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MARS projects - J. Tetz foamshell
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Click HERE to go back to the main Projects page
Click HERE to see the Spollen V1 foam fairing under construction... excellent photos of this construction methodin action!
Click HERE to see Rich Sadler's foamshell, which was built of the same materials, but using a completely different method.

Constructing the Foamshell
by John Tetz email

The streamlined, suspended bike shown on this page is unusual. It's a 20/20 carbon fiber lowracer with a soft shell made of a little-known heat-formable foam material. This foam is radically different from more commonly used fairing materials, which fall into three categories: hard shell (fiberglass/carbon/Kevlar); medium shell (Coroplast) and soft shell (Lycra/Spandex). This article details the advantages of this material, where to get it, and how to work with it.

How would you like to have a full fairing that weighs only 7.2 pounds (3.2 kg)? And is relatively low cost, requires only simple tools, and avoids noxious substances (no fiberglass, carbon fiber, Kevlar or their associated chemicals)? The fairing you see in the photos is made from a flexible foam material (See Ref 1) that can be heat formed into compound curves. The edges can be sanded and shaped, it is quiet over bumps, and it comes in a variety of colors.

Foam and similar but little-known new materials on the market can be used for streamliners, tail boxes and other popular aerodynamic additions to a bike. The foam I have located can make a tail box with nice lines and compound curves, yet with a shape simple enough that a full mold might not be necessary. A tailbox may be a good starting project to learn how to handle the foam.

With lightweight foam and a 24 pound bike (10.8 kg), we have a streamliner that weighs 31 pounds (14 kg). The fun thing is you're adding only 7 pounds (3.2kg) and you are getting an improvement in flat ground speed in the 35% range. The real surprise is the ease of climbing lesser grades. The people on unfaired bikes are generating power both to climb and to overcome aerodynamic drag. You are using most of your power to climb. On steeper grades the 7 extra pounds doesn't significantly slow you down.

A few years ago I saw foam being used by a variety of builders in Europe. When I met Harold Winkler and Frank Lienhard, two young and extremely creative German builders, I saw their lightweight foam fairings wrapped around their very low bikes. I knew immediately that this was something to be explored.

I built a fairing using similar polyethylene foam around a 20/20 carbon lowracer, expressly designed to fit inside the shell (note the upright seating angle, necessary to see over the nose). It worked and was light (6 pounds or 2.7 kg). But the foam came only in white and the surface was extremely fragile. A fingernail could cause a deep un-repairable scratch. However, this at least gave me a prototype which I used for well over a year to explore and to learn what can and cannot be done.

I began a search for a more suitable foam. Color was further down the list of priorities so when I found that this new foam met the physical requirements and came in color, I knew it was a breakthrough material. This foam is almost as light light but stiffer than the polyethylene, has adequate surface smoothness and the ability to be heat formed into compound curves along with much better surface toughness. Many people believe that foam is so soft that it should have some kind of a covering. This foam seems to be tough enough to withstand daily use and an occasional slow speed fall and still not show serious damage.

High-speed racing streamliners need exact control of shape over the entire surface of the fairing. With foam, the shape cannot be controlled as precisely as with the materials used in a hard shell. Also, the foam’s surface is satin textured rather than glass-smooth (note dullness in photos).

Therefore this material is best used for streamliners intended for use on the road. The CdA (coefficient of drag x frontal area) on my vehicle is around 0.8 sq. ft. (0.07 sq. m) which is quite adequate for a road vehicle. Because it is used daily, other issues become more important than the compromises one is forced into to arrive at the lowest CdA. For example, ease of getting in and out is a design choice that takes priority over a minimum CdA. This vehicle has a canopy that hinges to the right and a side door that hinges down making climbing in and out of the cockpit relatively easy and quick. But this creates separation lines perpendicular to the flow of air which are not conducive to really low CdAs.

