G64 vs. G104

I'm sure I'm being stupid, but why does a G64 sim at a much higher altitude than a G104? Acording to Open Rocket, a G64 will give me a litle over 900ft, but a G104 will only give me a little over 500ft. The average and peak thrust on the G64 are both lower than the G104. What am I missing?

https://www.rocketreviews.com/aerotech-g64.html

https://www.rocketreviews.com/aerotech-g104t.html

View attachment bullpup_3in_316_29mm.ork

Total impulse is much higher on the G64 (118 vs 82 Ns). This will win out in the end- there's more total thrust.

Thrust = how many pounds can my rocket safely lift?

Impulse = (assuming thrust is adequate) how high will it go?

djs said:

Total impulse is much higher on the G64 (118 vs 82 Ns). This will win out in the end- there's more total thrust.

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+1.

djs said:

Total impulse is much higher on the G64 (118 vs 82 Ns). This will win out in the end- there's more total thrust.

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I missed that. See? I was being stupid.

qquake2k said:

I missed that. See? I was being stupid.

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Not really, your powers of observation failed you 😛

rharshberger said:

Not really, your powers of observation failed you 😛

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In my defense, I have been away from the hobby for a couple of years. And I'm old.

This is why I like the CTI way of labelling their motors- because you get both pieces of information (how many total Ns, and how fast it burns).

djs said:

This is why I like the CTI way of labelling their motors- because you get both pieces of information (how many total Ns, and how fast it burns).

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Unfortunately, our onsite vendor has been unable to get CTI MPR reloads since the fire. So AT it is.

djs said:

This is why I like the CTI way of labelling their motors- because you get both pieces of information (how many total Ns, and how fast it burns).

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I agree. It seems to me that an even better system could have been devised that classified motors by listing their average thrust and burn time. So a D12-5 would be classified as a D10.2-1.7 (5) by the system that I just proposed. Not as easy to say but more informational.

Be what it may, the G64 is one fine motor. Been around a long time. For most midpower rockets, just the ticket. AT, CTI, Loki, all have loads that are their standouts. For AT the G64 may be their best overall load. IMHO

Well, I'm glad you could come back!

Greg

I was going to talk about higher drag forces created by the higher thrust motor, but with that much of an impulse difference, there's no need lol.

Personally, I like a percentage indicator. The total newtons Infront of Cesaroni designations are pretty clumsy when things get bigger

Which looks better:
263H120R
Or, 64% H120R

Nytrunner said:

I was going to talk about higher drag forces created by the higher thrust motor, but with that much of an impulse difference, there's no need lol.

Personally, I like a percentage indicator. The total newtons Infront of Cesaroni designations are pretty clumsy when things get bigger

Which looks better:
263H120R
Or, 64% H120R

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263H120R looks better, the percentage is harder to convert to burn time for the average person. Of course usually I am more interested in the thrust during the first .5 second.

rharshberger said:

263H120R looks better, the percentage is harder to convert to burn time for the average person. Of course usually I am more interested in the thrust during the first .5 second.

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Not sure I've ever needed to pay attention to the burn time, but then again, I'm not a staging flier (yet).
Things like 16803N1560P just look like an ugly string of smoshed together characters to me.

For the motor designations, I wish they would have put thrust in pounds instead of newtons. I think that would have been more intuitive.

Swissyhawk said:

For the motor designations, I wish they would have put thrust in pounds instead of newtons. I think that would have been more intuitive.

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Well, not if you grew up in a country using the Metric System. But don't get me wrong. I still have a better feeling for a motor's power by seeing thrust in pounds. Being on old timer, the first Estes motors I used in the early 60s were designated using pounds / pound-seconds.

Swissyhawk said:

For the motor designations, I wish they would have put thrust in pounds instead of newtons. I think that would have been more intuitive.

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Yeah, but if we use pounds for force then we should refer to mass in slugs...

Honestly, If having the motors coded in Newtons will help familiarize people with metric and its benefit to physics, I'm totally ok with that.

Rockets can be a great boost of knowledge and experience, a learning activity.

Or it can be "I make tube fly with fire!"

Nytrunner said:

Honestly, If having the motors coded in Newtons will help familiarize people with metric and its benefit to physics, I'm totally ok with that.

Rockets can be a great boost of knowledge and experience, a learning activity.

Or it can be "I make tube fly with fire!"

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I want that last on a tee shirt !

You're right about metric. It's not hard to learn; a person just needs to step trying to convert to English units all the time.

I think you just named someone's next build.

5x7 said:

I think you just named someone's next build.

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Hmmm...

gdjsky01 said:

Hi Captain...

Total area under the thrust curve. Remember?
Average thrust has nothing to do with it. And impulse ranges (letters) become exceedingly wide above a F (F is 41-80ns).
G's are 81ns to 160ns. An IMO each letter on gets worse (IMO). People certify on what is little more than a full G.

That is why I always think in terms of percent of a full <LETTER>. I have flown K's that were, according to the specs, just a few newton seconds over a full J. In other words 2% of a full K. A baby K for sure, yet technically a K.

And a J (like the CTI 1266J760-19A) that is 15ns short of a 'K'. Or 98% of a full J.

So many times I have rolled my eyes :eyeroll:... Ooooooh a J350... BFD?
Which is, as certified, (697.4Ns) BARELY a J. 57ns over. A 9% J. A J for sure, but only because you have to put a line in the sand someplace, but BARELY a J. Think of it. My J760 was also a 'J' but virtually double a J350.

This is also why I have ALWAYS applauded CTI. They designate their motors with Total Impulse - Letter Designation - Average Thrust - Max Delay Range
Like 140G145-15A - 140ns - G impulse range - 15 second adjustable delay.
We need BOTH total impulse and average. The letter is almost meaningless.


Aerotech for whatever reason does not follow suit.
But IMO it's the way ALL motors should be listed.
JMO

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Personally I have always disliked the % of X system, a K is a K even if its only 2 Ns more than a max Ns J. CTI's descriptors are definitely more informative, and Aerotechs system leaves a lot to be desired.

I personally do like the CTI system better. There's more info at a quick glance. But, with the Thrustcurve app on my phone, the AT info is just a few taps away. And since I've been flying more AT lately due to my vendor only getting a few CTI here and there, I'm slowly becoming more familiar with the AT system. One thing I do like about AT much more than CTI is that I get to assemble the motor. I love putting them together. There's another feeling of accomplishment when your J540 burns loud and proud.

Try it with a G138T

terryg said:

Try it with a G138T

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Now that you mention it, I think I have a G138 reload somewhere. I've only ever flown one. They used to have a reputation for splitting the 29/40-120 cases, but I didn't have a problem. Blue Thunder isn't my favorite propellant, and it sims at 1600ft. That's higher than I want to go on the small field.