From: traurig@ncavax.decnet.lockheed.com (Scott Traurig)
Subject: Re: AAD cutters vs. pullers
Followup-To: rec.skydiving
Date: Tue, 12 Jan 93 14:37:53 GMT

In article <1993Jan11.165808.28463@newsgate.sps.mot.com>,
beutel@chdasic.sps.mot.com (Jim Beutel) wrote:
 
> Am seriously saving for some type of AAD unit for my rig.
> The three contenders are Cypress, FXC, Sentinel. I have 
> a twin pin reserve in my rig. 

     Get the Cypress if you can afford it, otherwise get the Sentinal. The
FXC is too big, heavy, and inaccurate for experienced jumping. This is, of
course, just my personal opinion.
 
> Any input out there on cutters verses pullers...?

     Pyrotechic cutters are smaller and simpler than pyrotechnic pullers.
Both are much smaller and less complex than mechanical pullers. If you want
a pyrotechnic line cutter then the Cypress is your only choice. If you want
mechanical then the FXC is your only choice.

> Having two pins only doubles the issue for me. When I 
> am ready to buy a brand new rig, it will be a single pin.
> In the mean time however, I feel it would be safer pulling
> the pin a small half inch back from under the loop. The cutter
> I would think, stands a fairly good chance of NOT actually cutting
> the loop. It only gets one shot at it I believe. It is not like 
> cutting a steak where you can cycle the blade back and forth.....

     Pyrotechnic line cutter technology is very mature. We've used them for
years on a variety of military airborne towline applications.  They are
simple and powerful. The Cypress unit, the only one so equipped, has a
cutter that is way overpowered for the application.

     I would actually worry more about using a pyrotechnic or mechanical
puller. They are more difficult to install properly because they must be
rigidly affixed in the proper place such that the required pulling force
and length of pull is generated.  There is also the possibility of
misrigging the ripcord/puller assembly so that the ripcord and/or RSL
interferes with the operation of the puller. With a cutter you only have to
remember to thread the closing loop(s) through the hole in the cutter(s).
Finally, there is little variability in the resistance to cutting of kevlar
or dacron closing loops, allowing accurate engineering, while a tight
reserve pack job can result in a hard pull for both the ripcord and the
puller.

> Also, if the loop is cut from inside the reserve container, such
> as the Cypres design, what are the possibilities that the loop
> may hesitate from feeding its way out..? Any delay at under 1000
> feet is not exceptable.

     That loop isn't going to hesitate any more than if you pulled the
ripcord.

     There is an excellent review of all the available AAD's in the January
Parachutist. There is also a small review of the Cypress in the January
Skydiving, and there's that very informative Cypress advertisement in the
December Skydiving.

     Finally, it seems that all of the available AAD's are more than
accurate enough. If you maintain it and calibrate it properly before each
jump, it isn't going to go off unless you are dumping or about to dump at
an altitude you shouldn't be at (i.e. too low).  Do I have one? No. Do I
want a Cypress? You bet. Now if that Publishers Clearinghouse prize van
would just show up .... ;-)

Scott (traurig@ncavax.decnet.lockheed.com)
D-13279