Aerodynamics

General Discussion about electric bicycles.
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Re: Aerodynamics

Post by jbalat » Nov 05 2013 6:21pm

I've been toying with this for a while after I began chasing a friend of mine on a recumbent bike while I was a racer road bike (no motor).. Within a few minutes he was well out of sight, no chatching him.

Something like this is ideal since it still maintains a good visibility in the traffic. Best part of it is that it would travel at a nice pace on the bike paths without a need to add an electric motor !!
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Here is a comparison of recumbent vs normal bikes
http://www.flyingfurniture.com.au/info/ ... faster-yes
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Re: Aerodynamics

Post by Pat Eaton » Jan 15 2014 9:04pm

Just adding wheel covers makes a noticeable difference. :D
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made_in_the_alps_legacy   10 kW

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Re: Aerodynamics

Post by made_in_the_alps_legacy » Jan 16 2014 1:03am

(This topic should be linked to "power calculator" topic)
From a very good doc
The Aerodynamics of Human-Powered Land Vehicles
Albert Gross Chester Kyle Douglas Malewicki
Image

Read the complete doc HERE
Pay attention to the chart on page 6 :
Image

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Re: Aerodynamics

Post by jbalat » Feb 03 2014 5:50pm

Very interesting chart. On my road bike (unpowered) I gained about 3-4kms/hr going from an upright into a racing position and another 3-4 kms/hr going to a tucked low position. So about 27-28km/hr to 35km/hr at the end. The problem is the tucked position is not very comfortable.

I've been talking to my aero eng mate about perhaps adding an electric fan in front and behind the rider blowing air upwards. This should create an air pocket around the rider and help the oncoming air to wrap around and maybe reduce the amount of detached airflow. Not sure about the efficiency of the system but worth a try anyway just out of curiosity :D
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Re: Aerodynamics

Post by made_in_the_alps_legacy » Feb 04 2014 2:33am

jbalat wrote:Not sure about the efficiency of the system but worth a try anyway just out of curiosity :D
Yep, even if 3D computationnal fluid dynamic tools (CFD) are not too bad in calculating aerodynamics,
there is still a lot to play with on the experimental side... :D

NB: The Funny thing about these table and chart is that they also took into account "rolling resistance", what I like too is that most endlesssphere builts could be compared to those numbers, from a KMX kart with fairing to a e-skate rider...

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cal3thousand   1.21 GW

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Re: Aerodynamics

Post by cal3thousand » Feb 04 2014 2:31pm

The issue isn't really if aerodynamics play a role in efficiency, because they clearly do.

The question comes to practicality and ROI (return on investment). Most of the gains on aero are not as beneficial when compared to the cost to acquire such gains. As your speed increases, aero's ROI increases. But with speed increase generally comes concerns of road handling and safety.

So to gain aero advantage, people have to "give up" something. Recumbents trade maneuverability and ride height for aero, but gain other things like static balance and cargo etc. Adding fairings trades "looks" and "fitting" in for a small bump in Aero. And the better it looks, the more it generally costs. If you can make them look good and not cost much, let me know. (Kingfish is a bit along these lines)


It also depends on how far off the "ebike"-end that you're willing to go. If you want to maintain a stock stealth "bicycle" look, aero doesn't usually fit in. If you're ok with your bike being unmistakable for an ebike, there's plenty of options.

I would like to see someone experiment with CAD (cardboard aided design) and come up with various fairing shapes for ebikes that we can re create out of polycarbonate.
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Re: Aerodynamics

Post by Hillhater » Feb 04 2014 6:43pm

The ZZipper fairings http://www.zzipper.com/Products/prod_upright.php have often been shown to significantly improve aero efficiency and rider comfort.
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Re: Aerodynamics

Post by bdc43 » Feb 13 2014 7:19pm

There's an interesting design from the late 80s that was used on a bmx bike and apparently they hit 40 mph on pedal power alone. The fairing was made out of styrene (incredibly light but also fragile):


http://www.culturecycles.com/2012/06/19 ... rbike-bmx/

I wonder how difficult it would be to make such a complex shape out of high density polyethylene (HDPE)?

