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I read E12 and was getting ready to reply “no way” then saw you’d already flown it. 
I would think the E30 would be perfect for that rocket, maybe an E15/E20 (would need to check). 17 oz is pretty heavy.
Lesson: never assume! If you don’t have a proper OR or Rocksim model, throw the numbers into Thrustcurve and get a tough estimate. It will save you from heartache and mishaps.
Hope you can get her back into flying shape soon!
I would think the E30 would be perfect for that rocket, maybe an E15/E20 (would need to check). 17 oz is pretty heavy.
Lesson: never assume! If you don’t have a proper OR or Rocksim model, throw the numbers into Thrustcurve and get a tough estimate. It will save you from heartache and mishaps.
Hope you can get her back into flying shape soon!
E30-4 should give a lot of thrust and speed coming off the rod.
Believe it or not D12-3 and E12-4 are also recommended motors.
Maybe with a long rod and no wind at all.
I notice that on the #1969 box the D12 motor is no longer recommended.
I wonder why.
P.S. Estimated weight for the #2157 is listed at 12 oz., so you might have built yours a little heavy.
Believe it or not D12-3 and E12-4 are also recommended motors.
Maybe with a long rod and no wind at all.
I notice that on the #1969 box the D12 motor is no longer recommended.
I wonder why.
P.S. Estimated weight for the #2157 is listed at 12 oz., so you might have built yours a little heavy.
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bobbyg23
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I am wondering if I need any nose weight at all? The only cg suggestion I could find on the internet said 20" from the top. When I rebuild, I will send it without any extra nose weight.E30-4 should give a lot of thrust and speed coming off the rod.
Believe it or not D12-3 and E12-4 are also recommended motors.
Maybe with a long rod and no wind at all.
I notice that on the #1969 box the D12 motor is no longer recommended.
I wonder why.
P.S. Estimated weight for the #2157 is listed at 12 oz., so you might have built yours a little heavy.
Did you pack the two pats of clay into the capsule? If you built the kit stock, that should be enough.
Bobby, here's a page from which you can download a Rocksim file for the #2157.
You can check your CG location against the file's, and add or subtract nose weight as needed.
https://www.rocketreviews.com/unknown-estes-saturn-v-1100-scale.htmlDisclaimer: A Rocksim file is only as good as the person who drew it up. No guarantees on the accuracy of this file.
You can check your CG location against the file's, and add or subtract nose weight as needed.
https://www.rocketreviews.com/unknown-estes-saturn-v-1100-scale.htmlDisclaimer: A Rocksim file is only as good as the person who drew it up. No guarantees on the accuracy of this file.
bobbyg23
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That is actually the one place I found the cg was that file. 19.88. Don't have rocsim so i just went by the file on that page.
bobbyg23
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Mine didn't come with clay and it didn't say anything about it in the instructions.
I just realized that your build isn't stock, it has the 3D printed fairings in the back. That will add substantial extra weight in the back end to the build.
So yes, you will need nose weight to offset that.
And due to the extra weight the minimum recommended motor does not have sufficient thrust off the rod for stability.
You can download a free trial version of Rocksim from the Apogee website, or you can download Open Rocket for free, it can read Rpcksim files.
Modify the file for the extra weight of the parts and run simulations with different motors to see which will provide a stable flight.
So yes, you will need nose weight to offset that.
And due to the extra weight the minimum recommended motor does not have sufficient thrust off the rod for stability.
You can download a free trial version of Rocksim from the Apogee website, or you can download Open Rocket for free, it can read Rpcksim files.
Modify the file for the extra weight of the parts and run simulations with different motors to see which will provide a stable flight.
bobbyg23
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I have open rocket but I didn't know it would run rocsim files. I will look into that.
I seem to remember reading somewhere that the smaller motors are probably only if you build quite lightly. If you use lots of glue and extra mass then all bets are off, except maybe on a dead calm day.Believe it or not D12-3 and E12-4 are also recommended motors.
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.rkt file works with both RockSim and OpenRocket (OR).
If you save the .rkt file as .ork in OR, that format will preserve both the design of the rocket as well as the motor configurations and flight simulations.
I am enclosing mine, for your infotainment.
It's a bit heavier than yours at 552g / 19.5oz, but that includes my heavy duty 29mm motor mount and 58g / 2oz of ballast in the nose cone.
Remove the nose ballast, and mine weights similar to yours. Except that you have a LOT more weight near the aft of the rocket due to those 3D printed boyce aerospace fins+fairings. I bet you they were not light, and shifted the CG further back, and reduced your stability by a materially significant margin.
On my model, E12 gives 0.95 calibers of stability with the ballast in the nose. Removing the ballast reduced stability to 0.37. That's beyond marginal, and that's before accounting for the extra tail weight.
Add more weight to the aft of the rocket, and the rocket will do what you saw in your video. Actually, it would have been a way more spectacular sky-writing flight, had you picked a motor with higher impulse (and yet more weight in the tail)!
I would strongly advise you against doing that.
At least not until you've measured the actual weight and CG of the rocket you had built (balance it on a pencil yourself - don't rely on internet measurements!), and modeled everything in OR to make sure you obtain a stable flight!
Good luck either way!
bobbyg23
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Thank you for all of that info. Just a brief history. The 3d printed find only weigh 2.25oz. I dont know how much the stock ones weigh but I don't think they weigh too much more. I added 3oz of ballast to the nose cone to get my cg to the 20" mark. I did a string test before launching and it passed. I thought I had my bases covered. I did a lot of research on engine choice, weight and balance. I guess sometimes it just doesn't go as planned.
I think it was stable, just way too slow off the rod, at which point all bets are off.
bobbyg23
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I just realized that was my 3ft rod. Shoot, I meant to use my 4ft rod.
