Landracing Forum
Bonneville Salt Flats Discussion => Bonneville General Chat => Topic started by: xxobuick on July 15, 2014, 08:56:43 PM
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We have a car that weighs about 4250 LBS. Wheel Base is 120". We are going after a record that is close to 175. Therefore we will probably need to have a parachute on the car. I have heard that a "landspeed" chute is different from a drag chute. The line is a longer line, to allow the chute to be a long ways from the car. Is this true? I was looking at this chute:
http://www.ebay.com/itm/231266141346?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649
It is a STT Safety, 10 Foot diameter, 8 line chute.
Will this be Ok, for Landspeed? Any opinions?
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I could not get it to come up -- but your car is 1000 # heavier than mine I run 6' diam Stroud ring chutes-- with a 45 and a 60 ft shrouds
It is very easy to lengthen the shrouds---any Parachute rigger can make you an extension you may have to enlarge the Pack
or buy and new one---mine is packed in a 36"x 6" alum irrigation tube.
The length on lsr is usually just trying to get into clean air so it doesn't kite
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What class would you run? You should call Stroud, DJ safety, or someone chutes need to be correct, it could save your life.
Don't use something just because you have it or it is cheep. Lives have been lost and your life is worth more than just the next rule change.
John
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Thats a big chute & the tow line is too short. The reason we run a longer tow line on the salt is to lessen the deflection angle between the chute & the vehicle. You've no doubt seen a drag car jerked sideways by short chute, that will likely spin a car on the salt & you're having a bad day when you run over your laundry.
Sid.
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XXBuick:
Pick Diest or Stroud and call them, they will recommend and assemble the proper chute. I run a 4,000 lbs Camaro with a 30' tow line. The chute I have from Deist. I have to run a larger chute bag and a bigger pilot spring and pilot chute. Deist figured all of that out. In he end it is probably cheaper than finding all the components yourself. Also I have heard it said the tow line should attach at the same height as the cam shaft to avoid lifting the back.
Packing the chute with the extra tow line takes some getting used to.
Good luck
BR
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. . . or contact SST Safety(?) if they're the manufacturer and ask them how they could modify it for you.
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Small is good. You can "choke" down a large chute by zip tying the lines at 3' intervals from your attaching point on the car and taping over them so they don't catch on anything. This will soften the hit on deployment. You do not want your eye balls hitting the face shield or testing the effectiveness of your Has device. I use an 8 foot triangular at 30' and it's choked down at least 15'. Good luck.
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This might help you visualize what folks are running and some of the issues with chutes at bonneville.
http://blackhorsephoto.net/car_tech_chutes/chute_systems.html
http://blackhorsephoto.net/fast_cars/racing.html
Larry
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Does anyone know of a source for parachute tether lines? The usual source websites don't show any tethers.
Regards, Neil Tucson, AZ
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I would contact Stroud Safety directly. They are nice to deal with.
Doug :cheers: :cheers: :cheers:
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With their name on the product they will want the chute & tow line to their spec for your application for obvious reasons. If you're using a chute from some other source you might be on your own with that.
Sid.
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Sparky, with much respect I take umbrage with Your recommending that ANYONE alter or have altered a manufactured piece of SAFETY EQUIPMENT.
Nolan White lost His life when someone other than the manufacturer altered His parachutes. I realize that this is talking apples and oranges here but in My view We should never suggest or condone using any Safety Equipment that has not been repaired or altered by the Manufacturer. In this particular case changing the tow line length might change the impact design as engineered (far fetched but possible). A quick call to the manufacturer should always be done first and foremost.
Bob Drury (who is a fan of Yours) :cheers: :cheers:
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OK, here is my parachute problem: I have a 16 foot ring-slot parachute with a spring-launched pilot chute. This sounds like it is too large for my application but here are calculated results based on:
1. Introduction To Parachute Subsonic Aerodynamics by Georgio Guglieri
2. Parachute Definitions, Nomenclature, and Types by Vance L. Behr & Steve Lingard
According to these sources, a 16 ft ring slot-chute has a deployed diameter of 0.68 x 16 ft = 10.88 ft and a Cd of about 0.6. Going through the standard drag equation, the chute should generate 1427 lbs drag @ 100 mph.
For a car weighing about 2200 lbs wet, this isn't an unreasonable deceleration G force but at 200 MPH the drag force goes up by a factor of four to 5708 lbs. This sounds really high but is it too high?
Trying to find tech info on-line about drag parachutes is frustrating. How is anyone supposed to choose a parachute with such little information? Many manufacturers don't even provide information on the length of the shroud lines, or even a picture of the shape of the canopy! Simpson's website is particularly bad but I'm sure they make good stuff. I'll talk to the manufacturers before I order a chute but first, I'd like to have some recommendations regarding the size, style, and manufacturer. All suggestions are appreciated.
Regards. Neil Tucson, AZ
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After using a chute, clean it out real good in water and hang it out to dry, it will be a lot easier to pack. We used the warm water out of the intercooler to clean the chute.
