Developed by F1 aerodynamicist Barnaby Garrood, the Aerosensor is a clip-on device that attaches to the front of the bike via a GoPro style mount that can measure aerodynamic drag in real-time when used in conjunction with a speed sensor and power meter with ANT+ wireless technology.
According to Garrood, the Aerosensor “gives accurate wind speed and angle measurement in practically all wind conditions” to +/-0.1%.”
“Using the latest pressure measurement sensors, coupled with a cycling speed sensor and power meter, [Aerosensor] can measure aero drag in real-time with unrivaled accuracy: +/-1.5% on the road, and better than +/-1% in the velodrome. “We can’t measure aerodynamic drag directly, so instead we measure all other power sources i.e. user power = Kinetic power + Gravitational power + Friction power + Aero power. The bike has five forces acting on it: user (pedalling), kinetic (momentum – so accelerating works against user force; the harder you are accelerating the more user force it uses), gravitational (going uphill works against user force), friction (rolling resistance and drivetrain friction, always working against user force), and aero (always against user force),” says Barnaby Garrood. “At all times these forces must add up to zero, so we use that fact to deduce aero from the other four. We can’t measure friction, but since it is a relatively small component, an estimate of tyre rolling resistance and drivetrain losses is sufficient to give highly repeatable aero drag data,” Garrood further explains.
How does the Aerosensor determine if the rider is climbing or descending?
“The system uses barometers to calculate elevation, so we know how quickly you are going uphill or downhill. With the road speed, this is effectively slope. In fact, as our barometer is so sensitive, we can provide much greater accuracy on road slope than bike computers which typically have lower sensitivity barometers. The calculated aerodynamic drag coefficient (CdA) is transmitted to a Garmin cycle computer for display and logging using an app,” points out Aerosensor.
How does Aerosensor distinguish itself from competing products?
According to Garrood, “there are two main things, the first is that we measure wind yaw angle up to +/-50° with our patented probe design, meaning not only that we measure the angle, but we also use that to compensate the wind speed measurement. Current aero meters in the market use simple pitot tubes which give poor results above 5-10° yaw. Secondly, our system is much easier to use than current aero meters in the market. You need no special software or phone app. You download our Connect IQ app to your Garmin, pair it to the devices and that’s it. The Connect IQ app is used to change settings etc.”
Garrood says the Aerosensor underwent no fewer than 185 design iterations, 21 wind tunnel sessions and “countless computer simulations” before arriving at the final product, with the probe requiring the most amount of research and development.
“The probe is designed so that the duct turns the flow onto the duct axis, so the central pressure measurement [marked ‘PT’ in the image below] is always seeing head-on flow. That gives us what is known as “total pressure”. At the probe inlet, we measure pressure on the left (PL) and right (PR) surfaces, and the difference between them gives us a measure of wind yaw angle. You can use all three pressures to calculate dynamic pressure, which is a function of wind speed. This image shows a simulation of a typical probe at 40°. Red is high pressure, blue is low pressure,” elaborates Garrood.
Additionally, the start-up is also offering an accessory called the Aerobody, which can be used separately from the Aerosensor in order to calculate the distance from the bike’s stem to the rider’s head and chest via a “safe infra-red laser device”.
This function allows the rider to alter his or her riding position in order to reduce drag, relying on a color-coded display to determine if he or she is on target, too high or too low, while a warning light alerts a deviation in position.
Another add-on is the Aerodrome, which is a wireless lap/route timer that can send info direct to Aerosensor, “facilitating accurate lap averaging, and giving instant feedback to the rider.”
“This drag and time data are transmitted to the Garmin for instant feedback to the rider via our Connect IQ app, and recorded to the FIT file for post-ride analysis,” Garrood adds.
How does the Aerodrome work?
The device relies on a pressure-sensitive strip that is taped to the road or track surface. As soon as the front wheel presses on the strip, the time is transmitted to Aerosensor, providing data lap-by-lap.
After a successful crowd-funding campaign on Indiegogo last year, the Aerosensor ACS can be purchased directly from Aerosensor, as individual components or as part of three system bundles.
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