Skip Wolfe

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Geo:
<strong>Anyone want to risk their life to that? I don't have a clue what these cars could weigh, but even if you assume an ultra light 2,000 lb car, these would barely cover a 3.5 G force.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Not particularly no. I wasn’t trying to make any conclusion regarding the number, just trying to accurately report it. I saw that there were several numbers getting thrown around so I just wanted to do the math for myself (I need to prove to myself every once in a while that my ME degree is actually useful). I think sometimes people get caught up in the raw psi tensile and yield strengths and don't realize how those actually translate into a shear strength.

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica"><strong>Also, the implication being made by saying "per bolt" is that you can somehow add up the numbers per bolt. Perhaps with certain impacts that evenly distribute stresses to more than one bolt, but such is seldom the case with a racing accident.
</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Sorry, I guess it does sound like that but that was not what I was trying to imply. I was just signifying that my calculation was for a single bolt. With that said, I agree that about the only time all bolts will be in equal shear is if the car falls flat on it s roof. In reality the car will most like hit at an angle, which could put some bolts in shear, some in tension, and some in compression. Now I do think that the bar is rigid enough that all of the bolts will weigh into the equation, and that they will all be subjected to a similar force rather than one being subjected to a much larger force than others. The difference is how the force is being applied – shear, tension, etc. Since a bolt will be weakest in shear, it is probable the best, worse case strength measurement.

The one thing I have no clue on is to what strength does one need to design to. You state 30-75 G’s is more appropriate. At what load can the human body survive? I don’t have a good feel for any of this so I’m just trying to get a handle on it.

BTW I don’t have a DAS bar or a 911 for that matter, but I do have a 944 turbo with a Redline bolt-in bar for DE purposes only. I do think I’m going to upgrade to mil spec Ti bolts, and I have always planned on going to a welded full cage if and when I make the jump club racing

Geo

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Skip Wolfe:
<strong>Not particularly no. I wasn’t trying to make any conclusion regarding the number, just trying to accurately report it. I saw that there were several numbers getting thrown around so I just wanted to do the math for myself (I need to prove to myself every once in a while that my ME degree is actually useful).
</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Sorry Skip, I didn't mean for it to sound like I was picking on you. Actually, I quoted you because I thought you brought some reality to the whole discussion.

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Skip Wolfe:
<strong>Sorry, I guess it does sound like that but that was not what I was trying to imply.
</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Again, I didn't figure you were, but I didn't want folks to think they could just add the numbers up and think they were safe.

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Skip Wolfe:
<strong>The one thing I have no clue on is to what strength does one need to design to. You state 30-75 G’s is more appropriate. At what load can the human body survive? I don’t have a good feel for any of this so I’m just trying to get a handle on it.
</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Well, as I said, I'm not an engineer by training and I don't have any numbers to help here in terms of strength to design to. I will say that I see a lot of cages that could have been designed better very easily. And I've seen some 944 cages with main hoops that have major bends in the verticle tubes. God, that wouldn't get near my car. That's Sir Newton's way of saying "fold here."

As to what G force crashes are survivable by the human body, it's pretty significant. I don't have numbers at hand, but I know there have been many a crash in Champ Cars that have registered well above 70 Gs. Of course, at this level, it's pretty hard to beat a HANS device or similar for being able to survive (but for the record, folks have survived these forces long before the HANS was in significant use).

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Skip Wolfe:
<strong>BTW I don’t have a DAS bar or a 911 for that matter, but I do have a 944 turbo with a Redline bolt-in bar for DE purposes only. I do think I’m going to upgrade to mil spec Ti bolts, and I have always planned on going to a welded full cage if and when I make the jump club racing</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">While bolt-in cages are not generally nearly as good as a welded cage, a well designed bolt-in cage can be pretty good and probably better than poorly designed weld-in cages. It's important to not only have a large mounting plate, but to attach each mounting plate with a back-up plate and 4 bolts at each plate. I think the mounting method of the bar or cage in question is what makes it unsafe for racing.

Skip Wolfe

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Geo:
<strong>Sorry Skip, I didn't mean for it to sound like I was picking on you...</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">No worries George. I didn't take it personally.

Does anyone know if any of the ameteur sanctioning bodies have a design criteria for roll bars in terms of force i.e. a cage should be designed to withstand a 50 G crash. I'd be curious what the target is. Unfortunately some of the rules I hace seen regarding saftey equipment seems to be based on seat of the pants engineering and not on any epirical data. For instance the PCA's stance on not mounting harnesses directly to a harness bar for DE is in reality making things more dangerous rather than safer. I would be curious if PCA, SCCA, NASA etc have any data based guidelines.

Geo

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Skip Wolfe:
<strong>Does anyone know if any of the ameteur sanctioning bodies have a design criteria for roll bars in terms of force i.e. a cage should be designed to withstand a 50 G crash. I'd be curious what the target is. Unfortunately some of the rules I hace seen regarding saftey equipment seems to be based on seat of the pants engineering and not on any epirical data. For instance the PCA's stance on not mounting harnesses directly to a harness bar for DE is in reality making things more dangerous rather than safer. I would be curious if PCA, SCCA, NASA etc have any data based guidelines.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">I just checked through the SCCA GCR. It specifies how cages must be built at a minimum. However, it does allow for alternative construction, but it must be accompanied by engineering specifications signed by a registered engineer. In practice, I would think it would generally need to be FIA homolugated or be accompanined by extensive test results. I'd think the best place to look is the FIA regulations on their web site.

