Aerodynamics

General Discussion about electric bicycles.
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electr0n   1 kW

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Aerodynamics

Post by electr0n » Aug 26 2013 6:03pm

Just curious how many of you have put any effort into aerodynamics with your setup and what were your results?

I notice when playing with the simulator there's a big difference in range at a particular speed depending on the rider position. For example to go 60kph on a mountain bike with the parameters I used the simulator predicts 2320 watts. Changing to a race bike tuck at a similar speed reduces the power consumption to 1658 watts , semi recumbent 1410 watts, full recumbent just 985 watts! That's a huge difference in power requirements. The full recumbent can go 60kph using almost 58% less power than the upright mountain bike.

I haven't noticed a whole lot of discussion on aerodynamics here. The velomobile and low recumbents obviously are the most aerodynamically advantageous but probably not practical to use in areas with much traffic due to the low visibility. As a compromise riding drop bars, aero bars, or any recumbent which has a seating position higher off the ground would probably be more ideal.
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Re: Aerodynamics

Post by bowlofsalad » Aug 26 2013 6:21pm

Some here use recumbent ebikes.

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Re: Aerodynamics

Post by swbluto » Aug 26 2013 6:25pm

I'm interested in energy efficiency, which includes aero and rolling resistance. I'm not alone in that concern - nature is all about efficiency.

I ride a recumbent, make sure the battery pack is in the streamline behind the seat and even limit my speed depending on my range requirements. That's my aero.

I'm also interested in rolling efficiency, which is why I run the lowest rolling resistance tires pumped up as much as possible (100psi).

I get figures of 14wh/mi at 25mph but I mostly ride at 15-20mph and pedal at the sametime. Extends my range to 200 miles, which significantly extends battery cycle life for my measly 80 mile trips.

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Re: Aerodynamics

Post by spinningmagnets » Aug 26 2013 6:32pm

I know these aren't bicycles, but the principles of what works are the same.

From MadRhino, "Isle of Man" racer?

Image

From Craig Vetter. When it comes to reducing drag, the tail portion is as important as the front fairing. Low-racer velomobile HPV's are extreme, sleek, and impractical.These two examples I am posting are near the ideal for a working real-world aerodynamic system.

Image

1963 Renault R8
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1939 Porsche type 34
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Re: Aerodynamics

Post by swbluto » Aug 26 2013 6:33pm

electr0n wrote:I haven't noticed a whole lot of discussion on aerodynamics here.
It's not a popular concern. If you post too much about it as if you're *interested* in it, you'll get the people who start threatening the mod's ban hammer because we all know aerodynamics is soooo irrelevant to electric vehicles with limited range. Silly stuff, really, for the clueless chumps when it's really all about POWER and LOOKS, after all.

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Re: Aerodynamics

Post by Pat Eaton » Aug 26 2013 6:56pm

Anything you do to improve aero, will improve range and speed as long as it is not to heavy. Wheel covers over the spoke make a noticeable difference. Try a few things and you will see.

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Re: Aerodynamics

Post by amberwolf » Aug 26 2013 7:46pm

electr0n wrote:I haven't noticed a whole lot of discussion on aerodynamics here. The velomobile and low recumbents obviously are the most aerodynamically advantageous but probably not practical to use in areas with much traffic due to the low visibility. As a compromise riding drop bars, aero bars, or any recumbent which has a seating position higher off the ground would probably be more ideal.
That's basically why CrazyBike2 is built the way it is--a compromise between aero and riding position and visibility (mine to see others and others to see me, in traffic).


I have yet to get around to actually doing any aero shell or fairing stuff for it, but I can tell you that even with it's big cargo boxes and all the other drag on it, it's about the same as a mountain bike for power usage, when I use the Grin Tech simulator page to model it's components' performance.

When I take the cargo boxes off, it's a lot better (several Wh/mile). If I were to make a tailbox for it, it'd probably be even better. I dunno how much a front fairing would do for it.

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Re: Aerodynamics

Post by Kingfish » Aug 26 2013 8:06pm

There are several thread here on aero; use the search tool 8)

In brief, the aero on my ebike has increased my top speed by 5 mph above 40 mph. I'm near the kV of the motor, and aero is making a huge difference. Heading downhill from work, I have to brake to keep from freewheeling into the back of a typical roadie - and I've got the parasitic drag of 2WD. It really makes a huge difference whether it's a clear bubble up front or a recumbent shell, or side panels for the triangle... it all adds up to slipperiness.

