I'm a little surprised nobody has mentioned the opaque fairing, visibility, or the camera.
At first I thought it might be to keep the weight down, as there are plenty of composite materials that are lighter than (even thin) plexiglass. But then there's the weight/complexity of the camera, display, and battery.
Then I thought, well, the rider in in such an odd position, maybe he wouldn't be able to see very much even if there was a window.
But apparently the actual reason is that the rider produces so much heat that a window would fog up, and it would be too difficult/unsafe for the rider to wipe it. Given the white coloring, I suspect they're also trying to avoid cooking their human power source.
Here's part of a Q&A where they discuss visibility:
I'm guessing something can't get much more aerodynamically shaped? I wonder if they used a power meter to measure the driver/rider's power output and whether the driver was an accomplished cyclist. It seems that at this point, it would simply be a matter of getting a stronger cyclist, say someone like Brad Wiggins who can push 430 watts for an hour over an amateur, but still respectable rider, who puts out something more like 250 watts for an hour.
The article states that riders have 5 miles to speed up before they cross the speed trap that measures. Assuming the average speed of the whole endeavor is, say, 60mph, you would want a pro time trialist who excels at hard 5-minute efforts. This chart[1] states that a world class cyclist should be able to put out 7.5 watts/kg for 5 minute efforts. Brad Wiggins weighs 77kg, so I guess theoretically he should be able to put out 577 watts, versus a "good" with the same weight who might "only" put out 350 watts in the same 5-minute period.
I would be very interested to see what would happen if you simply replaced the 85mph rider in the submission with Brad Wiggins.
1.2 horsepower for a minute is a damn fine effort. A college friend of mine is a domestic pro. Last I heard his max power was 1100 watts and his 30 second power was 1050 watts.
One horsepower is 732 watts so 1.2 * 732 = 878 which is an entirely reasonable number for a 60 second power test.
Also remember that drag goes with the speed squared, so getting a cyclist who is 20% more powerful might cause less than a 10% increase in speed, especially considering that the power of the cyclist may not be the limiting factor but instead the ergonomics of the vehicle, getting the run exactly right (being at max speed over the right 200m rather than any 200m), or something else entirely.
I guess he has also the advantage that he can train specifically for this kind of burst power. All his other projects were of this kind -- a minute or two of maximum possible power.
It's actually a very specific power profile. It'll be 10-20 or so minutes of work for the actual run (at 30mph it's 2 minutes a mile and you'll spend plenty of time under 30), but perhaps with an hour or more surrounding. Some amount of warm up almost for sure possibly with some substantial efforts.
The body has only a few kilojoules of oxygen debt that it can get into before the pain becomes too much and you're forced to slow down to stop the pain. It's important that you spend those kilojoules just right. So that means accelerating aerobically as long as possible, which is going to be a slow acceleration. You might not use all five miles, but I would wager a good portion of it. And using a power meter to ensure that the cyclist doesn't go anerobic before the critical portion is actually really smart (I don't know if they did this).
The goal is to be doing 50-60mph aerobically (or whatever you can actually do) and then have a 30-60 second interval start at exactly the right point to lead to maximum speed over the 200m. But because the human body isn't as precise as our measurements, you'll never get it exactly right. Some days at the end of the 200m you'll say "I still had some legs left" and other days you'll start to fall apart before the start of the timed 200m.
A highly optimized pedaling plan might even include a coasting section with a strong focus on breathing after the initial aerobic acceleration but before the final effort. If your vehicle is slick enough you might only lose 0.5 to 1 mph but if you can trade that for flushing all the CO2 out of your system, that might be worth it.
This is interesting; 1.2hp is about 895 watts. Assuming he's probably 65kg (total guess from the looks of him). That means he can do about 13.7 Watts/KG for 1-minute. According to the chart I posted above, looking at 1 minute power, that puts him as a Far to Moderate level cyclist. Even giving the benefit of the doubt and assuming 55kg, making the ratio a better 16.2 Watts/KG, that just moves him up to the "Good" category.
So perhaps a lot of improvement could be had moving to a professional cyclist.
