Supermileage Projects

[SparWeb]

Lots - O - people use MathCAD at Behrend.... I have not been converted yet.  I have seen it used before, and I was impressed.

Algebra written as algebra, and solved.
Matrices written as matrices, and solved.
Integrals integrated, derivatives derived.
Units conserved and combined.
Curve fits that spit out the equation to be used in subsequent calculations.
2Mb of spreadsheet tables replaced with 55kb of equations.

Just sayin....

[taylorp035]

Going over to mathcad would require me figuring out all of the logic and formulas that go into my excel sheet... I have never written it down before.  There is an simplified version of the calculation at a constant velocity, but its not even close to accurate for what we are doing.  Last week, I was seriously considering on trying to write it all down in one equation using integrals, sums, and variables... but I would probably run out of variables and space on a sheet of paper.  With the data entry and graphical viewing capabilities of excel, I'm happy with what I have now.  Also, we can use excel on an I-Pad at competition...

I can upload a copy of my version 2 of the MPG calculator is anyone wants to look at it.  I would rather not have it public for everyone to see, since other teams would find it extremely useful.  Message me if you are interested.  It's less than 1 mb.

[Madscientist267]

I think your best bet is to insulate the whole motor as a unit and preheat it by running it.  If you only heat the intake and carb, the fuel will just condense in the valve chamber and cylinder.  You'll want the whole thing hot so the fuel vaporizes and stays that way.

But FEED the engine air as COLD as you can get it from the atmosphere!

Cold air is more dense and results in more bang fer yer buck!

Steve

[taylorp035]

The cooler air also helps keep the intake temps down so the fuel condensates.....   We could fix all of this by using our EFI system.  But first we need to finish our rocker idea.

Sometimes I wish we were making a supermileage dragster   


I was doing some calculations so see if a turbo was feasible.... spinning up the blades takes a lot of energy, especially when looking at the amount of gas that is used in a supermileage car divided by 20 something starts.  Depending on the rpm level we are shooting for and the mass of the rotor, the results will be close.  If a turbo is in the mix, it may motivate us to start the engine less times (time for some serious bench testing).

Maybe a homemade ceramic turbo rotor could be built or even an aluminum one with a heat coating....  At least on the output side.

[Bruce S]

The energy using a turbo usually comes from the exhaust, unlike a super charger that uses a pulley/electronic system to kick it in.
IF you want to go the route of Al try snagging a few HDDs the disks in those are ultralight and can take a lot of heat, and free.
NOW if you're into building them with ceramic, that would be way cool! .

The more I dig into the rocker idea the better it looks.
It will be interesting how well going this route would allow you to tweak it.
Cheers;
Bruce S

[taylorp035]

I was able to draw most of the head for the rocker set up today.  The engine will definitely breath easier.  We are trying to use the stock valves and valve seats on this for simplicity.

Our latest budget just got passed   The new turbo was on it, so we should have it here in the next 2 weeks.... there are a lot of possibilities with this, including maybe even a mini flywheel storage set up so we only have to start the engine 10 times instead of 20.... this would allow us to run the turbo for a longer time so the spool up effects are not so great.

Would it be possible to make a vacuum sealed mini flywheel?  Obviously ceramic bearings would be a must...  efficiency would be ~60% at best if you were to use an electric motor to spin it up and generate electricity + drive wheel electric motor...  It would allow for a constant speed of 15 mph every other burn, which would allow for a big mpg boost....

If you skip the initial spin up and use the turbo via a viscous clutch to spin it up, then you could boost that efficiency to ~75-80%...

We will need to measure the rpm of the turbo with the oscilloscope.

