I hope Tom doesn't get upset at me for passing on some of the
information about his chute deployment after his 450mph WOS 2000 run. " The
high speed parachute deployment shows up as a spike on the accelerometer
about 6000 feet after shutoff, right passed the 6 mile marker as your video
shows( Herbie Furgusons) at 370mph. A shade fast but not so much that it
should have failed the riser. That chute had been deployedat close to 380mph
during speedweek 98 without any problems. The second high speed chute shows
up at under 350mph about 3/4 mile further down the track. The riser failure
on it looks like it may have tangled into a knot which effectively strangled
it to failure. These chutes are being modified to include a front coverpanel
to keep the canopy contained until they are streamed out with line tension
established before the canopy inflates to reduce shock loads applied to the
risers. The low speed chute will be replaced with a ribbon style canopy to
maybe survive the back up highspeed scenario better. The risers will be in
deployment bags to stretch them awayfrom the carand prevent tangles and be
made from stronger materials than the broken ones."
. L>Kvach Butters in N.Idaho with winter breathing down my neck and only
1/2 the wood I need for the winter in the wood shed
----- Original Message -----
From: Nafzger <nafzger@vtc.net>
To: <land-speed@autox.team.net>
Sent: Sunday, November 05, 2000 9:29 PM
Subject: Re: Parachute
> Wes,
> I may be wrong, so check me out but I believe Ed Tradup used a Kevlar
> towline a few years back and had failures with it because it lacked the
> shock absorbing qualities of a PROPER nylon tow line. I had chute problems
> at Speedweek this year and Jim Diest spent quite a bit of time working
with
> me on it. He has a computer program that considers speed, weight,
altitude,
> etc. and determines fabric porosity and strength, area of canopy, and tow
> line size requirements based on a 150 percent safety factor. Some of these
> cars are going so fast that anything less than that kind of information is
> dangerous.
> This is not a paid commercial for Jim and I hope I haven't said anything
I
> shouldn't, but I am following his advise from now on. I took two trips to
> the 8 1/2 or 9 this year and did some damage to the car. I don't like that
> very much.
> Howard
>
> ----- Original Message -----
> From: "Wester S Potter" <wspotter@jps.net>
> To: "Nafzger" <nafzger@vtc.net>; <land-speed-digest@autox.team.net>
> Sent: Sunday, November 05, 2000 9:13 PM
> Subject: Re: Parachute
>
>
> > Howard, List,
> >
> > One of the things that has disturbed me has been seeing the main tether
> snap
> > and leave the canopy fully deployed but just staying there. In that
case
> > the size of the chute and vehicle speed determine the pull on the
tether.
> > If the canopy can come out and stay deployed it can handle the pressure,
> > just makes me wonder what type of tensile strength is needed to hold it
to
> > the car. Having done some fiber tensile strength testing at much lower
> > pressures I know that there are some fibers and yarns that are very much
> > stronger than others. In this case the flexibility is a factor as is
the
> > way the fibers are twisted into a yarn/thread. When the tethers snap as
> > cleanly as they did on Burklands's car or on the Hoffman/Markley car a
few
> > years ago there has to be some way to strengthen the fiber in the tether
> and
> > prevent it. The fibers were only shredded over a 3/4" length, a pretty
> > clean snap. Obviously they were the same strength across the width of
the
> > tether. If there were some other fibers such as a carbon fiber that
were
> > core spun with the nylon in the tether, that would result in some
stretch
> > and a tear at different places along the line, not all in the same exact
> > area. This might help to save the line and keep the chute on the car.
> > Nylon is stronger on that kind of a tug than a steel wire of the same
size
> > and I'm wondering if carbon fiber could be strong and flexible enough to
> do
> > the job.
> >
> > I'm guessing Jim Diest will suggest two things about the canopy, either
a
> > way to allow less air to be captured at the speed in question, a smaller
> > canopy probably, or a ribbon canopy that will have slots to allow the
air
> > through. The ribbon will be more easily damaged and the smaller canopy
> > won't slow the car as well. Dragging a chute over the salt can't be
good
> > for the fabric either way. The "slow" speed chute on Burklands car was
in
> > ribbons, obviously the tensile strength of the fabric was not up to the
> > task. The military contractors developed ripstop nylon for that
> originally
> > but the weight of the canopy as used in military applications is a much
> > higher tensile strength and a heavier fabric. A jeep also has a
different
> > problem with canopy depoyment coming out of an airplane and only
freefalls
> > at around 147 mph anyway. Even the space shuttle isn't as hot as these
> > liners. Burkland is using compressed air to kick the chute out of the
> tube
> > so I'd guess deployment isn't the problem. He is using the clamshell
air
> > brake then three chutes in sequence, Perhaps the triggers are set at
too
> > high a speed for the canopy size.
> >
> > Maybe if Rick Vesco is right about the salt, we'll be back on the long
> > course and stopping won't be such a major problem next year. A three
mile
> > shut down is much better than what we have had the last few years.
> >
> > Wes
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