Canting engines

[MetricKerbalist]

Hi KSP colleagues,

Just one time, I would like to build a rocket so that a cluster of engines were canted.  In other words, instead of the engines all being parallel with the center of thrust, they were instead installed at any angle.  I just want to see if doing so induces a spin on the rocket.

So, is it possible to install the rockets with an angle.  Using symmetry, all the engines could be placed that way.

Mind you, please, I am not contending that canting engines is desirable.  I just want to try it.

Thank you.

Stanley

[Hotel26]

I've explored this with spaceplanes Geist and Poltergeist pictured below.

     

Geist features a center-line NERV with a low-slung Whiplash.  Atmospheric flight control has to compensate for the Whip on the ascent.

Poltergeist took the opposite approach by centering the Whiplash thrust and mounting a canted NERV underneath.  The NERV is aimed directly in the general direction of the CoM and has its own aligned probe controller for control reference.  (See the comments about its flight in vacuum resembling a crab 'scuttling'.)

It's quite doable and the benefit was LETO ("less engines to orbit").  Take note of the RW count in each.

It is true, though, that I made some effort to get the engine thrust centered through the CoM.  (Fuel balance becomes important.)

I recently collaborated with two others on an SSTO that had low-slung engines (mainly for appearance).  First observation is that, for the price of some drag, the asymmetry can be managed.  The resolution was to top-mount the engines on the wing, which is unconventional but looked even cooler.  Still asymmetric (since wing incidence was a main driver in the design), but within limits.

I guess the simple tl;dr is "yes, it's a factor and will cause rotation if unchecked".  Don't let that stop you experimenting and do have fun!

Edited June 12, 2021 by Hotel26

[18Watt]

Try using the ‘Rotate’ tool.   It looks like three intersecting rings.  After selecting the Rotate tool, ‘grab’ one of the rings and drag it.   Once you’ve figured that out,

• Hold Left-Shift as you drag the ring(s).  That rotates items in 5 degree increments, instead of the standard 15 degree increments.
• If you need smaller angles, turn off ‘Angle-Snap’, which is an icon that normally looks like a hexagon.   Clicking on the hexagon will turn it into a circle, and turns off Angle Snap.
• If you placed your engines with symmetry, all engines will rotate the same amount.

Note that most engines are mounted on gimbals, and will rotate to produce thrust in the direction the game thinks is appropriate.   So you may need to disable engine gimbaling to get the effect you are shooting for.   KSP does indeed model off-axis thrust, more or less as you would expect.

• Disabling engine gimbaling can be done in the engine’s PAW (Part Action Window).   This can be configured in the VAB (Vehicle Assembly Building), and also during flight by right-clicking on the engine.
• If you have action groups available, you can also set a key (action group) to toggle engine gimbaling on/off, which is handy.

I suspect you are going to want to use the build tools, such as Rotate and Offset, so report back if you have trouble working (or finding..) those tools.

[18Watt]

I just re-read your post- you’re trying to induce spin (roll) on a rocket.  You can also do this without mounting the engines ‘canted’ if you want.   Use engines which are capable of gimbaling, and leave the gimbal free (not locked).

To induce spin, use the roll controls, usually the Q and E keys.   The engines will gimbal to achieve a roll moment.   This does work better with multiple engines- a single engine mounted inline with the vertical axis won’t produce much of a roll moment.   But it will try..   Multiple engines mounted slightly laterally from the vertical axis will do much better at producing a roll moment.

I’m not sure how well KSP models gyroscopic effects however.   I suspect the game will not simulate accurately the effects of a spinning rocket.   But worth a try!

[MetricKerbalist]

I thank everyone for their answers to my question about canting rocket engines.

Stanley