Low Wing Analysis

People keep talking about the rear wing and its placement behind the rear arches.  Comments vary from "does it work like that" to "you're an idiot if you think that'll work" and everything inbetween.  After the off at Castle Combe, mud sprayed onto the bottom of the wing and the distribution of the dirt showed that the air was attached to the underside of the wing.

I've been playing around with Khamsin, a plug-in for Sketchup, and thought this might be the starting point for some analysis.  I drew a basic side profile of the ADR, extruded it out and added in the wing elements in the appropriate place.  It's amazing how quickly this sort of thing can be done in Sketchup!  I made three components (body, main plane and flap), copied them into a virtual wind tunnel, configured Khamsin and started the analysis.  The results clearly showed that in the centre of the car, the rear wing is working effectively.

Rear Wing Centre Section

I then did the same using the shape of the rear wheel arches and, whilst the effect isn't so great, the wing is still clearly effective.

Rear Wing Outer Section

What intrigued me next was to see what a 500mm diffuser would do to the results, so I drew one and re-ran the simulation.  The results were dramatic with the rear wing driving the diffuser hard.  The figures showed that the downforce had increased by 45% and the drag had reduced by 11%!  Admittedly, this is far too simplified to be taken seriously, but it correlates with the "mud-viz" used at Combe and suggests that a new diffuser will really improve downforce for little or no drag penalty.  It's next on the list!

Big Diffuser

2013 Llandow Sprint

Clay Pigeon isn't my only bogey track.  I'd not made it to Llandow either, aside from a half-day test session last Summer.  I had to pull my entry thanks to a wheel failure and a breakdown in the tow car last year, just like Clay Pigeon.

This year, I arrived to find a rather damp track.  It wasn't wet though, so the slicks stayed on.  The track was slippy, but I discovered the kerbs were slippier when I touched one and exited stage left (but right side first).  Side-stepping the clutch soon got me back underway and I somehow finished the first practice run fastest in class.  Clearly everyone else was running wets or having a slow start.

In second practice, I managed to stall the car going to the line.  My starter pack was helpfully retrieved by Nick (cheers!) and I was able to restart the engine.  Coming down the back straight on the second lap, I could hear a loud metallic vibration and I saw red flags waving.  Slowing down, the noise abated and I saw Tom's car stranded next to the track, a victim of an ECU failure.  As I slowed down, I started to feel the vibration much stronger and it felt like a wheel was going to come off (again!) so I stopped.

After hopping out the car, I could see nothing obvious and the wheels were attached.  As the Clerk of the Course arrived, I spotted the swarf beneath the chain.  The tensioner had failed again and the car was immobile.  The only recovery at Llandow was a rope on the back of the truck, so I hitched a lift back to the paddock and recovered the car on my trailer.

Having annoyed all my fellow competitors with a 15 minute stoppage, I returned back to my paddock space to find a bunch of them stood around wielding pry bars, drills and screwdrivers.  They were out to get me ... on track!  This is what club motorsport is all about and a load of truly awesome people skipped lunch and got up to their elbows in oily stuff to get the car fixed.

Dave provided a pry bar to get the tensioner un-tensioned and it was soon in my hands.  A few swift blows with a mallett and screwdriver got it close to its original shape, but the bottom was properly mangled and needed Brian's file and Julian's trailer-mounted vice to get the sprocket spinning again.  Once back in place, a new strap was fabricated from scraps of aluminium and screwed in place with Andrew's screws.  A piece of aluminium angle replaced the missing metal on the tensioner mount and after fitting my new chain, the car could drive again.

The rattle I'd heard down the straight was a different problem.  I discovered the cause as the car was recovered onto the trailer.  A floor bolt had come adrift (probably on one of the kerbs) and the floor was hanging down.  A suitable replacement couldn't be found, but ample lockwire did the job.  I was ready for the timed runs and I was almost due out.  Julian didn't get to his car until Nick brought the double-driven car back into the paddock to swap drivers.

