ROL NEWS--CP Technologies Motor Class

You're forgetting aerodynamics. I'd rather be hit with a pound of loose feathers than a single brick.

How did these occur? If it happened when the pyrotechnic was ignited, it means they were too close -- or at least much closer than you'd be when launching a rocket. If it happened any other time (such as during manufacture or transport), it had to be the result of using volatile, unstable compounds. The propellents typically used in PVC motors are APCP and ANCP, both of which are pretty safe in that regard.

Irrelevant, since we're talking about EX, not certified motors.

CP's FAQ page talks about PVC and the cap blowing off in most instances (much like a closure failure). I've not tested the failure of PVC, but it's pretty hotly debated on rec.woodworking for air compressor lines.

Joel. phx

JFJ: "What about using PVC pipe and fittings for the motors. I keep hearing that it is dangerous to use PVC. That it fractures which will produce tiny pieces of flying plastic if a motor explodes?

It's simply the nature of the material. Fracture with shrapnel is bad and requires much farther safe distances, regardless of whether the source is a mortar gone bad, or a rocket motor cato. The piece flying at your from

50, 100, 200 feet away doesn't really care.

Absolutely NOT irrelevant! Especially when a more dangerous technology is being presented as 'just as safe'.

You may wish to discount this discussion of large plastic motors (for some apparent reason). But, you are doing a disservice (as is John Wickman) to the growing number of EX/Amateur rocketeers that may not be aware of the increased danger of projectile shards. People get complacent and think these motors can follow the same safe distances of the NAR/TRA/

1127 safety code. Splitting an aluminum casing is much safer and more predictable than fracturing PVC. (I know this from personal experience :)

-John DeMar

If build according to guidelines that make the closure blow first, then the odds are much better. Seeing what some "EXperimenters" tend to do, it is no longer a safe bet, especially if people assume they can follow the NFPA 1127 safety codes with large motors with fragmenting casings.

-John

PRECISELY.

That is the most wrong aspect of that code anyway. That makes a very poor baseline for reasonable or right on offset distances.

Hmmm. Part right mostly wrong. About par for John and Ray.

Like Aerotech hardware?

Gary proposed the rule. He knew his hardware was not tested to that standard, but it "sounded good". If you have ever seen an RMS fail it never fails as the code suggests which means it was also never designed to do so.

On both of these comments, I have to ask what proof do you have to back them up? I just don't see how a small piece of lightweight plastic can travel far enough, fast enough, to be a danger to anyone at the distances used for certified motors. Especially in light of the fact that the fragments would first have to pass through the airframe of the rocket.

For that matter, how are PVC fragments any more dangerous than the G10 or carbon composite fragments from the rocket itself?? Or batteries, metal screws, etc that may be located in the airframe next to the motor?

1. PVC fragments as opposed to rips or tears, thus assures the initial conditon of shrapnel exists.
2. Given 1., There are calculations one can perform on shrapnel distances but they are STATISTICAL studies and thus have inherent UNCERTAINTY. Bottom line is the proper procedure on offset distances is max shrapnel distance.

TRA for example has an offset distance for HPR consumer, low shrapnel motors, over TWICE the fragmenting shrapnel distance, thus putting people in the MODAL IMPACT RANGE.

Safety is a science, not an arbitrary "that sounds good" thing as Kelly, Rogers and others would have you believe.

The result of course is RRS launches are safe and Tripoli launches have NUNEROUS near misses all the time.

And ambulances time after time.

How sick is that???

Ignore crap.

Jerry

I have a small taste of what AC does day to day and I find it wildly halarious he was injured by a Nerf-tm ball and NOT X,Y,Z (I can't say).

ROFL

AC I hope you recover and stop playing with toys. We need Pro98 in Wal-Mart.

Jerry

may i ask why?

To shoot from a PVC potato cannon? :)

Mike Fisher

Seems like thats what the NASA managers said about foam.

Bob

Been watching Mythbusters, maybe? Searching for that perfect bullet...

In NASA's case, it was a large piece of foam weighing a couple pounds or more, with a speed differential of about 500mph, striking the wing only a short distance away. That's a big difference between a tiny fragment of PVC weighing a fraction of an ounce from a pad located at typical launch distances.

Ray it is simple math either way. Speed, distance, mass, relative velocity, angular momentum, whatever. To follow your posts is to let your mind drift away from anything remotely scientifically based.

Jerry

We had a 54 mm PVC cased sorbitol motor CATO at the launch last weekend. The pad was 150' from the LCO table. Pieces of the casing and propellant were found 100' *behind* the LCO table, some pieces as large as 1.5" x 3". Being hit by pieces would not be life threatening but might cause cuts or eye damage. (Nobody was hit.)

We will be banning PVC cased flight motors at Orangeburg, this one got up about 50 feet before it CATO'd.

Tom

Hmm. Well, at least now you know how far away the pad should be when flying PVC motors. :)

For that particular situation, maybe. In general it's easier to NOT have fragmenting motor casing material and not have to worry about it. This is the conclusion that professionals with many years of experience have made. Well, all of them except for John Wickman.

Or maybe next time Ray will volunteer to let everyone stand behind him at NFPA1127 safe distances (or your new 'hunch' for safe distances) for big toy plastic motor launches?

Should we expect some sort of contrition for your ignorance of this matter? You and Jerry both have a problem of not being able to say "I don't know". ;)

-John