The Tail End of the Race Car Build

If you remember way back in the ancient early days of this build, back in January of the year 2022, I had a realistic goal of having this car done for Speed Week of this year. Well, I didn't, but it didn't matter because Speed Week didn't happen due to the fact that the dry lake was an actual lake. But no matter, a month later was World Finals, an event I would make if not for the fact that it was also cancelled due to rain. That left the September El Mirage event as this car's first race, except that was also cancelled due to rain. In a year with sweeping droughts and water reservoirs at record lows, I cannot race my car because there's too much rain. Some of you may be thinking that the weather has a beef with me in particular, but I'm not narcissistic enough to think that it's all about me. Anyway, let's get back to my video on my channel where I will talk about nothing but me and my projects. While the racing is on hold, the project moves on. Someday I will get this car to go fast. There are two more events this year, but it's not unlikely that the water gathering on the lakebed now will still be there through November, so don't hold your breath. The major component missing from this race car is the body, the aerodynamical penis-shaped skin that will allow this to slip through the air undetected. It's not going to happen until next year regardless, but there are a few more things that we need to wrap up before this car is ready to race in all its nakedness. For instance, the tail. All streamlined things need a tail. Rockets and submarines and race cars and lawn darts. This car abruptly ends just behind the rear wheels, and this is not great for aerodynamics. This doesn't really matter because without a body, all of the car is not great for aerodynamics. But the tail does a little bit more than just help pull in the wake behind the car. It also holds the parachutes, and that's pretty much it. It's just a place for the parachutes. The parachutes are required by the rules, although there are not a lot of specific rules on them. They require an approved parachute, but don't get into any details about what is or is not approved. So I got two. Three actually. The first one is from DJ Safety. I called them up, told them all the pertinent info, they charged me a few hundred dollars, and sent me a very nice parachute. It is well made and sized perfectly for my car. For my next parachute, I bought one for $50 on eBay. This is, best I can tell, a drogue parachute, maybe a pilot chute to pull out the full size parachute when a plane is dropping supplies out the back. Normally I would not recommend sourcing your safety gear from used military surplus stores on eBay, but I know for a fact that another team has been using this exact parachute for years without any problems. Also, I have a second parachute, so let's go for it. It'll be interesting to see how different these parachutes feel when using them at speed. The chutes go in tubes. Long tubes. Often people will use irrigation tubes for this. 6 inches is a very common size. I went with 5. 5 inch diameter requires the tubes to be longer, but that's fine because I have tons of space back here. Why do I have tons of space? Well, that's due to aerodynamics. One of these days when I get around to actually building a body for this thing, the taper at the rear will need to be very gradual. If it's too abrupt, the air will become detached and angry and all hell will break loose, aerodynamically speaking. But if I use a nice gradual taper, the air will gently glide back in behind the car. A gradual taper means a long tail, and a long tail means plenty of room for parachute tubes. I got some cardboard tubes and tried stuffing the parachute into a 4 inch tube, but it was not happy. The military chute would have worked, but the racing parachute fit a little too tightly. 5 inches is one of those tube sizes that's not super common. Fortunately, you see it a lot on exhausts for big trucks. So, I bought a 6 foot section, cut it in half, and I have my tubes. But how to mount them to the car? That will require some sort of structure. Generally, you want your heavy stuff as far forward as possible on a car like this. That makes it more aerodynamically stable. That means we don't want to make this part too heavy, but also weight doesn't really matter that much in land racing. In fact, a lot of times you want to add weight to get traction. I like this. Makes it easier to build stuff. There are three major forces acting on this tail. One is the load from the parachute. By rule, the parachute has to attach to a 1 inch diameter mount. I'm going to put this just in front of the tubes. When the chute deploys at whatever 100 miles per hour, there's going to be a hard jerk on this mount. It would be really awesome if this jerk did not rip off the whole back part of the car. There's also the load from the air. When this thing is traveling straight, that should be zero, but if there's a side wind or if the car gets sideways, there's a lot of area here for the air to act on, especially if I put a fin on it. I don't currently have the car designed for a fin, but adding one might happen in the future to keep the car straight. So we want to make sure that when the air hits the side of the tail, it doesn't rip off the whole back of the car. Lastly, we have this little guy. Lots of cars get a push start because it's cheaper than fitting a custom ultra wide ratio transmission. I'll probably need this at some point, so I'm going to add it now. The wheel allows for some relative motion between the push car and the race car so that the push car doesn't accidentally rip the tail off the race car. So I made a structure. This structure connects the four rear nodes of the car here with the parachute mount and the back to the roller pushy thingy. I added some triangulation because the possible side loads and because all good structures need triangulation. This was an easy build. I just cut out the tubes and welded them in. I had my friends over at SenCutSen laser me out some tabs for the parachute mount and some nice mounts for my roller blade wheel here in the back. The tubes themselves are welded together with a couple of strips of metal on each side