DeltaV Between Motor Manufacturers

[AlexBruccoleri]

Hi All, Has anyone tabulated the delta V (ln(mass_ratio)*exhaust velocity) for the three different motor manufacturers? I primarily fly Aerotech since I like their designs and love white lightning. That being said, I am curious how all three manufacturers compare in terms of performance.

Thanks, Alex

 

[WoShuGui]

No tabulation I am aware of. An Isp like metric using propellant plus motor hardware weight in 1 G is an easy way to compare efficiencies using readily available motor data.

Isp of motor = Total Impulse in N-s / ( 9.8 m/s^2 x (Mass Propellant in kg + Mass Case in kg))

Yes, I know Isp should be just for the propellant; but Isp with total motor weight reflects differences in hardware weight which is worth considering when comparing manufacturers.

 

[prfesser]

Doesn't delta-V require the mass of the rocket? Mass ratio comes from empty mass vs loaded mass (of the rocket, not just the motor). A "standard" rocket would be needed for the calculation.

Delivered Isp should be a pretty good indication of performance. Though that will vary with motor size; larger motors are inherently more efficient than small ones at converting matter to thrust.

 

[AlexBruccoleri]

Doesn't delta-V require the mass of the rocket? Mass ratio comes from empty mass vs loaded mass (of the rocket, not just the motor). A "standard" rocket would be needed for the calculation.

Delivered Isp should be a pretty good indication of performance. Though that will vary with motor size; larger motors are inherently more efficient than small ones at converting matter to thrust.

I am only looking at delta-V of the motor. The purpose is to compare the manufacturers.

 

[Antares JS]

I am only looking at delta-V of the motor. The purpose is to compare the manufacturers.

Delta-V of the motor alone without a rocket would be a meaningless number since motors don't fly by themselves.

There's a reason we classify motors by total impulse. For a motor by itself, it's a much more useful comparison metric, and that's why every motor has a listed total impulse for you to compare. If you want to compare the motor manufacturers and propellant types, look at total impulse vs. propellant mass for each motor. Note also that specific impulse = total impulse / (propellant mass * g)

 

[AlexBruccoleri]

Delta-V of the motor alone without a rocket would be a meaningless number since motors don't fly by themselves.

There's a reason we classify motors by total impulse. For a motor by itself, it's a much more useful comparison metric, and that's why every motor has a listed total impulse for you to compare. If you want to compare the motor manufacturers and propellant types, look at total impulse vs. propellant mass for each motor. Note also that specific impulse = total impulse / (propellant mass * g)

I disagree. Its the theoretical limitand that is very useful to know. The “rocket” will only lower it.

 

[Antares JS]

I disagree. Its the theoretical limitand that is very useful to know. The “rocket” will only lower it.

Disagree if you want, but you'll notice in this pdf catalog from Northrop Grumman that Delta-V is not listed for any of the motors, while total and specific impulse, maximum and average thrust, and burn time are.

https://www.northropgrumman.com/wp-content/uploads/CASTOR-Motor-Series.pdf

 

[AlexBruccoleri]

Disagree if you want, but you'll notice in this pdf catalog from Northrop Grumman that Delta-V is not listed for any of the motors, while total and specific impulse, maximum and average thrust, and burn time are.

https://www.northropgrumman.com/wp-content/uploads/CASTOR-Motor-Series.pdf

They clearly state the propellant and burnout weight. Anyone using their motors will need that info.

I am looking at it because if one wants to correlate catos, or just see how a rocket could theoretically perform, having a tabulated theoretical delta-v is useful.

Edit: It is a trivial calculation too. I was just looking to see if anyone compiled it in a clean format.

 

[Antares JS]

They clearly state the propellant and burnout weight. Anyone using their motors will need that info.

I am looking at it because if one wants to correlate catos, or just see how a rocket could theoretically perform, having a tabulated theoretical delta-v is useful.

Estes and Aerotech both also give total motor weights and propellant weights, from which an empty weight can be derived. What's your point?

 

[AlexBruccoleri]

Estes and Aerotech both also give total motor weights and propellant weights, from which an empty weight can be derived. What's your point?

