ReklinedRider
Zen MBB Master
Was wondering about this just the other day....
Amateur aerodynamics
- Thread starter Jim Gerwing
- Start date
scabinetguy
Well-Known Member
Has anyone experimented with closing off the rear triangle? I thought it might be effective in combination with a rear disc. I made this shroud out of carbon fiber and I'm using Velcro tape to hold it on.
MrSteve
Zen MBB Master
Jim Parker wrapped a rear V triangle with plastic sheeting and he has not published anything further.
My guess is that there is no advantage... and here's why.
I have experimented a lot with fairing round tubes and round tubing responds well to fairing.
Those tubes on the rear of the V are already aerodynamic; adding skin surface area in an attempt
to fair faired tubing only adds surface area.
More surface area adds more parasitic drag and is more fun in cross-winds.
What does help a bit, especially with those rear wheel covers, is adding a splitter
between the wheel and the spine of the bike's frame.
Search for photos of the very first Vendetta and you'll see a small aluminum splitter
welded in the spot I'm talking about.
You will still be a bit more sensitive to side winds with the splitter added to the wheel cover's area.
I accept donations... thank you, thank you very much.
-Steve
My guess is that there is no advantage... and here's why.
I have experimented a lot with fairing round tubes and round tubing responds well to fairing.
Those tubes on the rear of the V are already aerodynamic; adding skin surface area in an attempt
to fair faired tubing only adds surface area.
More surface area adds more parasitic drag and is more fun in cross-winds.
What does help a bit, especially with those rear wheel covers, is adding a splitter
between the wheel and the spine of the bike's frame.
Search for photos of the very first Vendetta and you'll see a small aluminum splitter
welded in the spot I'm talking about.
You will still be a bit more sensitive to side winds with the splitter added to the wheel cover's area.
I accept donations... thank you, thank you very much.
-Steve
JOSEPHWEISSERT
Zen MBB Master
What do you think of putting a single sheet of stiff plastic in the area under the boom and above the front tire? This would be in a plane that is perpendicular to the ground (so it would be vertical) and would be in line with the bike from front to back. It would effectively stop air flow from going back and forth (in the left and right direction) under the boom. But would it have an aerodynamic advantage?
1happyreader
zen/child method
http://cyclingexperiences.com/2010/07/19/cruzbike-vendetta-exclusive-photographs/
https://www.flickr.com/photos/fayncbikerjaa/albums/72157624541844190
Someday Cruzbike will have a history/story page maybe with previous models info, ect.
MrSteve
Zen MBB Master
Try it!
I always mock things up with cardboard and gaffers tape.
Instead of my painting word pictures, just go look up some photos of the
Velokraft NoCom.
See how the frame frames the wheels? "Splitter plates." You know, splitting the slipstream.
On my Sofrider, the stock paint has lots of dull stripes, testament to all the tape abuse.
The frame aero-mods that made the most difference?
-Narrow handlebars. The bullhorns on my V work fine.
-Reclined seat. The V's stock seat is almost reclined enough.
-Rear wheel covers. I built some for my V: I love rear wheel covers.
-Fork leg fairings. The bike picked up a bit of speed. I removed them because they were not pretty; the Vendetta fork is very aero, stock.
-Rear wheel splitter plate. The bike picked up a bit of speed. I removed it because it was not pretty: I'm thinking of building one for the V, but not very seriously.
-Front wheel splitter plate. Never got around to it: I'd just fair the gap between the front wheel and the down tube/frame.
-Pedal fairings. Watching the flat soles of my feet punching through the air drives me nuts! They don't seem practical for street use, but boy, I betcha they'd work great.
-A really nice, light, long and Kamm-backed tail fairing looks good... just like we see Jim Gerwing doing and his seems to work great.
Have fun!
scabinetguy
Well-Known Member
As a follow up I have tested my vendetta with the rear triangle fairing and rear wheel disc. I used a garmin vector 2 pedal power meter. To my surprise my vendetta is much faster without the rear fairing and rear wheel disc.
