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Seat belts attach points - am I confused?

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jaybrinkmeyer(at)yahoo.co
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Posted: Sat Nov 18, 2006 10:21 am Post subject: Seat belts attach points - am I confused?

Skimming posts regarding need for additional seat belt hard points leaves me...

puckering. Are folks saying that the current -10 seat belt attach points are

"inadequate"? 



For the most part, we the building community, place our lives in the hands of a

few structural aero engineers. Unless you have that sort of background the rest

is speculation - at best.



Jay



Do not archive

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AV8ORJWC

Joined: 13 Jul 2006
Posts: 1149
Location: Aurora, Oregon "Home of VANS"

Posted: Sat Nov 18, 2006 4:07 pm Post subject: Seat belts attach points - am I confused?

Let me go out on that limb and say Yes, David McNeill's mount appears to

spread the concentration of attachment force over a wider area and

provide greater retention of the passenger in a survivable crash (IMHO).

Passengers tend not to always limit their body weigh to 177 pounds and

carry only 35 pounds of baggage (which should be positively secured to

the floor).



VAN must say that their current design is adequate.  This is a

perception of degrees of improvement.  I don't think VANS could/ would

ever discourage pursuit of David's correction technique.  I think

multiple point straps will do even more retention.  I attended an

interesting PPT from the Oregon State Medical Examiner on post mortem

evaluations.  Limb fractures were most interesting.



His Halon suppression system also an improvement.



He also sought aeronautical engineering perspective in his decision.

David gets my Safety Award for 2006. Boeing has many Apache Helicopter

engineers at Mesa to drawn on.  An unexpected autorotation when you suck

a shoulder launched (RPG) mounted rocket can really make your day.



John Cox - 600



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dlm46007(at)cox.net
Guest

Posted: Sat Nov 18, 2006 5:41 pm Post subject: Seat belts attach points - am I confused?

Inadequate?  probably only in a crash. Before starting to reinforce the 

existing  hardpoints, we asked two questions: What do we need to attach the 

inertial  belts/airbags? Is the existing hardware and hard point adequate? 

Although my  background/degree is mathematics and computers and I have an 

A&P, I did  need feel that these were sufficient to answer the questions? 

Fortunately I  have a neighbor couple who hold Mechanical Engineering and 

Electrical  Engineering PhDs who provide free advice. In addition my building 

partner  has access to engineers who use composites and sheet metal to build 

military  aviation hardware. Both sources indicated that a single 5/16" CS 

screw would  pull right through the glass in any significant crash.  It is 

standard  procedure in composite construction to spread the load of the metal 

fastener  over as large an area as possible. If you decide to go with the 

existing  hard points, I suggest you make a large washer out of .020 

stainless and  dimple it for the 5/16" screw, this will spread the load from 

the screw  (area = PI radius(.025) squared ) to the washer diameter ( PI 

radius (.5)  squared). Check the calculations and find that the load is 

spread over about  6 times the area. We elected to spread the load by using 

multiple fasteners  each with its own stainless CS washer and reinforce the 

whole area with  additional E-glass . The aluminum plate inside is the 

strongest aluminum  alloy 7075 or 2024. We use the aluminum to attach the 

belt roller brackets.  My engineering friends said that the weak point would 

still be the  composite. We then used a structural mat to tie all the 

hardpoints  together.



I am sure that Vans believes that the hardpoints are  sufficiently strong but 

this is there first use of structural composites.  Except for cowl I don't 

know of another structural component that they use  on their aircraft.



The change of the hardpoints were not done on a whim  or without consultation 

from those who should know. Just my  $.02.



    [quote][b]

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