yuri_base

You're right, until linestretch it's more like a single pendulum with the suspension point (PC) able to oscillate due to feedback from the suspended weight (canopy). When the suspension point moves with the frequency equal to the natural frequency of the pendulum, a resonance occurs. The system begins to oscillate with high amplitude. The period of oscillations of a L=9ft. pendulum is T = 2*Pi*sqrt(L/g) = 2*3.14*sqrt(9/32) = 3.3s. What frequency the PC oscillates at? Although it's more chaotic motion rather than harmonic oscillation, it still has some characteristic frequencies. They depend on airspeed, size, construction, etc. If the PC oscillates with the period of 3.3s, then we have resonant coupling between the PC and the canopy, which can cause an offheading. If we can make the PC oscillate slower than the canopy does - slower than 3.3s - than this energetic coupling will be broken and onheading performance will improve. One way to make the PC oscillate slower is to use a vented PC. It inreases the "effective mass" of the PC and slows down the latteral motion. Will a longer bridle make the PC oscillations slower? Yes, but the canopy oscillation will be proportionally slower, too, so it won't kill the resonance, although the onset of resonant oscillations will be slower and the canopy will twist less. Anyone have experience using substantially longer bridles, e.g. 15ft? Android+Wear/iOS/Windows apps: L/D Vario, Smart Altimeter, Rockdrop Pro, Wingsuit FAP iOS only: L/D Magic Windows only: WS Studio

Thank you, Tavarish!

Brian Germain posted an article which has useful tips on how to minimize the altitude lost when recovering from a stall, etc. The Stall Android+Wear/iOS/Windows apps: L/D Vario, Smart Altimeter, Rockdrop Pro, Wingsuit FAP iOS only: L/D Magic Windows only: WS Studio

Nick, in these two accidental WLO releases, was the velcro unpeeled or the pin just "slipped down"? Apparently in the new V.2 design, the pin's eyelet is tucked by the rising toggle's grip, so it reduces the chance of the pin slipping down on opening shock. However, how is it sensitive to a side blow? Quite often, the stiffened toggles have a tendency to lay on their sides when packed. If toggle hits the side flap on opening while oriented sideways, can the pin make its way out of its retainer? It seems 1/2-3/4" longer pin wouldn't hurt... P.S. Also, in V.2 - with the channel now in the top part - does the pin move at all when steering with toggles? Android+Wear/iOS/Windows apps: L/D Vario, Smart Altimeter, Rockdrop Pro, Wingsuit FAP iOS only: L/D Magic Windows only: WS Studio

I second the kudos to Apex BASE. Received the email which details the problem, complete with detailed instructions and pictures for rigging a workaround. And free 3-month replacement offer. Excellent job, Apex!!!

No, WLO v.1 was released early this year. Android+Wear/iOS/Windows apps: L/D Vario, Smart Altimeter, Rockdrop Pro, Wingsuit FAP iOS only: L/D Magic Windows only: WS Studio

Nick, I used WLO v.1 on several jumps, my concerns were 1) the pin goes into its tab just by 1/4 inch, a little dispacement of the pin during opening can disconnect the toggle from the line, and 2) you need 2 motions to clear the lineover: release the pin by pulling the ring attached to the red strip, pull the toggle from the eyelet brake setting. How V.2 is more secure? Thanks Yuri Android+Wear/iOS/Windows apps: L/D Vario, Smart Altimeter, Rockdrop Pro, Wingsuit FAP iOS only: L/D Magic Windows only: WS Studio

There's an interesting physics problem: double pendulum. "A double pendulum is a pendulum with another pendulum attached to its end, and is a simple physical system that exhibits rich dynamic behavior. Above a certain energy its motion is chaotic." Extracted canopy and PC at bridle stretch make a double [inverted, driven by drag and gravity] pendulum. Could it be that some PC oscillations can be caused not by asymetry of the PC, but by chaotic double pendulum effect? (A recent antenna strike in Russia, when the properly centered and symmetric PC wildly oscillated and caused 180, is one example.) If we can figure this out, then perhaps this tendency for chaos can be reduced by chosing a certain ratio of bridle length to line length and PC weight to canopy weight? Kind of avoiding the resonance frequency. See the attached animation. Looks familiar? Yuri Edited to attach an animation. Android+Wear/iOS/Windows apps: L/D Vario, Smart Altimeter, Rockdrop Pro, Wingsuit FAP iOS only: L/D Magic Windows only: WS Studio

