Open Rocket

[user 30299]

Ok. Thanks for that tip. This file I sent you is from Jason with Loc and that is the stock file. I haven’t done anything to it. So I should weigh the avbay, main section and booster separately and then with a string balance and find the CG of those and input each one into RS? Is there anything else that I should weigh and correct? Is it not good enough to just balance the final built Rocket all put together and input the CG of that isn’t RS? I have not done that into RS yet as I am still learning this program. Thanks for the help.

Yes - in the end once the rocket is finished you weigh the whole thing, find its CG with the string method, and input those two numbers into RS in the Mass Override Tab. This will override all the individual component weights and CGs. Use that for all future stability checks and motor simulations.

All the initial weights & measures help give you a feel for how the rocket may perform, and gives you a heads-up on any possible severe stability issues.

And you may want to correct the fin tabs in the RS file. The fin profile got tagged to the 54mm motor tube and not the 75mm motor tube. Take a close look at how the fins pass thru the wall of the body tube.

If you're using an Aero Pack 75mm motor retainer, like in the photo, you will need to add about 135g to the end of your rocket. That will pull your CG back to the CP real quick. You can enter it as a Mass point. The other picture shows how I can simulate the retainer so that I have a 2D & 3D design that pretty much resembles the build.

 

[Steven88]

Ok so I should have done all this before I put the rocket together! It is already glued and painted. I guess this is hindsite and I’ll know for next time!

 

[user 30299]

Ok so I should have done all this before I put the rocket together! It is already glued and painted. I guess this is hindsite and I’ll know for next time!

Since it's built - just pick the Mass Override Tab and you're good to go. As for next time - everyone has a different take on how much they want to know about a kit's performance before they build it. Good luck!

 

[Senior Space Cadet]

Hello. I am trying to get my Loc Big Nuke 3E data entered correctly into Open Rocket before I fly it. I did get the file for my Nuke sent from Loc but of course it is different in weight from how my Rocket ended up being. For example, my avbay has three lipo batteries and two altimeters and is heavy, over two pounds in itself. I was told that instead of inputting EVERY item (such as every screw, battery etc) into the program I could just weigh each section of the rocket, booster, avbay and main and input it into Open Rocket as a unit. However, I don’t see a way to do that. Open Rocket wants to break each piece down individually. Can someone lend me some advice as the best and yet not complicated way of correctly entering my data is so that I can know that my rocket is flight worthy? Thanks in advance

I use Open Rocket to find CP because it's easier and more accurate than any method I could come up with, but there is a better way to find CG.
Maybe trickier with big rockets, but what I've been doing is build the rocket and then find the balance point. This way I'm sure to take into account every variable, such as how much paint I put on it or how much glue I use in the fillets, or how much balsa I sand off the fins. I already know the CP from open rocket, so I can measure how far ahead the CG is or needs to be. If I come up short, then I can add weight to the nose cone. If it's over stable, I don't worry about it unless it's quite a bit over stable. Then I can always shorten the body or something. As an alternative, I'd recommend getting a gram scale and measuring major components, rather than going by printed data, which is most likely not 100% accurate. For instance, I might build the motor mount and then weigh the complete mount, rather than adding up all the parts. I might also weigh all the fins, after I've shaped them. If I use a baffle, that's a substantial weight, so I'll weigh that by it's self.

 

[Chad]

I use Open Rocket to find CP because it's easier and more accurate than any method I could come up with, but there is a better way to find CG.
Maybe trickier with big rockets, but what I've been doing is build the rocket and then find the balance point. This way I'm sure to take into account every variable, such as how much paint I put on it or how much glue I use in the fillets, or how much balsa I sand off the fins. I already know the CP from open rocket, so I can measure how far ahead the CG is or needs to be. If I come up short, then I can add weight to the nose cone. If it's over stable, I don't worry about it unless it's quite a bit over stable. Then I can always shorten the body or something. As an alternative, I'd recommend getting a gram scale and measuring major components, rather than going by printed data, which is most likely not 100% accurate. For instance, I might build the motor mount and then weigh the complete mount, rather than adding up all the parts. I might also weigh all the fins, after I've shaped them. If I use a baffle, that's a substantial weight, so I'll weigh that by it's self.

that's pretty much what i do too, another technique i do with a dual deployment setup is build out an electronics bay completely then weight it and find the CG. Once i have that information, i drop it into openrocket as a plain mass object and override Mass/CG and match the length. Then i can move that chunk of mass up and down the body tube to adjust the overall rocket CG if needed.