The CdA could be lower if the fairing were longer, but I chose to limit the length to 80 inches (2 meters). This is very important when parking the vehicle in limited spaces or when transporting it in a car or airplane -- a feature of a practical vehicle. It is impossible to maintain ideal low-drag attached flow, given the constraints of physical dimensions of a short vehicle. Looking at a top view, the shape is dictated by the width at the forward pedal/shoe location, followed by the continuing shape to the width at the handlebars, followed by the width further back at the shoulders. A rather sharp contraction starts at the shoulders changing into a concave section ending with a squared cutoff tail (about 4.5 inches max. width -- wide enough for a LED tail light). I was hoping to get a turbulent bubble at the contraction to pull the air back to the surface according to an aerodynamic CFD (Computational Fluid Dynamics) computer program I have, but in actuality I don't think it is working properly.


The simple tools needed to build the fairing are several razor blades, contact cement, and a professional heat gun (the kind you find in a hardware store, NOT a hair dryer), plus some thin vinyl upholstery material for hinges and some hook and loop material (e.g. Velcro). Other materials you might need are some Coroplast (Ref 2). Seems like no fairing is complete without some Coroplast which is used to regain lost stiffness around the side door and along the "bomb bay" doors.


The big project is building a mold. That is if you want a low CdA vehicle. There may be ways to pre-cut the foam and then assemble it into a useable but not ideal shape without a mold. Maybe a FLoft or similar program would give the necessary flat shape cuts. Not having access to such programs I chose to build a mold from common rigid home insulating foam (see Mold Photo). After spending the winter months creating exploratory sketches of a bike and a fairing that work well together (dreaming and imagining the possibilities, but loaded with compromises determined by Nature's rules), the next step is to make detailed quarter-scale side and top views. My top view consists of horizontal slices taken every 3 inches (7.65 cm) or so from top to bottom. These airfoil shapes are derived basically from the physical width requirements of toes, handlebars, shoulders etc. The maximum top to bottom side view dimension of this fairing is 30 inches (76 cm). Maximum width is 19 inches inside the fairing. An attempt was made to further fine tune these foils by observing lower Cds calculated by the aerodynamic CFD program.

Along with the side and top views, vertical sectional views every 7 inches (170 mm) from front to rear along the length are generated. All three views are adjusted during the drawing process to get the required clearances, optimum foil shapes and smooth top to bottom roundness. Stay away from flat surfaces. They are too weak. I feel drawings are necessary on a complicated project if you want a reasonably finely finished vehicle. Drawing gives one a chance to think through each area and each process rather than wind up with a big "whoops!" after the material has been cut and formed.

Eventually the sectional views are transferred full scale to the mold material and roughly cut to shape. Each section is slipped on a 6 inch (150 mm) diameter plastic drain pipe. To cut the hole use a 4 inch section of the pipe, cut some fine teeth and by hand rotate this saw through the ridged foam. The pipe is mounted such that the whole assembly can be rotated to ease the work on the bottom or other difficult sections. Rotating the mold helps when laying the side sections of foam on the mold or working on the bottom.

This makes a useable mold with minimal raw materials. If you laid out a grid on the vertical sections the same as on your drawings then this can be a reference guide to make accurate line drawings to check for clearance for toes/heels, sides of shoes, handlebars, arms, shoulders, seat, drive trains etc. while you do the fine sanding and shaping. However when it comes time to do this sanding, those empty spaces between the sections can be maddening. I used a thin strip of wood .030 by 1/2 by 36 inch length to lay on the sections to visualize the uniformity of curvature. The strip should touch three to four sections without air gaps to give smooth contours. Sighting by eye at low angles along several sections is another guide.

This is also the time to decide where the top and side and bottom cut lines will be. I used masking tape to lay out the cut lines, then marked the mold. This took quite a few evenings of constantly making small adjustments and standing back to check for visual acceptance. Placing the joint where two colors come together is an advantage. It hides the joint somewhat but more importantly it is where a full piece of foam would typically be cut in order to follow compound shapes without excess strain.

Laying on the Foam

I start with the top, from the cockpit to the nose. Then add the sides later. To hold the foam on the mold I cut the foam larger than it needs to be, then tape the edges to the mold. Start at the cockpit and work your way towards the nose. This will be a compound curve shaping process, heating and forming the foam and taping as you go. I generally heat about 15 inch square section at a time making sure to keep the heat gun in motion all the time to prevent overheating which will change the color. To get the heat to penetrate through to the back side generally takes at least a minute.

