Ever wondered how to design a land speed record winning vehicle?

On the weekend of 22/23 May 2010 team Runningblade took the World Land Speed Record for lawnmowers. The magnificent machine was driven by Don Wales, grandson of Sir Malcolm Campbell, on the legendary Pendine sands reaching a speed of 87.833 mph and taking the record for the British team.

Pendine sands at 90mph on a mower!

The original idea was the brain child of team chief Steven Vokins, who’s day job is playing with cars at Beaugleigh Motor Museum, and I was thrilled when he asked me to come on board as technical advisor.
Making a genuine lawnmower do that speed is no mean feat, the machine was built by seasoned mower racers at Countax in their spare time, a quite magnificent effort which not only goes damn fast but is also very stable at speed, looks good and even cuts grass!
In fact part of the regulations required us to cut some grass before the speed attempt, so the lawn outside the Pendine Museum of Speed benefited from a quick trim in front of the world’s media. Currently the museum houses Bluebird, Malcolm Campbell’s land speed record car from the ’20s, so it’s fair to say there is a lot of family history there.
Runningblade also raises funds for two heart charities, so please look at the web site and spread the word. The record breaking run was witnessed by the previous record holder Bob Cleveland who has vowed to take the record back to the USA next year, but he also raised over 1000 dollars back home for our charities, now that is a damn good sport.

Designing a land speed record machine is a skill hard leaned by the pioneers of speed, luckily for us we can draw on their incredible tales to reduce the amount of pain we have to endure. The same rules apply no matter what sort of machine is being designed; stability at speed is essential for safety and to allow the pilot to apply full power, secondly you need to balance power and drag so you can reach the target speed in the distance available.

Early concept work with key parts held roughly in place.

Most speed machines gain stability by using a very long wheel base, in fact it’s the ratio of the track width to the wheel base length that influences the twitchiness of the car, or yaw stability if you prefer the technical term. But making a car to narrow makes it easier to roll, so we start by setting the track width then altering the wheelbase to suit.
The width is a big problem though, for speed we need to make the frontal area as small as possible so it pushes a small hole in the air. Air is heavy stuff, each cubic meter (about the amount of air under a coffee table) weighs about 1.1 kg, driving at 100 mph means that the average car (2 square meters of frontal area) is pushing 110kg of air out of the way every single second!
The ease or difficulty with which it manages to move the air is down to the shape of the car, sleek slippery shapes carve through the air but brick shapes shovel the air in front of them in a massive pile of pressure slowing the car horribly.
And here is the first problem; lawnmowers are traditionally shaped like tractors with a brick shaped bonnet. Luckily Countax make a fairly well streamlined bonnet which became the starting point for the whole vehicle. We also leaned the driver back as far as possible, unlike race cars the view forwards is surprisingly unimportant, usually they are looking a long way in front and so they can be sunk deep into the vehicle with their eyes at bonnet height.
In fact getting everything as low as possible is vital, a low centre of gravity helps stability and crucially reduces the effect of side winds. One of the great problems with a land speed machine is that the aerodynamics are set for minimal drag which means minimal down force, so at very high speed even a slight side wind can blow the car badly off course.
This means that land speed record cars run with a fairly high weight to hold them down at speed, the complete opposite of nearly every other form of motorsport. It’s not that we add weight, more that we don’t try to minimise it, making the structure very strong and the such like. Where the weight sits is very important though, we try to put the majority of the weight over the front axle so the steering wheels have grip, the worst case is the front going light at speed because then the car can spin and roll or on faster machines could flip over backwards. Loosing grip at the back makes the car twitchy and with rear wheel drive obviously acceleration is lost but generally the car stays on course. Going back to the problem of side winds, as the wind blows on the side of the vehicle the most force is applied in the biggest side area, on a mower this would normally be somewhere at the back of the engine area, the point where the car is pushed is the centre of pressure. setting the centre of gravity in front of the centre of pressure means the car is more stable, that’s one of the reasons why proper land speed record cars have a big tail fin.
Brum brum, beep beep...

With all these factors in mind one of the first things we did was to lay all the main components on the floor and get Don to sit on the seat so we could get everything in the right place. Apart from being a useful exercise it is also very funny, and yes we did force him to hold the steering wheel and make brum brum noises.
So now we had the height, width and length sorted out it was time to resolve the details, the most important one being the tyres. Again we have a dilemma, bigger diameter makes a smoother and more stable ride, a wider tyre reduces ground pressure on the soft sand which reduces rolling drag. But the greater the tyre frontal area the greater the aero drag. The decision was constrained by the fact there are no standard lawn mower tyres rated for 100mph, so we had to use ordinary car tyres. Tread pattern is critical on sand, to minimise power lost in breaking up the beach surface we needed the least aggressive tread pattern possible, we even considered slicks at one point, which may seem surprising. But remember we are not doing any cornering, just a straight line, and too much lateral grip could be a problem if it makes the steering too twitchy, if the vehicle does spin it is
Testing, testing and more testing, one day is not long enough.
desirable for it to slide rather than dig in when going sideways to avoid rolling.
Indeed, to stop the steering being too twitchy the rack ratio is reduced making it a lot slower to turn and increasing the turning circle many times.
With all these factors set, we needed to sort out the shape, the aerodynamics and crucially the drag dictates the power required from the engine. At this point well funded teams would model the vehicle on a computer and hone the bodywork in a virtual wind tunnel. We weren’t well funded so we had to do it the old fashioned way, we built a prototype and drove it down and airfield to see how fast it went. Using a data logger lent to us by Racelogic we could see how fast the vehicle accelerated and get accurate top speed readings. As we knew the weight of the vehicle and the engine power curve it was fairly straight forward to work out the drag coefficient.
Who needs a Stig, we've got a Don!