I'm doing a build right now where i'm tracking mass closely, i'm very interested in the impact rocketpoxy based fillets make on fin mass. Rocketpoxy seems pretty dense and on a fin with a 12" root cord and 1/2" radius fillets it seems to me there could be a big difference than what open rocket says the fillet mass will be.

EDIT: just as a reminder, it's always important (and easy) to figure out CG of a flight ready rocket. That way you have a measurement per reality and not software. (i say this as a software engineer hah )

 

[Steven88]

Yes - in the end once the rocket is finished you weigh the whole thing, find its CG with the string method, and input those two numbers into RS in the Mass Override Tab. This will override all the individual component weights and CGs. Use that for all future stability checks and motor simulations.

All the initial weights & measures help give you a feel for how the rocket may perform, and gives you a heads-up on any possible severe stability issues.

And you may want to correct the fin tabs in the RS file. The fin profile got tagged to the 54mm motor tube and not the 75mm motor tube. Take a close look at how the fins pass thru the wall of the body tube.

If you're using an Aero Pack 75mm motor retainer, like in the photo, you will need to add about 135g to the end of your rocket. That will pull your CG back to the CP real quick. You can enter it as a Mass point. The other picture shows how I can simulate the retainer so that I have a 2D & 3D design that pretty much resembles the build.

View attachment 427868View attachment 427869

Since I am overriding the file and putting the rocket in at 15 lbs (what it actually weighs with me extending it 16”) then it’s not necessary to add the retainer at the bottom of the rocket and correct the fins to meet the 75mm motor tube. Or am I wrong? Should I still correct everything? Although I would still need to correct the length of the entire rocket to add on the 16”. Than I overrode the CG to 57 5/8” (what it actually is when I balance it from a string). Am I on the right track?

 

[Dan Griffing]

Does anyone believe RockSim, is easier than open rocket and if yes WHY? Because whe I tried it..I could not find a way to undo a mod I made to an establish design since the SW did not do it correctly. Can you "undo" a change as we use to say with a Windows Program. I keep on getting out and in of the program..not saving changes...a pain and time waste

Prior to RockSim10 coming out, I used both OR and RockSim for each rocket design I worked with.

As someone who's used many kinds of software since before Microsoft came along 40 years ago, my conclusion is that many arguments over what brand of software is easier to use is a matter of personal preference and an invitation to get into a religious war about.

Being able to undo things is a really nice thing to have but its not the end-all in requirements about what constitutes a good rocketry design and simulation package.

But having rocket design elements that match the real ones, having simulation modes and parameters to make a simulation match reality, and having rocket motor sets that match what can be used in a launch, are pretty essential to having good rocketry simulation. Part of this comes with a package that is so widely used that it is almost a standard that everyone depends on.

And while I generally like open source software packages (for example, I've been a great fan of KiCad over Altium for years), one problem with them in general, is that there's much less incentive to respond to customer problems or to stay current with customer needs. A product that no one gets paid for, and that is both no one's and everyone's responsibility for fixing and updating goes wanting for timely updates. And this generally shows in the quality of the end product.

After using RockSim10 since it came out, I have become extremely pleased with it, to the extent that I find it quite preferable to using Open Rocket at all -- even for comparing the output of the simulations. The real killer is when you cannot make an Open Rocket design match the RockSim design with the motors you can buy that RockSim has and Open Rocket doesn't have. And I RockSim's modification to the basic Barrowman stability equations to be more precise than what Open Rockets has.

Open Rockets has some serious catching up to do and its not enough for serious high power rocketeers, who spend thousands of dollars on rocket building kits, materials and launching supplies for a rocketry software design and simulation package to be free.

 

[thzero]

Prior to RockSim10 coming out, I used both OR and RockSim for each rocket design I worked with.


After using RockSim10 since it came out, I have become extremely pleased with it, to the extent that I find it quite preferable to using Open Rocket at all -- even for comparing the output of the simulations. The real killer is when you cannot make an Open Rocket design match the RockSim design with the motors you can buy that RockSim has and Open Rocket doesn't have. And I RockSim's modification to the basic Barrowman stability equations to be more precise than what Open Rockets has.

