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.

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.

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.

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.

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.

Is this kind of what you mean elhigh?
It looks like the design could be adapted to be more aerodynamic.

https://www.youtube.com/watch?v=ZiejAhol4Ps

So much yes. I picked this up a few days ago and have similar aspirations:

http://i.imgur.com/orhj3KL.jpg

I'm running a debian linux machine, so .exe files are a no go. Oh well. It looks like a very useful tool.

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.


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.

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.

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.

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.


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.

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.

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.

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.

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.

Thanks. I might try that.

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

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.

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.

Yup, similar to that. You get the curved facets appearance.

I like that guy, I've watched a lot of his vids.

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.

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.

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.

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...

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.

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.

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.

template
 

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!:)

Noted. I've seen bluff bodies with a Cd in the low 0.3 range and figured that I could get similar results, and then tweak it over time after the turbulent areas were found.

Would this be very close to the NACA 0025 and 0026 airfoils?

Noted. I worry about speedbumps and potholes. I will have a ground clearance of roughly 5.5 inches when all is said and done.

Thanks. I have not even heard of this book and feel compelled to read it. I do plan to put solar panels on this thing some day, and a body with a lot of flat-surfaced top area with minimal sources of shade would be good for this. Fitting a 0.5 m^2 set of panels at some point in the future is a nice thought.

I didn't know what it was for the open top car. I knew that the enclosed model was a 0.28, roughly what the average 2017 model year car claims to have(and usually, independent wind tunnels put their figures a bit higher, Tesla being about the only exception that has consistency between manufacturer claims and independent verification).

Noted. I plan to make a removable ducted cover section with a roof and windscreen to shield the rider's head, but I'd like the aerodynamics to be good enough to where it isn't really needed.

I've seen pictures of it:

https://jnyyz.files.wordpress.com/20...pg?w=300&h=199

Unfortunately, my trike is too wide to make that sort of body work for my needs. It is well done.

Lots more curved edges, more complex - a different path.

2009?
Quattro
Kingcycle - Quattro
http://www.kingcycle.co.uk/USERIMAGES/m%20d%201.jpg
http://www.kingcycle.co.uk/USERIMAGES/m%20cad%201.jpg
http://www.kingcycle.co.uk/USERIMAGES/m%20f%2012.jpg
http://www.kingcycle.co.uk/USERIMAGES/H51(1).jpg
http://www.kingcycle.co.uk/USERIMAGES/m%20w%202.png

Some cool history behind it.
http://www.kingcycle.co.uk/page6.htm

At least three other projects documented.
http://www.kingcycle.co.uk/page7.htm

Have you taken any measurements to determine the gains from that tailbox, Ecky? I'm curious to see if it increased your cruising speed and top speed.

I've come across the Quattro during many online searches. It is an interesting machine and I'm sure Mochet would have been floored had he been alive to see it. I suspect that it's overall aerodynamic drag is similar to that of a Quest velomobile.

However, I'm more partial to the commercially-produced QuattroVelo:

https://www.velomobilcenter.dk/galleri/velomobiler

That is the sort of shape that modern entry level sportscars should have.

I need to wait for my motor to get here for that. The controller and display I use have a watt meter and speedometer.

https://www.flickr.com/photos/okpete...7651905111646/
This a popular design currently being used. See The Recumbent Bicycle and Human Powered Vehicle Information Center
I use the cut and tuck method too. Start with cereal box cardboard 1/4 scale models. Sailplane designs are very similar. Air intake along the canopy cowl and exit behind the head. Cooling at the neck is very effective.

"Race Car Aerodynamics: Designing for Speed" by Joseph Katz is useful also.

Try to think of this project as an easy-to-modify experiment to get familiar with the issues and how they affect your enjoyment on the road. I have drawings for faired and unfaired pedal trikes on my board, and the chassis have distinctly different proportions, suspension, gearing and braking, for very good reasons. Adding power has similar effects.

I just reached 29 mph today on flat ground. No motor. no body. The only aeromod is wheel disks. It was my first time testing the new Schwalbe Tryker 20x1.5" front tires I put on it to replace my Maxxis Hookworms. This was during a 30 mile ride to the next town over and back. I'm really looking forward to a body shell on it...


