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cwhittak

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OK, need some pointers on RocSim which I just got. I am sure i missed the solution somewhere, but I give up

My design is stable, till I put the motor in, and it says not stable, fine, how can I design it to be stable? Where can I add noseweight if the pressures are off? CAn anyone give me a quick kick in the ars to get me going

Thanks tonz

Craig
 

BlueNinja

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You need a mass object in the nosecone. A motor brings weight behind the CG, moving it backwards behind the CP, which makes it unstable. Just add weight in small amounts to the nose until you get a stability margin of 1 or 2. I'm sure someone who knows better can explain it more in-depth than I can.
 

Zippy

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You can also make the fins larger and or the tube longer, unless your designing a scale rocket of course.
 

cwhittak

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Thanks Blue & Zippy.

As it turned out, I rebuilt my design from scratch and it looks much better. My confusion came from not being able to "see" the mass object (weight) in the nosecone. Do I have a wrong setting? This was my first build wiht RocSim, and it is great so far.

Does it factor in epoxy joint in the weight calcs ??

Thanks to all, nebie in the learning phase:)
 

flying_silverad

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Anybody know if it's possible to design pods on fins using rocsim? Sorta of like the Estes Renegade:rolleyes:
 

teflonrocketry1

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I resemble that remark!

Besides side pods this article updates tube fin and ring fin simualtions for RockSim version 7 using the fin mount concept from my new "Fins on Fins" technique.

Feel free to ask me for help with your simulations,

Bruce S. Levison, NAR #69055
 

flying_silverad

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Originally posted by teflonrocketry1
I resemble that remark!

Besides side pods this article updates tube fin and ring fin simualtions for RockSim version 7 using the fin mount concept from my new "Fins on Fins" technique.

Feel free to ask me for help with your simulations,

Bruce S. Levison, NAR #69055

Bruce- This might be a great thread to keep running Rock Sim issues/tips/tricks! Loving every minute of this new software. I have heard something about cluster rings and the program,,,can you shed some light on this?
 

teflonrocketry1

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RockSim Version 7.0.1.0 had printing problems with centering ring and fin templates. The centering rings came out as ovals or had bumps on them and the fins got distorted. RockSim Version 7.0.3.1 fixed the distortions but now the centering ring templates come out with only the central hole in place. I don't think Apogee knows about this since this is the first time I noticed the problem as well! I will e-mail Tim Van Milligan and let him know what I found.

One note, if you got upgraded to RockSim version 7.0.3.1 from version 7.0.1.0 be sure that either you uninstall the old version of the software before installing the new version or you use the correct shortcuts to the updated software.

I hope Paul Fossey incorporates my fin mount (tube fin, ring fin, side pod, and boost glider) concepts into the next version of RockSim software, but I hear RockSim 8 is going to be the Mac compatable version.

Bruce S. Levison, NAR #69055
 

Stymye

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Bruce I sent an email about the problem a few days after the last version was released.. no word on a fix so far
 

vjp

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Originally posted by teflonrocketry1
RockSim Version 7.0.3.1 fixed the distortions but now the centering ring templates come out with only the central hole in place. I don't think Apogee knows about this since this is the first time I noticed the problem as well! I will e-mail Tim Van Milligan and let him know what I found.
I sent an email to Apogee (t s . v m @ a p o g e e r o c k e t s . c o m) on 11-15-2003 about this issue, but I never heard anything back. I didn't follow up to verify that he had actually received my email, though (some time back, I think I read that they were no longer accepting communications except those posted via their website feedback tool).
 

Stymye

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I do not recall where I sent my email but
I did get an immediate reply that they would "look into it"
 

teflonrocketry1

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Originally posted by vjp
I sent an email to Apogee (t s . v m @ a p o g e e r o c k e t s . c o m) on 11-15-2003 about this issue, but I never heard anything back. I didn't follow up to verify that he had actually received my email, though (some time back, I think I read that they were no longer accepting communications except those posted via their website feedback tool).
That is Tim Van Milligan's correct e-mail address; I am surprised he didn't follow up with you on this issue immediately. Although I can say he has been very busy these past few months which is why my articles have been appearing in the Apogee Peak of Flight Newsletter.

I E-mailed Tim late last night and he responded this morning about this problem with RockSim version 7.0.3.1. Tim indicated: "Yes. We know about this bug. You're only the third person to find it. Paul will be fixing it in version 7.04."

