Why this font is everywhere

[Antares JS]

Pound-force is not mass, it's force. Slug and Pound-mass are the Imperial units for mass (though slug is more common because it matches nicely with the lbf)

1 N = 1 kg-m / s^2

1 lbf = 1 slug-ft / s^2

The reason people find this confusing is that when something is weighed in metric, you are given a result in grams or kilograms, which is actually a unit of mass. In Imperial, you get a result in lbf, which is a unit of force and is actually a weight, not a mass.

Bear in mind that weight and mass are not the same thing, but we're all rocket guys and probably no this.

Metric scales are set to report a mass based on weight, which is fine in 1G, but would not report an accurate mass in a non-1G environment. The fact that metric system users talk about mass while Imperial system users use a unit that is actually a force is indeed a source of endless confusion for people who can't grasp this. I never had much trouble with it though and have not-so-fond memories of my frustration when other engineering students had to have this explained to them repeatedly while I wanted to move on to the next topic.

Also, 1 kgf = 9.81 N because it's 1 kg * g. They don't convert directly into each other.

 

[DaHabes]

BTW, I like Comic Sans too... although I wouldn't use it for a resume.

Comic sans is the font people either love or hate or love to hate. Most hate it. I think the moniker "comic" is why it's a resume' no-no. I'm retired so I don't give a sh!t what others think. I like it. We all need to laugh more and bitch less.

Never have heard of the slug as a unit of mass., and I have an engineering degree. Learn something (useless) every day...

 

[DaHabes]

Also, 1 kgf = 9.81 N because it's 1 kg * g. They don't convert directly into each other.

Ah! There is my 9.81! The force of gravity in metric at 1G. Now I can proceed to forget this notable factoid once again....

 

[Blast it Tom!]

It's all the nomenclature. It's simply confusing. A Newton can be converted into a Pound-Force (mass), which is not the same as a Pound (weight). A Newton-Meter (torque) converts to a Pound-Force foot (foot-pound). Ugh! Actually, a Newton converts into a Kilogram-Force (the "bastard" unit referred to above). Some scientific sort with bad language skills came up with the names and they stuck because no one else could understand them and rationalize the naming conventions.

So, to calculate TTW ratios you need to convert Newtons to Pound-Force (not Pounds). 1 Newton = .225 Pounds-Force. So take Newtons, multiply by .225 and divide by the weight of the rocket in pounds.

Now, when I derived this, I came up with the formula so that all of the factoring was on the right hand side of the equation. Don't ask my how I got to this, it's not intuitive and I can't remember how I got here. My brain still hurts from it, but if you divide 9.81 by 2.2 you get 4.45. 1/4.45 = .225. Go figure. Here is my formula for calculating a TTW ratio:

Thrust [in Newtons] / ((Weight [in Pounds]/2.2) * 9.81) which also is the same as Thrust [in Newtons] * .225 / Weight [in Pounds]

You can use this with Average thrust or Maximum thrust. Max thrust is the most important assuming that max thrust peaks right after ignition, which is typical, which is what you need to get the rocket off the pad safely. For clusters just use the total sum (average or max) of Newtons for all of the engines in the cluster. For staged rockets only use the weight of the rocket that the staged motor(s) are pushing (I'm designing some complex multi-stage clusters).

Mike,

That's because there are ~2.2 kg per pound (mass). 9.81 is the acceleration of gravity in meters/sec^2. So in the first equation you're converting pounds (mass) to kg and multiplying that by gravity thus getting the weight in kgf- "kilograms force" - because pounds-mass and pounds-force are equal numerically in our lovely Imperial system. Whereas the definition of a Newton is not gravitation-based. So you need to know the force exerted by gravity on the mass of your rocket, which is it's mass multiplied by the acceleration of gravity. Then you have a consistent TTW ratio. You could do the same thing converting the thrust from Newtons to pounds and using the rocket weight in pounds, but then you get into ounces and all that happiness! That's why I like Mathcad...!

ETA: A minute too late...

 

[fyrwrxz]

How frickin cool is this thread? Can we make it a sticky? Am I being too geeky? When I took early retirement from Areospace engineering, they gave us free re-training and I opted for web design. Was I an Art Major? Hell no! However, I helped a lot of these 'rainbow warriors' (weak color wheel joke) understand the computer interface to their creative dreams, so I survived with a B+ . Learned a lot from these right brained people and a new respect for the 'softer arts'. Not my cup of tea, but I can still design some cool logos and actually made a little money at it. The digression is priceless and I am furiously writing down some of these formulae for posterity (or my posterior, unsure which at this moment). Somehow one of these factorials will become a rocket name, replete with ComicSans font! I know Stickershock has my back, and may enjoy the hijinks also. I love TRF!

 

[stealth6]

How frickin cool.......snip.........love TRF!is this thread?

I fixed it for you:



ssixsixsix

 

[fyrwrxz]

Hence the phrase "Always check your six"
Love ya bro'! Do you still make any launches? Us Daves have to stick together or the Kevins will take over.....

 

[John Kemker]

Worked in a print shop in my younger days, running a Linotronic 100, a photo-typesetting machine. Didn't use a WYSIWYG interface. Instead, you had to learn various symbols in the keyboard to get what you wanted. Got pretty good at it.

My personal favorite typefaces are Goudy Old Style and Garamond. (What computers call "fonts" a printer/typesetter would call a "typeface." A font is a particular typeface and size combination. Ergo, "Goudy Old Style, 12 pt." is a different font than "Goudy Old Style, 14 pt." )