You are looking at maximal power output for 5 seconds (the left most column) while you should be looking at maximal power output for 1 minute (the 2nd column from left) :)
He also has a PhD, and was part of the team that designed and built it. From the wikipedia page about the helicopter:
"The peak power of 1.1 kW (1.5 hp) was only generated during the first few seconds to climb to the required 3-metre (9.8 ft) altitude. By the end of the flight, power had reduced to 600 W (0.80 hp). Todd Reichert, the pilot and a racing cyclist, had specifically trained for such a power profile."
You could really probably optimize for the 200m speed zone. As long as you can get to your top speed before it, you dont need to fly through the 5 mile zone. Better to save energy for an explosive finish.
Track cyclists sometimes do a "flying 200m." The record is 9.347 seconds which is 47.86 mph. Thats on a non aero bike with drop handle bars. It would be very interesting to see them in a perfectly aero recumbant bike like this.
Absolutely. Being trained for such short intervals, I wonder how much their power output would drop in the final 200m after that 5 mile buildup. In any case, there has to be some optimal cyclist build for this event. I suspect it's probably somewhere between a time trialist and a pure sprinter.
Would it be within the rules to include a power capturing mechanism like a flywheel or spring that can be unleashed at the end? That would change the game to maximizing total energy output over the 5 miles, and make the whole section count.
Even without reading the rules - no. Otherwise, why not spend 8 hours to go the 5 miles, charging up the system the whole time, and get a brief burst of 100+ mph at the end? It'll end up seeing who can build the better power capturing mechanism, not seeing how fast a human powered vehicle can go.
"Actiflow has assisted us in computational fluid dynamics software in order to further optimize the promising shape of the VeloX IV. The result: a mature aerodynamic design with 10% less drag!"
They also write that this design is optimized for the 200m sprint. Their previous designs also were made for a one hour time trial, but this design doesn't take in enough air for the rider that long.
I highly recommend reading "The Fullness of Wings". If I remember correctly, they devoted a whole chapter to the process through which they selected the cyclist who powered Daedalus.
I would imagine that power to weight ratio is more important than just the power. Also the smaller the cyclist, the smaller they can build the aerodynamic shell, thus reducing drag.
Air drag is proportional to the front facing area of the vehicle, that is 2nd power of cyclists dimension (for example, height, we are assuming that humans have approximately similar shape, regardless of size). Max power grows to 3rd power of cyclists dimension, because it's dependent on the cyclists muscle mass. Maximum aerobic power grows somewhere between 2nd and 3rd power, because of the fractal shape of lungs and veins (for example, think about lung surface area, the smallest folds in lung have same dimension in bigger and smaller guys, so the area grows faster than 2nd power of cyclist's dimension).
It then follows that bigger guys do well pushing against air (since frontal area grows slower than maximum aerodynamic capability), and smaller guys do better dragging themselves uphill (since mass grows faster aerodynamic capability).
You can easily find practical examples of this: say Fabian Cancellara, who has won time trial world championships 3 times + almost anything else riding in fairly flat ground, including several tour prologues and stages before getting into mountains... but when you get to the mountains, it's the featherweights that rule, so likes of Cancellara can't ever win the tour.
So... to propel something as fast as possible against air, you need big and strong cyclist (with huge lungs to match), just like the guy in the video looks like.
Power/weight has little to do with it, since air drag is most of the resistance, and they can accelerate for 5 miles before measuring speed (you would need power/weight if you needed to accelerate fast, which is not the case).
Actually, on a flat surface with a constant speed or acceleration, weight matters much, much less than frontal area. Weight comes into play much more when many quick accelerations or elevation gains come into play.
Because frontal area doesn't increase proportionally with weight, I would argue that power output should be the primary concern and that typically increases substantially with weight. For evidence of this, look at world class time trialists versus world class hill specialists.
Fabian Cancellara [1] is considered one of the top time trialists in the world at 181 lbs as he can put out much more absolute consistent power than someone like Nairo Quintana who is considered one of the world class climbers and weighs 128 lbs, [2] even though Nairo Quintana may have a better power:weight ratio.