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Re: Aerodynamics

Post by Frank » Feb 14 2014 8:18am

Great to know that Zzipper is still around! I still have one on my eighties road bike and found it's "good" for two gears I.e. for same effort I could be two gears higher.
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Jonathan in Hiram   1 kW

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Re: Aerodynamics

Post by Jonathan in Hiram » Feb 14 2014 11:59am

This is certainly aerodynamic appearing, it has two wheels and last but not least it's electric.

For a regular upright bicycle with maybe electric assist one of the Zzipper windshields/fairings and maybe a wedge tail box would be hard to beat without a lot of work.



And then there's Craig Vetter's Alcan (after the highway) fairing.

Image

Image

This is an old Vetter design for a smallish (by today's standards) motorcycle.

Image

Image
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Re: Aerodynamics

Post by Joppo » Feb 15 2014 8:14am

I did read an article about aerodynamic a while ago.
It's more drag in the avererege biker than the avererege car on the road, something to think about when you choose your clothing before you ride :pancake:
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Re: Aerodynamics

Post by DrkAngel » Feb 18 2014 9:21am

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Re: Aerodynamics

Post by LockH » Feb 18 2014 12:11pm

Ummm... One corollary to reducing wind drag perhaps is "lift"? As a recreational sailor I have spent many decades not using motors to get lots of places (on the water, but one time at least, on shore/land).

Look Ma! No batteries involved!

So as much as I recognize/lust after electric traction for vehicles on /in water, on land and in the air, I am still curious about how baddery (sp?) consumption might be reduced (aka "assisted") using the power of the wind on occassion?

AFAIK, re wind, the two choices are "lift" plus "drag". I am quite used to "bending" winds to move my vehicle ("vessel") in a different direction (the wind direction isn't always/often in the same direction I want to go).

Anyway... I am usually more concerned with "hydrodynamics" (eg "slippery hulls", "wings" as rudders, used as centerboats/ daggerboards), but it seems to me it may be a fine distinction to label "dynamics" as "aero" or "hydro"?

I am quite used to "flying" (not TOO high off the water, one hopes) by "lifting" one hull completely out of the "hydro", w/ perhaps only a centerboard or one rudder still partly submerged in the "hydro", using only the force of the wind (see "wind pressure"). Helps to employ a long stick to raise the tall "thin" sail (water folks call that stick a "mast").

Anyway... While I am currently stuck on shore, I may be still interested in "aero" dynamics as a means of propelling my vehicles.

So while "reducing drag" might be of interest to most here, and I know ya can't easily "drop" slippery thingees into any water, there may be occasions where a "sail" (spinnaker, kite, etc) might help ebikers to "save fuel".

I apologize in advance if any of the above is maybe too "OT" or "too complicated" for some.
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Re: Aerodynamics

Post by cal3thousand » Feb 18 2014 12:22pm

Joppo wrote:I did read an article about aerodynamic a while ago.
It's more drag in the avererege biker than the avererege car on the road, something to think about when you choose your clothing before you ride :pancake:

Means we should all look into painting our bodies and waxing them up nice and slick. Anything for speed :mrgreen:
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Re: Aerodynamics

Post by Joppo » Feb 18 2014 2:22pm

cal3thousand wrote:
Joppo wrote:I did read an article about aerodynamic a while ago.
It's more drag in the avererege biker than the avererege car on the road, something to think about when you choose your clothing before you ride :pancake:

Means we should all look into painting our bodies and waxing them up nice and slick. Anything for speed :mrgreen:
Hehe, no I'm not one of those ppl :lol: but I see a lot of ppl with some big raincoats etc. just saying you don't need your biggest hoodie when going riding
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Re: Aerodynamics

Post by LockH » Feb 18 2014 2:59pm

Whike.jpg
Whike.jpg (90.96 KiB) Viewed 5028 times
Why pedal? Why hike at all?
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Re: Aerodynamics

Post by jbalat » Feb 18 2014 9:11pm

Joppo wrote:
cal3thousand wrote:
Joppo wrote:I did read an article about aerodynamic a while ago.
It's more drag in the avererege biker than the avererege car on the road, something to think about when you choose your clothing before you ride :pancake:

