Rear Impact Solutions

[Santiago]

Since this topic has come up recently I thought we should start a separate thread to address ways to protect the rear of the 818 in the event of either a car-on-car collision or an off-track incident that sends one into a wall backwards.

Let me say up front that the intent of this thread is NOT to debate if one should do something to try to protect the rear. If you’re not yet sure or don’t think that something should be done, please start another thread to discuss the merits of the project. Maybe try, “Should we try to protect the rear from impacts?”

This thread is for those who have already answered that question with a “Yes, something should be done to better protect both the transmission/trans-shift linkage as well as the occupants in the event of rear end damage.” As it stands right now, the only thing protecting the trans is fiberglass – and that offers no appreciable impact protection at all. So the point here is to begin a discussion on different strategies and solutions for addressing the rear.

I don’t have any set plans for how this should be done. I’m not an engineer, and I’d really like to hear from folks with such backgrounds. I do have some ideas I’ll share later, but I’m not wedded to any of it.

For now I thought I’d frame some concerns to give a sense of what sorts of goals we might each have in trying to come up with a suitable solution. These are not in order of priority, since different folks will prioritize their goals differently. If folks think we should add goals, by all means suggest them. For now, some basic goals might include:
1. Protect the trans shift-linkage –at least from low-speed impacts

2. Protect the occupants from a major high-speed impact. This could include any of the following
a. Engine/trans intrusion into fuel cell area and/or occupant area
b. Dissipating impact energy

3. Protect other components in the trunk area

These were some areas of focus I’d like to see considered/discussed. Maybe this will help guide us in our design process:
1. Tubing stock size (for rough est. of strength)

2. Tubing arrangement

3. Mounting location (and poss. mounting strategy if it’s part of the protection strategy)

4. Influence/interference of above on the rest of the chassis (and components), both:
a. As an initial design parameter
b. In the event of an impact

Ok, so that’s a start I think. In the next post I’ll throw out some ideas and images I’ve been collecting to start the ball rolling. Looking forward to sharing ideas.

Best,
-j

[Santiago]

So as I see it, we’re going to quickly find a division of strategies based on one major line drawn in the sand: bumper clearance.

Folks in camp A are going to wish to preserve the supplied bumper and treat it as the reference for interference with any proposed strategy. Folks in camp B are going to be willing to cut the bumper and discard what needs discarding in the service of their proposed strategy. I think this is really important to note, because my sense is that there are a lot of assumptions about what’s to be done with the bumper that are going to influence how we evaluate different proposals. So we should be clear on this (and this is what I previously meant by 4.b. above).

I’m firmly in camp B. I’m building an R-car and with what I have in mind overall, there’s hardly a panel that isn’t going under the knife in some fashion. So for me it’s no big deal to cut the bumper as needed – indeed, I suspect I’ll only preserve about 40% of it. I don’t need the rest. That opens the door on my end to accomplish some key objectives:

1. Gain distance! I want my bumper bar (at least the one directly behind the shifter linkage) away from the trans by at least 6” or so. That takes me well past the plane of the existing bumper, so it just got to go

2. Allow for some damage to the bars w/o interfering with shifter operation. The distance goes a long way to achieving this

3. Allow for crush room. Again, the distance is a major support for this, though other methods can be employed to help (some independent of bumper clearance)

Another key objective is taken from Chad Plavan (but doesn’t bear on bumper clearance): separate the functions between trans protection and wing mount. This would allow you to absorb damage to the bumper without adversely influencing your aero loads. I’m guessing some folks won’t think this is super important, but I think it’s an interesting proposal to consider.

Alright, so here are some pics of designs I thought were interesting. First, the Ferrari tank:

26416

Note that this design bolts into the existing frame rails that are near the actual bumper structure. That means they get away with such a heavily built structure with generally short tubes compared to what we’d need in the 818 for something similar.

Also note that this design incorporates wing mounts as an integral part of the protection structure. Probably not a big deal for them, since they may have figured if that thing is significantly damaged, your day is done no matter what you were hoping to accomplish.

Now on to the more “delicate” (and ridiculously fabulous) Palatov D2, whose bumper bars are arranged in ladder formation:

26417

If it’s hard to tell from that pic, note that the rear bumper bars bolt onto the primary frame structure. Engineer-types might want to have a closer look-see at how he designed it (I can’t quite make out the intention behind it, but maybe others know better). Here’s a look:

26418

I favor this overall style for a few reasons. First, the general format seems easy to adapt to what we’ve got going on in the 818. The long-ish longitudinal legs of it could easily extend back into whatever frame member we wanted. The upper and lower ladder bars might be modified to tuck into the supplied bumper (a tight squeeze, but maybe?), so it might be feasible to camp A folks.

