Wind observations

[lazarus2405]

So, this whole week in Oklahoma, we have steady winds out of the south of at least 20mph with gusts 5mph above that. This is fatal for my other electric-powered hobby, RC flying, but I figured it wouldn't matter much with a 5304 at 84v. Needless to say, I should have known better.

So I northbound was on my way to Lowes on an interstate frontage road that had a 35mph speed limit. I thought I being kind to my batteries and putting along at about 25, enjoying the smooth ride and taking my time. Then I looked at my CycleAnalyst.

I was doing 45mph. I was stunned. It felt like I was doing 25, 30 tops. If that wasn't good enough, I then checked the current. 9 amps. Gentle on my batteries indeed! Still, I wonder what I could have done under those circumstances. If I had had more juice left in my batts, I would have done a top speed test then and there. To be sure, I know where I'm going tomorrow!

Of course, the funny thing about round trips is that there's always the second half. On my way back down that same strip of road, I kept a closer eye on my CA. Holding at 30mph, it took >50a to fight the headwind. With my e-molis closer to the end of their discharge curve than the beginning, and after the sag at that current, I was only running on ~70v. Because of the wind, which I had not anticipated, I reached my LVC about a mile from the dorms. The only good news about this leg of the trip was that my x5 was far more pedalable than I remember.

There was something I also learned. When I had the tailwind, my relative airspeed was ~25mph. Now, I do run a full-suspension mountain bike, but the ride was very, very smooth. There was little wobble, and things felt safe and comfortable, especially compared to the times I've done 45 with no wind. I should have expected as much, though.

See, it isn't that bikes aren't built to go so fast and aren't stable at high speeds, but that mountain bike aerodynamics are so atrocious at such speeds. The unaerodynamic shape not only produces drag, but turbulence too. Eddies of swirl around the bike and rider, pushing and shoving. The absence of this is what I felt, that led me to believe I was only riding at 25mph. It was glorious.

So... all the more reason to look into fairings, or to wish I had a velomobile.

 

[Ypedal]

Or more Amphourage.. :lol:

 

[Lenk42602]

Laz,

I just purchased a pocket bike fairing to mount on to my fast bike - the stealth bike. Similar to lowell's, except no duct tape... In my experience, with no headwind, amp draw REALLY begins to increase over 27mph. I am curious to see how much it actually helps. This may be the secret to increasing mileage / Ah on the road if intended travel speed is averaging above 25mph.

In my first test last year with my 74v/10.5ah set up, I pushed air @ 43 mph on my fast for about 8 miles WOT and pretty much used up all my juice....

Len

 

[fitek]

You can estimate power required by your bike. Here's a link I thought was pretty good:
http://downloads.openchannelsoftware.org/HEVA/docs/appx_a.html

Over about 20-25 mph the aerodynamic term grows very large and you can pretty much ignore the rest (unless you are going uphill).

Power of aero drag=Frontal Area * Coef. of drag * Velocity ^3 * density of air / 2

Google density of air to calculate air density for your application.

It's tough finding frontal area and coef. of drag numbers for bikes separately (usually you get the product, a CdA value), this was the best list I found, which has Cd, A and then CdA:
http://www.bhpc.org.uk/HParchive/PDF/hp54-2003.pdf

Anyway, an upright MTB is somewhere about 1.5-4 times worse off than an unfaired long wheel base recumbent.

The aerodynamic properties of an MTB are really awful. Your options are fairings, convert to a recumbent, or both...

 

[Lock]

Your options are fairings, convert to a recumbent, or both...

or slowing down
tks
loK

 

[Link]

I made the mistake of going with the wind for the first half of a ride I took at the beach once. I could pedal at like 35mph barely breaking a sweat, and could do about 40 if I wanted to. I turned around about 6 miles later.



Daaaaaaaaaamn what a difference a headwind makes. I was already a little tired from the ride, and I was dying trying to maintain 7 or 8 mph.

I haven't made that mistake since.

 

[lazarus2405]

The problem simply seems to be human nearsightedness, the desire to live in the moment. With that tailwind, the temptation is to just go for it, consequences be damned.

The wind always gets the last laugh.

 

[Eric G]

I did a run of ~10 km's last fall and the winds were blowing at about 50km's an hour with gusts reaching 70km/h.The wind was at my back the whole way there and I had used a mere 15% of my battery's capacity.On the way home I had to pedal really hard with the motor and when I finally got home I was pooped and the batterys had used up 52% of their capacity.It's the lowest my poor ol' sla batts have ever gone.

Eric

 

[Lock]

If anyone is into fairings, did you catch this design aspect of the Aptera? That they pump air through the cabin for comfort, but that the way the air exits out the back serves to further lower drag from turbulence? Thought that was kinda interesting...
lOCK

 

[Link]

If anyone is into fairings, did you catch this design aspect of the Aptera? That they pump air through the cabin for comfort, but that the way the air exits out the back serves to further lower drag from turbulence? Thought that was kinda interesting...
lOCK

Damn, I'm starting to think that thing was designed by aerospace engineers .