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Onyx by Loc

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deangelo54

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I am helping a friend build an Onyx. It is mostly stock with a few modifications:
Rail Buttons
Eye bolt on forward centering ring to attache Kevlar line.
Kevlar line just before the end of the body tube then that elastic shock cord Loc provides.
Inserts in the aft centering ring for engine retension.
Metal clips for engine retension.

I read a lot of rocket reviews and I noticed no one has added nose weight. We intend to use a composite E20 and then an F20 engine. Any tips hints or suggestions are welcome.
 

Nytrunner

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Welcome to the forum.

Sounds like you've put a lot of thought into building the thing. Have you heard of the program OpenRocket? It's a free java-based download. You can make your rocket digitally and simulate flights with a huge variety of motors to get a rough idea of how it'll do.
 

H_Rocket

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Build it stock. With the motors you list, you don't need any nose weight. I think an E20 will be iffy at best for it.
 

patelldp

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The Onyx flies like a dream on the F20. The E20 will be great as well.
 

deangelo54

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Do you think the E20 does not have enough thrust? Considering we are using epoxy which adds weight, that may be so.
 

Nytrunner

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The E20 and the F20 only have a 5 newton difference in initial peak thrust (35 vs 40).

As long as it doesn't weigh more than 25 oz with motor, the E20 will provide at least a 5:1 thrust/weight.

If you don't want to go through OpenROcket, check out prospective motors on ThrustCurve
 

DavidMcCann

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built mine just about how you describe. F20, F23, F27, and F42 are perfect motors for it.

I love the F42T in it. zoom. gone.

I was getting 755' ad 138 MPH on F20W's

788' and 180 MPH on F42T's
 
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mcderek

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The Onyx flies real nice on a CTI H54 White Longburn:)
 

deangelo54

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Sounds interesting but I think my friend was planing on recovering the rocket so that he could fly it again. Plus he is not level 1 certified. I don't think the Onyx is a good rocket for certification. Then again two years ago a guy flew a Partzion on an H for his Level 1.
 

deangelo54

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800 feet at the Berwick, ME field is certainly recoverable. Can you believe Loc lists a D12 as a recommened engine? The 5 to 1 Thrust to weight ratio is a key statistic when deciding which engine to use. A friend of mine from CMASS has an excellent spreadsheet to claculate important statistics including stability ratio depending on where the CP and CG are located. 5 to 1 and at least one caliper stability are very important factors on which engine we will use.
 

dhbarr

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d12 has a very high off-the-pad peak thrust relative to almost any other in-production BP motor.
 

DavidMcCann

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5:1 and 1 caliber of stability are good guidelines, but don't get super hung up on them. Wind conditions and rail length can affect how much of each are required. Most of my onyx flights were under 5:1. Don't go crazy with epoxy, a little bit goes a long way, and honestly this kit would be fine with wood glue. The joints will still be stronger than the wood and cardboard the rocket is made of.
 

Steve Shannon

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Although a 5:1 thrust to weight ratio provides a nice margin, the official minimum average thrust to weight ratio is 3:1.
From NFPA 1127
4.9 Weight and Power Limits.
4.9.1 The maximum liftoff weight of a high power rocket shall not exceed one-third (1∕3) of the certified average thrust of the high power rocket motor(s) intended to be ignited at launch.


Steve Shannon
 

Nytrunner

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5:1 and 1 caliber of stability are good guidelines, but don't get super hung up on them. Wind conditions and rail length can affect how much of each are required. Most of my onyx flights were under 5:1. Don't go crazy with epoxy, a little bit goes a long way, and honestly this kit would be fine with wood glue. The joints will still be stronger than the wood and cardboard the rocket is made of.
In the case of the thread starter, he may want to stick with 5:1 until he has more experience choosing motors and flying bigger rockets.

Although a 5:1 thrust to weight ratio provides a nice margin, the official minimum average thrust to weight ratio is 3:1.
From NFPA 1127
4.9 Weight and Power Limits.
4.9.1 The maximum liftoff weight of a high power rocket shall not exceed one-third (1∕3) of the certified average thrust of the high power rocket motor(s) intended to be ignited at launch.


