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Speedy
recumbent guru

USA
907 Posts

Posted - 11/14/2018 :  14:54:25  Show Profile  Reply with Quote
Matt Weaver built a bike with boundary layer suction.
Suction was created by a custom design centrifugal air pump driven by the rear tire.
Suction flow being exhausted out the rear tire opening.
The bike publicly ran at Battle Mountain 2000 / 2001 and Casa Grande 2004
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Balor
recumbent guru

Russia
704 Posts

Posted - 11/14/2018 :  16:05:02  Show Profile  Reply with Quote
Oh, so it was implemented on a streamliner! (I know it was done on aeroplanes it worked with limited success, but incurred too much maintenance costs).
Is there any data available about this bike?

I kind of suspect that for this system to work with limited human power, there should be *no* tire openings (completely sealed wheel wells) - otherwise tires will pump much more air *in* than out due to magnus effect, hence with holes in your fairing you will get boundary layer 'inflation', not suction. Dumping air should be only at the trailing edge...
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Balor
recumbent guru

Russia
704 Posts

Posted - 11/16/2018 :  08:03:07  Show Profile  Reply with Quote
An other interesting book on active laminar layer control:

https://www.nasa.gov/centers/dryden/pdf/88792main_Laminar.pdf

Well, after reading some papers on the stuff, I find this to be way over my head. There is a certain 'goldilocks' zone where you must have porosity, suction/speed coefficient and distribution of suction surfaces/slots/perforations *just right* for it to have intended effect. Too little is ineffective and once transition took place suction cannot reverse it. Too much can trip the layer by itself, not to mention that power to pump it is not free.
That fact that it was avoided by university teams suggest that it is too complex even for them, so for a lone builder to try it is a lost cause, unfortunately.

Boundary layer *blowing* into separation bubbles is a more interesting concept for a *practical* vehicle, because you can have the system to be passive (inlets and air hoses), I've already thought something along this lines, but a true liner should avoid separation bubbles/wide wake in the first place...

P.S.
Something alone this lines:

Drag can significantly be reduced by channeling the high pressure from the stagnation point at the leading edge and into the wake by means of a bypass channel. Drag reductions in the order of 50% have been measured in a wind tunnel on a sphere with a hole through the middle.

Edited by - Balor on 11/16/2018 08:46:23
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Matthew Martin
New Member

USA
62 Posts

Posted - 11/17/2018 :  08:38:06  Show Profile  Reply with Quote
Wow cool ideas, but I am not sure if they are practical in the real world. These were some of the ideas that I believe Matt Weaver tried to use. Ultimately I think there needs to be a balance between theoretical ideas and overall practicality of it. I believe if Matt Weaver kept the bike simpler, it would have gone faster. But at the same time, I think its people like Matt Weaver who keep trying less conventional ideas, that will eventually find something that works. I think the next generation of stream liners may incorporate some of Matt's aero devices.

But for my bike, all I am going to do is keep it simple and efficient. Once I have the molds, If I want, I could experiment, but I will see what my budget looks like then. I am going to stick to what has worked in the past the best, mostly because I don't have the cash to invest in a untested idea.

That brings up the question from aveland, how will I build the thing? Well, I would love to CNC a plug, and I currently looking for places that offer this service. However I am not seeing anything near me. So I may have to go the old fashioned way and do it by hand. Though less efficient, there is a lot more to learn when doing it by hand. However I still want precision, so I will use many bulkheads (3mm ply wood) taken directly from CAD with a stack 2in foam in between them. Then once I get is roughly to shape using the bulkheads and templates as guide, I am planning on taking a 3D scan of the plug, and comparing it to the CAD model. then I will use bondo, or another automotive body filler to find the low spots for me. then surface primer, and polish to a mirror finish. I plan to use a method very similar to what Mike Arnolds used to build a world record plane. I am so thankful they decided to post these videos after he past away.
https://www.youtube.com/watch?v=qStFDcZs5Og
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Matthew Martin
New Member

USA
62 Posts

Posted - 11/21/2018 :  08:15:11  Show Profile  Reply with Quote
Well, further refinements and many iterations later I stumbled upon my current design. It has a Cd of .04003 and a frontal area of .337555m^2 and a Cda of .013512 m^2. I think this may be the limit for my frontal area. I don't think it will get much lower than this.


Also more refined image of the pressure distribution.

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strayray
Warren

USA
10 Posts

Posted - 11/23/2018 :  08:18:35  Show Profile  Reply with Quote
Looks very sleek! Maybe you know the answer to a question that has bugged me for a long time: Why do high speed fairings go almost all the way to the ground? Wheel speed (relative to ground & air) is zero at the contact point, and nearly so nearby, and so has little drag. Meanwhile, an added fairing around it encounters full velocity drag against both the outside air and the air entrained by the wheel.
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alevand
human power expert

USA
3478 Posts

Posted - 11/23/2018 :  11:23:32  Show Profile  Visit alevand's Homepage  Reply with Quote
Sam Whittingham once said that the wheel openings have as much drag as the whole bike.

