directly oppose a 45° impact. It could have an inerter device at the attach end.
    Not sure how much load arm pits can withstand.
    Something like a skydiver harness should work, they take a tension load when the chute opens. Mostly from belts under crotch, I think. Same could work for a pilot in his seat to augment the safety seat.
     
  11. Mar 30, 2016 #51

    ekimneirbo

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    In an ultralight, anyone wearing a helmet could incorporate a simple Hans device like Nascar drivers use. Its a cable attached to the helmet to prevent excessive forward movement and maybe sideways movement too. Might even attach it to an inertia reel. As for an airbag, I think it would be difficult to make one work with a sensor and never deploy inadvertantly. What would be easy and sensable would be an airbag that could be activated by a thumb switch on the control lever or yoke. Since a pilot would often have some time to realize they were going to crash, it could be activated just prior to impact.


    Here is a video on race car seat technology. https://www.youtube.com/watch?v=3q4GzggRumI In researching this, the comment was made that carbon fiber absorbs impact better than aluminum...more forgiving.
    While some of this may help someone, I would still feel that additional compressive foam below the seat would be beneficial. Also, there are points of no return where virtually nothing you do will save you. Looking at the
    degree of survivable impact, adding an airbag, and also taking a serious look at the landing gear being utilized could add immensely to the equation. If you look at the landing gear employed by some of the STOL homebuilts
    being used today ( Just Super Stol and Slepcev Storch) anything short of a nose in might be survivable. While larger draggier landing gear might not be part of a design, it can be adapted to many highwing airplanes. On low
    wing airplanes, redesigning landing gear to offer additional shock transition can be done. Lets face it, traditional landing gear design is lite and simple, but it certainly could be improved.



    On a lighter note......some people are just naturally better equipped to survive than most of us. i_like_big_butts_43.jpg :gig:
     
    Last edited: Mar 30, 2016
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  12. Mar 31, 2016 #52

    nucleus

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    Sure you can engineer crush space under the seat in an ultralight. Perhaps not to part 23 standards.

    Did you look at the catalog I linked above? It how them testing in various vectors, including forward.
     
  13. Apr 1, 2016 #53

    ekimneirbo

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    Shock 4.jpg Looked up some info on shock absorbing seats. I thought maybe some of the new breed of industrial mowers might have them.
    Anyway I stumbled across some pictures that might be of interest. It should be easy to incorporate something similar during the construction of an airplane.

    Shock 1.jpg Shock 2.jpg Shock 3.jpg Truck Seat Shocks 1.jpg Last pic is from "over the road" truck seats
     
  14. Apr 1, 2016 #54

    Topaz

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    A lot of those look like seat mounts for ocean-going speed boats. Man, they look heavy! No need for them to be reusable like that in airplanes.
     
    Last edited: Apr 1, 2016
  15. Apr 1, 2016 #55

    cluttonfred

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    Beer cans. Show me a solution using empty beer or soda cans. Seriously. Readily available, dirt cheap, very light, easy to experiment with. Maybe filled with expanding foam or foam beads? Maybe sealed with an epoxy patch to make them compress the air inside before bursting rather than crushing? Maybe staggered in height under the seat to provide steadily increasing resistance? Twelve cans, two high, four medium, six low?
     
  16. Apr 1, 2016 #56

    Topaz

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    How much load? Have to know that first.
     
  17. Apr 1, 2016 #57

    don january

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    I won't BS, the last thing I think about is how cozy the seat is when I crawl into a new bird, It's more about the stick or wheel and rudder peddle fit. and if I can see over the dash...
     
  18. Apr 2, 2016 #58

    cluttonfred

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    OK, based on a quick read here -- http://www.niar.wichita.edu/agate/Documents/Crashworthiness/WP3.4-034043-036.pdf -- and our prior discussion, I suggest designing for an "effective weight" (since legs are supported by the floor, arms may be on controls or other structure) of 50-75 kg hitting the ground at about 10 m/s, which is a straight vertical drop of about 5 m. I don't have the exact numbers for vertical deceleration tolerance, but I think a maximum of 25 g would be a good ballpark figure. I wonder if there ought to be a "breakout" deceleration of 10 g or so, just so the seat doesn't collapse every time you bit a gopher hole. Presumably the landing gear and perhaps the rear fuselage would have taken much of the load before the belly bottoms and the rest is on our unfortunate pilot, so 10 m/s is really a worst case scenario. Still, if there is 7 m/s left to aborb, then decelerating from that at 25 g would take about 10 cm. So a 15 cm beer can gives some extra room.

    PS--This topic came up before in the DESIGN FOR SAFETY thread.
     
  19. Apr 2, 2016 #59

    don january

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    My father put a seat through the bottom of a Pawnee during a crash and broke his back, So i think a seat does not have much to do with being safe in those type of circumstance's. If ya want something comfortable sling seat's are hard to beat. It's all about flight length, because bathroom seems to come first..
     
  20. Apr 2, 2016 #60

    Topaz

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    That resource recommends a vertical design loading of 16.5 g, and a 4-6" decelerator stroke with a loading during the stroke of 1200-1300 lbs. (g-loading on page 6-3, decelerator stroke recommendation on page 7-9 to 7-10.)

    Human load tolerance parallel to the spine is about 1500 lbs for a young, seated, adult male. Drops to a bit under 700 lbs for those over 60 years of age.
     

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