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Blowing my nose
Steps in blow molding a Zote foam nosecone
by Rich Sadler

I, with Paul John & Tom Janovitz, am in the Martian racing contingent. I’ve been racing in the HPRa series since 97, and the racing bug keeps biting deeper & deeper. This fairing is for racing in Superstreet class, which requires that I be able to get in the bike without opening any panel: the foam construction works well for this as it yields a little when I’m trying to squeeze into a too-small opening. It was designed to be smoother, narrower & less ugly than my first attempt, which resembled the bride of Frankenstein as it was stitched together from bits & pieces. I saw a demo of blow molding at Don Barry’s shop after one of the Indy races; My new wrinkle is to heat the foam from the inside rather than building an oven around it.

The basic concept:
1. Heat softens Zote foam, allowing it to be formed
2. Blowing the heated foam forms it into a rounded, naturally (I hope) aerodynamic shape.

What’s involved:
1. forming the shape
2. attaching the sheet of foam to the form
3. sealing it (mostly) airtight
4. heating it
5. inflating it with compressed air
6. trimming
7. attaching


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Forming the shape
I cut a nice parabolic shaped hole in a sheet of plywood; this became the floorboard of the form & defined the shape of the nose in plan (top) view. On another piece of plywood, I sketched the out line of the vertical section at the rear of the nose. My bike is pretty laid back & my view of the road is between my feet, so this section has two humps for my feet with a valley between them to see through. I cut out this shape with a saber saw & attached it square to the first plywood, so it stuck up like a tombstone. Since this two humped tombstone would have the compressed air pushing on it with considerable force (around 500 lbs.!), I worried about it falling over like a scene from a bad horror movie, so I added a diagonal brace between the two pieces of plywood.

Attaching the sheet of foam
I loosely draped the Plastazote foam sheet over the tombstone, then pushed the excess through the hole in the horizontal (floorboard) plywood. After running a bead of caulk along the edge of the tombstone, I used pre-hole punched steel strap and sheet rock screws to secure the foam sheet to it. The portion of foam sheet that I pushed through the hole in the floorboard was persuaded, with a little help from my heat gun, to lie flat against the far side of the floorboard.


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Sealing it
I glued up scrap pieces of foam sheet to form a flange completely encircling the floorboard hole. This foam flange was destined to be sandwiched between the floorboard & another, solid, sheet of plywood. To the solid sheet, I attached a 1000 watt electric heater, the kind with a fan you buy to warm up a chilly room. Two sheet rock screws into the plastic body of the heater held it fine. To conduct the compressed air to the interior of the nose, I drilled a hole in the solid plywood & pressed into it a valve stem from an old inner tube (visible in the photo below to the right of the heater). After squirting copious quantities of caulk on both sides of the foam flange & the cord for the heater (and checking the heater’s switch was turned ON), I screwed this plywood to the floorboard with yet more sheetrock screws.


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Heating it
I plugged in the heater and waited for something to happen. I wasn’t sure if the event would be the desired softening of the foam, or if enclosing the heater in a small, insulated space would cause the whole contraption to go up in flames. I waited expectantly with a bucket of water at the ready but didn’t have to use it: after 2 minutes or so, the foam started to sag as it softened.

Inflating it with compressed air
I attached the air chuck from my compressor to the tire valve stem and inflated to the desired shape. Things didn’t go well on the first blow. The foam not only expanded upward as I wanted, but also sideways over the lip of the floorboard hole, so much so that what was supposed to be svelte & aero looked instead to be about 9 months pregnant. Fortunately, I found that when deflated & re-heated, the foam loses all memory of its former shape. To prevent my nose from getting in the family way again, I surrounded the sides with sheets of masonite, curved to follow the shape of the hole in the floorboard. Thus contained, the foam could only inflate upward. I found that if I wanted some area to expand more than the rest, I could locally heat it so the foam was more pliable there & would inflate more. The foam tends to shrink a little as it cools: to counter this, I would keep adding bursts of air to compensate for the inevitable small leaks & keep the inside pressurized


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Trimming
I cut it off the form while it was still screwed on. The foam cuts easily with a razor knife: a wet blade slides through the material more easily.


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Attaching
I built a fairing frame from 1/2 x 3/16 & 3/4 x 3/16 aluminum bar: it’s thin enough to be shaped by hand, sturdy enough to rigidize the fairing. The frame was fastened together with sheet metal screws. I glued the foam to the frame with contact cement; (roughen the aluminum and foam with sandpaper before spreading on the glue). The section of fairing behind the nose had 2-D rather than the 3-D curves of the nose, so I could form it more easily. I’d glue a sheet of foam to the frame on one (vertical) side, heat the bend line until it draped over the frame, then glue that section & repeat.


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The lower part of the nose was blown by a variation of this technique; It was blown from a flat sheet in a flat (no tombstone) form,


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So how’s it work? It’s about 1 mph faster on my test hill than my old fairing, thought it’s not quite as fast as John T’s machine. To visualize the pattern of air flow over it, I taped yarn tufts to one side & had my son photograph me as I sped by:


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Most of the tufts flowed nicely except for a couple near the front that got tangled up with their neighbors. Some didn’t , though: on the top of the foot pod, along the cockpit sides & in back of my head, there are tufts flowing lackadasically or worse, perpendicular to the airflow. These are probably areas where the airflow is stalling or forming eddies. Hopefully, after I attack them with knife, heat & glue gun, I can whip them into shape in time for my first race in 2002.