|100 Horsepower Wheel Driven Racing Kart!|
To see the continuation of this project, click here
5/10/04- In between testing the kart, we've been looking for a way to lower the engine idle speed on the JFS-100. This week my cousin Gerald and I started pulling apart our spare JFS. First, I stripped off all of the wiring, and unnecessary components, as I am going to rewire the engine for a manual start. Then, I pulled off the power turbine assembly and stripped that apart so that I can rotate the housing to re-route the exhaust gases.
After that, we removed the accessory gearbox assembly, which is held in place by four bolts. After removing the bolts and a couple of fuel and air lines, the accessory gearbox assembly and all the accessories pulled right off, revealing a tiny jackshaft that transmits rotation to and from the gas producer shaft.
Then we pulled the starter off, revealing the infamous centrifugal starter clutch, the very thing we need to replace or modify in order to get the engine to idle lower. As you can see in the picture, the clutch has three pawls that will allow the engine to over-run the starter. Once the engine speed increases above approximately 63%, centrifugal force causes the pawls to retract and completely disengage from the starter shaft, by about 65%. The hard part is going to be to figure out how to mate the smooth surfaces of the sprag clutch rigidly to the starter shaft and accessory drive shaft so that it can transmit torque. We have also considered modifying the existing clutch to disengage at a lower rpm.
While we were pulling everything apart, we also disassembled the fuel governor assembly, to see what we will have to do to increase the governing range of the control. The governor is a very simple yet elegant piece of machinery. Two flyweights on either side of the ball bearing in the picture move outward as engine rpm increases. In turn, this causes two fingers to push the bearing assembly and attached sleeve upward, covering small metering holes in the center of the shaft, reducing fuel flow until an equilibrium rpm is found. Pressurized fuel from the engine driven fuel pump feeds fuel into the governor housing which then finds its way into the metering holes. When the throttle plunger is pushed, the spring tension on the large coil spring is increased, which pushes down against the bearing, pushing the sleeve down, fully uncovering the ports, and allowing more fuel to flow through control; the engine accelerates. Acceleration is controlled by a separate pneumatic acceleration limiter. Rpm increases, which, again, causes the flyweights to move apart, which push the bearing and sleeve upward to cover the fuel metering ports at a new equilibrium governed speed. In this way moving the throttle lever gives very accurate control over engine rpm. Our goal will be to adjust the governor to increase the governing range of the control from approximately 52% idle to 104% full power. This should not be too difficult.
After spending quite a few late hours disassembling and imbibing, Gerald and I thought it best to call it a night... (next entry)
"Hey cuz, have you seen the electric starter anywhere?"
"Uh, no, but this beer sure tastes funny..."
4/19/04- As promised, this weekend we ran Formula Turbokart on an extended test session. We learned alot about the handling and performance of the kart, and we're getting closer and closer to our ideal picture of a road racing kart. I will admit that it does exhibit the qualities of a race car, in that it is temperamental, hard to predict, and can be downright dangerous at times.(I was going to make a crack about how women are in many ways like my go kart as well, but my girlfriend wouldn't let me.)
Anyway, we ran the test for a few hours and went through a few tankfuls of kerosene. We clipped speeds of 90+ mph during the test, but the bumpy surface of the parking field makes going any faster unsafe. We will need to find a smoother surface to really exercise the beast's potential, and ideally I'd like to get it out on some sort of road course. We experienced some minor problems, like a tendency for the engine to flameout when the throttle is chopped from full power, and a mysterious grinding sound the chassis makes under full acceleration. (It seems like the rear brake rotors may be rubbing on the ground under acceleration, due to the compression of the rear tires caused by rear weight transfer.) But part of the fun of building a vehicle like this is putting it through test sessions like this, finding the problems, and then finding a solution. Ultimately our test was cut short when the massive torque of the little turboshaft ripped the drive chain apart after I did a hole shot. (Click here to see a quick video clip of that) But the chain has already been replaced, and next time we'll bring a spare. Thankfully the engine was not damaged.
