Is it a guarantee pretty much than its gonna need nose weight no matter what?Instructions can be downloaded from the website. It states the CG as 28" from nose tip. Amount of nose weight needed will vary according to weight of motor and building technique. Most people weight according to the heaviest motor they intend to use.
Or you can add a variable weight ballast system into your nose and add/subtract according to which motor you use.
I appreciate all the replies, im new to high power (previous kits are estes pro series ii on g motors) so im unsure of how to put the nose weight in the nose cone in the first place. Lead shot with epoxy through a drilled hole is what I gather.I'll check my sim for CG and CP when I get home. It has all the weights I use for different motors
Agreed with statement above, the weight I use may be too much/little depending on how you build it.
(I've got ~8oz fixed in the tip for 2grains, and I have a 2oz and 3oz donut to add for longer motors. Doesn't take much extra, the longer motors move the CG up too)
Love the rocket. It was my L1, and has flown on H-J. I'm going to be making an e-bay for it so I can use plugged motors soon.
Also is it possible to fly a 4in patriot stock without any nose weight on an H?I'll check my sim for CG and CP when I get home. It has all the weights I use for different motors
Agreed with statement above, the weight I use may be too much/little depending on how you build it.
(I've got ~8oz fixed in the tip for 2grains, and I have a 2oz and 3oz donut to add for longer motors. Doesn't take much extra, the longer motors move the CG up too)
Love the rocket. It was my L1, and has flown on H-J. I'm going to be making an e-bay for it so I can use plugged motors soon.
No. As Joe said, download the Rocksim file from the Madcow website. Run the sims with your chosen engine.Also is it possible to fly a 4in patriot stock without any nose weight on an H?
Is Rocksim a free program to download? Would be the first time using itNo. As Joe said, download the Rocksim file from the Madcow website. Run the sims with your chosen engine.
Ran a quick sim on Open Rocket with an H238. With 12oz mass in the nose it shows only .391 caliber of stability.
With no nose weight it looks like the CG will be behind the CP.
Increase the nose mass and see how the CG moves forward. You want it at 28" from the nose or less.
Laters.
PS Forgot to mention, your build may be different depending on technique (heavy on glue, etc.). As mentioned, use the sim to get an idea of the weight needed, and fine tune to the actual CG on your rocket.
Is Rocksim a free program to download? Would be the first time using it
Wow! I appreciate all this! There is definetly alot of information to learn and digest. Im going to download open rocket right now and start playing with the files and seeing how everything works. I think this is the hardest part about going for my L1 cert for sure, calculating the nose weight based off the motor. I really do appreciate all the help!Rocsim isn't free, but Openrocket is and will be fine for your needs as you start out. (go to the software/electronics part of the forum and use visit the top link where Neil has packaged installers for it)
Here's a snip of the simulation for its most recent flight on a J316.
-Pay attention to the CG/CP locations. The locations are the only thing that matter since my weight and finish will be different than yours.
--It has 6oz fixed in the nose for 2 grain Pro38 flying, and I added 6oz removable weight to bring the CG forward. (I just rough up the inside tip, pour in 30 min epoxy, and then dump the lead shot in so it sinks down and settles)
--I design for the CG to be ~10-12% of vehicle length ahead of the CP. Most often you'll hear folks describe stability in 'calibers' (body diameters), but I've found that convention limited.
View attachment 394102
*caveat* If you use the part dimensions of the kit, Openrocket will give a CP that's further forward than what is in my sim, and it will appear under-stable with my weights. I used a CFD software program to run some tests and determined that the CP for this model is ~35.4" from the tip, so I added those square faux fins (massless) to simulate the rearward CP. It has flown using this CP position (and corresponding CG per motor) on I's and J's so I believe my results have real world validation.
Here it is (as I built it) with no nose weight and a 38mm 2 grain (H) motor. That CG/CP separation is only 5% of the vehicle length (or .6 calibers for other folks)
This has a very low static margin meaning the rocket must get up to much higher speed to be stable on rail exit, and the CP could possibly shift forward causing an unstable flight if it passes the CG
View attachment 394103
Ah thanks! I was just having issues attempting to install it from the main website but that worked perfectly. As far as files go, do I just download and save a rocket file and open it in the program from my computer?There is a version (current one) of Open Rocket here on the forum that has a built in installer program (by Neil_W iirc). Sorry I don't have the link handy at the moment.
Edit: https://www.rocketryforum.com/threa...d-mac-to-solve-all-your-java-problems.143540/
What is a good stability number to look for? I was able to load in the patriot file just now and am playing around with different motors. Is .276cal a good number, or what number should I be looking for? Thanks!Hopefully you'll get plenty of help here on the forum, although therell be plenty of confusion too. You're absolutely right, knowing how to balance a rocket for a safe stable flight is key to being a successful high power flier. The power gets much greater than low and mid power motors.
Rocsim files will open in OR, but some complex geometries like outboard pods or ring fins arent in OR yet. Fortunately your Patriot doesnt need either of those.
My recommendation is to take your parts and make a sim file from scratch. Weigh and measure your parts, load them in, and you'll get great practice using the program. (You can override each part's weight, or override the weight and cG of the whole rocket/stage)
Though mine will only make it to about 10' (my office ceiling),
(NYTs has flown repeatedly; well)
I don't know, but whatever it is, it probably requires a lot of fact-checking.What does the New York Times have to do with anything?
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