See I feel then total opposite, and glad it was a cheap upgrade. It still crashes all the time, the icons are much worse than they were, and it really doesn't do that much more than it did before.
If they had solved the consistent crash issues with RockSim 9 then ok.
That being said Apogee was great; when I had issues with my key due to running Hypervisor (its a dev laptop, and yes it has updated OR compiled too), they were johnny on the spot and had it accounted for with their licensing scheme. So props there.

Not sure which motors RockSim has that OR doesn't... if its on thrustcurve you can import them into both sims. Or if you construct an .eng or .rse file yourself.

If someone isn't a fan of the stability equations in OR; then at least they can go put the math together, put it to code, and submit a pull request to OR (now when we ever get an update off the what is nominally the dev branch is a different story).

And your argument is that someone spends thousand on kits, so the simulation (or other software) that free is a bad thing? Does not compute. Why not use both? And RSAAeroII? And AeroFin too which is cheap all things considered.

 

[Dan Griffing]

See I feel then total opposite, and glad it was a cheap upgrade. It still crashes all the time, the icons are much worse than they were, and it really doesn't do that much more than it did before.
If they had solved the consistent crash issues with RockSim 9 then ok.
That being said Apogee was great; when I had issues with my key due to running Hypervisor (its a dev laptop, and yes it has updated OR compiled too), they were johnny on the spot and had it accounted for with their licensing scheme. So props there.

Not sure which motors RockSim has that OR doesn't... if its on thrustcurve you can import them into both sims. Or if you construct an .eng or .rse file yourself.

If someone isn't a fan of the stability equations in OR; then at least they can go put the math together, put it to code, and submit a pull request to OR (now when we ever get an update off the what is nominally the dev branch is a different story).

And your argument is that someone spends thousand on kits, so the simulation (or other software) that free is a bad thing? Does not compute. Why not use both? And RSAAeroII? And AeroFin too which is cheap all things considered.

I've used the heck out of RockSim10 and have never had a crash. I've also used RockSim9 and was never troubled by crashes. I've used RockSim10 really hard and have had many instances of it open at the same time under Windows 10 on my dual screen workstation, along with many other programs. So I'm simply not buying that it crashes all of the time.

While I find certain aspects of Apogee annoying, like the commercial angle there is to everything that's not distinguished from general rocketry issues, and whether its advice about rocketry is that thoroughly based on rocket science -- as a retired engineer, I do find them a welcome general source for rocketry supplies and knowledgeable rocketry advice to a point, so long as you understand that they do exist as a business.

But the preferences of RockSim versus Open Rockets seems to be much like the preferences for Intel versus Motorola CPU architectures of the early 80's or Microsoft versus Unix, or Microsoft versus Apple in the 90's, or programming language wars between C and C++ versus everyone else. There seems to be a religious-like crusade or animus against "mainstream" products by people whose strong belief in what they favor is a major part of their motivation.

So, with regard to RockSim versus Open Rockets, why are so many people willing to put down hard money for RockSim when Open Rockets is free? The mass effect of people wanting to use the same standard that most other people are using is a significant motivator, but this would be irrelevant if the majority who are using RockSim were dissatisfied with how it worked. The fact is that they aren't at all dissatisfied, even when the alternative is free. That ought to tell you something.

I have used both RockSim and Open Rockets in the past and am not doing so now. Because the added effort isn't worth it to me.

 

[Dan Griffing]

I just realized that the problem was with me for having stumbled into an Open-Rocket thread.

Pardon me.

Based on my childhood of being raised Catholic more than half a century ago, its simply unacceptable to go into a Catholic catechism class or theological seminary and start questioning transubstantiation. I won't be commenting on this thread further.

Some issues aren't really open for discussion, even with open rockets.

 

[Ronz Rocketz]

5 Our Fathers and 3 Hail Marys and you'll be fine. (yes, I'm also Catholic)

OR isn't as versatile as RS is. Tim has many rocket designs at Apogee that won't load properly into OR, for example adding a BT to the end of a fin. Someday, OR will be able to do this, someday...

Tim talked about the RS10 problems in the recent NAR video.

 

[user 30299]

Since I am overriding the file and putting the rocket in at 15 lbs (what it actually weighs with me extending it 16”) then it’s not necessary to add the retainer at the bottom of the rocket and correct the fins to meet the 75mm motor tube. Or am I wrong? Should I still correct everything? Although I would still need to correct the length of the entire rocket to add on the 16”. Than I overrode the CG to 57 5/8” (what it actually is when I balance it from a string). Am I on the right track?

