Amateur aerodynamics

[JOSEPHWEISSERT]

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

So Larry, will you test (or have you already tested) these things in your super secret test facility? I'm very interested in this topic for my own (admittedly) selfish reasons (specifically, the 2016 batbike). I'm wondering, scientifically, if the results are reproducable. I would do the scientific experiments myself, but my wife has denied the funds for my own personal wind tunnel project. Regarding a wind tunnel test, it seems like the best way to get to the truth. The angle of wind could be changed in all directions while the force of the wind is being measured. Then this could be repeated so that all four combinations are measured for all wind directions. Then it seems the question would be answered once an for all. And we would know if the answer is complex. For instance, maybe a disc wheel is better for some wind directions and worse for others. If so, an option would then be to develop a dynamic response to wind direction (but that's another topic and may not necessary). But the solution's objective would then be obvious - and the strategy could be determined to satisfy the objective based on available technology, cost, and other factors. Anyway, just my random thoughts on the issue. Where can I rent a wind tunnel?

 

[LarryOz]

So Larry, will you test (or have you already tested) these things in your super secret test facility?

I have tested many many things at the SSTF. Also replicated many tests with matching results. It is time consuming and really hard to get a low to no-wind/constant conditions.

but my wife has denied the funds for my own personal wind tunnel project.

This is my next project.. - Of course must sell it to the boss lady too!

Joe, so much stuff to deal with as far as wind angles, yaw, etc.
I believe you are correct:

maybe a disc wheel is better for some wind directions and worse for others.

That is why the only way to really test some of this stuff against each other is in a wind tunnel when you can precisely vary the yaw angle.

But, if you just want to know can I go faster with wheel A or wheel B, pretty easy to do at on a track in a windless condition using a power meter.

 

[JOSEPHWEISSERT]

I have tested many many things at the SSTF. Also replicated many tests with matching results. It is time consuming and really hard to get a low to no-wind/constant conditions.


This is my next project.. - Of course must sell it to the boss lady too!

Joe, so much stuff to deal with as far as wind angles, yaw, etc.
I believe you are correct:

That is why the only way to really test some of this stuff against each other is in a wind tunnel when you can precisely vary the yaw angle.

But, if you just want to know can I go faster with wheel A or wheel B, pretty easy to do at on a track in a windless condition using a power meter.

So what did you find in your testing of a disc wheel vs a regular rear wheel? Or have you not tested those two against each other?

 

[JOSEPHWEISSERT]

Larry, do you have specific plans for a homemade wind tunnel? It seems like you could get or make a big, industrial fan capable of 30mph winds, put it in a large, cylindrical, smooth room, build a sliding platform with a rotating upper deck, connect the sliding platform to the stationary floor by a spring, and measure the distance the platform moves with the bike and rider in one position. Then take measurements each time the bike angle is changed. Another factor could be to repeat all the angles with different wind velocities. And of course, there would be the four combinations of wheel, disc wheel, wheel and splitter, and disc wheel and splitter. The sliding platform could be mounted on two rods with industrial bearings. You could tilt the platform down slightly and away from the fan so that it starts at a zero position (like a tare on a scale). Seems like a fun project.

 

[JOSEPHWEISSERT]

Larry: P.S. Can you get the wind tunnel results before the N24HC? Recumbents are going to be treated without "bikeism" this year. Yes! So you must come help annihilate some records. It will be legendary. But anyway, build a wind tunnel. You only live once. How many times in science do you get the chance to start a measurement with the phrase, "Okay, you can blow me"?

 

[LarryOz]

Joe,
I have found that a nice 88mm rim depth on my CF wheels from China performed equal to or better than a full disc wheel (with similar tires and tubes of course), same with 65mm Tri_spoke wheels.
(I really think each one would probably be more beneficial under certain wind conditions.. Lots of testing to determine that, and then even if you "knew" and picked a certain wheel, on long rides conditions could change that rendered the benefit not that great or even less had you gone with something else.
The top ones however all all really close I think. (+/- .2 mph) - which can still add up to a lot over 12 or 24 hours, no doubt in that.
Best thing is to make sure your "engine" is as good as it can be given the time before each event = training, diet, rest, etc.

Here is a link to "many" figures on wheel, tire and tube testing I have done this year.
https://docs.google.com/spreadsheets/d/1BawIBqIAwX62NG0UogT5uovByt0iqxMPpTFaJdw3wM4/edit?usp=sharing
Sometimes there was wind and/or other conditions and I noted them to the far right.

Yes, building a personal wind tunnel is "on my to-do list", but if could "see my list", you might wonder when I would ever get to it! haha. (Need a sponsor really - volunteers?)
Good ideas from your above posts. Lots of things are possible, including adding in and having the rider actually ride under a given power level at different positions (hip angle, BB height, etc), and off course varying equipment
I have a contact that has built a "bike-only" tunnel that I intend to go take a look at as soon as I can.
After seeing what he has done, I may start making "more definite" plans - Who knows it may turn into a real business (maybe even a "traveling wind tunnel"

Can you get the wind tunnel results before the N24HC? Recumbents are going to be treated without "bikeism" this year. Yes! So you must come help annihilate some records. It will be legendary.

Not sure about doing the N24HC. One thing that is a really a turn-off for me is the way they are doing the timing. How archaic. Stopping and having to wait - really????. But more importantly, I am probably going to concentrate on the 1 hour TT this next year, and my "mentor" has already told me that if I go around riding in 12 hour or greater length events it will drastically hurt my training. Last year I kind of did everything (someone jokingly told me that I "danced all over the staircase" - haha), and in the end I did "OK" in everything I rode in, but not "GREAT" in anything.
Since I am basically new to all this racing and endurance stuff I am still kind of learning too.
So the basic idea is to train for the 1 hour TT to really build up my speed this year, maybe build up to a decent Century time at the very end of the year, then "build up" to longer events in the following years.
There is a part of me that would just want to go to every event that I can, just to ride in it with everyone else - especially if we really had a strong team of bent riders! That would be awesome.

 

[scabinetguy]

News flash! when installing the vector2 power pedals it helps to enter your crank length! ( which I did not ). I found my power output for a 19 mph ave. to be between 130-135 watts ave. , quite a bit higher than 115 watts. I figure Larry noticed that already. However, I'm still showing very little difference between the Bontrager 50 mm wheels, with or without a disc. I think this demonstrates the effectiveness of aero wheels and bladed spokes. Live and learn I guess.

 

[bazzawill]

Joe,
I have found that a nice 88mm rim depth on my CF wheels from China performed equal to or better than a full disc wheel (with similar tires and tubes of course), same with 65mm Tri_spoke wheels.

What china cf / tri wheels do you have?

 

[LarryOz]

I figure Larry noticed that already.

Yes - get the crank length wrong and power numbers are off.

However, I'm still showing very little difference between the Bontrager 50 mm wheels, with or without a disc

I concur again. I think the difference is so small it is hard to measure without being in a wind tunnel or maybe an indoor velodrome.

What china cf / tri wheels do you have?

I got my CF 3-spoke wheels from asiancyclexpress.com
They are very fast wheels. On my first set however, then wheel lips did not hold form (may have been because I keep them inflated to 100+ psi for a long time - not sure if they should be able to handle that or not, but they built me a new set since I had had them less than a year. Every bit as fast as the full discs in my opinion, plus more forgiving in crosswinds.

 

[Bentas]

Could something like this be the future for slippery MBB bikes?

 

[Bentas]

The genius of Tom Traylor , decades ago, not so different

 

[Itripper]

Did this guy just fall off the face of the earth? He was making some really interesting aero stuff and then...