4/15/04- This weekend we will be doing some more testing of the go kart, in an attempt to understand better its performance and try to tweak the handling. We will try to shoot some quick video clips of the test as well.
I have also started to modify my spare JFS-100 engine to make it idle lower. I received a tiny overrunning sprag clutch from Tim Arfons. The clutch will transmit torque from the starter in one direction, but in the other direction it turns freely. This will allow us to eliminate the centrifugal clutch on the starter shaft; the sprag clutch will take its place and operate effectively at any rpm.
The picture on the left shows the exisiting JFS-100 centrifugal flyweight clutch carrier on the left, with the springs removed. The middle picture shows the tiny sprag clutch. The picture on the right shows the clutch with the inner race removed. The tiny needle rollers only rotate in one direction, the freewheeling direction. In the other direction, the clutch locks up and the inner and outer race turn as one, allowing the clutch to transmit torque in that direction only. In the next weeks we will be working on a way to couple this to the JFS-100 starter shaft. (next entry)
3/30/04- This past weekend I drove Formula Turbokart on an extended test session, the first since the modifications to the kart. It was really nice to have the kart back in action, as it continued to provide thrills to its owner. Unfortunately I was unable to take any photographs or videos of the test. Regarding the new modifications: The addition of an extra brake rotor at the rear of the kart greatly improved braking feel and control. The engine still has the same high idle speed so I still had to ride the brakes to keep it going slow, but I found that I needed less pedal pressure to keep the kart under control, which should translate to less brake wear and better drivability. High speed braking was also improved dramatically by the additional brake.
That's not to say that the test was perfect. The kart was extremely skittish over the bumpy surface, more so than I remembered. I think this winter's frost might have affected the surface of the parking field. At high speeds approaching 100 mph I had a couple of scary moments when I hit bad bumps and immediately got onto the brakes which seemed to want to toss the kart out of control.
We intend to test the kart much more frequently to see if we can improve the kart's handling. We are also working on putting together a couple of cool videos with the go kart using a helmet cam, and hope to film a video of Formula Turbokart competing against a Ferrari 360 Modena in a drag race.
We are also about to start work on pulling apart another JFS-100 to see if we can modify the starter to allow the engine to idle lower. Once this engine is complete we will swap it out for the engine in the kart, and then perform the mod on that engine as well. Stay tuned for some exciting stuff in the near future! (next entry)
1/06/04- We have completed our modifications on Formula Turbokart by adding the wheelie bar. This system came off of a Competition Engineering Wheel-E Bar Kit, which is used on street drag and pro stock drag racing cars. We didn't need the complete kit for the go kart, and just ended up using the polyurethane wheel assemblies and housings, and bolting them onto the kart chassis. We actually just fit the wheel assembly housings over the rear tubes, and bolted them in place under the mounting plate that we used to mount the alternator. The wheelie bar will keep the kart frame from grinding against the pavement when we lift the front wheels under acceleration, and should help to keep the kart under control.
We need to finish bleeding the new braking system and do a little more wiring to incorporate the 24 volt alternator, and then we will do one or two shakedown runs to make sure that everything works right, before we begin to scope out a good location to run our kart and film some more videos. I'm looking for a lipstick style helmet camera so we can shoot some onboard footage. (next entry)
12/10/03- As these images show, we are finished mounting the 24 volt alternator and rigging the belt drive off of the rear axle. The alternator will charge the two 12 volt motorcycle batteries on the kart to keep the oil pumps and cooling fans running. Also shown is the 4th brake, added to the left rear corner of the kart, to improve the braking performance, and keep the kart under control at lower speeds. All that is left now is to wire the alternator and fill the rear brake master cylinder with fluid and bleed it. We are still waiting on the Wheel-e bar which we will modify and add to the rear of the kart to keep it from lifting the front tires off the ground too far under acceleration. We expect it in about a week. Once that is finished, the kart will be ready to run. I wonder how it goes in the snow...
