Draftbags

A Draftbag DECREASES your aerodynamic drag, rather than increasing it. You carry luggage for free. Less than free.

"Draftbag" refers to the well-know bicycle racing technique of drafting the cyclist ahead, staying close behind in their airflow wake. As is well known, drafting confers a considerable advantage to the following cyclist. Drafting also confers a lesser advantage to the leading cyclist, who is pushed forward by a pressure wave generated by the following cyclist.

The Project

A quest for elegance and simplicity. Adding luggage to your bicycle, but not bogging it down with poor aerodynamics, as panniers do. The bag cleans up the airflow behind you, making you and your bicycle more aerodynamic and faster then without.

Using free and low-cost tools in innovative ways to design and analyze aerodynamic forms. Coming up with efficient materials shaping and forming techniques to create a functional product. Using computational fluid dynamics simulation to optimize shapes. Using experimental aerodynamic flow visualization to refine shapes. Leveraging available bicycle power meter technology to compare aerodynamic drag of different configurations and provide proof of effectiveness.

This is a bootstrap operation. There is not yet a marketing department, nor a marketing budget. There are opportunities for sophisticated ride testers and early adopters.

Is it a business? What is the plan? Good questions, answers evolving.

This is for fun. This is about riding your bike, commuting to work, getting some exercise. Keeping your wheels on the pavement and not getting hit.

Computational Fluid Dynamics

An example of Computational Fluid Dyanamics (CFD) analysis. The video displays the disturbed airflow in the wake of a rider. More details on the CFD page.

More CFD

Development History

Several Generations of Draftbag Experimentation

Q&A

Draftbag Q&A

Backstory

In the 80's with the UC Berkeley HPV team, I shaped an aerodynamic fairing design for a recumbent tricycle. The shape was based on NACA airfoils, extruded, rotated, angled. The subsequent year teammates went on to build a much superior faired bicycle, which evolved into Cheetah, which set a human powered vehicle speed record of 68.73 mph.

Fairings are hot and can vacuum up road dust. Not for Texas. Recumbents have some excellent characteristics, but tough to push up the Austin hills. Tricycles are cool, but require full aerodynamic shell to keep drag under control. To remain stable, a tricycle must be very low compared to its width, leading to challenges with rider visibility of traffic and traffic visibility of the tricycle.

Observed some development of front fairings applied to bicycles. Seemed to me those front fairings might be addressing the less critical end of the problem!

Commuted on my bike in the Austin, TX weather. Didn't like wearing a backpack while I sweated in the heat. I carried my work stuff in panniers, but they slowed me down.

Imagined a properly shaped rear fairing, one which could carry a good bit of stuff. My clothes, a lunch, an oscilloscope, a case of beer, stuff like that. Realized I couldn't afford to wind tunnel test, or build dozens of prototypes. Mashed up an odd assortment of bike CAD models, human form models, and my own aero shapes, slammed it through CFD and visualization software. Confirmed with hand-built prototypes and instrumented road testing. So here we are.