Nick, what do you think about using pins vs. velcro for SL jumps? Your thoughts about dynamic loading and occasional canopy damage/close calls got me thinking that the pin rigs may have higher black death factor than the velcro rigs and thus should be avoided on SL jumps. Here is why. When pilot chute opens the container (pin or velcro), there's some snatch force in the first milliseconds followed by the weaker, but quickly increasing force of PC drag. If for some reason snatch force was not strong enough to open the container, the increasing PC drag provides the backup. There is no strict geometrical restriction on where in space the opening must take place (except, the ground is the limit ). The container opening may coincide with the snatch force or may be delayed by a fraction of a second. Static line has completely different timing. At the end of 9ft. bridle, you're falling at a speed of 24ft/s = 7.3m/s. Extracting 1/2-inch (half-primed) pin at this speed takes 2 milliseconds. If the pin did not pop within this 0.002s window, something must break from the huge dynamic force and that's the weakest link - the break cord. This maximum force can be estimated using formula F = ma: for something slowing down from 7.3m/s to 0 in 0.002s, a = 7.3/0.002 = 3650m/s^2, or 370G's! So to develop 80lb. dynamic force, only m = F/a = 80*0.454*9.8/3650 = 0.1kg = 3.5oz. weight needs to be stopped from 7.3m/s in 2ms. That is, the weight of the flaps/top surface of the container is enough to break the cord if the pin was somehow snagged. There is at least one known case in skydiving when the pin punctured the bridle and caused PC in tow. On the other hand, velcro distributes the force over much longer time. If the flap is 1ft. long, it takes 40ms to peel it. That’s 20X less dynamic force! 20X less chance for black death. Given these arguments, do you think it’s reasonable to recommend to NOT use pin rigs on static line jumps? Yuri Android+Wear/iOS/Windows apps: L/D Vario, Smart Altimeter, Rockdrop Pro, Wingsuit FAP iOS only: L/D Magic Windows only: WS Studio

I have seen one in LB live and i think Czaber had one in Brento For jumps not over fast river, is there any reason not to 'shut down' the 3-rings by tying off the small ring to the grommet with a piece of line? (in case of tree landing, that line can be cut with the hook knife, then cutaway) Android+Wear/iOS/Windows apps: L/D Vario, Smart Altimeter, Rockdrop Pro, Wingsuit FAP iOS only: L/D Magic Windows only: WS Studio

Is it possible to fingertrap the [thinner] cascades inside the thicker lower line so the cascade transition is smooth (vs. current design - snaggy loops)? Does parasite drag from lines really matter for a 7-cell 260sq.ft. canopy with a 48" uncollapsible pilotchute dragging behind? Android+Wear/iOS/Windows apps: L/D Vario, Smart Altimeter, Rockdrop Pro, Wingsuit FAP iOS only: L/D Magic Windows only: WS Studio

Maybe, less chance of snag with 16 lines instead of 32? Less confusion when you need to use a hook knife? Or what line to pull when you have a linetwist? How about just 4 lower lines (1 per riser) cascading not only chord-wise, but span-wise as well, 8-way. Or maybe 8 lower lines cascading 4-way each. Android+Wear/iOS/Windows apps: L/D Vario, Smart Altimeter, Rockdrop Pro, Wingsuit FAP iOS only: L/D Magic Windows only: WS Studio

Here is the error analysis for non-uniform winds. If the windspeed on the 1st leg is W1 and on the 2nd W2, G1 = A1 + W1, G2 = A2 + W2, so A = |G1 - G2 + dW|/|B1 - B2| where dW = W2 - W1 is the [vector] differential of windspeed between the layers. For "U-turn" pattern, |B1 - B2| = 2, so the maximum error we get in A is dA = |dW|/2 For 90-degree pattern, dA = |dW|/1.4 For example, if the wind on the 1st leg is 30mph average and on the 2nd leg 20mph average, with change in direction 30 degrees, then |dW| = sqrt(30*30 + 20*20 - 2*30*20*cos(30)) = 16mph, so for U-turn the error in calculated airspeed is 8mph, for 90-turn 11mph. If your fallrate is 35mph, this translates to an error in L/D of 0.2 and 0.3, respectively. Quite an error, but it's still better than no wind correction at all. Yuri Android+Wear/iOS/Windows apps: L/D Vario, Smart Altimeter, Rockdrop Pro, Wingsuit FAP iOS only: L/D Magic Windows only: WS Studio

In the method above, you sample the wind at place and time of your jump, instead of relying on the forecast numbers. Android+Wear/iOS/Windows apps: L/D Vario, Smart Altimeter, Rockdrop Pro, Wingsuit FAP iOS only: L/D Magic Windows only: WS Studio

The trick is to use vector algebra, not scalar. Then you can cancel out the wind vector, so its actual direction and speed don't matter. Android+Wear/iOS/Windows apps: L/D Vario, Smart Altimeter, Rockdrop Pro, Wingsuit FAP iOS only: L/D Magic Windows only: WS Studio