That would have helped a little, but probably not enough in this case. But definitely use the 4 ft rod.
Well , Hey Bob...it still looked great and you did it in just 6 days. Repair it as you stated and use a bigger motor.
JPalmer621
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With the Boyce fins make sure to check for stability since you are adding some extra weight also of you upgraded to the E engine? More weight
bobbyg23
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OK, dumb question, but should I be looking at the number for my engine selection and not the letter? I thought going from a D to an E would be a boost, but since I stayed at 12 it doesn't make it any more powerful, just a higher altitude?
In general yes, *but* different motors can have different-shaped thrust curves, so just looking at the number doesn't tell you exactly how it'll behave off the rod. Case in point: the new Estes C5, which has a much bigger initial thrust peak than the C6, so it's better for getting heavier rockets moving off the rod.
Easiest way to check (if you don't have a full sim in OR or Rocksim) is just to throw the parameters into thrustcurve.org and see what it says.
Easiest way to check (if you don't have a full sim in OR or Rocksim) is just to throw the parameters into thrustcurve.org and see what it says.
I also really like this site for comparing two motors. Sometimes it is missing data for some motors, but here is the D12 and E12:
https://www.rocketreviews.com/compare-motors-619551.html
and the C6 and C5:
https://www.rocketreviews.com/compare-estes-c6-to-estes-c5.html
bobbyg23
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Here is what happened when I ran it in thrust curve. They all failed. I think an E30 would work just fine. They work fine in Open Rocket, but not thrust curve.
Motors That Fail
These motors fit your rocket, but failed one safety check or another. They may actually work, but you should use them only with caution. We encourage you to run a more complete simulation to verify flight safety; see the simulators page for more info.
| Motor | Reason |
|---|---|---|
G | speed at end of launch guide too slow (40ft/s) | |
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G | speed at end of launch guide too slow (34ft/s) | |
|
G | speed at end of launch guide too slow (21ft/s) | |
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G | speed at end of launch guide too slow (29ft/s) | |
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G | speed at end of launch guide too slow (44ft/s) | |
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G | speed at end of launch guide too slow (33ft/s) | |
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G | speed at end of launch guide too slow (34ft/s) | |
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G | speed at end of launch guide too slow (42ft/s) | |
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G | speed at end of launch guide too slow (40ft/s) |
bobbyg23
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So this is what I wanted. For my fat, heavy rocket I need the initial thrust within those first couple of milliseconds.
https://www.rocketreviews.com/compare-motors-983586.html
Kevin O'Dell
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To my knowledge, there have been 3 versions of the Estes/Centuri Saturn V. The 1969 versions were both listed as 9.9 ounces. Both had thick corrugated paper body wraps and LOTS of plastic detail pieces. Both were designed to fly on 3 C6-3's....Until the advent of the then D13-3. I got my Estes version 1 for Christmas 1969....They hadn't figured ho to shove it all into one box. Mine came in 3 boxes! the Estes V1 separated at the command/service module joint. The command module came down on a 12" chute and the rest on two 24" chutes. The Estes had scale sized balsa fins with clear plastic fins that slipped over the balsa ones. Centuri separated at the second/third stage reducer as the current version. Centuri also used slightly oversized fins to avoid the clear plastic ones. Both had the engine at the very bottom of the rocket.
Version 2 was essentially the Centuri version for D12-3's with paper wraps. Then V3 (#2157) is Centuri modified with the recessed engine, the plastic wraps that carry most of the detail work, a listed weight of 12.2 ounces and still flying on a D12-3.Version 1 flew so-so....Version 2 flew GREAT! I'm working on Version 3 with my grandson.....I'll let you know....
Version 2 was essentially the Centuri version for D12-3's with paper wraps. Then V3 (#2157) is Centuri modified with the recessed engine, the plastic wraps that carry most of the detail work, a listed weight of 12.2 ounces and still flying on a D12-3.Version 1 flew so-so....Version 2 flew GREAT! I'm working on Version 3 with my grandson.....I'll let you know....
Kevin O'Dell
Member
Where did you find a paint layout for the service module?
Thrustcurve
The motor comparison on RocketReviews is indeed great, and it's really interesting and informative to look at them. But the Thrustcurve results tell you what you really need to know (you can also see the thrustcurve for each motor, although I don't think it has a motor-motor comparison like RocketReviews.) It is pretty conservative, targeting 50 ft/s off the rod to be considered successful. Most folks in reasonable weather would be happy with a bit less than that. But you get the raw numbers and you can make your choice.
bobbyg23
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Looks like at least an E30 for my rocket.
bobbyg23
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Stickershock23.com. I bought the set for this rocket. The service module is a wrap with everything printed on it.
Nytrunner
Pop lugs, not drugs
Here's the next step in rocketry learning: what do the motor codes actually mean, and why is a thrust curve important?
The letter is total impulse range: D is 10.1 to 20 Newton-seconds, and E is 20.1 to 40. An E can have twice the power of a D, but that doesnt necessarily mean twice the thrust.
The Number after the letter is average thrust of the motor. Thats total impulse divided by burn time. Notice thay the D12 and E12 both have 12 Newtons of average thrust, so they are near equal in their lifting power, but the E burns longer.
A motor doesn't burn exactly at its average thrust either. BP motors have an initial spike thays stronger than their average thrust, then it tapers off to lower than avg. Composite motors have even more varied thrust profiles. Check out thrustcurve.org, look up a motor, and you can see the thrust curve for each one. The thrust during that initial 1/4 second of burn is closely related to how heavy a rocket it can lift safely.
Keep flying and keep learning!
Nytrunner
Pop lugs, not drugs
40 ft/s is really low exit speed, only do that when there's low to no wind.
Looks like you're well on your way
Looks like you're well on your way
