platypii

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Everything posted by platypii

  1. Applied Wingsuit Equations: Reconstructed roll angle from GPS data, overlayed on terrain. @yuri_base
  2. When I said "satellites are mostly near the horizon" I meant that statistically at any given time, you are more likely to have satellites off to the side, than overhead. And If you're trying to use triangulation to measure height and vertical speed... that's going to be less accurate without satellites overhead. Geometrically it's a fact that they are more likely to be near the horizon than overhead. Here's why. If you draw a line extending out 45 degrees above the horizon, then the area of sky "above" you is much smaller than the area to the sides. I get a ratio of more than 2:1 "near the horizon" vs "above" at GPS altitudes. Picture is drawn to scale. I will say though, I expected a bigger ratio. But because GPS orbits are actually quite high, this is less of a factor than if they were in lower orbit.
  3. GPS units generally have a physics model of what is "realistic" speeds and accelerations. These are used in kalman filters to clean up noisy GPS data. It probably thinks that falling at 120mph is not realistic. Also the satellites are mostly near the horizon, so GPS is inherently less accurate on altitude than position. And finally -- check where it's mounted on your body. If its chest-mounted, you're going to be blocking its view of most of sky. Do you backfly? Cool project!
  4. He's wearing a BASE rig, so no, he doesn't need emergency handles :-)
  5. The 3-ring wikipedia article is surprisingly detailed, with a nice animation of the mechanism: https://en.wikipedia.org/wiki/3-ring_release_system
  6. Just released a new version of BASEline tonight that will scale text with the android system font size. Thanks for the feedback. Keep us posted on your project!
  7. I've done this using Google Glass and it works well. I'm the developer of BASEline Flight Computer, so it was fairly easy to port the Android app to Google Glass. You can find used Glass on ebay for around $400. As you mentioned, the advantage of a HUD is that you can see horizontal speed, vertical speed, total speed, and glide ratio all at once, and with much faster update than you could ever get with audio. I personally chose to display your speed as a "polar chart". Horizontal and vertical speeds on the axes, total speed equals the hypotenuse, and glide is shown by the slope: To get good data, pair the phone with a bluetooth GPS like the XGPS160. Let me know if I can help with anything. I would love for this to exist! But I don't expect most people to deal with google glass. If interested, the google glass version of BASEline is available on a github branch: https://github.com/platypii/BASElineFlightComputer/tree/glass
  8. Computing velocity from noisy position data can introduce a fair amount of error. Here is an example. Your true velocity might be constant and actually look like: But GPS will have errors that might make the position look like any of the black dots here, and you can see how much error that can introduce to the velocity if computed using distance / time: It's possible to smooth this out by adding a Kalman Filter. But a filter will introduce its own errors and create a lag time before it accurately estimates your true velocity. However, as pointed out by @crwper, GPS actually has the ability to compute position directly, not using position and distance. Instead, many GPS chips can actually use doppler shift from the satellites to directly compute velocity. The accuracy and response time is much better. It is not clear whether the GoPro uses doppler velocity to compute 2D and 3D speed, but its definitely NOT giving the individual velocity components (vN, vE, vD) which would be nice to have.
  9. Actually I find the touch screen to be one of the biggest selling points of Dekunu over the X2. I own both and I HATE using the 3 button interface on the X2. Using the touch screen is so much more intuitive, way easier to find things in the menu, easier to use while on the ride to altitude, etc. On the topic of the screens, they are very different! The Dekunu has lit up screen (like a cellphone), whereas the X2 has a passive screen (more like a watch screen). Neither is strictly better than the other... X2 might be a bit better in direct sun, but overall I find it easier to read the dekunu in most cases. Dekunu has wider viewing angle, and usually its in the shade on my chest strap while wingsuiting, so the lit up screen it more readable. Plus the LCD screen on the X2 sometimes interferes with polarized sunglasses. Overall, I like the Dekunu more, but I am excited to see how both these units get upgraded over time.