Reducing the residual (idle) power of the engine is a long term goal with a view towards making the kart more driveable. The main problem with the JFS-100 is that its idle speed is too high at around 67% N1, which is the equivalent of trying to creep along in a car with your foot halfway down on the throttle pedal. Here is the problem; the JFS-100 electric starter has a clutch which disengages it from the accessory gearbox after the starter has done its thing. The starter clutch is a pawl type clutch which uses the centrifugal force of rotation to disengage the pawls. Above 67%, the accessory geartrain is spinning fast enough to keep the clutch disengaged, but if the speed drops below that, the centrifugal force drops and the starter clutch begins to re-engage. The partial engagement causes the pawls to rub against the ratchet gear, wearing out the teeth in a matter of seconds, and thus rendering the starter useless.
Starter cutout speed for a JFS-100 is 50% N1, which means that at that speed it is self sustaining. There is no reason why idle can't be lowered to around 52-55%, if the starter clutch problem was resolved. With the help of Tim Arfons, we are currently working on a way to modify the starter clutch to eliminate this pawl issue, to allow us to set the idle speed lower. I have pulled my newly acquired JFS-100 apart and will be looking at ways in which it can be modified. More information to follow. (next entry)
11/26/03- We are still in the process of modifying the kart, and we are making decent progress. We procured the braking hardware, and have fitted it to the kart. The 4th brake rotor will go on the left side of the rear axle, on the outside of the axle bearing, just opposite of the other rear brake. We fabricated a bracket out of steel plate to mount the brake caliper to the kart axle bearing carrier bracket. Our machinist fabricated our alternator drive pulley, which will be mounted onto the rear axle on the keyway that was originally intended for the stock kart's rear brake. We've also installed a steel plate and bracket to which the 24 volt alternator will be mounted.
Still left to do is to mount the wheelie bar to the rear of the kart, finalize the brakes, and install a pulley for the alternator and run all the necessary wiring before we can run the kart again. We expect this to be completed in the next few weeks.
We are also thinking ahead to our engine modifications which will allow the engine to idle at a lower compressor speed so that residual torque is reduced. We have gotten our hands on another JFS-100 which we will be using to test some new concepts. More on that soon... (next entry)
First of all, I'd like to thank the people who emailed in with ideas for how I can make the kart more driveable at low speeds. Many ideas were entertained, including putting extra brakes on the kart, installing a transmission to control gearing and speed, installing a combination clutch and output shaft brake to disengage the engine from the wheels, and even installing an electromagnetic braking system to absorb some of the surplus power at idle.
In the end, we have decided on two solutions, one short term, and one long term.
Our short term solution is to add another brake to the rear axle. The kart's brakes are extremely powerful, and have no problem stopping the kart. However, I am more concerned about long term brake wear and even more so brake fade, which is a temporary reduction in braking power due to high brake temperatures. Adding an additional brake to the rear axle will mean that the braking loads are now distributed to four brakes instead of three, and that means less brake wear and fade, due to increased brake surface area and lower brake pressure and temperature. The brake parts are on order and the rear axle is off the kart for the modifications.
While the axle is removed, we are also going to add a pulley so that we can run an alternator off of the rear axle. The alternator will charge the two onboard 12 volt batteries so that the kart can run indefinitely as long as you keep the fuel tank full. I am also going to seal off the underside of the kart with an undertray to protect the engine and wiring from pebbles and other foreign objects. Finally, we are going to add a wheelie bar to the rear of the kart frame, to keep it from bottoming out under heavy acceleration, which is happening currently. It will also make the kart easier to load and unload off the truck.
Our long term solution requires taking the engine apart and performing modifications to it, so we are holding off on it for a little while, or we will try to get our hands on another JFS so we can modify that one while we still use the kart. More information to follow... (next entry)
This weekend we tested the kart extensively, logging in a few tankfuls of solid running. Everything seems to be holding up great so far. Running on the bumpy concrete surface of a nearby parking lot, we reached 122 miles per hour on GPS. The kart has much more speed in it, but we were running out of room and also out of nerve as the kart darted and danced across the broken up pavement. We hooked up our G-Tech Pro performance meter to one of the kart's 12 volt batteries and recorded a 0-60 time of 3.2 seconds, smoking the tires almost the whole way to 60 and trying to keep the kart going straight. We didn't have enough room to go for a 1/4 mile time yet; we'd like to wait until we get a smoother track surface before really wringing it out. With a smoother, stickier surface and shorter gearing, we can expect to see 0-60 times in the 2 second range and a quarter mile in the 9 or 10 second bracket.
