OpenRocket - Adjusting Cluster Motor Pitch

[lp48]

Gents,

I'm working on designing a payload separation system for a lvl 2 (&3) build. Essentially I would like to put "escape thrusters" near the nosecone. Is there a way to do this within OpenRocket. The thought is the escape thrusters would be angled between 15-45 deg from the centerline of the vehicle. I know how to input cluster motors but having difficultly adjusting the pitch of the motors. Would appreciate any input.

 

[H. Craig Miller]

The "pitch" of the motor that you are describing is not a feature in either the current version of OpenRocket or the new release being developed. The thrust of all motors are and can only be input parallel to the centerline of the rocket; RockSim has the same limitation.

 

[mjennings]

Not sure about OR but I know folks have edited motor files in RS for canted motors. Thrust times the appropriate trig function and the angle is your knock down.

 

[H. Craig Miller]

To the extent that editing motor files is useful, both OpenRocket and RockSim allow for the use of edited motor files. But, neither simulator allows a motor tube to be angled so that it is other than parallel to the centerline of the rocket.

 

[jqavins]

[N]either simulator allows a motor tube to be angled so that it is other than parallel to the centerline of the rocket.

Which is a darn shame, but whutcha gunna do? RS doesn't do canted fins either; does (will) OR?

 

[neil_w]

Yes, OR does canted fins.

 

[jqavins]

And the "Fin Rotation" directly above it; is that for going off normal to the tube surface?

 

[neil_w]

And the "Fin Rotation" directly above it; is that for going off normal to the tube surface?

No, that's rotating the whole set around the body. By default one fins is always at 0 degrees, but I can change it with that setting. So I could have, say, 2 sets of 2 fins, each 90 degrees off from one another. I'd set Rotation on one of them to 90 degrees.

 

[jqavins]

Yeah, got it. I should have realized. That's pretty much essential, and it wasn't anywhere else on that screen. A 4FNC with one fin a different color from the rest, for example, is done with three fin "sets". One set is two fins, one is a single fin at 90°, and finally the odd color one at -90° (or 270°, obviously). And there are a thousand other uses (or maybe just 360) so I should have known.

 

[SpaceManMat]

It’s probably reasonably easy to build a plugin for OR that would adjust the thrust based on the cant angle. Would you mind posting your simulatio? I may have a play with this sometime.

 

[Cape Byron]

A 4FNC with one fin a different color from the rest, for example, is done with three fin "sets".

It took me a long time to work that out for a Nike Smoke# clone that I wanted to do a "fin 'n lug shuffle".

#therocketthatlooksmostlikearocket

 

[jqavins]

It’s probably reasonably easy to build a plugin for OR that would adjust the thrust based on the cant angle. Would you mind posting your simulatio? I may have a play with this sometime.

Which degrees of freedom does OR simulate? Pitch forward motion resolved into altitude and down range are enough for most of us. Adding canted engines would require expanding to full six DoF simulation. That sounds like more than a plug-in.

 

[SpaceManMat]

Which degrees of freedom does OR simulate? Pitch forward motion resolved into altitude and down range are enough for most of us. Adding canted engines would require expanding to full six DoF simulation. That sounds like more than a plug-in.

My Thought was to just scale down the trust according to the geometry. If you have a canted cluster then the sidewards component of the thrust from one motor is cancelled out by the sidewards component of thrust from the others. If this wasn’t the case then it would not fly straight. If you used it on a single motor or mismatched motors then it would not work but that’s a reasonable limitation.

 

[jqavins]

I've built one (haven't tried launching it yet) where the canted motors are oriented such that they make the rocket spin. I'm not sure how much that would change things, but I'm sure it changes them somehow.