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shooky56
recumbent guru

USA
545 Posts

Posted - 10/25/2015 :  07:57:04  Show Profile  Reply with Quote
Drivers: You forgot texting. At least in our country mostly teenage girls in my experience (passing another vehicle with their head down texting!). But I do understand your concerns as they parallel mine (and probably all of us). Funny thing is I'd be totally happy tooling laps on a velo away from all that stuff.

Kamm: Point I'm trying to make about the software is that it's easily doable with the software. Have it dump ribs and space them so one of the last few is at the point you'd like to Kamm. That's your tail block. Just don't make any shell beyond it. Same for the strips. I bring them up in something to print them (everyone has to do this) and simply crop the picture to length. The only part I think it'd help is the svg files (for the banner printers) and then only to save paper and costs. My paper guide for my banner printer was turning into quite a project (try #3) and I had more pressing matters so I "dropped back and punted" with 8.5x11's. But anyone with the construction skills to make these will have no problem cropping the shell. Regardless, I'm working on it mentally about how I'll implement it. Thought about just doing it in the output windows but then thought it'd be nice to know the surface area of the tail both in units-squared and as a percent of the maximum cross-section.
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Speedbiker
human power expert

USA
3760 Posts

Posted - 10/25/2015 :  12:18:03  Show Profile  Reply with Quote
As Balor says, dimples, turbulators, and vortex generators are the realm of real aerdynamic engineers. Just as is shaping a fairing. Without a true understanding of dimples and such, their use almost universally makes you slower. Even with a proper knowledge of them, it will take a series of controlled tests to make them effective. The same goes for fairing design. Over the last 20 years I've tried to help many people build fairings. Many deamt that adding a full fairing to their bike would make them faster. Many made little to no significant gains. Just because you build something that looks like it will make you faster that does not mean it will. Many times the frontal area increases so much it offsets the reduction in drag. The opposite very often happens with front or tailfairings. They are either too small to be effective (like Wayne's ), too big, or just not shaped right. Only the right design makes you faster. And this takes knowledge. While I don't have a formal education in aerodynamics I took flight school in high school, aircraft mechanics in college, been educated for over 20 years by a true expert (my brother), and have had long discussions with Matt Weaver and others. This doesn't even put me on the same page as guys like the Aerovelo team who have masters and doctorates in this stuff. But it does give me enough sense to realize my limitations and n ot try to impress people by trying to sound like I'm smarter than I am. Despite my limitations I've built some the fastest nonfaired, coroplast and composite bodied liners going. If you use terms like NACA foils, laminar flow, Kamm tails, boundry layer, dimples, turbulators, etc, I sincerely hope you build something fast that provides hard proof that you know what you're talking about. Because that is what this sport/forum is really about. Building and racing!

Edited by - Speedbiker on 10/25/2015 12:18:49
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Joel DIckman
recumbent enthusiast

USA
129 Posts

Posted - 10/25/2015 :  14:14:13  Show Profile  Visit Joel DIckman's Homepage  Reply with Quote
quote:
Originally posted by Speedbiker

As Balor says, dimples, turbulators, and vortex generators are the realm of real aerdynamic engineers. Just as is shaping a fairing. Without a true understanding of dimples and such, their use almost universally makes you slower. Even with a proper knowledge of them, it will take a series of controlled tests to make them effective. The same goes for fairing design... ...Just because you build something that looks like it will make you faster that does not mean it will. Many times the frontal area increases so much it offsets the reduction in drag. The opposite very often happens with front or tailfairings. They are either too small to be effective (like Wayne's ), too big, or just not shaped right. Only the right design makes you faster. And this takes knowledge... If you use terms like NACA foils, laminar flow, Kamm tails, boundry layer, dimples, turbulators, etc, I sincerely hope you build something fast that provides hard proof that you know what you're talking about. Because that is what this sport/forum is really about. Building and racing!



I think Thom needs another Snickers bar. I do not read the posts by Grant53, Aviationmetalsmith etc. and get royally pissed off by them. So what if people sometimes talk about stuff they only have an imperfect grasp of? I do that half a dozen times everyday before breakfast! Nobody gets hurt, as far as I can tell.

