For the engineers and framebuilders
 

Since we have reached a point where wheel manufacturers claim that in certain crosswind conditions their wheels actually provide forward thrust, why cannot this be replicated with frame tube shapes for tandems since we are not restricted by UCI rules like road bikes.

Since the tube shapes are not available could they just be 3d printed?

To take this to the extreme could a panel be added to inside the frame triangle that acted as a sail?

While on the subject of 3d printing why not print a monocoque (sp?)frame? Unlimited design possibilities, could even add golf ball dimples all the way around???

Just trying to start a winter discussion and as per Pateka these ideas are Patent Pending ;-)

We often see wind surfers some with parachutes on a lake near one of our routes but only on the when the winds are well in excess of 20 mph. The mental image of our tandem leaning at 30 degrees or more on a straight road to take full advantage of a cross wind is appealing to me but I think my stoker would have some issues with it.:lol:

On the serious side I think there is a marginal gain there but it would be limited by the instability of a two wheel vehicle and the requirement that the bike stay in its lane.

With the caveat that I am an electrical engineer having very limited experience with 3D printing and absolutely no special expertise in aerodynamics, here are my thoughts:

From what I know about sails, tube shapes that provide forward thrust sound plausible to me. The boats that compete in the America's Cup use solid sails now, so why not? Having said that, the sail on a boat is very large relative to the size of the vessel which is also large relative to the passengers. So, I wonder how big of an effect is even possible within the constraints of a tandem frame. Also, how much gain is possible if the goal is to make it work over a wide range of angles?

With respect to 3D printing, I've been thinking about this a lot lately. The bike used by Bradley Wiggins to break the hour record earlier this year used a 3D printed titanium handlebar. I think this sort of thing is going to start popping up more often in cycling, and it will offer the opportunity for customization of specific components and eventually experimentation and innovation in frame design. I'm not sure 3D printing is relevant to fabrication of carbon composites. I know it's possible to 3D print in steel and titanium, but not sure about aluminum and I don't know whether there any particular properties of different metals that make them better or worse suited to this. I'm going to assume titanium to be the primary metal of interest for cycling applications. Here's a very interesting example of how Triton, a Ti framebuilder based in Russia, has done some very creative things using CNC to achieve tube shapes that would have otherwise been difficult. It seems to me that 3D printing is the next step. I could envision a full bottom bracket region of a frame being 3D printed and then having the other tubes welded to it in a more traditional manner.

I agree, shaped tubing usage on tandems is sorely lacking. Unfortunately, monocoque frames seem out of reach for the small tandem market. For eye candy from a few years ago, see: Specialized Shiv Carbon Fiber Tandem ? AKA: The Supersonic Divorce Machine. Also this vid: https://www.youtube.com/watch?v=O-Ly31R0AKY and a old Bike forums discussion thread here... http://www.bikeforums.net/tandem-cyc...s-concept.html .

Up until recently, direct metal laser sintering with metals seems to be the only way to produce strong 3D printed products.

Everything I've read on the 3D printing topic indicates that tensile strength is not good with this process with either plastics or carbon. Carbon tubing especially gets its strength from careful consideration of directional fiber layup, which is not done well by current 3D printing. There is a new "Carbon3D" (google it) printing process that is supposed to produce very strong, well bonded components, but I'm not sure of the maximum object size those can produce. Since bike tubes are fairly long, it may not be practical/feasible in the near future to produce them.

You could add a CF fairing to round tubes? The fairing could then be non structural just aero just like many wheels.

My thought was not necessarily provide 50 watts of forward thrust but how about net zero.

Also you could add under boom as well that could offset a some force trying to push you over, or the need to lean into the wind.

Where is that guy who built his own carbon tandem last year**********?

We should give him a challenge for this winter.

Maybe start some fundraising to pay for his materials.

I sailed all my life. Studied sailing and naval architecture, focusing on aero and hydrodynamics. I used to use a Zipper fairing. When the wind was from the side and a little behind, it acted like a sail. I did a ride once with that wind direction at midwest winter strength for about 20 miles, flying like I was sitting in a fast pro field but with the bike leaned hard to my left, into the wind side, sorta windsurfer style. The fairing felt just like a sail, distorting like a spinnaker in the puffs and pulling the same way.

Ben

To get the most benefit from the fairing: don't bond it on or shape the tubing form. Keep the round tube. Make a fairing that is several times the tube diameter in length and say 25% wider at its max. Let it pivot on the tube. Now, make a control that sets its rotation. Now you have a real wing sail.

If anyone here wants to do this and cannot afford wind tunnel time, PM me and I will design a section for you based on your tube diameter and the fairing length and width that will work for you. You will get full size sections, offsets if you want them and an AutoCAD file. Dead serious. This was my passion for much of my life. I have on my shelf the bible of wing sections and many years of AutoCAD experience. Putting the appropriate section into AutoCAD wold be fun and the rest is easy.

Ben

I was thinking of fixed "tubing" shapes, and a couple came to mind.

http://bikeforums.net/attachment.php...hmentid=493080

On the left is an open double half tubes. It may give minor benefit for direct down wind (with wind faster than the rider), or side-winds up to a few degrees past a full cross wind.

The right is similar to a teardrop, but indented sides, also potentially of benefit with side-winds.

My guess is any benefit would be minimal.