To make the very complicated compound nose curves I laid a single layer of fiberglass on the solid built-up nose (see Nose Photo, above). To keep the glass from sticking to the foam use a layer of thin plastic film (e.g. Saran Wrap). The foam can be contact cemented to the glass as you heat and pull it down around the nose. The fiberglass is a permanent part of the fairing and, yes, it slightly increases the weight but it helps make a nicely shaped nose.

After the entire top section is formed it's trimmed along the cut line with a razor blade. Patience is important here... go slowly and check the line often or it will come out wavy. I also find that it's easier to follow the line if you push the blade instead of pulling it (the foam is stiff enough to allow you to do this).

Once the top section is finished and trimmed, the sides can be attached. Gluing the sides to the top at the edges requires working with small sections at a time (about 6 to 8 inches). Before contact cementing always use coarse (80 grit) sandpaper to rough up the edges to give a tooth for the contact cement.

I start at the midpoint of the fairing and work towards the nose and tail. This is a tricky process requiring pulling it up against the mold to see if it fits to the top section and up against the vertical mold sections, then marking the overlap and cutting the edge of the side foam to match the edge of the top section. Having the bottom edge of the side panel firmly attached to the mold is important, because you'll be pulling pretty hard on the foam to get a good fit. I use pieces of masking tape every 2 inches.

The overlap between the side foam and top foam is small... about 1/4 inch. I pull up on the side and make a mark on the side foam 6 inches away from the last glue joint, where the edge of the top foam is (I can tell this more or less by feel... the side foam is lying over the top foam. I make a line with a water-based marker pen and then cut along the line with a very sharp razor. Then I hold it up to see the fit. Quite often I have to take off a bit more material.

This is a repetitive process, working in increments of six inches. Pull the side foam up, heat if necessary to get it to curve, check fit, trim, re-check fit, re-trim if necessary, and glue. As you progress forward (and backward) from the initial glue point in the middle, the compound curve will get more severe. You'll have to use more and more force to get the foam into the right shape. Also, you'll have to start using heat to mold the foam as the curve gets more severe and the forces increase.

By the time you're approaching the nose you're forcing the foam pretty hard to conform. If you dont do this, then when you get to the nose there is so much material that you have to cut a wedge out to get the foam to curve.

Sometimes when I get near the nose I see I'm not going to have enough side foam to reach the edge of the top foam so I use the razor blade to trim the joint further back and pull harder, taking up more slack.

When you get to the nose you have to pull with just about all you have to get the foam to form on such a tight compound curve. Here you absolutely need the fiberglass nose to glue the foam to.

And you need to limit the amount of wrap by having a relatively wide center section (an extension of the top) down through the nose.

Also notice where the dividing line of the top and side is. The top is easier to form. I minimize the amount of wrap at the top (and bottom) of the side by having a fairly low color line. The side has much more of a compound curve to deal with.

When heating and forming the flexible foam over the mold sections, the foam has a tendency to have high and low areas resulting in a slight waviness (a no-no for good air flow). A solid mold would relieve this problem but would require much more material. The reasonably low CdA shows the waviness is not a big problem. Vacuum bagging in a female mold would give smooth uniform control of shape with much more work. How to uniformly and thoroughly heat the foam needs to be thought out for any of the processes used.

The fairing between the bottom of the nose and the front edge of the bomb-bay doors is completed on the mold. The actual length of the bomb bay door openings may need to be adjusted after the fairing is on the bike (see bomb bay doors
). The fairing is lowered onto the bike from the top, so the bottom has to have a split from under the seat to the tail. The fairing can be put on in about 3 minutes including hooking up the lights and rear luggage carrier.

I cut the side door and canopy while on the bike. Coroplast is used to regain the lost stiffness around the door (see Door Photo). I use thin vinyl for the hinges. The upper rear section behind the riders head is Velcroed to allow access to the deeper luggage area or if you want to experiment with a cover over your head. I find an open cockpit is crucial for hearing traffic and on those foggy nights it becomes necessary to lean your head out to see around the fogged up windshield. Haven't completely solved this problem yet.


