The Future
The Future of Fast & Furious
A look into the future of going REAL fast, with human power
An editorial by Len Brunkalla
8/1/00


Many articles have been written on the topic of human powered speed. Some of those articles have tried to predict the future of human powered speed achievements and design. Most of the thinking in these articles falls into two categories, that of pure speculation, and the largely non-negotiable engineering formulas and calculations that help describe real world physics.

I write this article to address the more speculative of these authors, who have for the most part, and in my opinion, failed to look past their own cycling experiences, to see where technology in many other different but related fields, is heading, or has already been.

Who am I to write this article? Well, ...I'm Len, I have a typewriter or at any rate a computer, and an opinion to air. In that respect, it makes me as knowledgeable as some of the others that have already voiced their opinions. Beyond that however, I have had interests in the field of aircraft design and construction, and past affiliations with local Experimental Aircraft Association members. Both my father and brother have built and flown their own aircraft. I have designed and built several model aircraft. I also have at least 14 years of affiliation with HPVs, designing, building, and racing. My interest in cycling goes way back to the 1960's. 

What I have observed over the years, is that there are very few "successful" high-speed HPVs. Those notable and successful HPVs, are nearly without exception, the results of a dedicated team. There was the Easy Racer team of Gardner Martin, the designer, and Freddy Markham, the Olympic class rider. There were some other people involved with that team, but their names are not important to this explanation (and I can't recall them at the moment). Gardner Martin is a drag racer, a pilot, and a model airplane designer, besides designing the Easy Racer recumbent bicycles. Freddy Markham was a dedicated and competitive cyclist, that trained on the recumbent that he would later power to a record. There was also Team Cheetah, which assembled a group of builders, an Olympic class rider, and some professional engineering. Notice that most record setting HPVs, are not ridden by their designers. There is some great logic to this.

There are a great many factors that go into a human's ability to go fast, under their own power. First and foremost, is the athletic ability of the rider, or in simpler terms, the motor. This motor must perform well in and of itself. Fitness and the ability to generate the power required are the most basic duties. It is also very important that this motor be well matched mechanically, with the machine that it is assigned to propel. 

You may have heard of riders being referred to as "mashers", or as "spinners". This refers to the rider's best output mode. A masher, is usually an individual whose best power output is at a lower cadence, and therefore pushes harder, or mashes the pedals to achieve the necessary power input. This mashing, requires a higher gear ratio than the "spinner" to achieve the same top speed. The longtime masher, may also eventually require knee surgery to correct problems resulting from the higher loads experienced in the leg joints.

The spinner must spin the crank at a high rate of speed to achieve his or her best output mode. This is much easier on the knees, and requires a lower gear ratio than the masher, to achieve the same results. A benefit of being a spinner, is that inertia lends assistance in your objective of keeping the pedals rotating. This inertia factor, could breed a whole new argument on the design of power input, when compared to linear drive designs. We'll save that argument for another time.

The vehicle that is to be carried to a new speed record, must be designed around the "power settings" of the individual that will power it. Just as you would not design a Jumbo Jet to fly on the engine for a Piper Cub, you don't design a spinner's drive-train, for a masher. This is where the designer of the vehicle must be in-tune with the rider. This is not a difficult union, although there are often conflicts when riders decide that they are also the designers. This is not to say that a rider cannot design a proper vehicle. Let me sidestep this issue by saying that not all designers are bike riders, just as bike riders are not all designers. Moving right along...

I suppose that a simple way to make a long story short, is to say that, a record breaking vehicle is the result of a team that works well together, and understands the task at hand. It is doubtful that teams comprised of people that have no experience with human powered vehicles designed to go very fast, will be able to design a vehicle that will go fast on the first try. 

"Well, of course, not on the first try," you say. It does sound unlikely when you read it in print, but it is amazing just how many people approach the subject with just that in mind. All too often, I hear of a group of people that are determined to set a new record without a clue as to what has preceded them. Hence, their first move is a giant step backward. To make this part of the explanation much shorter, suffice it to say that serious attempts at new speeds with human powered vehicles, will be by teams that know the task at hand, are familiar with the medium that they are working in, and work harmoniously together. Enough of the obvious character and experience factors, and on to the scientific outlook.

The Faster Vehicle
There will have to be improvements in studies on human power output, with the human in this equation positioned more aerodynamically. There have been past studies that compared upright riding positions with recumbent positions. The need is to explore specific positions that are aerodynamically advantageous. This may sound like a trite statement, but I believe that most studies have taken the wrong approach to this research. 

A major problem with designing efficient machinery, is when you interject a human involved with its running. The toughest streamlining job on a record breaking HPV, is trying to get the human to be aerodynamic. By researching power positions that are more aerodynamically advantageous, the human in the overall picture will be treated as more of a modular drive unit, when designing the vehicle. This modular drive unit, though the rider would be in a specific position within that module, the module can be rotated and positioned as needed to facilitate getting the optimum aerodynamic shape. In my opinion, the designer that is closest to that now, is George Georgiev, of Vancouver, BC, Canada. His Varna HPVs seem to take good advantage of aerodynamics, while forcing the human motor to merely do his job, without great concern for comfort. After all, the human is only in the vehicle to provide power and control. Matt Weaver, of California, was also working on a design with these qualities, the last time anyone heard of his work.