This was my result on a 14 mile loop from my house:
With fairing and wheel disc: 18.4 mph ave. @ 118 watts ave.
Without fairing or wheel disc: 19.1 mph ave. @ 113 watts ave.
By my calculation, I'm a full 1 mph faster at 100 watts power without the cool looking stuff.
This was my result on a 14 mile loop from my house:
With fairing and wheel disc: 18.4 mph ave. @ 118 watts ave.
Without fairing or wheel disc: 19.1 mph ave. @ 113 watts ave.
By my calculation, I'm a full 1 mph faster at 100 watts power without the cool looking stuff.
Charles.Plager
Recumbent Quant
As a follow up I have tested my vendetta with the rear triangle fairing and rear wheel disc. I used a garmin vector 2 pedal power meter. To my surprise my vendetta is much faster without the rear fairing and rear wheel disc.
This was my result on a 14 mile loop from my house:
With fairing and wheel disc: 18.4 mph ave. @ 118 watts ave.
Without fairing or wheel disc: 19.1 mph ave. @ 113 watts ave.
By my calculation, I'm a full 1 mph faster at 100 watts power without the cool looking stuff.
Ha ha!
Hey, you tried. That's the thing about aerodynamics: it's really not obvious (at least to me). I would have thought your changes would have helped.
Shows how much I know, huh.
JOSEPHWEISSERT
Zen MBB Master
Holey moley!As a follow up I have tested my vendetta with the rear triangle fairing and rear wheel disc. I used a garmin vector 2 pedal power meter. To my surprise my vendetta is much faster without the rear fairing and rear wheel disc.
This was my result on a 14 mile loop from my house:
With fairing and wheel disc: 18.4 mph ave. @ 118 watts ave.
Without fairing or wheel disc: 19.1 mph ave. @ 113 watts ave.
By my calculation, I'm a full 1 mph faster at 100 watts power without the cool looking stuff.
trplay
Zen MBB Master
Before getting to carried away consider a 14 mile loop with what I assume was a one trip each could provide really skewed results. Any stops along the route? I would propose another blind test in which one rides the route twice on the bike without changing anything at all. It wouldn't surprise me if you saw a significant difference between the two rides. Which one is accurate?
scabinetguy
Well-Known Member
(Before getting to carried away)
I actually made 4 trips, one was with the triangle fairing only. On this trip I was 18.9mph ave. @ 114 watts ave. The results seem to be in line.
I actually made 4 trips, one was with the triangle fairing only. On this trip I was 18.9mph ave. @ 114 watts ave. The results seem to be in line.
trplay
Zen MBB Master
Heck at this rate try it without a rear wheel. Without trying to be overly skeptical or Brol'ish my personal experiences have shown that without stringent testing conditions quickie tests can provide very misleading results (you can find gazillions of them on BROL). There is nothing wrong with doing these tests and I do them all the time and find yours interesting. What I also have found is when I do repetitive tests over a long period of time I think I get a better feel and more accurate results. The covered triangle looks good. I would make sure it's slower before you give it up.
scabinetguy
Well-Known Member
trplay,
I know what you're saying, these are only early test results. I do try to ride in the 18-19mph range so that the aerodynamic effects are close to equal. I tend to ignore the average watts. I ride at the same time of day and wear the same clothing each trip. I agree, further testing will produce a more reliable average.
I know what you're saying, these are only early test results. I do try to ride in the 18-19mph range so that the aerodynamic effects are close to equal. I tend to ignore the average watts. I ride at the same time of day and wear the same clothing each trip. I agree, further testing will produce a more reliable average.
LarryOz
Cruzeum Curator & Sigma Wrangler
I do my testing on a closed loop (track of some sort - so you never have to stop or change pace), with little or no wind, and also back to back (i.e. Run a 5 mile with one wheel, stop and switch wheel and then run 5 miles again with new wheel.)
Something else I do that I think helps is this:
I program a "page" on my Garmin that shows lap distance, lap time, lap average watts, lap average rpm, etc.
Start the Garmin to collect the data
Then I practice at what wattage and rpm I want to run the tests at, so I can duplicate those values as close as possible for each test.