I like this design a lot. I first came across it on the internet about 2 months ago. The doorway clearance issues prevent me from using it for my build without radically altering it, and given that my trike is a wide 39", my version would likely have a frontal area around 0.75 m^2 were I to replicate it.

I need to find a copy of that book as well.

It is a rolling science project for sure, but it is also going to meet the majority of my transportation needs. In the long term(possibly this winter) I plan to make a 200 mile trip to Austin, TX in it. The motor I am putting in it is going to produce 4 kW or more, and the top speed will be in excess of 45 mph, maybe up to 55 mph depending on gearing.

J. Baldwin, long-time tech editor of Whole Earth Review, says that it usually takes three tries to be satisfied with a new design. The second prototype fixes up the obvious problems with the first, and the third smooths out most of the remaining irritations.

I have sort of figured this project wouldn't be completed until at least the 3rd body. I do want the first one to be at least usable and practical with a decent drag reduction. That's why I've been taking my time with it. I'm only designing to cruise at 30 mph or so, but the high top speed will be a consequence of gearing to do 30 mph with a cadence of 80-90, when I'm still capable of holding a cadence of 140 for shorter durations. I know of a KMX build with a 6.5 kW middrive though and it's rider can safely cruise at almost 40 mph and has been taken to 60+ mph a few times. The steering knuckles and stock wheels are the weak points of the KMX frame kit when it comes to tolerating road imperfections and hazards, but the knuckles can reliably handle cruising at 30 mph or so *IF* you have a front suspension setup, according to this builder.

I'm also partially inspired by the efficiency that Cedric Lynch has achieved in his electric recumbent motorcycle, roughly 30-40 wh/mi to do 50+ mph:

https://www.youtube.com/watch?v=b4BAnH52-g4
https://www.youtube.com/watch?v=KnqoH0YaCsE

Adding a small amount of human power to that will yield more than marginal improvements in efficiency, and pedal power is awesome for extending your possible range to the point that even if you somehow cannot get electricity anywhere, you'll be able to still go anywhere that you can pedal it. It must be light enough to be pedaled, and geared so that at least a fit rider could climb steep grades at 4 mph. I think 100 lbs or less is a good target. There's a lot of efficient custom-build vehicles out there that are too heavy, but are worth drawing ideas from.

Adding some ass-hauling capacity with an overpowered drive system would make the vehicle fun and more appealing to hoons, and less prone to getting laughed at by the general public, as well as the practical application of being able to get away from a dangerous situation as well or better than most cars.

I would change that to "3rd body and chassis." In automobiles, just doubling the power usually is as much as one chassis can be modified to take gracefully. The electrics have the best chance of staying suitable, but they are evolving quickly and that could also change your mind, as might the performance numbers on #2. With my body weight added, I'd have about 40 lbs/hp, so I wouldn't out-accelerate many cars, unless your motor is just rated at constant duty and the controller can heat it up.

Have you compared estimates between fairing the wheels separately vs installing a 40" door? Some houses are much improved by double doors, too.

Make the head fairing detachable? The book by Katz I purchased on Amazon; there is a 2nd ed.

It's not just power to weight ratio that matters, but torque. The Leafbike hub motor that I plan to use can make car-like torque without destroying itself, in a vehicle whose laden weight is 1/10th that of a car. In order to get this thing to take on cars at lower speeds, the traction of my rear tire will be the limiting factor, and I do not yet know precisely how much traction it has. It's a Schwalbe Marathon Plus, and if I pedal with full strength at a stop in 1st gear in either the 28T or 38T rings, I can make the back tire break traction without a motor. So its traction isn't all that great if it can't even handle human power, let alone human power coupled with an electric motor.

