Been Away a Long Time... What's going on with Estes B6 Motors?

[ihbarddx]

ThrustCurve.org lists their impulse as 5.6 ns. Isn't that too much for a B motor? Estes lists it as 5.0 ns, which is the usual nonsense. What is it?

 

[Scott_650]

The data from Thrustcurve is typically derived from the information recorded by the certification organization - in the case of the Estes B6 that would be from the last time the NAR tested it for certification, 1995, which matches the date for the motor info in TC.

https://www.nar.org/SandT/pdf/Estes/B6.pdf
https://www.thrustcurve.org/motors/Estes/B6/

 

[BEC]

Something is goofy in ThrustCurve's data then. Here's the current NAR cert data for an Estes B6: https://www.nar.org/SandT/pdf/Estes/B6.pdf

It shows a tested total impulse of 4.33 N-s (which is what i use when putting my stats into the Newton Tally threads) and a certified value of 4.90 N-s (which puzzles me in that it's different). No idea how ThrustCurve could have them in as a low C.

It appears that the cert data entry on ThrustCurve for the Estes B6 (https://www.thrustcurve.org/motors/Estes/B6/) goes to the same place.

@JohnCoker ?

 

[Scott_650]

Something is goofy in ThrustCurve's data then. Here's the current NAR cert data for an Estes B6: https://www.nar.org/SandT/pdf/Estes/B6.pdf

It shows a tested total impulse of 4.33 N-s (which is what i use when putting my stats into the Newton Tally threads) and a certified value of 4.90 N-s (which puzzles me in that it's different). No idea how ThrustCurve could have them in as a low C.

@JohnCoker ?

Some of the numbers are close but not an exact match:

NAR Average Thrust 5.03 N
TC Average Thrust 5.0 N

NAR Burn Time 0.86 seconds
TC Burn Time 0.9 seconds

While Total Impulse isn’t close as Bernard posted:

NAR Total Impulse 4.33 N-s
TC Total Impulse 5.6 N-s

Which is more than a little off and well outside the acceptable allowed variance - puzzling!

 

[BEC]

Of course, rounded to ThrustCurve's precision, the numbers match....except total impulse. Since simulator programs use the curves, not that tabulated total impulse data (I think!) other than making us wonder, there probably is little harm done having the total impulse value be typo'd or however it got that way.

 

[SecondRow]

Some of the numbers are close but not an exact match:

NAR Average Thrust 5.03 N
TC Average Thrust 5.0 N

NAR Burn Time 0.86 seconds
TC Burn Time 0.9 seconds

While Total Impulse isn’t close as Bernard posted:

NAR Total Impulse 4.33 N-s
TC Total Impulse 5.6 N-s

Which is more than a little off and well outside the acceptable allowed variance - puzzling!

5.0 N times 0.9 s doesn’t equal 5.6 N-s. It should be 4.5 N-s.

 

[ihbarddx]

FWIW, I just checked the downloadable RASP thrust curve on ThrustCurve.org. The (trapezoidally-integrated) impulse of that curve appears to be 4.328 ns, rather than the 5.6 ns in the summary data.

 

[BEC]

...which squares with the 4.33 Ns in NAR cert data.

 

[UhClem]

NAR shows a propellant mass of 5.6 grams. Which is probably where that number came from. Just a data entry error.

 

[Scott_650]

So we should see good data from TC for rockets using an Estes B6 motor. Next time I launch I’ll see if my altimeter data matches with what TC predicted. This kind of stuff is part of what makes rocketry such an awesome hobby!

 

[waltr]

NAR shows a propellant mass of 5.6 grams. Which is probably where that number came from. Just a data entry error.

That is probable where the 5.6 come from.
At the very bottom of the motor page in ThrustCuve is a email link to report errors. "It is under "Motor Notes".

I found an error on another motor last year and reported it and it was corrected.