Discontinuity in rocket body diameter

[AcadiaRockets]

My OpenRocket design for my modded Mean Machine has the error "Discontinuity in rocket body diameter" I have tried looking this up and can't find the right solution. Most are regarding nosecone sizes. I suspect it has something to do with my TTW fins but I don't know how to fix it.
I flew it this weekend on an E20 and an F67 successfully. In the attached file I have a selection of G motors for my 29/40-120 case. Before I go much further though I would like to resolve the "Discontinuity in rocket body diameter" error. Any help would be appreciated including mods to my design.
Thanks.

 

[K'Tesh]

It is the most frustrating error message out there. If all the important dimensions match, I suspect that it might be a fractional error that hides beyond our ability to see (.001 we can see, .0001 we can't). I just ignore them.

Also... Often with my personal sims, I'm forced to use Phantom Body Tubes to mount fins (including the Engine Hook (which is simmed up with a fin). If the rocket isn't a minimum diameter, then the error will present itself.

 

[neil_w]

Also note that you should delete the phantom body tube at the end (along with its fins) to get proper sim results.

 

[AcadiaRockets]

View attachment 491180

Also note that you should delete the phantom body tube at the end (along with its fins) to get proper sim results.

Huzzah! Thanks neil_w, that resolved it. Now a couple weeks ago when this presented itself I did try checking the "automatic" boxes on many of the parts but it made a mess so I didn't save it. May I ask how you ID'd THAT component as the offender?
I see its a common frustration that the program does not id the error locations.
I appreciate everyone on this forum and the generous help given. I enjoy the Open Rocket program and look forward to understanding it better.
Thanks,

 

[neil_w]

Huzzah! Thanks neil_w, that resolved it. Now a couple weeks ago when this presented itself I did try checking the "automatic" boxes on many of the parts but it made a mess so I didn't save it. May I ask how you ID'd THAT component as the offender?

Nothing clever:
1) click top airframe component (nose cone tip)
2) note "aft diameter"
3) Click on next airframe component
4) Check that "fore diameter" matches previously noted "aft diameter"
5) Note "aft diameter"
6) If there's more, go back to step 3.

I see its a common frustration that the program does not id the error locations.

Indeed, we need to do (much) better there.

 

[Bill S]

Rocksim is similarly useless in helping the user diagnose where the problem lies... and we pay for it.

 

[AcadiaRockets]

Nothing clever:
1) click top airframe component (nose cone tip)
2) note "aft diameter"
3) Click on next airframe component
4) Check that "fore diameter" matches previously noted "aft diameter"
5) Note "aft diameter"
6) If there's more, go back to step 3.


Indeed, we need to do (much) better there.

Thanks so much. I went back and checked my work. I will do the above steps in the future. Thanks. I love the program.

 

[Jeff Lassahn]

In cases where there's a mismatch that's too small to see in the printed numbers, I sometimes go from front to back and for each component I click the "automatic" button on and off and watch whether the error goes away. Then whichever one makes the error go away, retype the numbers on both the front and back components.

 

[Bruiser]

neil_w is an OpenRocket Ninja!

That's how

-Bob

 

[AcadiaRockets]

OK, that was fantastic! neil_w? What about this one? My son is building a minimum diameter Mini Mean Machine. It has a "Jagged edge fin predictions may be inaccurate?" - its the same profile as my larger one. I can't seem to resolve it? Any help or direction is appreciated.

 

[OzHybrid]

Your motor retention hook is a fin...........remove it.

 

[AcadiaRockets]

Your motor retention hook is a fin...........remove it.

Thanks, that did it. And I think I will go friction fit as well. Why not - right? Keep it simple

 

[OzHybrid]

Just designed a rocket with jagged fins. Recognised the error. Took 5 seconds to find the problem.
Never seen a rocket with a motor retainer fail because of the motor retainer. Have seen a rocket fail because of either poor or too high a friction fit. The mean machine isn’t going to win an altitude competition, so there is nothing to be gained by going friction fit and a lot to lose. if you wanted to include the retainer in the sim, just Sim it as a straight flat fin at the same weight. No z clip or front bend.

