Round Openings with Diapers

[TomAiello 26]

I'm looking for info on the opening altitude required for a diapered round. I know that this will vary with the particular round. I'm more interested in what happens when you put the diaper on, in terms of how much more altitude is used than with no diaper.

Basically, here's the situation:

I've got around 100 jumps on rounds. Virtually all of them have been from about 500', with no diaper (and a rubber band pushed down over the apex vent).

If I use the diaper on a round that I'm already familiar with, how much slower will the opening be?

For comparison, I'm using (among others) a Phantom 22. It takes about 200 feet to open in this situation. If I diaper it, and jump it from the same altitude as a go and throw, am I going to snivel into the ground (water, actually)?

Thanks for any help!

-- Tom Aiello

Tom@SnakeRiverBASE.com
SnakeRiverBASE.com

[riggerrob 643]

Excuse me while whip out my copy of Theo Knacke's "Recovery Systems Design Guide"
Hee!
Hee!
Sorry, but it is not beside my computer.

My knowledge of round canopy is biased towards the pilot emergency parachute market with deployments considerably faster than 100 knots.

And sorry, but I cannot give you exact numbers, because the whole process of deploying round canopies is a highly variable process.
The primary function of a diaper is to stage openings, ensuring that lines are tight before the skirt catches air, reducing confusion and inversion type malfunctions.
A large part of the problem is that round canopies have very little spreading force at the skirt, when they reach line stretch.
The worst case - without a diaper - is for part of the skirt to blow under and try to inflate outside, on the wrong side. This type of Mae West malfunction led to the "line over" mis-nomer.
Diapers seem to increase in importance as airspeed increases (i.e. greater than 100 knots).
Some diaper designs are better than others, with the Type 3 diaper installed on Phantoms being the worst. I distrust Phantom diapers because they place the skirt cross-wind at the critical phase of diaper opening. The other problem with Phantoms is that they are essentially low-speed canopies, but are frequently "operated outside their envelope" by pilots of high-speed airplanes.
I suspect that one reason diapers have not been used more in the BASE community is the weight of all the lines distorting the canopy. Maybe you should re-visit Type 2 diapers that only have two or three stows (ergo minimal additional weight) on the diaper.
Another avenue I would explore - for improving opening reliability and speed - is some sort of Webb chute. Webb chutes are basically, soft, hand-deploy pilot chutes suspended at skirt level, to increase spreading force. Butler Parachute Systems incorporated a Webb chute into their BAT Sombrero slider.
Because of the unpredictable nature of round canopy deployments, I would test any new design hundreds of times from airplanes before jumping it off a low cliff.