The kart is now back in the shop undergoing modifications at the moment. More updates to follow... (next entry)
The first test run was very promising, but more than anything, the sheer level of uncompromising performance that this beast is capable of was made readily apparent. This go kart is not a cruiser; it's definitely not designed for a sunday stroll down the boulevard.
Even with N1 turning at idle speed, the kart is constantly tugging at the reins, trying to accelerate away. At idle power, the overall performance is similar to that of my thrust powered kart at full power. Indeed, for the first few runs, my foot was constantly holding the brake pedal down to keep the speeds in check. As I started getting more courageous, I would let the brake pedal go for a while and feel the kart smoothly and briskly accelerate. The bumpy road made it hard for me to keep my foot off the brake pedal, and this resulted in me riding the brakes, which will undoubtedly cause excessive brake wear over time. Thankfully, these go karts have incredible brakes, so I was able to keep the kart under control and I could regulate my speed at will. From an outside observer's standpoint, it looks as if the kart is perfectly comfortable cruising around slowly, but for me, it was all I could do to hang onto the brakes without cooking them. This kart is designed for one thing, and one thing only. To go fast.
As I started getting braver and braver, I would take a stab at the throttle pedal here and there. The best way to describe the feeling of acceleration is like a time warp. In an instant the scenery goes from just passing by to a complete blur. I've driven a lot of fast cars, including a number of high powered race cars, and I can't say that I've ever felt such overwhelming power, uninterrupted by shifts. A few times I lifted the front tires clear off the ground. I couldn't keep my foot in it for more than a second or so before my better judgement told me to lift off. I don't think I ever mustered enough courage to call on full power (104% N1), but in at least one of those quick bursts of speed, I crossed into 90 mph territory according to my GPS, and that was without even really trying!!!
I was surprised at how little wheelspin I was getting, in relative terms. I mean, with that much power, you'll always get some, but the kart put the power down very well, even going around turns. I attribute this to the extended wheelbase, and the very high gearing. I have the kart geared for about 170 mph, so that reduces the torque at the rear wheels to a managable level. Nevertheless, when I really wanted to spin the tires, it was just a matter of stabbing the throttle pedal.
Engine lag was basically a non issue. With the idle speed set at a very high 67%, engine response to the throttle was immediate all the time. In really big power changes, like idle to full power, there was a momentary delay, but I've driven turbocharged piston engined cars that have more turbo lag than this engine. Definitely nothing that would make the kart difficult to drive around a race track.
The first test yielded a ton of information. It's far from perfect yet, but I have to say I was very surprised at just how well it works so far. The gearing, in my opinion, was spot on in terms of being a good balance between acceleration, top speed, and drivability. The fact that I was able to hold the kart on the brakes and come to a rest with the engine running supports this. The kart handles extremely well, put the power down well, and was a blast to drive.
The speed issue is not a problem. The kart is super fast. My next goal, however, is to make the kart more driveable, especially at lower speeds. I am considering adding anothing brake to the rear of the kart if I can fit it, and I will see if I can upgrade the rotors and pads to a larger size. I will also switch to a harder brake pad so that they will last longer. At the same time, I want to depend less on the brakes, so that I can get some kind of useful service life out of them. I need to find a way to be able to slow the go kart at low speeds without using the brakes. I am already throwing around some ideas in my head for how I may do this.
Stay tuned as more developments arise. And please, check out the two new videos in the mutimedia>videos section if you haven't done so already.
Please email me with any questions or comments on the kart, or the website in general. I always welcome emails from interested individuals.