If you are still working in RockSim : 1) You still need to correct the fins. Just make the 75mm tube the motor tube. (there's a "check the box" to do this) 2) You still need to add in the 16". 3) You do not need to add the retainer on the end. 4) Use the Mass Overrride Tab to input the 15 lbs. and the CG of 57-5/8". And you are good to go. I am curious as to where you added the 16". Is it between the electronics bay and the bottom body tube?

I'm assuming the 15 lbs. is the weight of the fully loaded rocket; chutes, harnesses, batteries, motor retainer - everything but the motor & motor case.

I forgot to mention that I am still running RockSim 9. I have not had a chance to brush up on RockSim 10 yet.

 

[Buckeye]

I do agree with Dan Griffing's sentiments about Open Source projects. Without financial incentive, it will not keep up. OR started as a thesis project for a college student in Europe, and he blatantly ripped off RockSim. It has been 5+ years since the last release, and the development focus still seems to be merely replicating RockSim's existing capability, ie, pods. There would be nothing wrong under GNU for Open Rocket to charge a fee, which may help spur the development.

However, there is not much left to accomplish in Barrowman tools like RockSim and OpenRocket. I'd like to see consumer-level CFD analysis as the next push in hobby rocket simulation. Not just panel methods, but Navier-Stokes solutions and maybe GPU computing.

If someone isn't a fan of the stability equations in OR; then at least they can go put the math together, put it to code, and submit a pull request to OR

How often does this happen in reality? People like the "free" cost of OR, but how about the "freedom" to use the source code? I can recall only one or two OR user subroutine add-ins discussed in this forum. I don't program in Java or Java Script, but I hear complaints from programmers who do (or have to).

 

[Steven88]

If you are still working in RockSim : 1) You still need to correct the fins. Just make the 75mm tube the motor tube. (there's a "check the box" to do this) 2) You still need to add in the 16". 3) You do not need to add the retainer on the end. 4) Use the Mass Overrride Tab to input the 15 lbs. and the CG of 57-5/8". And you are good to go. I am curious as to where you added the 16". Is it between the electronics bay and the bottom body tube?

I'm assuming the 15 lbs. is the weight of the fully loaded rocket; chutes, harnesses, batteries, motor retainer - everything but the motor & motor case.

I forgot to mention that I am still running RockSim 9. I have not had a chance to brush up on RockSim 10 yet.

Yes, I added the 16” tube between the electronics bay and bottom tube, and yes the 15 lbs is ready for flight minus the ematches, 4F powder, dog barf and motor. I was wondering how to sim a launch using the 75m motor tube since it has a 54mm motor adapter tube inside the 75mm motor tube without deleting the 54 mm adapter. I will fly this rocket in both 54 mm and 75 mm motors. I finally deleted the 54mm adapter to simulate the 75mm motors but than do I have to add it back to simulate the 54 mm motors or is there a simpler way?

 

[user 30299]

Yes, I added the 16” tube between the electronics bay and bottom tube, and yes the 15 lbs is ready for flight minus the ematches, 4F powder, dog barf and motor. I was wondering how to sim a launch using the 75m motor tube since it has a 54mm motor adapter tube inside the 75mm motor tube without deleting the 54 mm adapter. I will fly this rocket in both 54 mm and 75 mm motors. I finally deleted the 54mm adapter to simulate the 75mm motors but than do I have to add it back to simulate the 54 mm motors or is there a simpler way?

Thanks for posting a picture. Looks like a good build!

Unless they changed the motor conditions in RockSim 10, you do not need to add the 54mm adapter back into the design to load a 54mm motor and run a simulation. RockSim will load and run the 54mm motor even though you have a 75mm motor tube. The screen will just show this smaller diameter motor just floating there in the 75mm tube. And it will still show the motor starting at the ass-end of the rocket.

You can add the adapter back in if you want just so that the picture looks correct. But other than that it's just all visual. You needed all those adapter components if you planned on inputting all their weights and CG during the build phase. But your rocket is built, and your using the final and actual overall weight and CG in the simulation.

What you need to do is get the rocket's Weight & CG without the adapter, and get the Weight & CG with the adapter in place. Use the "Without" weight and CG when you run a 75mm motor. Use the "With" weight and CG when you run a 54mm motor.