Got it, so ignore my email. NOW the friendly TF librarians kickin Android+Wear/iOS/Windows apps: L/D Vario, Smart Altimeter, Rockdrop Pro, Wingsuit FAP iOS only: L/D Magic Windows only: WS Studio

Jason, I'm in Twin Falls public library, the only place in this town with internet computers. They only allow 1hr of internet use per day here. I added the pass to cart at 2:02-2:03, then stuck at payment. I sent you email with CC info. The latest message (2:51) I got is: Fatal Error Miva Merchant has encountered a fatal error and is unable to continue. The following information may assist you in determining the cause of the error: Error Code: MER-OUI0-00003 Description: Too many Authorization attempts! Please verify that you're entering the correct credit card number and expiration date. Please wait 1292 seconds and try again or Contact Us. (../../common/oui_system.mvi:1586) I can't wait 1292 seconds, they're kicking me o Android+Wear/iOS/Windows apps: L/D Vario, Smart Altimeter, Rockdrop Pro, Wingsuit FAP iOS only: L/D Magic Windows only: WS Studio

The deceleration - less than 1mph per second, according to data - was not noticeable at all, and it definitely felt like stable sustained flight that can last indefinitely given unlimited altitude and strength. I simply made more adjustments and stretching into the flight as the air was so amazingly quiet that I could feel any change much better. I bet if you were flying nearby, we could talk, so quiet it was. 30mph! (some points are even low 20's, but the average is 30) Those additional adjustments caused, I believe, the slow decrease in speed. I don't think 1mph/s deceleration can make 225lbs. brick fly at 30mph for 25 seconds by milking the kinetic energy into planeout. Are you saying that if there was a big haystack right at that point, you'd land the wingsuit? Practice that move, Brian, maybe someday you'll wonder, "why I wasn't doing it many years ago, it's so EASY!?" I'll definitely try all these experiments in a couple of weeks, for now I'll be jumping Blue Gay Shoes in zero L/D environment.

Yo! So you bought your 20lbs. "Fly Like A Pro" clown shoes - leather tops with replaceable lead soles - and are eager to let them fly your body in the clouds forever. How do you calculate L/D on a plane jump? How to eliminate wind from your GPS data? Here's the method. Your groundspeed G (bold font denotes vector, regular denotes vector's length) is equal to the vector sum of your horizontal airspeed A and windspeed W: G = A + W Your GPS data shows G, but how do you extract A from this sum if you don't know W? A very crude approach is to use the winds aloft forecast for W. However, the forecast is usually far from being accurate for our purposes. Another approach is to fly directly into the wind on one leg of your flight, then turn 180 and fly downwind. The average of the two groundspeeds will give you your airspeed, since the wind will be cancelled. But again, you need to know the direction of the wind, and this direction is oftentimes incompatible with the jump plan. Can we eliminate the wind while flying an arbitrary pattern? Suppose you fly at a constant speed A and make two legs at some angle to each other. On the 1st leg, G1 = A1 + W, and on the 2nd leg, G2 = A2 + W. By subtracting the two equations, we eliminate the wind: G1 - G2 = A1 - A2. Airspeed vector A can be represented as a unit vector B (B = 1) multiplied by A: A = A*B. B is your magnetic bearing vector. Thus, A*(B1 - B2) = G1 - G2 and A = |G1 - G2|/|B1 - B2| (|...| denotes vector's length) If g is the course of your groundspeed and b is magnetic bearing (both measured in degrees), then |G1 - G2| = sqrt(G1^2 + G2^2 - 2*G1*G2*cos(g1-g2)) |B1 - B2| = sqrt(B1^2 + B2^2 - 2*B1*B2*cos(b1-b2)) = sqrt(1 + 1 - 2*1*1*cos(b1-b2)) and finally A = sqrt((G1^2 + G2^2 - 2*G1*G2*cos(g1-g2))/(2 - 2*cos(b1-b2))) For two particular cases - when you change your bearing by 90 or 180 degrees, the formula simplifies to: for b1 - b2 = 90 A = sqrt((G1^2 + G2^2 - 2*G1*G2*cos(g1-g2))/2) for b1 - b2 = 180 A = sqrt(G1^2 + G2^2 - 2*G1*G2*cos(g1-g2))/2 So here's what you do. 1. Put your magic clown shoes on. 2. Find two reference points far on horizon at 90 or 180 degrees to each other - mountains, lakes, etc. They should be very far so they set the direction (bearing) for your flight, not the course on the ground. Sun is not very practical, since you need to lift your head up to check your bearing and that changes your speed. Another possibility is to use compass mounted on your chest strap. 3. Fly two legs at the same speed maintaining your heading/bearing in the chosen directions. 4. Plug the averaged groundspeeds G1 and G2 and the courses g1 and g2 into the formula above. Calculate your true L/D. 5. Rebalance your shoes and repeat.

