Nozzle question

turbosnip.

are you suggesting that they may be in violation of NFPA 1125 where it spells out quite clearly what is required for labeling....

"if the A8 is actually an A3, then it should be labeled as such according to the requirements of NFPA 1125"

"The real question is will the NAR S&T enforce NFPA 1125 ?" "I would submit that if the NAR wants to have any credibility in its motor certs for safety or contest, they would have to...."

Those seem like your words. In context too.

Jerry

That's the most accurate statement ever written on rmr. ; )

Randy

Wal-Mart hasn't sold D engines here for over 2 years. Kmart never did and seemingly has dropped rockets altogether.

Randy

Well, I went back and looked at the A10, the A8, and the B6 for some comparisons, and here's what I 'think' is going on. The A10 and A8 have extremely low thrust tails, and they are 'effectively ineffective'. IF you change your assumptions such that 'propellant burn time' ends when the 'effective thrust' ends, then you can, indeed, come up with an A10 and A8 as average thrust values (bear in mind that I'm eyeballing the area under the curve, but that is ROUGHLY what it looks like). In other words, there appears to be some thrust level below which the engine is considered ineffective, and even though there is some small thrust occurring, it is so small as to be ignored.

You can look at a comparison of the A8 and B6 thrust curves to see just exactly what this means -- the A8 has a tail of about 2.3 newtons, and the B6 has a tail of about 4.5 newtons (almost twice as much!). So, the tail portion of a B6 comes to a substantial percentage of the 'average rated' thrust, thus it is actually a 'sustaining thrust'. The A8 has a sustaining thrust of about 33% of the 'average rated' thrust, and so it is not doing much for 'sustaining'.

I'm sure somewhere in the Estes labs is some document that defines all this, and there must be some kind of understanding with NAR S&T as well. For example, I can well imagine that somewhere it is defined that the sustaining thrust must be > 50% of the 'average' thrust for it to be considered 'effective', and that propellant burn time is considered 'complete' at that point.

My point is that by choosing the definitions (and the above are not unreasonable definitions), one can drastically affect the measurement. NAR is making the motor thrust curves and is basing their values on the measurements they have made. There is also nothing in the code that defines the accuracy of the equipment being used. If Estes, for example, has their equipment 'calibrated' differently (i.e, if their sensor shows no propellant burn after .2 seconds), it could simply be that they placed the threshold for that measurement at a higher level.

To add fuel to the fire (pun intended), there must be SOME thrust occurring from the delay charge. It may be small, but it's measurable. This simply points out the fact that one has to draw the line SOMEWHERE.

One last 'factor' in all of this -- we also don't know (precisely) how long the propellant burn is. We are measuring the thrust, not the propellant burn time. If the pressurization/nozzle size has an effect on how long it takes for the gas to escape from the pressure chamber, it would stand to reason that the propellant has stopped burning at some point PRIOR to the thrust dropping to (near) zero. I don't know what that exact number is, but it may have been factored into some of the equations as well.

The bottom line (realistically) is that the numbers given (A10, A8) actually DO tend to reflect the usefulness of the motor, and their true capability for placement in a rocket. Therefore (looking at the results), there probably were/are valid reasons for the above cutoff levels to have been defined.

David Erbas-White

Point.

Hence my point.

Please bring common sense back to rocketry administration. (too late)

Jerry

NFW! But Jerry, with your expertise you should be able make a WAG withing 20%, or at least be able to run Burnsim or something similar to answer the question.

BTW, are the couple of Toronto guys from the '70s still with us, or did they blow themselves up?

Alan

More or less... The motor label is really a manufacturers marketing thing. If NAR S&T changed the motor designation at certification to anything different, it would only confuse the matter more.

The NAR has no enforcement tools; no JBTs, fines, jail terms, etc. They try to influence the manufacturer by maintaining a cordial working relationship. When that fails, they can decertify a motor. That is very bad enforcement tool, since it deprives users of the opportunity to fly those otherwise good motors.

IF you ran S&T, you would probably decertify 80$ of the certified motors. Rocketeers would tie you to a stake and pile on recently decertified motors...

Alan

Certainly. You take the motor designation from the label and look at the motor certification spec. sheet.

Alan

That part is mostly false.

This part is mostly true.

The E5 was catalog spec'ed at 22 N-S, and was NAR certified as an E motor for a long time, even when it was not a true E. NAR S&T was never successful at getting FSI to change their motor designations. Eventually NAR S&T recertified the E5 as a D motor. This was great as that FSI E5 was a decent contest D motor. I won NARAM-22 D SD with it. But all too soon, S&T notified FSI that they were going to decertify that FSI D motor bearing the E5 designation. FSI responded by boosting the total impulse of their "E5" just enough to get it recertified as a true E motor. Of course this made it nearly worthless as a contest motor.

Alan

The last time I did those experiments it must have been circa 1972. The only thing that happens when you do it wrong is the motor catos on remote electrical ignition.

Jerry

NAR playing around with the labeling and certifications is an example.

Details in this very thread.

DOT also was changing the treatment of large BP motors (7887 was a reply), but FSI just mailed their motors.

Yes it does. It can deny a manufacturer access to the process. It can and does ask manufacturers to "relabel" motors, despite decades of tradition and continuous production (FSI).

It AUTHORS and causes to be INSTALLED NFPA codes that generate NEW outlets for fines and jail terms.

You JUST said, "The NAR has no enforcement tools"!

Instead they do it selectively and motivated by personal bias.

No.

The only rule is the "effective thrust curve goes from 10% of peak to

That part is almost entirely false.

This part is mostly true.

I would not.... thats pure hyperbole on your part...... I would just make sure that labeled motors were labeled as they tested..... and I also don't agree that they are just a marketing tool.....perhaps the NFPA codes are just a marketing tool ?

shockie B)

david: good explanation, I was going to say the same thing, but you did a much better job....

shockie B)

Of course!