Was wondering the same since, this is about top speed and not about acceleration the weight shouldn't matter much at all, since it has no direct influence on the air resistance.
Would be interested in knowing, if a human powered vehicle on steel rails with steel wheels with the same air resistance could be faster than this just due to the lower rolling resistance.
Weight shouldn't have as much of an impact on acceleration because as muscle mass & power goes up, weight goes up as well.
But more weight inside the shell doesn't increase air resistance, while it does increase power. So a heavier rider with greater sustained power output will, in an environment where wheel friction is trivial, go to a considerably faster top speed on flat ground.
Did anything happen to F = m × a in the last 20 years?
Acceleration a is heavily dependent on the mass m.
Since a = F / m having half the mass would result in double the acceleration with same amount of force F available.
If they're putting athletes into this thing, the bigger the athlete, the more force (okay, the more power) is available for propulsion. They have bigger muscles which store more glycogen and have greater total mitochondrial activity, because there are simply more of these cells available to do the work.
Unlike in high school physics, we have to account for drag, which is a lot more important than mass at these speeds. F=ma is true, of course, but you have to think more about what F really is.
So my question is now: In terms of aerodynamics, what aren't they doing?
Some commentators have noted that the shape of this bike is just about as good as it can get. The rider/engine is also not going to see any vast improvements. So rather than this become a pure athletic event, where can engineers look for improvements? Will they have to start dealing with boundary layer issues? Will the next generation of bike be covered in golfball-like holes to reduce turbulence?
I found out they have great Q&A videos on their YouTube channel. They answer here why golf ball dimples are unnecessary for a fin-like shape. https://www.youtube.com/watch?v=ZXpZy_A7mMk
Golfball-like dimples are only half my question. In aircraft much work has been done on reducing boundary layer issues with suction holes that actively remove turbulent air. Some aircraft engines, the SR-71's in particular, do this to ensure 'clean' intake air.
Speaking of the SR-71, you guys should all read the heavily reposted stories about it. It's such an amazing plane. While it's not flying in the sky anymore, it deserves to fly in our imagination every time somebody speaks about it.
The majority of the drag affecting a modern HPV racer is caused by the wheel aperture. Perfectly fitting the fairing to the tyre isn't practical, due to flex in the wheel and the tyre casing. Managing airflow around this gap is a largely unsolved problem.
Some improvements could be made by reducing the rolling resistance of the tyres or the efficiency of the drivetrain, but this will have only a relatively small impact; this drag increases linearly with speed, whereas aerodynamic drag increases geometrically.
this is very interesting. What if the vehicle flew in ground effect (small retractable wheels for takeoff)? You'd also need a propeller for propulsion. You'd drive off the road easily though.
Dimples on golf balls help in inducing turbulence, not the other way. Turbulence in this case reduces drag significantly. This is a well known counter intuitive result in flu mech.
Weight, air flow for rider, friction, even more arodynamic profile, ergonomics, better fit for rider. I suspect a better bike might get you 10% more speed, but each 1% is going to keep getting exponentially harder.
Maybe the road surface? I'm assuming an actual highway has some friction that could be sacrificed perhaps? Not sure what the cutoff is there before too little traction becomes problematic?
Just spitballing here, I have no idea how most of this stuff works.
Related to road surface, are properties of the tires used. The goal is to optimize for rolling resistance. On a long brevet, different tires can shave hours off your time.
Since their requirements for durability are much lower (i.e. they don't need to get days or months of use), they could optimize for tires that are just durable enough for the event and have minimal rolling resistance.
Suspension losses are another area where power is lost. I'm curious if it is possible to perform these tests in a velodrome where gains from better tires suspension would be minimal.
Also check out motor-paced records, where the current record is 166.9mph by Fred Rompelberg.
Contrary to what it might look like, rowing is almost entirely dependent on your legs, your arms/back merely keep the momentum going at the back of the stroke.