Because foam is flexible it needs several mounting points to hold it on the bike and to maintain control of shape. I have 8 mounting points; a Y yoke to hold the nose up and control width, and nose location; and a vertical rod from the BB down to just in front of the wheel to keep the bottom of the nose from swinging left or right from cross winds. A strip of hook and loop material along the bottom of the frame between the wheels holds the bottom together. I also use the end of the luggage rack to stabilize the tail and I rely on my arms for some side support in heavier cross winds. Two attachments at the ends of the top horizontal seat bar (a mesh seat with frame) are the main position locators of the fairing in respect to the bike. The mounts on the foam here are 1/4 inch thick x 4 x 4 wood shaped to fit the fairing curve then contact cemented to the foam. Simple aluminum strips are screwed to the wood with male posts that plug into the top bar of the seat back. This number of mounting points makes for a reasonably stiff and stable fairing. The attachments added very little weight; I made an effort to keep the weight down. Carbon tubing was used in two places (nose supports). Be careful when working out the mounts and bracing -- there comes a point at which the total weight approaches that of a hard shell. There simply is no need for interior frames. Other designs are possible, such as a stiff tub bottom section that would make a stable base for a foam top section.

Crash Protection
How well does this material hold up in a crash? Its much better than Spandex which provides essentially no protection (from my own experience) and the foam is not a lot heavier. In many ways it has better features than my hard shell (Ref 3). That vehicle has a single layer of glass on both sides of _ inch stiff foam. A stiff stable fairing, but even on a slow speed crash the outside layer is easily punctured and torn if there are stones or rough surfaces on the road. This means spending a week or so doing body work (and adding weight - the hard shell weighed 11 pounds before a couple of crashes). On a hard crash, fiberglass or carbon can break up and slash the rider with razor like edges. Plus its noisy over the road.

This foam is tougher than composites on similar slow speed crashes. It bends rather than cracks or breaks. The surface may become scratched but can be repaired some what with heat (need to find a suitable filler for repairs). If its used a lot over a couple of years it will eventually start to get shabby. It can be sanded and reheated but the surface will not be quite as smooth. Anyway by that time you will have all these new ideas floating around in your head and will want to make changes. You have the basic mold which can be modified plus the experience to build another. The second will be much finer. The third will be super.

How does it hold up to high speed crashes? A few months ago I crashed at the end of a 40 mph (64 km/h) grade with the first foam shell, when the Sachs 3x7 hub locked up after hitting a high-speed bump (one of the pawls jammed). The bike slid for about 75 feet (22 m) flipping back and forth until wearing the tire flat, I lost it to the right hitting the ground hard. But interestingly I got out of the vehicle on the left side! It must have done a complete roll-over. Also, it did not slide very far - another advantage over slippery hard shells.

An after crash inspection showed a deep scar in the foam on the right side where the seat frame was located along with several scratches and a scatter of deeper scars. The left side also had scratches and a couple of deeper scrapes, evidence that it must have rolled. Basically nothing happened to me. No loss of precious skin, except my little finger must have been bent in a way that a tiny bone in my hand was sprained, possibly fractured. Not bad for a high speed crash. I shudder to think what I would look like on a unfaired bike. This foam can indeed make a light fairing and still have reasonable crash protection. I have a seat belt in the hard shell - I need to add this in the foamshell to stay inside when crashing.

Is it worth the effort?

All this work may sound like too much for many individuals. After all, you can get quite an aerodynamic improvement by slapping a garbage can on a bike; but if you want a more serious vehicle then it will require attention to detail and much more work. Using this method, you can wind up with a very light weight, clean, attractive vehicle that is pushing the envelope. To me that is worth all the effort. Yes, on your first fairing you will spend an inordinate amount of time thinking through how to solve various problems but it becomes easier as you get into the project. In any case it's a lot less work than using composite materials.

And it's a lot of fun, too boot.

Ref 1; Material; Plastazote (R) LD45 cross-linked foam; also called Zote foam
Available from;
2501 Guyan Ave.
Huntington, WV 25703

LD 45 comes in sheets 40 x 80 inches, any thickness. I use .5 to .54 inches. For tail boxes .4 inch may be adequate. Density 2.8 lb/ft^3 (45kg/m^3). Several colors yellow, blue, navy blue, orange, white, black.
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Ref 2; Coroplast in the USA is two thin sheets of plastic separated by ribs. It looks like and handles like corrugated cardboard.
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Ref 3 ; Streamliner as a Road Vehicle. Human Power Vol. 12, Number 4, Spring 1997 pg. 3.
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