G64 vs. G104

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

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That's because aerotech is the leader :) as they were available first. Actually though, aerotech has new labels that show the thrust curve, total impulse, burn time, propellant weight, motor weight, and dimensions. I like that better.
 
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!"

I expect more often it means they never have any idea how much thrust it has.

Reading this thread made me finally look it up, because despite knowing the approx. conversion factor, I had no idea how newtons fit into the "system" that metric always does. I found:

1 N = 1 kg * 1 m/s^2

and the acceleration of gravity is 9.80665 m/s^2. So it is a gravity-independent unit of force. NOT convenient for those who have handy earth gravity to convert mass into weight units at all times. Or use weight units already.
 
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I expect more often it means they never have any idea how much thrust it has.

Reading this thread made me finally look it up, because despite knowing the approx. conversion factor, I had no idea how newtons fit into the "system" that metric always does. I found:

1 N = 1 kg * 1 m/s^2

and the acceleration of gravity is 9.80665 m/s^2. So it is a gravity-independent unit of force. NOT convenient for those who have handy earth gravity to convert mass into weight units at all times. Or use weight units already.

Very few physics equations use weight. For one thing, weight is only important along the vertical axis. Mass is important in every direction.
Mass x acceleration = force
Mass x velocity = momentum
1/2 mass x velocity ^2 = kinetic energy

For any of the equations above you would use slugs in the English measurement system. In English units:

1 slug x 1 ft/s^2 = 1 pound-force(abbreviated lbf).

To convert slugs into weight you have to multiply by 32 ft/s^2.

It is possible to use the pound as a mass unit. When that's done you abbreviate it lb. In that case you use the poundal as the measure of force.

1 lb. x 1 ft/s^2 = 1 poundal (pdl).

What were you saying about convenience?




Steve Shannon
 
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

In addition to what everybody else said, there is the optimum mass thing. For every motor+aerodynamic drag combination, there is a unique mass to achieve maximum altitude. Make your bullpup heavy and draggy enough, then the G104 will fly it higher.
 
What were you saying about convenience?
Steve Shannon

No kidding. Any freshman engineering student can tell you that SI units are far more "convenient." I work in a stereotypical, old school, rust belt industry, and we have used SI units for 30+ years. I can't believe resistance still exists in 2017.

And yeah, I don't care what letter the motor is. Give me the N-s.
 
You sound just like a guy who builds a house next to an airport and then complains about the noise. It never occurred to you that like that airport, Aerotech, following what by then was standard industry practice was in business before CTI.

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 :)


 
I expect more often it means they never have any idea how much thrust it has.

Reading this thread made me finally look it up, because despite knowing the approx. conversion factor, I had no idea how newtons fit into the "system" that metric always does. I found:

1 N = 1 kg * 1 m/s^2

and the acceleration of gravity is 9.80665 m/s^2. So it is a gravity-independent unit of force. NOT convenient for those who have handy earth gravity to convert mass into weight units at all times. Or use weight units already.

Eh, a pound (force) is just as gravity independent. 1 kg *g (9.81 m/s^2) = 9.81 N :: 1 slug *g (32.2 ft/s^2)=32.2 lbs
Single unit of mass times single unit of acceleration equals single unit of force.


Problems come in when people assume lb-force and lb-mass are interchangeable.

Back of the envelope calculations? I'll multiply pounds by 4.5 to get Newtons any day rather than have to wrestle with Slugs.
(I don't think I've Ever used a poundal even in a textbook problem)

Back to my original position, I really hope people research and look up what these numbers mean. To better understand how Both unit systems work together and how this amazing sport/hobby really works.
Otherwise people are just sticking numbered tubes into bigger tubes and hoping for the best.
 
....
Problems come in when people assume lb-force and lb-mass are interchangeable.

Back of the envelope calculations? I'll multiply pounds by 4.5 to get Newtons any day rather than have to wrestle with Slugs.
....
Otherwise people are just sticking numbered tubes into bigger tubes and hoping for the best.

I couldn't agree more.
 
No kidding. Any freshman engineering student can tell you that SI units are far more "convenient." I work in a stereotypical, old school, rust belt industry, and we have used SI units for 30+ years. I can't believe resistance still exists in 2017.

Ya know, being Canadian, we're in a unique situation. We are metric, yet the US is our largest trading partner. So, all my design life I've used both imperial & metric measurements, depending on who I was working for and who my end customer was. Also, in some cases, who my supplier was.. For the most part, it's imperial, sheet metal in gauges, and so forth.

I did try to search for why the US is imperial, and there are arguments, but none I found completely compelling. I then noticed / read somewhere that the US, along with Yemen & Burma are the only countries that still "officially" use Imperial measurement system..
 
I appreciate that metric is a "system" as I said that is convenient in a lot of ways, and smarter. Just maybe too smart when it came to weights and masses! It reminds us constantly that Mass Is Not Weight and we could be anywhere in the universe or even just floating free and just "happen" to be on Earth. Maybe that's the downfall of metric in the U.S., most prefer to be reminded their feet are on the ground (or we're stubborn.. only). Besides, the public truly accepting a system means they no longer think about it or need to understand it, even with metric.

Also in model rocketry or manned rocketry, or anything inside orbit, we still talk g forces. In comparison to earth gravity, usually familiar in units of weight, even if really Kgf.
 
I'm enjoying this conversation a lot since my biggest issue with the rocketry community is the mixed units. Body diameter in inches, thrust into newton's, thrust to weight ratio in lbs....

As a scientist, I prefer si but would happily do imperial if it was consistent!
 
I'm enjoying this conversation a lot since my biggest issue with the rocketry community is the mixed units. Body diameter in inches, thrust into newton's, thrust to weight ratio in lbs....

As a scientist, I prefer si but would happily do imperial if it was consistent!

Well, thrust to weight ratio is dimensionless :wink:

I agree with you, though. However, I am just as guilty in mixing units in my builds. I think the airframe diameter standard is slowly converging to mm, due to proliferation of fiberglass tubes and minimum diameter kits. That's a good thing. The most annoying to me are the old Estes body tube designations. I couldn't tell you the diameter of a "BT-20" if my life depended on it.

Even our good neighbors to the north, Cesaroni, have mixed bag of SI and English units, which is a bit surprising to me.
 
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.

FWIW, it got a lot easier for me once I worked through the conversion to pounds and then realized that one newton equates to just a tad over 100 grams thrust. I weigh my rockets on a scale that reads in grams anyway. It makes thrust to weight computations pretty easy. I also realize that might not be as convenient on much bigger rockets than what I fly.

-Sean
 
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