A velomobile is, essentially, a human-powered car with enclosed bodywork. The bodywork, or fairing, in the case of machines designed for racing, serves to improve the aerodynamics of the vehicle in order to make it go faster for a given amount of "horsepower" input. In the case of non-racing "Street" velomobiles, the bodywork also serves to make the vehicle more visible in road traffic, and more usable in less than fair weather, thus giving a much longer and more comfortable "cycling season". Many VMs seem capable of carrying a fair amount of cargo, too.
VELOMOBILE GALLERY:
Below are shown some of the more technically- interesting and attractive commercially-produced velomobiles. Not surprisingly, most are from Europe. However, some North American companies are beginning to get into the act as well.  Considering the current wretched state of  the US dollar in relation to the euro, this is a very good thing for American velomobile fanciers.
Click on © images to go to the respective makers'/distributor's websites.
The header image at the top of this page is of Flevo Technology's Versatile, designed by Flevobike. This image is a view of its cockpit. Among other features, it sports a Rohloff 14-speed hub used as a jackshaft, I presume,  which is probably about as pricey as a Rolex. The rest of the package is up to the same level of luxe techno detailing. And, of course, it also looks incredible.
Versatile is available in North America,  through bluevelo.
The incredibly slick Go-One, designed by Michael Goretzky, is manufactured in Germany by the Beyss Corporation. It is distributed in North America by Go-One LLC of New Jersey, USA. Its standard gearing is  9-speed Shimano, with the 14-speed Rohloff as an option.
From the same maker as Aerorider, Sunrider is smaller and lighter, making the need for electric assist more optional.  Although less all-weather capable than   fully-enclosed velomobiles, exposed-head models are still warmer than bare 'bents in cold weather, and are still a bit more popular in Europe.
Produced in the Netherlands, Aerorider comes standard with (extremely useful in this case) electric power assist. Aero has very little benefit when going uphill in a vehicle weighing considerably more than a bare 'bent. Good things have been said about Aerorider's weatherability and beauty.
Aurora, designed by Steve Schleicher, is produced and distributed by Cambie Cycles of Vancouver, Canada. Its dramatically-styled composite shell has a cargo stowage volume of 160 liters. Gearing is by SRAM Dual Drive as a jackshaft, with a triple chainring at the BB location. Electric power assist is an option.
In continuous production since 1982, Leitra, produced in Denmark, is a well-proven design. Standard gearing is SACHS 3x7, with Rohloff as an option. Unusual in velomobiles, the composite shell is available in three different sizes. BionX electric-assist motor with 6-speed chain gear is an option.
Stormy Weather, designed by Reg Rodaro, shown above with the SW prototype, is produced and distributed by Lightfoot Cycles of Montana, USA. Its T-top composite shell with marine fabric/polycarbonate elements, is a nice compromise between weatherability, stiffness, and lightness. Electric-assist is an option. Rear-wheel aircraft-style "spats" will be available.
The lovely WAW, designed by Frederik Van De Walle and produced by Fietser in Gent, Belgium, is distributed in North America by bluevelo, of Toronto, Canada. Standard gearing is by Shimano XT rear derailleur and       9-speed Shimano rear cassette (11-32), with Rohloff optional. BionX electric-assist is also an option.
Alleweder (all-weather) was designed in the late '80s by Bart Verhees, who had an arrangement with Flevobike of the Netherlands to manufacture it in kit form. Almost unique to velomobiles, it is based on aircraft-style monocoque construction fabricated from sheet aluminum. After reorganization as Flevo Technology, that company no longer makes the kits, but VelomobilesUSA now produces and markets them in North America, with some parts still made in the Netherlands. Under continuous refinement since introduction, the FAW is a well-proven design, and among the DIY-oriented, it's considered a bargain-priced velomobile entry, and certainly not outmoded in its  muscular "racer" style and bare-metallic sheen.
Racing velomobiles tend to run on two wheels, as weight is of great consideration in human- powered-racing vehicles. They are also extremely cramped for the same reasons. Non-racing velomobiles tend to run on three wheels, for slow-speed stability and for standing still, since fully-enclosed bodywork doesn't lend itself very well to putting feet down on the pavement.
Racing VMs, like the beautiful
Varna Diablo, designed by Georgi Georgiev and ridden by Sam Whittingham to many world HPV speed records, are impractical for normal street usage, but extremely cool-looking!
They are also considerably roomier inside than racing streamliners, since they need to accommodate some cargo, in addition to drivers of various size.

Many of the tasks for which automobiles are currently used: neighborhood shopping errands and short work commutes by a single person, could just as well be done using a trike velomobile, at huge environmental and operating cost savings, once weather is not so important a factor in usage. 

All that said we also like them just because they're so cool and futuristic-looking. After all, this is the 21st Century, innit? Curiously, an owner-built 2-wheeled racing streamliner is one of the earliest entries in our Gallery and, ten years on, an owner-built 3-wheeled VM is one of the most recent- with none in between. This gives an indication that what was once rare and exotic, is now becoming more widespread. I expect to see many more VMs in our pages in the future, and ideally, much cooler-looking ones, within the BR&K aesthetic context, of course.

There are two basic forms of VM structure. Not coincidentally, I'm sure, they correspond to the ones most automobiles are based upon. 

Monocoque, or "Unibody" in Detroit vernacular, uses the vehicle's bodywork as an integral part of the load-bearing structure. In theory, this can result in a lighter and stiffer vehicle. However, it is considerably more complicated to design, as more inter-related factors need to be taken into account. For this reason, many first-time builders/designers prefer to add a non-load-bearing lightweight shell onto a typical fabricated-tube recumbent tricycle frame. 

