New Motor Certified May 2019

[Alan Whitmore]

On May 18, 2019 Tripoli Motor Testing certified the Aerotech G72DM-14A, a 29mm single-use motor using the Dark Matter propellant. The total impulse is 105.0 N.s, the average impulse is 80.8 N, and the burn time is 1.30 sec.

Alan Whitmore
Chair, TMT

 

[JohnCoker]

Thanks Alan!
https://www.thrustcurve.org/motorsearch.jsp?id=1127

 

[djs]

Anyone know if this will make it's way into the 29/40-120 case as a reload?

 

[emckee]

Woohoo! Always enjoy those DM motors.

From what I recall in the AT Open Thread, there are additional regulatory compliance requirements around getting the motor set up in 29/40-120 hardware, so they were intending to keep it as a SU motor, at least for the foreseeable future.

Someone (with actual knowledge) please tell me I'm wrong! I'd love a DM reload in 29mm.

 

[Steve Shannon]

By NFPA sparky motors are subject to the restrictions of high power motors, even though their impulse doesn’t place them there. That may be a reason not to sell reloads for a case that hasn’t been associated with high power.

 

[rharshberger]

By NFPA sparky motors are subject to the restrictions of high power motors, even though their impulse doesn’t place them there. That may be a reason not to sell reloads for a case that hasn’t been associated with high power.

The G138T is already in 29/40-120 case and its subject to HPR restrictions.

 

[aerostadt]

Keep in mind some clubs do not allow sparky motors at certain launch sites. In the Far West there are concerns about starting massive grass and brush fires.

 

[jimzcatz]

H178 29/180.

Woohoo! Always enjoy those DM motors.

From what I recall in the AT Open Thread, there are additional regulatory compliance requirements around getting the motor set up in 29/40-120 hardware, so they were intending to keep it as a SU motor, at least for the foreseeable future.

Someone (with actual knowledge) please tell me I'm wrong! I'd love a DM reload in 29mm.

 

[Rocketjunkie]

H178 29/180.

Interesting. All my H178's fit the 38/360 case.

 

[Rob702Martinez]

Anyone know who has this for sale yet?

 

[Steve Shannon]

Anyone know who has this for sale yet?

It was just tested last week and I wouldn’t expect the manufacturer to begin production until the motor was certified. Give it a little more time. [emoji851]

 

[UhClem]

By NFPA sparky motors are subject to the restrictions of high power motors, even though their impulse doesn’t place them there. That may be a reason not to sell reloads for a case that hasn’t been associated with high power.

Don't forget the Consumer Product Safety Commission

There isn't anything in there specific to sparky reloads but they might attract unwanted attention.

 

[jimzcatz]

Interesting. All my H178's fit the 38/360 case.

Yea, my bad. I stand corrected.

 

[Ez2cDave]

Don't forget the Consumer Product Safety Commission

AKA, the "Product Nazi's" . . .

 

[jqavins]

The total impulse is 105.0 N.s, the average impulse (sic) is 80.8 N...

Then why isn't called G81DM-14A? Why do motor manufacturers do that?

Thanks Alan!
https://www.thrustcurve.org/motorsearch.jsp?id=1127

John have I mentioned how much I appreciate you doing this?

 

[Walter Longburn]

I was wondering the same thing. We can't buy it without being certified anyway right?

 

[rharshberger]

Then why isn't called G81DM-14A? Why do motor manufacturers do that?

Why are the 300 Winchester Magnum and the 308 Norma Magnum named the way they are? Both are .30 caliber, marketing might have something to do with it. The manufacturer may have submitted as the G72 but due to differences in test equipment and methods it tested slightly higher than the manufacturers tests ( guessing here).

 

[heada]

I thought that per NFPA, they could name it +/- 10% of tested. If it tested at 80Ns, then it could be named anywhere from G72 to G88.

 

[Alan Whitmore]

I thought that per NFPA, they could name it +/- 10% of tested. If it tested at 80Ns, then it could be named anywhere from G72 to G88.

The relevant NFPA 1125 passage says that "Labeled value of average thrust shall be within 20% (or 10 N, whichever is greater) of the average thrust that is computed by dividing the mean total impulse measured during propellant burn time by the mean propellant burn time." There might be any number of valid reasons why a manufacturer would not use the precise tested average thrust for the label number. In one case it might duplicate another motor made by them or a different manufacturer, and they wish to avoid confusion. In another case, such as the Aerotech Warp 9 series, all had average thrust labels that end in "99", and this was done as a marketing tool. Perfectly legit.

Alan

 

[jqavins]

The relevant NFPA 1125 passage says that "Labeled value of average thrust shall be within 20% (or 10 N, whichever is greater) of the average thrust that is computed by dividing the mean total impulse measured during propellant burn time by the mean propellant burn time"... Perfectly legit.

Well, OK, but I don't have to like it.

 

[cerving]

They probably didn't want to confuse THIS G80 with the other DMS G80...

 

[jqavins]

But rounding the average of 80.8 N would make this a G81. So it... Oh, never mind.

 

[Steve Shannon]

But rounding the average of 80.8 N would make this a G81. So it... Oh, never mind.

But the next lot might test to 77.8 N. The one after that might be 75.6...
The manufacturer submits the motor with a label name already chosen based on their designed thrust and in-house tests. They may even have announced the new motor type as such. As long as it fits within the limits as Alan explained, TMT cannot require a change to the name. Nor would we want to.
In other words, TMT does not name the motor. Our tests are just to verify the manufacturer’s data within the tolerances required by NFPA. Every production lot will test slightly different, so the ones place (and maybe even the tens place in larger motors) is really meaningless except as a means of differentiation from other motors.

 

[SecondRow]

But the next lot might test to 77.8 N. The one after that might be 75.6...

Slightly off topic, but how is it determined whether a non-sparky G that tests above and below the 80N threshold is a high power motor?

 

[jqavins]

I'm trying to drop it, but just have to say that I understand TMT has basically nothing to do with the naming.

 

[tbonerocketeer]

Slightly off topic, but how is it determined whether a non-sparky G that tests above and below the 80N threshold is a high power motor?

All sparky motors are high power.

 

[JohnCoker]

There's one sparky F, the CTI F50, under 80Ns but probably still shipped with restrictions.

You can now search for sparky motors on ThrustCurve.org

 

[jqavins]

Slightly off topic, but how is it determined whether a non-sparky G that tests above and below the 80N threshold is a high power motor?

All sparky motors are high power.

There's one sparky F, the CTI F50 under 80Ns, but probably still shipped with restrictions.

Did either of you read the question carefully?

 

[Steve Shannon]

Slightly off topic, but how is it determined whether a non-sparky G that tests above and below the 80N threshold is a high power motor?

It’s based on the average:
3.3.24.4 Model Rocket Motor. A solid-propellant rocket motor that has a total impulse of no greater than 160 N-sec (36 lb-sec), an average thrust of no greater than 80 N (18 lbf), and that otherwise meets the other requirements set forth in this code.

 

[Nytrunner]

I guess his question targets those motors that ride the line of 80N. At that point it's almost subjective to whoever is running the test