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Re: Aerodynamics

Post by electr0n » Aug 26 2013 8:19pm

swbluto, that's impressive 14 wh/mi at 25 mph is inline with the simulator predictions, that's with the bike-e correct? How is the ride quality on that, particularly at higher speeds. I'm seriously contemplating modifying the bike I posted above into a short wheel base recumbent to see if I can get aerodynamic advantage. I've never tried a recumbent but they look comfortable and the aerodynamic benefits make them very interesting.

spinningmagnets, those are great examples of what I had in mind for practical aerodynamics that aren't dangerously low to the ground. I'd like to have something like that on my bicycle. I think the top picture might pose some difficulty with side winds but with some modification it is probably workable for a good non recumbent but still aerodynamic position. The lower photo looks very comfortable and I've seen recumbent bicycles with similar fairings.

Pat Eaton, I've been experimenting a bit recently by tucking and using bar ends like improvised drop bars or aero bars. I've also tried lowering my seat very low and even sitting on the rear rack just 3 inches above my rear 20" wheel and stretching forward to the handlebars. It's hard to get conclusive results due to variations in wind speed and slight gradients. So far I seem to be consuming close to 700 watts, give or take 50 watts, to go around 41 to 42kph in an upright mountain bike position. I've gotten just under 500 watts at times using various aerodynamic positions but again it's hard to get definitive data due to varying terrain and conditions.

It's easy to just add more batteries but addressing aerodynamics first then adding batteries later, if necessary, seems like a better approach. This seems like the ideal place to discuss aerodynamics as it is especially pertinent to electric vehicles with limited power

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Re: Aerodynamics

Post by Samd » Aug 26 2013 8:56pm

Resistance will be the cube of speed I think. Under 28kph I don't notice sitting upright via a wattmeter to hold speed, but as you head up to 40 or 50kph the wattage to hold that speed shoots up.
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Re: Aerodynamics

Post by swbluto » Aug 26 2013 9:51pm

electr0n wrote:swbluto, that's impressive 14 wh/mi at 25 mph is inline with the simulator predictions, that's with the bike-e correct? How is the ride quality on that, particularly at higher speeds. I'm seriously contemplating modifying the bike I posted above into a short wheel base recumbent to see if I can get aerodynamic advantage. I've never tried a recumbent but they look comfortable and the aerodynamic benefits make them very interesting.
At 15 mph, it's OK - potholes are easier to identify in time and avoid and most bumps and grooves aren't a problem. At 20mph, going across roads with potholes is a little challenging but not impossible, but going across "ripple roads" and/or roads with grooves is a little on the bumpy side and crashing is a real risk (Wouldn't advise it). It's OK at 25 mph on good roads but I certainly wouldn't go that fast on a road with potholes and grooves. At that speed, a front wheel larger than 16" would be a good idea and so would a dual suspension bike (Almost every bike needs a dual suspension once you go faster than 25mph). Hit a pothole or something similar with the bike-e's 16" front wheel at speed means you're going down, and you have a lot less time to identify and avoid problem spots at 25+ mph.

If you plan on going high speeds pretty regularly, I would definitely look for a dual suspension recumbent.

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Re: Aerodynamics

Post by Miles » Aug 27 2013 12:39am

Samd wrote:Resistance will be the cube of speed I think.
Resistance is the square. It's the power required to overcome it that is the cube.

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Re: Aerodynamics

Post by swbluto » Aug 27 2013 12:45am

Miles wrote:
Samd wrote:Resistance will be the cube of speed I think.
Resistance is the square. It's the power required to overcome it that is the cube.
Using more precise physics terms....

Aerodynamics:
Force is the square to velocity. Power is the cube to velocity. Work (i.e., energy) is the square to velocity over some given distance.
Force is linear to the frontal area.
Force is linear to the drag coefficient.

Rolling resistance:
Force is constant to v. Power is linear to v. Work is constant over some given distance.
Force is linear to the weight. Power is squared to the weight. Work is linear over some given distance.

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Re: Aerodynamics

Post by www.recumbents.com » Aug 27 2013 11:36am

For those of us that ride at speeds above 25MPH, aerodynamics play a huge factor in watts/mile. Your typical MTB is about the worst of all bikes from an aerodynamics perspective. Unfortunately, there is a trade-off with aerodynamics. The more aerodynamic a light, 2 wheeled dynamically balanced vehicle is, the more it is affected by side winds. On my non-faired commuter recumbent ebike I am pushed around a bit on days with 30 MPH gusts, but otherwise ok. When I had the body pictured below on the bike, it was great on calm days but too scary on windy days. There were a few times when I was blown into traffic and I decided it was not worth it.

Image

A body on a trike is good because you are not pushed around by side winds so much. IMO, Velomobiles are too low for in city commuting. A trike commuter with a taller stance (eyes at least at same height as the drivers of cars) would work well, but then you start getting more looks from the local authorities...

I'm just sticking with the non-faired recumbent for now as that what seems like the best solution (for me!).

-Warren.

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Re: Aerodynamics

Post by Chalo » Aug 27 2013 12:09pm

bowlofsalad wrote:Some here use recumbent ebikes.
Not all recumbent bikes are aerodynamically better than normal bikes. It's not just ineffective pedaling position that makes most of them so slow.

