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5 Our Fathers and 3 Hail Marys and you'll be fine. (yes, I'm also Catholic)

OR isn't as versatile as RS is. Tim has many rocket designs at Apogee that won't load properly into OR, for example adding a BT to the end of a fin. Someday, OR will be able to do this, someday...

Tim talked about the RS10 problems in the recent NAR video.

 
neil_w said OR has an undo in the Edit menu. Dunno about RockSim. I never looked for one. What I meant was that nothing is irreversible in either software. If you change a body tube length to X and don't like the CP result, then change it back to Y and the CP dynamically reverts back. That is the beauty of the interactive design software. I guess an Undo history would be convenient in the GUI, but I never thought much about it.

Yes, two files are the way to go when flying with motor mount adapters. I do the same in Thrustcurve.
RockSim lists "Undo" and "Redo" in the Edit menu but I could never get them to work. I don't know if this has been corrected in RockSim 10. I'm old school on design changes - I save major revisions in a new file; Name-rev01, Name-rev02, etc.
 
Thanks guys
Attached is a RockSim file I put together for your rocket. It has your extra section, the thrust plate and the motor retainer. I guessed at the thrust plate thickness (0.25"). Anyway, take a look at the component flow and labeling. This is how I do it, everyone is different - but you can see how the components are grouped and flow from tip to base. RockSim allows you to move component positions Up & Down the design component tree.

I took out a lot of the Mass components since you are using the final weight & CG. They were just cluttering things up for this example.

Thanks! I got your file downloaded and it looks a lot like the most recent file that I came up with, only mine doesn’t have the Aeropack retainer added to the bottom. Also my flange plate is homemade out of 1/2” plywood using 6” centering rings. I did that so it would be lighter than a purchased aluminum one. I suppose that is irrelevant since we are overriding the mass though on the entire rocket. I still haven’t figured out what you mean that I need to change the fin tab on mine to fit the 75mm mmt. It looks like to me it stops at the 75mm tube. Could you please walk me through how to change that so it is correct? Also with an L850 motor your design cal is .94 and mine is 1.83. I can send you my latest file if you’d like to study what the difference could be.
 
Since I’m replying about RockSim10, I’m not strictly sinning about not responding on this OR thread. (Although its been over 50 years since I’ve considered myself Catholic, some of the habits of parsing about what’s a necessary sin avoid or confess still remains. 😊)

I haven’t upgraded my Windows 10 OS since installing RS10, and none of my designs have clustering, so its not surprising that I haven’t encountered any of the bugs that Tim vanMilligan referred to with RS10.

But many years of my engineering career were spent programming, and I can testify how difficult it is to get all of the bugs out of a mature software application, especially one that was written by someone else.

Once a codebase that’s hundreds of thousands of lines of source code long and hundreds of files gets to be decades old, it becomes almost impossible to know how any change will affect the rest of the code.

And since OS providers aren’t constrained, it’s also nearly impossible to prevent OS upgrades from breaking the code. Microsoft and Apple work with big software providers to root out such problems, but small fry like Apogee can only hope that new OS releases don’t hurt them too badly.
 
Thanks guys


Thanks! I got your file downloaded and it looks a lot like the most recent file that I came up with, only mine doesn’t have the Aeropack retainer added to the bottom. Also my flange plate is homemade out of 1/2” plywood using 6” centering rings. I did that so it would be lighter than a purchased aluminum one. I suppose that is irrelevant since we are overriding the mass though on the entire rocket. I still haven’t figured out what you mean that I need to change the fin tab on mine to fit the 75mm mmt. It looks like to me it stops at the 75mm tube. Could you please walk me through how to change that so it is correct? Also with an L850 motor your design cal is .94 and mine is 1.83. I can send you my latest file if you’d like to study what the difference could be.

Sure, go ahead, post your file and I'll take a look at it.

I should have explained the fin tab condition better. The sloped edges of your fins were meeting up with the vertical edges of the tabs below the outside face of the body tube. They should be intersecting at the outside face of the body tube.

But come to think of it, that may be an "optical illusion". I may have the 2D orientation on the wrong set for a 3-fin design. LOL. Just kick me to the curb.
 
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Here it is. Thanks a bunch!

I looked at your file. You are using RockSim's stability equations on the 2D calculation, and I'm using Barrowman.

That's why we have such different stability margins.

As to which and why to use - I can't go down that road. There's a whole lot of territory to cover. You may want
to look up Apogee Newsletter 238 to start with. And maybe drop Tim, at Apogee, an email.

I do know that the Barrowman option has always done a fine job for my designs. But you can see the numbers
are conservative.
 
Ok thanks for looking at that file. Also, did my fin tab look like it was set on or do I need to change something? If it’s good to go I think I’ll be ready for launch!
 
Ok thanks for looking at that file. Also, did my fin tab look like it was set on or do I need to change something? If it’s good to go I think I’ll be ready for launch!

The basic simulation looks fine. As the motors get longer in the 75mm class, that's when the stability margin drops into the 0.95 to 0.85 range. And again, that's when using Barrowman on the stability calculations. That's a discussion to have with the people whose launch day you plan to attend. Just don't pop it on them on launch day.

