I'll be damned, Squad buffed the RAPIER in 0.24 - twice!

[Geschosskopf]

If you check the wiki you'll fin a note that the price of the RAPIER was reduced from 5900 to 3600: http://wiki.kerbalspaceprogram.com/wiki/R.A.P.I.E.R._Engine

What the wiki doesn't seem to know yet is that the RAPIER's mass was reduced from 1.75t to 1.2t! That is a pretty significant change, especially considering that the turbojet brings 1.2t to the table as well. Hot damn! I was feeling a bit light in the bottom department lately. Erm, that came out wrong...

And don't forget the 4 nozzles of the RAPIER now gimbal independently so can provide some roll control / SAS stability.

[LethalDose]

Was there any reason given for dropping the RAPIER's weight? It just does more than than the turbojet... It feels like it should be weight more, too.

It seemed reasonably balanced in 0.23.5, I guess I'm just not clear on why it was changed.

[Col_Jessep]

Was there any reason given for dropping the RAPIER's weight? It just does more than than the turbojet... It feels like it should be weight more, too.

It seemed reasonably balanced in 0.23.5, I guess I'm just not clear on why it was changed.

I might have an answer for that question. The weight the RAPIER has now balances planes pretty well (the red dot is the dry center of mass):

If you add some weight which roughly simulates the old mass you'll find that the CoM and DCoM move back and separate.

The problem becomes even more prominent if you use two or more engines as we all know. And at some point it becomes very hard to keep the DCoM anywhere near the CoM which means a notable shift in balance and possibly a very unstable plane with half-empty tanks (even if you use fuel lines to draw fuel from the center tank).

PS: The mod I'm using to display Dry Center of Mass is called RCS Build Aid and is extremely useful for planes, SSTOs, VTOLs and placing RCS thrusters.

Edited August 1, 2014 by Col_Jessep

[Beachernaut]

Apparently I LOVE easy mode....

I like the Rapier, but it isn't the end all that some people like to make it out to be. It'd had been a long time since I'd designed spaceplanes, but .24 got me going again. I had a great medium size SSTO that used 1 turbojet and 2 48-7s. The turbojet took it to just above 35k then the 48-7s's to orbit. Replacing the turbojet with a Rapier, and removing the small engines all together still produced a viable SSTO. However, with just the rapier it uses much more fuel, exactly as expected. Small design changes helped alleviate the difference in fuel usage, but only marginally.

IMO the biggest impact of the Rapier on SSTO spaceplanes is design. The Rapier allows a simpler design to perform the same function at the cost of more fuel. I know complicated designs are cool and all, but I prefer simpler designs to perform the same job. Also, I just can't help but dismiss a design when it's functionality relies on an aerospike or Nerva clipped inside the turbo jet.

Use of the Raiper also depends on the role of the SSTO. I have a small spaceplane I use to shuttle kerbals to my station in LKO with the same engine configuration as above (1x tjet, 2x 48-7s). Works great in that configuration, but when used with a Rapier there's no error fuel (error= have to fly a bit to get to the runway). So this design doesn't use the Rapier.

Disclaimer: I am by no means a spaceplane expert, so your results may vary from mine.

Edited August 1, 2014 by Beachernaut