Aerodynamic vs. vehicle stabilty

[WKM]

I have found the discussion about chutes very interesting.  As a new team with a first time car and driver, we have been relying on the experience and advice of others who have "been there, done that".

Using some of that advice during our build, we went with Stroud chutes with long tethers, the chutes came with deployment bags, but at our tech inspection, we were told to remove them.  Which we did.  I find it intersting (and confusing) that so many posts have recommended their use.

Being a new car, with so many unconventional items on the car, we were a bit intimidated with the tech process, so I didn't ask the relevent questions when told to remove the bags.  So, I would appreciate any comments as to why the gentlemen in tech would insist we not use them.

Our chutes are mounted with about a 15 degree angle, as recommended by the manufacturer, are there any cars that have run on the salt with chutes mounted straight up?   I suppose the proof is in the pudding, so I would like to hear about results they may have had with this orientation.

Kevin Marsh
RSL racing, car 7007

[Cajun Kid]

Kevin, 

Mounting angle and location "can" be differant depending on type of car.

Stroud had me send him pictures, weight and expected speed of my car when he built my chute. he also told me where he would want my chute mounted etc..

As you can see by my video in an early post a page or two back, I do use the D bag that came with the chute and as you can see it came out quick and perfect ?

Who am I to argue with the actual designer of the chute system ? as to the tech guy who said don't use the "D" bag... I have no idea why he said that.. but I would do what ever the chute mfg says to do.

just my 2 cents.

Charles

[bvillercr]

I agree will Charles, in tech they usually ask to deploy the chute to make sure it pops open.  What kind of car are you running and how fast do you plan on going?  Do you remember who the tech inspectors was?

[doug]

I have found the discussion about chutes very interesting.  As a new team with a first time car and driver, we have been relying on the experience and advice of others who have "been there, done that".

Using some of that advice during our build, we went with Stroud chutes with long tethers, the chutes came with deployment bags, but at our tech inspection, we were told to remove them.  Which we did.  I find it intersting (and confusing) that so many posts have recommended their use.

Being a new car, with so many unconventional items on the car, we were a bit intimidated with the tech process, so I didn't ask the relevent questions when told to remove the bags.  So, I would appreciate any comments as to why the gentlemen in tech would insist we not use them.

Our chutes are mounted with about a 15 degree angle, as recommended by the manufacturer, are there any cars that have run on the salt with chutes mounted straight up?   I suppose the proof is in the pudding, so I would like to hear about results they may have had with this orientation.

Kevin Marsh
RSL racing, car 7007

Just a thought...  Would the inspectors say that because they don't want the bags to end up on the track if it were to tear away?

[jl222]

Jl222,

Not sure if you watched my video ?  On Thundersalts car is he using a LSR chute like mine or the shorter lined Drag type?   

From the almost spin to saving it, looks like the chute was a major factor to keeping the car from going around,, that was most likely because of good driving, followed by quick decision to pull chute, followed by good reaction time in getting chute pulled, followed by chute deploying in good air quick enough, followed by quick canopy blossom.

I would say I listed it in the actual order of importance,  as the by the time you do all of those things in the correct order, the .8 to . 9 second LSR chute blossom to the .5 or.6 drag chute blossom is not as big a deal as one might think, a fast blossom if you don't do everything else quick and correct is not going to help,, just tear up a chute.

That's my thoughts.

Charles

  Bville has a video of Thundersalts [save of a spin] on his Utube videos. Looks like they have a short...big drag race style chute. The car is starting to spin for a while before the chute blossoms, the short lines and quick opening time[and Celia's great driving] saving car from spinning.
  It would be interesting to here the manufactures reason for long lines. My understanding is less shock to car and driver but long lines take more time to react to stop a spin.
  Watching the drags at Indy this weekend all pro classes used a spring loaded pilot chute and prostock used a spring assist behide the main chute in addition, all chutes opened extreamely fast.
  Watching the video of our 222 car on my shut off early 271 mph 21/4 run I slow for a while before pulling chute but still about 250 mph and if you watch helmet it hardly moves from chute deployment.


             JL222
 

[Stan Back]

Different cars, different parameters. 

Like a Street Roadster.  We use a Stroud chute, tailored to our car.  First time use, the pilot came out and sat on the bumper all the way to the return road.  Second time, it came out but wouldn't pull out the d-bag.  Bob Stroud sent longer tethers for the pilot and a bigger pilot.  Seems the roadster had a lot of dead air behind it.  Works like a charm now (when and if we use it.  Going only 200 plus in a Street Roadster, when you unapply the throttle, it slows down instantly.  In fact, the first two times described, we thought it had deployed as the car stopped so fast).

