Liquid Engine Spool-Up IRL?

[MAFman]

I've noticed that in real-world launches, the engine ignites a few seconds before the launch clamps release, apparently to allow the engines to spool up to full thrust. Why do engines do this?

[Cavscout74]

The short version is moving parts (like the fuel & oxidizer pumps) have to build up speed to provide all the fuel & oxidizer needed to produce full thrust.   I know there are some people on here that can give a much more detailed account if you want.

I would guess it also gives a chance to abort if something starts to go wrong with an engine rather than realize 2 seconds after the launch clamps are released that an engine is failing.

Edited March 1, 2023 by Cavscout74

[HansAcker]

On 3/1/2023 at 8:20 PM, Cavscout74 said:

I would guess it also gives a chance to abort if something starts to go wrong with an engine rather than realize 2 seconds after the launch clamps are released that an engine is failing.

There are mods for things to go wrong in KSP, too 

I start up the liquid engines first (if there is a failure, they can be shut down and the launch scrubbed), then any solid boosters (on failure, the launch clamps keep them grounded until they burn out) and finally release the launch clamps when all engines run and produce thrust.

Edited March 3, 2023 by HansAcker

[Cavscout74]

1 hour ago, HansAcker said:

There are mods for things to go wrong in KSP, too 

I know, makes launches much more interesting when you never know for certain you'll make it to orbit, even on a tried & true design.  The "best" failure I had was a spaceplane with 6 kerbals, the whole back half blew up.  I had to bail them out & splash down via their personal chutes while never letting anyone get outside physics range from the others.