I did not have a point in my original post. I was just asking to see if there was tabulated data. Given we are on this, my point is that this information is useful. Loki claims to have the lowest failure rate. It would be interesting to see how their overall performance compares. Maybe they just have more motor material? Maybe their design is better? I do not know and am looking for data.

And just to pick an extreme example to clarify my point. A G motor with a casing weight of 50 pounds is not as good as an F motor with a weight of a few grams. The weights listed on the Northrop site are exactly what engineers need.

 

[mh9162013]

And just to pick an extreme example to clarify my point. A G motor with a casing weight of 50 pounds is not as good as an F motor with a weight of a few grams. The weights listed on the Northrop site are exactly what engineers need.

To build off your extreme example, what point would there be to calculate a deltaV for the hypothetical G and F motors? As Antares JS already mentioned, these engines don't fly themselves. So manufacturers won't include deltaV in the motors' specs because those values would depend on the rocket's weight and other characteristics.

I mean, do you ever see car manufacturers include 0-60 MPH specs with a standalone engine? No, you see other specs, like displacement, torque, power, RPMs, etc.

 

[AlexBruccoleri]

To build off your extreme example, what point would there be to calculate a deltaV for the hypothetical G and F motors? As Antares JS already mentioned, these engines don't fly themselves. So manufacturers won't include deltaV in the motors' specs because those values would depend on the rocket's weight and other characteristics.

I mean, do you ever see car manufacturers include 0-60 MPH specs with a standalone engine? No, you see other specs, like displacement, torque, power, RPMs, etc.

It is an overall performance metric. I can see why the manufacturers would not post it, but it is useful to compare motor designs. If the data was readily available I would not be posting asking for a list. I posted since maybe someone had the same thought I did and wanted to analyze various motors.

Anyway what is useful and contains the same info is the initial and final weight of the motor, along with a thrust curve. That info is available on the thrustcurve site so I will just calculate performance from there. It is not a big deal.

 

[mh9162013]

but it is useful to compare motor designs.

How?

If you have a motor's specific impulse, thrust and weight already, what does the deltaV give you that those 3 values cannot?

I'm not sure if you're into baseball, but if you are, your'e probably aware of ISO, or isolated power. It's derived from subtracting someone's batting average from their slugging percentage (SLG). ISO is supposedly used to measure a batter's hitting power.

Honestly, I think it's a statistic in search of a purpose. I don't see what benefit you gain from ISO that you can't get my looking at someone's slugging and on-base percentage (OBP). Perhaps you've got some algorithm where it might be easier to work with 1 number (ISO) instead of 2 (SLG and OBP).

A motor's deltaV stat reminds me of a baseball player's ISO.

 

[AlexBruccoleri]

How?

If you have a motor's specific impulse, thrust and weight already, what does the deltaV give you that those 3 values cannot?

I'm not sure if you're into baseball, but if you are, your'e probably aware of ISO, or isolated power. It's derived from subtracting someone's batting average from their slugging percentage (SLG). ISO is supposedly used to measure a batter's hitting power.

Honestly, I think it's a statistic in search of a purpose. I don't see what benefit you gain from ISO that you can't get my looking at someone's slugging and on-base percentage (OBP). Perhaps you've got some algorithm where it might be easier to work with 1 number (ISO) instead of 2 (SLG and OBP).

A motor's deltaV stat reminds me of a baseball player's ISO.

I prefer a single number instead of 2 for plotting purposes. I think it would be interesting to look at cato percentage versus motor delta-v as an example. I can think of other examples too.

Is there a file that has the motor stats for all the commercial motors? A big spread sheet that essentially has what the thrustcurve site has.

 

[mh9162013]

I prefer a single number instead of 2 for plotting purposes.

Can you elaborate further? I'm just curious and I'm not trying to judge. I know you mentioned cato versus deltaV, but are you trying to see if there's a correlation b/w a motor's deltaV and failure rate or something? But in that case, wouldn't it make more sense to compare more "fundamental" numbers, like a motor's specific impulse, weight, or max thrust?

It's your hobby and you do w/e you want with it (as long as you're not endangering others, of course). I was initially confused, but now I'm just curious.

