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Old 10-02-2020, 02:42 PM   #31 (permalink)
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HPVA bicycle drag table

Before the HPVA became the IHPVA, they published a rather comprehensive drag table to aerodynamically-modified bicycles, including measured Cds for each configuration depicted.
I printed mine from online years ago.
The table is entitled: HUMAN POWERED VEHICLE PERFORMANCE
it shows 20-configurations.
upright and recumbent

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Old 10-02-2020, 05:49 PM   #32 (permalink)
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Quote:
Originally Posted by freebeard View Post

I like the space frame. Can you use the trusses as a luggage rack?
The front luggage rack mount (takes a Brompton block) and rear luggage carrier are my constructions.
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Old 10-02-2020, 05:56 PM   #33 (permalink)
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Old 10-02-2020, 06:29 PM   #34 (permalink)
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The birdcage X-member was stock?

I'd imagined you modeled it with soldered wire and vice grips.
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Old 10-02-2020, 06:35 PM   #35 (permalink)
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Originally Posted by freebeard View Post
The birdcage X-member was stock?
Yes, stock Moulton.
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Old 10-03-2020, 04:59 PM   #36 (permalink)
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What Cd is needed to a get 0.40 meter sq. frontal area machine to achieve 50 kph using 100w of power? I will continue to reinforce the nose section and add side panels. Cost down tests to measure the effects.
"If was easy anyone could do it and they wouldn't pay us the big bucks."
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Old 10-03-2020, 05:40 PM   #37 (permalink)
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Originally Posted by Grant-53 View Post
What Cd is needed to a get 0.40 meter sq. frontal area machine to achieve 50 kph using 100w of power? I will continue to reinforce the nose section and add side panels. Cost down tests to measure the effects.
Looking at the table I posted, and remembering that required power goes up with the cube of the speed (ie your nominated speed of 50 km/h will require 2.7 times the 36 km/h aero power shown in the table), I wouldn't think you'd be able to get the Cd down sufficiently to achieve that outcome.

Using the table, at 36 km/h, a bike with a frontal area of 0.35 square metres and a Cd of 0.13 requires a total (aero + rolling resistance) power of 50W (of that 24W is aero power, so a total of 90W at 50 km/h).

So that would imply that to meet your criteria, you'd need a Cd of something like 0.13 - pretty hard.

Happy to have someone check my maths - never my best area.
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Old 10-04-2020, 04:44 AM   #38 (permalink)
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Quote:
Originally Posted by freebeard View Post
www.bikeboom.info/efficiency/: How the bicycle beats evolution and why Steve Jobs was so taken with this fact

Quote:
“When one compares the energy consumed in moving a certain distance as a function of body weight for a variety of animals and machines, one finds that an unaided walking man does fairly well (consuming about .75 calorie per gram per kilometer), but he is not as efficient as a horse, a salmon or a jet transport. With the aid of a bicycle, however, the man’s energy consumption for a given distance is reduced to about a fifth (roughly .15 calorie per gram per kilometer).

“Therefore, apart from increasing his unaided speed by a factor of three or four, the cyclist improves his efficiency rating to No. 1 among moving creatures and machines.
Yes, a really important citation. And what if we gave a bike decent aero drag, and a recumbent position to reduce frontal area?

About 15 years ago I fell in love with recumbent trikes - most of the efficiency of a bike, but with vastly more comfort and stability.



In short:

... I rode a Greenspeed recumbent trike...
... loved it...
... bought a secondhand one...
... felt I could do better...
... found I couldn't...
... designed and made another...
... got closer...
... designed and made another...
... was getting better...
... designed and made another - and was mostly happy.



I didn't do any aero at all (we then lived in Queensland - think Florida for climate), and no canopy would have been bearable.

But I remember my initial absolute arrogance - how I was just soooo going to improve on the Greenspeed (little did I then know that the late Ian Sims was one of the very best engineers I've ever met) because I just knew about proper design like suspension. After years of development, I got to the point of shaving anti-roll bar brackets for reduced mass - every gram was so critical. But it did have what I think was probably the best pedal vehicle ride comfort in the world.

It was fun, and a great engineering exercise. It was also a bit like on this group: the main recumbent discussion group in the US very soon became cross with me when I challenged their longstanding, prevailing wisdoms. What prevailing wisdoms? Boom flex, ride comfort, construction techniques, handling assessments, etc.

They kept on insisting their trikes handled so well, and in the end I did a simple circular skid pan test that easily showed maximum sustainable lateral g's. Certainly not the be-all and end-all of handling, but a comparison starting point. To do well, you had to be able to pedal hard, hold the steering line, and go fast. One guy, who had a tilting trike, was going to smash me. It was very interesting - I waited with great anticipation. Then nothing happened. (Looking at his machine, I think he couldn't pedal at the required steering lock.)



Some investor heard about my projects and sent his expert to ride one of my recumbent trikes. It was very weird. The guy plunged down my local hill at full speed and then yanked on maximum steering lock. Not surprisingly, the trike did a barrel roll...

I also built a long wheelbase, full air suspension recumbent bike (not trike), but I hated it.



But now I am mostly into bikes, like my Moulton.



And I wrote a book on small wheeled bikes, but almost no-one has bought a copy!



But if you want engineering at its absolute purest, no rules and no restrictions, pedal-powered bikes and trikes are it.

(And a last pic - my first trike. Far too heavy - the start of my learning curve!):

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Old 10-04-2020, 04:53 AM   #39 (permalink)
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How do upright bikes with fairings behave in crosswinds? (That one bike looked like a rigid sail basically)
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Old 10-04-2020, 05:15 AM   #40 (permalink)
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Quote:
Originally Posted by jakobnev View Post
How do upright bikes with fairings behave in crosswinds? (That one bike looked like a rigid sail basically)
I haven't specific experience in changing the stability of a bicycle but...

It depends on where the main 'side' area is with regard to the centre of gravity. So the centre of gravity on a bike is going to be (basically) at the middle of the person riding it, so we want more 'side' area behind the person than in front. (Think feathers on an arrow.) It's why all the speed record motorcycles run rear fins.

Lovely NSU example:


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