Means we should all look into painting our bodies and waxing them up nice and slick. Anything for speed :mrgreen:
Hehe, no I'm not one of those ppl :lol: but I see a lot of ppl with some big raincoats etc. just saying you don't need your biggest hoodie when going riding
Ha ha.. you guys made me re-think my idea again. A blow up jacket that inflates into an aerodynamic shape... and waterproof too :)
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Re: Aerodynamics

Post by cal3thousand » Feb 19 2014 12:20pm

LockH wrote:
Whike.jpg
Why pedal? Why hike at all?
That definitely handles the visibility issue with recumbents
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Re: Aerodynamics

Post by made_in_the_alps_legacy » Feb 26 2014 10:19am

trying to assess the drag of an e-skate assuming it is a "perfect bike" (meaning the drag is mostly from the rider, and rolling resistance is neglected)
the motivation is to evaluate the most likely realistic top speed while knowing the "no load top end speed" (based on KV, V, reduction ratio, wheel size).
I come up to some kind of rought idea that even if the power to invest against the drag might look marginal (about 10% of the output power)
the effect on the top speed is quite high (realistic top speed is about 2/3 of the "no load top end speed")

would someone disagree :?:

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Re: Aerodynamics

Post by Hillhater » Feb 26 2014 4:43pm

Ride it "luge" style !
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Re: Aerodynamics

Post by jbalat » Feb 26 2014 6:20pm

Check out the bike simulator to get an idea of real top speed

Change the coeff of drag and rolling resistance and you can get an idea of what a big part aerodynamics plays in the equation

http://www.ebikes.ca/tools/simulator.html/

eg 9C 2807, 48V 15S, 20A AOT460 Controller, 26", 100% throttle

Mountain bike does 40.3 Kms/hr
Full recumbent 45.8 kms/hr
awesome low drag aerodynamic fairing 53.3km/hr

My Crystalite 5404 (using 5403 on the simulator) goes up from around 69km/hr to 100km/hr !!
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cal3thousand   1.21 GW

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Re: Aerodynamics

Post by cal3thousand » Feb 26 2014 6:26pm

jbalat wrote:Check out the bike simulator to get an idea of real top speed

Change the coeff of drag and rolling resistance and you can get an idea of what a big part aerodynamics plays in the equation

http://www.ebikes.ca/tools/simulator.html/

eg 9C 2807, 48V 15S, 20A AOT460 Controller, 26", 100% throttle

Mountain bike does 40.3 Kms/hr
Full recumbent 45.8 kms/hr
awesome low drag aerodynamic fairing 53.3km/hr

My Crystalite 5404 (using 5403 on the simulator) goes up from around 69km/hr to 100km/hr !!
Yeah... it's pretty disappointing to see that my 40mph bike could be a 45mph if I had a Cd that was as good as an decent car (.25Cd)
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Re: Aerodynamics

Post by Kirk » Feb 26 2014 7:57pm

Typically most car drivers can't see my recumbent until they're within a mile of it and don't pay attention to it until they get within a few blocks, or so they say. Unloaded @ 25 mph with some pedaling going on, around 12 Wh/Mi. Coming back from the store with six or eight bags of groceries and a bag or two of pet food strapped to the deck, over hill and dale @ 35 mph in traffic. Around 21 Wh/Mi as a rule. Expensive? All depends on what it is for. If its a hobby for you, the cost of aerodynamics and recumbents is too much. As a primary means of transport. A recumbent trike with a bit of aerodynamic help, is a damned good idea. Costs less then a car and the ROI is pretty good.

This is a my daily driver.
Image

This one is for going fast. Mid drive and battery are hidden by the fairing.
Image Image

Its all relative at the macro level.

As always YMMV
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Re: Aerodynamics

Post by Marc S. » Feb 27 2014 3:28pm

Kirk wrote:Image
Kirk, you got a very nice looking Cat there! I would love to have a fairing like yours on my ICE Sprint 26!

btw, I ride about 200km per week on my commute and ain't got any problems being seen on my low recumbent trike in traffic...

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Re: Aerodynamics

Post by jbalat » Feb 27 2014 10:51pm

Nice looking tri and very stealthy in terms of hiding your electric propulsion, I just never liked them because they take up too much width on the bike track.
Would prefer a recumbent high racer although aerodynamics on that tri would be almost unbeatable without going overboard !
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