Second, the middle bars allow us to gain distance from the trans shift linkage. For camp A folks, you’d need to ditch the lower center mesh on the 818 and run it open (like many do with the Lotus cars). Note that this might be a problem for license plate placement if you opt to open the upper deck up as well.

Last reason I favor this design, there seems to be a lot of options for building in crush structures to the basic layout. To me, the idea is that in the event of a heavy impact you’re no longer trying to save the trans, you’re aim is to preserve life. So we might use this to avoid transmitting all of the force directly into the cabin structures that are keeping us safe (a worry I have with the tank-like themes of the Ferrari example). Even a simple bend in the longitudinal bars would go a long way to pre-establishing weak-links along which forces can migrate.

Here’s an image of what the body looks like over the bars (may give some sense of how this style might work for the camp A crowd):

26419

Since Plavan once said he planned “a simple bumper bar” I thought I’d put up some of these images of literal bumper bars. I don’t know if this is what he had in mind, but I thought I’d throw it out there anyway:

26420

There are some other styles that I think might be kind of interesting, but that should give the basic theme for that route.

Well there you have it. Some things to sink our collective teeth into.

Best,
-j

[Goldwing]

This is an area I planned to look at more closely later on in the build, but this can be a great planning discussion. For the rear, I had in mind using a simple bumper bar with a trailer receiver hitch also bolted to it, that I have been pretty sure would sit proud of the current rear panel. Fiberglassing/shaping a bumper cover like most cars have now to aesthetically hide it was my not-really-thought-through plan. Or trying to fit it interior to the current rear panel but sit above and/or below the linkage to offer light protection. I hadn't worked out mounting points yet. Those were just my thoughts tucked away until I felt it was time to tackle it.

I really had no solid ideas for the front yet. FFR's site refers to crumple zone planning, so it would be good to be careful where a bar could or should be mounted. My biggest fear there, like many sporty cars, is the ramp the front of the car makes up to the cockpit. The higher any concealed bar is mounted, likely, the better.

All that said, I'm not an engineer either. My rear treatment ideas revolved around the desire to have a trailer hitch. I have a light trailer I pull kayaks with. I may end up pulling track gear in that trailer too, once I enter that world. A bumper and trailer hitch are pretty much a pair. If I'm going to do one, seems silly not to address the other. I planned to hide the hitch behind the license plate using a hinge like some cars used to hide a gas cap. I look forward to the ideas.

[Goldwing]

The rear probably wouldn't need a very wide bar. The rear is triangular shaped. It seems we may only need it wide enough to protect the middle. Once something hits off-center towards either rear corner, it seems most offending stuff would deflect to the side ripping off the rear suspension in its wake. Any rear bar, perhaps, ought to encourage this deflection of energy.

[Xusia]

This is an area I also planned to look at as well, so thanks for starting this thread (and so well thought out!). A couple things on my mind are:

Given how low everything is, I'm a bit worried about a rear end collision resulting in the offending vehicle "climbing" up and over the engine, so some crash protection mounted as high as possible in the trunk area seems like a good idea.
I'd like to protect the transmission shifting mechanism from minor crashes (i.e. a "fender bender"). For major crashes I'm more concerned about keeping my body intact! I can always build another car, so in that case I have ZERO problem with sacrificing the engine, transmission, frame, or all of them.
I'd like some structure to use as a mount for a trunk. Without getting too specific about that in this thread, my idea is a removable bin and it would require some kind of supporting structure underneath and around the top. I see no reason a crash structure can't do dual duty here.
I'd like for any crash structure to be at least partially removable so as to not hinder the ability to remove the engine.

[Goldwing]

I just came across this looking for something else, and did come up with a mod to the transmission shifter bracket that could help protect the shifter as well. See my build thread starting at post 71:

http://thefactoryfiveforum.com/showthread.php?13026-Goldwing-s-818-Street-The-Phoenix/page2

Doing that block thing, with less beveling on the transmission side (oops), then adding a bar superimposed above the block off plate that would sit just beyond the normal movement of the shift linkage (in 1st, 3rd, or 5th) could add protection to the more sensitive pieces inside. In the event of a minor rear end collision, the offending car would push the linkage to its stop, then hit the bar you mount transferring the energy to the transmission case. So, that bar should be bolted into the bolts holding the block off plate and sit in between the transmission block off plate and the shifter bracket itself, but be just beyond the normal movement of the bracket to prevent interfering with normal operation. When I get around to doing the bar thing, call it a shift bracket bumper, I'll post a picture up, as a picture is worth 1,000 words, or at least all the words I typed so far, lol.