Landracing Forum
Bonneville Salt Flats Discussion => SCTA Rule Questions => Topic started by: Chaz on January 07, 2008, 10:55:32 AM
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I've never seen it done, but has anyone here used PVC for their parachute tubes? It seems to me to have some advantages. Slippery, lightweight , and inexpensive.
Would there be any problem rulewise?
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I have seen plastic tubes but I think they are weak and crack pretty easy. Alum is better and can be welded on for mounting brackets etc. Plastic is not good around heat or fire. I would submit your idea to the tech committee for their input.
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Water main plastic tubing is easily available and in common use.
It can be drilled, bolted in a number of ways, and is very tough.
Usually tougher than the skin of the racer. :wink:
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These look pretty good!
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Just don't use as a push point. Other than that, pvc works great
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:-D What diameter and what length would be recommended for about a 1500lb ride and something around 200mph + ? :?
Sorry if this might be a little redundent, I've been away on business and wasn't able to get to the computer. :-) Thanks for putting up with me.
Terry
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:-D What diameter and what length would be recommended for about a 1500lb ride and something around 200mph + ? :?
Sorry if this might be a little redundant, I've been away on business and wasn't able to get to the computer. :-) Thanks for putting up with me.
Terry
Bob Stroud ( http://www.stroudsafety.com/ ) told me that if I put in 6 inch by 36 inch tubes I would be covered for about anything I would ever want. Tom Burkland said while I was at it put in two tubes and also be covered for about any situation. Since I respect both of these guys that's what I did.............
(http://purplesagetradingpost.com/sumner/bvillecar-2/12-15-7-11.jpg)
( http://purplesagetradingpost.com/sumner/bvillecar-2/construction%20page-80.html )
........................... so there is something to chew on,
Sum
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We make our tube 30x6. Seemed fine at the time -- even put a roll of duct tape down in the back to take up the slack. When the chute gets dirty or salty, take the tape out. (Yes, I know you're supposed to wash it every run.)
After Stroud made us a longer lead from the pilot to the chute, and a much larger pilot because of the dead air behind the roadster, it's a bear to get it all in clean. 36'' would probably be a good idea -- you can always fill in the void as we did.
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Hi Sum,
Thanks for the picture. Your chute tubes look kind of high. Does that have any effect on deployment? Where are you going to attach the chute line to your LSR?
Thanks,
Terry
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chutes don't much care where they ride---but Bob, TECH & you sure need to care where and how you tether and deploy them--- :-D
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Hi Sum,
Thanks for the picture. Your chute tubes look kind of high. Does that have any effect on deployment? Where are you going to attach the chute line to your LSR?
Thanks,
Terry
(http://purplesagetradingpost.com/sumner/bvillecar-2/1-17-8-13chute-attach.jpg)
The attach point is somewhat adjustable vertically. More about how the attach points were made here:
http://purplesagetradingpost.com/sumner/bvillecar-2/construction%20page-92.html
c ya,
Sum
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Nice work on the "spools" for the 'chute anchors, Sum.
There's a sore point with me on the wording regards parachute mounting in the rulebook that IMHOP is REALLY ambiguous and I've been told, even though a change was suggested, that it WONT be changed in the '08 version.
3.M PARACHUTE
". . .Parachutes must be securely mounted to a suitable crossmember."
And that means the shroud lines, the anchorages, the 'chute packs or WHAT?
I brag all the time about the excellent definitions put forth by the SCTA rules, especially compared to the NHRA rulebook, but I think we have a failure to explain here.
DW?
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There's a sore point with me on the wording regards parachute mounting in the rulebook that IMHOP is REALLY ambiguous and I've been told, even though a change was suggested, that it WONT be changed in the '08 version.
3.M PARACHUTE
". . .Parachutes must be securely mounted to a suitable crossmember."
And that means the shroud lines, the anchorages, the 'chute packs or WHAT?
IB, what was the rule change you submitted? Which part did you think needed more explanation or control?
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8-)For whatever it's worth, let me share what Jim Deist told me. My only experience on the salt is with liners so take that into account. His advise worked very well for me.
Try to find the cg of your car. ( I balanced mine fore and aft with a large wooden beam across the frame rails). The vertical point is usually about the camshaft on a V engine. Attach a string to that point on the side of the car and walk back the length of the tow line plus the chute and hold the string at arms reach over your head. Where that string intersects the rear of the car is where the chute attachment point should be.
It not only makes sense when you think about it but it works. When the chute hits it does not upset the car at all, It just puts your eyeballs against the helmet visor.
Howard
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I am just curious and don't have any answers, but does anyone care about disreefing speeds? Back in the last century when I did data processing for USAF parachute testing in El Centro, I saw chutes that opened in a controlled fashion (initially looking sort of like a tube) in order to minimize the Gs on the chute and tether lines. If you deploy a chute when going fast (supersonic for example) you don't want it to open all at once or it won't be attached to the vehicle for long. I once saw a drag chute deployed by a F106 that was in a flat spin - it just wrapped around the vertical stab and the pilot ejected, but that is off subject. Maybe it is not practical or costs too much or is too complicated for cars or something. Anyone got any theories?
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We used to tape the shroud lines together every three or four feet with six or eight wraps of masking tape. It made a noticeable difference in the impact and worked for us until we got back home and could get the correct chute for our application.