 

[AlexBruccoleri]

Can you elaborate further? I'm just curious and I'm not trying to judge. I know you mentioned cato versus deltaV, but are you trying to see if there's a correlation b/w a motor's deltaV and failure rate or something? But in that case, wouldn't it make more sense to compare more "fundamental" numbers, like a motor's specific impulse, weight, or max thrust?

It's your hobby and you do w/e you want with it (as long as you're not endangering others, of course). I was initially confused, but now I'm just curious.

The motors delta-V is much better than ISP, weight or max thrust. It captures its bottom line and is more meaningful. For example great ISP in a heavy case will not tell you anything.... In liquids ISP and thrust-to-weight are often used together. Also propellant density comes into play a lot since it affects the overall mass ratio due to the influence on tankage, valves, pumps etc.

 

[WoShuGui]

Edited with corrected Theoretical Maximum Delta V:

Delta V = Total Impulse / Mass Propellant * ln (Motor Mass with Propellant / Motor Mass Empty)

Designation	Manufacturer	Diameter (mm)	N-s	Propellant (g)	Loaded Motor (g)	Isp w case	Max DeltaV (m/s)
J460T-L	AT	54	850	390	833	104.1	1,376
J540R-L	AT	54	1180	621	1100	109.5	1,580
K480W-P	AT	54	2295	1232	2059	113.7	1,699
K1100-T-L	AT	54	1594	733	1368	118.9	1,669
K695R-L	AT	54	1652	830	1450	116.3	1,691
J275W-L	AT	54	850	440	883	98.2	1,332
K2050ST-P	AT	54	1400	626	1283	111.3	1,497
J510W-L	AT	38	1152	662	1080	108.8	1,652
K1127-LB	LOKI	38	1285	624	1172	111.9	1,565
L1050BS-P	CTI	75	3,727.00	1774	3,448	110.3	1,518
L1350CS-P	CTI	75	4263	1905	3570.7	121.8	1,706
L2200G-P	AT	75	5104	2516	4751	109.6	1,530
L1365M-PS	AT	75	4780	2648	4908	99.4	1,400
L645GR-P	CTI	75	3,419.80	2072	3572	97.7	1,432
L800CL-P	CTI	75	3,757.00	1795	3511	109.2	1,498
K1275R-P	AT	54	2224.9	1222	1986	114.3	1,739
K1440W-14A	CTI	54	2372	1129	1893	127.9	1,906
K300CL-P	CTI	54	2546	1265.7	2270	114.4	1,640
K250W-P	AT	54	2553	1529	2211.33	117.8	1,963
L1090W-P	AT	54	2671	1400	2432	112.1	1,635
L1000W-14A	AT	54	2714	1400	2194	126.2	1,970
L935IM-P	CTI	54	3147	1567	2542	126.3	1,924
K270W-P	AT	54	2020	1162	2083	99.0	1,419
J570W-14A	AT	38	1060	524	892	121.3	1,791
J595-16A	CTI	38	985	511	866	116.1	1,719
J150MY-P	CTI	38	949	567.7	951	101.8	1,519
K740CS-18A	CTI	54	1873.9	846	1469	130.2	1,900
K630BS-15A	CTI	54	1679.4	912	1412	121.4	1,912
J355RL-17A	CTI	54	1190	669	1175	103.3	1,499
J449BS-15A	CTI	54	1260.5	624	1122	114.6	1,641
I165-17A	CTI	54	518	230.1	594	89.0	1,103
I364FJ-M	AT	38	450	302.1	581	79.0	1,093
I600R-L	AT	38	640	323.7	617	105.8	1,470
J350W-L	AT	38	700	375	665	107.4	1,549
I800VM-15A	CTI	38	419.2	221.3	457	93.6	1,254
J357-17A	CTI	38	657.6	337	601	111.7	1,605
J290W-15A	CTI	38	683.6	381.5	659.8	105.7	1,547
J270W-14A	AT	38	700	381	642	111.3	1,654
I303BS-16A	CTI	38	537.6	270	500	109.7	1,546
I59WN-P	AT	38	486	252	461	107.6	1,526
I161W-14A	AT	38	320	180	385	84.8	1,120
I357T-14A	AT	38	340	163	337	102.9	1,379
H210R-M	AT	29	220	110.8	251	89.4	1,156
H220T-14A	AT	29	220	106	239	93.9	1,216
G77R-M	AT	29	105	55.4	155	69.1	838
G76-10G	AT	29	118	60	147	81.9	1,032
G64-7W	AT	29	115	60	155	75.7	938
H180W-M	AT	29	230	117.2	264	88.9	1,152
I200W-M	AT	29	330	175	364	92.5	1,236
J90W-L	AT	54	770	391.4	834	94.2	1,246
J315R-L	AT	54	763.3	438	851	91.5	1,260
I327DM-14A	AT	38	546	340.7	553	100.7	1,534
H180SK-14A	CTI	29	258	150	314	83.8	1,117
H123SK-12A	CTI	29	176.5	100	228	79.0	1,019
D10-5W	AT	18	20	9.8	25.8	79.1	975
G138T-14A	AT	29	157	70.4	152	105.4	1,387
F52-11T	AT	29	80	36.6	123	66.4	772
F52-8T	AT	29	80	36.6	123	66.4	772
F40-7W	AT	29	80	40	126	64.8	764
G40-10W	AT	29	97.14	53.8	125	79.3	1,016
F42-4T	AT	29	55	27	77	72.9	880
F20-4W	AT	29	56.1	30	80	71.6	879
F27-8R	AT	29	49.8	28.4	80	63.5	769
K550W-14A	AT	54	1700	880	1515	114.5	1,680
K185W-14A	AT	54	1500	783	1418	107.9	1,539
H550ST-14A	AT	38	312	176	316	100.7	1,443
K375NW	AT	54	2228.1	1318	2106	108.0	1,662
K700W-P	AT	54	2261	1303	2035	113.4	1,774
G80T	AT	29	136.6	63	128	108.9	1,469
J180T-L	AT	54	764	437	809	96.4	1,358
J800T-L	AT	54	1229.11	618	1086	115.5	1,674

