Rocksim Help for Level 1 Cert

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lowga

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BAR, just getting back into the hobby. I've just built my first high power rocket, a Madcow Cowabunga that I'm hoping to certify Level 1 on. The rocket kit was modified from original slightly because I wanted to fly a lot of electronics. First of all, I modified the nose cone adding a head end altimeter bay from Atteberry Performance Engineering.

https://ape-rc.com/#!/Head-End-Alti...se-Cones-Plywood/p/56354898/category=11909535

Exchanged a few parts here, replacing the u-bolt with a stainless steel model, and adding lock nuts, and SS washers. Plan is to mount a Tracksoar 2 Meter APRS telemetry/tracking unit with GPS here, along with an audio beeper beacon.

www.tracksoar.org

Additionally, I'm going to mount a Big Red Bee BRB 432 MHz 100mw tracker in the altimeter bay (as a backup for Tracksoar), along with a Jolly Logic Altimeter 3.

Also added a Apogee camera hood so that I could fly an 808 HD Keychain camera. It's glued to the side of the rocket using epoxy, and painted to match the black color of the rocket.
https://www.apogeerockets.com/Build...pies/Camera-Hood-for-4in-98mm-Dia-Tubes-WHITE

As you can see from the picture, I did a bad job with the epoxy (man that stuff is tough to work with) and the fin fillets look horrible. Paint job isn't too great either--but I'm hoping it will fly straight. "Low and slow" was the plan--so maybe all the extra drag I've induced will help with that.

My hope is that the additional weight in the nosecone will move the CP forward increasing the stability of this rocket. I've purchased RockSim software, and downloaded the file from Madcow for this kit. However, I'm not experienced at using the software to this point. I know that i need to weight the nosecone and account for the additional weight. I also need to model in the Apogee camera hood and account for the air flow around that protrusion in order to accurately model the rocket.

I'd love to get some help from an experienced RockSim user before attempting these modifications. Any help gratefully appreciated!

Les Rayburn
Birmingham, AL

Level 1 Madcow Cowabunga.jpg
 

dhbarr

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If you've got all those electronics, batteries, & recovery gear in I'd just find the CG the old-fashioned way, by balancing it on a dowel or small piece of PVC. Weigh it. Now override the CG & total dry weight in RockSim, then try out different motors.

HTH,
-dh.
 

aerostadt

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In using RockSim I like to use actual data. For example, you can weigh your model and see how if compares with Rocksim. Things like epoxy can add weight, which are probably not included in the original model. If you add things like screw eyes or bolts that are not included in the original Rocksim model, you can add them into the Rocksim model using the added-mass option. Finally, if you have launch lugs, you can put a small wooden dowel through the launch lugs and tie a strong string around the dowel and slide the string back and forth to find the balance point or center of gravity (c.g.). You may want to put added mass at locations in the Rocksim model so that the real c.g. coincides with the Rocksim model. Once you have the c.g. of the simulation and the real model coinciding, you can add weight at the simulated c.g. to bring the mass up to the real model. There are a lot tricks you can play.

I don't know of any way to experimentally measure the center of pressure (c.p.) and I use the Rocksim c.p. instead. If the c.g. is about one diameter ahead of the c.p., the model should be stable. Also, Rocksim will call out whether the model is stable or not. If the weight of the real model is similar to the simulated model, Rocksim should do a fairly good altitude prediction. In some cases the Rocksim original weight may be near the measured weight. Once, I had a scratch-built model that Rocksim told me should weigh 6 pounds. I weighed the model just before going to the annual rocket meet and found it to be 10 pounds. I cancelled taking that model to the annual meet, until the next year when I had resolved this issue and the model flew fine.
 
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MikeyDSlagle

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What motor are you planning to cert on to necessitate all those electronics? I'm guessing this is the 4" version? I flew mine as the victory lap after I got my level 1 cert. It has an Adept22 in the nose and flew fine on an AT H148R to 1333 ft. I think I have a 2oz ballast added in my ORK file and it is still stable with 38/360 and 38/600 loads, I'll be running sims on it tomorrow night in preparation for Saturdays launch and see what I come up with.. She may go up on a I245G, will have to see.

What motor?

Mikey D
 

lowga

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Sorry I should have provided more details. I decided to add all the electronics purely for fun. As a boy, I used to lust after the Estes Transroc system, Cineroc, etc. Getting back into the hobby years later, I thought it would be great fun to fly a lot of telemetry, HD video, etc. Basically to build a sounding rocket and then review all the data after each flight. I don't expect the rocket to reach any kind of crazy altitude, or worry too much about recovery/tracking. If the airframe proves to be worthy, I may attempt my level 2 certification on the rocket as well.

I haven't made any decision on motor yet. Wanted to get the Rocksim file modified, and figure out CG and CP first. Then run some simulations with different motors. Have access to two fields, one with a 4,000 foot waiver and the other has a 20,000 foot waiver.

In addition to rockets, I'm a lifelong ham radio operator (N1LF) so the idea of flying a lot of ham radio telemetry on the rocket will help combine the two hobbies.

73,

Les Rayburn
 

MikeyDSlagle

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Sorry I should have provided more details. I decided to add all the electronics purely for fun. As a boy, I used to lust after the Estes Transroc system, Cineroc, etc. Getting back into the hobby years later, I thought it would be great fun to fly a lot of telemetry, HD video, etc. Basically to build a sounding rocket and then review all the data after each flight. I don't expect the rocket to reach any kind of crazy altitude, or worry too much about recovery/tracking. If the airframe proves to be worthy, I may attempt my level 2 certification on the rocket as well.

I haven't made any decision on motor yet. Wanted to get the Rocksim file modified, and figure out CG and CP first. Then run some simulations with different motors. Have access to two fields, one with a 4,000 foot waiver and the other has a 20,000 foot waiver.

