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Old 08-16-2017, 02:22 PM   #11 (permalink)
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Some thoughts on your drawing:

-The upward taper at bottom of the nose may be worse than having a sharp edge - it encourages more air under the velomobile.

-The taper in the rear may be too rapid.


Last edited by Ecky; 08-16-2017 at 02:27 PM..
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Old 08-16-2017, 02:31 PM   #12 (permalink)
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Quote:
Originally Posted by Ecky View Post
Some thoughts on your drawing:

The upward taper at bottom of the nose may be worse than having a sharp edge - it encourages more air under the velomobile.

-The taper in the rear may be too rapid.
Air dams are a popular hack to reduce drag and lift with a rough undercarriage, but with a smooth bottom, more underflow gives a venturi effect for downforce. The trick with this construction method is to minimise flow over the edges, which is very disruptive and hard to predict by eye. However, it may help to spoil the "lift" in a crosswind by encouraging early separation on the downwind side.
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Old 08-16-2017, 07:08 PM   #13 (permalink)
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Quote:
Originally Posted by Bicycle Bob View Post
How do the open wheels help with the doorway?
My doorway is 30" wide and has three steps to the ground. My trike from wheel to wheel(measured from the outside end of each wheel) is just under 39". Without a body, to get it into and out of my residence, I have to pick it up, rotate it 90 degrees, fit the front and front wheels through the door, step through the door holding the trike, then rotate it 90 degrees back to fit the seat and back through and finish stepping through, careful not to trip and fall. The easiest method is to pick the trike up by the front of the frame near the boom section with my right hand, and by the seat frame with my left hand. It's currently close to 50 lbs, although I haven't weighed it.

I designed the body so that I could continue picking the trike up the same way. I would take the lid piece off(shown in the side and top view of the drawing), and stand in the doorway holding the trike, with my body wedged in the empty space between the doorway frame and the space that would otherwise be occupied by the absent lid piece while the trike is rotated 90 degrees to the side.

A body wide enough to enclose the wheels while ALSO fitting the Aerodynamic Streamlining Template on this site, would fit the front through just fine, but I wouldn't be able to get the rear through while standing in the doorway. It would be too wide. The stairs are also a hazard and I don't think I would be able to get the trike through standing 2 feet from the doorway.

Thus, open wheels were a design criterion. Were this a narrow Ice Trice or similar, it would be a totally different design because of the narrowed width.

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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.
Thanks. I might try that.

I'm using the 4mm coroplast due to its strength.

Quote:
Originally Posted by Ecky View Post
Some thoughts on your drawing:

-The upward taper at bottom of the nose may be worse than having a sharp edge - it encourages more air under the velomobile.
Maybe. I put it in the design for purposes of safety. If I fit a curb head on or get a rough patch of road, or a speedbump at too high of a speed, I don't want the body to be ripped apart. If you were to draw a line from the ground at the center of the front tire contact patch at a 16 degree angle from the ground to the front, you will have the modified front section.

Quote:
-The taper in the rear may be too rapid.
Someone I know who is an aeronautical engineering/physics major told me that as well. It fits Phil Knox's streamlining template perfectly though. Tuft testing will tell me in the end when I get around to it.
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Old 08-17-2017, 04:15 AM   #14 (permalink)
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Quote:
Originally Posted by The Toecutter View Post
Someone I know who is an aeronautical engineering/physics major told me that as well. It fits Phil Knox's streamlining template perfectly though. Tuft testing will tell me in the end when I get around to it.
The streamlining template is a reasonable first guess and an excellent one-minute introduction, not a Holy Grail to preserve. The rest of the aerodynamics lessons are about exceptions and other considerations, and how to handle them.
BTW, the NACA duct is a handy way to bring in a bit of air at a convenient location, with minimal disturbance along the surface compared to a scoop. For serious quantities, a nose opening is better. Put the effort into making it open and close while staying slick at all settings, and building a diffuser. The air exit should also be a gently tapered duct.
As usual, the devil is in the details.

Other solutions to your doorway dilemma might involve seat mods, a special "sled" stowed by the door, and/or a deformable body section, taking advantage of the self-hinging possibilities in Coroplast belly pans.
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Old 08-17-2017, 03:14 PM   #15 (permalink)
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Quote:
Originally Posted by gtOmologato View Post
Is this kind of what you mean elhigh?
It looks like the design could be adapted to be more aerodynamic.
Yup, similar to that. You get the curved facets appearance.

I like that guy, I've watched a lot of his vids.
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Old 08-17-2017, 07:08 PM   #16 (permalink)
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Quote:
Originally Posted by Bicycle Bob View Post
The streamlining template is a reasonable first guess and an excellent one-minute introduction, not a Holy Grail to preserve.
True. I am curious as to what others think the ideal boattail would look like for the parameters of this first body design, and why.

