I attended Formula Bharat in Coimbatore, India last month and thought I should comment on a few
technical things I noticed. The standard of the cars in the mid pack and lower end seems to have
improved, but again we saw so many unfinished projects brought to the event.
I am sure this is not what the teams imagined when they commenced their build a year earlier!
So this is clearly a failure of project management. So many teams wasted time doing what I call
‘Chasing Butterflies’ that is, getting distracted by stuff that has no bearing on the result.
A big culprit here is teams trying to incorporate an aero package.
Unless the team is scoring well (more than 800 points) and are searching for some more points,
a poorly designed and constructed aero package just consumes valuable time.
Remember Pat’s advice! There are three things you need in a successful team, People, Money and Time.
You can always get more people and more money, but you cannot get more time.
Nine women cannot produce a baby in one month!
As usual, the twin ‘mortal sins’ of rod ends loaded in bending and excess rear toe compliance were
commonplace. Rear toe compliance (and its twin brother, excessive assembly clearance stacking) makes
the car almost undriveable.
Teams should concentrate on ensuring the rear wheels cannot steer when cornering, driving or braking
loads are applied.
The solution does not need to be big and heavy, just smart design to ensure the rear wheels stay pointed
in the direction the designer intended.
I noticed several cars where the hydraulic ratio of the brakes was too high.
A mismatch between master cylinder and caliper piston diameters meant the brake pedal was long and
mushy and in a couple of instances, it was quite easy to turn off the brake over-travel switch with a good
solid push on the pedal, this despite the brakes being properly bled.
A shift to larger diameter master cylinder(s) would result in a harder pedal with shorter travel.
The drivers would surely prefer this and there is less chance of a DNF due to tripping the over travel
switch.
Whilst on the subject of Master Cylinders, many of the cars seen were fitted with a tandem master
cylinder, sometimes with diagonally crossed brake lines.
This might be a fine solution for a little FWD hatchback, but has no place on a FS car. Remember, the way
the Rules are written, the brakes on a FS car must stop the wheels (rather than stop the car) before the
car can compete in the Dynamic events. The light weight, grippier tyres and very different weight balance
of a FS car means it will be almost impossible to lock all four wheels in the brake test when using a
tandem M/C. Twin master cylinders, sized appropriately and connected to the pedal via an adjustable
balance bar is the universal solution.
Again, the engine of choice was the KTM 390, with a smattering of Honda 250s.
The use of a Harley Davidson V twin by one team did make me smile.
The KTM and Honda singles are very highly tuned in standard form and this must be taken into account
when adapting them to FS use.
Both engines use large diameter throttle bodies and unadjustable ECUs. The first issue is, if the team wish
to use the standard T/B, the airflow through it will saturate the restrictor at less than 50% opening.
This was a very common situation despite my highlighting the issue (with pictures) after last year’s event.
Find that thread on the 'FSAE Advice and Support' group on Facebook and read it again.
The T/B needs to be replaced with one more suitable for the application. The smaller KTMs have a
suitable unit as do the different 150cc fuel injected motorbikes and even the Royal Enfield T/B at 30mm
can be adapted. For teams really on a budget, a recycled T/B from Tata Nano car is 30mm, about the
right size.
The KTM has the injector in the throttle body as standard. Teams should probably retain this, but remove
the butterfly, shaft and TPS sensor. Make sure there are no air leaks in this area after the modifications.
Connect the TPS on the new T/B to the ECU.
The standard ECU poses a problem as the fuel map is not suitable for the engine as adapted to FS use.
The KTM (and Honda) engines have a very high compression ratio in order to generate torque when in the
bike.
To prevent detonation, the A/F ratio is set to about Lambda .85, or 12.5 to 1 stoichiometric if you prefer.
This is normally seen as a very rich setting and the situation is made worse in FS specification by the
restrictor reducing airflow.
It is unlikely that an aftermarket ‘piggyback’ ECU controller will have enough resolution to properly tune
the standard ECU for FS use. The real answer is a programmable ECU and some time spent on a
dynamometer to properly tune the fuel mixture and ignition timing with the restrictor.
Keeping in mind the very high compression ratio in these engines, if tuning on a dynamometer, reject the
notion of tuning for ‘lean best power’. Retain the makers setting of Lambda .85 or you are courting a
disastrous engine failure, as one team did after only two laps on the track!
Tuning a KTM to Lambda 1.01/1.02, even with an appropriate T/B, ECU and plenum design will kill the
engine! You have been warned.
I saw several teams with a flat plate restrictor (some even with a carburetor,
but I will talk about that in a few minutes).
A flat plate restrictor absolutely kills airflow into the engine.
Simple research about gas flow through a plate restrictor will introduce you
to something called ‘Vena Contracta’.
Study the effect and take appropriate action with your restrictor design.
An angled approach and departure cone from the restrictor will recover most
of the lost flow if designed properly. Again some research on gas flow
through restrictors will steer a team in the right direction.
Or you could just copy what the fast guys use.
Do not inject the fuel before the restrictor.
Adding fuel to the air flow will reduce the air mass through the restrictor.
One team at FB moved their Kato throttle body up to the entrance of the air
intake, before the restrictor, plenum and intake tract.
They retained the standard injector in the T/B. This would have three big
drawbacks.
Firstly, there would be catastrophic throttle lag,
Secondly, they were pulling fuel through the restrictor as discussed above
and finally, the air/fuel mixture in the plenum would make a powerful bomb
if the engine backfired through the intake valve!
Okay, carburetors.
Firstly, by design they will require you to pull the fuel through the restrictor
with the air. That’s potential power thrown away right there.
Secondly, carburetors work by accelerating the airflow through a venturi,
therefore lowering the pressure and so drawing a carefully measured
amount of fuel through the jets.
Having an even smaller venturi (the restrictor) after the carburetor, does
horrible things to the airflow, making it almost impossible for the carburetor
to carburate. Don’t do it!
Speaking of airflow.
Air has mass. A cubic meter of air (a tea chest full) weighs more than a
kilogram!
If air has mass, then it also has momentum.
So, why would air change direction by 90° just because you would like it to?
Air will not just turn and go through a radiator that is mounted at 90° to the
airflow!
The radiator needs to be sealed in a properly designed duct (more online
research required) and if you choose to put a fan at the back of the duct,
don’t mount it direct to the radiator, move it back a little bit!
A few teams were still using the Royal Enfield 500 air cooled engine.
Placed in the normal position, this poor engine has to live in the air shadow
of the firewall. It will be starved of cooling air and after a little running, it
will overheat because those uncooperative little air molecules will not turn
around behind the firewall and blow through the cooling fins as well as
carrying away the heat generated at the front of the engine by the exhaust
pipe.
If I were designing a FS car with an air cooled engine, I would consider making a ‘sidewinder’, that is, mount the engine beside the driver where it could be exposed to the air stream.
That’s all for now. If something more comes to mind, I will make another post.
Pat
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