Aerodynamic innovations today often make relatively modest claims: gains of a handful of watts or a few percent less drag than existing products. Hong Kong-based brand RAF’s inaugural product, launching on Kickstarter, is far more bold. The RAF1 (Ram Air Fairing) is a wearable backpack-mounted fairing that is inflated, parachute-style, by the passing airflow aiming to improve the flow of exiting air from around a rider. In the brand’s product video, the brand claims that the RAF1 can offer a reduction of up to 19.6% in wind resistance.
This is a lofty claim. Upon closer inspection, it’s not backed up by any apparent data (RAF did not immediately respond to a request for information). Further, RAF seems unclear on its target market, sidestepping a question in its brief FAQ about whether the fairing is legal in races (it’s not). Finally, there are likely safety concerns regarding crosswind performance. Given all that, the RAF1 looks to have faulted at the first hurdle.
Big if true
Along with the eye-catching claim of reducing wind resistance by 19.6%, the brand also claims that the “cutting-edge air-filled backpack, has been meticulously crafted to revolutionize your riding experience.” As great as this might sound these open-ended buzzword claims are not backed up by any published data on the Kickstarter or RAF sites.
The rationale behind the fairing is well-founded: the blunt and abrupt shape of a rider’s back makes smooth detachment of air incredibly difficult. As a result, the area behind a rider’s body is filled with turbulent air rushing in to fill the void the rider has just created. Using a tapered fairing exploits the same principles as time trial helmets or aero frame tubes, simply on a far larger scale and with larger theoretical benefits.
Arguably racing is the sector that would have the most to gain from aerodynamic fairings, especially time trials, but the rules governing equipment for use in competition quickly put an end to this possibility. The UCI has extensive regulations around equipment and clothing, with article 1.3.033 saying, “Items of clothing may not modify the morphology of the rider and any non-essential element or device, of which the purpose is not exclusively that of clothing or protection, is forbidden. This shall also apply regarding any material or substance applied onto the skin or clothing and which is not itself an item of clothing.”
It was this rule that put an end to the vortex-generating Castelli Body Paint 4.0 skinsuits used by Team Sky in 2017. The skinsuit used small strategically placed nodes to generate purposeful vortices that created a smoother detachment of exiting airflow. The official ruling allows for modifications to the surface of the fabric up to a limit of 1 mm allowing for ribbed designs to still be permissible in most cases. RAF says in its FAQ that “compliance depends on race regulations” and to consult with organizers, but in UCI and even national-level competition, the fairing is clearly not allowed.
Fairing, parachute, or sail?
First things first, although this might look like a backpack it is not actually for carrying anything. Instead, the RAF is purely an “aero aid” that inflates into a tapered wedge shape that in theory should increase a rider’s efficiency through the wind. This means you’ll still have to resort to jersey pockets for storage – if you can access them.
The ram-air design of the RAF uses the passing air to inflate and hold the shape of the fairing as can be seen in the brand’s video. There are several problems with that. Most prominently, it means the RAF1 is essentially a parachute. Even in calm conditions with the fairing perfectly inflated, the only way it could improve aerodynamic efficiency is if the savings from smoothing airflow over the rider’s back is higher than the losses from the intake ports. If the fairing was rigid with no intakes its performance would likely be significantly improved, however this would bring its own world of issues.
The promotional video from the brand does little to stave off concerns over the RAF1’s credentials. The rider initially using the aero fairing is riding a road bike whilst the fairing-less cyclist he overtakes is riding a gravel bike. On top of this, the road cyclist with the fairing is visibly pedaling harder during the overtake whilst the gravel rider appears to be soft-pedaling. That alone doesn’t itself mean RAF’s claims are invalid, but those subtle sleight-of-hand elements raise questions about whether the video really shows what it claims.
Second, the soft-body construction means that anything other than calm conditions could subject the fairing to deformation, which will cause turbulence and harm the product’s performance. We all know how much difference having tight-fitting clothing makes on the bike, with any creases or loose sections that flap in the wind responsible for a significant increase in aerodynamic drag. Rule 28, for example, found its Neo skinsuit increased aerodynamic efficiency by around 7.2% over its TT skinsuit 2.0. At 45 km/h this equates to 13.15 watts. Both fit and fabric have massive implications on aero performance and the non-rigid design of the fairing may struggle to retain its shape when out on the road. This buffeting would likely not only reduce purported aero benefits, it could also compromise rider control.
Third, at higher yaw angles the side faces of the RAF represent a significant increase in surface area. This could result in the RAF becoming more of an uncontrolled sail rather than an aero aid. With the RAF1’s inflated dimensions measuring 95 cm x 35 cm x 65 cm, this adds roughly an extra 1.6 meters squared of surface area for the wind to act upon. For reference, an average rider’s side-on surface area sits closer to 0.5 meters squared meaning the RAF1 effectively quadruples the area exposed to crosswinds. The RAF1 looks to extend a long way behind the rider tailing off in line with the rear axle. This profile means a lot of load could be leveraged against the rider in anything other than calm, low-yaw conditions.
Finally, there is also the safety concern for both individuals and groups. The prospect of having an almost meter-long inflated fairing protruding behind a rider creates big questions about how it would function in any pack of riders. And there is also the issue of what happens when you stop at a traffic light or junction. Due to the size of the fairing, as it deflates there is a real potential that it will sit on and around your rear wheel. With the fairing mounted directly to the rider, getting it caught in your wheel as you pull away could result in an unforeseen and sudden dismount.
A failure with a future?
With all of these points in mind, it raises the question who this is for. At 299 grams the RAF is certainly light enough to carry around without too much issue but in the real world, it’s not allowed in races and would be problematic on group rides – two of the primary use cases for any performance-minded rider.
The principle behind the RAF1 is certainly commendable. Aerodynamics is an area where the hunt for gains has become ever more marginal and thinking outside the box could be what it takes to find the next great leap forward. In this case, the RAF1 looks to miss the mark with some unavoidable flaws. If there’s a bright spot, it’s that the concept might open up a new space for future aero developments that incorporate aero considerations beyond the routine way of thinking.
What did you think of this story?