example of a bad fairing attempt :( ..ideas for attempt #2?

[jeebus]

At first I was all proud of myself for making such a simple minimalist fairing, then I took it for its first ride tonight, and it was like dragging an anchor behind the bike. Below 18mph it was largely indistinguishable from before, but above 20 it was very noticably slower with the fairing. After coming down a nice hill into a straightaway that normally begs you to go 22-24 for a good long while, I was struggling to hold 22 and ran out of steam fast.

So, next time there's nice weather and I have free time, I'll go to a hill and do some coast-downs just to confirm quantitatively what I already strongly suspect about this design before trying something else.

But it seems like it should have worked. Any ideas how to improve it? My knees tuck reasonably well behind it when in the up-posistion entering a pedal stroke. I figured this design would actually be better than the ones that cover your feet since there's so much room for the wind to close back in that the foot-fairing was a wasted wind-break. This one was supposed to focus on the chest and head, and knees part of the time. It's a piece of lexan cut 21 inches wide and 18 inches tall, with a very slight curve in it.

Should it be longer with more curve so it wraps a bit further back maybe? Also I thought the top might be a little higher than necessary, but not more than an inch or so I didn't think. I can try to take a pic with me on the bike if that helps, but that takes a little more skill.

 

[John Tolhurst]

Without a fairing, your body is a single volume for the air to pass around. With a fairing the challenge is to create a single more aerodynamic volume. Any distance between your fairing and you invites the air to treat you as two volume, each with its own drag. As the speed increases, the tendency for the wind to treat you and the fairing as a single entity increases, so your design might not start working till you get to 60 kph or something.

The fairing seen on my Silvio http://www.cruzbike.com/blog/2007/03/silvio-update.html seemed about neutral to 35 kph, then assisted above that. Around town and sprinting, I prefer without it. Long steady rides, I like.

 

[Robert Stewart]

Now that I have the position pretty much dialed in, the Streamer fairing on my Silvio feels like it gives me a significant aero boost, but I haven't got a computer setup for objective comparison. See my brag board thread to see the fairing position. YMMV of course.
Cheers,
Rob

 

[Mark B]

Everytime I ride into a headwind, I get to wondering about a fairing. When I turn the corner and it's a crosswind, I put it out of my mind!! I have to say, though, the last few days of riding in the wind tunnel have me feeling a little more secure. I'm still not sure I want to attach a sail out front of my bike! :shock:

Mark

 

[Robert Stewart]

Hey Mark,
It only feels like a sail when there's a tailwind, and then it's the best thing in the world - effortless cruzing...

In a headwind, it's like a cross between a shield and a sword, if you catch my drift. As for crosswinds, take a close look at my pics and you'll see that there isn't actually that much surface area to get pushed around with an open fairing design like the Streamer.

Cheers,
Rob

 

[jeebus]

Man, I hate running performance tests and getting only semi-consistent results. I rode to a hill today that I thought would be a good place for some roll down tests. I tested it three ways:

1. fairing as shown in pics (relatively flat, just a little curve to it)
2. tightening that middle zip-tie to put a much bigger curve in it
3. removing the fairing

Here's what I got, using my speedometer's "max speed" as the metric for each roll down:

1. 23.0mph, 23.0mph, 22.8mph => avg 22.93mph, max 23.0mph
2. 24.7mph, 22.2mph, 23.7mph => avg 23.53mph, max 24.7mph
3. 23.0mph, 23.5mph, 23.3mph => avg 23.27mph, max 23.5mph

I'm afraid I goofed in either my hill selection or my chosen metric, because the decline isn't as constant a slope all the way down as you might hope. If you happen to take a particularly good path and not make any steering correction when you briefly pass through the steepest part you can get the best max speed.

But the results were still surprising to me. The comparison between 1 and 3 doesn't particularly jive with my initial experience going around the lake. There I found it positively oppressive trying to hold 22mph, which normally wouldn't be a big deal, at least not for a little while. On my rolldowns, the differences are all so small, unless you interpret that the minimums should be thrown out as just representing poorly ridden paths down the hill and the max's are more meaningful.