Then I "get up to speed" on the track and level off so I don't have any spiking wattage or rpm values. Then when all that is perfect I hit the lap button, which starts my test at the period.
I attempt to keep the wattage and rpm at my desired "average", the wattage being the most important.
I vary my effort up and down slightly during the "test" so that when I am done the average wattage for the lap is exactly where I want it. (Obviously looking at the Garmin "page" that shows average lap wattage figures in real time)
When my "test" distance or "time" is done, then I hit the lap button (so that lap is now the test data I'm looking for for that test).
Then stop and switch whatever equipment I am testing.
Then do it all over again with the equipment change.
The longer the test the better, but also the higher the chances that other conditions that you cannot control (wind mostly) will change.
Also, the more you can keep the wattage even and level the better. Spikes are not good for the data.
3-5 mile tests seem a good a good compromise.
I have had very good results testing equipment mods this way, and have duplicated many tests (i.e. helmets, wheels) and have found that my results match pretty closely, which gives me a rather high confidence level that the data is good.
Hope this helps
Something else I do that I think helps is this:
I program a "page" on my Garmin that shows lap distance, lap time, lap average watts, lap average rpm, etc.
Start the Garmin to collect the data
Then I practice at what wattage and rpm I want to run the tests at, so I can duplicate those values as close as possible for each test.
Then I "get up to speed" on the track and level off so I don't have any spiking wattage or rpm values. Then when all that is perfect I hit the lap button, which starts my test at the period.
I attempt to keep the wattage and rpm at my desired "average", the wattage being the most important.
I vary my effort up and down slightly during the "test" so that when I am done the average wattage for the lap is exactly where I want it. (Obviously looking at the Garmin "page" that shows average lap wattage figures in real time)
When my "test" distance or "time" is done, then I hit the lap button (so that lap is now the test data I'm looking for for that test).
Then stop and switch whatever equipment I am testing.
Then do it all over again with the equipment change.
The longer the test the better, but also the higher the chances that other conditions that you cannot control (wind mostly) will change.
Also, the more you can keep the wattage even and level the better. Spikes are not good for the data.
3-5 mile tests seem a good a good compromise.
I have had very good results testing equipment mods this way, and have duplicated many tests (i.e. helmets, wheels) and have found that my results match pretty closely, which gives me a rather high confidence level that the data is good.
Hope this helps
Charles.Plager
Recumbent Quant
I'm pretty sure that will be significantly slower. Riding a MBB unicycle is notoriously difficult...
I'll be here all week folks!
scabinetguy
Well-Known Member
(I have two questions: first did you try the disk wheel alone without fairing; secondly, is the fairing covered underneath or only the sides? Sorry if this was mentioned already and I missed the information.)
No to the first and yes (underneath) to the second.
No to the first and yes (underneath) to the second.
scabinetguy
Well-Known Member
Larry,
What I’ve found is that if I try to keep the average watts constant, my speed varies greatly depending on the wind direction. This difference is quite often 5 mph. I’m thinking that the aerodynamic effects would be exaggerated at higher speeds compared to lower speeds, thus complicating the conditions. I’ll try a few runs at a steady wattage and see if that changes anything….Steve
What I’ve found is that if I try to keep the average watts constant, my speed varies greatly depending on the wind direction. This difference is quite often 5 mph. I’m thinking that the aerodynamic effects would be exaggerated at higher speeds compared to lower speeds, thus complicating the conditions. I’ll try a few runs at a steady wattage and see if that changes anything….Steve
These are two different arrangements you can try next if you have the time, one with just the rear disk and the other with open fairing bottom to help identify the main source of additional drag. You can also test fairing (both versions) with standard rear wheel if you haven't already tried it.
I tested similar things on DFs long ago. The faired rear triangle helped with a disk wheel but my version extended to only about a third of the way back from the seat tube because of the marked outward flare of a DF rear triangle, and there was an open bottom (didn't try closed due to wheel proximity). On a DF bike there's a LOT of turbulence in that area caused by the rider's rotating legs and understandable why it may have worked better.
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