New race car build

[sebring67]

Hello all,
This is my first post on the forum, so hello to everyone. My back ground is racing classic cars, MGBs in particular but i have a new rather different project for the 2017 race season which i could do with some advice on.

The car is a grand prix midget, these in case any of you dont know are single seater race cars with inline 4 max of 1.4L engines with very open rules regarding chassis design, suspension, aero and virtually everything else. I bought a chassis as a base that was first built i believe in the 1980s then i gather it won a number of championships including the worlds at some point. Since then things went rather down hill for it so i have stripped it down and i am basically starting again from the basic chassis.

The overall design i am aiming for will be rather like a slightly smaller F1 car. The chassis,as is places the engine at the rear, it has independent double wishbone suspension at all 4 corners with coil overs and disc brakes again at all 4 wheels. The chassis itself if made up of tubular steel and did have a "skin" of 1.5mm aluminium sheet. But as i said i am starting again with it so the old body has gone and i am building a new one. I have purchased a F1 front and rear wing for the car but i will be constructing the nose, body and side pods myself. I am of course aware F1 parts e.g. wings are for want of a better term "compromised" by the rules the designers have to follow so i have been very careful about what i have bought so far. I have also puchased a prototype section of one of the Brawn F1s blown diffusors (the section of the diffusor where the exhaust exits) and plan to build that into the cars diffusor. I am not sure however what to build the cars flat floor and the rest of the diffusor out of, what are peoples thoughts?

Kind regards

[Gatecrasher]

Which F1 front wing did you get without a nose ? F1 aero is designed for high speed. A 1.4ltr might not be enough

Pics first of what you have please

[sebring67]

Hi,

Thanks for your reply, il get you some pics of the front and rear wings when they arrive in the next few days. I know the rear wing was a high downforce varient used at Monaco by williams. Similar for the front too.

The 1.4 is pretty highly tuned, forged bottom end, dry sump, crank fired ignition, tapered throttle bodies etc approx 190 bhp. The car will weight between 375 and 390kg.

Thanks

[Pierce89]

Depending on available funds I'd do the flat floor either from aluminum sheet or if in the budget carbon fiber.

[sebring67]

We have a reasonable budget for the car, its mostly about trying to get the best material for the job, i had considered carbon but was also looking at one of the various aluminium honeycomb products?

[Tim.Wright]

Consider that the lighter you floor is, the higher your CG will be.

I would only go super light weight on the floor if you know you will be cutting things fine on the minimum weight.

Custom composite parts are a good way of sucking up money which would be useful for other things like a suspension system designed to carry the aero loads which were not considered in the original chassis design.

I don't really see the point of the F1 diffuser as its one of the most heavily restricted aero components. Also, that diffuser was designed to be fed by a vertical opening in the floor to get around a loophole in the 2009 regs. If you aren't working to the same regs and/or your upstream geometry isn't the same as the original car I can't see the diffuser working well at all.

[sebring67]

Hi Tim,

Thanks for your reply, i totally agree with your points regarding C of G and spending avaliable funds on things that are likely to make more of a difference overall. Im just looking at material options at the moment.

With regard to the blown diffusor the section i am reusing from the F1 car is literally just the exit of the exhaust as is "blows" through the proximal part of the diffusor. Not the diffusor itself. I am building the diffusor and that is not a copy of an F1 diffusor. The car itself is around 2/3rd the size of an F1 car and should be capable of going fast enough to make a blown diffusor worth experimenting with.

With regards to the flat floor, my concern with using aluminium sheet is it would need to be around 3 - 4mm thick in order to be rigid enough not to flex along the less supported sections and with a car as i said above not that much smaller than an F1 car we are talking a fair bit of weight there.

After work today im planning on working on the design of the side pods. I am fitting the aluminium rad in one side pod and the oil cooler in the other side. Both placed at an angle and ducted so that air enters the side pod, is ducted to flow through the rad/oil cooler, the question is what to do with the air then? i have considered ducting the air post rad for example then downwards to the floor of the side pod then have a exit within the flat floor with ducting/strakes that direct that air flow into the start of the diffusor along with the exhaust gases. So effectively you would have the exhaust exiting mid floor just as the diffusor starts and one exit either side of the floor again at the start of the diffusor for the air from each side pod.

Thanks again

[Tim.Wright]

Aluminium honeycomb might be the answer for the underfloor. It's nice and light but it can be bulky. A 5mm thick pamel would probably do the trick but I don't know if it's available in such a small thickness.

Alternatively - use 1.6mm sheet and reinforce the unsupported sections only with bonded on ribs (bent lengths of alloy with an omega cross section).

In the end, if the floor really is completely flat it shouldn't cost too much to do it in composite.

[sebring67]

Thanks Tim,

I will see if i can find a souce for honeycomb that sort of thickness and compare the price of that with composite i think (the floor is absolutely flat from the extended section part way along the nose, under the cars mid section, to the edges of the side pods right up to the start of the diffusor.

Its a really interesting project because essentially the body and chassis design inc wings, diffusors and really everything else is totally reg free essentially. It actually makes designing the car more difficult in some respects.

Any thoughts anyone on the side pods?

[Jolle]

Just a thought, with the freedom of the rules and to keep things a bit simple (a blown diffuser needs also a engine mapping, else it will work against you), is a copy of an early lotus ground effect floor not better and easier to construct/calculate?

