OPENROCKET- discontinuity in body diameter... Booster Fins Issue

[NCTex]

I keep coming across the "Warning: Discontinuity in Body" pop up the moment I add fins to the booster section. :bang: I've searched TRF for someone having the same issue but have had no luck... Anyone run across this one in particular? I've simmed the sustainer alone and have zero issues. The sustainer/finless booster combination works too (with mass added to the nose cone ~100oz) I've attached the file with the hope that someone could point out where exactly I'm screwing up.:bangpan:
Thanks,
NCTex

View attachment Albireo Pre-Build Discontinuity Issue.ork

 

[wfcook]

I've seen this a lot, especially with multi-stage rockets. It seems to be the error that pops up when OR doesn't like something about your sim. Try reducing the step size...

It's a frustratingly in informative message because it seems to pop up when OR doesn't know what else to say. One of these days I'll step thru the code and figure out why.


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[astronwolf]

I did not experience any issues with your file.

There were no fins on the booster, so I copied your sustainer fins to your booster. I ran the sim. No issues.

-Wolf

 

[NCTex]

Thanks for the quick replies
Wfcook - Yep, reducing the step size was the first thing I did... Still no luck. I think I will just accept it as is...
Wolf - I did that exact thing multiple times and would get the same error. What version of OR are you using?

 

[BLKKROW]

No issues on 13.11.2 for me.

I had this issue a long time ago when the body tube was sightly bigger then the nosecone.

 

[K'Tesh]

I keep coming across the "Warning: Discontinuity in Body" pop up the moment I add fins to the booster section. :bang: I've searched TRF for someone having the same issue but have had no luck... Anyone run across this one in particular? I've simmed the sustainer alone and have zero issues. The sustainer/finless booster combination works too (with mass added to the nose cone ~100oz) I've attached the file with the hope that someone could point out where exactly I'm screwing up.:bangpan:
Thanks,
NCTex

One thing that I find is that if you don't choose to use a preset body tube (drop down menu found at top right corner of the Body Tube Configuration popup), it'll often do this. I like to pick my BT from the list, then tweak the length. That eliminates a lot of those problems, then the coupler will auto size to the correct ID of the BT.

 

[kruland]

The discontinuity problem is independent of step size. Basically it attempts to verify the aft radius of the previous body tube/transition/ nosecone, matches the fore radius of the current body tube/transition/nose cone. It's unclear to me why this would change if there are fins on the booster. There is also a check for gaps between adjacent body tubes, transitions and nose cones. I'll try to see what is going on with this particular file which trips up the logic.

In general, the discontinuity problem is simply a warning that there might be issues with the simulation since these discontinuities are not accounted for in the aerodynamics. If you build the rocket and there are no steps or other unsightly problems, odds are the simulation is accurate enough for you to trust.

Kevin

 

[kruland]

NCTex, can you please post the ork file with the fins which shows the warning? Also what version of OpenRocket are you using?

Thanks

Kevin

 

[wfcook]

Here is an example of a file which produces the warning, but only for a particular motor configuration. I guess this is why I assumed it must be defaulting to this warning somewhere - it's hard to imagine that there would be a discontinuity when an E12 is in the lower section but not when there is a D12. This is using OpenRocket 13.11.2.

Bill _/)_

View attachment BigBertha-ThreeStage2.ork

 

[kruland]

Thanks. That is weird.

Here is an example of a file which produces the warning, but only for a particular motor configuration. I guess this is why I assumed it must be defaulting to this warning somewhere - it's hard to imagine that there would be a discontinuity when an E12 is in the lower section but not when there is a D12. This is using OpenRocket 13.11.2.

Bill _/)_

 

[kruland]

Well, I figured out what's happening with this one. When the second booster separates it's still traveling upwards so the simulation of that stage's recovery starts OpenRocket models it as a rocket without a nose cone.

It's safe to ignore the warning - though I agree that it is disturbing.

I don't have any information on the other rocket posted, but I suspect that when it has fins, the booster is stable and again OR has this problem.

Kevin

Here is an example of a file which produces the warning, but only for a particular motor configuration. I guess this is why I assumed it must be defaulting to this warning somewhere - it's hard to imagine that there would be a discontinuity when an E12 is in the lower section but not when there is a D12. This is using OpenRocket 13.11.2.

Bill _/)_

 

[NCTex]

Thanks again for all the replies.
Kruland - I'm using 13.11.2
The ORK file attached has fins copied from the sustainer to the booster with the same warning message. I suspected the nose cone issue first, but as I mentioned previously, the sustainer performs fine alone.

NCTex, can you please post the ork file with the fins which shows the warning? Also what version of OpenRocket are you using?

Thanks

Kevin

View attachment Albireo Pre-Build Discontinuity Issue.ork

 

[NCTex]

I tried to avoid this issue by copying the original BT created for the sustainer.

 

[kruland]

Hi NCTex, Gotta say, that's a cool rocket. HPR staging is on my bucket list - hence why I added stage recovery - but I haven't gotten there yet.

Anyway, the discontinuity which is being detected is on the booster after staging. Basically the booster continues to fly upwards after separation and OR thinks this is a rocket without a nose cone - which it doesn't simulate well. My suggestion is to just ignore it - the booster will not fly as high as simulated (because of the extra drag).

Kevin

I tried to avoid this issue by copying the original BT created for the sustainer.

 

[NCTex]

Thanks Kruland! I'm a perfectionist and find it hard to ignore a warning without fully understanding the issue. I have been sitting on the idea for a bit and finally decided to follow through with it since the design keeps entering the vicious cycle of thinking and re-thinking without any testing. I'll create a build thread once all the components arrive.

NCTex

Hi NCTex, Gotta say, that's a cool rocket. HPR staging is on my bucket list - hence why I added stage recovery - but I haven't gotten there yet.

Anyway, the discontinuity which is being detected is on the booster after staging. Basically the booster continues to fly upwards after separation and OR thinks this is a rocket without a nose cone - which it doesn't simulate well. My suggestion is to just ignore it - the booster will not fly as high as simulated (because of the extra drag).

Kevin

 

[Leo]

...
Anyway, the discontinuity which is being detected is on the booster after staging. Basically the booster continues to fly upwards after separation and OR thinks this is a rocket without a nose cone - which it doesn't simulate well. My suggestion is to just ignore it - the booster will not fly as high as simulated (because of the extra drag).

Kevin

Thanks for the info. I've been having the problem for a Long time and never could figure out what I was doing wrong. I then just simply ignored it.

 

[wfcook]

Thanks, Kevin! It's good to know what's happening here.


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