Howard
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Howard your anchor points worked well at 250....but put me on my head at 300.... after my incident at speed week last year I started doing a lot of research about anchor points and tow line lengths planning for 350 speeds...both Deist and Stroud have 2 completely different views on anchoring placement, both do throw CG and balance points into their sentences, but neither will give you a concrete answer. Howard< Deists location sounds logical but lacks 1 big factor and another is questionable... first, Deists finding of vehicle centers is logical but then he has you walk back behind the vehicle to an imaginary point and hold your string up... the overhead height is where he wants you to fly your chute... I'm not sure i want to fly my chute 10' in the air.!.... I think I will hold my chute about chest high... but the biggest problem is "how long is the string?" the string length is supposed to be the "tow" line length.. And when pressed for an answer he said, "However long you want it" when I continued to ask I got the " how fast and how hard you want it? So basically a vague answer and something I need to find for myself....
So on to the Stroud conversation.... Bob's anchor point is cut and dry "vertical and horizontal centerlines" no variations.... this answer doesn’t take in consideration for balance like Deist’s but hey you could always hang your vehicle like Akatiff did just to be safe... and as for tow length? "Whatever you want?".... So after some more consulting I have decided on Deists anchor location and 2 times vehicle length for low speed tow lines (50') and 3 times length for hi speed (70')
Now lets talk about tow line... my current chutes have no tow line as the risers go all the way to the anchor and are 4straps of .74" wide line.... very thick and bulky.. I plan to replace it with 1 strap 1.25 wide tow line... it should reduce the bulk of my complete system...
Kent
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Stainless: Re your query a few above, my contention on the weakness of the statement re; mounting I believe it should say SHROUD LINE (or TETHER) ANCHORAGE.
The last sentence of my above post should have described clearly my dilemma.
DW already contacted me off the website with an answer that in spite of his irrefutable reputation and clear-mindedness, still didn't satisfy me .
Being a non-participent, although a BNI member, -hence -INTERESTED BYSTANDER -my suggestion was relayed thru a long-time SCTA record-holder for the '08 rulebook.
A couple of my/our suggestions were implemented, I've been told.
My background is a mostly drag car builder for thirty plus years who constantly looks for ways to bend rules and although the chute mount rule isn't something ANYONE would want to scrimp on I try to read everything I can into ALL rules hence my concern about it being vague.
With that, here's a quote from the late Colin Chapman for ALL designer/fabricators:
"Rules are for the interpretation of wise men. . .and the obedience of FOOLS"
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Kent,
I used the same system on the new liner I built and drove to 305. It worked great. Earl Wooden and Charles Nearburg have gone over 370 with the car and it worked well for them. It appears the chute towline attachment was not the problem in your incident.
I'm sorry it happened and glad you weren't hurt but that car has been changed so much since I sold that I have no idea what's going on with it now.
Howard
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I'm with Kent on this one. Stroud and Deist both gave me instructions where to mount the chute anchor. I respect both of them but using the suggested methods of finding the anchor position gave results that were over 18" apart.
I tried to buy from Deist first but couldn't seem to get a cost estimate. I tried Stroud (he answered the phone) and got a price and time of shipment (optimistic) but I told him I wasn't in a big hurry. He suggested I mount the chute at the CG. Made sense to me. Still, the first time I pull the chute it will be with a big question mark in my thoughts. I think the chute anchor would have to be perfect not to unload one end or the other. Seems like it would be better to unload the front a little than the back.
Thoughts of a rookie. :-o
Harv
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I'm with Kent on this one. Stroud and Deist both gave me instructions where to mount the chute anchor. I respect both of them but using the suggested methods of finding the anchor position gave results that were over 18" apart.
Harv
Harv, the length of the shrouds make a difference, as does the size and shape of the chute. I am surprised at 18 inches difference, that is a lot. If ours was 18 inches different, it would be in the air, on either above or below. If you are talking fore and aft, properly done, I don't that makes a difference.
Go with the recommendation of the manufacturer you chose.... 8-)
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The information is quite scattered isn't it ?
Each has their own theory based on their experience.
All things that should be considered are not mentioned.
The USAF tests are the closest to getting it right, and the results were only really valid for that airplane package and the repeatable speeds.
Does anybody remember the 200mph + a little bit, Ardun roadster with the short coupled 16 foot ring slot ?
What a mistake that was.
It deserves a chapter in a book. :wink:
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An idle thought followed by a rhetorical question: How fast is the space shuttle when it touches down and where does NASA have the chutes attached?
Mike
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Watch the chute carefully and you will see that it is made to open at a designated rate so as to not shock anything and unnecessarily increase the loading.
It also benefits from the aerodynamic loading when the nose is held up as long as it will.
As it rolls to a stop. the attitude of the machine changes quite a bit, and with it the geometry of the pull of the chute.
Bigger ain't always better.
Every animal is different, and 1 size doesn't fit all. :wink:
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get a small digital camera and mount it on the tail fin---it will tell you where your "trailing wake is" that will give you some clues as to where let the canop end up.. I caught all kinds of flack about where and why I wanted to mount my chutes---I now have film of my chute coming out straight and flying straight and LEVEL--- for anyone that wants to look at it..
Wake May change as I change the rear of the car...
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-----I now have film of my chute coming out straight and flying straight and LEVEL--- for anyone that wants to look at it..............
http://www.youtube.com/watch?v=PtGmGTHK6qc
http://www.youtube.com/watch?v=fPnvgj1Bdgk&feature=user
Sum
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Makes my cheeks pucker every time I watch those... realism at its best... :-o