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Thread: Seat belt mounting........

  1. #11

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    Quote Originally Posted by 1600vw View Post
    My little bird......Fisher Avenger.....
    Looks good!

  2. #12
    rosiejerryrosie's Avatar
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    Quote Originally Posted by martymayes View Post
    Looks good!
    It would look better if he stopped calling it a bird - its an AIRPLANE!
    Cheers,
    Jerry

    NC22375
    65LA out of 07N Pennsylvania

  3. #13

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    Quote Originally Posted by rosiejerryrosie View Post
    It would look better if he stopped calling it a bird - its an AIRPLANE!

    LOL.......Agreed......My airplane was built by Charles Lovett. He was a small man of 5'5" 150 lbs. I am 6' 180 lbs. Its a bit of a tight fit but I do fit. I need to move my peddles and or reshape my conopy. The peddles I can do with some help, the canopy that is outside what I can do. These mods won't happen this year but maybe next.

    This year its a panel upgrade. Transponder with Encoder, Traffic alert system with GPS along with a EIS.

    H.A.S.
    Last edited by 1600vw; 01-07-2013 at 10:22 AM.

  4. #14
    steveinindy's Avatar
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    Everything in aviation is a trade-off. The Army can apply $$ and horsepower to the problem. An installation appropriate to an AH-64 is not practical in an ultralight. And the military sends aircraft places where the expectation is for a higher crash rate. Most civilian aviators are much less likely to have an uncontrolled contact with the ground than any military aviator. So the trade-offs are different.

    The safest airplane is one that never leaves the ground. But they aren't any fun either.
    It doesn't stop us from learning from our money that they spent. The issue of weight in safety is minimal and is a cop-out that gets touted out when people don't want to put forth the effort or want to adhere to their old beliefs. The difference between a crashworthy restraint and a top of the line system in terms of weight can be under five lbs even if you have to re-engineer the attachments. Most people waste more weight on excessive upholstery or unnecessary instruments.
    Unfortunately in science what you believe is irrelevant.

    "I'm an old-fashioned Southern Gentleman. Which means I can be a cast-iron son-of-a-***** when I want to be."- Robert A. Heinlein.



  5. #15

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    Amazing how wise wives are. I once wanted to put shoulder harness in a Beechcraft, but the STC was real steep. Most of the cost was beefing up the semi-monocoque roof structure where it had to anchor. Why couldn't it have been a Piper or Maule? Why the roof? As you say, the anchor must be upward. never down.

    I once took a course in A/C crash survivability at Arizona State and they did a lot of work in this area. (Steve, you have heard of DRs Turnbow & Robertson) Their guidance is that shoulder harness should come off the shoulders and angle upward at least 20 deg. They cite that if angled down, enough "eyeballs out" Gs will cause bilateral collar bone fractures. This is based on crash tests with dummies and cadavers.

    I flew some commercial & military A/C that the straps went over a small SS bar on the seat back a little above the shoulders. Some passed over a simple roller, some had a pulley in the headrest. Some anchored in the heavy sub floor structure, some on the base of the seat. Those ( Huey variants) depended on the seat-to-floor tracks. They prove to be reliable and effective. I've crawled through some wrecks.That was my area to check.

    There is a T-28B restoration in the area that did away with the little roller structure on the seat back leaving the pilot's shoulders the high point. A popular kit plane is apparently designed this way from the get-go. Both are easy to fix.
    A pal of mine has a Fisher bi-plane and they have a wood structure. I bet that you can come up with a plan to put a small hunk of oak in the right place a get a good anchor. Good luck.

    Bob

  6. #16
    steveinindy's Avatar
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    A pal of mine has a Fisher bi-plane and they have a wood structure. I bet that you can come up with a plan to put a small hunk of oak in the right place a get a good anchor. Good luck.
    If I had to bet my life on the integrity of a piece of wood as a restraint anchorage I would be looking for some pieces of live oak. It's expensive, hard to locate and very dense but the stuff is tough as hell if well maintained. After all, they used it for the walls of the USS Constitution ("Old Ironsides")
    Unfortunately in science what you believe is irrelevant.

    "I'm an old-fashioned Southern Gentleman. Which means I can be a cast-iron son-of-a-***** when I want to be."- Robert A. Heinlein.



  7. #17

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    We should get you up to speed on the names and characteristics on the different species of wood. Prof Hoadley's book "Understanding Wood" is a great place to start. The USDA Forest Products Lab's book is another great reference. Oak is not well suited for aircraft sontruction.

    To construct a hard point in a wood aircraft, I suggest a fine grained and strong wood - hard maple. Or even better, West System epoxy with structure filler mixed in to the consistency of peanut butter...

    Best of luck,

    Wes
    N78PS
    woodworker...
    Last edited by WLIU; 01-08-2013 at 10:23 AM.

  8. #18

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    A pal of mine has a Fisher bi-plane and they have a wood structure. I bet that you can come up with a plan to put a small hunk of oak in the right place a get a good anchor. Good luck.
    ...and luck is something you'll need a lot of to find an attach point 30 degrees above the pilots shoulders in a fisher biplane. I guess you could anchor the shoulder harness to the top of the vertical stab. That would be cool, it would automatically tighten the faster you go so you won't fall out.

    I would think having the "acceptable" 5 degee angle below the horizontal shoulder harness is much preferable to nothing at all and while other geometry might be better, it's not an option here because of the contraints of the Fisher Avenger fuselage. So it's not a matter of choosing between good and better. The choice here is good or bad.


    If I had to bet my life on the integrity of a piece of wood as a restraint anchorage I would be looking for some pieces of live oak. It's expensive, hard to locate and very dense but the stuff is tough as hell if well maintained. After all, they used it for the walls of the USS Constitution ("Old Ironsides")
    Excluding the wood IKEA makes furniture out of, I can't think of a more unsuitable wood to use in an aviation application. Even a statisfactory hardpoint is only as good as the remainder of the structure. Is the next of kin supposed to feel better because the hardpoint ripped away from the structure vs. the harness attachment pulling free from the hardpoint?

  9. #19

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    I would think having the "acceptable" 5 degee angle below the horizontal shoulder harness is much preferable to nothing at all and while other geometry might be better, it's not an option here because of the contraints of the Fisher Avenger fuselage. So it's not a matter of choosing between good and better. The choice here is good or bad.




    My A&P was looking at this last winter and said just what you did. He did say it might be better to have the seat belt mounted to the seat down low so the seat belt and seat stays intact incase of plane breakup.
    He then said its a trade off. Crush your spin..or be hooked to the tail? He thought go for the crushed spin. Speaking from someone whom has broke his back 5 times, I did not think that was a good idea.
    I thought I would ask this question here now because my bird is going back into the shop and I know the A&P will ask about this again.

    H.A.S.

  10. #20

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    The most important part of the anchoring of the shoulder harness is to do it in a way that the hard point will not pull loose from the remaining structure. Just wrapping a cable around a spruce bulkhead part creates a point load that is likely to fail sooner than say a bolt through enough material that the stress is spread out to be below the yield strength for the wood and the glue joint(s). In plain english this usually translates into plywood doublers on either side of the material that the bolt goes through. If you are attaching to a horizontal member of the fuselage, you might also look at whether the gussets that attach the horizontal member to longerons need to be beefed up. Don't want the cable attachment to hold and the whole horizontal member to rip out...

    FAA AC43.13-2b actually has a good discussion of mounting belts, but the structures described are metal, not wood. You have to go back to CAM-18 to get guidance as the older publication was written closer to a time when wood structure was state of the art.

    Best of luck,

    Wes
    N78PS

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