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Old 10-05-2020, 01:37 PM   #41 (permalink)
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I'm screwed for aero...

I hate the crouch and look up position, puts a kink in my neck in no time.

I do not like the lack of a control position in a recumbent, and the neck bent forwards eventually puts a kink in my neck as well.

I could probably stomach riding a trike on a long, straight and preferably mostly level path that was free of obstacles, stops, vehicles, etc. dispite the eventual neck kink. But good luck with that.

...Sitting upright but with feet forward wouldn't be bad, like in a car, but you can't pedal worth crap like that.

In other words, I like a nice upright position, where I can lean in to turns and put my feet down firmly when I come to a stop...so terrible aero.

I'll just have to go slower or accept the energy loss.

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Old 10-05-2020, 05:11 PM   #42 (permalink)
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Quote:
Originally Posted by Stubby79 View Post
I'm screwed for aero...

I hate the crouch and look up position, puts a kink in my neck in no time.

I do not like the lack of a control position in a recumbent, and the neck bent forwards eventually puts a kink in my neck as well.

I could probably stomach riding a trike on a long, straight and preferably mostly level path that was free of obstacles, stops, vehicles, etc. dispite the eventual neck kink. But good luck with that.

...Sitting upright but with feet forward wouldn't be bad, like in a car, but you can't pedal worth crap like that.

In other words, I like a nice upright position, where I can lean in to turns and put my feet down firmly when I come to a stop...so terrible aero.

I'll just have to go slower or accept the energy loss.
All valid points - but you need to remember that people with bikes often go to extremes. So for example a recumbent doesn't need to be very recumbent to drop frontal area, and there has been at least one bike produced where you sit upright with a forward pedal position:



It wasn't so good up hills but was a lovely comfortable bike on the flat (Giant Revive).
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Old 10-06-2020, 03:43 AM   #43 (permalink)
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I will be sitting like that on the bike I'm just starting to build, though lower with the pedals a bit farther forwards. More chopper-style, though not as extreme...cruiser motorcycle style. Should be a bit better than almost standing upright, as you point out.

I want an inflatable faring/aero shell...it could be taken on and off in moments, and take up no space. I'd use it for specifically long, higher-speed trips and could still enjoy open-frame styling the rest of the time.
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Old 10-06-2020, 03:47 AM   #44 (permalink)
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I want an inflatable faring/aero shell...it could be taken on and off in moments, and take up no space. I'd use it for specifically long, higher-speed trips and could still enjoy open-frame styling the rest of the time.
No that sounds interesting. How do you make it so that it inflates to the right shape (and holds air too, I guess)?
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Old 10-06-2020, 04:04 AM   #45 (permalink)
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No that sounds interesting. How do you make it so that it inflates to the right shape (and holds air too, I guess)?
I didn't say I was doing it, but...I figure to make it like beach balls and other inflatable toys...rubbery plastic, cut sections with the seams melted together, like you were sewing a garment together. Like how a beach ball is made from...convex...strips to get an over-all spherical shape.

You could probably do the seams with a hand-held version - assuming such a thing exists - of something like those food vacuum sealers for food that melts the pouches edges together.

Probably take a lot of time, and trial & error...more than it's worth for me to be able/willing to put in...maybe when I retire and can presumably have the time to pursue my interests more.
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Old 10-06-2020, 01:26 PM   #46 (permalink)
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Inflatables are of two type. Single-walled with interior pressure, and double walled with the interior at ambient pressure. I presume you are going for double-walled.

The shape can be easy.


Antfarm used an electric iron with the material drapped over a thin edge:


https://www.foundsf.org/images/9/98/...inflatable.jpg

The hard part is attachment and ingress/egress. (I'm not retired, I just between gigs)
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Old 10-06-2020, 09:59 PM   #47 (permalink)
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It is common to ride a mountain bike or a touring bike with a 45 degree back angle. Any change in position requires a period of acclimation. Have made and used homemade aero bars. I don't get super low and use the handlebar bag or fairing to direct air flow. I read Zinn on triathlete bikes. Even moving the bar grips inboard on the mountain bike gave me a 1 mph increase at 13 mph. I ride in windy conditions to test stability. By mounting the fairing to the head tube instead of the handlebars the stability is vastly improved.
The ideal would be to reduce the Cd below 0.2 or less.
Any kind of sturdy back rest would help leg push.
A one piece shell I would hinge at the nose to flip forward like a sailplane canopy.
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Old 10-09-2020, 01:28 PM   #48 (permalink)
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Cd 0.13

Quote:
Originally Posted by JulianEdgar View Post
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.
Cd 0.13 seems very plausible.
I was unsure of the all-up weight, and used data for the 0.40 m-squared rig, thinking Grant-53 might be able to tuck his head inside the enclosure.
* If the R-R was 38-Watts @ 36 km/h, and tires were below standing wave, and increasing resistance arithmetically, then @ 50 km/h, R-R power would rise to 52.7-Watts. Leaving 47.3- Watts budget at the higher speed for aero.
If it's 47.3 @ 50- km/h, then it'd be 17.65-Watts @ 36 according to the cube law.
One of the bikes had a 24.2-W aero power consumption with CdA = 0.044 m-sq.
Adjusting for 17.65-W available power, the CdA would need to fall to 0.0325 m-sq.
Dividing by 0.40-m-sq, Cd 0.0813 falls out of the equation.
Really low!
At Battle Mountain, Nevada, the 'laminar' bikes doing 85-mph ( 137-km/h ) are around Cd 0.11 according to the university teams.
It's okay checking my math as well. I stayed with metric, where typically I switch to US standards, then convert back.
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Old 10-09-2020, 01:32 PM   #49 (permalink)
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inflates

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Originally Posted by Stubby79 View Post
I didn't say I was doing it, but...I figure to make it like beach balls and other inflatable toys...rubbery plastic, cut sections with the seams melted together, like you were sewing a garment together. Like how a beach ball is made from...convex...strips to get an over-all spherical shape.

You could probably do the seams with a hand-held version - assuming such a thing exists - of something like those food vacuum sealers for food that melts the pouches edges together.

Probably take a lot of time, and trial & error...more than it's worth for me to be able/willing to put in...maybe when I retire and can presumably have the time to pursue my interests more.
Have you seen the Goodyear Tire & Rubber Company's inflatable airplane, designed for the U.S. Military during WW-II?
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Old 10-09-2020, 04:11 PM   #50 (permalink)
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https://en.wikipedia.org/wiki/Goodyear_Inflatoplane


https://www.aerotoons.com/blog/goody...latoplane.html
Quote:
The airplane was made of a special sandwich of rubberized materials called "airmat".

Inflatoplane folded upThe inner portion of this airmat material was composed of numerous meshes of nylon threads which, when inflated with air, would form a strong "I" beam structure.

The shape of the wings and other flight structures were maintained inflight by a steady circulation of air provided by the aircraft's engine after the initial inflation of the airplane, (which took as little as 25 psi. and 5 minutes to inflate) and was said to be quite rigid. The fuselage was made of airship fabric with high-strength, fan-shaped patches of rubberized material providing attachments for struts and metal supports that connected the landing gear and the pilot's seat to the aircraft.

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