lml@lancaironline.net Mailing List Archive

<<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> << Lancair Builders' Mail List >> <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> Posted for Srxtreme2@aol.com: In response to your concerns of spinal injury from the shoulder harness in a hard landing situation, your airforce comrade unfortunatly got the physics backward. During a hard landing the body is rapidly decelerating in both a forward and downward direction. This causes the weight of the upper body multiplied by the G-force of your deceleration to compress the spinal cord down into the pelvis resisted by the bottomed out seat. If the momentary maximum force generated exceeds the burst point of any of the componants of the back, a spinal cord injury will occur. The most common failure points are the intervertebral disks, the vertebral bodies, and the ligamentous attachments. In addition there is a significant risk of avulsion of the attachments of various internal organs from the same mechanism of rapid deceleration. While this is certainly some thing to avoid if at all possible, the attachments of the upper ends of the shoulder harness do not play a role in the genisis of these injuries. Remember when you feel the tug of the shoulder harness? Its with the negative Gs generated during turbulence or acrobatics. Hard landings generate possitive Gs. There is not much head room in the smaller lancairs especially if you are very tall, and under negative G conditions it could be possible to hit the canopy with enough force to injure the upper spinal cord. In this situation a lower placement of the upper shoulder harness attachments would have a protective benifit. One could compromise the primary benifit of the shoulder harness, that of forward deceleration during a frontal impact, however, by placing the attachment points too low. If the body is allowed to accelerate forward any significant distance in relation to the decelerating aircraft, prior to the shoulder harness coming taut, the "snap" that ensues can be devastating. The position of the attachment points in order to maximize their overall benefit would be as close in a fore-aft direction to the shoulders as possible and just below them vertically. One additional protection that you can put in with little cost or weight, is a piece of trocellin closed cell foam. This foam unlike any foam utilized in the upholstering industry is designed not to bottom out even under extreme impacts. It is the same foam used on the new top of the line gymnastics floors and it greatly increases the curve during deceleration which allows the force to be spread over a longer period of time therefore doing less damage. This comes in 1 3/8" and 2" thicknesses and is available from Resilite and other gymnastic supply houses. I guess in the end the best protection is the judgment we exibit when we finally mount the steeds we have created. Steve IVP LML website: http://www.olsusa.com/Users/Mkaye/maillist.html Builders' Bookstore: http://www.buildersbooks.com/lancair Please send your photos and drawings to marvkaye@olsusa.com.