In addition to rockets, I'm a lifelong ham radio operator (N1LF) so the idea of flying a lot of ham radio telemetry on the rocket will help combine the two hobbies.

73,

Les Rayburn
Ahh.. I gotcha. I'm all about gadgets and stuff myself. I have several dual deploy altimeters, only one of which has actually flown. And I have a Jolly Logic Altimeter 3 to ride along on all my flights. And would love to get into the telemetry side, that will come later...no hurry. I have rebuilt one of my sleds 3 times so far just trying to make it better. I plan to put a few cameras in and on my Tyrannosaur if I ever get it finished.

The Cowabunga should be able to handle a J motor for you to get your level 2. Just lay you some good fillets, maybe use some sort of chopped something on the internals. May want to consider a Jolly Logic Chute Release, never used one, but they receive high praise here. I never intended to fly mine on J's and didn't build it with that in mind. But it is built solid and can probably handle a mild one. I got a Tembo in the works upgraded to a 54mm for that kind of stuff. My Cowabunga should be able to fly on G's through I's, maybe a J. Heck maybe even a F if I wanted to try it, but that would be pushing it.

The longer motors help shift the CG forward a bit as well. My sims show J's to be more stable than some H's and I's.

Here is my ORK file, not sure if Rocksim can open it or not. OpenRocket is a free program like Rocksim, in case you didn't know. The weights for all the kit components are accurate. The nose cone bay should be close. I thought I overrode the CG for the entire model, but don't see where I did. I may have to go back and do that. But of course yours will be different. As for the CP, Madcow gives it to you on the cover of their instructions.

The ballast tube in my nosecone, that was a "prototype" adjustable weight system I was trying. It was held in place with epoxy and broke loose during flight. So I scrapped that and will do something different for this weekend's flight.

View attachment 311347

Here it is finished. Sorry, couldn't help tossing in that one of my daughter. She even helped polish and ground test it. :)

View attachment 311348 View attachment 311349 View attachment 311350

Feel like driving 6 hours? Come out to Winnsboro, LA and watch it in action Saturday. ;) I hope to get it on video. It's maiden flight, my camera got bumped and was outta focus for some reason and my camera man was filming...I don't know what he was filming. LOL. That H148R sure had a pretty red flame though.

Welcome to the forum,
Mikey D
 

lowga

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lowga

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MikeyD,

Your building and finishing skills far exceed my own. I had never worked with epoxy before, and found it pretty difficult to keep it smooth and even. Your rocket looks great! And your daughter is cute as she can be. Nothing like having a great ground crew. My own daughter was admiring my Cowabunga last weekend, and asked me a lot of questions about HPR. We watched some videos on YouTube so that she could see some launches. At one point, she exclaimed, "I wanna build a rocket!" (She's 29...) So of course, Daddy immediately drove to Michaels Craft Store and bought her an Estes Starter kit, another Skill Level 1 low power rocket, and a selection of motors. :)

Just hoping mine will stay together for Level 1.


Ahh.. I gotcha. I'm all about gadgets and stuff myself. I have several dual deploy altimeters, only one of which has actually flown. And I have a Jolly Logic Altimeter 3 to ride along on all my flights. And would love to get into the telemetry side, that will come later...no hurry. I have rebuilt one of my sleds 3 times so far just trying to make it better. I plan to put a few cameras in and on my Tyrannosaur if I ever get it finished.

The Cowabunga should be able to handle a J motor for you to get your level 2. Just lay you some good fillets, maybe use some sort of chopped something on the internals. May want to consider a Jolly Logic Chute Release, never used one, but they receive high praise here. I never intended to fly mine on J's and didn't build it with that in mind. But it is built solid and can probably handle a mild one. I got a Tembo in the works upgraded to a 54mm for that kind of stuff. My Cowabunga should be able to fly on G's through I's, maybe a J. Heck maybe even a F if I wanted to try it, but that would be pushing it.

The longer motors help shift the CG forward a bit as well. My sims show J's to be more stable than some H's and I's.

Here is my ORK file, not sure if Rocksim can open it or not. OpenRocket is a free program like Rocksim, in case you didn't know. The weights for all the kit components are accurate. The nose cone bay should be close. I thought I overrode the CG for the entire model, but don't see where I did. I may have to go back and do that. But of course yours will be different. As for the CP, Madcow gives it to you on the cover of their instructions.

The ballast tube in my nosecone, that was a "prototype" adjustable weight system I was trying. It was held in place with epoxy and broke loose during flight. So I scrapped that and will do something different for this weekend's flight.

View attachment 311347

Here it is finished. Sorry, couldn't help tossing in that one of my daughter. She even helped polish and ground test it. :)

View attachment 311348 View attachment 311349 View attachment 311350

Feel like driving 6 hours? Come out to Winnsboro, LA and watch it in action Saturday. ;) I hope to get it on video. It's maiden flight, my camera got bumped and was outta focus for some reason and my camera man was filming...I don't know what he was filming. LOL. That H148R sure had a pretty red flame though.

Welcome to the forum,
Mikey D
 

lowga

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Typo in original post: I'm hoping that all the additional weight in the nosecone will move the CP rearward so that the model will be more stable. According to the Madcow provided Rocksim file, the stability is only about 0.5 caliber so it's not the most stable rocket for a level 1 attempt.
 

aerostadt

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Typo in original post: I'm hoping that all the additional weight in the nosecone will move the CP rearward so that the model will be more stable. According to the Madcow provided Rocksim file, the stability is only about 0.5 caliber so it's not the most stable rocket for a level 1 attempt.
Weight placement won't effect Cp. More nose weight will move the c.g. forward. Is that what you meant?
 
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