 

[Steven88]

Thanks for all the help. I’ll see if I can get that figured out on RS. I’ve been working on this build off and on since last October. Was actually quite a bit more work than I anticipated , but is rewarding!

 

[neil_w]

However, there is not much left to accomplish in Barrowman tools like RockSim and OpenRocket. I'd like to see consumer-level CFD analysis as the next push in hobby rocket simulation. Not just panel methods, but Navier-Stokes solutions and maybe GPU computing.

I too would love to see some movement in this direction.

I don't program in Java or Java Script, but I hear complaints from programmers who do (or have to).

Just as an FYI Java and Javascript are completely unrelated. OR is purely Java, which was a reasonable choice back when it was originally written. Nowadays I can only wish it were Javascript, but that's not going to happen any time soon (or ever).

 

[user 30299]

Yes, I added the 16” tube between the electronics bay and bottom tube, and yes the 15 lbs is ready for flight minus the ematches, 4F powder, dog barf and motor. I was wondering how to sim a launch using the 75m motor tube since it has a 54mm motor adapter tube inside the 75mm motor tube without deleting the 54 mm adapter. I will fly this rocket in both 54 mm and 75 mm motors. I finally deleted the 54mm adapter to simulate the 75mm motors but than do I have to add it back to simulate the 54 mm motors or is there a simpler way?

Attached is a RockSim file I put together for your rocket. It has your extra section, the thrust plate and the motor retainer. I guessed at the thrust plate thickness (0.25"). Anyway, take a look at the component flow and labeling. This is how I do it, everyone is different - but you can see how the components are grouped and flow from tip to base. RockSim allows you to move component positions Up & Down the design component tree.

I took out a lot of the Mass components since you are using the final weight & CG. They were just cluttering things up for this example.

 

[jrap330]

Prior to RockSim10 coming out, I used both OR and RockSim for each rocket design I worked with.

As someone who's used many kinds of software since before Microsoft came along 40 years ago, my conclusion is that many arguments over what brand of software is easier to use is a matter of personal preference and an invitation to get into a religious war about.

Being able to undo things is a really nice thing to have but its not the end-all in requirements about what constitutes a good rocketry design and simulation package.

But having rocket design elements that match the real ones, having simulation modes and parameters to make a simulation match reality, and having rocket motor sets that match what can be used in a launch, are pretty essential to having good rocketry simulation. Part of this comes with a package that is so widely used that it is almost a standard that everyone depends on.

And while I generally like open source software packages (for example, I've been a great fan of KiCad over Altium for years), one problem with them in general, is that there's much less incentive to respond to customer problems or to stay current with customer needs. A product that no one gets paid for, and that is both no one's and everyone's responsibility for fixing and updating goes wanting for timely updates. And this generally shows in the quality of the end product.

After using RockSim10 since it came out, I have become extremely pleased with it, to the extent that I find it quite preferable to using Open Rocket at all -- even for comparing the output of the simulations. The real killer is when you cannot make an Open Rocket design match the RockSim design with the motors you can buy that RockSim has and Open Rocket doesn't have. And I RockSim's modification to the basic Barrowman stability equations to be more precise than what Open Rockets has.

Open Rockets has some serious catching up to do and its not enough for serious high power rocketeers, who spend thousands of dollars on rocket building kits, materials and launching supplies for a rocketry software design and simulation package to be free.

Ok, but can you undo a change..if SW does not do what you want correctly. I hate having to close and re-open a program.. Does RockSim have an Help menu...does it have tutorials built in...not what Tim has on his website.

 

[neil_w]

Does RockSim have an Help menu...does it have tutorials built in...not what Tim has on his website.

Built-in help and tutorials is nice but is no longer standard practice across a wide range of software products. If adequate help information is available online and is easy to find, that is generally considered sufficient (and has the advantage of being easier to update and add to on a continual basis). Our company's software has all its user manuals and help online.

Undo function, on the other hand, is obligatory.

 

[Buckeye]

Ok, but can you undo a change..if SW does not do what you want correctly. I hate having to close and re-open a program.. Does RockSim have an Help menu...does it have tutorials built in...not what Tim has on his website.

There is nothing in the SW that can't be undone by you during a session. Maybe if you made a lot of changes since the last save, it may be easier to just reload the previous model and start over, but this is rare. 99% of the time, closing and relaunching software, or worse, uninstalling and reinstalling the software, does absolutely nothing. User error is the problem.