I think that the emphasis on lighter and more exotic materials has been misplaced. Sure, lightweight is good, but it is not everything. If a rider can stand to lose ten pounds of weight, that's ten pounds that is useless on the rider. If the vehicle the rider is using could benefit from a few more stiffeners, some of the useless ten pounds of the rider could be traded for structural integrity.

I believe that the real blessing of the new and exotic composite materials, lies in the ability to mold these extremely lightweight and stiff materials, to better utilize structures that must fit the modular concept of the rider/motor, while still keeping structures and aerodynamics within optimum parameters. More simply put, it's easier to mold a foam and carbon box section spar in a curved section, than it is to duplicate that same structure in other more common materials. Monocoque structures will be the way to go, and composites are the way to get there.

The Real, New Stuff
The rider position vs. aerodynamics is not the biggest development that HPVs will achieve. The next rise in top speed, will come from careful boundary layer control, and precise control of the direction of air flow over the skin of the vehicle. Although there are many slippery designs out there, they all have several deficits in common. They all rely on simple smoothness to reduce parasitic drag, they all rely on reduced frontal areas to minimize induced drag, and they all operate in ground effect.

Most likely, there is no way of getting out of ground effect without severely affecting high-speed handling qualities. If a vehicle is designed taller, or tall enough to effectively eliminate ground effect, it would likely be a hazard to control.

Reduced frontal area is an important factor in the equation for speed. The smaller hole that you punch in the air, the less wake you will make in that air. Making a wake means stirring up the air, creating eddy currents and low pressure areas that induce drag, slowing the vehicle down. It is like dragging a parachute. Contrary to many people's views on drag, the bulk of the induced drag is not just pushing the air out of the way, it's filling the hole that you made in it. This is where I believe the next big development will be. 

Improvements in boundary layer control, aiming vortices, and surface pressure control will raise the bar to new speed records. This will be particularly important to those of you who have been drooling over the .deciMach Prize.

Surface Pressure Control
When a solid body or shape moves through the air, the air must be moved out of its way. When HPVs are streamlined to achieve this movement, designers do not take into account, the compression of the air that they are moving. Working in ground effect, basically indicates that you are operating close to the ground. Since it is undesirable to have the vehicle drag on the ground, the vehicle is usually designed to ride just above the ground, with the exception of the contact of the drive wheels. When the vehicle moves through the air, and air is displaced, air that moves around the vehicle is compressed to varying degrees. Since the ground restricts the movement of air beneath the vehicle, there tends to be a buildup of pressure beneath the front of most of these types of vehicles. This is the most common area to experience high surface pressure. This compressed, denser air, is harder to move. The surface of the ground, depending on its texture, will add some amount of resistance to the air movement, and further increase the drag beneath the vehicle. My suggestion is to do tuft testing, and/or wind tunnel testing, to determine where these compressed or high pressure areas are along the surface of a particular vehicle. Once the higher pressure areas are located, vent those areas to the inside of the vehicle. 

While there are most certainly higher pressure areas along the surface of a vehicle, there are also certainly low pressure areas as well. These low pressure areas will be found at the same time that the high pressure areas are located. The low pressure areas are where the inlet air from the high pressure areas will be exhausted out of the vehicle. So as not to pressurize the interior of the vehicle and thus reduce the efficiency of the pressure venting, outlet or exhaust vent area should be slightly greater than inlet or intake area. I know that some record-caliber teams charge the interior of their vehicles with oxygen before a run. This would still be possible during the pre-run staging by placing covers over these vents. There will be loss of this oxygen charge after the covers are removed and the vehicle proceeds on its run. There is the benefit however, that the rider will receive the cooling benefit from air moving through the fairing, both by the movement of the air, as well as the displacement of used/heated air and CO2 with cooler fresh air. This could be just as beneficial to the rider as was the charge of oxygen. Moving air through the fairing will also help to alleviate fogging of windscreens and canopies.

That Darned Boundary Layer
I have spoken with several people over the past three years, questioning why nobody has tried to exploit that which we already know about boundary layer control, and layer reattachment. The boundary layer in this case, is the air that is right at the surface of that which is moving through the air. In this explanation, it is the streamlined fairing that is moving through the air, and the boundary layer is that air that is touching the fairing and getting pushed around.

There are several devices that have been in use to control this boundary layer, though they are all in different applications. 

Dimples, concave, like those used on a golf ball, are designed to reattach the airflow that moves around the ball as it flies through the air. These dimples allow for further flights of the ball with the same energy input as a ball without dimples. How many of you recall golf balls without dimples? They have been around for a while. Dimples need not be concave to accomplish similar results. A recent issue of a popular science magazine noted a Japanese firm that had designed a woman's swimming suit. That suit employed one hundred or more, small raised dimples in the area under the breasts, to smooth water flow over what is usually two larger obstacles. The intention is to maintain boundary layer control. The firm boasts a measurable increase in speed, although I suppose that it would depend on the actual attributes of the wearer. If this sounds a bit fishy, then stop and consider a fish, the scales of which can themselves act as tiny ridge turbulators. Fish are pretty darned fast in the water, eh?

