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Old 09-25-2020, 05:04 PM   #1 (permalink)
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Drag reduction for upright bicycles

Consistent with aerodynamic improvements made to other vehicles I would like to see more done to reduce drag and energy consumption of common commuter bicycles. A typical bicycle has a frontal area of 4 sq. ft. and a drag coefficient of 0.6. A rider's body acts like a pump vane. A front fairing and tail box can offer weather protection, cargo capacity, and drag reduction.
I have been experimenting with simple fairings using cut and fold methods of 4 mm Coroplast. The wind load on a fairing attached to the head tube compresses the top of the fairing. The sight line needed to view the speedometer can be blocked. I am continuing to reinforce the front fairing with various forms of tubing. I do coast down tests on a hill where there is a 30 ft. drop in 0.1 mile. A full body fairing that resembles a sailplane fuselage with a Kamm tail can be designed using the HPV body shell software at recumbents.com. There is provision in the software to make a shell for uprights. The file can then be used in CFD software to evaluate the shape.

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Old 09-25-2020, 05:30 PM   #2 (permalink)
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We probably need to exclude some options if they're not going to be available.

- Recumbents are out?

- Small wheel bikes are out?

- The fairings have to be simple to make and cheap?
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Old 09-25-2020, 05:55 PM   #3 (permalink)
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I like the form of the PVC frame. Will the next generation have some taper in plan?
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We are operating at an overall mechanical efficiency of only four percent… Therefore, we find that if we increase the overall mechanical efficiency to only twelve percent we can take care of everybody. That three-fold increase in the overall efficiency can only be accomplished by redesign. – R. Buckminster Fuller

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Old 09-25-2020, 05:56 PM   #4 (permalink)
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There is already much being done for recumbents so my focus is on the more common upright. The small tired folding bikes would use a similar shell. The wheel base of 41 in. for an adult bike is typical. The weight would need to be around 6 lb and cost of materials to be under $100 USD. The shell would be from the rider's shoulder to the upper calf. The overall length would be about 60 in. I started this originally as a middle school student project. Wheel treatments would be a disc in the rear and faired spokes on the front. The bike pictured has the same coast down speed as the naked bike.
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Old 09-25-2020, 06:01 PM   #5 (permalink)
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I just bought some rigid 1/2 in PVC pipe and 45 elbows for a frame. Side panels are also being considered that hinge to the upper part "lambo" style. A full shell will need turn signals.
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Old 09-25-2020, 06:28 PM   #6 (permalink)
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I quite like this.



Fibreglass nosecone and zipped stretchy cloth side/rear fairings.
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Old 09-25-2020, 08:06 PM   #7 (permalink)
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Something like the red cycle is what came to mind when I saw the title of the thread.

Bending down can reduce frontal area by a bit but not everyone wants to ride a bicycle with their head touching the handlebars.

I've thought about fairings along the side and wheels similar to the red concept above, with the driver sitting upright. A tapering storage area would be behind the driver's back, either for storage or a battery system for an electric bike. Maybe an aero helmet? although I'm not exactly sure how much aerodynamic benefit that would have.



I've always liked the idea of making an electric bicycle and improving the default horrible aero of a bike and rider, but I don't really have a practical use for one.
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Old 09-25-2020, 09:21 PM   #8 (permalink)
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Quote:
I just bought some rigid 1/2 in PVC pipe and 45 elbows for a frame.
PVC is such nasty stuff. It creeps and shatters.

What about a welding rod frame with a Dacron skin?
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Old 09-25-2020, 11:38 PM   #9 (permalink)
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I have a supply of 9 mm aluminum honeycomb but that is not as available as PEX tubing, Lexan, or Coroplast. I went to PEX first due to crash concerns as the neck is vulnerable. I might try short pieces of PEX filled with foam along with the elbows. Fiberglass was used by Craig Vetter on motorcycles but that requires building a mold. I used 1 inch hex wire mesh bonded between 0.005 in. plastic tarp material on the rear cover. Again the need for a rigid space frame. I will look into 1/2 in. foam insulation board bonded to plastic or aluminum sheet. Cloth lycra has been used and I would like to see something waterproof. Padding at the should and hip would be a plus. I appreciate the suggestions.
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Old 09-26-2020, 12:02 AM   #10 (permalink)
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Quote:
Originally Posted by Grant-53 View Post
Fiberglass was used by Craig Vetter on motorcycles but that requires building a mold.
I think to get decent results you're going to need something with compound curves at the front. I'd probably try blowing a dome from acrylic sheet. Acrylic domes are also available off the shelf in lots of sizes.



In the past I have cut one up with a 1mm cutting disc in an angle grinder.

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