Extending the body-tube length of a LOC Warlock

[MetricRocketeer]

Hi TRF colleagues,

I am hoping to fly a LOC Warlock this summer at the MARS Club, of which I am a member, to go for an L2 certification.

I purchased the kit a few months ago, and up to now I have had the time only to do a dry fit. In a couple months’ time, I plan to build and paint the kit. I have uploaded both my RockSim and my OpenRocket files, and those two files indicate the actual measured weight of each component.

I plan to dual deploy using a Jolly Logic Chute Release with the drogue parachute set to open at motor ejection and the main parachute programmed to open at approximately 150 metres. I intend to use a Cesaroni J430WT — assuming I can purchase one at Geneseo — with a 10-second delay.

Here is the situation. Using RockSim, every simulation works beautifully, even though my stability margin is a little less than 1.0. With OpenRocket, however, I am getting negative stability, and not even one simulation has succeeded. I have applied the base-drag hack, which has tremendously helped the stability margin, but then I get the discontinuity warning so that I cannot run the simulations.

I am thinking of ordering a custom-made body tube from LOC/Precision. The kit comes with a 76.2-centimetre body tube, and I would like to replace that with a 100.0-centimetre body tube. That should improve the rocket’s stability, although I am already getting successful simulations with RockSim. Even using a 100 cm body tube OpenRocket continues to show a negative stability margin.

So, what do people think of this idea — modifying my LOC kit to have a rather longer body tube?

Thank you.

Stanley

 

[Rob Campbell]

I am going for my L2 cert this weekend with a Warlock. Lengthening the airframe tube is a viable way of improving the stability margin. I opted to add 14 oz of shot to the nose cone, held in place with cross rids and three bottles of Gorilla Glue.

Many here have posted that stubby rockets like the Warlock and Mini Magg fly differently and recommend the "zero mass" base drag cone hack to Open Rocket. I haven't figured that out myself, so I opted for good old fashioned ballast.

 

[user 30299]

Hi TRF colleagues,

I am hoping to fly a LOC Warlock this summer at the MARS Club, of which I am a member, to go for an L2 certification.

I purchased the kit a few months ago, and up to now I have had the time only to do a dry fit. In a couple months’ time, I plan to build and paint the kit. I have uploaded both my RockSim and my OpenRocket files, and those two files indicate the actual measured weight of each component.

I plan to dual deploy using a Jolly Logic Chute Release with the drogue parachute set to open at motor ejection and the main parachute programmed to open at approximately 150 metres. I intend to use a Cesaroni J430WT — assuming I can purchase one at Geneseo — with a 10-second delay.

Here is the situation. Using RockSim, every simulation works beautifully, even though my stability margin is a little less than 1.0. With OpenRocket, however, I am getting negative stability, and not even one simulation has succeeded. I have applied the base-drag hack, which has tremendously helped the stability margin, but then I get the discontinuity warning so that I cannot run the simulations.

I am thinking of ordering a custom-made body tube from LOC/Precision. The kit comes with a 76.2-centimetre body tube, and I would like to replace that with a 100.0-centimetre body tube. That should improve the rocket’s stability, although I am already getting successful simulations with RockSim. Even using a 100 cm body tube OpenRocket continues to show a negative stability margin.

So, what do people think of this idea — modifying my LOC kit to have a rather longer body tube?

Thank you.

Stanley

The RockSim simulation works great, but that's because the Mass locations for the following
components are in the wrong locations; nose cone, body tube, motor tube and fins.

On three of them you have the component mass at their most forward location (0.0), and
not at their center of gravity (CG). This puts the rocket's overall CG way forward of where
it actually is.

 

[MetricRocketeer]

Hi @QFactor,

Thank you for this important information.

OK. Now I see. Even so, the length of the body is 76.2 cm, so half of that is 38.1 cm. The length of the fin root chord is 27.1, and half of that is about 13.6 cm.