 

[AlexBruccoleri]

The theoretical maximum DeltaV as being described is Total Impulse / Total Motor Mass (including the hardware).

That is not correct. It is the exhaust velocity*ln(mass_initial/mass_final), ignoring pressure effects in the exhaust and atmosphere.

 

[WoShuGui]

That is not correct. It is the exhaust velocity*ln(mass_initial/mass_final), ignoring pressure effects in the exhaust and atmosphere.

Thanks. Yes, you are correct. I have edited the table above to use:

Theoretical Maximum Delta V = Total Impulse / Mass Propellant * ln (Motor Mass with Propellant / Motor Mass Empty)

The equation assumes exhaust velocity and thrust are constant, so that is a limitation with using readily available motor data.

 

[JohnCoker]

"I_sp with case" and your "non-rocket delta-v" are interesting measures.

 

[tsmith1315]

Maybe it should be called it the Bruccoleri Efficiency.

 

[Loki Research]

Alas, there are no high performance Loki Research motors in the chart above. :-(

Something to note here. Once upon a time, the former TMT chairman told me that he weighed all of a given cert motors propellant grains (paper propellant casting tubes and all) and that weight was recorded as the official "propellant" weight used for that motor on the thrustcurve.org site. FYI, our 38/480 motors have an average casting tube weight of 11.5g. Smoke grain? That's propellant too...right? No idea if it's included. This was learned after the majority of our motors were certified.

There is slightly inaccurate data scattered all over the place so if you find something that doesn't add up, that's probably why. Take it for what it's worth. This is after all a hobby, so I guess we can't expect everything to be perfect all the time.

 

[WoShuGui]

Alas, there are no high performance Loki Research motors in the chart above. :-(

Yes, the list of motors I have flown needed to be updated to include the K1127-LB. Us Californians don’t get too many chances to fly Loki Research

 

[Loki Research]

Californians don’t get too many chances to fly Loki Research

No they don't, and that really sucks. The regulators make the fees so high that small manufacturers simply can't afford to enter a normal marketplace there. Funny how that seems to be happening around the country for many small businesses these days. (not)

 

[AlexBruccoleri]

Alas, there are no high performance Loki Research motors in the chart above. :-(

Something to note here. Once upon a time, the former TMT chairman told me that he weighed all of a given cert motors propellant grains (paper propellant casting tubes and all) and that weight was recorded as the official "propellant" weight used for that motor on the thrustcurve.org site. FYI, our 38/480 motors have an average casting tube weight of 11.5g. Smoke grain? That's propellant too...right? No idea if it's included. This was learned after the majority of our motors were certified.