Have you read how Sean Costin made his Swift bike fairing? I though it was clever.

I made a nice cad model one time only to find only one CNC shop quoted my request, and it was $10k so that kind of was the end of that pursuit. I though of making a hot wire foam cutter. It would cut a 2d profile lengthwise and then the part would be rotated manually to cut the next facet. I don't know if a female mold could be machined directly from foam or wood. Larry Lem is a prodigious fairing maker.

C:
Tony Levand
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Speedy
recumbent guru

USA
907 Posts

Posted - 11/24/2018 :  09:00:51  Show Profile  Reply with Quote
In the world of streamlined racing bicycles Georgi Georgiev is the pinnacle of artisan hand craftsman. No computer models or CNC machines.
Looking back at the pictures of the Varna thru the years of competition you can see how the wheels / tires are less and less exposed.
The tire openings get smaller and smaller.
The fit to the rider is improved year to year.
A "gotcha" with a tiny tire opening is : when the eventual flat tire happens the body grinds the ground ... guaranteed loss of control.

For CNC machining help maybe snooping around user forums for a local garage shop craftsman. Forums for places like : shopbot, vectric, CNCzone
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Balor
recumbent guru

Russia
704 Posts

Posted - 11/24/2018 :  10:07:14  Show Profile  Reply with Quote
I wonder if gyroscope active balance system (like those on Lit car) would be legal on BM. Making it human-powered would be impractical... but as much as I understand, camera systems are not human powered, so why not a gymbal-controlled gyros? It does not add propulsion, but safety.
It would not have to be massive or very fast-spinning either, even a liner is nearly two orders of magnitude lighter than a car, and those in Lit look positively tiny.
If such system is to be refined, it might make for very practicable human-electric fully or semi-faired two-wheeled hybrids.
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alevand
human power expert

USA
3478 Posts

Posted - 11/25/2018 :  07:06:16  Show Profile  Visit alevand's Homepage  Reply with Quote
One could 3d print replaceable TPE wheel skirts that one would not cut the tire and two would deflect when tire is flat.

C:
Tony Levand
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Balor
recumbent guru

Russia
704 Posts

Posted - 11/25/2018 :  07:19:07  Show Profile  Reply with Quote
quote:
Originally posted by alevand

One could 3d print replaceable TPE wheel skirts that one would not cut the tire and two would deflect when tire is flat.

C:
Tony Levand



That's actually a great idea. TPE or SBS. You can even have the drag on the ground after installation a bit - after a few test runs they would automatically take optimal shape :).
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strayray
Warren

USA
10 Posts

Posted - 11/25/2018 :  18:49:44  Show Profile  Reply with Quote
I'm not sold on the TPE idea - deflects too easily under load unless you bulk it up. But some sort of breakaway parts that pop off for a flat would
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strayray
Warren

USA
10 Posts

Posted - 11/25/2018 :  18:55:08  Show Profile  Reply with Quote
>Sam Whittingham once said that the wheel openings have as much drag as the whole bike.

Seems like there'd be more of discussion on proper wheel opening design than fairing shape then.
Or interior wheel fairings and how they join to the exterior. (But that's just my armchair talking)
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alevand
human power expert

USA
3478 Posts

Posted - 11/26/2018 :  06:51:24  Show Profile  Visit alevand's Homepage  Reply with Quote
Well, he was at Battle Mountain sanding the wheel opening on the Varna when he said it in the video..https://www.youtube.com/watch?v=U7tc5ijzFxY&eurl=

Its suppose to deflect, that's the idea to protect the side wall..and not spread debris on the track.

quote:
Originally posted by strayray

>Sam Whittingham once said that the wheel openings have as much drag as the whole bike.

Seems like there'd be more of discussion on proper wheel opening design than fairing shape then.
Or interior wheel fairings and how they join to the exterior. (But that's just my armchair talking)



C:
Tony Levand

Edited by - alevand on 11/26/2018 07:05:37
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Speedy
recumbent guru

USA
907 Posts

Posted - 11/26/2018 :  23:12:14  Show Profile  Reply with Quote
Just watched the video again ... after having seen it so many years ago
wheel openings on the final version(s) of the Varna's were much smaller with less tire showing
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Matthew Martin
New Member

USA
62 Posts

Posted - 03/24/2019 :  18:54:47  Show Profile  Reply with Quote
Well, a little update. First I have started and am almost done with a training bike, just a simple and heavy steel frame bike. I have also, once again redesigned, but this one is it. I am building a jig now to make sure I fit.