Apropos the OP's question, the first and most effective thing we as bike riders can do to improve aerodynamics is to get our backs low and as flat as feasible. It doesn't matter much how aero the bike is if there's a "bluff body" sitting up straight on it.

That's why I don't mess around with aerodynamic aids. I sit up high enough that anything I did to the bike itself would be irrelevant, and if I attached enough fairings to streamline myself the bike would be hot, heavy, ugly, fragile, and a lot of extra work to maintain.
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Re: Aerodynamics

Post by swbluto » Aug 27 2013 12:13pm

Chalo wrote:
bowlofsalad wrote:Some here use recumbent ebikes.
Not all recumbent bikes are aerodynamically better than normal bikes.
True. Usually, however, they're awfully designed recumbents with the aero of a bus and their 'recumbent' label is questionable, like this one.

Image

I get the feeling this is what ebikes.ca considers a "semi-recumbent".

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Re: Aerodynamics

Post by www.recumbents.com » Aug 27 2013 12:23pm

+1 Not all recumbent bikes are aerodynamically better than normal bikes.

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Re: Aerodynamics

Post by electr0n » Aug 28 2013 2:21pm

This wouldn't be my first choice as far as aerodynamics are concerned but I found it available locally for $125. It's a ccm evox 120, but missing the back rest. Any thoughts on this? It looks like the cranks are a bit too low and it doesn't look like I'd be able to have a very reclined seating position conductive to good air flow. I'm not sure how much of an improvement aerodynamically this would be over a tucked position on a mountain bike, I'm guessing probably not a whole lot but I could be wrong. My other concern with this bike is the lack of suspension and 16" front wheel. Hitting potholes at 40 to 50kph might damage the bike or cause an accident, no?

I think something like a high racer with a nicely reclined position would be a good compromise between visibility and aerodynamics but I haven't found anything on the cheap like that. I'm leaning towards rigging something up but I don't particularly want to be a focal point of attention riding my contraption around.

Warren, that enclosed recumbent looks very good aerodynamically but like you mentioned the side winds have got to be a real concern and moving to a high speed faired trike would probably get a little too muchhttp://ecomodder.com/imgs/ccm-evox-120.jpg unwanted attention but that would be the most ideal for not only aerodynamics but bad weather as well. So like you I think a regular recumbent is probably the way to go.

Image

I also found a video of this same bike with a front fairing and a body sock, the rider went from Banff to Calgary, 130km in 3 hours. That's pretty impressive. I'm not sure I'd feel comfortable rocking a body sock but that does look like a pretty big improvement over a standard mountain bike.


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Re: Aerodynamics

Post by swbluto » Aug 28 2013 2:59pm

electr0n wrote:This wouldn't be my first choice as far as aerodynamics are concerned but I found it available locally for $125. It's a ccm evox 120, but missing the back rest. Any thoughts on this? It looks like the cranks are a bit too low and it doesn't look like I'd be able to have a very reclined seating position conductive to good air flow. I'm not sure how much of an improvement aerodynamically this would be over a tucked position on a mountain bike, I'm guessing probably not a whole lot but I could be wrong. My other concern with this bike is the lack of suspension and 16" front wheel. Hitting potholes at 40 to 50kph might damage the bike or cause an accident, no?
What would likely happen is that the pothole would wrangle the front wheel and handlebars sideways, dumping the rider.

I think something like a high racer with a nicely reclined position would be a good compromise between visibility and aerodynamics but I haven't found anything on the cheap like that. I'm leaning towards rigging something up but I don't particularly want to be a focal point of attention riding my contraption around.
Indeed, it seems like most economic high-racers are made by hand. You can find a few racers on Craigslist and eBay if you wait long enough and assuming you live near a populated area, but they're typically in the $600-1000 range. There's some recumbents with pretty good aero that appear on craigslist every now and then in the $350-500 range, at least in my local area. (Well, actually, I did have to extend my search to a city about 150 miles south of me to get a good selection)

I also found a video of this same bike with a front fairing and a body sock, the rider went from Banff to Calgary, 130km in 3 hours. That's pretty impressive. I'm not sure I'd feel comfortable rocking a body sock but that does look like a pretty big improvement over a standard mountain bike.

Seems like the aero could be further improved by placing the batteries behind the seat. If one could make a rounded streamlined enclosure for the batts, like a tailbox, that'd be ideal. Most of the "aero" is in the overall frontal area and the tailend's shaping.

Also, he chose a relatively poor recumbent for aero. The frontal area is going to be the biggest factor for cyclists who don't have the time/energy/funds for significant improvements. (The typical body sock, I suspect, does little aero-wise most of the time. They're typically too porous and malformed to have a significant impact on Cd and actually increase the frontal area.)