[taylorp035]

We are now registered for competition... so far 19 teams have signed up.  I expect at least another 10-15 to sign up, if not more.  A few more teams from Canada and some other countries still need to sign up.

http://www.sae.org/servlets/collegiateCompetitionInfo?OBJECT_TYPE=CollegiateCompetition&OBJECT=CollegiateCompetition&EVT_NAME=SUPERMILEAGE&PROD_GRP_CD=STUD&SORT_ORDER=A&PAGE=teamRegistrationList&EVT_SCHED_GEN_NUM=null

Hopefully the new body design will be drawn up during Thanksgiving break... it is by far the hardest thing I have ever tried to draw.  My first attempt had 1500 dimensions and it looked like crap.  We have the design layed out on paper, but getting it into a nice 3D model is the hard part.

Else, we got our ceramic bearing on the crank shaft in the engine earlier this week.  Surprisingly, it didn't shatter, which we proceeded to take it up to 3.1 hp.  We also found that the engine maxes out at 2 hp with a AFR of 15:1 or higher... I'm not willing to go any lower, so it looks like we should have traction this year    .... as long as it doesn't rain.

[Bruce S]

I am looking forward to the new design. Are you staying with the carbon body?
If my memory serves me this AM with only 1/2cup-o-coffee  .
There was a team looking into blow-molding or injection molding to get the entire body down to 1/2 the previous weight.
Have you seen / heard of this?

Cheers;
Bruce S

[Bruce S]

Taylor;
Don't mean to possibly hijack your post but as I get nearer to building my vehicle, I have been doing some work on a 23cc gas-powered unit with a former employer who WAS and go-kart pro-racer here is StL.
We been reworking the engine to be able to accept the 160Proof and above Alky I produce and home :-).
What are you're thoughts on dual spark heads? I can certainly build the unit out of flat stock Al or pot-metal if I need to and firing the sparkies mill-second apart isn't all that hard either.
Just would like to get your experiences on this matter before I request time at the Bridgeport mills.

Thanks for any input
Bruce S

[taylorp035]

23 cc is a good choice I would think... you really only need ~1/4 hp - 1/2 hp.  If you have special fuel and higher compression, it will be more fun.  You can always throw a bigger engine in there if need be.

As for the two park plugs, previous teams have done this, as well as some other schools (university of ottawa comes to mind).  Since your friend is a go-kart racer, I am sure he knows enough to keep you out of any potential pitfalls.  I don't know how high of a compression ratio you can get out of Alky before pre-ignition, but getting the compression ratio high on a small engine is hard enough.   Is it going to be an L-Head or OHV?  What is the engine?  Obviously not a briggs... 23cc is also in the range of some high performance 1/5th scale rc cars...

As for the body, the new one will definitely be made of carbon fiber.  We hope to shoot for less than 15 lbs total (frame and body), which is how much Laval's new car is.  We are thinking only two layers, which means about $300-$500 worth of material.  We are hoping to have a female mould without making a male one first.  Hence we would need some help from a large 5-axis cnc gantry router.... which I happen to pass one everyday going to school and we have a few contacts with the company.  When we go ask them in a few weeks, we obviously need to be done with the design and have it tested in CFD.  Female and male moulds are usually valued in the $30,000 range... so we better not screw it up.  Depending on how quickly the whole process goes will determine if we use the new body this up comming year.  Currently, the old car weighs about 45-50 lbs with just the windows in it, 41 without.  This weight difference hurts us by about 100-150 mpg on a good run....

This morning, we commenced work on reviving an old flywheel based acceleration dyno.  Hoepfully we can get it going this Friday, since it isn't realistic to have the engine run at a constant speed.  A rolling resistence tester is going to be made too, so maybe we can give a good suggestion for tires on your car.

[SparWeb]

Taylor,

I hope you don't mind me asking:

What's the point of carbon fiber in the shell?

If you say "strength" then what load is it supporting?  Air loads?  There won't be more than 50 pounds uplift and 50 pounds of drag on a teardrop like that.  If you go 60 mph.  The chassis, seat, controls, battery and engine are all on the bottom frame (in last year's model).  So the shell looked like it just rested on top to smooth the aerodynamics.  The windshield is a 4-foot sheet of plexi, which is also a negligible weight, structurally.  Do you need "strength" or just "stiffness"?