And while some of us are focused on racing like Thom, others like me are more interested in vehicles for commuting and street riding. If I want to build a bike for Battle Mountain and try to set a record, an advanced knowledge of aerodynamics like that of Thom's brother is necessary. But if I just want a pretty fast street bike the higher learning is not needed. Just make your fairing look more or less like a teardrop lying on it's side, and make it as small as possible while allowing the bike and rider to squeeze inside. It will not be optimally fast, but it can still be pretty damn quick. For some of us that is good enough.

If the Snickers bar does not work, maybe a deep inhalation of some wacky tobacky. Or a drink of your favorite liquid refreshment.

Safe riding,
Joel Dickman
http://lightningriders.com

These three prevent most accidents: seeing, being seen, & (usually) common sense.
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shooky56
recumbent guru

USA
545 Posts

Posted - 10/25/2015 :  15:53:04  Show Profile  Reply with Quote
My only thing about the dimples, and I also think they will do nothing but make you slower, is that the same effect can be had w/o mucking up a slick body. Won't a piece of tape trip the boundary layer? Saves ruining a nice slick finish; which could be repaired I guess but.

Got a new view control: Kamm. Drag a slab, sort of like a big tug mark, left and right through the model. When you're happy click the Kamm button and (this part doesn't work yet) it chops off the back. Really ought to make it "chop off the front" so you can do a nose and tail w/o the middle for the Lycra/Spandex guys. The GUI is getting pretty crowded, it'd probably be easier to just let you have a front/back switch. Do the nose, dump the output, do the tail dump the output just not both at once that would much hard to implement.

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warren
human power expert

USA
6118 Posts

Posted - 10/25/2015 :  16:49:53  Show Profile  Visit warren's Homepage  Reply with Quote
Thom, just because we use terms and concepts doesn't mean we have to be experts. We are all learning. None of us are professionals. None of us have to be professionals to build a fairing that does what we want it to. Despite all my accomplishments, I am not an expert, yet I built a bike that went 64 MPH at battle mountain with my meager power and a tire rubbing on the frame. We are on this site to learn and to teach and be ethusiastic.
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Jerry
recumbent guru

USA
982 Posts

Posted - 10/25/2015 :  17:32:05  Show Profile  Reply with Quote
Well said Joel Dickman and Warren. I build and ride to have fun, not to be an expert! It takes all the fun out of building something if you have to get it right the first time, every time. Mistakes make it a lot more interesting, unless you are a professional racer. I learn from my mistakes, and usually the redo is way better. And from what I have heard, you'll need a whole box of Snickers if you inhale!! lol

With all that aside, I have my new heavy duty Lycra to make my new body sock. Richards was yellow, mine will be bright Coral, fancy for orange.
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Speedbiker
human power expert

USA
3760 Posts

Posted - 10/25/2015 :  19:44:54  Show Profile  Reply with Quote
What would be the use of a technical discussion if nobody challenged your ideas? Beyond originals ideas, of which there are few, what of accuracy? Would you rather ramble on with poorly understood facts or be challenged to do better? How many times has someone been upset with me for challenging their ideas or understanding, only to see them do better? Do you defend bad or unsubstantiated data? How does that better the sport we love? I've struggled against bad data and bad attitudes for years. I've offered my full collection of knowledge of every aspect of recumbents and hpvs to anyone who asked. I've never acted smarter than (I think)I am. That includes competition, commuting(yes Joel, even commuting) and just having fun. Funny how all the builders don't post here anymore. Are me, and Tony, and Warren the only ones left, not yet tired of arguing with people? Maybe I'll leave it to you have built little, type a lot, and prefer not to be challenged. Or maybe I won't! You can say I'm too hopped up on Soda Pop, Red Bull, or whatever, but I'm going to go on trying to make the sport better. Sorry if it wrinkles your tailfeathers. Now, go out, build something, and teach me a lesson! You have Wayne's design app, a tube miter app, and Warren's indepth instructional website. Go for it. But disappoint and you'll probably hear about it.
I hope I don't twist my ankle getting down off this soapbox.....
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Balor
recumbent guru

Russia
514 Posts

Posted - 10/26/2015 :  00:05:44  Show Profile  Reply with Quote
quote:
Originally posted by Speedbiker
Because that is what this sport/forum is really about. Building and racing!



Let me see... Nope, 'Recumbent bike forums->technical / bike building'.
For a moment I thought that I've messed up my tabs and posted into a 'IHPVA forums->Advanced aerodynamics' :P.

Well, to be serious, I've already stated that my goal is not racing, but to be safe and weatherproof... preferably w/o making my bike slower at the very least. And safety comes first. Hence, crosswind resistance trumps 'speed aerodynamics'.