Changing the center of gravity to those values did indeed lower my stability margin, but the simulation was still successful. Or am I wrong?

Stanley

 

[Rschub]

I would check with LOC to see if that size tube is available. My Doorknob is 42" body length, which is attained by a 30" and a 12" tube coupled together. A longer tube will need a longer shipping box, and I believe once the box gets above a certain length it adds shipping cost. It might get expensive.

 

[user 30299]

Hi @QFactor,

Thank you for this important information.

OK. Now I see. Even so, the length of the body is 76.2 cm, so half of that is 38.1 cm. The length of the fin root chord is 27.1, and half of that is about 13.6 cm.

Changing the center of gravity to those values did indeed lower my stability margin, but the simulation was still successful. Or am I wrong?

Stanley

You're almost there. Sounds like you found the Mass Override Tab for each of the individual components.
There were masses there, but the CG's were set to a "0" location.

• The CG location is half the length of the body tube, and the same for the motor tube for these two components.
• The Mass override for the nose cone was not "checked", so the listed mass & CG were not used. Did you "check" the box for override?
• The CG location for the fin is probably wrong. You can find the correct CG location (good approximation) with the pencil eraser technique.

Don't laugh. Take a fin and set its face on the top of a pencil eraser. Keep moving it around until you find
the fin's balance point. Then just measure from the leading edge down along the fin's root. That's the fin's CG.

If you have a CAD program you can put the whole fin profile, including the fin tab, in the program and it will
calculate the CG for you.

Please check and see which stability method you are using. You can use either RockSim's method, or Barrowman.
The file you posted has you using both methods; one for calculation and one for simulation.

 

[neil_w]

With OpenRocket, however, I am getting negative stability, and not even one simulation has succeeded. I have applied the base-drag hack, which has tremendously helped the stability margin...

Stability on that rocket, as modeled, is marginal even with base drag CP correction.

but then I get the discontinuity warning so that I cannot run the simulations.

The discontinuity warning does not interfere with simulation.

https://openrocket.info/tutorials/base-drag.html

 

[Back_at_it]

I flew a Warlock for my level 1 on an H550. Following that successful flight I decided that I wanted to use the same rocket for my level 2 but I wanted to kill some of the altitude of the J motor so I decided to extend the body tube by 15 inches. I picked up a length of tubing, coupler and bulkhead from LOC to do the extension. While I chose to cut the tube myself, I'd highly recommend that you have them cut it. They can do it for you quickly and cleanly.

As for stability, at stock length mine was at .811 cal with the H550 loaded ready to fly. The flight was dead straight and stable.

After adding the additional 15 inches and updating the motor to a J435, my stability jumped with 1.03 even with the larger, heavier motor.

I have a complete build thread here. I'm planning to fly for my level 2 this spring.

https://www.rocketryforum.com/threads/loc-warlock-build-rocket-for-my-level-1.167964/

 

[MetricRocketeer]

Hi TRF colleagues,

I very much appreciate all the thought-provoking insights that you rocket experts have provided me. I will consider everything, including fixing up my RockSim and OpenRocket files. Also, I may well buy extra tubing and a coupler — that was a good suggestion.

For right now, however, let me please ask this bottom-line question. Given the Warlock that I now have and its current length — so, I am saying without adding any extra tubing or without adding any nosecone ballast — is this a viable rocket? If I construct it well, should I expect a successful L2 flight out of this Warlock?

Thank you.

Stanley

 

[Neutronium95]

Tons of people have built and flown Warlocks. It'll fly fine, take a look at other build threads on here to see how much nose weight people have added.

 

[user 30299]

Hi TRF colleagues,

I very much appreciate all the thought-provoking insights that you rocket experts have provided me. I will consider everything, including fixing up my RockSim and OpenRocket files. Also, I may well buy extra tubing and a coupler — that was a good suggestion.

