[How does thrust change as a function of pressure?]

On 2/1/2016 at 8:10 PM, FancyMouse said:

For rocket engine I wasn't talking about curve in KSP but IRL (http://www.braeunig.us/space/propuls.htm, note A_e is fixed for a particular engine, so it should be linear to ambient pressure). I didn't look at the actual curve in KSP, but I would be surprised if it's not the case - I thought they've fixed that back in 1.0 when they don't change fuel mass flow for simulating atm ISP change.

I'm assuming you're referencing F = mdot*V_e + (P_e - P_a)*A_e

You do realize V_e is not constant either? It changes non linearly, see equation 1.22 in the link you posted. 

Here is a more complete equation for thrust with various efficiency variables:

Sforza, P. M. Theory of Aerospace Propulsion. Waltham, MA: Butterworth-Heinemann, 2012. Print.

On 1/31/2016 at 7:28 AM, FancyMouse said:

For rocket engines the relationship is simple: {actual thrust} = {vaccum thrust} - {some engine-specific constant} * pressure, i.e. it's just linear, and ASL number is just plugging in the pressure at Kerbin sea level. That should also be how KER calculates thrust at different altitude on different planets.

Jet engines follow a more complicated curve, and often includes velocity as one of the parameter as well.

You're going to need a source for that equation.

[Delta V Calculator]

Nice! Really useful! Should this not be in the applications forum though?

Yes, it would appear I did post in the wrong forum and did not follow the rules. I will update the OP soon with proper licensing and source code.

[Launch �V-Formula?]

Of course there are formulas! You really thing actual engineers just guess and hope they have enough fuel? There are 5 main components for total change in velocity:

- Burnout velocity (basically what velocity is needed for a certain orbit)

- "Loss" due to gravity

- Launch velocity

- Drag losses

- Steering losses

When paired with MechJeb KSP is extremely consistent. Drag losses and steering losses are the hardest to predict in real life and virtually impossible to predict in KSP. However, in my testing, when using MechJeb drag losses can be closely estimated for a planet and steering losses are negligible. You also need to factor in launch azimuth angle, flight path angle, launch latitude, and desired orbit inclination. These are all relatively simple "plug and chug" equations.

[Delta V Calculator]

**Updated to comply with forum rules. Download now contains source code and license**

Hi guys, thought I'd share a little project I've been working on. The aerospace engineer in me wanted a way to accurately calculate delta V requirements for getting into orbit about various planets. The KSP wiki page has some estimates, but I like accuracy. Paired with Mechjeb this makes for more efficient rocket building. In it's current form it just calculates delta V to get into a desired orbit, where orbit height, flight path angle, orbit inclination, and launch latitude are input variables, along with choosing what planet/moon. I'd like to eventually flesh this out as a full mission planner.

I decided to use Matlab because that's what I'm most familiar with in terms of programming. My only other option was Xcode and write an OS X application, but I don't really know objective-C (only know C++) and that's restricting with no Windows support. Matlab is great because it has a GUI builder that's easy to use. It also has a compiler for running GUIs outside of Matlab. The only downside is you have to have Matlab Compiler Runtime (MCR) installed to run the program. This is a bit prohibitive because it's a large program, at almost half a gig. It is free thought so anyone can run it. If someone is interested and has and would like to write a new GUI I'd be happy to collaborate.

You may also be wondering how I did the calculations for planets with atmosphere. For simplicity, I assumed the delta V due to drag was constant, and through testing figured out a number to use for Kerbin. I don't currently have numbers for Eve, Duna, and Laythe because I haven't gotten there. The numbers for Kerbin are pretty accurate though.

Here's a picture of the GUI.

VERSION 1.02

Delta V installer for Windows

Source Code

The installer will automatically download and install MCR if you don't have it. If you do have MCR installed it will skip that step and just install the application.

Planned features:

- Orbit changes

- Inclination changes

- Hohmann Transfers

- Orbit Insertions

- Landing

Notes:

For best results use MechJeb and enable the "Keep under terminal velocity" function when ascending on planets/moons with an atmosphere.

Change Log

Version 1.02 -March 22, 2014 
* Fixed error message for to low an orbit about Eve, Kerbal, Duna, and Laythe. Error was being superseded by another less important message

Version 1.01 -March 22, 2014
* Fixed font size of messages, some longer messages were getting cut off

Version 1.00 -March 22, 2014 
* Initial release