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I use the term "windcatch" because the term "bike sail" probably brings to mind a bike with a giant ship's sail above it. This has been baked on 2- and 3-wheel bikes.
I'm suggesting a smaller, more modest "sail" which can be attached to the front wheel of a bike. The windcatch forms a triangle on
each side of the bike. One triangle goes from the front wheel axle, to the pivot of the handlebar, to the tip of the handlebar. This provides added surface area for downwind biking on an accessory level, so your bike does not become a "sail bike", it's still just a bike with a little sail/kite material on the front.
It could be stored in the front fork tubing and deployed/retracted through some handlebar cables/levers.
It might seem like this would be in the way, but the triangles formed from handlebar to axle are not in the pedal path or knee area (on my bike anyways), and would not interfere with steering tension as the front axle is bound to the handlebars.
The added surface area of this windcatch might not seem like much, but if you've ever biked in wind you know the smallest bit helps (or hurts)!
Probably baked, but I couldn't find it. If this is already burnt to a crisp, I apologize.
The Sail Bike
http://www.vsv.cape...rharb/windbike.html
[Klaatu, May 20 2008]
Wind catcher
http://freewayblogg...bike-high-wind.html
Similar idea (but on the back) [spidermother, Oct 27 2009]
[link]
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ahh... so a bike sail; just kidding, but your proposal does sound like a particular kind of sail (the one on the bowsprit). |
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Unless you are cranking up a steep hill, riding in a huricane, barely exerting yourself, or a weakling, you will invariably ride with a steady state speed greater than that of the tail wind i.e. the apparent wind is generally always head-on. The sails described will therefore be an impediment to progress. |
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//The sails described will therefore be an impediment to progress.// |
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Hmmmm... I'm not sure I agree. I live in South Dakota where the wind is regularly faster than my desired biking speed. Any amount of wind to the back increases speed and/or decreases the needed output of leg power. The larger the surface area I present to the wind, the more intense this effect. Isn't this basic sail physics? |
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So it's not something in the saddle to catch farts then. |
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It’s a bike spinnaker. I like the idea but you’re both off a bit. It doesn’t have to be a hurricane [Texticle] but any amount won’t do [napoleonbag]. To help, the wind would have to be faster than the speed you are already moving. However, it may have to be a somewhat larger than what you described to be a noticeable improvement because much of the sail area would be in the wind shadow of your legs. |
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If you're cycling with a 20-29km/hr (13-18mph) tail wind - a 'moderate breeze' on the beaufort scale - you should be able to easily ride at 30km/hr plus. Say 35km/hr. That means you've got an effective 6-15km/hr head wind. |
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"On a flat road, aerodynamic drag is by far the greatest barrier to a cyclist's speed, accounting for 70 to 90 percent of the resistance felt when pedaling." |
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Which is to say that [Texticle] is correct, indeed. On a good bike, you should be able to out-pedal any tailwind, as most of your work just goes away. |
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If you want to take your old beater out for some spinnaking, go ahead. But this design doesn't sound like much more area than sitting up and spreading your jacket, which is a lot more fun. |
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[Texticle] and [baconbrain], why are you assuming that a biker would always want to exceed windspeed? |
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15-20km/hr may not be fast for a professional racer, but is plenty fast for a bicycle commuter, who may prefer to coast when possible, rather than exerting himself 5km/hr beyond windspeed for the sake of it. |
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I'm not assuming that every biker would always want to exceed the speed of a tailwind. I'm just stating that a good cyclist on a good bike almost always can. |
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This idea would be fun, but as an aid to cycling it's not much use. The description doesn't say which kind of cyclist would use it--racers, tourers or kids--but it does include the word "helps". |
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//a good cyclist on a good bike almost always can// |
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...at the cost of exerting additional energy. |
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If your goal is to constantly go as fast as possible, you're right... a sail will impede you, just as a sail attached to a speedboat will impede it, and a sail attached to a Porsche will impede it. |
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If your goal is to move efficiently with the wind at a liesurely speed (commuting, for example), *any* increase in windward surface area will reduce the force needed from your primary power source (legs, engine, etc.), up to, and sometimes slightly beyond, the speed of the tailwind. |
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I feel you are underestimating the effect of a modest tailwind. |
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I feel you are overestimating the effect of a modest tailwind. |
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In still air, I can go 15 mph pretty easily on my commuter bike. With a 15 mph tailwind, which I'd not regard as modest, I could just as easily go 25 mph by pedalling along at my usual effort. Coasting with a sail, I'd be doing at best around 12.5 mph, or half as fast as if pedalling, and slower than normal. What am I to tell my boss? "I was late because of the fierce tailwind."? |
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I'm not dragging around a sail just so I can go slower on the few (very few) times that I have a kick-ass tailwind. I'd love to go down to a parking lot and go bike-sailing sometime, sure, that'd be a giggle. But this idea says it "helps", and I say it doesn't. |
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I took the handlebar fairing off my bike after deciding it wasn't useful. I'm not seeing this idea as useful, or as much fun as other bike sails. I'm also, finally, fishboning it. |
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//pedalling along at my usual effort// |