In Detroit vernacular, this would be a "Body-On-Frame" structure. Of course, this automatically results in a higher vehicle gross weight than an un-bodied equivalent machine. However, the improved aero efficiency can offset this somewhat, along with the added benefit of weatherproofing. 

Naturally, the greater weight efficiency of a monocoque- structured vehicle still won't make it any lighter than a more typical human-powered un-bodied vehicle. Volume and surface area, unless composed of a helium-inflated unobtainium membrane, will usually translate to more weight to be propelled by the rider. Largely for this reason, makers of commercial VMs almost invariably offer optional or mandatory electric-propulsion assistance packages. 
This molded fiberglass carbon-reinforced shell for Lightfoot's Stormy Weather
prototype weighs 20 pounds.
As VMs have many of the same design considerations as aircraft: strength and minimum weight with maximum aero efficiency, the materials used to make them are common to both. Molded fiberglass and carbon fiber composites are most popular, followed by thermoformed reinforced plastics. Fabricated sheet aluminum, while not as common in commercially produced VMs, is very suitable for do-it-yourself builders, and has been used for home-built aircraft for decades. While I've never seen a VM body made with stretched and heat-shrunk dacron fabric over light wood    framework, it is a popular medium for home-built aircraft,
so it should be considered. Those wishing to explore this medium should study its applications in aircraft and kayaks, to see the possibilities of form, and how they're made. 
Rutan "Quickie" plans-built aircraft, made of fiberglass over shaped foam.
For those wishing to build a lightweight body shell over a metal recumbent frame, carved and shaped foam skinned in lightweight glass cloth and resin is very popular with plans-built aircraft designers such as Burt Rutan. Called 
"moldless composite" this medium has been used for years, in both owner-built aircraft and the ground vehicle plan designs of Robert Q. Riley.
Coroplast VM shell, designed by Lee Wakefield.
Builders who prefer working with sheet materials other than metal frequently choose Coroplast hollow internally- ribbed PVC sheet, as it is weatherproof and comes in integral colors. Paint can add considerably to the weight of a large-volume shell, so this is of no small   consideration.
As Coroplast has directional internal ribbing, it can be a challenge for shaping, But Lee Wakefield shows the possibilities of the material, above. He is planning a kit.
Bugatti Type 59 replica body- foam, foamcore, spandex, fiberglass, epoxy.
My own kiddy car Bugatti replicas, some of which are pedal powered, could easily be considered "vintage-style" velomobiles. For their body shells, I use shaped foam for the compound-curved parts of the body, and paper-clad foam core board for the simple-curved parts. The parts are then glued together and covered in 
stretched spandex and thin fiberglass cloth saturated with epoxy resin. The bodywork is the lightest major part of the vehicles.

This would be a good time to mention that although most velomobile designers go for a swoopy aerodynamic/ futuristic look to their creations, this is not the most vital aspect of them as street vehicles. The truly important aspects are weatherability, visibility, and crash protection. 

The average person is unlikely to hit the speeds reached by Sam Whittingham (who has topped 80 MPH on the straightaway flat course). Yes, although the slippery aerodynamics of that type of racer certainly help in achieving that speed, most people riding in city traffic are unlikely to ever hit 35 MPH, especially since most unlicensed electric-assisted velomobiles in the US are forbidden by regulations to top 25 or even 20 MPH, in some locations. Therefore, the aero aspects are not nearly as critical. This opens up interesting possibilities for hot-rod, classic car, or even aircraft styling applied to velomobiles.

Those streamlined bubble canopies as used on the Go-One and the Varna racers look pretty cool and space-ship like, but they also remind me of some of Big Daddy Roth's show machines. He didn't drive his around in the rain and snow, but that doesn't mean something wild-looking like his machines couldn't be ridden around under pedal/electric power, while keeping the driver warm and dry. Fortunately, the Zzipper fairing folks  will  blow mold you a polycarbonate "experimental" bubble canopy in any shape you want, for a modest $200 set up cost.  (Examples Below)
Before military fighter aircraft had those cool blown bubble canopies on them, they had a different sort of canopy, when they didn't have open-air cockpits. The high-visibility canopies on WW2-era aircraft were quite a different style- one which wouldn't be very difficult to fabricate from stock aluminum extrusion stock and sheet plastic. I suppose that's why the designers of the time developed them. Naturally, considering the look, they were commonly called "greenhouses". Below are six examples of WW2-era greenhouse canopies, in end, plan, and elevation views.These would look very good on a "Flash Gordon" or military aircraft-themed velomobile.
I've often thought that a back-to-back recumbent tandem would be a great candidate for being enveloped in a velo body evocative of a WW2 two-man aircrew plane, such as the Junkers Stuka (#2 above) or Douglas Dauntless torpedo bomber. A Browning .50-caliber machine gun for the stoker/tail-gunner is optional.
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Our types of hardcore designers/constructors are never able to stop at doing only one bike creation. In many cases, this is resulting in increasingly more baroque   and outre stylistic aberrations within our normal medium, merely because the creators have already done
everything else within the style. Any day now, I expect to see a chopper frame in the shape of a Swastika or 
Hammer and Sickle. The Iron Cross, the Perfect Circle, and the Valentine Heart have already been done.

However, the velomobile form is still ripe for exploitation, and can be worked-within for quite a while, before  sinking into total stylistic degeneracy. As a side benefit, velomobile design can lead to the mastery of new skills and materials expertise, in addition to the traditional metal-tube-forming skills so many of us are already way too facile at. And the more surface area, the more interesting graphic schemes possible for decorating it, eh? Oh yeah, and there might be a side benefit of serial builders actually riding what they create, if they were more comfortable in less than ideal weather. Jim Wilson
 Flevo Technology: "Versatile"
Lightfoot Cycles