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 Streamliner Fairing Construction and Design

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T O P I C    R E V I E W
Matthew Martin Posted - 09/19/2017 : 20:42:30
Hi, I am a high school student who has been interested in the concept of streamliners and their construction. The question that has been bothering me is not knowing how to attach a windscreen (canopy;plastic view port) to a fiberglass fairing almost seamlessly without the use of tape. I have been working tirelessly on a cad model of a bike that I hope to build. The bike is a somewhat practical streamliner that is high enough to be moderately visible in traffic. I need to be able to attach a large vacuumed formed windscreen to go with my design.As I don't know how to insert my image ( not online so no url) my windscreen needs to be similar to the velotilt
25   L A T E S T    R E P L I E S    (Newest First)
Speedy Posted - 11/26/2018 : 23:12:14
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
alevand Posted - 11/26/2018 : 06:51:24
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
strayray Posted - 11/25/2018 : 18:55:08
>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)
strayray Posted - 11/25/2018 : 18:49:44
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
Balor Posted - 11/25/2018 : 07:19:07
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 :).
alevand Posted - 11/25/2018 : 07:06:16
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
Balor Posted - 11/24/2018 : 10:07:14
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.
Speedy Posted - 11/24/2018 : 09:00:51
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
alevand Posted - 11/23/2018 : 11:23:32
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
strayray Posted - 11/23/2018 : 08:18:35
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.
Matthew Martin Posted - 11/21/2018 : 08:15:11
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.

Matthew Martin Posted - 11/17/2018 : 08:38:06
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
Balor Posted - 11/16/2018 : 08:03:07
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.
Balor Posted - 11/14/2018 : 16:05:02
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...
Speedy Posted - 11/14/2018 : 14:54:25
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
alevand Posted - 11/14/2018 : 13:33:22
How are you going to make the fairing?

C:
Tony Levand
Balor Posted - 11/14/2018 : 10:04:46
Interesting "to read" material concerning boundary layer suction:
http://sci-hub.tw/10.1007/s11012-015-0100-9
Balor Posted - 11/14/2018 : 06:28:36
By the way, you may want to take a look at this for some "expectation vs reality" pictures :)

http://sci-hub.tw/10.1016/j.proeng.2012.04.054
Balor Posted - 11/14/2018 : 04:16:54
By the way, an interesting tidbit from Bicycling Science:

By 'sucking in' increasingly turbulent air at and beyond transition point, you can (highly theoretically, of course, I don't think any real experiments were made) delay boundary layer detachment and 'reattach it', and extend laminar flow from 60% to 95%, which should give you much greater savings (hundred(s) of watts) in aero drag at cost of about 20 watts of 'suction power' (even given inefficiencies of generating it using some sort of human-powered fan).

Section on bicycle aerodynamics, pages 193-196
I don't recall it mentioned anywhere here, great book btw.
I wonder how this 'suction inlets' should look like... a series of Naca ducts? A simple mesh grille?

This section also stresses that minor undulations from pedalling (and balancing corections) and road vibration will wreak havoc on laminar flow. Plus, a perfectly 'laminar' airfoil will likely stall at a hint of yaw in wind direction, be it 'undulations' or side wind.

I wonder if you can have your shell not just suspended, but gyroscopically stabilized as well?

Edit:
Totally not NACA ducts, they were designed *exactly* to deflect boundary air away and dip into freestream for better airflow with minimum extra drag.
Balor Posted - 11/07/2018 : 01:30:35
That's comfy, I think even I can fit that :). Make sure that you your width does not taper too fast compared to your shoes, or you'll be scraping your toes when ankling (which is a good idea to maximise power).
Matthew Martin Posted - 11/06/2018 : 17:43:18
It all makes sense now...

I was still thinking about the cd value that I was getting from the simulation, and just knew it had to be wrong, if Eta had a Cd of .038, and my bike, which I believe should be less aerodynamic than Eta, had a lower Cd value.

So I re-started my investigation. I already knew that my simulations had no errors and the conditions were set up correctly, however I could not see what I was missing. I almost began to doubt the Open Foam solver's reliability, but was reassured that the system was capable of producing accurate results, after seeing that Mercedes F1 uses it to design there cars. So after getting frustrated I decided take a break for a few hours, when it came to me. I had forgotten to take into account viscus drag! I had previously only been taking into account pressure drag. I then solved for both viscus drag and pressure drag and came to a much more reasonable result.

The model shown had a Cda around .016, so with further refinement I managed to get this number down.
I eventually made some changes to the front wheel fairing, and tail to achieve a Cd value of .04249 and a frontal area of .3409m^2, giving a Cda of .01448.. Now I am satisfied with this result, however on the road it will more than likely be higher due to uncontrollable variables. I am still tring different devices such as different tail shapes and front wheel fairings, however I think I am set on the main body, which has nice 46cm(18.1in) at the shoulders and gives the rider at least 12.5cm(5in) width for the feet when using a q-factor of 150mm


Now I redid the calculation for Eta and,a lower rolling resistance was all it took for the numbers to make sense.
Balor Posted - 11/04/2018 : 13:48:13
By the way:

"I also did some calulations for the Cda of based off a statistic that I found in an article which stated that Eta would only need 198 watts to go 90 kph. This would require (using a Crr of .005 and a bike weight of 6o lb and a air density of 1.22kg/m^3) a Cda value of about .007 @ 90 kph which is far lower than the cda of my design. of course this value would decrease a higher speeds."

Given their custom tires, assuming crr of 0.002 is not unreasonable, given that you can get very close to that with Corsas (0.0023 CRR)
Balor Posted - 11/04/2018 : 09:32:28
Well, theoretically, using fat(ish) low-pressure tires takes care of that as well, but practically it would likely result in too much rolling resistance/aero hit at speeds you are willing to attain. At 60+ mph speeds and given extra fairing weight rolling resistance losses are huge. Of course, fatter tires actually roll a bit BETTER everything being equal, but the best tire you can get without going custom (huge $$$) is tubeless Vittoria Corsa speed, 23mm as far as BRR site is concerned, and I tend to trust their data. Pumped up to "near" max pressure it should provide outstanding rolling resistance (nearly half that of most racing tires) and still quite adequate vibration absorption.
So far as I know, Eta used some kind of custom tires, 20mm, likely tubulars and pumped up to enormous pressures. If you play around with your tire pressure, you *might* get away without any 'shell suspension' with a relatively small rolling resistance hit.
Matthew Martin Posted - 11/04/2018 : 07:04:33
Balor I completely agree, however the first fairing I will make, will probably be made with fiberglass and a thin foam core, and have a steel frame (no shell suspension)

My point is that once I have the molds I can begin to work towards eliminating sources of drag and to maintain laminar flow using internal devices. I will build another frame to accomplish this. My current thinking is, if I design a fairing that has enough clearance for the rider (what I am doing now), later on I can design a frame with various internal devices to make the bike as efficient as possible. That's what I meant by later, but you are right, I need to be thinking about these things now.
Balor Posted - 11/04/2018 : 00:30:08
Point is, a typical unibody liner and something like ETA with entire 'laminar' portion of the shell mounted externally and suspended are very different designs - not something you can add on later.
I think this is why ETA owns speed record despite not being the slipperiest shape 'on paper'. I don't think this is much harder to do (I might be very wrong though) - just *different* and a design choice you should make from the start.

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