ISAAC Install
- Thread starter spnkzss
- Start date
planet6racing
New member
Good thing I'm getting a new helmet, then! Mine were farther rearward than that...
Wreckerboy
Member
With regards to the picture above - the ISAAC mounting may be good (thanks for posting it Gregg) but is the routing of his shoulder straps okay?
Specifically, it appears that the holes in the seat are much lower than the driver's shoulder line, and that the belts go from the harness mount down through the seat and back up to the driver. It is my understanding that as straight a line as possible was more desirable between the harness mounting point and the shoulders.
Is this true, is it even relevant, or is it just an optical illusion?
Safety nerds need to know!
Specifically, it appears that the holes in the seat are much lower than the driver's shoulder line, and that the belts go from the harness mount down through the seat and back up to the driver. It is my understanding that as straight a line as possible was more desirable between the harness mounting point and the shoulders.
Is this true, is it even relevant, or is it just an optical illusion?
Safety nerds need to know!
<groan> This comes up every time that pic is used. Gonna have to get a new one!!
Actually the observation is correct. It was something I never noticed myself until we posted that pic on this forum two years ago and it was pointed out. We have since re-routed the belts through a new hole higher up in the seat. The belt bar on the cage is level with my shoulders, it was only the seat that caused the belts to deviate from a straight line.
This is exaggerated by the fact that the shoulder belts are loose, and so the weight of the dampers further pushes the belts down.
The actual guideline is not merely to have a straight line between belts and shoulders, but more importantly to have the belts be close to horizontal when going forward from the cage to the driver's shoulders.
Thanks for worrying about me!
Actually the observation is correct. It was something I never noticed myself until we posted that pic on this forum two years ago and it was pointed out. We have since re-routed the belts through a new hole higher up in the seat. The belt bar on the cage is level with my shoulders, it was only the seat that caused the belts to deviate from a straight line.
This is exaggerated by the fact that the shoulder belts are loose, and so the weight of the dampers further pushes the belts down.
The actual guideline is not merely to have a straight line between belts and shoulders, but more importantly to have the belts be close to horizontal when going forward from the cage to the driver's shoulders.
Thanks for worrying about me!
Aha, found it: Head mass properties from 1979 German paper via the DTIC.
Long story short, the theoretically optimum location places the center line of the damper pointed toward the CG of your head, to avoid rotating the head forward or backward. Where's the CG? About 1" above and 1/2" forward of your ears. (The "Frankfort plane" referenced runs between the bottom of your eye socket and your ear canal.)
To tune this further, you would want to locate the mounts slightly forward of the CG to offset a naturally occurring backward bending, but that's a bit over the top.
Does any of this really matter? Nah. We initially tested with the mounts about 2" too far to the rear, not appreciating the bending moment issue. We decided to keep that location in subsequent testing because a change would introduce another variable. Even the 70G hits at Delphi still passed with this location. So, you have to be way off and hit something extremely hard before this becomes an issue, and that's with the dummy anatomy, which puts the dampers nearly vertical.
Bottom line is that if you can point the dampers toward your ears, perfect. If you can't, get as close as possible and don't worry about it.
Long story short, the theoretically optimum location places the center line of the damper pointed toward the CG of your head, to avoid rotating the head forward or backward. Where's the CG? About 1" above and 1/2" forward of your ears. (The "Frankfort plane" referenced runs between the bottom of your eye socket and your ear canal.)
To tune this further, you would want to locate the mounts slightly forward of the CG to offset a naturally occurring backward bending, but that's a bit over the top.
Does any of this really matter? Nah. We initially tested with the mounts about 2" too far to the rear, not appreciating the bending moment issue. We decided to keep that location in subsequent testing because a change would introduce another variable. Even the 70G hits at Delphi still passed with this location. So, you have to be way off and hit something extremely hard before this becomes an issue, and that's with the dummy anatomy, which puts the dampers nearly vertical.
Bottom line is that if you can point the dampers toward your ears, perfect. If you can't, get as close as possible and don't worry about it.
To the contrary Greg. I as you know, use the ISAAC. I want to make sure that any information put out there from ISAAC is as accurate as possible as I believe it has no competitionand will save lives. I remember someone blowing up the ISAAC on this BB in the past. Just wanted to make sure there was no sticking points. Unified front.
Very good DAve!!
R
Very good DAve!!
R
lateapex911
Super Moderator
Knowing Dr. Bro, and knowing he chose the Isaac, makes me feel even better about my choice. I'm even happier that I don't have to transfer the Frankfurt plane thru my helmet to get the only acceptable mounting spot....
Happy 4th of july racing to those who will turn a wheel in anger, and don't forget your head restraints...
Happy 4th of july racing to those who will turn a wheel in anger, and don't forget your head restraints...
Wreckerboy
Member
Learn something new every day. And all this time I thought that the "Frankfort Line" was the result of an 1857 treaty that separated the Isles of Langerhans from the Medulla Oblongata and created a lasting peace between the two warring nations.