  10. Overall really happy with the site redesign. Great work! One super minor request: it seems like with the new CMS, the favicon disappeared. I like to keep my favorite sites on my bookmarks bar with just icons and no text:
  11. Cool application of WSE: Roll Angle from GPS data! Basically, by finding the angle of the Lift vector relative to flight path, you can compute the roll angle of the suit. Here's an example of pitch, roll, and yaw reconstructed from FlySight data: This shows initial steep exit from a cliff, followed by leveling out, a slight right turn, a corkscrew (!), then a long commute before deploying. Note that the visualization assume AoA = 0. Credit to Hartman for the roll angle calc, and DFR for the corkscrew line. BASEline - Wingsuit Flight Computer
  12. I'm going to preface this by saying that I'm highly skeptical of this idea, especially since you haven't even addressed how deployment would work. But... You should check out "hot wire foam cutting". There are super cheap tools available on amazon so you can do manual sculpting of foam. There are automatic hot wire cutting machines that can make them. Also some clever DIY hacks to make it cheap. High end professional hot wire cutter with overly dramatic music Very relevant DIY foam cutting of an airfoil (very long video) BASEline - Wingsuit Flight Computer
  13. Yea working on an edit now, something looked wrong. In my defense, in baseline the formulas are implemented in 3D, and I had to re-do the math today for the 2D version. BASEline - Wingsuit Flight Computer
  14. MAGIC-FREE L/D I mentioned in my earlier post that you don't need yuri's "magic" coefficients from WSE to compute L/D. Thought I would share the math here in case it helps someone's understanding of wingsuit dynamics. [inline magicfree1.png] The net acceleration A of a wingsuiter can be measured by GPS, and is equal to the sum of the force vectors: A = L + D + G Split the equality into its vector components. The obvious thing would be to align our coordinates with earth (x and y axes), but that makes the math tricky. Much easier if we project it onto the Lift and Drag axes: [inline magicfree2.png] Rearrange to get: [inline magicfree3.png] Since we know the velocity components from GPS: sin(theta) = vy / v and cos(theta) = vx / v. Substitute to get: [inline magicfree4.png] Boom, L/D from GPS velocity and acceleration data! No magic As a sanity check, when A = 0 it's easy to see that L/D = vx / vy = glide ratio. Exactly what we would expect for steady state flight. But this also works when accelerating. This doesn't work if there is wind, because lift and drag forces will no longer be parallel and perpendicular to the velocity vector. But it works well in low-wind situations, especially BASE jumps. Wonder if there will be more math skeptics... (edit: fixed negative) BASEline - Wingsuit Flight Computer
  15. I'll let those Formula1 teams know that they should stop using wind tunnels to fine-tune their aerodynamics. I'm sure they will be grateful to save the $. In more sophisticated aeronautical engineering fields (eg- not wingsuiting) there is good uses for all these tools: instrumentation, CFD, and wind tunnels. Instrumentation might be great for measuring the absolute L/D of different suits, but if I was trying to design a better suit, tunnel and CFD will allow for much faster iteration. To be later validated by instrumentation. BASEline - Wingsuit Flight Computer
  16. Yuri, wouldn't the tunnel be the PERFECT place to validate if your vane is actually giving accurate results and where to mount it? Would be great to know how much error it introduces and the stdev of the output. It's really only statistically useful for comparing suits if the difference is greater than error of the measuring device. BASEline - Wingsuit Flight Computer
  17. I feel like the chart I posted could benefit from some additional explanation. This is how it maps to a skydive or base jump at a high level: [inline state-machine.png] There's a fair amount of noise, but also its possible to hit a wide range of glide ratios, as has been discussed to death in this thread. The polar view is especially interesting when it comes to flares. Here's a single wingsuit BASE jump with a really nice flare. You can see the exit, initial build up of downward velocity, followed by steady increasing horizontal speed. At the end of the jump, speed is converted into lift in the flare, and then gaining altitude before deploying the canopy. [inline polar-flare.png] The background ellipses are approximations based on the previous plot, so that you can have a quick visual reference for your speeds (UX design is research too) BASEline - Wingsuit Flight Computer
