OK guys, since my car was the reason to re-start this thread let me give you
all some background. This is a very complicated situation. And requires some
experimentation in order to sort thing out.
As some of you have mentioned LSR cars are different that Drag cars and
there are many reason why what works on one does not work on the other. My
personal belief is that weight and aerodynamics plays the major role in
this. Our cars are usually more aerodynamic and much heavier. Here's my long
story, and I'm open to suggestions.
My car was originally built with a Mustang II body as a chopped top Comp
Coupe. Using a Simpson 12' crossform drag chute, standard tether line.
Everything was fine, safe and secure after repeated 200+ MPH runs. The
problem came up after I changed the body to a Chevette, same chassis. Now,
for what ever reason, probably an aero issue, using the chute at high speeds
caused the car to turn left and slide until the chute drag would pull it
straight again. It was later reported that the chute goes up in the air at
about a 45 deg angle, which probably unloaded the rear off the car. Remember
the ONLY thing changed here was the body.
Here's what I tried to solve the problem after discussions with various
manufactures and racers:
Raised spoiler angle to create turbulence, no change.
Tried Stroud drag chute, approximately 10' diameter, no change.
12' tether line extension, no change.
Smaller 8' crossform chute, now sometimes whips back and forth.
30' tether line extension, better chute angle, about 30 degrees now, no
whipping, but still have problem.
Raised chute mount (as per Jim Diest) by 12". Problem is now worse as
the car pulls right and won't pull back when the chute is open.
With this particular car "everybody" is guessing. Obviously the air behind
the new body is going up in the back and taking the chute with it. Would
love to see that in a wind tunnel. Must be a ton of drag. How much faster
would this car be if the air came together smoother?
We had made the decision to go for a longer tether, 60' to 80', along with
lowering the mounting point back to the original location, when Joe made his
off road excursion. I personally feel this will solve the problem. We need
to get the chute to deploy well beyond the weird air behind the car. I don't
see any other solution. As Joe mentioned we are also going to be working
with Bob Stroud to solve the problem and will keep you all posted on
results.
Another part of the problem here, is the time it takes to experiment. I've
learned that each and every car is different in LSR. Bonneville is a
relatively safe place to experiment with these issues (wide open space), but
the time (typically once a year) and the seat time factor is a problem. If
we raced more frequently (as typical drag racers do) we could sort these
problems out much sooner and our collective (LSR) learning curve would be
quicker. Maxton offers us Easterners six time a year to experiment, but due
to other engine problems we were dealing with we didn't get the time to
investigate the chute problem as we should have. Obviously we should have
addressed the chute issue first, but with a typical racers mentality we
concentrated on going fast instead. In retrospect a poor decision.
So that's the story.
John Beckett
----- Original Message -----
From: "Glen Barrett" <speedtimer@earthlink.net>
To: "DOUG ODOM" <popms@thegrid.net>
Cc: "Wester S Potter" <wspotter@jps.net>; <land-speed@autox.team.net>;
"Jonathan Amo" <webmaster@amoproductions.com>; "Keith Turk" <kturk@ala.net>;
"John Beckett" <landspeedracer@email.msn.com>
Sent: Sunday, November 05, 2000 11:18 AM
Subject: Re: Parachute
> Hi List
> Last tuesday night this drag chute issue came up again on the chat line.
As a
> person that see's every run on the dry lakes and at Bonneville from my
seat in the
> timing trailer I would once again say a couple of things.
>
> When the chutes first started coming out in the early sixties on the salt
it was a
> guessing game as to size, mounting, weather to pull it under power, or
during
> decelaration, how long the tow line should be etc.
>
> Jim Deist has more experience then anyone on high speed chutes. He was the
key
> player for a lot of the pioneers on the salt and the lakes. The drag
racing scene
> is a whole different world. The cars are basically the same by class
design, and
> are under different course conditions. Our courses are 1 3/10 long on the
dry lake
> to 13 miles long on the salt.
>
> The winds can very from a cross wind to a tail wine from one run to the
next on
> the dry lake. At Bonneville along the long course from start to turn out 7
miles
> down the course the wind, depending where you are can be blowing different
> directions as you make the run
>
> Other then the typcal questions and many answers about chute mounting, tow
line
> length, size, type of canopy the other thing that is a critical factor is
taking
> proper care of the chute during and after the exent.
>
> The conditions we run under are far different than drag racing. So forget
about
> drag racing. At El Mirage and Muroc we run under two differnt kinds of
desert
> dirt. The dirt at El Mirage is more gritty and at Muroc a fine talcum
powder like
> base. Muroc is more dificult to get rid of on anything. El Mirage is dirty
but can
> be cleaned a lot easier.