Wouldn't want to use it to stop a spin and wrap it around the exposed front suspention and the roll cage, too.

Stan Back

[Cajun Kid]

I was trying to use slow mo replay and and figure out haw fast the chutes deployed at Indy... yes the short lines and large canopy seem to deploy faster, but from what I can tell.. I timed prostock cars as I had a few good shots where I could see the deployment and the blossom and it was right at .6 to . 7 seconds... where my lsr chute is right at .8 seconds...  Now they are going about 195 vs me 175 in the tests,,, I would only assume if I was going 20 mph faster my chute would react a bit faster too ?? 

either way we are only talking  .1 to .2 seconds... so my point is using a chute to prevent or spoil the spin has more components to it than just the speed of the chute deployment (based on line length and canopy size)

It has many factors
1. Drivers Mental State/Awareness vs skill,experience and or luck.. (can they save the car / correct/ drive out of it, or do they abort the run ?
How long does this thought take ??

2. Once they decide to abort and pull/push the chute release , how long from that thought until they react and the hand pulls/pushes  the chute release or button ?

3, Now once they pull the chute, the chute pack mounting location and mounted angle come in to play as well  with air in the deployment zone.

4. Next is line length and canopy size to full blossom.



Charles

[thundersalt]

http://www.youtube.com/watch?v=KrJIiumxgqY
I'll just put Troy's Video of Celia here for easy viewing. It is a Simpson 12' crossform with 16' lines. Bret Kepner let us see his video through the viewfinder right after it happend and she got almost 180 degrees backwards (twice) with the chute never loosing bloom. When I spun in 07, we had a Simpson 10' with 12' lines and only got 90 degrees. Both spins were at +/- 200 mph. I do believe that a chute can save you from a 360 degree spin if you get on the lever fast enough.http://www.landracing.com/gallery/displayimage.php?pid=7548&fullsize=1
Now about aero, start and stop Troy's video when he is zoomed in and notice where the salt rooster starts.It doesn't start from the tires.

[jl222]

  Charles all your points make for a quick opening chute especially for a slow reacting driver.

  I think your off on your times especially the top fuelers at 300 mph thats 488  ft a second, at 320 mph thats 1/2 the track length and the chutes are out close to finish line and a lot don't pull the chute early.

  How fast can you start and stop a stopwatch? Its a lot easier watching a video with the seconds counting.

                 JL222

[Cajun Kid]

jl222,

Please, show me where I referenced 320mph top fuel cars. I specifically said pro stock cars at approx 195mph.....

also the main point is not the time to deployment in my examples, it is the "difference in time" between them,

more importantly it is about all the other factors that come before the deployment...

Charles

[mike mendoza]

don't forgtet the weight involved in LSR   

[SPARKY]

I am not an active inspector---but when I was inspecting and a competitor took issue with something I didn't think was right, or I saw something that I had a question about ---I always got a second opinion--usually the chief inspector.  That is what he is there for and the reason we have a "Chief Inspector".

I would recomend ALWAYS asking for the chief inspector to make a ruling---we have new inspectors at every meet and occasionally and old hand with a grouchy attitude. 

[robfrey]

I don't want to be a party pooper but I think you guys are getting off the point (of this thread) with all this parachute stuff. As far as the topic of the thread goes, deploying the parachute as a spin starts is like closing the barn after the horses are out. Let's build em aero stable and work with the SCTA with rules to make it easy for us to do just such.
None the less, it's great stuff. LOL.

[jl222]

I don't want to be a party pooper but I think you guys are getting off the point (of this thread) with all this parachute stuff. As far as the topic of the thread goes, deploying the parachute as a spin starts is like closing the barn after the horses are out. Let's build em aero stable and work with the SCTA with rules to make it easy for us to do just such.
None the less, it's great stuff. LOL.

  yea just let it spin and barrell roll with slow deployment


   jl222

[jl222]

jl222,

Please, show me where I referenced 320mph top fuel cars. I specifically said pro stock cars at approx 195mph.....

also the main point is not the time to deployment in my examples, it is the "difference in time" between them,

more importantly it is about all the other factors that come before the deployment...

Charles

  You point makes mine

 jl222