[Tim.Wright]

I don't have much to add on the aero as it's not my field of expertise.

Yea, really open rules can be more difficult to take the first steps. What's the class and what kind of tracks do you run on? What tyres are you running and what's the minmum weight?

[sebring67]

The class is Grand Prix Midget oval racing, they are single seater race cars, usually home built or converted from other cars e.g. formula fords, westfields etc as a result the cars are very varied. Some rear engined, some front and other have the engine situated at the side of the car along side the driver......

The rules are essentially as follows:
- Inline 4 cylinder max of 1.4L engine from the approved list
- Pump fuel only
- Normally aspirated only
- No porting of the head is allowed
- Valves, springs, cams, carbs are free
- Rear wheel drive only
- Locked, LSD or open diffs
- Gearboxs are free
- Supension design entirely free other than having a minimum travel of 3" at each corner and dampers may only have single adustable valving.
- No 4 wheel steer
- Wheels and tires entirely free other than having a max width of 10"
- No wings that are adjustable while the car is moving
- Body, aero, wing shape/design/ number otherwise entirely open.

Thats basically it rule wise apart from safety bits and pieces.

Regarding the blown diffusor i agree it may be easier to run a plain diffusor but its something i would like to experiment with and yes there is the issue that it does add anything when the throttle is off which is ironically when you typically need more rear end grip i.e in the corners but its something im going to try and see what i can do to get around that problem if possible.

Thanks again

[cheechthechi]

Take what I say with a grain of salt as I'm not a seasoned aero designer (perhaps Andrew Brilliant or one of the other guys will comment on this thread), however here is my take. Before you start designing your system it would be helpful to figure out your design constraints and what exactly is needed to make the car fast for the style of racing. One of the biggest mistakes I see guys in grassroots motorsports do in terms of aero is copy ideas from professional motorsport and expect it to be a good solution for their cars. What you have to remember is that at the professional levels, racecar aero is optimized to the rule set, so the the solutions that arise may not necessarily be the best for your car.

Having said that, one of the biggest defining constraints I think you'll run into is power output. It seems that the rule set dictates naturally aspirated 1.4 litre engines. I assume then that you'll probably be power limited to under 300 hp, which means you won't be able to explore options that are typically more drag intensive (aggressive wing and large tunnel setups).

Another few constraints you have to figure out: what tracks are you racing on and how fast are your top speeds at these tracks? What are the high speed handling issues that you are trying to solve? Does the car nee more front/rear grip? Does the car need lower drag so it can get a higher top speed? Is the car pitch sensitive?

Assumptions and generalizations are hard to get correct, but here are some that I have found (in my limited experience) to be somewhat valid:

- Focus on underbody/ ground effect based aero (splitter, flatbottom, diffuser etc) as it tends to give higher df to drag results than a wing centered setup
- Complexity is not always your friend. A properly sized simple diffuser will outperform most of the blown diffusers you'll see at the track (as they have not be designed based off testing and data)
- Rear df is easier to make than front
- A data logger is the best first investment you can make towards aero development
- Given equal drivers, a simple aero setup that is designed with testing and data will outperform 90% of the aggressive setups seen at the track that were based solely on copying high level race series


Finally, since you are oval racing, if you wanted to look at professional series to get an idea of general trends they do with aero then I would look at champcar, indycar, and nascar. Remember that all these cars have been designed to optimize the car within the ruleset of the series, but if you are careful you can see trends (for example on a Nascar racecar how do the setups change from a high speed oval to a low speed oval?)

Hope that helps, good luck, and most importantly have fun!

[bhall II]

Regarding the blown diffusor i agree it may be easier to run a plain diffusor but its something i would like to experiment with and yes there is the issue that it does add anything when the throttle is off which is ironically when you typically need more rear end grip i.e in the corners but its something im going to try and see what i can do to get around that problem if possible.

Something to consider: F1's first generation of blown diffusers was abandoned, not because of any changes to the regulations, but because they tended to destabilize the car due to the on/off nature of downforce that's reliant upon the application of throttle. It wasn't until off-throttle blowing was introduced that the concept was made truly effective, and even then, it came at the cost of reduced horsepower and fuel efficiency.

In your case, I think the gains would have to be massive in order to justify the time/effort/resources you would spend trying to make it work.

[sebring67]

Hi,
Sorry about the limited reply but im at work at the moment. I really do welcome everyones input so thanks for the above post.

Some additional info that maybe helpful regarding the car and the type of racing:
- Regarding power we are talking about 200 bhp at least in the first year but i agree there is probably a max of 300 realistically.
- Likely weight of the car wet with driver 380 kg
- Top speed on circuit currently around 80 mph, however there is considerable scope for this to be higher, a fair amount of the current cars have little to no aero, of the cars that do have wings a fairly common set up is a Caterham like car with a huge Brisca F1 type rear wing fitted above the driver running on 9" wide avon slicks.
- The oval circuits vary a fair amount some banked other flat, some very small and tight others moderately large.
- The primary issue with most cars currently is lack of any degree of cornerings speed. It is not uncommon for most cars to apply the throttle down the straight and essentially free wheel around the corner then not apply the throttle again until the car is 1 to 2 car lengths out of the corner. Iv been racing for 20 plus years (250cc gearbox karts to circuit racing classic cars) and was amazed by the lack of cornering speed when i first saw these cars.
- I have a race technology dash 2 with DL1 data logger to go in the car.

Thanks