I ran a simulation of this hypothetical vehicle fitted with a 1500W continuous Leafmotor with the 5T wind at 72Vmax, 6 kW, 83A, 120A phase current, 30/40/60T front chainring, 42-11T in the rear, and the rider pedaling with 500W going through the rear gears up to top speed. At a 0.25 Cd, 6 sq ft frontal area, 300 lbs laden weight, 0.008 Crr, 26” wheel, controller voltage/current limiting factors(assume for this calculation a battery powerful enough to run this with minimal sag and that traction won't be an issue), and the rider starting out in a 60T front and 28T rear gear, no traction limit accounted for, I get the following performance:

0-10 mph: 0.8 seconds

0-20 mph: 2.3 seconds

0-30 mph: 4.1 seconds

0-40 mph: 6.6 seconds

0-50 mph: 12.3 seconds

Top Speed: 53 mph

1/8 mile: 11.8 seconds @ 49.6 mph

That's very car-like. I don't know how close reality will bring me to the above figures, but my acceleration will certainly be adequate for merging into traffic and accelerating like a low end car.

With modifications, the Leafbike motor could be allowed to peak at 10 kW. This will require drilling holes in the casing and installing fans. I plan to start with 4 kW, because among those on endless sphere who have used this motor, unmodified, the general consensus is that you won't hurt it at 4 kW. At 10 kW, acceleration would start matching some $30,000+ modern sports cars, *if* I can get enough traction(highly doubtful).

Installing a door is not an option. I don't own the place I live in, and the landlord is not keen on the idea.

The Schwalbe Crazy Bob is available in 26x2.35 and is rated for E-bikes. Weight distribution and tire pressure are key in maximizing traction.

It isn't just specifically the front that is going to pose clearance issues with the door. The trike can always be tilted on the side no matter how wide it is and slid through as long as the height of the cover piece over the rider's legs was skinnier than the door. But the height is also 1 m from ground to the top of the turtledeck. The widest point will ideally be where either the axle line for the front wheels or steering bars are, depending on shell. My initial bluff body design had max width in all three sections, BUT since the rear end will house the turtle deck and also future roll protection, I can tilt the trike back to original position and fit the rear through, if I leave an opening in the midsection to fit me through the door while I hold the trike tilted, and if the trike is narrow enough that I can do this easily standing on the steps while sliding the back end through the door.

If I make the body as wide as the trike width, even if the front section were completely removable, I wouldn't be able to fit it through once I tilt it back if I want to have a decent taper and avoid having to stand 2-3 feet from the doorway trying to hold this thing by the front after carefully balancing it in place and avoided dropping it while trying to get down some stairs.

Also, the bottom and rear must be attached the the frame in some manner to be to my satisfaction. I don't want the body coming off and cutting me in the event of a wreck. I will be building a frame for this body as well, possibly out of PVC pipe, but a metal mounting bracket is all I think I will need to begin using it reliably, if not yet safely, having already mostly finished a body that will go unused/unfinished and beat on it a little for testing. Coroplast is surprisingly strong stuff, in spite of its weak points.

I'm still working on the new drawing based on Phil Knox's input. It will be a simpler shape by far than what I was first building, and will be designed to allow sections to be cut out in the future for modification that is cosmetically pleasing(doesn't leave excessive errors with zip-tied repairs everywhere to make it more aero later on).

Give me a day or two and I might have the drawing done. I'm off to go on another ride before it gets dark.

The nose is too blunt. Check out Velomobiles Coroplast and Recumbent Homebuilt groups on facebook and the Recumbents.com site.

https://www.facebook.com/groups/1564...ocation=stream

Tony is a top notch builder who has helped a number of people at recumbents.com. Coroplast comes in a hex cell form now so check a local supplier for sizes and prices. I have used semi flexible 5/8" OD PVC tubing from a plumbing supplier as supporting hoops for my fairings.

I couldn't find that as a Coroplast product, but polyproplene is also used for PP panels

They claim heat-formability, which probably means "with less fuss than corrugated."

Home Depot supposedly has 4x8 foot panels reasonably priced. Use the 4mm thickness. Corrugated polypropylene copolymer sheets. I got mine from a local plastic supply house for about $10 a sheet.
https://www.copeplastics.com/coroplast.html A print shop may have some in stock or could order it for a premium. The hexcell you are referring to is probably more expensive to manufacture, but interesting.