and that assembly was welded to the structure in a few places. These tubes are galvanized so I used a grinder to grind down to bare metal before I welded it. Welding on galvanized metal is bad. I hit it with some spray paint so it wouldn't rust in the areas where I ground it down. I suppose I should paint this whole thing, but you know what? I'm not gonna. Now I have a tail, but how to mount it to the rest of the car? How about four bolts? Three eighths inch grade eight bolts? I didn't do any actual engineering on this to make sure it was good, but it's probably good. You know what? Let's do it. Let's dust off the old engineering hat. The minor diameter of these bolts is about 7.6 millimeters. That's a radius of 3.8 millimeters. Square that and multiply it by pi to get the area of one bolt, but there's four bolts, so we get a total area of 180 square millimeters. The tensile strength of these bolts is about a thousand megapascals. A megapascal is just one newton per square millimeter, so canceling the square millimeter we get 180 kilonewtons. Is that a lot? I have no idea. I grew up in the United States, so all I know about newtons is that they're named after a British guy who never got laid. So let's redo that engineering in American. These are three eighths inch bolts with a minor diameter of about three hundred thousandths of an inch. To calculate the area in America, we multiply the radius by apple pi. This gives us an area of 30-06 with a tensile strength of eight linebackers. We come to a total force of 42,000 double cheeseburgers. That's double cheeseburgers force, not double cheeseburgers mass. This gives us a total acceleration of over 14 moon missions. Converting back to metric, that gives us 60 g's. Is that strong enough? 60 g's would smash my racing harness into my crotch, exploding my testicles, detaching my retinas, and probably killing me. So we're good. I sleeved the tail side so I didn't crush the tubes, and then I threaded the car side so I wouldn't need nuts. I want this easy to get on and off. When I threaded the bosses on the car side, I made sure not to drill all the way through. This way the threads are protected from dust and salt and all sorts of other stuff that will make this a pain in the ass to remove in the future. I also welded on a little hookup here. This makes it super easy to put the tail on the car with one person. The parachutes are shoved into these tubes at the very end here. There is a spring-loaded pilot chute. The spring and pilot chute, and therefore the rest of the parachute assembly, is held in with this little flappy flap here. When the flap opens, the spring pops out, the pilot chute opens, and the parachute gets pulled out where it inflates and hopefully does not rip the back part of the car off. To actually release these little flaps, I have this contraption here. I didn't bother to see how anybody else does it. I just kind of assume this is how it's supposed to be done. I took a piece of thin steel rod and bent it into this shape using a bench vise and some extra bolts. Then I welded it into place on the parachute tubes. Sliding this flap tab over it, I can shove some metal solid wire from this pull cable. Then I just need to pull the other side of the cable and it all dumps out the back like a party popper. To deploy this parachute, I'm using the power of air. Compressed air. This is super easy since I've already set up an air shifter. When I press the upshift button, this air cylinder gets pressurized on one side and shifts the transmission up. Downshift goes the other way. After my first outing with the car, I decided to add a manual shift lever so I could get it into neutral easily. I welded it up with some lightweight aluminum so it won't have a lot of momentum flapping around. Anyway, I have air, so I just tapped into that with a third solenoid for the parachute. I can just press this button and that sends high pressure air to this cylinder, forcing it backward, which pulls the cable and releases the chute. Currently, I only have one parachute button, even though I have two parachutes, but I'll get to the other one later at some point. This air-powered parachute release should work just fine, but according to the rules, I have to have a manual backup. I can't just rely on the button and air pressure. I wasn't really sure the best way to do this, but I had an extra pedal lying around, so I'm using that for now. Whenever I press on the pedal, it pulls on this cable and pulls on this end of the air cylinder. So, there it is. When I drive through the timing lights, I just press this button and... and... I just press this button and... I just push this pedal and there it goes. First try. Some of you also noticed a piece of spray-painted wood up here at the front. I have the flaps to keep the parachute from falling out the back, but I need something to keep them from falling out the front. So, I cut a piece of hardwood I had and drilled holes for the parachute loop to sneak through. I got these holes right in the center by taping a sharpie to a tube and tracing out the tube outline. I don't love making race car parts out of wood, but this fits the space nicely and it's pretty far from the hot fiery bits, so I think we're good. There is actually one other thing the tail needs, and that is a 12-volt shutoff. I have one of these on the side of the car here, but by rule, it needs to be at the front or the back of the vehicle. You don't actually need the switch at the front or the back, just a way to shut it off. So, I'm running this pull cable back and mounting it to this angle bracket here. To shut off the 12 volts, you just pull this guy here. And that's it. Aside from the body, this was the last big thing the car needed. I am ready to race as soon as it stops raining. Also, I know this was a short video, but I have been busy lately because I am getting ready to move, and boy do I have a lot of crap to move. And yes, you are not imagining things. I did just do this about a year ago, but this time it's better because I am moving into a three-car garage. It used to be that you had to impress people to get people to watch your show. Now, you just have to impress the algorithm. So, do me a favor, hit that subscribe button. All hail the algorithm.