Steve Shannon
Law is law, but I can't shake the feeling that ruling based on AVerage thrust doesn't take into account some longburn or highly regressive burning motors with significantly higher initial thrust than their average.

Oh well, that's just my protocol peeve.
 

DavidMcCann

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Officially.... NFPA 1122 doesn't set a thrust to weight requirement that I can find ;)
 

DavidMcCann

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In the case of the thread starter, he may want to stick with 5:1 until he has more experience choosing motors and flying bigger rockets.



Law is law, but I can't shake the feeling that ruling based on AVerage thrust doesn't take into account some longburn or highly regressive burning motors with significantly higher initial thrust than their average.

Oh well, that's just my protocol peeve.
NFPA isn't law. That's my pet peeve.

but I agree, it's better to look at max initial thrust, and the whole curve when considering a motor
 

Nytrunner

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NFPA isn't law. That's my pet peeve.

but I agree, it's better to look at max initial thrust, and the whole curve when considering a motor
Good point. I never actually looked into its 'authority' scope. Interesting.

I guess as long as I'm operating in an official community (such as a club, or the forum) I err on the side of following the NFPA standards since that provides some baseline to compare our activities to that a regulator with NO knowledge of rocketry At All, can understand. That doesn't mean I won't gripe about certain rules (Like the 3:1 HPR rule that NAR adopted....grrrr).
and there's no guarantee I haven't loaded some of those rules to failure privately.
 

Nathan

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NFPA isn't law. That's my pet peeve.

but I agree, it's better to look at max initial thrust, and the whole curve when considering a motor
+1
Taken by itself, average thrust is a pretty useless bit of information.

A CTI H410 and L395 have similar averge thrust. But the L395 makes about 30 times as much total thrust.
 

DAllen

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I can say from experience a H128 is rather awesome in a LOC Onyx. Rail buttons are highly recommended as 1/4" rod whip can be...severe.
 

Steve Shannon

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In the case of the thread starter, he may want to stick with 5:1 until he has more experience choosing motors and flying bigger rockets.



Law is law, but I can't shake the feeling that ruling based on AVerage thrust doesn't take into account some longburn or highly regressive burning motors with significantly higher initial thrust than their average.

Oh well, that's just my protocol peeve.
I agree; I was just pointing out what NFPA 1127, which both NAR and Tripoli use as the basis of their safety codes for high power rocketry, specifies.



Steve Shannon
 

dhbarr

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I would think the onus would be on the flyer to show a) what they understand the thrustcurve to be, b) how much of what rod they need to achieve positive control given c) current field conditions.
 

Steve Shannon

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I would think the onus would be on the flyer to show a) what they understand the thrustcurve to be, b) how much of what rod they need to achieve positive control given c) current field conditions.
That would be ideal, but I suspect that many L1 flyers don't have that basic knowledge until they are exposed to it after certification.
 

Nytrunner

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DeAngelo, so sorry to be one of the ones that have so derailed your thread.

Keep building rockets, keep learning and asking questions, and above all keep having fun!
 

markkoelsch

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Then we can throw another log in the flame here. Wind velocity versus thrust to weight. I believe it was an NAR study that put forth essentially the 3:1 minimum until 10 mph at which point the needed thrust to weight ratio goes up substantially for a given wind velocity. I cannot remember the exact numbers or the name of the study.
 

DavidMcCann

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this is why I just fire at 30:1 and 4 calibers of stability ;)
 

blackbrandt

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I'll tell ya what really kicks an Onyx... try an H399! YouTube channel in my siggy has the link :)
 

deangelo54

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I think some people are missing the point. This is my friend's first mid power rocket. He has been out of rocketry for about 40 years. The Onyx is a relatively light rocket weighing in at 13 ounces. I can't see why anyone would use an engine larger than a G on this kit. Once it is out of sight what's the point of going higher. We put a lot of time planing and building the kit. We would like to have it land on the field.
 

DavidMcCann

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I think you're missing the point that we all regularly fly to 3500' visually and get them back ;)

that and discussion s ion tend to wander and this one did quite a bit off topic.

On topoc- most people are just saying don't worry about going slightly under 5:1 thrust to weight
 
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