Stay tuned!!! (next entry)
9/22/03- With the bodywork completed, we are a week away from our first test run. I know it's been a long time coming, but we are so close now, we can almost smell the kerosene burning. Keep an eye out for a report and a video clip of our first test in the following weeks. (next entry)
8/21/03- While we are waiting for the digital tachometer, we are continuing to do some of the finish work on the go kart. To protect the JFS-100 from foreign object damage we will need to fabricate some type of intake screen. While thumbing through an aftermarket auto parts catalog with the guys in the shop, we stumbled upon a pretty neat looking HKS automotive air filter. We thought it could be a good starting point for our intake screen, though we are going to need to modify it considerably to accomodate the much higher airflows of a gas turbine engine.
I've also started to paint the plastic bodywork on the kart. I am going with a dark red finish and then I am going to add some interesting graphics. The bodywork probably won't be ready for our first test, but keep checking back for progress. (next entry)
8/19/03- Before I will get into the kart and test drive it, I need to make sure that I am protected from a possible but improbable uncontained event... Because of the high temperatures and high speeds that occur inside of a gas turbine engine, there are high stresses on many of the components, particularly the turbine blades. Particularly worrisome would be a power turbine failure, which could occur if the chain were to snap under full power/full load. The sudden and dramatic decrease in load would cause the power turbine rpm to shoot up, and before the N2 overspeed cutoff switch can react, the power turbine could overspeed dramatically. This could cause the turbine blades to part company with the turbine wheel. This particular engine features a 1 inch thick titanium containment ring around the outside of the power turbine, to prevent parts from actually leaving the power turbine housing. Nevertheless, I don't wish to tempt fate any more than I already am driving a go kart at 160+ miles per hour, hence the scatter shield, as shown in the pictures below.
We made the scatter shield primarily out of Kevlar, the same material they make bulletproof vests out of. I ordered a roll of Kevlar from a company called Aircraft Spruce. We first fabricated the form of the scatter shield out of thin steel plate. Once we bent the plate into the desired form and fabricated the mounting brackets for it, we then laid up the sheets of Kevlar against the plate with a two part epoxy resin. We ended up using about 6 layers of Kevlar on each side of the plate to create a very strong scatter shield, which should protect us from any flying turbine blades. A couple of coats of black paint finished off the shield.
With that complete, all we have to do is replacing a malfunctioning digital tach and fabricate an intake screen, and we will be ready for our test drive. Things are really getting exciting now... (next entry)
8/12/03- Today we were successful in solving the no-start problem, and we fired up the JFS-100 turboshaft engine twice with the kart on the workbench. With brake pressure applied on the rear brake, the rear axle began to spin up and was turning at very high speeds, and applying further brake pressure would not cause it to stop. This leads me to believe that even at idle power, the kart is going to be difficult to stop with the engine torque fighting the brakes, and may require additional braking equipment. The next step is to finish up most of the details, including an engine scatter shield, and do a test drive, to see how the kart really works. Video and pictures to follow. (next entry)
8/08/03- With the engine back in place, we once again hooked up all the connections. At this point the whole crew is excited to see this thing run. This time the starter spooled up and the igniter plug was hitting, but for some reason the fuel solenoids were not opening to allow fuel into the burner. We made a number of starting attempts with no luck. We even have a video clip of the failed start attempts. It may be difficult to see on the video, but during the spool up, the airflow through the power turbine was enough to cause the rear wheels to spin up pretty quickly. This thing is going to be so fast!
The problem most definitely lies in the wiring. I am going to disconnect all the wiring and start from scratch. I am bent on having this kart running as soon as possible, and I'm not about to give up! Stay tuned... (next entry)
7/02/03- With the repaired engine set to come back in a few days, we made some final preparations to the kart. Once the engine arrives, we will immediately reinstall it in the chassis, and then test fire it. Assuming that everything works right, we will then finalize the kart, and it will be ready to run.
A forlorn kart sits and waits for its engine...