My good friends at Dunsfold Park, home of the Top Gear test track, very kindly let us use the runway for a day. It’s amazing how much work is required before a vehicle can actually drive onto the track, after arriving and unloading the van the initial checks are made and fuel added, I mounted the datalogger and set up the GPS speed reading. Don suited up and the engine was warmed up, that fairly large single cylinder mower engine sounded quite meaty with a race exhaust. A couple of low speed runs warm up the transmission and then it comes back in to check nothing is leaking before the propper test run.
Tring different seat hights and wind deflectors.

The prototype peaked at just over 60mph with a 27bhp engine, which may not sound impressive but it gave us the drag info needed to design the real deal. The prototype had another job to do too; every world land speed record team struggles to find the cash to go on and a vital part of the teams work is generating publicity and generating support, in fact if you saw Runningblade at the launch party at Beaugleigh you saw the prototype, the final version was still being built at that time.
A man with a blue helmet, behind Don is another Bluebird.

One key ingredient is power, in fact more than any other form of motorsport power is critical, and wee needed more. To cover the measured mile at the target speed the vehicle needs more power than you might think, first of all it needs enough power to maintain top speed as it overcomes drag and mechanical losses, but it also needs extra power to accelerate the vehicle comfortably in the run up zone. Not only this but the engine will be running flat out for a long time, so it needs to be able to generate this power reliably but also maintain it as everything runs at maximum speed and temperature, so a degree of safety margin is required and it is common to use an engine with at least 10% more power available than you need.
The problem on this project was the need to use a real lawnmower engine, these usually have the cylinder flat and the crank vertical to drive the front belt pulley. There are not many high power versions about. The 27bhp engine in the prototype was one of the biggest available, but this only gave us half our hoped for top speed, the trouble is the force due to air drag on the front goes up with the square of speed, and worse the power needed goes up with the cube of speed. So to double the top speed we need eight times as much power!
The bigest vertical crank mower motor we could find.

To meet the challenge we needed to drastically reduce the drag as well as increase the engine power. Kawasaki had just launched a new big mower engine and being fabulously helpful lent us one of the first in the country. This mighty 1000cc V twin engine produced well over 40bhp as standard and with a few tweaks we eventually got about double the power of the prototype.
To get the drag down the final version of Runningblade was slightly lower and narrower, the seat canted back a touch and the wheelbase extended to cope.
By now all funds and time had been exhausted, we had booked Pendine sands and the worlds media were pouring in, it was now time to prove we could do it even though we had no time for any final testing.
The view ahead. You need to double click and see this bigger to get it.

Pendine is a fantastically evocative place, there has been so much triumph and tragedy here and Don’s family ties are so great that the land speed museum there houses many of his ancestor’s artefacts. Tides dictate the days timing, as the water goes out it takes time for the moisture in the sand to ebb away, if you drive on it too soon it is too wet and the car will bog down, leave it too late in it is dust and the car digs in, there is a fairly brief window of opportunity of about an hour where the sand is firm and speeds are highest. As soon as the tide has gone the first job is to clear away all the debris by hand to prevent ‘foreign object damage’ or FOD, clearing the drift wood, shells and rubbish is known as fodding and a sterling band of volunteers form the local scouts assisted in this back breaking work. At the same time the course is laid out with the start and finish ‘gates’ being marked out and the electronic timing gear set up and tested. A FIA sanctioned timing official was hired for the day so we could give Guinness World Records verifiable data. Much of the setting up and moving kit about on the beach was done by the local Discovery Owners Club who’s help was vital, they also posted cars at set points on the course to act as emergency aid just in case.
Whilst all this was going on the mower was equipped with it’s cutting deck and a witnessed mow of the museum lawn took place in front of the officials and media, plus a fairly large gathering crowd. No pressure then.
Gina Campbell putting 'Mr Woppit' on Runningblade. Google them. Now!

Then the call came through that the course was ready and the tide time was spot on for the first run, so the cutting deck was removed for safety and we headed for the golden beach.
Initially we ran with a roll cage and harness as we had no idea how stable the mower would be at higher speeds, Don set off for the first timed run, the V twin sounded awesome with no silencing, a bit like a Harley. It soon got up to 80mph and was humming along brilliantly, but then disaster struck and the speed dropped dramatically. We all dived into support trucks and rushed to the scene, the Countax guys flipped the machine onto its tail stand and immediately we could see the drive belt has fragmented. The prolonged run at full power had made it so hot it just disintegrated. Adjustment were made to pulleys to minimise slip and flex and a new belt fitted.
On its tail stand you can see the pulleys that drive the axle and cutting deck.

The return run went without a hitch, Don got out and reported it felt incredibly stable at speed and the beach was at its best, so we decided to remove the roll cage to reduce drag.
The second run was faster, but still not near the target so more tweaks were tried, gradually run by run the speed crept up a tiny amount at a time. There was a gentle breeze up the beach and with a tail wind the machine broke 90mph, but the return run into the wind dropped the average to 86.7mph.
Sun, sand and sea air. How relaxing, oh hang on...

And that was enough to snatch the World Land Speed Record for lawnmowers, the mower had given everything it had to give and it was time to celebrate.

Speed records are strangely addictive, once you have had one you need another, it doesn’t matter how fast you go you want to go faster. Speed is a drug, and the competition at every level is fierce, there is a category for almost everything, even road legal furniture, you name it some one has driven it faster than you would think possible.
Just being part of a team is a real privilege and a thrill, if you love speed machines then why not get involved, I joined the Bloodhound SSC club who have loads of thing for members to join in with and it’s a real buzz. Go on, get involved!

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