Kev and Dunk,
Thank you both for your thoughtful replies.
My (mildly? :)) heated last post was a by-product of some recent discussions with some academics at the local Uni, where it dawned on me that they really do believe that the world is flat (metaphorically speaking, in a non-FSAE field). The derisory snorts they made when I suggested that the world is round (again, metaphorically) didn't help. But even worse was their complete disinterest in any sort of rational discussion of flat-earth vs round-earth theories.
I have now found this to be the case in several different fields. The Emeritus Professors honestly believe that they can teach anything they want, without ever having to give a rational justification of their teachings. The Education system is now a free-for-all with no quality control system to catch mistakes (and the above Professors are making some atrocious mistakes!).
That is why I like competitions like FSAE, because the stop-watch provides the error-checking procedure that decides which answers are more, or less, correct. I stand by my comments (on another tread) that in the most objective FSAE events, namely Acceleration and Skid-Pad, the "(in)correctness" of the answers has hardly changed in ~30 years. The bell-curve has got higher and wider, but its centre has not shifted.
This implies a lack of "learning" by the overall FSAE community. Or at a more local level, a lack of an effective "education process" from older team members (and supervisors) to the newbies. There are, of course, exceptions, such as yourselves and the other successful teams (eg. Monash, GFR, Stuttgart, Delft, Zurich, etc.). But the global bell-curve seems to be stuck in the 1980s.
By contrast, it is interesting to note that the global community of Toothless-Hillbillies (wonderful people, and perhaps "Toothless-Bogans" in Oz :)) must have a great education process going, because their times have been dropping steadily, year after year, for the last 50+ years!
~~~~~~~~~~o0o~~~~~~~~~~
So, in the interests of some sort of global FSAE education process, I requote some of your above posts, with some added emphasis and brief comments.
From Kevin.
Quote:
... I agree with your points about rear mass distribution. When we made the move in 2003 (UWA) to much more rear weight it was seen as the wrong path with just about every other team eschewing a 50-50 weight balance. In fact calcs support quite a lot more rear weight even with the same size tyres front and rear (60-65% with appropriate suspension changes).
Yes. With all equal-sized tyres and ~F35:R65 you simply carry most of your LLTD at the front, and lift the inner-front-wheel during cornering. This has the beneficial side-effect of allowing you to use an open-diff without spinning your inner-rear-tyre.
~o0o~
Quote:
Changing relative tyres sizes [ie. bigger rears, smaller fronts] and you could go much further, making RWD the way to go, with a car able to do well IN ALL CIRCUMSTANCES.
(My ADDED emphasis.)
This is the way the vast majority of circuit racecars have done it for the last 50+ years. Some historical notes here.
Pre-WWII, racing was mainly about top-speeds (and reliability, as always). Cars would get up to top-speed and travel long distances on (quite rough) country roads. Then heavy braking as they entered a small village, four-wheel drift around the fountain in the middle of the town-square, then back up to top-speed to the next village. Roughly 50:50 weight and equal tyre sizes worked well here.
Immediately post-WWII there was less money, more amateurs in motorsport, and lots of now unused airstrips. So the new airstrip-racetracks were shorter, with many corners connected by short straights. Initially, with low-powered cars (like the Lotus 7) the 50:50 weight and equal tyres sizes still worked OK. But as power increased, and still with RWD-only, the rear tyres couldn't take it anymore!. They kept melting! So, the simple fix was bigger rear tyres and more rear weight!
By the time of turboed 1,000+ hp F1 cars, the rears were monstrous ~20" wide slicks, still with relatively small fronts. Similarly in Sportscar racing (see turboed 1500 hp Porsche 917, much earlier than the F1s). Weight distributions of ~F30:R70 were common. These cars could use all their horses to accelerate very hard, AND they could also go around corners fast.
With interweb+++, all this should be BLEEDING COMMON KNOWLEDGE (:)), and is why I get annoyed when FSAEers say "Oh, but we CAAAN'T be good at BOTH Acceleration AND AutoX...".
In the 1990s Max Mosely decided that for PURELY AESTHETIC REASONS he liked the equal-sized tyre look. So he MANDATED it in F1! (Well, almost equal sizes, with fronts very slightly smaller than rears). This had NOTHING to do with performance. In fact, the cars became notably slower accelerating off the start-line and out of slow speed corners, but nobody was allowed to mention that.
Much more interesting history here, but briefly F1 cars DO NOT have their tyre sizes based on performance. It is just the (BRAIN-DEAD :)) Rules!
~o0o~
Quote:
WE WANT THE ENGINE AND DRIVER AS CLOSE TOGETHER AND AS REARWARDS AS POSSIBLE. You would probably agree that this means not having double wishbones at the rear. It also probably means hanging the engine out the back 911 style. Achievable, but has some packaging considerations. The newest ECU car tries push the weight further rearwards than before, including a live rear end.
(My ADDED emphasis.)
Agreed on the first sentence. From a "big-picture" approach to car design, the overall size of the car comes first (ie. L/W/H, and WB), and the overall mass-distribution is a very close second (ie. CG height, F:R weight, and Yaw-inertia mainly).
But I think you could get those right even with Double-Wishbones. However, the suspension type is of very low importance, and DWs are the most complicated type there is, so they should be the last choice. Also I reckon the right F:R mass distribution can be achieved with engine inside the wheelbase (just squashed up a lot), which then gives a lower Yaw-MoI.
~o0o~
Quote:
There are car configurations that make your assumptions work reasonably well, but they almost definitely involve powertrains currently unused in FSAE, as well as a vastly different car architecture. Not implementing these is not just a case of laziness...
Agreed that the standard powertrain layout needs changing, but I do not think it is a "vastly different car architecture". Just a simplified and squashed-up one. Like yours, but a bit more so!
It is in this area that I believe that the students are, by and large, really being lazy. It is the laziness of not wanting to break away from the rest of the flock.
So,
"Everyone else uses an off-the-shelf BIKE-ENGINE, which pushes the driver way too far forward, which then makes the rears light up with the slightest opening of the throttle. But we'll do that too, because doing anything else requires, err..., original thinking..."
There is a herd mentality that says that it is OK to spend ages designing and building a ridiculously complicated suspension system, and electronic-paddle-shifter, and carbonfibre-tub-and-everything-else, and other junk, but for some reason YOU MUST NEVER CHANGE THE POWERTRAIN LAYOUT! (Well, some do, but a tiny minority.)
Laziness? Stupidity? Whatever you call it, it is causing the performance of the cars to be stuck where they were 30 years ago. Namely, with the rear tyres on fire, while the car is all but stationary as it tries to accelerate hard out of a slow corner.
~o0o~
Quote:
The pace of improvement in FSAE is slow, with high student turnover, poor knowledge retention, and conservative design being the primary cause. But ... We are heading towards the go-kart slowly but surely...
...
- Evolution is slow and fast...
Yes, and lots of other things I would like to add. But better stay on message.
IMPORTANT POINTS for students.
1. GET THE BIG THINGS RIGHT FIRST.
2. Until you do, DO NOT WASTE TIME ON TRIVIALITIES (eg. push/pullrods&rockers, electro-pneumatic-shifters, drive-by-wire, and really STUPID things like traction-control to stop your rear-wheels spinning, simply because you did not put enough weight on them!).
3. Re-read Kevin's post above. Several times.
4. Take a close look at ECUs car. A good evolutionary change. See if you can evolve it simpler and better. (Hint: I might tilt the cylinders back by ~45 degrees, and only have ONE of them (though still ~600cc).)
~~~~~o0o~~~~~
More following ... (10k char limit!).
Z
