Dec 10, 2001, 4:16 AM
Post #1 of 7
Using Rear Risers
Another technique question, this one is on using rear risers. I guess the basic question is, "How?" When do you get on them? Do you use them or your toggles to plane out? Do you ever release your toggles? How much do you use? How do you terminate the approach? Do you release rear risers and land with toggles or do you land with rear risers and toggles in hand? Downside to using rear risers? Just to keep in the spirit of DZ.com, I have attached a Candadian $20 for payment.
The best is rear risers to plane out and surf, then the last part of your landing go to the toggles. No, Never release the toggles.
I'll tell you why this is Very dangerous though. If your a pilot, you will understand Angle of Attack. That is the angle the relative wind is hitting the wing (parachute). A wing will stall at any speed, even very high speed, if that angle of attack becomes greater than what the wing is designed to fly at. When you land with the rear risers, you are only changeing the angle of attack of the wing. If you are too deep in the corner and give it too much rear riser, the parachute stalls, and you keep going down. The only way to recover is get the wing flying again, that is let up on the rears. That will likely not be a pleasant option. You crash. All you can really do is dump the rears and stab with the toggles, but it will probably be to late anyway. We have a video of a guy doing this. The canopy was starting to plane out, then it just quit flying, although fully inflated, and he just biffed into the water. His shoe almost hit the camera man. Funny, but only because it was over water...
Planeing out with a toggle is different. Again if you are a pilot, you know about the Chord of the wing. The greater the Chord, if you can put it like that, the greater the lift. It is a line between the leading edge and the trailing edge. When you pull down the rear of the canopy (with the toggles) you increase the chord. This results in greater lift, which will swing you forward and start lifting you back up. It is much harder to high speed stall with toggles. With the rear riser flair, you don't increase the chord, only change the angle of attack. With the toggles, you don't change angle of attack, much, just increase chord, and lift.
I'll add my 2 cents here. I think the best is that the canopy has already nearly completed planing out on its own before using the rear risers to adjust the aoa for the best glide with the least increase in drag. Very tricky stuff. When you do an aggressive, carving front riser/harness turn, the canopy will want to plane out on its own when the risers are fully loaded and you ease back to neutral positions. Do it too high in the recovery arc and the canopy will plane out by itself....too high for a good swoop. Do it too low and you will have to either induce excess drag from the brakes (reducing the swoop) to plane out before chowing in or play Russian roullette with the risers (inducing a dynamic stall). I think the rest of James' reply explains the dynamics pretty well.
When he said "chord", I suspect that he really meant to say "camber."
Chord is fixed when they cut the ribs. The PIA definition of chord is measured in a straight line from the leading edge to the trailing edge. Chord ignores any curvature in the top or bottom skins.
Camber is the curvature of the airfoil. In practical terms, camber is a series of points half way between the bottom and top skins. Camber - at full flight - is fixed when they cut ribs. However, camber can be changed by pulling down on suspension lines. Pulling down on steering lines only changes the camber of the rear 25% of the canopy, but since it has the longest travel, is the most forgiving and easiest to learn. Pulling down on front risers changes the camber of the front of the canopy, decreasing lift. Pulling down on rear risers may change camber a bit, but mainly it flattens out the angle of attack.
Angle of attack is another whole discussion.
On a more general note, would posters please specify which class of canopy their advice works best on?
hmm. Ya, camber is probably the right term. I don't know much about building wings, or parachutes.
To be specific. When you pull down on the toggles, you change the chord line. That is, the chord line moves farther away from the top skin (Chord line is an imaginary line between the leading and trailing edges). It is also the line or direction, the parachute travels when it has 0 degree of angle of attack). So the toggles change the shape of the wing (camber) and chord line. The toggles then effectively change the angle of attack. Not because you move the wing (parachute) in relation to the wind, so much, but because you re-shaped the wing. They pretty much leave the leading edge the same, in relation to the wind, but bring the chord line down, because you brought the rear of the parachute down. That increased camber results in a dirtier wing that, although will have more drag, will also have more lift, and a slower stall speed.
That was the point. Pulling rear riser doesn't change the shape of the wing. Since it doesn't change the shape of the wing, the wing itself doesn't have an increased amount of lift. Because of that, you can easily stall the puppy, even if you are cooking.
Pulling the toggle is different. It changes the shape of the wing, camber. That results in a wing that has an increased amount of lift, for a given airspeed, and will also stall at a slower speed.
So, when in doubt, stab the toggles. If someone is trying to land on rear risers, realizes he is low, or not coming out the dive, more rear riser will do nothing for him. Many a pilot in WWII killed himself because he dove away from the enemy, came out of the clouds, or whatever, saw the ground and jerked back on the stick. That resulted in the high speed dynamic stall. Pulling back on the stick more does nothing.
That is why I expect some incident reports this coming year, as people hear more about this "new way to swoop". People will hear the pro's are using the rear risers to swoop farther, try it, get low, pull more rear riser to "save" it, and just bury themselves. Scary and sad.
So carefull with it. The whole point of a rear riser swoop is to not increase the drag of making your wing "dirtier", or slower flying because of the increased camber and lift the toggles provide. But at the same time, if you are trying to land with rear risers, and you give it too much, but not enough to fully stall it, you are creating turbulant air on the top skin. That turbulence will slow you down, too. So any gain you may get may be lost, with way decreased margin for safety.
Anyway. I probably typed this more for myself and own mental musings then anything else. But whatever, cool forum.