 

[Steven88]

Thanks for posting a picture. Looks like a good build!

Unless they changed the motor conditions in RockSim 10, you do not need to add the 54mm adapter back into the design to load a 54mm motor and run a simulation. RockSim will load and run the 54mm motor even though you have a 75mm motor tube. The screen will just show this smaller diameter motor just floating there in the 75mm tube. And it will still show the motor starting at the ass-end of the rocket.

You can add the adapter back in if you want just so that the picture looks correct. But other than that it's just all visual. You needed all those adapter components if you planned on inputting all their weights and CG during the build phase. But your rocket is built, and your using the final and actual overall weight and CG in the simulation.

What you need to do is get the rocket's Weight & CG without the adapter, and get the Weight & CG with the adapter in place. Use the "Without" weight and CG when you run a 75mm motor. Use the "With" weight and CG when you run a 54mm motor.

What I have for an adapter is just the three Aeropack rings that fit onto the 54mm motor casing and over the aft closure and center the 54mm casing into the 75mm tube, which makes it hard to place the rings at the proper places inside the 75mm tube to find CG of rocket without them sliding around.

 

[jrap330]

There is nothing in the SW that can't be undone by you during a session. Maybe if you made a lot of changes since the last save, it may be easier to just reload the previous model and start over, but this is rare. 99% of the time, closing and relaunching software, or worse, uninstalling and reinstalling the software, does absolutely nothing. User error is the problem.

Ok so how do you undo change in Open Rocket...I could not find a menu item .

 

[user 30299]

What I have for an adapter is just the three Aeropack rings that fit onto the 54mm motor casing and over the aft closure and center the 54mm casing into the 75mm tube, which makes it hard to place the rings at the proper places inside the 75mm tube to find CG of rocket without them sliding around.

No problem! We'll just use a little wingnut engineering. The picture shows my 54mm-75mm Aero Pack adapter rings. The same ones you have. They will add about 127grams (4.5oz.) to your overall weight. Just add that to your current weight and now you have you new weight for the 54mm simulation. To get the new CG, just insert the three rings, one at a time, pushing the previous ring forward. You want them in line, laying down, like in the photo, but edges touching. The last ring will be pushed in until it's outside edge is flush with the lip of the retainer. Now use your string method to find the CG. Will this be a perfect CG, not exactly, but it will be a modestly conservative one.

Don't forget to screw the retainer cap back on when you go to figure out the CG. lol

 

[neil_w]

Ok so how do you undo change in Open Rocket...I could not find a menu item .

I assume you mean RockSim. In OR it's under the Edit menu.

 

[Steven88]

The stock file wants to split the weight over the first booster and sustainer. This rocket doesn’t have a booster the way RS calculates booster, correct? I just need to override just the sustainer to 240 oz. (15lbs.) for total rocket weight?

 

[ChicagoDave]

When I run an adapter multiple times in a rocket (e.g. 74mm --> 54mm where I'll be using the 54mm loads a lot) I will create 2 different RockSim files, one for each configuration. That way I keep the CG and CP separate for each configuration and I don't have to remember to add the weight of the adapter and override the CG with the adapter.

 

[user 30299]

When I run an adapter multiple times in a rocket (e.g. 74mm --> 54mm where I'll be using the 54mm loads a lot) I will create 2 different RockSim files, one for each configuration. That way I keep the CG and CP separate for each configuration and I don't have to remember to add the weight of the adapter and override the CG with the adapter.

Yup! Do what ChicagoDave suggests for the 54 and 75 motors.

 

[user 30299]

The stock file wants to split the weight over the first booster and sustainer. This rocket doesn’t have a booster the way RS calculates booster, correct? I just need to override just the sustainer to 240 oz. (15lbs.) for total rocket weight?

Yup - just put the total weight on the Sustainer line, and zeros on the Booster lines.

 

[Buckeye]

Ok so how do you undo change in Open Rocket...I could not find a menu item .

neil_w said OR has an undo in the Edit menu. Dunno about RockSim. I never looked for one. What I meant was that nothing is irreversible in either software. If you change a body tube length to X and don't like the CP result, then change it back to Y and the CP dynamically reverts back. That is the beauty of the interactive design software. I guess an Undo history would be convenient in the GUI, but I never thought much about it.

Yes, two files are the way to go when flying with motor mount adapters. I do the same in Thrustcurve.