In the meantime, we added a second battery to the kart, this time on the lefthand side of the seat. I decided that with the amount of accessories I am running off the battery, I will need a second one on the kart. It will also greatly simplify the wiring of the 24 volt engine start system. I will still need external batteries to start the engine though. Weight gain with the new setup is minimal, and I believe it will save some headaches. I also cut down the output shaft to its final length. I decided that if there is a need for an extra brake to help slow down the kart at low speeds, I will add it to the rear axle, and not the engine output shaft. I am hoping I don't need one. (next entry)
5/06/03- A bit of frustration today with the project...We finished up the electrical system. We've installed a quick disconnect for the 24 volt batteries, so we can start the engines and easily remove the connection from the kart without worrying about alligator clips sparking.
24 volt quick disconnect
So we filled the two gearboxes with oil, fueled her up, primed the fuel system, connected the batteries, hit the starter switch, and nothing...The starter relay was closing, but the starter didn't spin. We tested the electrical system out and found that the electric starter is shorted out. We're not really sure how this happened because the engine ran fine before, and this is the first time we've had electric hooked up to it since we installed it in the kart. At any rate, I already have the engine in a box on its way back to Tim Arfons in Akron. He says he will most likely have to replace the starter. I guess I'll have to wait a little while longer before I get to experience what it feels like to have 100 horsepower accelerating a 220 lb. go kart.
"An empty engine bay is like a man with no heart" -Anonymous
I will update as soon as I get the engine back. Hang in there! (next entry)
4/25/03- Work has started back up on Turbokart II after a bit of a break. Today we installed an oil pressure gauge that will monitor oil pressure of the gas producer engine driven oil pump. Since the power turbine oil system is splash lubed, there is no mechanical oil pump, and therefore no way to measure pressure.
We also began to fill the brake cylinders with Castrol DOT 3 brake fluid, and then bled the system. Bleeding the brakes on the kart are actually quite difficult, due to the relatively small volume of the brake cylinders and the lack of a reservoir. The brakes have to be just right, because they are going to have to be able to hold back the engine torque at idle, and will also have to be able to stop the kart from very high speeds.
At this point, there really isn't that much more to do, and the work will be picking up again. In the next few days we will finalize the electric system, fill it up with oil and fuel, and test fire the engine, to make sure everything is on the right track. Stay tuned, this is where it starts to get fun... (next entry)
3/11/03- We started on the electrical system today. The kart is going to actually have two separate electric systems; a 12 volt and a 24 volt system. The 12 volt system receives power from the small motorcycle battery mounted to the right of the seat. The battery will power the 3 electric pumps and two electric fans through the five switches on the panel, as well as the digital tach. The 24 volt system will be used to start the engine. It will consist of two large external car batteries wired in 24 volts. I will install a quick disconnect plug that will allow me to easily couple and decouple with the external battery pack.
The pictures below show the control panels, the battery, and the starter relay mounted to the kart frame. We have connected to the engine via the cannon plug. The cannon plug connects the batteries to the various solenoids and switches that govern the automatic start system. (next entry)
3/06/03- The plumbing for the two oil systems and the fuel system is now complete. The pumps pull oil out of their respective gearboxes and then push the oil through the respective oil coolers, and back into the engine. I installed capped filler fittings for both oil circuits to make it easy to fill up and top off the gearboxes. Filling my last kart with lube oil was a bit difficult in that I had to remove one of the hoses every time I wanted to add oil. This should make the process a lot simpler. Just unscrew the cap and fill with a squeeze bottle, or connect a hose to the fitting and run the electric pump to draw oil out of a container.
Oil filler caps
The fuel system was also completed. Fuel is drawn out of the 2 gallon fuel tank by the electric fuel pump, mounted to the right side of the tank. The fuel is pumped past an emergency manual cutoff valve, before travelling rearward to the engine fuel inlet. The burner drain valve admits leftover fuel to a catch can that I installed behind the seat.
Note the battery in some of the pictures. It is mounted just in front of the engine on the right hand side. This small 12V motorcycle battery will only power the three electric pumps, two cooling fans, and the main instrument panel.
The next step will be to begin with the electrical system. We must make a switch panel for the pumps and fans first. (next entry)
To see the first part of this project, click here
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