FSAE notes page
So, I'm starting to get more information from all of you members, so I figured I post it up here so you all have access to it. Also, check the downloads page, Mike Beadle found the instructions (and program) we'll use to tune our engine. And now, exciting emails from people.
Kevin Glick - I remembered what I was trying to think of. Joe brought to my attention that there is a rule in the rulebook that there is no ground affects allowed on the vehicles, except for cooling. Although we could use it for cooling, we cannot use anything that purposely creates a change in pressure, so the fan idea should be tossed out, at least for the application suggested. But Mike Basch steps in "But if it is 'for cooling' and just happens to create a ground affect, is that within the rules? We'd have to justify it, but it is still worth considering. I'd have to say if we can't justify it well then it's not worth it, but we have to learn to think creatively. At the same time, how much downforce could we really expect to generate? How could we do that? Let's hear some ideas.
Ryan Mifflin - I have heard many times that the ideal weight balance of a car is 50/50, however, after watching videos of cars on youtube, it appeared that traction was a major factor in the lack of performance for many cars, and I began to notice that nearly every car had no weight behind the rear axle. Taking an existing formula car and replacing it's 4 cylinder engine with a much lighter 1 cylinder engine would reduce the weight over the driven wheels, and could theoretically negate any gains from reducing the overall weight. I thought the solution would involve a rear mounted engine with a shorter wheelbase, and this would have two benefits: 1) greater downforce over the driven wheels for increased traction, resulting in faster acceleration out of corners, unlike 4 cylinder mid mounted engines that easily overpower the rear wheels and require drivers to compensate by staying off the throttle. 2) Moving the rear axle forward creates a shorter wheel base, for improved cornering. It's unconventional, and unproven (pertaining to FSAE as far as I know), but consider this article from Car&Driver magazine describing der neuer Mercedes-Benz SLS gullwing: "As soon as I jump back on the throttle, the rear end slides a bit, but that oversteer is easy to control. The car feels well balanced, likely helped by a claimed weight distribution of 48 percent in front and 52 percent in back. Sitting so close to the rear axle also heightens the driver's sense of riding on all that power." In the real world, Porsche has proven that light, rear mounted engines can match or exceed the performance of exotics with bigger mid mounted engines. Since we're planning on using a smaller, lighter engine, it seems advantageous to have the engine rear mounted. Also, it appears that the tires on the orange chassis were over inflated, also resulting in a lack of performance. Is there any data on tire pressures that were used on that car?
I suppose the next step would be to produce some hard data, and try to calculate the weight distribution of existing cars and compare that to an estimate of a concept, and I think I would need to compile a list of weights of components like the impact attenuator, engine, trans, fuel tank, chassis, wheels. I brought up this idea before but no one seemed to warm up to it, and that's fine with me, but this can certainly be included in the final report. The attachments are simply two formats of the same sketch.
"Flight of the Gullwing" Juergen Zoellter, Car&Driver Nov 2009.
Dave Pearce - I want to point out before you guys finalize any seating / engine positions and stuff- just as, or if not more important than a balanced weight distribution - (*sometimes 50/50 may not be ideal, depending on your suspension, and drive configuration, IE: RWD might favor more weight bias towards the rear for traction etc, but 50/50 is a good point to shoot for, with the rear eng. configuration it will likely be heavier in the rear anyway.) - anyway just as if not more important, is how the the moment of inertia law applies. You know, the law that describes how it is harder to spin a dumbell than a sphere of the same mass. This applies directly to your weight distribution and basically tells you that for increased steering response and better handling (less tendency for the car to want to continue it's path when the wheel is turned), you want your biggest masses condensed as close to the center of the frame as possible, as opposed to spread out along the length / width. Just something to keep in mind when you guys finalize that stuff.
Alex Roy - As far as engine decisions are concerned, the obvious argument is the fact that the dynamic load placed on the 450 cc engine during normal usage is not as high as that of seen in the car. Thus, the decision was made that the quad engine would more likely suite the loads of the formula car, since the quads weight is higher than that of the bike. I think that a very important design variable is being overlooked; what type of fuel is going to be used. I believe the only reasonable fuel to be considered to make the 450 cc single cylinder engine a viable option versus the 600 cc 4 cylinder engines is e85. As the SAE rulebook states, competitors in california can't consider 93 octane used in the FSAE east competition. Instead, we are forced to choose between e85 or 91 octane gasoline. To achieve the performance necessary to make our engine competitive, forced induction would be an obvious choice. This would not be possible for consideration using 91 octane fuel. In a study performed comparing the performance and knock characteristics of 87 octane versus e85, a maximum compression ratio in a single cylinder four stroke engine was around 10:1, while a maximum compression ratio of 16:1 was attained with e85. Though fuel economy suffered due to the lower energy density of ethonal, maximum thermal efficiency was 29 percent for e85, versus 23% for 87 octane. A total gain of 13 percent in torque was also witnessed between e85 and gasoline. Also, maximum EGT (exhaust gas temperature) was 520 degrees Celsuis for e85 versus 600 for gas. This obviously is helpful in terms of reliability. You may ask what these figures have to do with engine selection, and the answer is everything. Based on these facts, I think it is pertinent to use the motorcycle (YZ450 F) engine versus that found in the quad (YFZ 450). Running on e85, knock will be of no issue for the higher compression motorcycle engine. We need power to compete with the street bike engines, and using 91 octane and the quad motor will not get it done. We must sacrifice some economy for performance, or else we stand no chance. Also, more design points will be given deviating from the naturally aspirated route. Lastly, the bike motor is all new for 2010, while the quad engine isn't. A major benefit to the new engine design is that the cylinder is offset from the crankshaft in a manner that increases the effective lever arm of the piston/ connecting rod assembly during the power stroke, creating more torque with the same relative dimensions and cylinder pressures. I hope this helps you reconsider your choice of quad versus bike engines.
Sources:
Yamaha Motor Corp.
An Experimental and Modeling Investigation into the Comparative Knock and Performance Characteristics of E85, Gasohol [E10] and Regular Unleaded Gasoline [87 (R+M)/2] SAE Document Number: 2007-01-0473
Ryan Mifflin's 95th percentile male and 5th percentile female sketches.
