Other Technical Discussions A place for technical discussions NOT related to Porsche or BMW. Other makes, home DIY, etc. |
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#1
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Seat/harness/roll bar
Lots of talk over the years about the down side of tack seats/harnesses in cars without roll bars or cages. Honestly we tracked our SC for years with just a bolt in roll bar of the type mentioned below. Roll overs like this are pretty rare but then cars are getting a lot faster than our SC. Pretty much a personal choice, balanced against the odds.
"This accident was widely circulated a few years back. This Mustang had a bolt-in cage without proper floor plates or boxes installed. Noticed the bottom left picture, in the circle the cage punched straight through the sheetmetal floor of the car. The roof completely collapsed, but luckily both people in the car walked away. Photos copyright: ThienNam Ninh Photography"
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#2
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Yikes! I have an OG Racing bolt-in bar, but properly installed by Charlie - bolted to plates welded to to tub, not the floor. The floor of the 911 is what? 1/16" sheet steel?
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Greg DuPertuis When in doubt, always mount a scratch monkey. Leesburg, VA |
#3
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I have only a roll bar in the 911 but it sat on the (reinforced) sills w/ large plates. I think its the autopower bar that bolts to the floor sheet metal. It would do the same as the pic above.
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Stephen www.salazar-racing.com 1970 914/6 - 3.0L GT 1983 911SC - 3.32L IROC 1984 930 2008 S2R1000, dirt bikes (some gas, some electric), Sherco trials bike Sold: 2001 Boxster (hers), 2003 996tt x50 , SpecE30, 1996 E36M3 GTS2 racecar, 2015 Mustang GT |
#4
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The Mustang is a heavy car and is known for its weak "just passes the rollover test" roof. Good thing it also has a high window sill line too.
SMD is spot on. The bolt through the floor bars likely offer little in true roll over and little to no side impact protection. I also suspect that most of the safety improvement a bolt in roll bar offers is a good place to hang 6 point belts from. A good seat and belt system is an important addition. Roof crushing rollovers are very rare but impacts are not.
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#5
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Quote:
Kinetic energy is energy of motion. Objects that are moving, such a track car, have kinetic energy (KE). Kinetic energy is similar to potential energy. The more the object weighs, and the faster it is moving, the more kinetic energy it has. The formula for KE is:KE = 1/2*m*v2 where m is the mass and v is the velocity. One of the interesting things about kinetic energy is that it increases with the velocity squared. This means that if a car is going twice as fast, it has four times the energy. So let’s walk through the equation and put this calculation into practical terms. By calculating the energy of a vehicle traveling 100 mph (3,000 vehicle with a driver and driving instructor both weighing 150lbs for a total weight of 3,300 lbs; 100 mph = 44.7 meters/second squared = 1,998; 140mph = 62.5 m/s squared = 3,917; times the weight = 6,593,400 = 3.297 mega (million) Joules of energy for the 100mph vehicle and 12,926,100 = 6.645 MJ for the 140mph vehicle = 2,431,631 ft lbs or 1,216 tons of energy for the 100 mph vehicle and 2,451 tons of energy for the 140 mph vehicle or a little over twice the energy to dissipate in a head-on collision with a speed of only 40 more mph. Accordingly, our safety concerns are much more viable as speed increases. The bottom line may be that as we encourage novice HPDE drivers to achieve high speeds in cars not designed or modified to reasonably protect them, we fail to use incidents as "learning tools" for fear of scaring these same drivers away from HPDE. We may in fact be failing to disclose known risk and some might say encouraging them into a false sense of security. The above photo is an example of when KE generated by very high speed is out of control. It does not matter how much safety equipment you have or do not have, the same car at the same speed can experience the same path of destruction. The outcome for the driver in a modified car at a high speed incidents will be very different than the outcome for the driver in a car relying on factory safety equipment in the identical incident. Lower the speeds or add safety equipment or we do nothing and expect a different results. (that is that the definition of?)
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#6
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Quote:
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Rob in Potomac |
#7
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Why can't you use harnesses without a roll bar?...as long as you get the right angles above the shoulder should be no issue. ..I believe they also make angle adapters for this reason
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Evan 87 911 E stock GONE.......: 84 911 Estock 2015 E stock national champion Close Motorsports - Driver Coaching and Data Equipment sales Website coming soon Old http://retaliatemotorsports.blogspot.com/ |
#8
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Based on the photo, it appears that an improper installation was the reason for the roll bar pushing through the floor. Not a defect in the roll bar, but an example of a poor install. Every bolt in roll bar I have seen, comes with reinforcement plates which are supposed to be used when installing the roll bar. Question is was this a bolt in roll bar purchased from a manufacturer, or a home built roll bar.
Seems like all too often fingers get pointed at the safety gear in examples like this, without looking at how it was installed. In this case, if a Mustang has weak floors, why would you bolt a roll bar through them without doing anything to reinforce the attachment points? Personally, if I was building a track car today, I would have a proper cage built and installed by a good cage builder like Piper or in the case of the attached photos, my friend Kenny who is a race engineer and fabricator for Flying Lizard Motorsports.
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#9
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Depends. Autopower early-911 bars come w/ backing plates that sandwich the floor in the middle. Isn't going to stop it from punching through the floor. Its just a poor design. There are better avail. OG used to sell one that was good and sat on the frame rails. I copied it when I made mine
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Stephen www.salazar-racing.com 1970 914/6 - 3.0L GT 1983 911SC - 3.32L IROC 1984 930 2008 S2R1000, dirt bikes (some gas, some electric), Sherco trials bike Sold: 2001 Boxster (hers), 2003 996tt x50 , SpecE30, 1996 E36M3 GTS2 racecar, 2015 Mustang GT |
#10
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Quote:
...but I'm curious about using the unit "ton" (or implied "ton-feet") for kinetic energy - I've not seen it used this way. As a unit of energy it usually means "equivalent to one ton of TNT" (1 ton = 4.18 gigajoules = 4180 MJ), or about six orders of magnitude greater energy than talked about in your post. As a unit of power (e.g. refrigeration), it is approximately the amount of power required to melt a ton of ice in 24 hours (3.52 kilowatts = 4.7HP). That said...in the above example, that same car dissipates the full 3 MJ of energy *every time* it brakes from 140mph to zero, so energy alone doesn't tell the whole story. As for the need...well, I certainly am of the opinion that harnesses, HANS, reasonable seats, and a roll bar are needed safety equipment beyond the first couple of events, and required or not, have had them installed relatively quickly. And I agree that students should be aware of the risks they face, even if they are way out on the tail of the probability curve. ed
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ed 2016 GT4 2005 Lotus Elise 1994 RX-7 R2 Last edited by Dandelion; 02-16-2015 at 12:12 PM. |
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