And even if I've tried, I'd have nowhere to race - there are ZERO HPV events in Russia. And flying abroad to BM is certainly not within my budget, unless I'll find a sponsor, and this is... highly unlikely.

However, if you see that I'm messing up something, please DO criticize it, especially if accompanied by explanation how to make it better :).

quote:
Originally posted by shooky56

My only thing about the dimples, and I also think they will do nothing but make you slower, is that the same effect can be had w/o mucking up a slick body. Won't a piece of tape trip the boundary layer? Saves ruining a nice slick finish; which could be repaired I guess but.



Point is, tape is directional, while crosswinds can attack from any side.
However, improper placement of dimples may not only make me slower, but MORE susceptible to side winds as well.
Perhaps simple surface unevenness will do the trick?
It comes with the coating, heh.

Gotta evaluate Autodesk CFD and see how it works from multiple angles... will likely take a few days to run all the simulations, but I hope that would be worth it :).
P.S. Though while I can emulate surface unevenness, I doubt that I can properly 'dimple' the surface w/o learning some CAD magickery. Maybe I'll try that, too.
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shooky56
recumbent guru

USA
545 Posts

Posted - 10/26/2015 :  05:43:30  Show Profile  Reply with Quote
Dimples: Was thinking ring(s) of tape and it seems that would be transverse to wind flow IMO. But you're doing the doing.

Racing: Too bad, wish you could come to one of our HPRA races. I started racing just to meet the gang and see the creations. People have tons of good ideas. Never met a machine I didn't like!

Autodesk CFD (aka "Falcon"): Nothing but impressed myself. They gave me a free seat (and mine could still be free) but after seeing how closely my results matched wind tunnel studies I decided they had earned their money and started paying for mine. They have several CFD->Wind Tunnel validations showing that their simulations closely match wind tunnel results. I found the same thing. Some of my runs used standard models for which there are published wind tunnel results. You have to set it up right and there's a lot of gotcha's to do that. If you get Autodesk, let me know. Drop me a line at wayne dot shook at hotmail dot com and I'll run you through the setup process. Put a title of This is Baylor or something so I don't permanently delete you (everybody is auto-delete folder unless you're flagged).




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shooky56
recumbent guru

USA
545 Posts

Posted - 10/26/2015 :  06:55:41  Show Profile  Reply with Quote
Autodesk-Dimples: Falcon allows cross-wind simulations but, if the model is correctly sized, the highest resolution yields 3mm voxel sizes. Since that's about the size of a golf ball dimple it wouldn't model one (it would appear as one flat triangle that was sort of like a man-hole cover over the pit), it would take about .6mm resolution to model the cavity. It actually would model tape because the tape is wider and also because it is flat. The thin tape displacement (elevation about the shell surface) should be modeled to very high precision, probably in the micrometers (depends on their internal precision variable typing).
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Speedbiker
human power expert

USA
3760 Posts

Posted - 10/26/2015 :  08:34:31  Show Profile  Reply with Quote
Wayne, many of the velomobile guys run those little (.375?) tall trip strips mounted longitudinally to help with crosswinds. Most report a noticeable improvement. Also, a round cross section and low ride height make a world of difference in crosswinds. Some of my early, taller, coroliners were a challenge in crosswinds, where as the smoother, lower, rounder Coslinger barely noticed crosswinds. And it has been used in events as long as 100 miles and regularly ridden on our local bike paths (with Richard Myers).
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shooky56
recumbent guru

USA
545 Posts

Posted - 10/26/2015 :  08:53:05  Show Profile  Reply with Quote
Strips: Wow, I'd never have guessed, thanks Thom. I was thinking about tripping for lengthwise flow not cross flow to the vehicle, doh! Would be interested in trying that myself. These hideous winds lately have been a chore, don't know how a shelled two-wheeler could do it.