  18. Not replying to any particular post, just bringing back the original topic of ws research, and thought I would share some real-world data that might be interesting to people. Data from over 2000 different wingsuit gps tracks (sky and base) plotted as a polar chart. Ground speed on horizontal axis, fallrate on vertical axis (mph). The tracks were classified by flight mode, and the points colored according to: Ground = brown Plane = red Wingsuit = purple Canopy = green [inline baseline-polar.png] This chart helped me understand the typical wingsuit performance envelope a lot better, and was critical in building a tool to automatically recognize different flight modes based on GPS data. BASEline - Wingsuit Flight Computer
  19. Chart attached with all speeds: total, groundspeed, fallrate. Plus glide and l/d. Accuracy on this track seems okay. Jump is sensitive, so can't share the data, but will see if I can find a similar one that I can. BASEline - Wingsuit Flight Computer
  20. Fair enough, you're right that with changes in airspeed and angle of attack, the L/D will also change. I glossed over this a little, but also tried to acknowledge it when I pointed out the variation in L/D in a typical glider polar curve. The L/D will change throughout a flight, but not by very much actually. It will change by moving along the wingsuit's characteristic polar curve. The l/d won't swing between wildly between 2:1 and 5:1 like the glide ratio does. Here is a chart of the "sustained speed polar" which uses the wingsuit equations to compute "sustained" horizontal and vertical speeds. In theory this is roughly what would be measured by aerodynamic instruments like airspeed and glide angle on an aircraft. The purple line shows the sustained speeds from the same jump as above, and you can see they fall within a fairly narrow range. The green line is my attempt at ballpark estimating a wingsuit's polar curve. That's why I would expect the L/D to not vary by much throughout the flight. [inline polar.png] Big caveat: the wingsuit equations can re-orient and change the frame of reference of the measurements, but wind still throws off the results. BASEline - Wingsuit Flight Computer
  21. It wasn't constant airspeed nor constant glide. The flight went through a few phases and angles of attack, but as much as possible, the same body configuration. The green line is groundspeed / fallrate, the purple line is L/D calculated based on wingsuit equations. Although, I guess technically it doesn't actually require yuri's "magic" kl or kd coefficients to calculate L/D. Just change coordinate system to be oriented along the velocity vector, subtract out gravity, and what remains are lift and drag forces. However the magic coefficients do lead to interesting results when it comes to modelling the effects of mass, surface area, altitude, etc. I'm still trying to wrap my head around sustained speeds. BASEline - Wingsuit Flight Computer
  22. Maybe you missed the part where I followed up with real world experience? And also explained how one can test if experience lines up with theory? Jump from a cliff, where you nail the angle of attack, hold the same body configuration through the whole flight, and then flare for deployment. Hypothesis: once up to speed, your L/D should be roughly constant throughout the flight. Here is an example of such a flight. [inline ld.png] You can see the l/d (purple line) quickly goes up to approximately 3.0 glide ratio, improves slightly with a bit more speed (typical of glider polar curves), and stays roughly constant through the flare at the end before deployment. Contrast with the glide ratio (green line) which starts low and takes nearly 10s to reach 3:1. Then some speed is converted into glide and so it continues rising to above 5:1 glide. But the debt must be paid, and so the glide ratio drops off below 3:1 before the flare. The flare again brings the instantaneous glide above 5:1 before the canopy opens. Data supports the theory. 1 track, small sample size? Sure. But I've seen this pattern over and over again on baseline. And since it agrees with the theory, and the intuition, and the data, I'm not sure why you are so skeptical? It provides an additional, more aerodynamically interesting, measure of wingsuit flight. BASEline - Wingsuit Flight Computer
  23. http://www.pureflyingmagic.com/Content/Knowledge/Resources/Articles/en/WingsuitEquations.pdf You don't need physical data to prove it. If you accept the underlying physical equations: F=ma and lift equation, and if there are no mistakes in the proof (I don't see any, but onus is on you to find one), then the equations are valid. That being said, I've played with them, and applied them to real world gps data, independently of yuri's software, and they appear to match observed reality. For example with wingsuit starts... using WS equations you can observe the L/D being close to 3:1 throughout the whole start arc, whereas the GPS glide ratio varies wildly and takes much longer to reach "steady state". This is what I would expect to see from a true L/D measurement. BASEline - Wingsuit Flight Computer
  24. Poll to see where people think we are, and where we're going with wingsuit performance. Not talking about with a flare, or with a tail wind. L/D BASEline - Wingsuit Flight Computer