There is slightly inaccurate data scattered all over the place so if you find something that doesn't add up, that's probably why. Take it for what it's worth. This is after all a hobby, so I guess we can't expect everything to be perfect all the time.

I had the same thought. There is a lot of debris in the motor while cleaning. It would be great to have burn out mass as a spec. Alas...while not perfect, maybe just divide the total impulse by the initial weight. While not as "pure", it is quick and dirty, and a pretty good metric too.

 

[prfesser]

It was not an exhaustive study...but during one test session I compared the before-and-after-burning weights of the motors to the propellant weight, subtracting the weight of the paper casting tubes. I was surprised to see that there was very little difference in the two. It appeared that the weight of the residue left behind and the weight of burnt casting tube nearly cancelled one another.

 

[G_T]

That will be quite specific to the propellant. I've burned EX motors that left only scraps of the phenolic liner behind (very fast burn, very high pressure, very hot, practically invisible flame in daylight and barely detectable exhaust), and recently one slow burn that produces essentially zero slag due to composition. On the other hand, try burning something high in carbonates and metals (say, calcium carb plus strontium carb plus Mg for a nice color flame) in a small motor... lots of slag will be left behind. But burn it in a much larger motor, and the percentage mass slag left behind will reduce. You might also find the result different for vertical vs horizontal test stand orientation.

I'd argue that essentially whatever mass is lost during the burn is the "propellant", even if it started life as a casting tube, liner, nozzle, or smoke, and the resulting effective characteristic velocity is likely lowered due to the additional rather non-optimal propellant mass. This is partially traded off in slightly higher mass fraction.

It all depends on goals. For effects motors, performance mostly doesn't matter. For high performance, I like a metric something like density impulse divided by burn rate at target chamber pressure. That essentially tells me how much total impulse I can stuff within a given diameter with roughly the same safety margin. For our rockets of modest size, drag dominates over mass. Diameter dominates drag.

Gerald

 

[AlexBruccoleri]

That will be quite specific to the propellant. I've burned EX motors that left only scraps of the phenolic liner behind (very fast burn, very high pressure, very hot, practically invisible flame in daylight and barely detectable exhaust), and recently one slow burn that produces essentially zero slag due to composition. On the other hand, try burning something high in carbonates and metals (say, calcium carb plus strontium carb plus Mg for a nice color flame) in a small motor... lots of slag will be left behind. But burn it in a much larger motor, and the percentage mass slag left behind will reduce. You might also find the result different for vertical vs horizontal test stand orientation.

I'd argue that essentially whatever mass is lost during the burn is the "propellant", even if it started life as a casting tube, liner, nozzle, or smoke, and the resulting effective characteristic velocity is likely lowered due to the additional rather non-optimal propellant mass. This is partially traded off in slightly higher mass fraction.

It all depends on goals. For effects motors, performance mostly doesn't matter. For high performance, I like a metric something like density impulse divided by burn rate at target chamber pressure. That essentially tells me how much total impulse I can stuff within a given diameter with roughly the same safety margin. For our rockets of modest size, drag dominates over mass. Diameter dominates drag.

Gerald

Those are all great points. Low mass is still critical though and a low-thrust motor is optimal in the lower atmosphere. Certainly there a trade offs though.

 

[rocket_troy]

I'd argue that essentially whatever mass is lost during the burn is the "propellant", even if it started life as a casting tube, liner, nozzle, or smoke, and the resulting effective characteristic velocity is likely lowered due to the additional rather non-optimal propellant mass. This is partially traded off in slightly higher mass fraction.

With the rather important caveat that for such mass to be useful "propellant", it needs to exit as a gas (or at least be gaseous within the chamber). That's where the slaggy residues in the smaller motor example might not have necessarily contributed that much to the propulsion in the larger motor other than a thermal contribution.

TP