RAPIER center of mass

[edrobotguy]

I've been trying to make a minimal SSTO using the RAPIER engine.  I found that when adding the engine to the back of my craft the center of mass moved forward.  Looking at the part definitions, there is no immediately apparent difference between version 1.1.3 and 1.2.0, both of which have a 

CoMOffset = 0.0, 2.6, 0.0

 

[Daveroski]

The engine had it's COM forward for quite a while. Because of this it was even used to artificially lower the COM on rovers.

Having the COM forward of the engine allows for the expected weight being behind the engine as the only part you are actually attaching is the exhaust pipe. The engine proper is imagined to be hidden by whatever you attach it to.

Having the COM forward on a part designed primarily for spaceplanes helps with design where the COM can be too far back to be able to make a comfortable COL.

 

[sal_vager]

Thanks for the informative post daveroski

Also, moving to gameplay questions.

[edrobotguy]

This is not a gameplay issue.  This is a bug.  I have a very small ship, the Rapier is half the mass of the craft, and the CoM is in front of the ship.  The center of mass of the part should be inside the part. If the part is actually longer, make the part model longer.

Edited October 31, 2016 by edrobotguy

[Daveroski]

16 minutes ago, edrobotguy said:

This is not a gameplay issue.  This is a bug.  I have a very small ship, the Rapier is half the mass of the craft, and the CoM is in front of the ship.  The center of mass of the part should be inside the part. If the part is actually longer, make the part model longer.

You do have a very small ship.

A ship with only twice the mass of a Rapier?

Why?

Actually this whole thing has been hashed out quite a while ago.

Some thought as you do. Most did not. The Aye's had it.

 

[FullMetalMachinist]

1 hour ago, edrobotguy said:

The center of mass of the part should be inside the part. If the part is actually longer, make the part model longer.

They tried. People complained. I think it's available as a mod, though. 

[edrobotguy]

6 hours ago, Daveroski said:

You do have a very small ship.

A ship with only twice the mass of a Rapier?

Why?

Actually this whole thing has been hashed out quite a while ago.

Some thought as you do. Most did not. The Aye's had it.

 

Because I'm trying to make the smallest SSTO I can.

I guess it doesn't matter.  I can edit the CoMOffset variable myself.

[Rath]

5 hours ago, FullMetalMachinist said:

They tried. People complained. I think it's available as a mod, though. 

That was fun.  Almost as much as the changing the ROUND-8 to xenon thing.

[Daveroski]

7 hours ago, edrobotguy said:

Because I'm trying to make the smallest SSTO I can.

I guess it doesn't matter.  I can edit the CoMOffset variable myself.

Yeah.. and maybe you can bump up the thrust and ISP at the same time and maybe lower the mass a little?

Bad edrobotguy! (gedit?) Vanilla means vanilla!

 

[Arugela]

I made this for fun after reading this. I don't think it's actually the smallest SSTO based on a rapier. But it's pretty small. Nuke and rapier. Made it to orbit with  300+ DeltaV.

https://www.dropbox.com/s/ngxbe92gq99xa8j/Smallest SSTO Rapier.craft?dl=0

It's based on a B-52 bomber a little. The wheels or something need to be adjusted to make it take off faster... This would save more fuel at LKO.

 

And holy crap. Salvagers Gif changed. No wonder I never recognize him in threads now. I always notice him by his little Gif.. 8)

I forgot about those engine designs. couldn't they have just let you toggle the long part on and off? Both things could have been achieved... How is this different from toggling shrouds etc.. they should put them back with a toggle so people can get rid of the extended parts if needed for plane designs. Maybe even bend them.... 8o

Edited November 1, 2016 by Arugela

[edrobotguy]

10 hours ago, Daveroski said:

Yeah.. and maybe you can bump up the thrust and ISP at the same time and maybe lower the mass a little?

Bad edrobotguy! (gedit?) Vanilla means vanilla!

 

Yeah, I know.  I really wanted to do this in stock.  That CoMOffset for the Rapier just wreaks havoc with takeoff. 

(Notepad.)

Meh.  Maybe I can do it without the Rapier.