For right now, however, let me please ask this bottom-line question. Given the Warlock that I now have and its current length — so, I am saying without adding any extra tubing or without adding any nosecone ballast — is this a viable rocket? If I construct it well, should I expect a successful L2 flight out of this Warlock?

Thank you.

Stanley

Yes, it's a viable rocket - just not the way you think it should be.

If you wanted a build & fly it kit, this is probably not the one for you.

This is the kit though that will help you develop good design and build skills.

These are the best kits for growing your knowledge and experience. Stick with it!

And your L2 goal makes this rocket that much more challenging. The physical motor
size and their weight distribution will have a noticeable influence on the rocket's CG.

What you need to do first is stop using two different simulation programs. Pick one and
stick with it. Until you get good at one, you'll never be able to confidently solve differences
in simulation results between OR and RockSim.

Scrap the sim files if they are ones you did not start from scratch. There's too much component
and motor "debris" in the files. You can use them to look at the nose cone and fin geometry.

There is good opportunity in this kit.

 

[user 30299]

I would like to point out that you started this Warlock project almost exactly 1 year ago.

You're still on the same square. Time to make a move.

https://www.rocketryforum.com/threads/nosecone-ballast.178065/

 

[user 30299]

I flew a Warlock for my level 1 on an H550. Following that successful flight I decided that I wanted to use the same rocket for my level 2 but I wanted to kill some of the altitude of the J motor so I decided to extend the body tube by 15 inches. I picked up a length of tubing, coupler and bulkhead from LOC to do the extension. While I chose to cut the tube myself, I'd highly recommend that you have them cut it. They can do it for you quickly and cleanly.

As for stability, at stock length mine was at .811 cal with the H550 loaded ready to fly. The flight was dead straight and stable.

After adding the additional 15 inches and updating the motor to a J435, my stability jumped with 1.03 even with the larger, heavier motor.

I have a complete build thread here. I'm planning to fly for my level 2 this spring.

https://www.rocketryforum.com/threads/loc-warlock-build-rocket-for-my-level-1.167964/

I looked at Back_at_it's Warlock build thread. Good stuff there.

 

[John Kemker]

I certified L2 with a stock length Warlok. It was beautifully stable. Only modifications I made to it were to trim the rounded part of the nose cone shoulder off and replace it with a plywood centering ring (4" ID) and put a 4" 'chute bay and an altimeter pod in the NC. That shifted the CG forward nicely and it flew on a Loki J326.

I wouldn't bother adding length to the kit, unless you want to add a payload bay for DD.

 

[T-Rex]

Deleted, going to mind my own business for a change.

 

[MetricRocketeer]

The discontinuity warning does not interfere with simulation.

Hi @neil_w,

But then I am confused on that issue.

The existence of a discontinuity automatically causes a simulation failure, doesn't it? Or am I wrong?

Thank you.

Stanley

 

[MetricRocketeer]

Deleted, going to mind my own business for a change.

Hi @T-Rex,

No. Please don't mind your own business, to use your words. I appreciate any and all feedback. I mean it. Whatever you say may be of use to me and to others.

Stanley

 

[neil_w]

Hi @neil_w,

But then I am confused on that issue.

The existence of a discontinuity automatically causes a simulation failure, doesn't it? Or am I wrong?

No failure. Just go look at your simulations, they all complete normally.

 

[MetricRocketeer]

I would like to point out that you started this Warlock project almost exactly 1 year ago.

You're still on the same square. Time to make a move.

https://www.rocketryforum.com/threads/nosecone-ballast.178065/

Hi @QFactor,

You are surely correct on that. I follow sport rocketry closely by reading and participating in The Rocketry Forum, going to vNARCON, and keeping up with events as reported in the NAR Electronic Rocketeer. I also frequently watch the RockSim training videos and I try to keep up with the RockSim and OpenRocket programs.

But I just spend don't much time building.

