OK, what is the deal with Quest?

markkoelsch said:

I doubt a Q2G2 would ignite a composite. If it was augmented with pyrogen sure.

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markkoelsch said:

I doubt a Q2G2 would ignite a composite. If it was augmented with pyrogen sure.

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taiwanluthiers said:

Man it sounds like that Quest C6 shouldn't have been certified to begin with. I mean if it behaves like a C3 someone could make the fatal mistake of thinking it could work in a heavier rocket,

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mikec said:

FWIW the Estes C6 has an average thrust of 4.74 N and the Quest C6 has an average thrust of 3.45 N. Both motors have roughly the same peak thrust spike.

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JohnCoker said:

A motor name like "C6" is just that; the name. The performance of motors changes over time, and in questionable situations the actual statistics should be consulted. Not only that, for convenience each motor needs a different name and multiple motors with different thrust curves could have the same average value.

More than that, the average thrust isn't what you care about for determining whether the motor is sufficient to safely launch a rocket. It's more like you want the "initial thrust," or better yet to run a simulation which takes into account the length of the launch guide.

We need to get away from thrust:weight ratio and to running actual simulations. This is why I built the ThrustCurve.org motor guide; it's completely practical to run mini simulations in real time for every motor. I hope to see this feature added to the full-fledged flight simulators as well, but for now at least you can narrow down your choices with ThrustCurve.org and the run full simulations if needed.

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lcorinth said:

I guess I don't see what the point is of having motor designations like C6- or whatever, if doesn't reflect the motor's performance.

All the books tell you that the letter indicates the total impulse class and the first number is the average thrust of the motor. But even Estes' Wikipedia page states that "A study at the Australian Defense Force Academy found Estes D11-P motor to have an impulse 11.4% below Estes specifications and the C6-0 motor to be 4.45% below Estes' specifications. A third study found the A10-PT motor to have a total impulse 20% below Estes' claims."

Not that I have any complaints with Estes' motor performance in my low power rockets, but why have an average thrust number on a motor if it's no indication of average thrust? Any why no comment on this in the Handbook or other books?

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billspad said:

... And altitude dependence of model rocket motors isn't anything new. I was able to demonstrate it with some pretty crude equipment when I was in high school in the 60's.

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billspad said:

Basically, the inaccurate average thrust labeling was allowed because 99% of the people using model rocket motors don't know or care to know what it means. NAR S & T has always published the as tested numbers. You can find them on the Engine Data Sheets located by following any link on this page so the rest of us in the 1% can have that information. As mentioned above, the inaccurate average thrust labeling is no longer allowed by S & T.

I couldn't find The Physics Teacher article online but the other article troubles me because of things like "actually achieves mean impulses of 2.232±0.029 N sand 2.006±0.022 N s, at high altitude and sea level, respectively" that would lead you to believe that model rocket engines are that precise. They are not. And altitude dependence of model rocket motors isn't anything new. I was able to demonstrate it with some pretty crude equipment when I was in high school in the 60's.

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