5 ms·

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 th

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] http://d4nuk0dd6nrma.cloudfront.net/wp-content/uploads/2009/07/powerprofiling.jpg http://d4nuk0dd6nrma.cloudfront.net/wp-content/uploads/2009/...

luminiferous 11y ago
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.
- irl_zebra 11y ago
  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. [1] https://en.wikipedia.org/wiki/Fabian_Cancellara https://en.wikipedia.org/wiki/Fabian_Cancellara [2] https://en.wikipedia.org/wiki/Nairo_Quintana https://en.wikipedia.org/wiki/Nairo_Quintana
  - QuotedForTruth 11y ago
    Track sprinters are even bigger, further showing your point. Chris Hoy is 205 lbs.
  - davidw 11y ago
    Exactly. https://en.wikipedia.org/wiki/Tony_Martin_(cyclist) https://en.wikipedia.org/wiki/Tony_Martin_(cyclist) weighs in at 75 kg - lighter than Cancellara - but not that light for a professional cyclist either.
  - mxfh 11y ago
    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.
    - mapt 11y ago
      You've got it reversed. 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.
      - mxfh 11y ago
        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.
        thedufer 11y ago
        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.
- Faint 11y ago
  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).
QuotedForTruth 11y ago
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.
- irl_zebra 11y ago
  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.
  - foobarian 11y ago
    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.
    - dalke 11y ago
      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.
yurisagalov 11y ago
Todd is actually a world-class rider (based on the chart you provided, as well). From the article before they won the Sikorsky prize: "Reichert, a national-level speed skater, can pedal at 1.2 horsepower for a full minute" http://m.thestar.com/#/article/news/gta/2012/08/26/humanpowered_helicopter_toronto_engineers_aiming_to_win_elusive_sikorsky_flight_prize.html http://m.thestar.com/#/article/news/gta/2012/08/26/humanpowe...
- irl_zebra 11y ago
  EDIT: Made a mistake with the numbers! 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.
  - yurisagalov 11y ago
    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) :)
    - irl_zebra 11y ago
      Wow you're absolutely right, my mistake! Todd must be a very, very fantastic cyclist!
      - jonknee 11y ago
        Hence setting the speed record!
  - deleted 11y ago
    [deleted]
- 11y ago
Someone 11y ago
"I'm guessing something can't get much more aerodynamically shaped?" The previous record holders claim otherwise. On May first, they wrote (http://www.hptdelft.nl/en/blog.php http://www.hptdelft.nl/en/blog.php): "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.
rebootthesystem 11y ago
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.
stouset 11y ago
A time trialist wouldn't excel at 5 minute efforts. A track cyclist would, though.

luminiferous 11y ago

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.

irl_zebra 11y ago
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. [1] https://en.wikipedia.org/wiki/Fabian_Cancellara https://en.wikipedia.org/wiki/Fabian_Cancellara [2] https://en.wikipedia.org/wiki/Nairo_Quintana https://en.wikipedia.org/wiki/Nairo_Quintana
- QuotedForTruth 11y ago
  Track sprinters are even bigger, further showing your point. Chris Hoy is 205 lbs.
- davidw 11y ago
  Exactly. https://en.wikipedia.org/wiki/Tony_Martin_(cyclist) https://en.wikipedia.org/wiki/Tony_Martin_(cyclist) weighs in at 75 kg - lighter than Cancellara - but not that light for a professional cyclist either.
- mxfh 11y ago
  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.
  - mapt 11y ago
    You've got it reversed. 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.
    - mxfh 11y ago
      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.
      - thedufer 11y ago
        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.
Faint 11y ago
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).

QuotedForTruth 11y ago

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.

irl_zebra 11y ago
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.
- foobarian 11y ago
  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.
  - dalke 11y ago
    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.

yurisagalov 11y ago

Todd is actually a world-class rider (based on the chart you provided, as well). From the article before they won the Sikorsky prize: "Reichert, a national-level speed skater, can pedal at 1.2 horsepower for a full minute" http://m.thestar.com/#/article/news/gta/2012/08/26/humanpowered_helicopter_toronto_engineers_aiming_to_win_elusive_sikorsky_flight_prize.html http://m.thestar.com/#/article/news/gta/2012/08/26/humanpowe...

irl_zebra 11y ago
EDIT: Made a mistake with the numbers! 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.
- yurisagalov 11y ago
  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) :)
  - irl_zebra 11y ago
    Wow you're absolutely right, my mistake! Todd must be a very, very fantastic cyclist!
    - jonknee 11y ago
      Hence setting the speed record!
- deleted 11y ago
  [deleted]
11y ago

Someone 11y ago

"I'm guessing something can't get much more aerodynamically shaped?" The previous record holders claim otherwise. On May first, they wrote (http://www.hptdelft.nl/en/blog.php http://www.hptdelft.nl/en/blog.php): "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.

rebootthesystem 11y ago

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.

stouset 11y ago

A time trialist wouldn't excel at 5 minute efforts. A track cyclist would, though.