Heading out in the first timed run, I had a few gear selection troubles, but I put a time in and that was good enough to lead the class by 7 seconds.  It was raining during the run, so there was the chance I could be beaten - I've seen people gain 7 seconds on the last run when conditions have not changed all day.  I had to do another run, whether the car would do it or not.  It was dry now and the sun was out.  It wasn't a great run, but a second improvement was enough to take the win by a big enough margin for 21 points.  I'd have been lucky to get more points by breaking the record!

A testing day, but the end result was a win and an extension of my ASWMC Sprint Championship lead by a whole point and that's all I could have hoped for.  Here's the video to see my maladies.

2013 Catch the Pigeon Sprint

It's my bogey track.  I entered twice last year and missed both.  I broke the ADR the event before the first round at Clay Pigeon and didn't get it fixed in time.  At the second event, I got almost all the way there before my tow car left me stranded.  This time, I saw the paddock, so it started well.  I also managed to walk the track, so that was good too!

In first practice, my camera wouldn't start, but I recorded a time that was close enough to be happy, despite catching the throttle under braking and nearly leaving the track.  Second practice left me filled with confidence.  So much so, that I had a spin at the second corner.  Still, the second lap was quick, so that was good news.

In the afternoon, there were three timed runs and I needed them.  On the first corner of the first run, the throttle stuck open and I was lucky to keep on the track.  I hit the kill switch when I was sure the throttle was sticking and got a tow in - better to do that than bin it or pop the engine.  After some investigation in the paddock, I couldn't see anything that was causing the sticking.  The throttle cable was in perfect condition, there was no snagging and the movement was fluid.  Was it my foot that had done it?  Unsure, I headed out for the second run.  I had three runs, so I could afford to cruise around and give myself enough time under braking to dip the clutch and hit the kill switch if anything went wrong.  What I didn't plan to do was hit the kill switch on the up-change out of the final corner of the first lap.  Needless to say the kill switch is being moved before Llandow!

That left it all to the final run and I still didn't know if the sticky throttle was the car or my foot.  I took a tentative first lap and then pushed harder on the second lap.  I'd broken the class record, but not by as much as Luke Trotman, who took the win in his Mallock.  When I got home, I discovered that the data logger hadn't worked and I had no data, so the data debug will be limited and a new logger is on the list of things to do.

The only data I have is gathered from the video, so I've taken apex speeds and peak speeds on the straights.  Top speed was just 68mph and the lowest speed was a paltry 26mph.  It's safe to say this track is not dominated by aero.  In fact, it probably has very little effect at all.  The average apex speed was 35mph and the average top speed on the straights was barely over 50mph.

Here's the video.

2013 Great Western Sprint

Mallory Park wasn't the best start to the season, going home after the convoy runs.  I bought some part-worn wets during the week to be sure I didn't have to go home if it rained.  Yet again, it snowed!  Luckily, despite the temperature and precipitation, the car was able to run on the new (but very old) wet tyres.  I don't know how old they were, but they're supposedly Formula Renault/BMW tyres, so they were not that soft when new in hillclimb/sprint terms and I discovered that these are particularly non-soft when I saw that the car was only generating 0.7G in the corners!

I didn't manage to complete practice without missing The Esses on the first lap and having a big oversteery moment on the exit of that same corner on the second lap.  Every other corner was nearly as bad and I was experiencing wheelspin in every gear down the straights, barely breaking 100mph all the way through.  On the first timed run, I managed to nurse the car all the way to Bobbies on the second lap before out-braking myself and missing the chicane.  That left everything to the final run and it dried out sufficiently that slicks were viable.  I went substantially quicker, but a rear wing mount sheared on the second lap causing a big vibration at the rear and I lifted off down the straights, wondering what it was.  Despite this, it was good enough for the class win and a good haul of points in both the Bristol Speed Championship and the ASWMC Sprint Championship.

So what can I learn from this?  Let's compare the best run this year with last year's best.  The weather was much better last year, but this was before the hubs/wheels were upgraded and before the rear wing was altered.  The first thing to note is that the run was around 15 seconds slower this year; an absolute age.  Off the line, I lost 3 seconds in the first 80 metres.  This is no doubt down to the freezing temperatures and because the tyres had not been used at all that day and as a result had no residual heat in them.  After 40 metres, I was 14mph slower this year, yet by 230 metres, I was just 3mph slower.  The car was clearly accelerating better, notably moreso at higher speeds.  At this point, I missed a gear change and lost a bit of time.  Unknowing of the conditions, I then proceeded to lose two whole seconds over Avon Rise and in the braking zone for Quarry.

