Tail heavy LOC Warlock - Review my stability analysis please?

[JSW]

I built a LOC Warlock for my upcoming L2 attempt. Trying to make sure it's stable. Would appreciate review of my analysis,...

The Warlock RKT file on the LOC site shows CP @ 36.3", CG @ 33.0", 115 oz with no motors. Stability 0.43 cal without motors. Stability 0.16 cal with a J270 motor.

My as-built Warlock is weighing in at 128oz with no motors. CG is 2" behind the CP. (Thought I was fairly judicious with the epoxy,... but I guess still used way too much?!)

I updated the ORK file with actual weight of the body, actual weight of the nosecone, and actual overall CG. (ORK file is attached.)

In order to get stability without motors back to 0.43 cal, I think I will need to add about 16 oz of weight to the nosecone. Stability with the J270 motor calculates to 0.21 cal.

1lb seems like a lot of weight to add, but worried it might still not be enough? Does this analysis sound right? Is a .43 cal stability (0.21 cal with motor) ok?

 

[artgsc]

I had the same question when I built my Warlock. Learned a lot from the responses to this thread….
https://www.rocketryforum.com/threads/my-loc-warlock-needed-a-lot-of-nose-weight.173511/unread

 

[bjphoenix]

I built a LOC Warlock for my upcoming L2 attempt. Trying to make sure it's stable. Would appreciate review of my analysis,...

My first impression from the title was "did you include the base drag hack" in OR?

 

[JSW]

@artgsc - Thanks for the reminder about your "My Loc Warlock needed a lot of nose weight!" thread! I actually had reviewed that several months ago, but hadn't yet looked at the stability calc in OR.

Now that I re-read,... I see that you had the same confusion as me: "Is the CP really at 33 inches?" (Because it will take a lot of weight to get the CG in front of a 33" CP.)

In order to get the CG acceptably positioned in front of the 33” CP I had to add about 24 oz. of lead in the nose of my Loc Warlock. Ready to launch weight is now at 12lbs. 5 oz. (DMS J250W 54mm motor). This seems excessive to me….

The LOC Warlock instructions on LOC's site say the CP is at 33", but the LOC Warlock RKT file on LOC's site says the CP is at 36". I double-checked the physical dimensions with the RKT file and had decided the 33" CP on the instructions is probably wrong. I reached out to LOC to ask about this discrepancy. LOC literally just responded,... said to use the RKT file 36" CP location.

I think the discrepancy of 33" vs. 36" CP was what prompted me to want a double-check (via this forum) on the calc'd stability. aka: "Maybe there are other mistakes in the instructions,... did LOC forget to mention adding nose weight?"

But given the 36" CP is the correct location,... and with the explanations from your original thread,... seems like my plan is fine. I'll add enough weight to get the CG back to the nominal 33" location shown in the LOC Warlock RKT file. Stability will then match LOC's design.

Appreciate the help!

 

[artgsc]

The total launch weight of my Warlock came in at 10 lbs. 15.4 oz. Among everything else this included 1.lb. 5.4 oz. of nose weight to put the CG at 33 inches. Had perfect Level 2 certification flight with it so all well and good BUT that much extra nose weight was certainly not needed!

 

[Back_at_it]

When I built mine the total weight with motor was 123oz. My CG was at 37.75 and my stability was at .137. This is without the base drag hack in OR.

I ended up adding 8oz of nose weight to get my stability up to .80 full loaded ready to fly. Mine flew perfect on an H550 for my level 1. I'm currently gathering parts to stretch my Warlock 15" for my level 2 cert. The rocket is stable for a level 2 flight without the added length. I'm just trying to add weight to kill altitude.

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

 

[JSW]

My first impression from the title was "did you include the base drag hack" in OR?

@bjphoenix, Thanks for your comment about the base drag hack. I've been searching the forum to try to understand what you meant.

I found this "How to switch the base-drag hack on and off" thread that shows the LOC Warlock with the OR base drag hack applied. Very helpful. (Thank you @lakeroadster.)

When I apply the 7.67"x24" base drag cone in OR, the CP moves 7" back to 43". Stability goes from 0.0 cal to 0.79 cal. (Without motor. And without adding any nose weight.)

Is LOC's "official" 36" CP wrong? Or how to reconcile?

 

[lakeroadster]

@bjphoenix, Thanks for your comment about the base drag hack. I've been searching the forum to try to understand what you meant.

I found this "How to switch the base-drag hack on and off" thread that shows the LOC Warlock with the OR base drag hack applied. Very helpful. (Thank you @lakeroadster.)

When I apply the 7.67"x24" base drag cone in OR, the CP moves 7" back to 43". Stability goes from 0.0 cal to 0.79 cal. (Without motor. And without adding any nose weight.)

Is LOC's "official" 36" CP wrong? Or how to reconcile?

This rocket definitely qualifies for the Base Drag Hack. Don't get hung up on what LOC states the CP is. Build the rocket and update the simulations based on actual weights. Add the flight hardware and recovery hardware then weight the rocket and adjust the simulation. Then at that point add nose weight to get the caliber of stability you want.

Also be sure to adjust the launch rail / rod length to reflect what will be used.

 

[4regt4]

Re-awakening a not-too-old thread....

Warlock is on the short list for a build in perhaps a few months.

Question:

When you walk up to the RSO with a rocket that at first glance appears unstable, is he likely to believe your argument about a "base cone hack"? I'm not questioning the validity of it, but the guy who will give the go / no-go might not be a believer.

Hans.

 

[Back_at_it]

Re-awakening a not-too-old thread....

Warlock is on the short list for a build in perhaps a few months.

Question:

When you walk up to the RSO with a rocket that at first glance appears unstable, is he likely to believe your argument about a "base cone hack"? I'm not questioning the validity of it, but the guy who will give the go / no-go might not be a believer.

Hans.

Yes. Odds are 99% that he will already know about Base Drag. If not you can bring it up. Also, you're flying a well known kit. The Warlock is very common and known to fly just fine even with no nose weight even on I motors.

I added a bit of nose weight to mine as I wanted to be safe and didn't care about altitude. The Level 2 that helped me didn't even blink when I showed him the CP/CG marked on the rocket. RSO looked it over and gave me the greenlight to head out to the pad.

 

[4regt4]

Did you mark the Cp using the base cone hack? Would that be the correct position, or should it be marked using the traditional (non-"cone") position?

Hans.

 

[Back_at_it]

Did you mark the Cp using the base cone hack? Would that be the correct position, or should it be marked using the traditional (non-"cone") position?

Hans.

CP was marked based on the SIM without the cone hack.

 

[ROCKETDAWG]

Shot mine today7.8 lbs. 0.0 nose weight. J450. Straight n clean.