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….
My Loc Warlock needed a lot of nose weight!
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ThirstyBarbarian
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You don’t really need that much nose weight for the rocket to be stable (unless you have an unusual amount of weight aft). For short, fat rockets, the rocket will fly stable with less than the one caliber of stability rule of thumb. These kinds of rockets benefit from “base drag”, which moves the CP aft and makes the rocket more stable than the sims will usually indicate.
Sim programs don’t automatically calculate base drag, but there is a trick you can use in the simulation programs to roughly simulate the base drag by adding a zero-mass cone to the aft end of the rocket. It’s really just to reassure yourself that the rocket is stable, and then you have to remove the cone for actual flight simulations to get accurate altitude and delay timing results. Do a search for terms like “zero mass cone”, “base drag”, etc. It’s been described many times.
The Warlock is a known, proven design that flies well. I don’t have any nose weight in mine at all, but mine is an earlier design that is a bit lighter in the aft end. There are a few designs out there, but as long as yours is not using their MMAS system and just has a regular 38mm or 54mm motor tube and fin tabs to the motor tube, you probably don’t need nose weight at all, or maybe just a little bit.
Sim programs don’t automatically calculate base drag, but there is a trick you can use in the simulation programs to roughly simulate the base drag by adding a zero-mass cone to the aft end of the rocket. It’s really just to reassure yourself that the rocket is stable, and then you have to remove the cone for actual flight simulations to get accurate altitude and delay timing results. Do a search for terms like “zero mass cone”, “base drag”, etc. It’s been described many times.
The Warlock is a known, proven design that flies well. I don’t have any nose weight in mine at all, but mine is an earlier design that is a bit lighter in the aft end. There are a few designs out there, but as long as yours is not using their MMAS system and just has a regular 38mm or 54mm motor tube and fin tabs to the motor tube, you probably don’t need nose weight at all, or maybe just a little bit.
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"acceptably positioned"?
Its a stubby rocket with lots of drag.
Its a stubby rocket with lots of drag.
H_Rocket
Death by Powerpoint
I fly a Warloc with mid to large J motors and zero nose weight. The OP has made the very common mistake of thinking if RocSim (or Open Rocket) is not happy and I don't meet the rule of thumb (>= 1 caliber of stability) that nose weight must be added to the rocket until those conditions are met. Short fat rockets do not fit neatly into the generic rules for stability.
Sharing my $0.02 since I just built and flew a Warlock 54mm for my L2. Mine came in at 7.5lbs with a CG of 33.25". OpenRocket gave me a CP of 36.13" and a stability margin of 0.375 cal w/o motor. This is without a zero mass cone. It flew nicely on a 38mm DMS J435 with 0.149 cal of stability.
The 54mm DMS J250 you noted would shift the CG a bit further aft...and in my rocket at least, CG/CP are almost equal (before adjusting with zero mass cone). If I were to fly that motor I might add a tiny bit of nose weight (maybe), but not too much or else I'd need to enbiggen my chute.
As others have noted...short fat rockets bend the CG/CP rules. I'm curious...what's your CG w/o motor?
The 54mm DMS J250 you noted would shift the CG a bit further aft...and in my rocket at least, CG/CP are almost equal (before adjusting with zero mass cone). If I were to fly that motor I might add a tiny bit of nose weight (maybe), but not too much or else I'd need to enbiggen my chute.
As others have noted...short fat rockets bend the CG/CP rules. I'm curious...what's your CG w/o motor?
Loc says that the CP on the Warlock is 33 inches from tip of nose cone. Without any added weight in the nose my CG was behind the CP. Anyway, I already epoxied the weight into the nose so now to go back to square one I will need to buy another nosecone from Loc and try and get a better handle on how to correctly sim. My intention was to try and do a Level 2 certification flight using this Warlock with a DMS J250W drilled to a 6 second delay and 3 grams of black powder for ejection (no electronics).....
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FWIW...adding a zero mass cone to my rocket gives me 0.99 cal with J435 and 0.890 cal with J250.
ThirstyBarbarian
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I don’t think the added weight is necessary, but I also don’t think it’s a problem. You’re definitely not the first person to have extra weight in the nose of your Warlock! You don’t need to pay for a replacement cone, unless you prefer it lighter. As long as your chosen motor gets the rocket off the rail at a safe speed, it will be fine with the extra weight.
Just be sure your chute size is adequate — the one that comes with the kit probably is not big enough for a heavier rocket. I upgraded my Warlock chute anyway. The Loc chute is a flat chute with no spill hole, so it tends to swing a lot. I like Spherachutes. https://spherachutes.com/
Based on your suggestion in a previous post I did get a 66”Spherachute but now that is even marginal according to their descent chart due to the overall weight of my Warlock. Also, it appears that the DMS J250W motor I have might be too slow off the rail but again I am still in the learning process on how to correctly sim (using trial version of Rocksim) so not certain yet. I am grateful for this forum!