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Neil, as relayed by many this parachute thing is best left to the suppliers. I have some of the same references that you mention and would not even think about recommending chutes to anyone
even especially myself!
Here are some notes from a seminar that Stroud did for ECTA:
Stroud makes drag chutes for a living and LSR chutes as a hobby.
Call & talk to Bob Stroud or Joe Timney before you order any whoa laundry! [Whoa IS more important than GO!]
Chute has two functions:
#1 Stabilize
#2 Slow: 2g load or less for cars, 1g load or less for bikes.
Drag chutes are short, LSR are long and smaller the faster you go!
Pilot chute pulls bag out, makes lines taut and then deploys main chute.
Chute must go into clean air! Should be out & up @ 45° for most cars! Some liners are straight up!?
[CFD can help determine this - ask Sparky!]
Spring deployment preferred over pneumatic! Monitor the spring health!
Do NOT use powder to pack chutes. Pack chute just prior to your runs.
Do NOT pack chute overnight or for extended periods. You WILL get bad deployment!
Springs do NOT like to be compressed near coil bind over long periods of time!
Always clean salt off with plain water! [Not necessarily in the shower like Joe! You'll have to ask Joe!]
Ideal attachment is center of mass for bikes. Suspend from a crane to find it!
Attachment for cars somewhere between cam & crank CL. [Technically at the CG!]
Pivot diameter should be 1"~1.25"
A parachute story: When they were developing the first Mars lander they did many tests after countless simulations and calculations [allowing for the difference in gravity and atmosphere]. Every test just augered into the ground! Finally, in desperation someone said they should talk to old Joe in the 'chute shop. What in Hades would he know about it was the expert response! Well, they finally relented and old Joe said do this, this and this! [Not necessarily in that order! :-D] Next drops went perfectly on Earth and Mars. Relayed to my by a JPL employee! Never any substitute for real experience. :cheers: :cheers:
If you want to have some real fun try to calculate the stopping distance! :-o :x :cry:
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A 16 footer is a really big chute for your car Neil & too much chute can really unsettle a car when it hits but I must admit I have no experience with ribbon chutes.
Racing chute manufactures don't wave their information around a whole lot, they want you to tell them your details then they'll sell you their recommendation & most of the time I think that's too big for the salt.
If you plan on anything other than a mechanical release mechanism you might want to read the rule book re manual backup.
Sid.
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To BD point---it is not something that I didn't talk over with Bob Stroud---but the bottom line is nearly all cars have somewhat of a rooster tail behind them--- some cars need to fly their chute in front of the bounce others behind the bounce, few chutes enjoy being flown in the area of the apex of it---bottom line---the reason I film behind the car---I want to know, how the chute is behaving back there--Bob and I seem to have gotten it right on the new car.
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Thanks for the suggestions and recommendations. I surely will talk to some vendors before I make my decision.
BTW, Sid- a ribbon chute is different from a ring-slot.
Regards, Neil Tucson, AZ
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Yeah I realize that Neil, my point was that I had no experience with open weave chutes & they don't have a tendency to spill & hunt if they are too big like full form & cross form chutes can do but too big will still hit hard & can upset the car's stability. I lean towards a little smaller & longer that what the chute people recommend.
Sid.
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I have a stroud land speed chute,and it opens smooth. other racers told me to be ready when the chute opened. they must have had drag chutes. my stroud was just a tug to slow me,what a relief.
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Fifteen years ago I told Bob Stroud what I had and took what he recommended. We had some minor problems with it in the dead (or cornfused?) air behind the roadster. Consulted with him -- he sent a new, longer main line and a bigger pilot. Been working fine since -- no charge!
I think with all the classes (and even very dissimilar cars in the same class), the best guess is just an educated guess. And one should trust those that have made those guesses for years and not try to adapt something they bought at a swap meet from an old dragster.
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We have a 4400# 3rd gen Camaro running in Production and Altered Classes. When we were running 225+ with our "D" motor in Production class and with a full canopy 'chute, everything was fine. When we added some "juice" in the Fuel Altered class, we came through the lights at about 248. Pulled 'chute, 'chute hit, we got sideways about 45 degrees until the car slowed down enough that the 'chute got out of the dirty air and the car straighted out. For a brief moment after it straightened out, I thought I had done a heroic rescue.
Lessons:
1. Amen to mounting 'chute camshaft high
2. There is lots of room to slow down - we now use a cruciform 'chute (not a full canopy) and longer shrouds
3. The faster you go, the further dirty air extends behind you, and you may need longer shrouds to get into clean air
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I run two ribbon chutes from Bob Stroud and they Hit nice and soft and once again "camshaft high" mount. I can't remember How big they are but I use the small packs for each and I am thinking they are around ten feet in diameter. I only use the second one above 220 because the car now weighs 5200# and it doesn't like to slow down (neither do I)!
The only bad thing is that I had to figure out How to load My Buddy's ashes which took a little bit of "field engineering" with a ribbon chute...............
One Run, out...........................................