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Old 08-14-2017, 11:22 PM   #1 (permalink)
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Critique this velomobile body

I've been putting together an electric assist velomobile with the goal of approaching less than 10 Wh/mile at 30 mph on flat ground with the rider pedaling with an input of 100W. I want to make sure that I have the body streamlined to a decent degree. The first body, depicted in this post, is being made out of corrugated plastic. It is not good at making compound curves, and generally only likes to be folded in one direction. I came up with the design below based on the Rumpler Tropfenwagen and the lakester salt flats racers, with a bit of influence by the LeMans velomobile. After that is a picture of the trike as it exists today. Open wheels are a necessity in order to fit it in and out of my doorway, and the body width is as narrow as possible while still providing clearance for the steering bars and without the wheels scrubbing. I estimate a frontal area of 0.6 m^2, but I am hoping to get a 0.25 Cd or below. Better shapes will be built after this one, but this will be the starting point.

The drawing of the body is done to scale. 1 square in the blue grid is 100 mm.

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Old 08-15-2017, 01:41 PM   #2 (permalink)
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Nice! That should be much better than the bare trike. I say build it as a version 1.0 and test it out. Sometimes simpler and doable is better than the optimal design that never gets built.
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Old 08-15-2017, 02:09 PM   #3 (permalink)
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You can use the HPV shell design software at recumbents.com and see the velomobile forum for similar projects. These guys are the experts. The file format can be used with CFD software too.
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Old 08-15-2017, 02:30 PM   #4 (permalink)
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Looks cool to me.

Might be nice to have a floor vent inlet to direct air-flow to your crotch area, then an exhaust vent at the rear to relieve any built-up pressure.

Might also come in handy against fog-up should you ever put a glass canopy on it.

Are you taping the body panel joins from one side only?

Which side?

I might want to do something similar someday, never figured out how to really glue the stuff or fill in the gaps well.
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Old 08-15-2017, 03:54 PM   #5 (permalink)
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A flat sheet won't do compound curves, but you can cut darts and stitch the pieces together to create some. It'll look a bit like the Hindenburg.

Obviously you want less frontal area than more, and the sooner you can start the taper rearward, the better, if only to slam the air closed behind you more gently.

The lowest w-h I've seen for an electric car was right at 100 w-h per mile, and that was a nearly full sized car. I don't remember how fast it was going, but it wasn't like an Electrothon vehicle, it was moving at traffic speed. The best plug-in hybrid in the EM Garage has a PB of 177 w-h/mi, so getting a recumbent trike to do a good speed at just 100w input should be pretty straightforward. That 100w of rider input might be all it takes.
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Old 08-15-2017, 06:55 PM   #6 (permalink)
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Is this kind of what you mean elhigh?
It looks like the design could be adapted to be more aerodynamic.

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Old 08-15-2017, 10:14 PM   #7 (permalink)
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So much yes. I picked this up a few days ago and have similar aspirations:

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Old 08-15-2017, 11:19 PM   #8 (permalink)
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Quote:
Originally Posted by Grant-53 View Post
You can use the HPV shell design software at recumbents.com and see the velomobile forum for similar projects. These guys are the experts. The file format can be used with CFD software too.
I'm running a debian linux machine, so .exe files are a no go. Oh well. It looks like a very useful tool.

Quote:
Originally Posted by kach22i View Post
Looks cool to me.

Might be nice to have a floor vent inlet to direct air-flow to your crotch area, then an exhaust vent at the rear to relieve any built-up pressure.

Might also come in handy against fog-up should you ever put a glass canopy on it.

Are you taping the body panel joins from one side only?

Which side?

I might want to do something similar someday, never figured out how to really glue the stuff or fill in the gaps well.
I already have footholes carved into the floor. I plan to add items not depicted in this drawing, which include mirrors, lights, signals, canopy with wind screen, NACA ducts for cooling, wheel pants, and vinyl wrapping(for coloring and uv protection), all of which will be features of the finished product, and depending on placement, as a combined total may or may not increase frontal area and/or drag significantly.