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Again, you're assuming/implying that this is somehow necessary or desirable. Imagine the same argument for a car. If you're driving with the wind, do you hit the gas and go 20mph faster just because it's windy, or do you absorb the efficiency benefits of the wind and go about the same speed, saving gas and $$$? |
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When the wind is at your back, you have the choice to pedal as usual & go faster than usual, or pedal less than usual and go the same speed. Maybe you have calories burning a hole in your pocket, and can't stand riding a bike without going AFAP, but I would wager most people take the second option, taking a prize of an energy boost over a prize of speed. |
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//I'm not dragging around a sail just so I can go slower on the few (very few) times that I have a kick-ass tailwind.// |
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Ok, so you don't live in a windy area, and the times you go biking, you would rather go fast than conserve your energy. This is not for you. But if it were for you, it's retractable for counter-wind or cross-wind travel. |
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OK, let's say you're happy to coast along at something approaching wind speed when you've got a tail wind. To use [baconbrain]'s numbers, let's say it's a 15mph tail wind and you want to go 12.5mph. That means your sails are filled with only a 2.5mph apparent wind. |
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You're going to need bigger sails for this, methinks. |
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Why would you bother when you could just as easily pedal along super leisurely, sipping a latte if you like, and be maintaining a speed that is in all probability faster. |
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Isn't it *good* to have a low apparent wind from any direction? The absence of apparent wind doesn't mean the wind isn't working on your sails, it means you are at a point of equilibrium. Or is my understanding of basic physics f'ed up? If a plastic bag goes floating across a soybean field, it is moving at very close to windspeed, and from the perspective of the bag, there is no wind. But the wind is indeed working on the bag. |
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Where do you guys live? Seattle? Not to be rude, but haven't you ever biked in 20mph wind? I grant that a bike sail is pretty stupid for other reasons, but must insist that the effect of tailwind is *significant*, and is highly dependent on even slight changes in windward surface area. |
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And one possible reason (of many) a person might prefer to coast at 12.5mph rather than pedal at 20mph occasionally is that they bike commute 20 miles round trip per day, and it feels good ride rather than drive, sometimes, when possible. |
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If the subway train is out of order, you walk to work. If the train is working, you ride it. Would you enter the subway train at the back and walk to the front while it's moving? |
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If there's a strong tailwind, I pedal, just for the fun of going faster. It's fun! Wheee! |
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I used to live in Seattle, yes. But I've bicycled across the Great Plains about seven times (Missouri to the Rockies and/or back), so I've been in windy country on a bike. |
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I've also lived in subway cities, and yes, I'll walk forwards in a train, or even backwards, if the stations exits work that way. |
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At equilibrium with this design, there will always be an apparent wind from the back. If the bike was frictionless, you could float along like a dandelion seed, yeah. But since the bike has friction, you'll travel at the speed at which the apparent wind from behind impacts with enough force to overcome wheel drag. |
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You can never go as fast as the wind unless you pedal or go downhill. |
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Well, as long as they looked like bat wings, maybe. |
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//a good cyclist on a good bike almost always can// |
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Most of us are not good and don’t have a good bike. |
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My average speed on the bike paths here is nowhere near 20 mph. I ride a crusty thrift store bike all over town. It’s up hill exactly half the time and usually with a 4 year old kid attached to the back on a trail-a-bike. I think a 15 mph tail wind would help quite a bit. |
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So the sail is not for a few world-class cross country cyclists in Missouri. Who cares? |
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How much wind resistance is there for a bike traveling with the wind at wind speed? |
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Well, none, obviously. But don't forget that the wheels are going around and the pedals and legs may be moving about. So you can't say there is no AIR resistance. |
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Why do you ask? Have you a point? |
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Let's say you're pedaling along on a flat surface at the same speed as the tail wind with your sail just sitting there not helping you. You need to take a little break and coast for a minute. Wouldn't your sail immediately fill up and keep you from slowing down as much as you normally would during that break? |
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Well yes, but it would be a pain in the butt for most other situations. Not worth it, overall, in my opinion. |
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Here is an idea, how about if the triangular wind-catches where mounted at a slant, with the leading point/edge being towards the line of travel. The sail would decrease drag in head/no winds, and increase drag from tail winds. |
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That _might_ decrease the drag coefficient, but the overall drag would still be increased due to the increase in frontal area. |
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Maybe the sails could be on a hinge and would open and close on their own like those frilled lizards- a sort of one way valve. It would have the added benefits of scaring off mountain lions (which stalked and killed some bikers in Southern California a few years ago) and attracting mates. |
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Now you're on it. Include some smart circuitry to make them pop open without warning periodically when conditions are right, and close up just the same way. |
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