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Re: Aerodynamics

Post by swbluto » Aug 28 2013 3:29pm

www.recumbents.com wrote:For those of us that ride at speeds above 25MPH, aerodynamics play a huge factor in watts/mile. Your typical MTB is about the worst of all bikes from an aerodynamics perspective. Unfortunately, there is a trade-off with aerodynamics. The more aerodynamic a light, 2 wheeled dynamically balanced vehicle is, the more it is affected by side winds. On my non-faired commuter recumbent ebike I am pushed around a bit on days with 30 MPH gusts, but otherwise ok. When I had the body pictured below on the bike, it was great on calm days but too scary on windy days. There were a few times when I was blown into traffic and I decided it was not worth it.

Image
Have numbers? (like watts at some speed, or wh/mi at some speed)
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Re: Aerodynamics

Post by speedmd » Aug 28 2013 3:39pm

Playing with the idea of changing the straight bars to drop bars on mine. I do not like the single hand position on the straight bars and thinking possibly a cross setup would get me the multi hand positions with access to brakes and also allow some center bars that are way faster than sitting up.

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Re: Aerodynamics

Post by MadRhino » Aug 28 2013 6:51pm

I have built the latest, lower, slacker, longer.
That is my aero effort. I am not ready to ride recumbent or to add any fairing.
Off road, aggressive riding safety has its own posture requirements, and only so much can be done to reduce aero drag.
Make it fool-proof, and I will make a better fool.
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Re: Aerodynamics

Post by electr0n » Aug 28 2013 8:37pm

swbluto, I pretty much agree that bike is going to be trouble going fast on bad roads and I'm not crazy about the position. I think I'll pass it up and just see what I can come up with on my own. I've got like 4 or 5 junk bikes sitting around for parts. I'm thinking I can pull the bottom bracket off one of them and figure out a way to mount it to the front of another bike and make my own short wheel base high racer type contraption. I'm hesitant to spend even $500 on used bike since I don't know how I'm going to like it.

Kingfish, I did come across your thread in my searches and your shell turned out very nice. I'm surprised you got a 5 mph increase from basically just covering the bike plus that bit up front. Since most of the drag, I assume, comes from the frontal area and the rider position. Just shows that a bunch of small improvements can add up. There are a few other threads discussing aerodynamics but they are mostly few and far between. There's a ton of super impressive build logs on this forum but I don't recall anything really focusing on aerodynamics.

Amberwolf, your crazybike lives up to it's name :lol: It's very creative and I like that do it yourself aspect. I don't know if I could ride something like that though I think I'd be self conscious. I prefer to blend in and not be noticed as much as possible. I get enough unwanted attention on my typical mountain bike conversion but I have tried a couple goofy ideas for testing purposes. I'm sure I must look funny sitting on my rear rack with my arms stretched out to the max and my legs in an unnatural position but I did manage to reduce my power consumption by 100 watts, from 700 to 600 watts typically. Hard to nail down a number. Those cargo boxes probably add a lot of drag but

Chalo, I agree about the rider position being the most important. I would expect the bike by itself, regardless of mods to have relatively little impact on the overall aerodynamics compared with the rider, although the results kingfish got with his bike fairing suggests every little bit counts.

I lowered my seat as much as possible with the idea that there would be less wind resistance lower to the ground, I then went into a tuck as much as I could with my head just over the handbars but do to the short wheel base I had to bend my elbows out and increase my frontal area so it didn't seem to be particularly effective. I did get a nice reduction in power by sitting another 2 to 3" lower and back on my rear rack with my arms stretched out front, no bend at the elbows. That was good for a 100 watt reduction at 41 kph in my brief testing.

Today I put the motor onto another frame, seat is way higher off the ground. The wheel base is longer too. I also flipped the stem and handlebar. It looks funny but my position is now much closer to being in the drops without having a drop bar. Not terribly comfortable but will be interesting to see what effect it has on power consumption. Riding it briefly this evening it showed some promise the power consumption appears to be about 600 watts for 41 kph. I'll keep messing around and see what I can come up with. Love to hear from others about their efforts.

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Re: Aerodynamics

Post by speedmd » Aug 29 2013 7:03am

Image
These type of center bars are the way to go for a simple, but way more aero position on most any set of bars. They were so good they got banned as packs found it impossible to catch a determined breakaway artist using them. Rider position and clothing is most everything here aside from full covers/ disc wheels. You can rule the last two out in even mildly windy conditions.

Not for MadRhino to use off road. :P But for smooth roads at speed they offer a bunch of extra body and hand positions and simple to adjust. Need to work out multiple throttle and braking controls.

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Re: Aerodynamics

Post by veloman » Nov 05 2013 5:25pm

I just started working on fairings for my main ebike. They are on the 3rd page in my build thread in my signature.
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