Help to Calculate TWR and Isp with the new NERVs combined with LFO rockets?

[Brainlord Mesomorph]

The old TWR Calculator web page (http://iyates.co.uk/ThrustCalc) doesn't seem to handle the the NERVs.

I have a ship with 2 NERVs and 4 Rokomax 47Ss

The LFO rockets are only on when needed. (usually NERVs only)

She weighs 26.5 tons full (a mix of 3/4 LF and 1/4 LFO) and 16t empty.

So what's my TWR on NERVs?

Whats my TWR with all engines?

And what's my Isp with all engines?

[Gaarst]

Use this formula to calculate the Isp of a stage with several engines:

The fuel doesn't matter, all you need is the consumption rate or individual Isp.

For TWR just divide thrust by mass*g

[Red Iron Crown]

TWR = (Sum of Thrust)/(TotalMass*LocalGravity), so your vessel has a Kerbin-relative vacuum TWR of 0.74 when full and 1.22 when empty using all engines, with nukes only it is 0.46 full and 0.76 empty.

Isp for heterogenous clusters is calculated by:

For your particular cluster, this yields a vacuum Isp of 492s.

[Brainlord Mesomorph]

TWR = (Sum of Thrust)/(TotalMass*LocalGravity), so your vessel has a Kerbin-relative vacuum TWR of 0.74 when full and 1.22 when empty using all engines, with nukes only it is 0.46 full and 0.76 empty.

Wouldn't the TWR be zero if I have no fuel?!

Thanks guys.

and BTW: that math is just Greek to me, (LOL) Sigma over "i" (but not divided by "i", or with a subscript of "i")?? "i" am confused.

I *AM* a computer programmer. so perhaps if you could rearrange that into one line of text, I'd say "OH!!!"

Edited November 3, 2015 by Brainlord Mesomorph

[el_coyoto]

BTW: that math is just Greek to me, (LOL) Sigma over "i" (but not divided by "i", or with a subscript of "i")?? "i" am confused.

I *AM* a computer programmer. so perhaps if you could rearrange that into one line of text, I'd say "OH!!!"

Gaarst's and Red Iron Crown's formulas are equivalent. "Sigma over i" means "Sum each item", just like you would iterate over an array and sum its contents.

A C like conversion with n engines would look like this :

numerator = 0

denominator = 0

for(unsigned int i = 0; i < n; i++)

{

numerator += F

denominator += F/Isp

}

Isp = numerator / denominator

[Brainlord Mesomorph]

Oh, looping through all the engine sets. gotcha!

[storm6436]

Oh, looping through all the engine sets. gotcha!

Yep. The character under the sigma tells you what variable is being counted. (So it could be i, n, etc) Depending on the equation, you might see "i=1" on the bottom with a number on top of the sigma, say 30. This is the same thing as a "For(i=1;i<30;i++);" in C++.

[Freshmeat]

As a teacher, I highly approve of this thread.

[Dawnstar]

As do I. Too many people giving equations neglect to provide English translations of the terms. Most of us don't, in fact, read math natively ... and even those of us who do appreciate it when variables are defined.