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rcode

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Basic question can you have too much noise weight in your rocket? My rocket with 3D printed fins was very unstable when I flew it. I used BB’s for noise wight and made even added a few extra to move the CG up from where the instructions stated CG location should be. So can you have too much weight in the noise besides not going over the motors weight limits?
 

Funkworks

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I don't think so. And I base that opinion on prehistoric arrows used by cavemen who used a rock at the end of a feathered stick. 🏹🎯🔥🍖😄
 

Nytrunner

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So can you have too much weight in the noise besides not going over the motors weight limits?
If the cg is Very far ahead of the CP, you get a condition called 'overstable'. It isnt a flight danger, but it does make the rocket more susceptible to lateral airflow (wind) and can result in flights that go further off vertical or have more of a gravity turn near apogee.

This happens because the moment arm between CG (pivot point) and CP is longer
 

kbRocket

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I would be hesitant to trust the CP/CG of most rocket instructions unless it is high volume mass production like an Estes kit. CG can vary quite a bit based how you glue together your rocket and what components you include. A few years ago I trusted the CP location in the instructions of a high power commercial kit and did a little sky writing even though the CG was 1.5 diameters in front of where the instructions stated the CP should be. A quick simulation in OpenRocket, RockSim, or RASAero II will provide more reliable information.

Did your instructions say where the CP should be? You only mention CG. At launch you want the actual CG, including motor, at least 1 body diameter in front of the actual CP. Preferably a little more than 1 diameter for comfort.
 

rcode

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The Instructions didn't state the location of CP. It took about a .5 Oz to get center according to instructions but I added .6 thinking a like extra would be better. The Rocket flight made 2 loops before hitting the ground on the 2nd still under power. I was trying to video the flight so I didn't get a good look as it flew.


1597029076660.png
 

markjos

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Well, a picture is worth a thousand words! Now that you’ve shared a picture of the rocket, things have become much more clear. The Nike Hercules has tons of fin, and way forward, so the CP is going to be much closer to the nose than a design with more conventional fins, and much more challenging to keep stable. Good that the instructions made it clear how important this is, and provided info to get it right. Clearly something is still amiss. Is there any chance that your nose weight didn’t stay in place (shifted rearward) at launch? Did you balance it with the motor in place, and fly it on the same motor?
 
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rklapp

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If the cg is Very far ahead of the CP, you get a condition called 'overstable'. It isnt a flight danger, but it does make the rocket more susceptible to lateral airflow (wind) and can result in flights that go further off vertical or have more of a gravity turn near apogee.

This happens because the moment arm between CG (pivot point) and CP is longer
This is overcome with More Power!

1597052013978.png
 

Ez2cDave

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Basic question can you have too much noise weight in your rocket? My rocket with 3D printed fins was very unstable when I flew it. I used BB’s for noise wight and made even added a few extra to move the CG up from where the instructions stated CG location should be. So can you have too much weight in the noise besides not going over the motors weight limits?
You must be very careful, in case there are "noise" abatement laws, where you are flying - LOL !

Dave F.
 

rcode

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The Weight (I used BB's) were glued into place plus the weight is also sealed into the nose cone when you glue the shoulder section to the nose cone. I used different D12-5s for balancing also with the parachute and wadding, and one of those on this initial flight. I was playing with Open rocket and Rocksim but they don’t work with 3D printed parts, at least for a beginner like myself. At this point I’m thinking I should add more weight to the nose cone shoulder since that’s the most forward I can do now. Thanks for all the advice.
 

kbRocket

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The complexity of this rocket is outside of my direct experience. I haven't launched rockets with fins on the middle section or front end.

My gut feeling is that the CP may be about where the instructions indicate the location of the CG. I haven't modeled rockets with multiple sets of fins. You can probably use OpenRocket and model the rocket as 3 body tube sections, each with a set of fins. I am also not sure if the rule applies well that the CG should be ahead of the CP by 1 body tube diameter, The effective rocket diameter is probably larger than the actual body tube diameter because of the fins all over the place. Aerodynamics are probably not literal about body tube diameter.

I don't think you can add too much nosy weight to this rocket as long as you have a proper thrust to weigh ratio for launch. Originally active stabilization, and staging, were probably the reason for all of the sets of fins. You are trying to compensate with front end mass.

If you want to try to add as much stabilizing mass as possible to the nosy, consider using lead or tungsten instead of BBs. Your existing BBs can probably be removed with a drill. Lead has the advantage that it is dense and available where fishing supplies are sold. Tungsten is more expensive, but is actually 1.8 times the density of lead. It is environmentally friendly and available on Amazon sold as environmentally safe fishing weights and weights for pinewood derby cars. I have purchased both. You can get an once or two of tungsten for $10 to $20. I have a preference for the fishing weights because the have a hole in the middle. For gluing it doesn't matter. At a launch the hole allows them to be tied into a rocket to reduce the number of loops observed in the previous flight.
 
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Ez2cDave

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Too much nose weight can cause "coning" issues.

