Speed and Collapses

David C.
Tucson, AZ

Fri Sep 19 22:00:53 2003
68.84.206.22

Tonight, conditions were just about perfect for the long awaited collapse tests with trimmers in and out, as suggested by Scott.

I donned my reserve and climbed up to 1500 feet or so with trimmers in, killed the engine, reached up and grabbed the left A-riser and pulled it down to initiate a 50% collapse of the left side of the glider. I did this several times and noted the amount of effort required to collapse the glider and hold it in, the tendency to turn, and the nature of the reinflation. Then, I let the trimmers all the way out and repeated. For reference, letting the trimmers out speeds up the glider beyond nominal trim by maybe 5 mph. Pulling the trimmers in all the way is the nominal glider trim. Here are my observations:

1) It takes more effort -- that is, downward force on the A-riser -- to collapse the glider with the trimmers out (sped up). This is contrary to conventional paragliding wisdom, but true nonetheless -- at least on my glider (Mac Para Eden 2 HDTV 1-2).

2) Once deflated, the glider falls off in a turn toward the deflation more quickly, further, and turns at a more rapid rate with the trimmers out (sped up).

3) The reinflation is definitely more radical -- the glider reacts more quickly and surges more quickly and further out in front -- with the trimmers out (sped up).

4) With the trimmers in (nominal speed) a 50% deflation is no big deal at all. With the trimmers out, get ready to brake the reinflation.

Ever since solving various dangerous tendencies of my old Edel Confidence glider under power by speeding the glider up, I have had strong opinions about this. I have also watched other pilots struggle until speeding up their gliders. For those motor pilots launching from flat ground with difficult gliders to get overhead, the safety margin gained during launch by speeding the glider up during takeoff, in my opinion, more than offsets the additional risk of a radical reinflation near the surface associated with the very remote chance of a major tuck in the laminar conditions motor pilots fly in. I have seen this with various gliders and pilots in Tucson and elsewhere.

In mid-day air -- all bets are off.

But here is the best policy -- buy and fly a glider that does not have even a slight tendency to hang back while launching with the motor. I've flown a few and can tell you some that do and some that don't. The launch category of DHV reports that say "comes directly overhead" means nothing when it comes to launching on flat ground under power. The differences in gliders are huge in this respect -- like night and day -- and the differences in the "enjoyment factor" associated with launching and flying are tremendous.

If purchasing the right glider isn't in the budget, then purchase motor risers that allow speeding up the glider beyond nominal speed for takeoff and slowing the glider to nominal speed in turbulence. The last resort is tying the speed system on about 1/4. This has worked for me in the past with my Edel Confidence DHV 1-2. Indeed this made the glider safe to fly since, in addition to unsafe tendencies during takeoffs, it was prone to enter a "spinnaker mode" and descend rather rapidly under full power in the right conditions. I have seen this work for other pilots, as well.

For what it's worth.

David