So I don't know where to go from here. Splurge on a real fairing? Keep seeing if my homebrew can be turned into something better? Data point 2 does show some promise for the design. And I'm positive mine is lighter than anybody else's fairing setup.

- Mark

 

[Doug Burton]

Mark,

Bully for you running multple tests on each version. It's really hard to get folks to do that, and it's the only way to get a real answer.

The standard deviations for each run were:

1: 0.115470054
2: 1.258305739
3: 0.251661148


This means while runs 1 and three are somewhat comparable, the variation in the second run is 5 times the third, inferring something else was at work here.

For rolldowns I usually use 6 runs in each config. as a base line.

For an SD of .25, to get a 95% confident estimate of difference in the averages, you'd need 15 runs. For an SD of 1.25, you'd need 365 runs!

This is why we don't make numerical claims about bike performance. To do it right, it ain't easy and it ain't cheap! And people just argue with you anyway!

Good onya!

Best,

 

[jeebus]

Going back to john's response, I know it's possible for the wind to close back in, but I thought there were lots of bikes like the easyracers goldrush that put their fairing about arms distance from the rider's body and I've heard those bikes do very well with a fairing. They do better with a full sock no doubt, but still do quite well with just a fairing.

I say that without any firsthand experience though. So now that you've got that SIGMA project in the works, what are the various fairing / tailbox / full-sock setups you've tried, and what do you like?

If I had any sewing ability I might actually try making a mini "shoulders and upper-torso sock" to go with my mini fairing. Keep the wind from closing in as much around the fairing, and anything below the fairing just leave it as-is. It wouldn't necessarily attach to the bike anywhere behind me, just be a sort of cape I'm wearing that velcros to the sides of the fairing in front of me.

About the numbers from my experiment, I think I need to pick a downhill with a more uniform grade to get more consistent numbers. I think with a little more care to what's being tested, more consistency is possible. When I first headed out this morning I had a specific hill in mind, but I found my terminal velocity on it was ~30mph which isn't the speed range I was trying to target, so I picked another spot that had the right speed but wasn't as good in other ways.

- Mark

 

[John Tolhurst]

jeebus wrote: Going back to john's response, I know it's possible for the wind to close back in, but I thought there were lots of bikes like the easyracers goldrush that put their fairing about arms distance from the rider's body and I've heard those bikes do very well with a fairing. They do better with a full sock no doubt, but still do quite well with just a fairing.

If you are sitting pretty upright, a fairing can more easily help. But a easyracer with front fairing won't be much better than a naked Silvio, probably worse if my testing experience counts for anything.

jeebus wrote:
I say that without any firsthand experience though. So now that you've got that SIGMA project in the works, what are the various fairing / tailbox / full-sock setups you've tried, and what do you like?

Front fairing only, so far.

jeebus wrote:
If I had any sewing ability I might actually try making a mini "shoulders and upper-torso sock" to go with my mini fairing. Keep the wind from closing in as much around the fairing, and anything below the fairing just leave it as-is. It wouldn't necessarily attach to the bike anywhere behind me, just be a sort of cape I'm wearing that velcros to the sides of the fairing in front of me.

About the numbers from my experiment, I think I need to pick a downhill with a more uniform grade to get more consistent numbers. I think with a little more care to what's being tested, more consistency is possible. When I first headed out this morning I had a specific hill in mind, but I found my terminal velocity on it was ~30mph which isn't the speed range I was trying to target, so I picked another spot that had the right speed but wasn't as good in other ways.

- Mark

My methodology is to benchmark against another bike. So go our with a friend who has a similar roll down performance and make tests based on the comparitive performance. This controls for the vagaries of local air movements, different slopes, road surfaces etc.

The easiest way to make yourself more slippery is to wear proper tight cycling clothes, and to get an aero helmet. And roadshoes that are only as big as they need to be and have no heal. Ride with straight arms.

My best fairing on Silvio was set up on narrow bars and just passed over the hoods of the brifters. I also extended it with polycarbonate so that to see the road in front of the bike I had to look through this extra shield.

My sunday riding on Perth can involve a few stops and starts, and the fairing seemed to bog me down as the bike did not swing into place so easily for each pedal stroke on the slow build up high torque cadence from start.