Yo! Here's the flight 24hrs after the first one. No clown shoes, plus top-mount camera. Same rig. L/D = 2.1 From this historical day on, if you don't jump in clown shoes, you can't fly, you can just hardly move forward. Yuri Android+Wear/iOS/Windows apps: L/D Vario, Smart Altimeter, Rockdrop Pro, Wingsuit FAP iOS only: L/D Magic Windows only: WS Studio

Also, on the same token, shifting the center of mass forward should be advantageous for tracking. When CoM is trimmed to make you headlow, the legs can be brought together - this way they will produce more lift than mere round tubes. Lead jackets, anyone? To summarize, people with big brains and small balls should be great trackers, and people with huge balls and no brain should be great wingsuit fliers. Yuri Android+Wear/iOS/Windows apps: L/D Vario, Smart Altimeter, Rockdrop Pro, Wingsuit FAP iOS only: L/D Magic Windows only: WS Studio

More thoughts. Suppose you are tracking at L/D = 0.8, that is, at 50 degrees to horizon. If you are in a flat track body position, with your body almost parallel to horizon, the angle of attack is 50 degrees. Very bad aerodynamics -- you're in deep stall. To track more efficiently, you have to go headlow to decrease the angle of attack. If you're 30 degrees head low, the angle of attack is 20 degrees. Looking between your toes, with shoulders rolled forward and moderately low angle of attack, your 'wing' is much more aerodynamic. Your speed increases, the air is hitting you from ahead of you, instead of from below, and you feel that you're producing lift, not just drag. Hence, the technique is born: gotta go headlow, spread your legs, push the butt up, go 'superterminal'. Now on to wingsuits. L/D is much better to begin with. Suppose you are flying at L/D = 2.2, that is, at about 25 degrees to horizon. If you try to go headlow, e.g. 20 degrees to horizon, your angle of attack is only 5 degrees. You can't achive maximum L/D with such a small AoA. Can you achieve L/D = 3.0 with headlow body attitude? You're flying at only 18 degrees to horizon now. There's no 'room' anymore to go headlow. So for wingsuits, the 'superterminal' technique doesn't do any good as it does for tracking. Rolling shoulders forward and tucking your head in (looking between your toes) is necessary to create efficient aerodynamic profile. This naturally puts you in headlow position, determined by the balance of center of gravity and aerodynamic forces. But then AoA is too small to achieve the best L/D. I see two ways to solve this catch-22. One is to balance the body using weights on your legs. ("When Performance Matters, Gotta Wear Clown Shoes!") Another one is to design wingsuit with about 15 degree angle of incidence (angle between the wing's chord and the line of your body). (See the illustration of this idea here.) The body will need to be balanced headlow at about 15 degrees to horizon. The wings will have about 15 degrees AoA. Placing the body completely in-line with airflow will reduce the drag dramatically. This suit will be much speedier than flying in clown shoes, yet it will fly at maximum L/D possible. Yuri Android+Wear/iOS/Windows apps: L/D Vario, Smart Altimeter, Rockdrop Pro, Wingsuit FAP iOS only: L/D Magic Windows only: WS Studio

Exactly! Maybe someday Phoenix-Fly and BirdMan will sell special clown shoes with depleted plutonium inserts. "When Performance Matters"... Android+Wear/iOS/Windows apps: L/D Vario, Smart Altimeter, Rockdrop Pro, Wingsuit FAP iOS only: L/D Magic Windows only: WS Studio

As soon as I felt the quietness of the air, I stopped leaning forward hard to go for speed and started flying more relaxed, in a totally flat body position trying to keep this wonderful quietness. So I stopped accelerating and instead entered the slow flight mode. It turned out to be also the best glide mode. After 35s into the flight, I stopped really flying and was looking for the place to land. I stopped looking down between my legs and looked forward. Arched body position lead to decreased forward speed and increased fall rate. At 44s into the flight, I closed my leg wing to slow down before the deployment and at pull time I was falling more or less straight down. Android+Wear/iOS/Windows apps: L/D Vario, Smart Altimeter, Rockdrop Pro, Wingsuit FAP iOS only: L/D Magic Windows only: WS Studio

I totally agree. Since human body was not created to fly, our CM is probably too much forward relative to wings (especially for those with big brains ). It's like your plane with CM at the forward end of that 7-inch range. You still can fly, but you have to trim the plane excessively with the tail, making it overall less aerodynamic. Same with wingsuit: we think that we can max it out just by adjusting the body position, but we might still be outside of that perfect trim. Yuri Android+Wear/iOS/Windows apps: L/D Vario, Smart Altimeter, Rockdrop Pro, Wingsuit FAP iOS only: L/D Magic Windows only: WS Studio