Also, the muscles in your back are nowhere near as strong/large as the muscles in your legs, there's nearly a magnitude of difference. Though if you added power from your arms in addition to fully utilizing your legs (it would be much harder to concentrate) then there would be a benefit. But then you run into how to engineer such a thing, especially with respect to aerodynamics.
The limit is cardiovascular, not muscular. World class rowers and cyclists have about the same power output. A rowing bike would be larger (so less aerodynamic) and difficult to engineer.
I wonder why for fastest human-powered they don't use more than one cyclist. I assume with eight humans like in rowing you could get up to a ridiculous speed. Might be a little dangerous though.
Im sure the rules state 1 human. That is an interesting thought though. A second person behind the first would add very little extra drag while doubling the power.
This isn't horribly safe, either. Wiping out at 85 MPH would suck.
I'm curious what multi-cyclist vehicles could do, now that you suggest it. With the lightness of these vehicles, at what point would you have to add spoilers?
While I know it would suck to wipe out, I'm hoping with this thing it may be more of a "slide for 1000ft and off the flat road" type of suck than a "life altering injury" type of suck.
I think the shape would change dramatically for such a thing... it would probably be pretty good at 3-4 cyclists and have a shape closer to the solar car challenges for a more optimum output... There would of course be additional weight to overcome. But it would be interesting.
Max speed has very little to do with weight as long as you have sufficient room to accelerate. Additional drag would be small if you put one rider in front of the other and both inside of a fairing. The frontal area and shape could stay the same. This is the major source of drag. There would be small amounts of additional drag from the air running along a longer fairing, but doubling the power would more than make up for it.
However, the speed would nowhere near double. Power required to overcome drag force is related to velocity cubed. So if you double power, the velocity will increase by a factor of (2)^1/3 or the cube root of 2, 1.259.
So if they added another rider of equal power and managed to keep drag the same (it would actually increase a little) they'd go around 25% faster or 107 mph. You may run into other problems like stability and bumpiness first though.
As someone wrote above, weight doesn't matter that much, and since the most likely configuration would be one behind the other, the aerodynamics wouldn't suffer that much.
The video ends with a brief second where the cyclist explains what prevented even higher speed. I make out: "too much vibration...", "knees rubbing...", "unable to continue increasing power output". Would love to hear more about this.
Note the video was from last year when they failed to set the record. This year they've done it. They probably will release a video of this year's efforts eventually.
I believe it is because the vehicle is very aerodynamically unstable. When you ride a normal upright bike, it will fall over unless you actively spend a little effort balancing it. Here is a video of a crash: https://www.youtube.com/watch?v=i5Dapy1xUq0 Note how it wobbles to the right when he pushes the right pedal, then to the left when the left pedal is pushed.
120km/h looks like the typical global speed limit, but I haven't calculated it. It includes China, India, Brazil, several countries in the middle east and Africa.
I wonder how much impact a professional track cyclist would have. Im sure the current pilot is a strong rider, but if you got a world record sprinter into the world record bike, how fast could they go?
A professional track cyclist would be quite inferior to these riders. These aren't some average Joe riding here: they're they best high-performance cyclists in the world. For example, this particular record was long held by Sam Whittingham: I invite you to see his Wikipedia entry. https://en.wikipedia.org/wiki/Sam_Whittingham
He's obviously very very strong. I'm sure the riders all the teams select are amazingly strong riders. They aren't, however, gold medal caliber track cyclists. The men with the strongest legs in the world. There is much more prestige and money in winning a track cycling medal than setting a record in human powered vehicles.
Im simply wondering, what happens if they get the best of the best. With proper time to adapt to the vehicle, its probably worth a few mph. Not too significant, but enough to reset the record.
> They aren't, however, gold medal caliber track cyclists.
Correspondingly, gold medal track cyclists aren't world record setting performance cyclists.
These tasks demand somewhat different skill sets, and at this level, "somewhat" is a big deal. There's a reason why the "top" track cyclists don't hold any of these records.
What I'm saying is that that reason most likely isn't lack of physical ability, but lack of ever trying. Why would they when they are chasing olympic medals and making way more money than would earn setting these obscure records?