Dave F.
 

steveh.jae

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Basic question can you have too much noise weight in your rocket? My rocket with 3D printed fins was very unstable when I flew it. I used BB’s for noise wight and made even added a few extra to move the CG up from where the instructions stated CG location should be. So can you have too much weight in the noise besides not going over the motors weight limits?
Well, a picture is worth a thousand words! Now that you’ve shared a picture of the rocket, things have become much more clear. The Nike Hercules has tons of fin, and way forward, so the CP is going to be much closer to the nose than a design with more conventional fins, and much more challenging to keep stable. Good that the instructions made it clear how important this is, and provided info to get it right. Clearly something is still amiss. Is there any chance that your nose weight didn’t stay in place (shifted rearward) at launch? Did you balance it with the motor in place, and fly it on the same motor?
Mark, Do yo suspect the CG/CP issues are what led to Estes discontinuing this model? I recall seeing this stunningly beautiful airframe in Estes catalogs before I got into rocketry. I’m surprised that nobody offers it as a kit. I do see that Apogee sells plans (only) for a tiny model, and ‘Uncle Mike’ offers plans (also ‘only’) for a larger model. I purchased UM’s plans and they are almost hopelessly vague on construction materials (e.g., specific paper type/weight for main body of the airframe). Besides Van Braun’s iconic Saturn V masterpiece, and Semroc’s OT; for those of us at a certain age, the Nike Hercules remains one of the most eternally alluring airframes designed, imho, and I wish it were offered as a kit.

When I gain more experience (and gumption) I’d like to tackle an X-3 Stiletto scratch build. Do you know if it was ever offered as a kit?
 
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Antares JS

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Nike Hercules remains one of the most eternally alluring airframes designed, imho, and I wish it were offered as a kit.
Wish granted. You can choose 1/24 or 1/14 scale from Boyce.


 

lakeroadster

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The Weight (I used BB's) were glued into place plus the weight is also sealed into the nose cone when you glue the shoulder section to the nose cone. I used different D12-5s for balancing also with the parachute and wadding, and one of those on this initial flight. I was playing with Open rocket and Rocksim but they don’t work with 3D printed parts, at least for a beginner like myself. At this point I’m thinking I should add more weight to the nose cone shoulder since that’s the most forward I can do now. Thanks for all the advice.
Do a string spin test... :headspinning:

 

steveh.jae

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Wish granted. You can choose 1/24 or 1/14 scale from Boyce.


Purchased it. Something that ACTUALLY flies is what I am talking about.
 

HHaase

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That's the problem with a lot of scale kits of SAM's and AAM's, they weren't designed to function as free-flight ballistic rockets. So the fin designs typically are FAR from optimal for our hobby...... though they did function quite well as guided missiles.

However, I'm really having to fight temptation right now, I'd love to grab that Boyce kit. Always been a fan of the Nike Hercules system, particularly once I got into the Army Reserves as a teen, and our armory was at a former Nike site. Too bad they had sealed off all the bunkers at that point, and I never got to check them out.

I am getting a lot of great ideas from that instruction set however. Hmmmmmm....... I may have to re-do a few things on my 4-29SS.

-Hans
 

kbRocket

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Purchased it. Something that ACTUALLY flies is what I am talking about.
Boyce models are flyable models...
The rocket rcode is having difficulty stabilizing is the Boyce model. I googled the title of the instructions from rcode's picture "Nike_Hercules_1-24th_Scale_Instructions.pdf" and found this: https://cdn.shopify.com/s/files/1/0031/0411/2685/files/Nike_Hercules_1-24th_Scale_Instructions.pdf.

Soon steveh.jae can compare notes with rcode. Others must have experience with this model.

Do the string test.
 

steveh.jae

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The rocket rcode is having difficulty stabilizing is the Boyce model. I googled the title of the instructions from rcode's picture "Nike_Hercules_1-24th_Scale_Instructions.pdf" and found this: https://cdn.shopify.com/s/files/1/0031/0411/2685/files/Nike_Hercules_1-24th_Scale_Instructions.pdf.

Soon steveh.jae can compare notes with rcode. Others must have experience with this model.

Do the string test.
Spitballing here ... for the two-stage model, it looks like the CG will crowd the CP in the sustainer. Am I way off base in that supposition?
 

steveh.jae

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Spitballing here ... for the two-stage model, it looks like the CG will crowd the CP in the sustainer. Am I way off base in that supposition? Or is that the source of the astable condition?
 

Blast it Tom!

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Spitballing here ... for the two-stage model, it looks like the CG will crowd the CP in the sustainer. Am I way off base in that supposition?
A two-stager would indeed be interesting, but the instructions make it clear that this is single stage. I'll bet it's do-able, though - with the nose weight all the way up front, and the CP of triangular fins at 2/3 of the distance back from their forward tips, it just might work.

It'd be fun trying to wrap the string around that second stage for that swing test, though!
 

markjos

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@rcode, have you reached out to Boyce about this stability issue? They might have some additional advice, and I’d say they should have an opportunity to help you resolve it. This will be a tricky one, as others have aptly said. Ballistic flight wasn’t really in the cards for missiles designed this way.
 

steveh.jae

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A two-stager would indeed be interesting, but the instructions make it clear that this is single stage. I'll bet it's do-able, though - with the nose weight all the way up front, and the CP of triangular fins at 2/3 of the distance back from their forward tips, it just might work.

It'd be fun trying to wrap the string around that second stage for that swing test, though!
That’s exactly my point! Please tell me how to ‘swing test’ the sustainer stage of the Hercules. I mean just look at it!! And the 1:14 scale 2-stage model IS indeed offered as an option.
 

Blast it Tom!

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Ah, I didn't know that! <Tom puts 1/14 2-stage NH on his "Hope to build someday" list>
So in that case I may just drill a hole, knot the string, and patch it up after the string test.... but yeah that is not easy...
 

Ez2cDave

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Mark, Do yo suspect the CG/CP issues are what led to Estes discontinuing this model? I recall seeing this stunningly beautiful airframe in Estes catalogs before I got into rocketry.
Steve,

I don't think that Estes has ever produced a Nike-Hercules model . . . They have done Nike-Ajax, Nike-X, Nike Smoke, and Nike-Apache.

Dave F.
 
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