 

[Rocketjunkie]

A Mean Machine is stable with 3 additional D12-0s hanging off the D in the rocket. I've done it. It works best with a total of 3 motors, the 4th one is awfully slow off the pad. Never simmed it so don't know the issues. (I did this in 1994.)

 

[AcadiaRockets]

A Mean Machine is stable with 3 additional D12-0s hanging off the D in the rocket. I've done it. It works best with a total of 3 motors, the 4th one is awfully slow off the pad. Never simmed it so don't know the issues. (I did this in 1994.)

I launched it with an F67W this weekend - It was pretty spirited.

 

[NoLimit]

Along those same issues.....building up the model for an upgraded Big Daddy in OR. Been reading through some of K'Tesh's OR files. (K'Tesh is the guru!!) Found his file for the rail buttons. Copied and pasted it onto my model as directed. Now the error messages pop up. After placing them on my rocket I deleted the phantom tube as instructed. Part of the error goes away, but from what I can tell is each of the components used to build the rail button was considered a fin. How do I make the rest of the errors disappear? Anyone?? K'Tesh??

BTW....first post here. This forum has been a great source of information for my reborn interest in rocketry. Downloaded OR and have been learning the program to further/enhance my skills in rocketry. Thank you to everyone that contributes!

 

[Banzai88]

Along those same issues.....building up the model for an upgraded Big Daddy in OR. Been reading through some of K'Tesh's OR files. (K'Tesh is the guru!!) Found his file for the rail buttons. Copied and pasted it onto my model as directed. Now the error messages pop up. After placing them on my rocket I deleted the phantom tube as instructed. Part of the error goes away, but from what I can tell is each of the components used to build the rail button was considered a fin. How do I make the rest of the errors disappear? Anyone?? K'Tesh??

BTW....first post here. This forum has been a great source of information for my reborn interest in rocketry. Downloaded OR and have been learning the program to further/enhance my skills in rocketry. Thank you to everyone that contributes!

I never bother with launch lugs and rail buttons for the flight sim model on anything other than black powder powered low power rockets. The larger the rocket and/or motor, the more the drag effect of such a tiny component is within the noise and variability of the motor itself. In total, after the first flight, OR can be easily and quickly tweaked to return results within 5% of real world, and most times within 1%.

 

[neil_w]

Along those same issues.....building up the model for an upgraded Big Daddy in OR. Been reading through some of K'Tesh's OR files. (K'Tesh is the guru!!) Found his file for the rail buttons. Copied and pasted it onto my model as directed. Now the error messages pop up. After placing them on my rocket I deleted the phantom tube as instructed. Part of the error goes away, but from what I can tell is each of the components used to build the rail button was considered a fin. How do I make the rest of the errors disappear? Anyone?? K'Tesh??

Please post the exact warnings your seeing and a screenshot. Even better, post the ORK file.

Generally, using rail button models built up from fins is unadvisable. Launch lugs are natively supported and I would use them without reservation. Buttons will be supported in the next release.

 

[NoLimit]

I never bother with launch lugs and rail buttons for the flight sim model on anything other than black powder powered low power rockets. The larger the rocket and/or motor, the more the drag effect of such a tiny component is within the noise and variability of the motor itself. In total, after the first flight, OR can be easily and quickly tweaked to return results within 5% of real world, and most times within 1%.

Thanks Banzai88. I can agree with that the small component may not have serious effect on the sim. At this point I’m really just learning the software more than anything. Figured if I could understand the nuances of adding such a small item to the program then later on it would give me a better understanding of when I had a real issue. I probably get as much enjoyment from the learning as the actual doing. Plus when I have an issue like this it drives my OCD crazy!

 

[NoLimit]

Please post the exact warnings your seeing and a screenshot. Even better, post the ORK file.

Generally, using rail button models built up from fins is unadvisable. Launch lugs are natively supported and I would use them without reservation. Buttons will be supported in the next release.

Will do Neil. Probably have to do this weekend. Slammed at the moment with Boy Scouts and then there is always life! I’ll walk through the process I did previously to recreate the problem and take some screenshots. Thanks for the help guys!

 

[OzHybrid]

If you'd posted the ORK file , you'd have the answer by now and have saved 2 posts...... Make you some spare time.