Bruce S. Levison, NAR #69055
 

teflonrocketry1

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Originally posted by flying_silverad
Bruce- This might be a great thread to keep running Rock Sim issues/tips/tricks! Loving every minute of this new software. I have heard something about cluster rings and the program,,,can you shed some light on this?
I have been wondering if we should request a separate forum for flight and stability simulations. The topic does fit well into the support and recovery forum, but many of the other forums have a few threads on this topic.

I am wondering if a new forum will work; when I post news about about RockSim developments, especially those I made from questions and ideas related to TRF posts, the response is minimal.

Bruce S. Levison, NAR #69055
 

wyldbill

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Originally posted by teflonrocketry1
..when I post news about about RockSim developments, especially those I made from questions and ideas related to TRF posts, the response is minimal.
I imagine that Hawking and Einstein had similar problems :D

I read 'em, but really can't comment as I'm way behind the curve on implementing a lot of the ideas. They're valuable and appreciated none the less....

-bill
 

flying_silverad

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Originally posted by teflonrocketry1
I have been wondering if we should request a separate forum for flight and stability simulations. The topic does fit well into the support and recovery forum, but many of the other forums have a few threads on this topic.

I am wondering if a new forum will work; when I post news about about RockSim developments, especially those I made from questions and ideas related to TRF posts, the response is minimal.

Bruce S. Levison, NAR #69055
Create it and they will come!
 

teflonrocketry1

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Tip fins are covered in one of my earlier publications from the Apogee Peak of Flight Newsletter Issue 113 from October 27, 2003:

http://apogeerockets.com/education/downloads/Newsletter113.pdf

This article introduces the fin mount concept that the recent "Side Pod Simulation.." article is based on.

In this article I show how to simulate a design like the Centuri Jayhawk, which I just finished cloning last night!

Here is the RockSim Version 7 file for the Centuri Jayhwk:
http://www.rocketreviews.com/rocksim/oop_centuri_jayhawk.rkt


Bruce S. Levison, NAR #69055
 

Rocketmaniac

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I am working on a "mile high" rocket....... I did a simple 2 stage rocket....... I put a Pro38 H153 in each stage, and rocksim gave an altitude of 5014....... Almost...... I went back and played with the fin design....... And added a parachute (oops got to have one of them!!!)....... Rocksim then said altitude was 2281!!!!!! I then took the parachute back out, with no other changes......... Now I am up to 5437'.......

Why does adding a parachute drop the altitude in half? It only was LOC 28" chute, 1 oz!!!!
 

vjp

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Originally posted by Rocketmaniac
I am working on a "mile high" rocket....... I did a simple 2 stage rocket....... I put a Pro38 H153 in each stage, and rocksim gave an altitude of 5014....... Almost...... I went back and played with the fin design....... And added a parachute (oops got to have one of them!!!)....... Rocksim then said altitude was 2281!!!!!! I then took the parachute back out, with no other changes......... Now I am up to 5437'.......

Why does adding a parachute drop the altitude in half? It only was LOC 28" chute, 1 oz!!!!
Check the delay, you might be popping the chute way before apogee. By removing the chute, you're telling the sim to coast all the way up, then all the way back down (i.e. spack city).
 

vjp

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I should have added -

Or, go into the "Flight Events" tab in the Simulation Preparation dialog, and change the parachute deployment event to occur at apogee, instead of at engine ejection.
 

Rocketmaniac

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Originally posted by vjp
Check the delay, you might be popping the chute way before apogee. By removing the chute, you're telling the sim to coast all the way up, then all the way back down (i.e. spack city).
VJP.....That was it...... I put the chute back in, adjusted the ejection delay on the Sustainer to 10 seconds (just a wild guess) and Rocksim now says 5515'.......... It is by no means done (designing that is, I need to add weight for epoxy, shock cord etc) but I really want a flight over 5280........

I am learning slowly.........

Thanks
 

Rocketmaniac

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Hey, I just noticed that on the 2281' flight, velocity at deployment was 1031' per second........ It is now down to 5.56' per second.......
 

vjp

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Originally posted by Rocketmaniac
Hey, I just noticed that on the 2281' flight, velocity at deployment was 1031' per second........ It is now down to 5.56' per second.......
That's a little better!

Try experimenting with the "Predict Optimal Mass" dialog, too. It will really help with getting the peak altitude out of a particular motor/rocket combination. Often, you can add a little nose weight, and by allowing a reduction in fin size, you can actually increase your altitude (especially with very fast rockets where the significance of fin drag increases exponentially).
 
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