The body panels will be held with a combination of zip-ties, Gorilla tape, and Loctite 406. Both sides of the joints get tape. They've so far only been zip-tied. I will take more pics when it is finally mounted, but I need to have a steel mounting bracket made to hold it onto the frame.


Quote:
Originally Posted by elhigh View Post
A flat sheet won't do compound curves, but you can cut darts and stitch the pieces together to create some. It'll look a bit like the Hindenburg.
I've considered such a shape for the front in a previous design, but clearance issues with the steering bars on the sides as well as the potential to generate oversized and unwanted vortices in the front(as the Spearhead coroplast shell is plagued with) made me decide against it in favor of a much simpler and more predictable(with regard to airflow) design.

Quote:
Obviously you want less frontal area than more, and the sooner you can start the taper rearward, the better, if only to slam the air closed behind you more gently.
The widest point of the body needs to be where the steering bars can move as far as possible while still giving as large a turning radius as possible, without any wheel scrub occuring. This, in turn, determined the parameters and placement of the boat tail section.

Quote:
The lowest w-h I've seen for an electric car was right at 100 w-h per mile, and that was a nearly full sized car. I don't remember how fast it was going, but it wasn't like an Electrothon vehicle, it was moving at traffic speed.
Reverend Gadget's GT6-bodied Triumph Spitfire achieved 100 wh/mi at a steady 60 mph on flat ground in fair weather. It had minimal aeromods. Better is possible.

Quote:
The best plug-in hybrid in the EM Garage has a PB of 177 w-h/mi, so getting a recumbent trike to do a good speed at just 100w input should be pretty straightforward. That 100w of rider input might be all it takes.
100W wouldn't get a Milan SL, the world's most efficient velomobile that remains commercially available, to 30 mph. It has a drag coefficient of 0.076. I've heard it can do 32 mph on 150W.


Quote:
Originally Posted by Ecky View Post
So much yes. I picked this up a few days ago and have similar aspirations:

Nice find. IMO, you will need a suspension for sustained high speeds. My KMX was quite squirrely over road imperfections above 20 mph before I put a front suspension kit on it.

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Old 08-15-2017, 11:40 PM   #9 (permalink)
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I've been thinking about what to do about the steering - it does tend to get squirrely at speed. I've already adjusted the toe a bit (helped a lot) and moved the seat and pedals back, to get a more centered center of gravity, but steering is very twitchy when I get close to 30.

Most seem to go for "mid drive" electric motors on these, mounted on the front by the pedals. Having multiple gears to select for the motor is attractive, but I'm thinking I'll probably instead go with a 750-1000w geared rear hub motor (still allows freewheeling) wound to give a top speed of 25-30mph. This will again shift more of the weight from front to center, and clean up the wiring and aesthetics significantly.
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Old 08-16-2017, 08:11 AM   #10 (permalink)
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Quote:
Originally Posted by The Toecutter View Post
I've been putting together an electric assist velomobile with the goal of approaching less than 10 Wh/mile at 30 mph on flat ground with the rider pedaling with an input of 100W. I want to make sure that I have the body streamlined to a decent degree. The first body, depicted in this post, is being made out of corrugated plastic. It is not good at making compound curves, and generally only likes to be folded in one direction. I came up with the design below based on the Rumpler Tropfenwagen and the lakester salt flats racers, with a bit of influence by the LeMans velomobile. After that is a picture of the trike as it exists today. Open wheels are a necessity in order to fit it in and out of my doorway, and the body width is as narrow as possible while still providing clearance for the steering bars and without the wheels scrubbing. I estimate a frontal area of 0.6 m^2, but I am hoping to get a 0.25 Cd or below. Better shapes will be built after this one, but this will be the starting point.

The drawing of the body is done to scale. 1 square in the blue grid is 100 mm.
How do the open wheels help with the doorway?
The second time I built a Coroplast body, I used mostly "Fine Flute" grade, which is lighter, and built Coroplast box beams for structure, with a few wooden blocks to take the mounting screws and some little bits of fiberglass in tricky spots.
For covering curved seams in Coroplast almost invisibly, I recommend 3M #190. It will stretch like electrical tape, but then not shrink back.

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