Richard: Enjoyed visiting and riding with him at North Manchester, an icon in the community.
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Speedbiker
human power expert

USA
3760 Posts

Posted - 10/26/2015 :  12:38:58  Show Profile  Reply with Quote
2 wheeled liner in crosswinds? It's called sailing. Hannon the Cannon and I were just talking about Tony L. getting blown off the Calvins course. Seems like he toured somebody's yard.
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Grant-53
recumbent guru

USA
544 Posts

Posted - 10/26/2015 :  13:02:43  Show Profile  Reply with Quote
[URL=http://s1187.photobucket.com/user/wgconnor/media/SAM_0104.jpg.html][/URL]
This is some sketches I did for the motorcyclists in the Vetter Challenge. This sounds much like the issues in liners.
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alevand
human power expert

USA
2935 Posts

Posted - 10/26/2015 :  15:54:49  Show Profile  Visit alevand's Homepage  Reply with Quote
Its more of a moment about the tires rather than differential lift, you want to minimize CoP * Fw. Yes, got too close to the edge of the road and oops.. through the ditch and a very close look at the lawn. 45 mph gust recorded at the airport that day. Had run down to the next turn to point it into the wind just to get back in.

C:
Tony Levand

Edited by - alevand on 10/26/2015 15:56:35
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Grant-53
recumbent guru

USA
544 Posts

Posted - 10/26/2015 :  20:13:29  Show Profile  Reply with Quote
Yes, the tire patch is assumed equal in each case. The attempt is to increase down force by lowering the relative air pressure under the shell without increasing drag. The motorcycles typically have ground clearance of 4". I take CoP as center of pressure but am unclear of the definition of Fw in this case.
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alevand
human power expert

USA
2935 Posts

Posted - 10/27/2015 :  05:05:11  Show Profile  Visit alevand's Homepage  Reply with Quote
By separating the flow at the top, you are making the situation worse, as now the leeward side has less pressure recovery.

C:
Tony Levand
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Grant-53
recumbent guru

USA
544 Posts

Posted - 10/27/2015 :  08:25:22  Show Profile  Reply with Quote
I take CoP as center of pressure but am unclear of the definition of Fw in this case. How are you measuring the distances between center of mass, center of pressure, and tire patches? We want to get enough down force on the front tire for adequate steering.
The purpose of the strip is to generate down force as an air dam does. Just enough to enhance the difference between top radius and bottom radius. The practice involves balancing the gain in down force versus the change in drag. Lean angle also plays a part in the change of lift and drag. The motorcycle shells have had positive results with vertical nose strips up to 1 inch on a shell that is 26" wide. It becomes an optimization issue. The caveat is that their Center of Mass is higher and further forward than a typical liner.
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Speedbiker
human power expert

USA
3760 Posts

Posted - 10/27/2015 :  16:29:37  Show Profile  Reply with Quote
I've never heard trip strips described as air damns. Normally they break up the crossflow to reduce side pressure and lift. Looking at the angles I don't see how they would create downforce. That runs contrary to every explanation I've heard.
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shooky56
recumbent guru

USA
545 Posts

Posted - 10/27/2015 :  16:41:02  Show Profile  Reply with Quote
I'll start another thread, there is a bit of the software mixed in this but, on this thread, got the Kamm export working decently. It actually needs a bit of silicon where the rear slab meets the shell body but it was good enough to export and test. The rest of this will be in a new thread.
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Grant-53
recumbent guru

USA
544 Posts

Posted - 10/27/2015 :  18:19:58  Show Profile  Reply with Quote
We are not talking about much force in a .375" strip. What down force is generated is reducing lift. Between the strip and the difference in the radii there is the potential for reducing lift. We are not talking inverted wings with hundreds of pounds of down force or NASCAR tail. It is a small but useful addition. There may be a better way to explain what is happening as in aircraft stall strips. We know that in practice that it works under some conditions. The trick is to quantify it and maximize it. It is on my test wish list for CFD and road resting.

Edited by - Grant-53 on 10/27/2015 19:06:55
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Victor Ragusila
recumbent enthusiast

Canada
402 Posts

Posted - 10/27/2015 :  19:40:16  Show Profile  Reply with Quote
quote:
Originally posted by Balor

quote:
Originally posted by shooky56

Structural: Gotcha.

Kamm Cut-off: If/when I get that working I'll publish it Baylor.

Dimples: Here's one discussion by the AeroVelo guys. https://www.youtube.com/watch?v=ZXpZy_A7mMk




Thanks! I know that simply chopping off in production is easy, but if you intend to implement it anyway - it would surely be useful not just for me, but for future users of the program - in case they would want to design a practical, streetable streamliner, cause it has to incorporate Kamm tail due to size constrains.

