Rockets: Center of lift vs. center of thrust.

[Aethon]

Tsup.

The story so far...

I recently started a new career after losing my last hard drive. I"m lowish in the tech tree- Kerbin's pretty well covered. I did double flybys of Mun and Minmus (high and low sci.). So I'm prepping a couple of flat Minmus landings with all sci finally unlocked (but not the claw,) when into my SOI, falls this silly type A asteroid who thinks he/she's some sort of a tough guy. Hrmph.

Comin' in over the poles-ish (no orbital influence from Mun or Minmus so it'll be stable) and all he/she needs is a love tap to put 'er/'im into a stable orbit, to be plundered later in the tech tree. So I cobbled together this piece of fecky to do just that. Don't laugh!

http://steamcommunity.com/sharedfiles/filedetails/?id=259234922 Angled for viewing purposes

I've played the game a lot for six mo. or so and have discovered many things that were hidden, but I'm not sure I know where center of lift should go in relation to center of thrust (on a rocket). I usually use fins to put the purple ball exactly on top of the blue ball.

What say Ye?

Edited May 13, 2014 by Aethon
Aswered

[InterCity]

Center of thrust is more related to center of mass than center of lift. It's generally good if they're all in the same axis.

That's about all.

[Taki117]

on a rocket CoL doesnt matter much unless it's above the CoM. (rockets are weired like that) Your current configuration, while odd, will get the job done, but keep in mind that even a "little tap" can be a few hundred meteres per second.

[Aethon]

Yep Taki. That ship is definitely a two bagger. A bag over her head and a bag over mine... In case her bag falls off.

[Taki117]

Yep Taki. That ship is definitely a two bagger. A bag over her head and a bag over mine... In case her bag falls off.

this statement confuses me, mind explaining?

also, I cant tell if you have fuel lines running from those small radially mounted tanks, but if you don't you should. (or get rid of them unless you need the extra fuel)

Edited May 12, 2014 by Taki117

[Red Iron Crown]

CoL is just about irrelevant for rockets that use mostly engine thrust for lift. It's absolutely critical for spaceplanes, though.

[xcorps]

this statement confuses me, mind explaining?

It means ugly. (She's a two bagger, meaning you need two bags to hide her face during coitus)

[Aethon]

this statement confuses me, mind explaining?

also, I cant tell if you have fuel lines running from those small radially mounted tanks, but if you don't you should. (or get rid of them unless you need the extra fuel)

So my carefully crafted view angle didn't convey all the info. Damn!

Fuel lines are a roger, tho I forgot them on the Mk.I.

Since you asked...It's actually a very crude joke cleaned up for family viewing. Let's just say she's so ugly I don't want to look at her, so I want to put a paper bag over her face so I can't see her while we're... er, flying- and I want to put a bag over my face, so if her bag falls off- I still cant see her.

Sorry, I'll let myself out.

Ahhhh Ninja'd

[SRV Ron]

For model rockets, there is a COP, center of pressure. So long as that is to the rear of the COM, center of mass, the rocket flies straight. That same flight characteristics remains true in KSP physic even with SAS off and no external commands issues. Let the COP get ahead of the COM and the rocket will swap ends at the slightest instability or issuance of a steering command.

In space, the COP becomes irrelevant. Of course, if the COM and COL are not aligned, the rocket will not only swap ends, but tumble out of control.

[araveugnitsuga]

CoL is related to Aerodynamic Forces

CoT is related to sheer booster force.

CoM is the average spot of where your weight is.

A rocket going up can ignore CoL because the fluids around it (in this case air) don't really do much beyond applying a force in the opposite direction (as long as the nose points upwards and the control surfaces are symmetric).

CoT is the point which represents from where the net force of all your boosters is applied; if it's in line with the CoM it's the same as directly pushing the whole craft up. If its not in line, it's equivalente to trying to push it slightly to the side; imagine pushing a revolving door from the centre; your hands are the thrust and they are also analogue to the CoT, if you have enough strength the door will move forwards from the frame without rotating, if its symmetrical the air hitting it as you push forwards also doesn't make it rotate because both sides get equally hit by the air. On the other hand if you push it from the side (anywhere not in line with its centre of mass); it will start to rotate, the farther from it the easier it is to make it rotate; you do not want your rocket to start rotating... in most cases.

In proper physics the offset from the centre of trust line to the centre of mass results in a Torque; CoL can also produce torque but only if the craft is not symmetrical (symmetry makes torque on both sides cancel each other out).