Turbulators, are small tabs, ridges, or fins that oppose/disturb the airflow, usually at right angles. A common baseball, is employed by a pitcher, using the raised and exposed threads to act as turbulators to alter the flight of the ball. Dependent upon the spin or rotation of the ball as it leaves the pitcher's hand, it reacts with the airflow over the threads to do the pitcher's bidding, except possibly in the case of the Chicago Cubs...but that's another story.

Turbulators are used on many different categories of aircraft, from low speed private and experimental category aircraft, to jet airliners, and military aircraft. Turbulators cause small eddy currents. These small eddy currents are used to break up larger eddy currents. This reduction of larger eddy currents keeps the airflow closer to the surface, reducing low pressure vortices that drag or pull on the vehicle, burning up energy, and reducing speeds. A common application in the aviation field, is using turbulators on the top surface of the wing, to extend the flow of air further along the top of the airfoil to give increased lift during low speed flight. Turbulators can also increase control, and reduce stall tendencies during hard maneuvering, lessening the chance of high speed stalls.

Turbulators have also been in use for quite some time, in the field of auto racing. I recall see Kenny Bernstein, a renowned drag racer, using turbulators on the upper, rear surfaces of his funny car, to reduce the amount of wake left by the race car. A large wake behind a race car, causes a low pressure area, or a vacuum, comparatively speaking, holding the car back, or causing drag. This is much the same problem that must be addressed in record attempts by HPVs. Although currently the drag coefficient of the fairings of some of the best vehicles is very low, I believe that it can be made better by use of surface textures, and fixtures.

Micro-ribbing, or riblets, are small raised ridges, that run along the direction of airflow, Riblets increase directional control over surfaces, while also serving double duty as another type of turbulator. At a 1986 IHPVA symposium, an engineer from Boeing Aircraft, described that company's experiments with micro-ribbing. The experiments were not intended so much for the aircraft industry, but were commissioned by the US Olympic sculling team, in search of a speed advantage.

In the case of the Olympic team, their watercraft only required riblets that were .005" in height, spaced on .008" centers. The eventual test apparatus, was a special mylar tape that was scored with a specially machined roller, forcing the ridges into the tape. The tape was then applied along the length of the rowing scull's wetted surface. Water is a much more viscous fluid however, and riblets for airflow applications would need to be somewhat larger.

The thinking behind the riblets as applied to fairings, is that air does not always flow in straight lines. Better put, air does not always flow as you would like it to. While a particular shape, may encourage airflow in a particular direction, air remains a fluid like substance. Air makes its way around a shape as best it can. That is not to say that we cannot have greater influence on the path that it takes. In the case of a fairing, riblets direct air at the surface of the fairing, making the air flow more readily in the desired direction. Some areas of higher surface pressure , such as the leading edge of a bubble-canopy, can be reduced by influencing airflow away from that area using riblets. 

Although most mortals are hard put to obtain access to windtunnel test facilities, there is a way to test surface modifiers that you are experimenting with. The venerable tuft test, is the simplest, and by far the cheapest validation test for the performance of surface modifiers. Simply tape many, many short (~2.0" or 50mm long) pieces of yarn over the surface of the fairing that you wish to test. Try to aim the tufts along longitudinal lines, over the entire surface, fastening the pieces of yarn down at the forward end of each tuft. Be sure to use yarn that is readily visible against the background that it is attached to (i.e. black on white, not white on gray). This is after all, a visual test. The idea being, that from an outside observer, the airflow over the fairing is indicated by the tufts as the fairing moves along through the air. The best case scenario, is that all tufts will be laying flat along the surface of the fairing, indicating that the boundary layer has not detached, and you have achieved the optimum airflow around the fairing. In reality, there will be tufts that do not lay flat against the surface, and may even be standing well away from the fairing's surface, twirling in the breeze. This would be a good indicator of an area of lower surface pressure, and a high incidence of disturbed air, or eddy currents. The clever experimenter, will devise ways to test non-permanent surface modifiers (taped on, or somehow removable parts), so as not to continually degrade the original surface of the fairing. Once the optimum results are achieved, it may then be determined what course of action to follow...add permanent surface modifiers based on your experimentation, or start over.

In closing, I am certain that experimentation with surface texturing will have to happen before anyone gets a significant increase in speed with an HPV. Stronger riders, on lighter vehicles with slicker surfaces, is not going to achieve significant gains in speed. We must look at a different approach to the elements that are very physically slowing us down, or holding us back.

All of the forenamed surface modifiers have been researched in the field of aircraft and aerodynamics. There have also been studies within the automotive industry and motorsports. I would suggest a trip to a reputable library to get exact numbers, to coincide with your design intentions. The IHPVA, has technical journals that have addressed some aspects of surface texturing. You may consider visiting your local college, if they have an aerospace department. If you're designing a swimsuit however, you may want to stroll by Frederick's of Hollywood to catalog your design parameters.

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