Quote:
The rest of the aerodynamics lessons are about exceptions and other considerations, and how to handle them.
Once I get it put together, tuft testing could tell me where the problem areas are. I'm hoping this first design gets a 0.25 Cd or below. Do you think this is a realistic goal? The open wheels, exposed brake calipers/rotors, exposed suspension arms, and exposed rider head are definitely going against it.

Quote:
BTW, the NACA duct is a handy way to bring in a bit of air at a convenient location, with minimal disturbance along the surface compared to a scoop. For serious quantities, a nose opening is better. Put the effort into making it open and close while staying slick at all settings, and building a diffuser. The air exit should also be a gently tapered duct.
As usual, the devil is in the details.
I may do a nose opening near the center of the front where a high pressure zone is expected. This could allow rider cooling with minimal drag.

Quote:
Other solutions to your doorway dilemma might involve seat mods, a special "sled" stowed by the door, and/or a deformable body section, taking advantage of the self-hinging possibilities in Coroplast belly pans.
When I finally go to a body designed for the best possible drag, I've considered making it removable using the kinds of quick release fasteners for roadbike wheels. Another idea I've been considering is keeping the open wheels for the next iteration, but installing rack and pinion steering to allow me to make the body narrower and cut the frontal area to 0.45 m^2.

I can worry about that later though...
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Old 08-17-2017, 08:18 PM   #17 (permalink)
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I'd say that .25 cd is more of a necessary goal. Getting there with outboard wheels will involve considerable fussing over small details. The difference in drag between a round tube square to the wind and the same frontal area well streamlined is 10X. The ideal tail is different for every front end situation.
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Old 08-18-2017, 12:42 PM   #18 (permalink)
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Toecutter, Here a couple of links that you may find helpful. The Recumbent Bicycle and Human Powered Vehicle Information Center Info on how to build a streamliner.
The Recumbent Bicycle and Human Powered Vehicle Information Center plans for the MOAT coroplast tail fairing.

Good luck with your project.
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Old 08-18-2017, 07:04 PM   #19 (permalink)
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I've read those links before.

I'm in the process of modifying the drawing. From the side view, I plan to keep the ratio of Phil Knox's template that it has now, but for the top down view for both the body and the turtledeck, my tail will use the tail from the following airfoil:

EPPLER 863 STRUT AIRFOIL (e863-il)

I'm thinking that might be a good place to start for a first shape. Then when I tuft test it, I can figure out the problem areas.

I've read "The Aerodynamics of Road Vehicles" by Wolf Heinrich Hucho back in college, and know a few things, but without some way to simulate the shape or figure out what the air is doing around it, I really don't know what is going on with the air as it passes the shape, and won't know until I build something and test it. I don't want the first body shell to be a total waste of time though, as I want it to provide a noticable benefit over the naked trike.
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Old 08-19-2017, 01:07 PM   #20 (permalink)
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template

Quote:
Originally Posted by The Toecutter View Post
I've read those links before.

I'm in the process of modifying the drawing. From the side view, I plan to keep the ratio of Phil Knox's template that it has now, but for the top down view for both the body and the turtledeck, my tail will use the tail from the following airfoil:

EPPLER 863 STRUT AIRFOIL (e863-il)

I'm thinking that might be a good place to start for a first shape. Then when I tuft test it, I can figure out the problem areas.

I've read "The Aerodynamics of Road Vehicles" by Wolf Heinrich Hucho back in college, and know a few things, but without some way to simulate the shape or figure out what the air is doing around it, I really don't know what is going on with the air as it passes the shape, and won't know until I build something and test it. I don't want the first body shell to be a total waste of time though, as I want it to provide a noticable benefit over the naked trike.
Your trike is gonna be more like a 2-dimensional airfoil than a 3-D bluff body.
A symmetrical airfoil section with an aspect chord-to-thickness ratio of 3.92:1 has been found to be the center of the drag 'bucket',with both minimum pressure and skin friction drag.
You could maybe think in terms of both the body and canopy designed around this geometry instead of the template.
I agree with the others on the front lower angle.I wouldn't do that.
All the intersections will have hook-vortices unless there's a fillet to smooth the intersections.Goro Tamai's book on solar racers would have some data you could use in addition to member comments,of which have,'been there,done that!'.
Rumpler's Tropfenwagen was Cd 0.28 for the closed limousine,and Cd 0.54 for the roofless,open touring car.Without a half-bubble windscreen Cd 0.25 may be problematic.
One of the IHPV members ran a all-Coroplast-bodied trike in 2014 at Battle Mountain,and I want to say that he came through the 5-mile trap at 47-mph.
I'm pretty sure that the wheels were enclosed and he had a bubble screen.
I've got photos in my camera at home.I'll look at those to help trigger my memory.
Fun project!

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