Nov 2

Nov 2, 2004

Scary FAST!

Yikes! Well - the first watts test today out at highway 22 and this thing is fast - exactly how fast, I'm not too sure just yet. Here's what happened:

It seemed like a very calm day - The weather forecast indicated 10km winds, but on my drive out I noted flags were pointed straight down to the ground. I started on my 3.6 km out leg feeling a bit disappointed. Typically on a calm day, the unfaired TCR1 will average about 26kph on the out leg which I have always thought was fairly flat. There obviously is a slight uphill grade because my return legs are always faster. Typically, I have been attributing most of that return speed to the prevailing tail wind, but I may have been greatly underestimating the grade of this slope. At the end of the out leg, my average was only 30 kph at 154 watts average input. I had calculated previously, that in order to attain my 40 kph target with this faired TCR1 streamliner, I would need to average in the mid 30's to end up with a 40 kph average, so I wasn't thrilled.

What I hadn't taken into consideration, was two things: 1. The upslope on the out leg, and 2. The weight of the fully faired TCR1. I lifted it up and set it on the scale this morning and was surprised to find it weighed 63 lbs!! Lugging a 63 lb bike up a slope at 30 kph average speed with 150 watts input power is pretty good. Just how good became very evident on the return leg...

After about 30 seconds on the return leg my power was up to 100 watts and I was over 40 kph and in my last gear and spinning too hard. At speeds over 40 with semi trailer blasting by and the occasionally side breeze and the rocking action caused by fast spinning, the faired bike feels sort of - well, I want to say scary, but I think 'unfamiliar' would be a better way to put it. About 45 seconds after the start of the return leg, the chain fell off. Ever since I put the fairing on, the chain has been falling off the big chain ring. The reason is that I'm always using the smallest gear now whereas I wasn't before, and the angle the chain takes between the large chain ring and the small gear is fairly sharp - so with fast spinning, it flies off. When it comes off there is not much I can do, but wait until the trike rolls to a stop so I can pop off my canopy lid, lean forward and pull the chain back onto the chain ring. Basically it means the end of the watts test.

So, I decided to simply glide as far as I could just to see what would happen. Well, it didn't stop until 4 km later when I got back to the car - and it only stopped because I put the brakes on! I was averaging 30 kph with 0 power input!

When I got back home and plugged the SRM computer in, I realized that my watts test was still very valid. I had an average watts input and average speed for the 3.6 km out leg, plus I had an average watts input and average speed for the 3.6 km return leg - even though, most of the return watts was ZERO due to no chain. Still - I realized I could average the two watts values and average the two speeds and derive an overall average for the round trip - then I could plug that value into my excel calculator and come up with a valid coefficient of drag (CdA) number that I could use to predict what my 150 watt speed that 'would have been'.

Out average watts 3.6 km = 154 watts
Out average speed 3.6 km = 30 kph
Back average watts 3.6 km = 20 watts
Back average speed 3.6 km = 30 kph

Overall average watts = 87 watts
Overall average speed = 30 kph

What is still unknown at this point, is exactly what my rolling resistance is. Knowing that effects what my predicted 40 kph watts requirement would be. Here are some averages based on a range of possible rolling resistance values that John Tetz and I came up with:

Crr Values: .007 .0045
CdA required for 30 kph average with 87 watts average input power: .7 1.3
Predicted power required to produce 40 kph average speed: 143 165

As you can see knowing the rolling resistance is very important in calculating CdA to predict other power/speed values. My predicted power required to hit my 40 kph goal could be anywhere between 143 watts (which would be GREAT!) and 165 watts (which would be tough). John feels that the rr number is probably around .007 because using the pwrdrag2.xls calculator, and a couple of my better TCR1 unfaired watts tests, .007 worked out to be about right. If that's the case, and I really hope it is, then my CdA (drag) of the fairing is almost exactly where John and I thought it would be at .7 - another advantage to the higher rr case is there is probably something I can do to improve my rr and be even more efficient.

The Kreuzotter calculator confirms a CdA of .7 for my 30 kph speed at 87 watts input using a "high pressure racing slick" as the front tire, and a "high pressure wide slick" as the rear tire (which would be about correct for the TCR1). Warrens calculator Predicts a CdA as high as 1 using their rr input options that closest match: .0045 for a Schwalbe Stelvio 406mm tire and .006 for a narrow racing tire. I used .0055 because slightly more than 50% of my weight is over the 650 narrow racing tire. However, still using Warrens calculator, with rr values as low as .0055 and a CdA as high as 1, my predicted 40 kph power requirement would be 150 watts exactly.

So to summarize, it looks like I'm fairly close to my target speed and I think it can only get better. I can lower my CdA by reducing the nose area by switching to a shorter crank. Also, that will allow me to set my seat back a bit more and will allow me to bring my steering column UP between my legs to a bar that sits about mid chest height. Then I won't require such a large area in the fairing to allow my current underseat bar to turn. The bubble top will also improve the drag picture, as will covering over the rear wheel strut slots. Also the final fairing should be a lot smoother than this one and my extend of laminar flow should improve a bit. Another area is adding wheel discs and/or wheel fairings on the rear wheels, and a fairing on the two rear struts. If my current CdA is really .7, then all these mods should get me to .6 or maybe even .5 ! (just to be silly, my 40 kph power requirement for a .5 CdA would be 126 watts!!!).


OK - on to other issues that todays ride brought to light. A semi trailer blasting by me when I'm doing 45 kph doesn't feel great. The pressure sucks the fairing (and me) to the left into the traffic. It takes a firm grip on the steering bar to counter the suction - nothing I won't get used to, but the fun would be greatly amplified at speeds upward of 45.... Definitely a concern regarding a cross country trip in this faired vehicle. Also at 45 kph and higher, slight wind gusts from the side are amplified. Again, nothing for any great concern, but higher speeds and/or higher wind gusts might not be pretty.

I'm staying focussed on developing this bike for a closed track for now. I'll deal with the cross country issues later...

gk


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. Make a new steering bar that rises up a bit higher - also takes up less room on the sides so fairing can be tighter
7. Adjustable seat height
8. Make fiberglass canopy top with acrylic bubble and tailbox
9. Paint this puppy!


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
745 km


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