Start to Quarry

The apex speed for Quarry was 8mph down on last year, but by the end of the farm straight, just 4mph slower.  That loss in apex speed carried down the straight lost a second before braking for The Esses.  The braking point was similar but, interestingly, the deceleration was greater this year, showing there was scope for improvement last year.  The first apex was 8mph slower than last year and the second a whole 10mph slower, possibly because I'd straight-lined the bit between the apices a little too much and that made the second half artificially tight.

Quarry to Esses

The acceleration out of The Esses meant I was travelling just 3mph slower at turn-in to Old Paddock, but instead of taking it flat, I took a heavy lift, losing two tenths through the corner and being 13mph down on the exit.  By the time I got off the throttle heading towards Tower, I was just 3mph slower, but 6 tenths had been lost in the process.  A further 7 tenths escaped before the apex at Tower, where I was 5mph slower on the apex.  This, however, allowed me to get on the throttle earlier and the speed to Bobbies was matched, although 3 tenths had ebbed away before that happened.

The Esses to Bobbies

Into Bobbies, I braked a little earlier this year, but only a tenth and a half lost.  At this point, we reach a corner where this year was quicker.  A 13mph higher apex speed led to a gain of half a second over last year's time.  By the exit, the speeds were matched and this continued all the way to the same braking point for Camp.  A quicker transition from throttle to brake led to a slightly lower speed this year and I stayed longer on the brakes, resulting in an apex speed 5mph slower and 3 tenths lost.  A further 3 tenths went on the way to Folly, by which time the 9mph difference from the exit caused by a late apex had been reduced to just 1mph.  I lifted through Folly as I heard the rear wing chattering on its mounting.

Bobbies to Avon Rise

Instead of going flat over Avon Rise, I braked being up to 25mph slower than last year and this cost two seconds before the apex at Quarry.  The chattering noise at the rear was unnerving and I wasn't sure of the cause at this point.  Despite being 8mph slower at the apex of Quarry, I was going quicker at the end of the Farm Straight.  I braked slightly earlier, losing a tenth, but carried good corner speed through The Esses.  This good speed through The Esses compromised the exit speed and half a second was lost to Old Paddock.  A lift through Old Paddock again lost 6 tenths through Hammerdown.

Avon Rise to Hammerdown

I lifted early again for Tower, coasting to the 6mph slower apex and losing over a second in the process. Interestingly, I braked 30 metres later for Bobbies, partly because of the lower approach speed, but also because I carried 13mph extra into Bobbies, which gained half a second.

Tower to Finish

In summary, it appears that I've learned a bit more about how much pace I can carry into Bobbies, but that I was more tentative than I needed to be through the rest of the lap.  It also seems that the car is quicker in a straight line, which suggests that the rear wing relocation has been successful in reducing drag, even over the small wing used last year.  It's hard to see if grip has been reduced as a result of the downforce because of the vastly different conditions.

2013 Mallory Park Sprint

I just about made it to Mallory Park on Sunday for the first sprint of the year.  I arrived soon after 08:00 to find a big queue for scrutineering.  True to form, I got to the scrutineering bay just as the drivers' briefing started.  Immediately afterwards, I hopped into the car for the convoy run.  Having spent some time playing with the gear linkage after the problems at Llandow last year and having had a misfire on the Friday night, I was keen to do a systems check from the driver's seat.  The gear linkage is fantastic with a tactile feel and each gear engaging with an encouraging click.  The misfire had also gone, which was good news.

Less good news was that it was damp and I was on slicks that were still at 25psi for travelling.  Wheelspin at part throttle in 3rd gear is not what I'd call normal.  Worse was to come though, as whilst waiting for my practice run, it started to rain.  Rain quickly turned to snow and I was on slicks.  Seeing rooster tails from the other cars, I decided to call it day as I have no wets and went home.  Strangely, just a few miles away at Curborough, it was bone dry - I should've tried to get a late entry on the way home!

Mallory in the snow

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