Re: [rss_v] Are manufacturer canopy sizing recommendations quite conservative?
In reply to:
Given how rare it is to find second-hand canopies over 200sqft (even 190s are uncommon), I could be waiting a long time to find anything a bit bigger. I have a decent offer on a Sabre 2 190 which Iím tempted by, but my first thoughts were that I ought to take something a bit bigger. A chart Iím looking at here suggests I stay on 210s and 230s until Iíve got over 200 jumps or so, and PDís Sabre 2 sizing chart recommends a 190 for only "advanced" and "expert" jumpers of my weight range.
Are my instructors and others being reckless in saying that a 190 is ok?
Yes. A 230 is the best idea.
Most skydivers think we're special snowflakes all unique with our own strengths.
This leads to the canonical new skydiver advice to "listen to your instructors" "who've seen you fly" when it comes to down-sizing, the implication being that those instructors can some how recognize skydivers' specialness and approve of more aggressive downsizing protocols which is complete crap.
People should be sizing their canopies based on the worst possible situation:
It's the sunset load, cute chicks flash the pilot for extra altitude, some one in your group gets hypoxic and catches their foot on the seatbelt so you take forever to climb out, you have a long spot so you're landing off, and the low light means you don't see power lines until you've almost on top of them so you make a low turn to avoid them for a down-wind landing on an asphalt road.
not the sunny-day scenario of into the wind in a sunny wide-open field that's neither hard nor taxing and gives skydivers an incomplete picture of their abilities.
Instructors and a skydiver could only observe that they're ready for a premature down-size if they're getting into such situations on a regular basis and handling them successfully. Either that hasn't happened and there's no basis for the special snow flake recommendation, or the skydiver in question is short bus special in the judgement department and shouldn't be downsizing faster.
Other sides to this are operating at a sufficiently low mental arousal level, developing muscle memory, and learning situational awareness.
People perform best in situations that are stimulating enough that they're not falling asleep, but not unfolding so fast that they're overwhelmed where things like freezing become common. Premature down-sizing makes it easy to over-stimulate yourself and do incorrect things like hanging onto a front riser or two until impact. You need enough jumps in slower situations with bigger canopies to get used to it so that's less likely to happen.
Although you can almost yank controls as far as you'd care to with impunity under larger parachutes, canopies get more sensitive to control inputs as they get smaller, whether intended or not. People with too few jumps on intermediate sizes instinctively make the big movements which worked on large canopies but turn little ones into the ground at unsurvivable speeds.
Situational awareness means you've been doing things long enough to notice that things aren't right hundreds or thousands of feet before you're in a dangerous situation. People need to ease into things, with a hundred or few jumps on the next larger size and easing into larger turns making it easier to notice what's wrong so they're less likely to hang on controls until it's too late.
Following Brian Germain's 1.0 + .1/100 jump wing loading formula (with more complications) seems to work well on those counts and combined with practicing the skills enumerated by Brian and Bill von Novak radically reduces your chances of ending up in the incident reports.
Instead of telling skydivers to follow their instructors' advice which probably won't be based on enough information and allows people to ask around until they get an answer they like we should be telling them to follow Brian's writings unless complicating factors (bad depth perception, poor accuracy, not flaring far enough to avoid running, etc) noted by them or some one else suggest they be even more conservative.
(This post was edited by DrewEckhardt on Aug 18, 2012, 1:18 PM)