>
> Now Bonneville is a different story all together as far as chutes. There
are
> vehicles that only run on the salt and the chutes and maintaing them are a
little
> different. The salt can be very dry as the this year or wet as past years.
> Regardless the chute must be clean, dry and properly packed to function
well.
>
> We in the tower see some very scarry chute deployments and some picture
perfect
> ones. Some come out in a blob and bounce along the course, others fly high
and
> whip or lift the back of the car off the ground, some spin and choke the
canopy
> down, and some simpley drop the pilot chute out and nothing happens. A lot
of
> times a small burr on the release cable will not pull through the nylon
loop,
> other times the chute pack is dirty, wet or starched with salt and let dry
in this
> condition.
>
> Simply rinsing out the chute will not always assure the chute is going to
work. I
> have seen on several occasions chute panels rip and cause the car to veer
off
> course. he main reason is the panels when folded are not dry and the seams
or fold
> with the starch effect allows the tear to start a little easier.
>
> At El Mirage because the events are smaller and closer to everything as
well as
> almost every run on video tape the drivers can see whats going on with
their car.
> We in the tower make note of anything unusual and then notify the crew in
the push
> truck and the inspectors. There have been several cases that we could see
daylight
> under all four wheels on cars. Short tow line, mounted to low, canopy to
large for
> vehicle, it goes on and on.
>
> The driver don't always know whats going on as he is busy getting things
shut down
> ond trying to turn out. The point here is there is never going to be a
perfect
> answer to how to mount, size, tow line length etc. But we try to help from
our
> standpoint in the timing stand to let everyone know when we see a problem.
> everything is critical at speed, everything is critical on how well it's
> maintained.
>
> If you are not sure what the vehicle send a crew member down the return
road and
> have them watch the car during shut off. Get a better idea what the car is
doing.
> Don't just put on a surplus chute and think it will work in a emergency.
It won't.
>
> Get used to using the chute every run as some time you might need it when
the
> car,cockpit is filled with dust or smoke. Having to look for something
like the
> chute release is poor under these conditions. It should be automatic as is
using
> the brakes. It could save a lot of problems.
>
> If you still have questions, ask the racers who over the years worked with
the
> experts and found thie chute can be your best friend or your worst night
mare if
> not correct for the vehicle. This site can get you a wealth of information
or
> where to go for it.
>
> Glen Barrett
> Chief Timer SCTA / BNI
>
> DOUG ODOM wrote:
>
> > Wes; My $.02 worth. The big difference between drag cars and LSR cars
> > is the size of the tire you have on the ground and the weight of the
> > car. I don't know of many drag cars that run 7 or 8 hundred pounds of
> > ballast. On the really fast LSR cars I would think they would copy the
> > Air Force or space shuttle type of parachute deployment. The other day
> > on TV I saw the space shuttle land and the chute was out before the
> > wheels touched the ground but it looked like it was rolled up so it
> > unfurled and got bigger the longer it was out. Is this a way to soften
> > the hit?
> > Doug Odom in big ditch
> >
> > Wester S Potter wrote:
> > >
> > > List,
> > >
> > > This braking parachute question always leaves me wondering why the
drag
> > > racers can slow from 300 mph passes with a parachute time after time
without
> > > very many incidents. What is the big difference in slowing from 300
at a
> > > drag strip and slowing from 380 or so on the salt? I'm sure I'm
missing the
> > > point here somewhere but something is at work on tethers and chute
design
> > > for land-speed applications that is primarily solved in drag racing.
The
> > > discussion early this year on how to find the optimum point for
placing a
> > > tether connection made sense as I read it. The cars that have
problems on
> > > the salt are primarily placing that connection in the wrong place and
> > > disturbing the balance of the car at speed. I realize that drag cars
differ
> > > so little that once someone gets it right it's easy for everyone to do
the
> > > same thing. Not so with land-speed cars. The basilc ability of
getting the
> > > parachute to deploy and do it's job seems to be the same however. The
> > > tether straps are able to handle the same loads on dragsters, ribbon
chutes
> > > and the cross panel chutes hold up, what is so different on the salt?
The
> > > Burkland's car certainly had enough thought in the design area for
braking
> > > but now Tom has gone back to the drawing board to see what he missed.
> > > Obviously the deployment of the chutes was at speeds higher than he
had
> > > intended. What's the answer?
> > >
> > > Wes
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