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Snowmobiles are getting colder. With the new minimalist styling, trying to make the sleds appear smaller, drivers are more exposed to bone-chilling winds.
Even with the best wind protection gear I have, I could only take about 10 miles on one of our long-term sleds last winter. By that time my chest was cold and one of my fingers had gone numb. I flagged down my riding buddy and got back on my old Polaris Edge with a full windscreen. My friend suffered the same fate a few miles later and we had to take a break at a restaurant before we decided to head back.
Short windshields and minimal snocross handguards may look trick, but you'll go faster, and be warmer, with a full windshield.
Putting wind to workWhen we asphalt raced my 600 Edge back in '05, we tried a lower windshield and promptly lost a tenth in elapsed time and a full 2 mph on top end. During the
AmSnow Real World Shoot-Out last winter, we repeated the test with a Ski-Doo XP 800, owned by Jon Zeimetz. With the stock windshield in place he ran a top speed of 101 mph, and with a full windshield the XP hit 103 mph.
The explanation is simple, with a small windshield the air hits the driver's chest and arms, which act as an airbrake, while a larger windshield directs the air over and around the driver. Air at high speed represents a large force acting on the snowmobile and its rider. The wind-chill factor also is considerable in winter.
Open-wheel racers, such as Indy and F1 cars, harness the wind force and turn it into downforce. Even the good old NASCAR boys are now spending a lot of their time in wind tunnels.
In 1979, we had the AMSOIL Sno Pro Oval Racing Team and experimented with aerodynamic downforce to improve handling on the racetrack. At that time there was no hard info available on how the snowmobile reacted to aero forces.
Since we had two Polaris factory sleds from their 1978 race team, Brad Huling's 3-cylinder 440 and Steve Thorsen's 340 twin, we decided not to work on the engines, since we felt that the factory probably had squeezed the maximum power from them already. Instead, we decided to see if we could develop an aero advantage.
The first thought was to rent wind tunnel time, but we found that just 2 days in a tunnel would cost us the whole year's racing budget. So, we dropped that idea.
DIY wind testingReading up on aero testing we found out how NASA tested rocket shapes. NASA strapped the testing object on top of a rocket rail sled, a rolling sled on a rail with rail wheels, and moved it through the air, instead of having the air forced around by a big fan. A rocket sled wasn't necessary as our race sled seldom topped more than 85 mph in turns. So we decided that Tim Bender's pickup would do just fine.
Tim was our driver and was not afraid of experimenting. Off to the lumber yard he went, and after a week of carpentry work, the Do It Yourself mobile aero testing rig was finished - total cost, $600.
A platform was constructed over the pickup bed and cab with a downward sloping ramp in front to get "clean air" with minimal turbulence flowing over the snowmobile. The sled itself sat on a separate platform cut into, and even with, the main platform.
Getting hard data required the test platform to float on steel wires that were hooked through a lever system that operated 3 hydraulic Stuska Dyno Scales. One scale would measure the downforce in the front of the sled, and the second would measure the downforce in the rear. The third scale was mounted horizontally and measured the drag force acting on the snowmobile.
After everything was mounted with the sled on top, we headed to a quiet back road with a nice long straight for testing. Turns out the practical testing speed was 50 mph. Higher speeds were not important, as aero force at higher speeds can be converted by using known engineering formulas.
Data above 50 mph was harder to record, as we started to pick up feedback from ripples in the road, and Tim was not comfortable in holding steady positions during testing on top of our moving test bed at much higher speeds.
Crude as the device was, we got some useful data. We first tested the original RXL setup, and found, surprisingly, that the front radiator intake's overhanging lip on the hood actually caused a 40-lb. up force that was lifting the sled's nose and taking weight off the skis.
Our new hood was modeled after a Can-Am road racing car with a down slope all the way down in the front and had just two slots in the high-pressure area for radiator cooling right above a small "splitter" lip. This configuration added 100 lbs. of downforce, giving us a 140 lb. advantage compared with the stock hood.
However, if we only increased downforce in front, the machine would become unstable at high speeds, so we had to increase rear downforce. We did this by incorporating a spoiler in the rear seat design. First tries were much larger than we needed, and the force also depended on the driver's position. We would need the force in the corner when the driver was hanging to the inside. So, we decided on a smaller windshield that would improve airflow to the smaller rear spoiler, because overall drag increased alarmingly with larger rear spoilers.
We also added a side panel on the right side all the way to the rear spoiler to make the sled more aerodynamic. This panel reduced overall drag considerably, and also added a large billboard surface for our team. All the bodywork added 20 lbs., and there was some concern that this would cancel out any new-found advantages.
Did it work?How did that aerodynamic downforce work on the track?
The concept worked better than we had hoped, but it took several races to sort it out. At the first race in Grand Forks, N.D., we didn't have stiff enough springs to match the higher downforce, and ended up scraping bodywork on the ice.
The second race in Kinross, Mich., was cancelled due to a blizzard, but not before Tim had been able to run the sled in practice. He came in and told Larry Rugland from Polaris' factory support team that the machine stuck so good he felt he could have held it wide open through the corner. To which Larry responded, "So why did you shut it off then?"
This made Bender curious to see if he could actually do it, and by the third race in Wausau, Wis., he did go around the track wide open in the last chance qualifier to make the final. In the final, he started well, but as the laps progressed the handling got worse and he drifted back. Back at the shop we discovered that the right front upper shock mount and frame had twisted by more than an inch due to the increased cornering forces.
Next, we reinforced the frame to handle the additional loads. This was done by running a new tube structure from the right shock mount tower to the handlebar cross-member, like today's pyramid-style frames. At the next race in Peterborough, Ont., all the pieces came together with Tim winning the 440 class.
Peterborough is a fast half-mile, and Tim noticed something we had not anticipated. The large flat side panel acted like the side fences on a World of Outlaws Dirt Car wing, and he could throw the sled hard into the corners and the aero side force on the flat panel would prevent the rear end from coming around.
Our team sled proved that aerodynamic forces could help an oval racing sled, and the concept was copied in the following years by several manufacturers. A large part of our success was due to Tim, who aside from being a top oval driver, also was a good fabricator and excellent in testing and sorting out race sleds. Tim went on to prove his race craft by winning 4 Formula 3 World Championships and is now the team manager for the Polaris/Hentges Snocross Team. As far as I know, no additional aerodynamic downforce engineering work that actually measures loads has been published since our efforts to streamline the sleds.
Help for todayToday, the drivers that are running into aero problems are mainly asphalt racers, but ice speed racers are fighting front-end instability too. We're seeing speeds of 150+ now! High-speed stability requires that the center of pressure is located behind the center of gravity, and large front air dams only make the problem worse, by moving the pressure center forward.
More rear downforce is needed to prevent the track from losing traction. Perhaps we will see future asphalt drag sleds with skinnier front farings, and downforce spoilers in back. This would move the pressure center behind the center of gravity, which would stabilize the sled at high speeds, and improve traction too.
None of this is a large concern at trail speeds, but getting cold and freezing your fingers certainly is. Higher windshields and better hand and leg protection is needed to encourage new riders. If I were new to the sport, a cold sled would be a major deterrent from me buying a new sled.
For me, well, I'll keep my trusty old Edge with that warm high windshield a bit longer.