Stanley

 

[user 30299]

Hi @QFactor,

You are surely correct on that. I follow sport rocketry closely by reading and participating in The Rocketry Forum, going to vNARCON, and keeping up with events as reported in the NAR Electronic Rocketeer. I also frequently watch the RockSim training videos and I try to keep up with the RockSim and OpenRocket programs.

But I just spend don't much time building.

Stanley

Acquired knowledge is good.

Applied knowledge even better.

Time to complete the cycle with the Warlock.

All is good.

 

[T-Rex]

The comment I deleted was to suggest that you build the model then locate the as built CG before deciding what (if any) nose weight was required.
I have, in the past, used a created sim and determined nose weight prior to complete construction only to discover that I had added unnecessary weight due to an error.

 

[neil_w]

The comment I deleted was to suggest that you build the model then locate the as built CG before deciding what (if any) nose weight was required.
I have, in the past, used a created sim and determined nose weight prior to complete construction only to discover that I had added unnecessary weight due to an error.

This is the way.

It's certainly good to have an idea before you start, but you can't know for sure until you build (unless you are extraordinarily good at estimating glue and paint weight).

 

[MetricRocketeer]

No failure. Just go look at your simulations, they all complete normally.

Hi @neil_w and anyone else,

I am following up on the issue of the Base Drag CP Correction.

I went into the Examples file in OpenRocket, and I loaded the example entitled "Base drag hack (short-wide)" and used all three motors indicated — C11-3, D11-3, and E12-4. I kept the massless cone in the rocket design, and all three simulation flights failed. Then I deleted the cone, and all three simulation flights succeeded.

Thus, doesn't keeping the cone indeed prevent the flight from succeeding?

Thank you.

Stanley

 

[neil_w]

The example rocket simulates fine. Define "simulation flights failed", and please attach your ORK file.

 

[MetricRocketeer]

Here are the two files, one with and one without the cone at the aft end of the rocket. Understand, please, that the one with the cone is exactly the same file that came with OpenRocket version 23.09. I have not modified it at all. The other file is the same design except that I deleted the cone.

On the very left column of the flight simulations tab, before I deleted the cone, I got a red exclamation mark explaining what went wrong with the flight. But after I deleted the tab, on the left column of the flight simulations tab I got a green check mark indicating a successful flight.

 

[neil_w]

The red exclamation point merely indicates that there were warnings; it doesn't mean that the flight didn't simulate. If you look at the simulation results you'll see that they're all there, and you can look at the plot and see that the complete flight was simulated.

There are certain conditions that can cause the simulation to fail, but the discontinuity warning is not one of them.

 

[tywain]

I called loc and talked to them about the stability issues that this rocket has in open rocket as I had to add alot of nose weight to make it stable. They told me that with any J motor you can fly it with no nose weight and it will be stable. I will try it in the spring but I am still just a little skeptical on it.

 

[Rschub]

 

[MetricRocketeer]

Hi @neil_w and everyone else,

The red exclamation point merely indicates that there were warnings; it doesn't mean that the flight didn't simulate. If you look at the simulation results you'll see that they're all there, and you can look at the plot and see that the complete flight was simulated.

There are certain conditions that can cause the simulation to fail, but the discontinuity warning is not one of them.

OK. So then I have these two questions, please:

First, what would the plot of a failed flight look like?

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?

Thank you.

Stanley

 

[John Kemker]

Hi @neil_w and everyone else,



OK. So then I have these two questions, please:

First, what would the plot of a failed flight look like?

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?

Thank you.

Stanley

The plot won't tell you if it's stable or unstable. Only how high it should go, what speed is expected off the rod, etc. In order to determine stability, you have to compare the CG to the CP. Rule of thumb is that the CG should be one to two diameters (calibers) forward of the CP. CG and CP at or very near the same point runs the risk of pinwheeling off the rod and other unpleasantness.

Trust LOC when they say you should be able to fly the Warlock on any J motor without problems. They've got a LOT of experience with that particular rocket, as they've been making it for over 30 years. Unless you do something silly, like put weight in the tail section, you should be fine.