As for aerovelo guys - yea, I've seen that video. Point is, they have carte blanche on length and size of the liner, it being a BM-only camera bike.
So they do not need to worry about cross winds, passing trucks and cargo space. I do.
Unfortunately, calculating proper turbulator placement and size seems to be a kind of black magic higher math that is certainly above much reach... I think I'll have to intuit it.

quote:
Originally posted by Joel DIckman
"Our best air-bag is not getting hit in the first place." My thinking exactly. The kinetic energy difference between the motorist in his 5000 pound 200 horse power Sport Utility Vehicle and the cyclist in his 40 pound recumbent streamliner is enormous. So trying to design your streamliner out of impact absorbing material strikes me as hopeless. Anything massive enough to afford real protection in a collision with a motorist will make your human powered vehicle too heavy for practical use.



Well, like I said, I was never intending to survive a head-on collision on a highway. It must withstand being rear-ended at moderate speeds, and provide cushioning due to a fall, rollover and slide at the very least.
As for seeing and being seen... unfortunately, it can help you only so much in case of drunk drivers, hot heads or outright psychopaths (I've seen some really scary reports). But this is a risk I am willing to take, especially if minimized.



I am the guy with the video. I agree that our bike is very much optimized for BM, but we did look a lot at bikes for the ASME races, thats where we started. We can race some of them on very tight street tracks, with crosswind. A few things about cross wind that we noticed, from our bikes :

bikes with head bubble (Vortex, 2011) ride quite well in cross winds. You have to lean into the wind.

Bikes without bubble (Bluenose, 2012-13) was terrible. It had a big old long nose, and a small tail surface. This meant that the point where the force (of the cross wind) was acting on the surface was in front of the nose of the bike! This turned the bike away from the wind, and leaned it into the wind, too strongly. So if the wind came from the left, you will fall to the left, with your nose pointed to the right. This meant that we had to add a big tail fairing to the bike, and that mainly fixed the cross wind issues.

Eta (2014, 2015) actually handles great in cross winds. We tested it in a runway in TO, where there are always winds. The trick was to have not a very steep steering angle, with a moderate amount of trail (I will see if I can release those numbers, but I doubt they will be meaningful if the body position chances). The tail is quite big since we got a 650c wheel there, and that helps a lot in counteracting the force from the nose.

I wouldnt mess around too much with the aerodynamics of the nose, to help with cross winds. Get those to be confortable, and provide little drag. Then play around with a tail section, and use that to help with cross winds. Remember, bug splatters and water or mud drops do the same thing as a dimple. Dont rely on such unreliable small surface effects to keep you bike stable in cross winds, use bigger wing surfaces in the tail.

Dimples really are there to make the flow non-laminar. On a street recumbent it is very difficult to get laminar flow beyond the first couple of cm in the nose anyway, so they would solve a mostly unreal problem.

I am also not Todd, who is our expert in aero, and my grasping of the subject is not as strong as his.
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shooky56
recumbent guru

USA
545 Posts

Posted - 10/27/2015 :  19:58:37  Show Profile  Reply with Quote
Thank you for your detailed comments on the subject. Enjoyed your video too! Gratz to the entire team on your record. Although a sprinter isn't my cup of tea I find it all fascinating. Your path to that record was long and diligent, well earned.

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Balor
recumbent guru

Russia
514 Posts

Posted - 10/28/2015 :  01:12:33  Show Profile  Reply with Quote
quote:
Originally posted by Victor Ragusila
I wouldnt mess around too much with the aerodynamics of the nose, to help with cross winds. Get those to be confortable, and provide little drag. Then play around with a tail section, and use that to help with cross winds. Remember, bug splatters and water or mud drops do the same thing as a dimple. Dont rely on such unreliable small surface effects to keep you bike stable in cross winds, use bigger wing surfaces in the tail.

Dimples really are there to make the flow non-laminar. On a street recumbent it is very difficult to get laminar flow beyond the first couple of cm in the nose anyway, so they would solve a mostly unreal problem.



Wow, thanks for the video and your contribution!

So, Autodesk Flow Design results are actually misleading, because they assume laminar flow while it is anything but?

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Balor
recumbent guru

Russia
514 Posts

Posted - 10/28/2015 :  01:22:45  Show Profile  Reply with Quote
By the way, I think Flow Design might indeed be helpful with testing crosswind stability: Use Wayne's new feature of 'tail cutoff', export tail and nose separately, and than test them for drag force from the side (90 degree orientation). If one half shows much greater numbers - manipulate it. Sounds reasonable?

Edited by - Balor on 10/28/2015 01:23:52
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