Joe@Fabspeed

Skip
the data you provided should be more than adequate? What would be the calculations if NAS super high quality hardware was used.
thanks

Skip Wolfe

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by 993 RS Clubsport:
<strong>Skip
the data you provided should be more than adequate? What would be the calculations if NAS super high quality hardware was used.
thanks</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">I'm having a tough time finding any good data for NAS titanium bolts. The NAS steel bolts I found doing a quick search really didn't have a significantly higher strength. Let me know if anyone has a website with some specs for high strength titanium bolts.

chris walrod

the total g-loading a human body will take isn't as critical as the amount of time the g-loading was applied.

I will look up some NAS specs here at work. I will try to find both 12point superbolt and standard 13thousand series hex head specs.

chris walrod

NAS specs of popular series of hex head bolts:

160,000 psi tensile / 95,000 psi shear
NAS 1103 alloy steel @450deg F
NAS 6203 """"""""""
NAS 1303 """"""""""
NAS 6603 """"""""""

NAS 653 Ti Alloy @ 500deg F
NAS 673 """""""""""
NAS 6403 """"""""""

Check out: <a href="http://www.coastfab.com" target="_blank">http://www.coastfab.com</a>
for more general info.

AN hardware for 7/16 dia. (in single shear) is 11,250lbs at full diameter.

Not really sure if this helps matters, but the more info available makes for an educated decision?...

Danno

Compare the cross-sectional area of that bolt to the floor-plates that's typically welded onto the floor. The footprint of the AutoPower roll-bar is about 8 square-inches and uses 4 bolts. Take the load-bearing capacities of 4 of those same aircraft-grade bolts in compression & tension as opposed to a single one in shear and you get the idea. Also the AutoPower uses a thick backing-plate on the other side of the bodywork. Actually with the way the AutoPower feet press into the floor on a roll, the bolts don't take much of a load at all.

smokey

The failure mode for the floor plates will not be in the fittings or bolts, but a shear failure of the sheet metal floor at the perimeter of the floor plate. Calculations, anyone? Will an 8 square-inch plate of sheet metal fail at a load of 14,250 lbs, which is equivalent to a NAS bolt in single shear?

Skip Wolfe

Smokey your right on as to the method of failure for the Autopower bar. Anyone know how thick the sheet metal is on 911 and 944's?

Skip Wolfe

Based on a 2" x 4" mounting plate/backing plate (8 sq inch) mounted to 22 guage galvanized zinc plated steel (floor pan) with a yield strength of 50,000 psi, I came up with a 9,000 lb shear strength for a single mounting point - about the same as using a high quality fastener with the bolt-in bar. I made some educated assumptions on the thickness of the sheet metal and used a middle grade yield strength for the sheet metal. Let me know if anyone has more specific numbers for the thickness, yield stress etc.

Really the only absolute safe way to go is to go with a full blown cage welded to structural members, which is not real practical for club racers. In the absence of the full welded cage, I am not really convinced that the Auotpower style roll bars are that much stronger that the DAS style bars. Unfortunately I doubt that PCA has actual run through any serious engineering analysis and is relying on intuative "it looks like it should be stronger" engineering.

smokey

Skip, your analysis is right on. A bolt-in roll bar mounted to the seat-belt holes with NAS bolts is about 50% stronger than one mounted to an 8 sq-in plate on the floor. However, there is no absolutely safe way to go racing, and the degree of protection really comes down to one's own individual preference based on sound analysis. I only do DE, and for that, the Redline roll-bar is ok for me. If I were ever to race, I would only do so with a welded-in cage with door bars. It all comes down to probabliities. Two NAS bolts should sustain 9G's, and landing on the roof at more than 9G's is a low probablity at most tracks. At Mosport, hard roll-overs are rare, but the last two fatalities (none P-car related) have involved t-bone collisons after a spin on a blind corner. Hence the need for good door-bars for racing, even more than roll-over protection. However, it ultimately comes down to personal choice. What bothers me most is rules laid down in complete ignorance of basic engineering, like the don't-connect-your-belts-to-the-harness-bar one. Sorry. End of rant. My excuse - the first DE at Mosport on April 11/12 was cancelled due to snow, and I haven't had a chance to try the new LEDA's yet, so I'm grumpy.

smokey

One further thought (too much time on my hands)- in a 50G impact on the roof, the roll-cage is completely irrelevant. Your belts would stretch about 50%, your helmet would hit the roof, and the little birdies would be singing.

chris walrod

Safe Racecar..Thats an oxymoron. The only thing we all can do is decrease the chance of injury, it would be impossible to eliminate the chance all together.

As far as the sheet material where the seatbelts anchor to, typically there is a local doubler in that area for reinforcement.

I agree with Skip and Smokey's views.