paragliding training center
by Angelo Crapanzano
Recently, while speaking about rescue parachutes, Alex Ploner told me in the US there is quite a bad reputation for "diaper" deployment bags (flat pods with normally four flaps), while there is a good reputation for "envelope" ones (a bag normally opened on one side only). I already knew in the US that there was a preference for envelopes (while in Europe it is for diapers) but I didn't know it was so strong.
The deployment reliability of a rescue parachute depends mainly on the pod design; that's why I feel important to point out the differences between different concepts and, even more important, what makes a good or bad pod. I'm a manufacturer and of course my own design is my preferred one (otherwise I would make it different), but I'll try to be as general and objective as possible.
In a good deployment bag, we need to have: easy extraction from the harness very low risk of accidental deployments, lines stowed inside the pod before deployment, ease of throw, very low risk of untimely opening, easy opening of the pod, staged deployment sequence.
1) An easy extraction may concern more the harness parachute container design than the pod itself. We need to have a big enough handle (remember it's always easier and safer to catch the handle using the thumb) and reachable with both hands (one could be injured or one hand could be better than the other in case of a spin).
The use of Velcro to keep the container closed is not reliable: often holds too little or too much. The Velcro should also be avoided to keep the handle in place because if the pilot, at first try, peels out the Velcro but misses to catch the handle, then the handle could become unreachable (this is especially true in paragliding for dorsal mounted parachutes).
Be extremely careful there is not male Velcro on the handle itself: it may have stuck on the lines loop holding the pod closed, thus impeding the opening. It's not only a theory: I've seen this happening during parachute clinics and, unfortunately, a German pilot died in Castelluccio di Norcia a few years ago, because of it.
There is one way only to know if your parachute is easy enough to extract: hang into your harness and try! Don't be too much surprised if you cannot get it out: during parachute clinics I've seen several pilots not at all able to extract their parachute.
2) Low risk of accidental deployments means the parachute must not come out by itself. The biggest improvement on this subject were the safety pins (introduced in the hang gliding world long time ago by Rich Pfeiffer) used at first as a safety for the Velcro but, if properly designed, are perfectly safe by itself. In some cases, one could add an elastic or a sewing tread to hold them in position (check you are strong enough to break it pulling the handle!).
Be sure there is no way for the handle to get tangled in the side cables or in the base mounted instruments (there have been several accidental openings this way). Be also sure the pins are not too long (longer than the slack in the handle) otherwise there is no way to pull the parachute out of the container. Pins should be properly curved or flexible (straight pins could stick if pulled in the wrong direction, as shown in several accidents) and be careful the head of the pin cannot pass through the loop (there have been several accidents this way too).
3) The lines stowed inside the pod before deployment are mandatory to reduce the chances of lines getting tangled into the wreckage (one line tangled is enough to get the parachute useless). Unfortunately, there are several old pod designs where the lines are exposed.
4) The ease of throw depends on parachute weight but also in handle shape and length. A long handle makes it difficult to control the throw and could tangle on cables (some handles designed as an anchor don't certainly help). A handle attached to the pod in two points gives a more solid hold compared to the, unfortunately now common, single point attachment.
Never attach the pod to the canopy: to save some dollars in case of deployment, you definitively increase the risk of a tangled parachute!
5) Low risk of untimely opening means the deployment bag shall not open before you throw it and let it go. This can easily happen in an old-style envelope pod where the handle is in the opposite side of the opening because only the elastics are holding the canopy inside the bag: if they are too old or weak the canopy will fall out before one throws it while, if they are too strong, the pod would be hard to open.
A good envelope pod design is to have both the handle and the opening on the same side, so the elastics don't have to hold the weight of the canopy. On some diaper pod designs the canopy or the lines can fall out if one shakes the pod (still holding the handle). In any case it's important to leave the right amount of slack in the bridle: the pod must not open until you let it go!
6) Easy opening of the pod is mandatory because, in case we cannot throw it forcefully (much easier to say than to do in reality), there is only the difference in sink-rate between a broken hang glider and closed pod to open it. Please note that, in most common accidents, the closed pod falls faster than a broken hang glider or paraglider.
In case both glider and pod are falling at the same speed there is still the aerodynamic drag on the bridle which could open the pod. It's clear we are never speaking of big forces, so we need to have the pod open with a very light pull.
7) The correct staged deployment sequence is: bridle – lines – canopy. We first want to have the bridle coming out because we want the pod (still containing lines and canopy) to go away as far as possible to reduce the risks of entanglements. Then we want to have the lines, and finally the canopy must come out only when bridle and lines are stretched. This is the best way to reduce the chances of canopy malfunctions and to reduce the opening shock on the parachute. In a well-designed pod, regardless of the strength of the elastics, the lines shall not come out until the bridle is stretched and the canopy shall not come out until the lines are stretched. Speaking of lines and bridle, I would like to point out that we need:
- long bridle to reduce the chances of a tangled parachute,
- long lines to get better sink-rate and stability from the same canopy
- a shorter sum of lines plus bridle to get a faster opening time (it looks impossible at first, but there is a clever solution to this problem).
IMPORTANT: To check out the extraction, hang into your harness, put your thumb into the handle, grab it and pull it out slowly: the pod must come out effortlessly.
To check out a pod for untimely opening, while still hanging, stretch your arm sideway to check the slack in the bridle, then shake the pod without leaving the handle: the pod must not open.
To check out if a pod opens easy enough, put the pod on the floor then pull up slowly on the bridle and then the lines: the pod must open easily without lifting the parachute and the canopy must get out easily. The deployment sequence, during the previous test must be: bridle – lines – canopy and must be correctly "staged" (should be the same regardless of the relative strength of the elastics used).
This simple test doesn't take more than 10 minutes (plus repack, which is always useful to get a fast opening) but it could save your life.
While you are there, check out how old is your parachute: if it's more than 10 years old consider replacing it. An old parachute behaves exactly as a new one, of the same model, if you are going to deploy it at low airspeed. However, parachute fabric is quite sensible to aging and ultraviolet rays: an old parachute cannot withstand the same high speed as a new one.
If your deployment bag doesn't work as it should, fix the problem if possible (and check it again!) or, much better, have an expert professional check and fix it (but check what the professional is doing too. It's your life which is involved!).
I practically didn't speak about the differences between envelope and diaper pods because it's not very important. What is important is that a pod works in the correct way and you can get it both with an envelope or a diaper one. Remember:
- Pods which don't stow the lines inside increase the chance of a line getting tangled.
- Old style envelope pods with the handle on the opposite side of the opening are dangerous because, in case of warn-out elastics, the canopy can easily fall out untimely (it happened to Gerard Thevenot: the pod came out of the harness but the parachute stayed inside!)
- Pods without a correctly staged opening sequence, bridle – lines – canopy, increase the risk of entanglement and malfunctioning.
Well, of course, I do prefer my 5 flap diaper pods because they fulfill all the previous requirements (as a good envelope one) but are "softer" to better adapt to the harness container, require less force to open and, when open, immediately let the canopy become fully free.
If you ask a good American manufacturer I bet he would agree on everything... except the last sentence :-)
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