Ever get a balloon or base jump when it feels all too good... you max out the suit, and you effortlessly fly at insane glide ratio, you experience the quietness and smoothness you've never experienced before and can't figure out what the hell is right?
You may think that increased concentration and strength made you fly better. Well, now you can praise basic aerodynamics instead of praising yourself (or clown shoes)!
The wingsuit equations are solved in the attached spreadsheet using the simple Euler integration method for some sustained horizontal/vertical speeds (which, as we saw, determine the adjusted lift/drag coefficients). For simplicity, we assume constant Cl and Cd (that is, the wingsuit geometry and angle of attack are constant) and zero-speed exit. You can change the values of Vxs and Vys to match your speeds. In this particular example, Vxs = 86mph, Vys = 43mph, L/D = 2.0.
The graph PlaneoutTheoryVsExperiment.gif compares the calculations with one of the Phantom flights (the above parameters were chosen to best fit the experimental data). As you can see, from about 12 seconds to 24 seconds, the glide ratio is higher than 2.0 - we have a planeout with maximum glide ratio as much as 35% higher than the sustained glide ratio.
The graph PlaneoutVsWingloadingAndLD.gif shows the dependence of the planeout duration (time period when glide is better than L/D) vs. wingloading. The heavier flyers experience longer planeouts which start later. The graph of glide ratio increase vs. L/D shows that the planeout effect dramatically increases with the increasing L/D: the better you fly, the more you can be fooled into thinking that your insane glide ratio is your L/D. PlaneoutVsLD.gif shows the trajectories and glide ratio vs. time for different L/D.
Unlike intentinal dives and spirals and subsequent high-speed planeouts with quite high g-forces in skydiving, the smooth transition into full flight on a base or balloon jump hides the planeout in virtually unnoticeable ~0.1g decelerations that bleed your speed ever slowly, but do make your glide substantially better than your actual L/D.
In conclusion,
- when analyzing GPS data from a base or balloon jump, discard the first ~30s of the flight, even if it has a linear portion that looks like a sustained flight... it's not! (or better yet, correct the glide ratio for acceleration using the formula above)
- planeout effects can also manifest themselves when you change your body position and feel the decreased fallrate and improved glide - only to lose it in a few seconds. It could simply be a planeout! (again, accurate acceleration data can help you see if the improved glide was real or "fake")
- after the planeout, you will experience temporary "drop", a decrease of glide ratio even below your L/D. Plan your "do it or die" jump accordingly.
- heavier jumpers will experience the planeout effect longer. Vampire will exhibit stronger planeout glide imrovement than Prodigy. The higher the performance, the better the planeout - and the worse the "drop" after it. Android+Wear/iOS/Windows apps:
L/D Vario, Smart Altimeter, Rockdrop Pro, Wingsuit FAP
iOS only: L/D Magic
Windows only: WS Studio