It's interesting to note that this record was once again set along a very specific stretch of highway in Battle Mountain, Nevada which is prized for its near perfect flatness and is often used for human-powered vehicle record attempts.
The course is not perfectly flat, but it is perfect for the contest.
The rules for this event stipulate that the track cannot be slopped downhill by more than 0.66%. Conveniently this track averages 0.64% downhill over the entire 5 mile duration. [1]
The story about how Raymond Gauge (what an aptronym!) happened to find this particular stretch of road makes for it's own fascinating big data tale. Months of mining away on USGS tables with Celeron processors to get 10 suitable tracks. A documentary made a few years back went into the specifics with plenty of dramatic shots of him driving the lonely stretches of Nevada, New Mexico, Kansas, etc whittling down his choice candidates until he settled on Battle Mountain.
The biggest limitation in these events is air resistance. Plenty of other folks have gone significantly faster on bicycles not facing a headwind[2]. Altitude helps.
Interesting that for land speed records you generally need to do two passes of a course one in each direction and your speed is an average of the two passes in order to prevent these types of shenanigans ;-)
I'm guessing that the rules prohibit using some of the pedal power to charge a battery during the initial part of the run, and then using that stored energy to provide an additional speed boost :D
I don't see why not. The initial run is essentially the storing up of momentum. From that, running up a flywheel inside the bike is just storing the same energy in a different place.
It stretches the concept of "human powered". Why not just pedal while stationary to charge a battery (take as long as you like), and then ride the course with no additional expenditure of effort.
Well, the course is a 5mile run up to a 200m speed trap. So if you allow batteries/motors, you could just sit stationary somewhere in that 5 miles pedalling for a while, and then use electrical acceleration to get up to speed for the trap. You're not bringing any additional energy, but its clearly not in the spirit of the challenge.
This is probably the few projects in life where you can say you've challenged your mind just as much as you've done your body. And one can see the impact of both of these in these young and beautiful "geeks". What a project it must be to work at - beautiful minds and beautiful bodies. And the happiness shows. :-)
I've met with some of the guys from Aerovelo and done a little bit of collaboration with them. They're top notch, and an all-around awesome team of engineers. And Todd is a beast (watch the Atlas human-powered helicopter video).
What software solutions are there that could be used to simulate mechanics and physics (including gravity, friction, ...) in order to prototype, say, a human powered heli_thing? :) No, I'm serious.
I was gonna say this makes me realized just how aerodynamically inefficient a regular bike is, but then I found out that the world record of cycling on flat surface is actually 83.13 mph [0], which is actually pretty close to this. Assuming the rider is also top notch, I guess the benefit from optimizations done on aero isn't much larger than the weight added.
The speed is for a human powered vehicle (fully fared).
Edit: All the flat records in the section you're referencing are for hpvs, not tradition bicycles, as a look at the pages of the riders will show.
The body will naturally produce more red blood cells at altitude so while there is a performance hit, it is mitigated. Also, the crucial power here is anaerobically produced anyway.
If must be, I think the rules don't forbid an oxygen tank.
I am a proud Canadian who lives in the USA and have a little Canadian sticker on my car. It's my little shout out to other Canadians on the road. I guess we're quietly showing our pride to others. Being loud about it is not in our nature. But I do like that luge helmet :)
The d&d fan in me thiks falling is a free action. A human powered plane doing a dive would go faster I'd bet. Not prepared to rules lawyer that case though.
At first I thought it might be to keep the weight down, as there are plenty of composite materials that are lighter than (even thin) plexiglass. But then there's the weight/complexity of the camera, display, and battery.
Then I thought, well, the rider in in such an odd position, maybe he wouldn't be able to see very much even if there was a window.
But apparently the actual reason is that the rider produces so much heat that a window would fog up, and it would be too difficult/unsafe for the rider to wipe it. Given the white coloring, I suspect they're also trying to avoid cooking their human power source.
Here's part of a Q&A where they discuss visibility:
https://youtu.be/mscVAb1VZJw?t=271