I've built molds for CF parts myself.  Though none so big as your canopy.  My approach was to make a huge number of thin plywood formers, based on the cross-section of the part, cut them out, then stand them up like dominoes on a large box, also plywood.  Then box around the formers, to hold them in place.  Build the mold surface on the edges of the formers.  Smoothing the surface requires several cm of material build-up on the mold surface, but this wall needs to be stiff anyway, and the thickness works to advantage in that regard, too.  Offsets required to account for the built-up thickness of the mold wall, planned in advance when making the formers.

If you contract that out to a specialty shop, yes, I would expect it to cost 30,000 USD.  If you did it yourself you could finish in a week and spend a lot less money.  At the hardware store.

Though programming a 5-axis gantry router would be cool.  I do agree.

Composite aircraft skins do what your car body will do.  They are not CF sheets.  They are fiberglass sandwiches, with 1/4" foam core, just a few layers of fiberglass weave on top and bottom.

Something to think about?

[Bruce S]

Taylor;
Thanks for letting me drift a bit !!
Believe it or not it is an old Briggs L-head  , I'll get a pic to you if you wish. Compression I've tested at 14psi already using some of the "High-Test" stuff I can produce using ice-filtering and zeolite extraction, ice-filtering alone will get me up in the 180P easy enough.
NO problem with knock or ping at all, I'm wanting to head into the 15psi range for a more complete burn. Alky can handle this easy.

The dual-spark plugs will come into play mainly for cold weather starting, with a little tilt towards better performance/emissions.
Since this is going to need to be road-worthy I'm leaning towards cold-rolled steel tubing for the frame.

BUT This is beyond what you're posting so I will at this point and add to my trike posting.
Thanks for the assist!!
Bruce S

[taylorp035]

Bruce-    I hope you are going to put a starter motor on this.  Maybe you can model it after ours, since it is lightweight and hasn't failed us yet after 1000's of starts.


Sparweb-  We do use the strength of the carbon fiber, since the shell is integrated right into the frame.  Our window from last year was WAAAY too big, which hurt us in stiffness and weight.  A much, much smaller window is planned for the next design.  The structural part of the car is mainly to support the driver and the drive train, since the passenger usually weighs more than the car.  Also, since there is no suspension, things have to be extra strong to take the shock loads. 

Our car that we ran my first year was made of fiberglass.  It was a little bit heavier than carbon fiber, but very weak, so it was reenforced with rope and steel strips.  The shell alone was probably 40-60 lbs, and this only covered the top half of the car.  The frame was made of 0.032" aluminum and pink foam, which proved to be very, very good.  From an engineering standpoint, it was pretty much perfect.  The carbon fiber rails of last year's car were good too, but they had too much carbon fabric and glue... probably 5x too much.  A 2" tall by 1" wide 2-layer thick frame rail set up could support about 500-1000 lbs easily at 48" long.

There was a team last year that used the aircraft skin stuff, which was great for the lightness, but bad for a smooth aerodynamic shape.  It doesn't matter which way you put your "hoops" (longitudinally or laterally), there will be all kinds of aero problems.  That being said, a car that gets 2000 mpg (with an okay engine) could be built with the aircraft material or fiberglass.  The carbon fiber shell could be made for ~$300 in glue and carbon fabric + a male or female of your choice.  Building the mold as you described it is probably close to the best way without a cnc.  Female will offer a better surface finish, but a male gives you a better idea for how the car is actually shaped.  For us, this will be our last car that we get to build, so it is going to be perfect.  Based on our experience building the first car, getting the shape smooth and how you like it is an immense amount of work and is very hard to achieve.  I'm guessing about 25% of the teams last year had a CNC machine do the work...



Also, carbon fiber is very easy to work with, especially for people who have never done anything like this before.  If anything isn't strong enough, just add another layer or two and it will be fine.