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PostPosted: Fri Jun 22, 2012 12:07 am 
Dirt Disciple

Joined: Sat Jun 16, 2012 4:17 pm
Posts: 59
Location: Isle of Man
Firstly the record's are sanctioned by these people http://www.whpva.org/

The world human powered vehicle association.

There rules are here http://www.whpva.org/WHPVA-CompetitionRules-2009.pdf

Sam Wittingham's records taken from wikipedia are;

Sam Whittingham is a Canadian cyclist who has held several world records on recumbent bicycles.
As of 2009, he holds the following world records under the sanction of the International Human Powered Vehicle Association:

The 200 m flying start (single rider, World Human Powered Speed Challenge, Battle Mountain, NV): 133.284 km/h (82.819 mph) on 2009-09-18.

First unpaced cyclist ever to break the deci-mach mark (1/10 the speed of sound, World Human Powered Speed Challenge, Battle Mountain, NV): 132.50 km/h (82.33 mph) on 2008-09-18. To date, still the only person to have accomplished this milestone.

The 1000 m flying start (single rider): 128.40 km/h (79.79 mph) on 2001-10-06.
The 1 mile flying start (single rider): 126.55 km/h (78.64 mph) on 2001-10-06.
The hour record: 90.724 km (56.373 mi) on 2009-07-17.[1]
In 1993 he also held the record for the 200 m flying start (multiple rider).

These are the record's record's I would imagine that Graeme Obree is interested in..


@ Jim

"The prone position isn't new, and it generally hasn't done well in competition. Aerodynamics depend mainly on fairing design, and the prone position tends to limit chest expansion."

If you look at Graeme's bike design his chest isn't in contact with the bike at any point he is supported solely by his shoulder blades and hips leaving the whole of his chest freedom to move..

@Lazarus

Human power even in the best athlete is rarely more than 600w constant

"Direct drive: Using the back wheel itself when it's upto speed to become the biggest chainring in the system ? Has it ever been done before ? Also to drive the back wheel directly via cogs ie NO chain ?"

Cogs are less efficient than chains which have a maximum efficiency of 97%. If you used cogs you would have higher friction losses and therefore less energy transferred to propulsion

"Dual drive cranks: (not sram 9x3 stuff) two cranks left & right on a pista BB (equal spaced) connected to a flipflop rear wheel. What does anyone know about how this idea works and why it never took off ? "

Again less efficient due to the losses of the second chain that's not being driven. Also how can two different sized chain rings linked to one wheel drive at different rates when they are both connected by the crank axle and the rear hub?

"Dual propulsion ie Simultaneous Front & Rear wheel drive, whereby both sets of wheels provide drive/motion to the cycle ?"

Why is dual drive needed when there is not enough power developed to loose traction driving 1 wheel? This would again cause more friction due to dual drive trains.

"Obree NEW bike.jpg"

This again has losses due to having 3 wheels which cause a higher rolling resistance than two.

From wikipedia again;

For example, assuming no wind, one gets the following results for kilocalories required and power delivered to the pedals (watts):
175 W for a 90 kg bike + rider to go 9 m/s (20 mph or 32 km/h) on the flats (76% of effort to overcome aerodynamic drag), or 2.6 m/s (5.8 mph or 9.4 km/h) on a 7% grade (21% of effort to overcome aerodynamic drag).

300 W for a 90 kg bike + rider at 11 m/s (25 mph or 40 km/h) on the flats (83% of effort to overcome aerodynamic drag) or 4.3 m/s (9.5 mph or 15 km/h) on a 7% grade (42% of effort to overcome aerodynamic drag).

Amateur bicycle racers can typically produce 3 watts/kg for more than an hour (e.g., around 210 watts for a 70 kg rider), with top amateurs producing 5 W/kg and elite athletes achieving 6 W/kg for similar lengths of time.

So given that the load i.e. rider and cycle are a constant weight, power is limited to the riders ability and that friction is a constant due to to the tyres rolling resistance and drive train losses the best gains in speed/kg/w can only be achieved by decreasing the aerodynamic drag.

The most efficient aerodynamic shape to reduce drag is the streamlined cigar shape with the widest end at the front tapering to the rear which has a drag coefficient of 0.04 (which is the design Graeme is using) unlike most recumbent's which are generally the same shape reversed which has a higher drag coefficient.

I'm really enjoying this thread and look forward to the reply s its good to get the brain working......

John


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PostPosted: Fri Jun 22, 2012 4:39 pm 
Retro Guru

Joined: Sun Mar 27, 2011 11:36 pm
Posts: 551
Location: Liverpool
Hi again everyone :-) Lot's to think about here, so I'll let it mull a while and post a reply. All the best Laz.


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PostPosted: Fri Jun 22, 2012 5:23 pm 
Retro Guru
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Joined: Thu Jun 23, 2011 11:25 pm
Posts: 1784
Location: It's not easy being a dolphin.
Anyone have any thoughts on his tire choice?

They seem not skinny enough, or is this well thought out too so it offers a larger contact patch and some cushioning (since his arse, legs and arms aren't really going to absorb much)?


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PostPosted: Fri Jun 22, 2012 5:29 pm 
Old School Hero
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Joined: Fri May 08, 2009 4:09 pm
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bikerjohn wrote:
The most efficient aerodynamic shape to reduce drag is the streamlined cigar shape with the widest end at the front tapering to the rear which has a drag coefficient of 0.04 (which is the design Graeme is using) unlike most recumbent's which are generally the same shape reversed which has a higher drag coefficient.


This is my point I guess, is the reduction in drag with Obree's machine greater than the power loss? I'm nowhere near clever enough to do the maths on that one!!

