Extending the body-tube length of a LOC Warlock

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First, what would the plot of a failed flight look like?
There are two kinds of "failed".

1) The simulation actually encounters an exception and can't finish. This is fairly unusual. You'll know it when you see it.
2) There is something badly wrong with the rocket design or motor configuration and the rocket performs poorly as a result. This could show up unexpectedly low apogee, high deployment velocity, high ground impact velocity, or other obviously wrong-looking numbers. Many (hopefully "most") of these scenarios are explained here: https://openrocket.info/tutorials/sim-results.html

Second, I have attached the plot of a simulation flight that I made with a LOC Warlock using a J430-10. Does this indicate a successful flight?
Look at the curves. What do you think?
Also pay attenion to how the CG/CP relationship changes as the motor burns (get's lighter).
To see what a 'bad' sim'ed flight looks like, just add a Mass Component at the back end of the rocket and increase the mass until the CG is behind the CP. Run the sim and compare to sim without added 'tail' weight.

Remember that one can run the sim many times without needing to pick up the pieces and glue the rocket back together.
A few things…

The Warlock is a rocket kit that has been around a long time and has a proven record of success. So use that information to reassure yourself that it’s probably going to work out fine, despite what your sims say. People have been raising this same concern about marginal stability in sims for years, but I’ve never personally seen one actually fly wonky. With that said, LOC has changed the design in certain ways over time, and some of those changes have added weight to the aft end, so if you bought a version with the MMAS motor mount system for example, then maybe you might want to consider some nose weight or added tube length, but don’t go crazy.

I think most likely the issues are with the sims, not the rocket. I can’t take a look at your sims, but I think if you are seeing negative stability, then most likely the sim is screwed up. And the sims already have difficulty accurately predicting the stability of the Warlock design, so any little boo-boos with your mass or CG overrides are likely to really throw off your sims. You might want to start fresh.

Also, sims have a few applications. One application is for planning the design of a rocket before buying the parts and building it — to see the overall look of the rocket, and check on the predicted stability, predicted mass, predicted flight profiles, and motor options FOR DESIGN PURPOSES. Then the second application is to perform flight simulations for the rocket AS BUILT. During that second phase, you might make some tweaks to you built rocket to get better results.

I feel like you are getting unnecessarily hung up on the first application of the sim program — the design step. You bought a kit with an established track record of success. You don’t really need to double-check it with a sim. Now is the time to start building your kit and move on to the second phase of simming your own rocket as built and making any final adjustments.

Here is how you do that. Build your kit. Finish it, including rail guides, motor retainer, primer, paint, clear coat, recovery gear, shock cord, chute, drogue, chute release, chute protector, and everything else you are going to carry on your flight. I like to put a big load of dog barf in my Warlock, so if you were going to do that, then put it in now, pack up your recovery system inside the rocket exactly how you intend to fly it. You want every last little thing loaded for flight, EXCEPT the motor and motor case. Screw on the retainer on the empty motor mount tube. Now weigh the fully loaded rocket. Next balance the rocket front to back and measure the distance to the balance point from the nose. The measured weight and measured balance point of your fully built and loaded rocket are your new mass and CG overrides for your rocket. None of the component masses or component CGs matter anymore. Open your sim program for your rocket, select the top-level item in the components list that represents the entire rocket — it might be labeled "stage" — and enter the Mass Override and Center of Gravity Override for the entire rocket.

Now you can do your simulations for your rocket as built. Check your stability. Sim your flights.

If you still feel like you are not comfortable with your stability margin, now you can consider adding some nose weight, but you probably won't need it. If you do think you want it, I would recommend not using the sim program to figure out how much. Use "practical engineering". Use the sim program to calculate the CP and mark that position on your rocket (put a piece of tape on the side, and mark the spot with a pen). If you want to use the cone trick, mark the CP with cone position on your rocket. For the next step, do exactly like you did before by fully loading your rocket, but this time, put the motor in the tube. Balance the rocket, and mark the spot. Where is the balance point compared to the CP you marked earlier? On a Warlock, it's never going to be 7.5" ahead. It's not that kind of rocket. What are you comfortable with? 2" or 3"? Maybe 4"? You decide and mark that spot. Get something like a ziploc bag and start adding weight to it and tape it to the nose of your rocket. Adjust the weight until your rocket balances where you want it. Now you know how much weight to add. After you add the weight, be sure to weigh and balance your fully loaded rocket without the motor and readjust your mass and CG overrides for the rocket. You should be ready to go.

Just one more note on the cone trick for stability. Adding the zero-mass cone is just to reassure you of stability. It's for your design sims. It's not for flight sims. I know there have been recent changes to OR for the cone trick, and I have not used those, so maybe this is different now. But in the past, you would add the cone to check stability, but you would remove it before running the flight simulations. Leaving it in place would mess up the flight sims. The cone is what also causes the "discontinuity" warning.

Good luck with your build and your certification flight!
One thing I did not include in my earlier reply is that adding a section of tube to a Warlock is super simple, if that’s still what you want to do. All you need is a section of tube and coupler. The body tube sections are 30” (I think) and couplers are 15”. So you could ask LOC to send you one of each and then cut the body tube in half for two 15” sections. Or you could ask them to cut it for you. Then just glue the coupler halfway into the body tube section. That gives you a 15” body extension with a 7.5” shoulder, and a 7.5” space inside the extension for your nosecone shoulder. The fun thing is that it can be removable. The extension does not need to be glued into the rocket. Friction fit is usually enough, or you can tape it in place. That way, you can fly your Warlock in the short configuration as usual. Or you can slide the extension in place for a longer rocket. I have a group of rocket buddies who all have extensions for lofting big payloads, like Halloween candy on streamers.

Here we are with our candy lofting rockets, and you can tell that some of the rockets have obvious extension sections in contrasting colors (the Jack-o-lantern and the black section on the green rocket). If you do install an extension, be sure to add a BP supplement to your ejection charge to pressurize the added volume.

Many (hopefully "most") of these scenarios are explained here: https://openrocket.info/tutorials/sim-results.html
Hi @neil_w,

That reference was extraordinarily helpful.

The following statement from that reference enhanced my understanding of rocket design in OpenRocket: "The correct move when overriding a stage is usually to check Override for all subcomponents for the mass or CG or CD override ...".

Once I put in that check mark, I got much more favorable simulation results, which moreover accorded more closely with what I was obtaining using RockSim.

Has anyone seen a Warlock built for 75mm motors?

Come on ThirstyBarbarian, I know you know someone who knows someone that has done this.
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Buy the correct sized coupler, and body tube them make it. Do it, it works...My L2, or is it an L1? Its Both, and possibly when the time comes to use an "M" class motor ot will work It works trust me, pictures below I'm building another one...

My very versatile, NAR L2 attempt, from LOC Precision, 5.5" Magnum 3E, with all they sell, to make a 75mm capable. But low power "adaptable" flyer. For "Low and slows" or maybe Mach 2, idk. For live testing soon its nice in Pennsylvania now. Starting maybe today.

Contact me directly for info, or not its your choice. But very cool build. Very nice, I like it. Apologies for "hi-jacking", your thread. Apologies, all. But its for education/fun, safety 1st. Thank you,

Michael B. 🚀....


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Just needed to sift through the boxes and shelves and voila - components for a Warlock with a 75mm motor setup.
Only missing an Aero Pack motor retainer.