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Aerodynamics /structural question (stock class)

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delcrossv
recumbent enthusiast

Vanuatu
243 Posts

Posted - 07/16/2012 : 09:52:58

(Assuming I get time to do this)

In thinking about building a laminated wood lowracer, the issue I am seeing structurally is that I really do not want any negative curvatures if I can avoid it. The CF bikes NoCom and M1 have negative curvatures since you can bend the CF as you like while wood veneers have a more limited curvature radius particularly along the grain. This may have been discussed previously, but is there an issue with making the rear stays have positive curvature from the spine (below the seat) to the top of the stay?
They'd be larger than on a nocom/M1 but would solve a lot of fabrication problems for me.
FWIW, the angle between the seat edge and the end of the stay would be too steep for laminar flow anyway.

Should I make a foam mock up and put it in front of a fan with tell-tales (tufts)?

Edited by - delcrossv on 07/16/2012 09:56:36

Larry Lem
human power supergeek

South Sandwich Islands
1971 Posts

Posted - 07/16/2012 : 12:41:02

Please define negative and positive curvature.
From the text, I think negative means the ends are low and the middle is high. So maybe your stays would curve upward?

Not sure why laminar flow is being mentioned when talking about a stock class bike. Assume there is none. Maybe you mean whether flow remains attached. As others have been pointing out, that is hard to do unless a tailbox is built that is HUGE.

Your suggestion to make a mockups is great as it is a relatively fast and easy way to try something instead of investing a lot of build time on something that might not work as hoped.
Good luck!

Larry Lem

delcrossv
recumbent enthusiast

Vanuatu
243 Posts

Posted - 07/16/2012 : 13:27:54

Well in the NoCom discussion there was talk about reattachment aft of the seat so yes I talking about reattachment of the streamlines rather than maintaining laminar flow over the bike.(i'm assuming no reattachment, like the NoCom and M1 leave the flow "detached")

By positive curvature I mean that the stays are rounded outward with no "hollow" as it goes towards the bottom of the bike. It may go flat as it meets at a "V" in front of the rear wheel but in cross section it would be more like a squished "C" than an "S". There'd be more coverage of the rear wheel as the lower edge of the stay would end at the base of the spine below the seat.
Compound curves are hard to do and make the structure much weaker.

I'll see if I can load up a sketch as this is unclear at best.

Also is it legit to sink the idler into the frame? The front of the idler would be open but as the spine gets wider the chains would run interior to the rear stay/seat back. Maybe a mid drive rather than an idler (2 sprockets on a spindle)?

Edited by - delcrossv on 07/16/2012 14:01:24

Speedbiker
human power supergeek

USA
1990 Posts

Posted - 07/17/2012 : 14:26:34

Delcrossv, nobody wants to rehash that whole NoCom discussion. Please reread it. Please learn about laminar flow and reattatching airflow. Neither of which apply to.nonfaired recumbents.

sean costin
human power supergeek

Lesotho
1917 Posts

Posted - 07/17/2012 : 19:08:44

Fran,
If you bring a sketch to practice on Wednesday I'll be happy to evaluate it. Using good quality plywood for a frame is not a bad idea especially since it reduces the time to make it.

I found the 24" tubulars for you and will bring them to the track.

Sean

delcrossv
recumbent enthusiast

Vanuatu
243 Posts

Posted - 07/18/2012 : 06:25:37

quote:
Originally posted by Speedbiker

Delcrossv, nobody wants to rehash that whole NoCom discussion. Please reread it. Please learn about laminar flow and reattatching airflow. Neither of which apply to.nonfaired recumbents.

I know a few things about flow and have NO desire to rehash anything. I'm in agreement that neither a NoCom nor an M1 operate as a streamlined bike. Maybe I wasn't clear, but I thought I was.

Edited by - delcrossv on 07/18/2012 06:28:16

delcrossv
recumbent enthusiast

Vanuatu
243 Posts

Posted - 07/18/2012 : 06:26:50

quote:
Originally posted by sean costin

Fran,
If you bring a sketch to practice on Wednesday I'll be happy to evaluate it. Using good quality plywood for a frame is not a bad idea especially since it reduces the time to make it.

I found the 24" tubulars for you and will bring them to the track.

Sean

Thanks, I'll see what I can do. Can't make it today. Friday definitely though.

To make this light I'll have to lay up veneers over a mold (DIY plywood)Glad I saved that old vacuum pump from the lab at school.

Edited by - delcrossv on 07/18/2012 12:08:36

delcrossv
recumbent enthusiast

Vanuatu
243 Posts

Posted - 07/27/2012 : 09:53:54

So here's the sketches. The question being is using the longer stays "Version 1" (better from a construction/structural angle for me) enough to remove this design from being a "Stock Class bike"? Version2 being similar to an M1 and so "okay".

Edited by - delcrossv on 07/27/2012 09:54:49

Speedbiker
human power supergeek

USA
1990 Posts

Posted - 07/27/2012 : 10:08:23

Build what you want, or what he thinks is cool. If he sets a world record the committee can decide if he is stock ot TFed. Having some experience in this area, I think the most important factors are rideability and minimizing weight.

Larry Lem
human power supergeek

South Sandwich Islands
1971 Posts

Posted - 07/27/2012 : 10:37:15

delcrossv,
When you say "stock class", to what organization are you referring? HPRA?

Larry Lem

Edited by - Larry Lem on 07/27/2012 10:38:00

delcrossv
recumbent enthusiast

Vanuatu
243 Posts

Posted - 07/27/2012 : 11:26:38

quote:
Originally posted by Larry Lem

delcrossv,
When you say "stock class", to what organization are you referring? HPRA?

Larry Lem

Yes, as it'd be raced at the WISIL events in Northbrook and Kenosha.

delcrossv
recumbent enthusiast

Vanuatu
243 Posts

Posted - 07/27/2012 : 11:28:52

quote:
Originally posted by Speedbiker

Build what you want, or what he thinks is cool. If he sets a world record the committee can decide if he is stock ot TFed. Having some experience in this area, I think the most important factors are rideability and minimizing weight.

He just wants to go faster- Can't really blame him. Anyway if I build it in this size, it'd fit Genevieve eventually- then watch out!

I don't think the geometry would be different between the two, but the one with the longer stays would potentially be lighter.(thinner layup). FWIW, I'd get no structural advantage extending the stay past where I'd put the crosstie (just behind the rear wheel). Talked with Sean about just extending the inside skin (facing the wheel) but I'm guessing it'd flex or vibrate.

Edited by - delcrossv on 07/27/2012 11:55:09

Speedbiker
human power supergeek

USA
1990 Posts

Posted - 07/27/2012 : 13:57:18

By the time he goes fast enough for it to matter, he will be begging you for an M1! Look at what my son did on a Gritter style lowracer. LWB til his legs got long enough to reach around a 16" wheel, then SWB. Charlie got on the lwb when he was 12. It was stable and easy to ride. I am sure there are grownups who remember drafting him. Two yrs later I Zeed the frame and made it swb. I routed the driveside chain over the wheel to make it easy to ride. As recent as a couple yrs ago he was still killing us on that bike(with a 90 tooth CR on the front!). Light and simple, low and laid back.

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