I decided to redesign in order to increase clearance around the feet area. I also wanted more room for the rear tire. This time I decided to use a 3d modeling software for the shape instead, with the hope of achieving a more even pressure distribution. I used Blender




By using the 3d modeling software I was able to create a shape with a much cleaner topology, and much more even control points for shaping the actual body.


the jig I am currently building


And I found a place to cnc the plug .
I also stopped simulating for laminar to turbulent transition, just because of how difficult that is to simulate. There is no turbulence model that I have access to that will let me do this accuratly. So I have been running the simulations in turbulent flow. this will give me a worst case scenario. In a completely turbulent environment (No Laminar boundary layer anywhere) the shape has Cda of .0245 m^2. I think the shape should be anywhere from .013-.015 in reality. I am leaving the design phase and entering the construction phase. At least for the shape, I still have to decide what I want to do for the frame.
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alevand
human power expert

USA
3478 Posts

Posted - 03/26/2019 :  21:28:49  Show Profile  Visit alevand's Homepage  Reply with Quote


C:
Tony Levand
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Matthew Martin
New Member

USA
62 Posts

Posted - 04/14/2019 :  16:03:54  Show Profile  Reply with Quote
I nearly finished the fitment jig. Just a few more slices then get one of my tall friends to get in just to make sure. Also once again redesigned, but kept the front 70% the same, (so that I don't have to re make a jig), just changed the rear a bit after talking to Calvin Moes, who suggested I make it shorter but keep the max width in the same location, so that the transition from max width is a little more aggressive.






No clearance issues around the pedals. I even put on a pair of size 10 basketball shoes which are longer than a normal size 10, just to see. No issues with the big shoes as long as my pedal stroke favored a path which kept the toes pointed and heel up.
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warren
human power expert

USA
6454 Posts

Posted - 04/18/2019 :  11:26:05  Show Profile  Visit warren's Homepage  Reply with Quote
Very cool, you are making great progress.
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Toecutter
New Member

USA
57 Posts

Posted - 04/18/2019 :  20:55:27  Show Profile  Reply with Quote
Which airfoils did you use as a template for the top-down layout as well as the sides? This is a great looking and slippery design.
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warren
human power expert

USA
6454 Posts

Posted - 04/19/2019 :  08:32:30  Show Profile  Visit warren's Homepage  Reply with Quote
That's not an airfoil. Fairing designers don't use airfoil designs any more because they are designed for lift, not minimun CdA.
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Larry Lem
human power expert

South Sandwich Islands
2539 Posts

Posted - 04/19/2019 :  12:49:39  Show Profile  Reply with Quote
If your rider and vehicle mass total 200 lb and you have 100 lb of lift, your rolling resistance drops by around 50%. Just hope there's no side winds.

Larry Lem
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purplepeopledesign
recumbent guru

Canada
698 Posts

Posted - 04/19/2019 :  13:24:08  Show Profile  Reply with Quote
False economy. Lift requires drag, and very likely much more drag than you'd gain back in lower rolling resistance.

:)ensen.

Those who claim to be making history are often the same ones repeating it.

Video of my trike
http://www.youtube.com/watch?v=MdSLRD_2vzc
Photos of my trike
http://www.flickr.com/photos/purplepeople/
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warren
human power expert

USA
6454 Posts

Posted - 04/19/2019 :  13:33:52  Show Profile  Visit warren's Homepage  Reply with Quote
Larry, you should totally design for that on your next BM speedbike.

Oh wait, I think we have see a few of those over the years, achieving liftoff after a side gust at 60+ MPH.

Edited by - warren on 04/19/2019 13:36:40
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Toecutter
New Member

USA
57 Posts

Posted - 04/19/2019 :  14:50:57  Show Profile  Reply with Quote
quote:
Originally posted by warren

That's not an airfoil. Fairing designers don't use airfoil designs any more because they are designed for lift, not minimun CdA.



He did mention on Page 7 he was using a NACA 6-series for his shape.

Do you have any links to design algorithms or math one can use to arrive at a very low CdA shape for their application without having to throw down money on software?

I really like the shape Matthew has come up with and would like to make a main body shell of similar purpose, except for an open-wheeled trike application(the application being the lowest possible CdA for a given set of design constrains). Being that the way the air interacts with objects is complicated and that our use cases, ergonomics and storage needs differ, I can't simply expect to copy his shape and get good results.

From the top down view, Matthew's design slightly resembles an S1016 airfoil.

http://www.airfoiltools.com/airfoil/details?airfoil=s1016-il

Matthew's design seems like it would keep laminar flow for longer than the S1016 since its chord is at a higher percentage of the shell length and his has a more aggressive taper.

I'm very curious how one goes about designing a shape and arriving at what he has gotten. For all the information this site has, I can find precious little info on the process of designing a shape to meet one's needs.

Edited by - Toecutter on 04/19/2019 15:11:35
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