A reserve pilotchute is designed to function at terminal. A cutaway main attached to a skyhook enormously improves its perfornce subterminal. It seems the Skyhook has covered both situations. There, however, scenarios where an open canopy can be cutaway and act as a super pilotchute while the jumper is still at terminal.
1. The cutaway handle is accidently pulled on exit or in freefall, the jumper deploys the main, the riser covers hold long enough for the canopy to come out of the bag and partially inflate before separating from the harness. This has happened at my DZ.
2. The jumper deplys the main, has a hesitation, goes for the cutaway handle as the pilotchute lifts off, cuts away just as the canopy comes out of the bag. This is a relatively common malfunction.
3. The jumper experiences a baglock. Just on cutaway the canopy comes out of the bag.
In these scenarios the jumper has not been decelerated by the main but it will be at least partially inflated as it lifts off. If there is a skyhook it will act as a super pilotchute with the risk of a catastophically hard opening.
Many people think that once the resrve is out of the bag the speed of the opening is determined only by the slider. The slider is critical for any opening but so is the pilotchute. BASE jumpers know this and have a variety of pilotchutes for use on different delays. RWS knows this so their drougues collapse on lift off so as to have just the right amount of snatch to lift the bag at optimum speed. If your kill line shrinks on your sport rig not only do you get slower bag lift off you get slower inflation.
A big pilotchute gives a harder opening because the bag is more rapidly decelerated. At the moment the canopy comes out of the bag the speed difference between the jumper and the canopy will be higher and therefore the load on the lines will be higher. That means the initial snatch will be harder but force on the lines also contributes to the next stage of canopy inflation.
Lets say standard bag lift off takes one third of a second. That suggests the bag is travelling at about 45 feet per second slower than the jumper. 135 ft/s vs 180 ft/s.
A fully open canopy with a suspended jumper has a descent rate of about 15 feet per second. A cutaway canopy with only a reserve freebag hanging under it will have a descent rate somewhere between 135 ft/s and 15ft/s depending on the degree of inflation. It d doesn't need to be inflated much to increase the speed difference between the jumper and the bag by a factor of 2 or 3 and possibly as much as 6 compared to a standard pilotchute.
Surely this creates the possibility of a severely hard opening. As I write there are 2 jumpers out of action at my DZ with injuries caused by hard openings with standard pilotchutes. The prospect of superhard skyhook openings has not been fully investigated.
I would like RWS to demonstrate that I am wrong by conducting a few tests along the lines of the following: Pack a main with no bag. Disconnect the risers but connect the skyhook. Throw it out with a heavy weight (please don't use a real person!) and either have a jumper or an aad dump it out. There are gadgets out there to measure the forces on the reserve opening.
To really ensure the main opens before popping the reserve try it with the slider down. Try it again with 10 or 20 pound break tie btween the risers and the harness.
The skyhook is like a wonder drug that can cure certain diseases. In this case low cutaways and unstable cutaways. The vendors of this wonder drug have an obligation to test for side effects that may be just as bad as the disease they hope to cure.
RWS's response was very poor to problems raised concerning the tandem fatalities in Guam and Tokyo where the skyhook was suspected of failing to clear the velcro running down to the RSL when bag locks were cutaway. These situations ended with main reserve entanglements.
One can only suspect that a huge investment in development and marketing won't be jeopardized by the small matter of safety