Initial thrust of the J250W is over 300N. 300/4.448 = 67lbs. 67lbs (thrust) / 12.5lbs (your rocket weight) = thrust to weight ratio of between 5:1 and 6:1
Thrust profile is progressive then regressive so it gains thrust for nearly a second as you lose propellant mass before thrust begins regressing.
Fly it.
Thrust profile is progressive then regressive so it gains thrust for nearly a second as you lose propellant mass before thrust begins regressing.
Fly it.
J250 in a 12.5lb rocket is going to need more than 6 feet of guidance:
https://www.thrustcurve.org/motors/guide/62c1d38ff926ea0004177fe2/complete.html
https://www.thrustcurve.org/motors/guide/62c1d38ff926ea0004177fe2/complete.html
Are you basing this off the "Slow off Guide" result?
The 12.4 m/s off the rail result, yes.
It is not a direct comparison. There is nearly a 2lb difference in the weight of the rockets. As well, you don't know if 1010 were used vs 1515, how sticking the buttons were in the rail, if they were aligned. Not disagreeing for no reason mind you. There is nearly a 6:1 thrust to weight ratio which is perfectly fine. That post is a single persons experience with no other data being available other than the mass, the motor, and a subjective opinion on its speed off the rail.
Either way, the OP has some thinking to do. Drill out some weight, change motors, fly it as it sits.
.5 cal with or without a base drag cone?
Just the standard flile, here is mine, mind you modified for my actual weights
ThirstyBarbarian
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I’ve flown mine with only fractional stability (without the zero-mass cone), and it always flies straight. Mine has flown well under .5 cal, like maybe .2 or so?
The shorter and fatter a rocket gets, the more it behaves like a saucer, and saucers are stable in flight. So there is a continuum of rocket forms going from extra long, skinny rockets with fins, through traditional 10:1 ratio finned rockets, to short, squat finned rocket like the Warlock and Big Daddy, all the way down to things like cones, pyramids, and saucers without fins. The 1 cal rule of thumb is great for 10:1 rockets. For longer rockets, maybe you want more than 1 cal. For short, fat rockets, you can have less. For a saucer, you can’t have 1 cal — the entire rocket isn’t 1 cal long. Rockets in that transition area between traditional rocket forms and saucers are hard to sim, and the rule of thumb breaks down.
The shorter and fatter a rocket gets, the more it behaves like a saucer, and saucers are stable in flight. So there is a continuum of rocket forms going from extra long, skinny rockets with fins, through traditional 10:1 ratio finned rockets, to short, squat finned rocket like the Warlock and Big Daddy, all the way down to things like cones, pyramids, and saucers without fins. The 1 cal rule of thumb is great for 10:1 rockets. For longer rockets, maybe you want more than 1 cal. For short, fat rockets, you can have less. For a saucer, you can’t have 1 cal — the entire rocket isn’t 1 cal long. Rockets in that transition area between traditional rocket forms and saucers are hard to sim, and the rule of thumb breaks down.
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Thank you for the information in this thread. I am finishing up a
4” LOC Phoenix and the LOC Goblin and was trying to rationalize why the Phoenix needs node weight and apparently the Goblin does not.
4” LOC Phoenix and the LOC Goblin and was trying to rationalize why the Phoenix needs node weight and apparently the Goblin does not.
First time I've seen these! They seem to be reasonably priced, might have to give one a chance. Thanks for the link
waltr
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Look at shape and placement of the fins on those two...
Goblins fins are way at the aft end whereas the Phoenix fins extend quit a way forward.
This puts the CP of the Goblin fins back and the CP of the Phoenix fins forward.
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AWESOME chutes! Highly recommended!First time I've seen these! They seem to be reasonably priced, might have to give one a chance. Thanks for the link
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Any recommended motors for L2?
H_Rocket
Death by Powerpoint
If you have access to the hardware, an Aerotech J350 or J420 are time tested and classic motors.
Best part of my successful Level 2 certification flight with my Warlock was watching it come down under the 66" Spherachute (42.02 Diameter) Hemispherical Classic Parachute that I put on it. A very smooth descent with no swinging back and forth due to the perfectly sized spill hole. Thank you "ThirstyBarbarian" for the recommendation!
My Minie Magg and Warlock also have zero nose weight and fly well.
green dragon
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Not one speck of nose weight in mine - old style ' pre twt version so light aft end - flies on 2 and 3 grain Kosdon/ AMW loads fine ( and those casings are heavier ) No worries ever.
Most rockets that are military scale will need nose weight to be stable. Remember, they were designed to deliver a warhead, which is a nose weight.
They are also often guided and have a set of moveable fins.
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