ROL NEWS--CP Technologies Motor Class

Mmmmmmm, lunches.

Replace little word with big-sounding word, forget to delete little word.

Must all be dwarfs. Snow White gets in free.

-John (buy a real book for real propellant, save $195 and travel expenese)

Sounds like a pretty good deal!

Considering how many toy motors I have made from this book including a near J-350 all the way to an M1190 I wonder what I would do with a real motor. Join NASA maybe?

Dennis

What did you use for casing material?

Who's safety guidelines do you use when testing and flying these motors?

Did you get your knowledge of motor-making solely from this book?

Now there's an idea. ;)

-John

Stupid sexy Flanders!

What does this post have anything to do with your remark about toy motors. None!! Good try at changing the subject. Cases were Ellis Mnt. Animal Motor Works, 1",1,5" and 2" Shedule 40 PVC. Teting area is a 23 acre area made available to me by its owner anytime crops are not in it. Saftey giudelines are mine. Whole dug deep enough for motor to be fully set below. Sand bags, no less than 100' away when test firring. Still this has nothing to do with the toy motor comment. My motors perform to my satisfaction which is the idea. Yes what I started with and what I use most of is the information obtained from John Wickmans Program. Have suplimented sense for my thirst for more knoledge.

Dennis

Sounds like you are doing much more than is suggested by John Wickman.

My toy comment has to do with the use of plastic casing material. Yes, it's convenient and easy to work with, but unwise and unsafe. Do you put sandbags around your rocket, too? Professionals cringe when I mention that some people use PVC for motor casings, not because it won't work but because of what will happen when one doesn't work.

I see no need to follow the example of a self-proclaimed expert who has said there are too many rules and too much worrying about safety. He has also proclaimed that he'd rather see 100,000 people flying amateur rockets with acceptable numbers of death instead of just a few thousand following the self-regulation of certified flyers and motors.

There are many other sources of information as good or better than paying for his book or class. I see no need for anyone to pay someone with such a cavalier attitude and a track record of spreading misinformation and fear about the hobby and regulations.

-John DeMar

Hmmm... is a case burn-through or rupture going to be so very much worse with PVC than metal or phenolic? I've had a G125 crack its case on the ignition spike; I've seen (too many) aluminum case RMS motors CATO in one way or another (seal and closure failures seem to be more common than structural failures)... why would a PVC motor be any worse than these, or than a wound fiberglass case motor like the RDC "Enerjet-8"?

(Actually, the Enerjet held together... the rest of the rocket wasn't up to it... when I came to the question about "shred" on the level 2 test, I thought: "Oh, so there's a word for when that happens!")

disclaimer: I'm not trying to start a flame war about anyone's book; I'm just curious about the actual safety issues...

-dave w

I can't speak for the other materials, but I do know that one of the problems with PVC fragmentation is that when they get embedded in the human body, they're awfully hard for medical personnel to find.

-Kevin

What are those HyperTek fuel grains? Actually they are just uncased fuel grains, correct?

Personally, I bought Wickman's book first, because I felt I got more for my money. I then went and bought McCreary's book. It is interesting to see the issue of motor making from the viewpoints of an engineer and a chemist. The software really helps, and hasn't let me down yet as far as failures go. As for using PVC pipe as a casing, I say no. They can only withstand the low temperatures and pressures associated with ANCP. Instead, I bought a Loki casing, which gave me a better range of what propellants I could use.

One hopes that somebody with the mental capacity to take on EX is also an independent thinker, and use the information given to them the way they feel it should be used. If you think PVC shuldn't be used as a casing material, don't use it. If you think there should be more safety rules, make your own. If you think that you have a safer way of making motors, by all means use it. Just don't blow yourself up.

Three factors: one is that the PVC fragments and doesn't simply split when overpressured. The dispersion pattern is much greater than 6061 aluminum which tends to splits without throwing shrapnel. Second factor is that a commercial motor with sufficient quality control of materials and manufacturing is more likely to fail "as designed". Closure fails before casing, nozzle shears, etc. An individual may try something outside the recommended methods (or just screw something up) and end up with fragments of plastic flying at them from the business end of their rocket, beyond the standard safe distance table recommendations. Then there is the fact that commercial manufacturers only use phenolic or G11 for the smaller motors (up to G currently). The dispersion is relatively small for a case fracture compared to the much larger motors recommended for PVC by John Wickman.

NFPA 1125 (code for manufacturing modroc and HPR motors) has requirements for the characteristics of the casing materials, the preferred failure modes, and the max 'projection distance' per motor size. Amateur rocketeers can follow whatever they feel safe doing, but I don't believe it is ethical to present something as "just as safe" when it is not.

-John DeMar

Correct

Nope. I've used PVC casings in single use APCP motors for a couple of years. No failures to date, but the motor must be designed to operate at sub optimum pressures.

The main PITA is that they don't fit standard MMT's.

Mike Fisher

In what way would this be a safety issue? Unless you're standing way too close to the rocket, the plastic fragments from a possible PVC motor cato are irrelevant.

I find it hard to believe that lightweight plastic fragments could travel that far and still have the energy to produce injury.

That was not always the case. Until reloadables came along, nearly all commercial motors used composite casings. The only reason they don't use them now has to do with the economics of reloads rather than any safety issue.

The materials he referred to are fiberglass and phenolic casings.

Ray take your meds.

Can I come by and help you with your wife?

Consider that the fireworks industry does not use PVC plastic for mortars. (The "guns" for lifting larger aerial shells.) ABS is used instead because it tends to split instead of fragment. This is also why aluminum is used for reload cases rather than steel.

Fragmentation motor tubes are a bad idea.

You could use PVC but you will need to be much further away or > casings, not because it won't work but because of what will happen when one