Oct 31

Oct 31, 2004

Another wind test and fairing tabs

Here is an illustration of what TCR1 will mostly look like with the canopy on. I found a local company who does vacuum forming of Acrylic bubbles for flower arrangements. It looks like they can make a clear bubble for me - I'll fabricate the rear of the canopy with fiber glass.

I spent today bonding tabs onto the top and bottom fairing halves.

The tabs are made of Sintra plastic and are bonded to the fiberglass fairing with contact cement. I could have used Krazy Glue or epoxy resin, but I found that contact cement works very well and dries quickly. One advantage to working with Sintra plastic is you can heat form it which comes in handy for curving the plastic around the nose and tail. The tabs alternate from the top half to the bottom half.

It was nearly IMPOSSIBLE to get both fairing halves together using these alternating tabs! I could get one side in and the other side would pop out, etc, etc. I thought it would be easier if I had a helper (Helen) to align the outside while I sat in the seat and aligned the inside tabs, but it was still really difficult. We eventually got them together and I took off for another test ride in the wind.

The fairing top bounced around less than it did yesterday using duct tape, but every major bump would lift the top up and out of alignment, so by the end of my ride the fairing top was falling off one side.

I need to round the corners of the tabs, and taper the edge with a file so that the two halves are easier to mate together. Then, I need some method to secure the two halves together and stop them from bouncing apart - not sure what the best way to accomplish that would be... Perhaps something pulling down on the top shell from inside the fairing - or even a few Velcro straps.

The next item on the list is to make some stiffener ribs, as the fairing moves around quite a bit in the wind and over bumpy road surfaces. I might construct the ribs with Sintra since it can be heat formed with a heat gun and it's easy to cut and glue. I also have a bunch of Coroplast, so I might try to make some ribs with that and see which one works better.

Again, I could really feel the wind buffet the fairing during a direct cross wind, but handling the trike was manageable using the steering bar. I can't imagine what it would be like controlling a faired two wheeled low racer in this wind!! Something I could experiment with is extending the tail end of the fairing so that the center of pressure moves closer to the pivot axis. That way, the wind won't actually 'steer' the trike because it will be blowing directly into the center of the steering axis. Another option is to add even more tail area so that the center of pressure moves BEHIND the pivot axis. Then a cross wind will help steer the trike INTO the wind and be self correcting. However, like I said, it's not a huge deal to manage with the steering bar, so I may just leave it.

John Tetz sent me this very cool excel spreadsheet and paper today called "Determination of Drag Parameters Utilizing a power Meter" by John Snyder and Theo Schmidt. The idea behind the calculator is to input two different watts values with two different resulting speeds. The spreadsheet then calculates the drag AND rolling resistance for the bike. This could be very useful in quantifying the Cda of the fairing and also knowing exactly what the rolling resistance of the wheels are. Unfortunately, the calculations are very sensitive to exact watts and speed values. To figure out exactly what my wheel rolling resistance was, I entered some of my watts tests values for 150 watts and 200 watts. I have done quite a few tests and some of the average speeds are 1 to 3 kph apart - this yields rolling resistance values from .008 to .015 which is over 70 watts difference at 30 kph.

I am concerned because in trying to predict if I will make my 40 kph average on 150 watts with the fairing on, I need to know exactly what my current rolling resistance is with the three wheels

Below are some various fairing progress shots:

Measuring the exact middle of the fairing for cutting the slot for the front wheel
Measuring the location to cut the slots for the rear strut
Front wheel slot cut out
TCR1 in the fairing bottom with the rear strut slots cut out
Nose fairing mount
Rear fairing mount
Two mounts on each side of the front wheel to prevent the fairing from rubbing the front wheel
One of the benefits to working with Sintra plastic - you can make all kinds of cool gadgets - like this SRM computer bracket which attaches to the side wall with Velcro.
The alternating tabs on the bottom shell.


TCR2 (track) 2Do LIST:

1. Make a platform for the wind trainer (mini-rollers)
2. Add front caliper brake
3. Mount first fairing and all the work required with that
4. Make CF front wheel fairing
5. Make CF rear wheel discs
6. Redesign steering bar to above waist (possibly brake lever steering for record bike???)
7. Adjustable seat height


TCR1 (cross country) 2Do LIST:

1 Add front derailleur
2 Run road, roll-over and watts tests for new suspension system
3 Worm gear steer prototype (Waiting for final design and parts list from Ben)

TOTAL distance on TCR1
704 km


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