Interestingly for Obree, there was a recent change in the HPV hour record, it's now up to about 94km/h... the machine that took it is called Eiviestretto and it's a normal recumbent position... but ridden backwards, so the rider's head is at the front wheel, and his feet at the rear wheel. Nuts. But apparently very effective!! The guys who build it, had ridden the hour in a comparable normal HPV, and they reckoned that taking advantage of the teardrop shape added about 8-9% to their speed for a given power.


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PostPosted: Fri Jun 22, 2012 5:52 pm 
Retro Guru
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Location: It's not easy being a dolphin.
...going forward by looking backwards at 100 Kph. CCTV head-up display or mirror ;-)


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 Post subject: teardrop shape
PostPosted: Fri Jun 22, 2012 6:01 pm 
Dirt Disciple

Joined: Sat Jun 16, 2012 4:17 pm
Posts: 59
Location: Isle of Man
This would also back up Graeme's theory that the teardrop shape is the most aerodynamically efficient. All the brief research I did prior to posting has also lead me to the same conclusion that the Cigar/teardrop shape is the best to use.


@Bob

"the reduction in drag with Obree's machine greater than the power loss?"

Hi Bob, this subject is really fascinating!

All I can say is that the Cigar shape will cause the lowest Aerodynamic drag due to the most efficient shape. This will mean that for a given amount of human power this shape will give higher speeds because it has a lower aerodynamic drag resistance.

I have not as yet addressed the power loss due to transmission and rolling resistance as I don't know the details of the transmission or chassis on Sam Wittinghams bike and as Graeme's is still unfinished I again have too few facts to compare.

What this does prove though is that for a given transmission and rider who has a head first riding position in a Cigar/teardrop shaped HPV is more efficient than one with the wide end of the body at the rear due to superior aerodynamics.

John


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PostPosted: Sat Jun 23, 2012 1:22 pm 
Old School Grand Master
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Joined: Wed Feb 20, 2008 12:21 pm
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Location: Lost in Translation
bikerjohn wrote:
@ Jim

If you look at Graeme's bike design his chest isn't in contact with the bike at any point he is supported solely by his shoulder blades and hips leaving the whole of his chest freedom to move..

http://www.youtube.com/watch?v=_bNH5pfcLWE


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 Post subject: Dem Bones
PostPosted: Sat Jun 23, 2012 4:10 pm 
Dirt Disciple

Joined: Sat Jun 16, 2012 4:17 pm
Posts: 59
Location: Isle of Man
@ Jim javascript:emoticon(':lol:')

Point taken Jim, Graeme's design should still allow him to breathe without restriction though..


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PostPosted: Sun Jun 24, 2012 1:15 am 
Retro Guru

Joined: Sun Mar 27, 2011 11:36 pm
Posts: 551
Location: Liverpool
Hi again everyone :-) John my friend - "All the brief research I did prior to posting has also lead me to the same conclusion that the Cigar/teardrop shape is the best to use." - sometimes life is easier than all that research, simply ask yourself what shape a raindrop is (teardrop) then ask yourself if nature knows best :-) Understand the nature of why a raindrop is that shape, and base ALL future thoughts around that constant. not remould the raindrop theory to fit the existing maths.

Off course the teardrop-raindrop shape is most effective, it's because gravity/laws of nature determine that anything that wants to gain velocity should do so heaviest end first, nothing in nature travels lightest parts first dragging the heaviest part behind it. I posted that I was dumbfounded by Obree's observation that Propulsion = Works / Dragging = doesn't. Its as cut & dried as that buddy :-) No matter how much we calculate the laws of nature with theorems/designs/equations the bottom line is " write down the wrong sums in the first place and the answer will also be wrong". Sure the maths will add up, but it is the values being placed that make no sense.

All of this information re: aerodynamics of drag is pointless because this is only 1 part of the whole equation. My proposal based on what I think Obree is trying to say is that "propulsion of the bodyweight will be more effective than dragging the bodyweight". First the correct theory must be understood, for the equations to be re-written in the correct formula.

Here is something to think about : " A raindrop changes shape due to gravitational pull. It changes because it can :shock: SOLID skins/fairing simply won't work, liquid skins/fairing will work best. The theory sounds great, but some poor sod (like me) has to actually invent a maleable/liquid skin for these bikes. I say to anyone, "sit on your bike, ass over the BB shell, place your body/chest over the handlebar area and feel the difference". If it feels this good as a test, then with the correct kit, it'll work :-) I'm into designing the kit myself, it's what I've always done, "used my knowledge of existing technologies/materials/sciences to re-design/invent new applications. Being 50 helps in that I've been fortunate enough to work with a vast array of materials each within a vast array of jobs & applications.

I am still gobsmacked by Obree's find, because it is and will be proven to be, the turning point in cycling speed records, HIS theory/discovery is IMHO without a doubt groundbreaking. I'm sure there will be a huge outpouring from near & far that they did it first, but in truth, they got it wrong first :-) Obree was 100% correct when they took the p*ss out of him all those years ago, and today he still does the same things, not to cheese people off, but because he simply looks for the answer to the question in his head = "how can I go faster (and live to tell the tale) ?" Later everyone, Laz.


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PostPosted: Sun Jun 24, 2012 10:51 am 
retrobike rider
retrobike rider

Joined: Sat May 29, 2010 3:44 pm
Posts: 1508
Location: Leeds
The teardrop works because it is falling vertically.

It will not be the same horizontally when the length will have to be 8ft+ then balanced over the 2 wheels then removing the drag from the wheels and gaps around the wheels. The tear drop shape will have to balance the drag difference top and bottom.

Build it in the kitchen yes. Design it in the kitchen, unless he has a wind tunnel, no.

I admire Obree greatly and belive if he wants it he will get it, but he needs assistance.

I hope i'm wrong.


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