As to being ready for a launch - that's up to the RSO at the launch. I don't know if this is your first large HPR or your 100th. I always have an experienced HPR person look over my builds before launch day; general construction, electronics bay setup, harnesses, chutes, eyebolts, GPS tracker, etc. But that's me. Big rockets are a big expense. I want the odds in my favor that I will have a good recovery.
 
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One more question with RS. How do I know if a motor is powerful enough and has enough inertia to get the rocket safely off the rail at 30 + mph? I am simming a 54mm J 135 in my big Nuke for starters and it says it will take it to 2100’, but how do I know if it will it have enough speed off the rail to not weather cock?
 
If it's not there already, add the column "Velocity at launch guide departure" to your flight simulations tab. This will display the expected velocity in fps.

You can modify the length of the rod / rail on the "start state" tab when you select the motor.

Edit: Forgot to mention you can double click on the simulation to display the simulation detail. Check out the section:

Launch guide data:

  • Launch guide length: 36.0000 In.
  • Velocity at launch guide departure: 65.7421 ft/s
  • The launch guide was cleared at : 0.090 Seconds
  • User specified minimum velocity for stable flight: 50.0000 ft/s
  • Minimum velocity for stable flight reached at: 21.0644 In.
 
It’s only showing 18.77 mph on a J135 with an 8’ rail so that won’t be a big enough motor for this rocket then, will it?

Are you still working in RS or are you back in OR ?

You should consider using the Thrust Curve program (just Google Thrust Curve) to generate you a list of acceptable motors for this rocket. That gets you in the ballpark - and use those motors in your simulations. But I show you need at least a J800 for a solid launch on a 15lb. rocket, 96" long rail, using 50 ft./sec. as the minimum stable velocity.

Mind if I ask what is your certification level?
 
Are you still working in RS or are you back in OR ?

You should consider using the Thrust Curve program (just Google Thrust Curve) to generate you a list of acceptable motors for this rocket. That gets you in the ballpark - and use those motors in your simulations. But I show you need at least a J800 for a solid launch on a 15lb. rocket, 96" long rail, using 50 ft./sec. as the minimum stable velocity.

Mind if I ask what is your certification level?
ROCKSIM
 
In RS you can set your "Minimum Velocity for Stable Flight" under the Edit Menu. Select Edit menu, then select "Preferences" - and you can input the velocity. As to what to use - I set it at 50 ft./sec. - which is average/conservative. Others may go as low as 45 ft./sec. You should ask the people you launch with what they feel is acceptable.

As for the Rail Length, you set that when you select the motor. You'll see a series of Tabs at the motor selection - click on the "Starting State" tab. That's where you put in the rail length.
 
Ya it’s been a couple years since I took the test, and I only make it to the launch about once a year as it’s three hours away to the closest one. Then, I think I also made too big of jump going from a 38mm simple one altimeters dual deploy Madcow Torrent to this rocket. I did not realize there was so much to learn with HPR.
 
Ya it’s been a couple years since I took the test, and I only make it to the launch about once a year as it’s three hours away to the closest one. Then, I think I also made too big of jump going from a 38mm simple one altimeters dual deploy Madcow Torrent to this rocket. I did not realize there was so much to learn with HPR.
Well do me a favor and please have an experienced HPR person put hands & eyes on this rocket a few days before its maiden launch. It wouldn't be fair to put the RSO in the tough position of telling you "No" at the launch because of some safety issues. Long drives and "Go Fever" don't make for a fun day when you can't launch. And please do a pop test long before launch day!
 
I’ll do what I can. I live in rural western Kansas and I don’t know of one solitary HPR guy out here! There probably is, but I’m not aware of any. Lol
 
I’ll do what I can. I live in rural western Kansas and I don’t know of one solitary HPR guy out here! There probably is, but I’m not aware of any. Lol
See if you can contact someone at the group you normally launch with - and start feeding them pictures of the electronics bay, harnesses, eyebolts, chute & deployment charge setup, any construction photos you might have. You know the drill. The wonders of the internet. Get them comfortable with the build, and launch day will be a happier event.
 
Also the latest version of RockSim has a "Recommended motors" options that you can use to get a general idea of motors that might work for you. My typical workflow was Thrustcurve.org to narrow down the range of possibilities then RockSim to sim several options before I buy the motor(s).

But now with RockSim 10 I can start with "recommended motors" and put in different variables (rod length, reload / single use, etc.) and start from there. Here's an example for my 3.1" LOC Sandhawk with a 38mm MMT. I never though about a J435WS but looking at the table it might be something to SIM and see what it looks like.

SingleUseAT.jpg
 
See if you can contact someone at the group you normally launch with - and start feeding them pictures of the electronics bay, harnesses, eyebolts, chute & deployment charge setup, any construction photos you might have. You know the drill. The wonders of the internet. Get them comfortable with the build, and launch day will be a happier event.
Thankfully Rob Martinez soldered me up two
altimeters and a receiver and I asked him a lot of questions with the electronics part of it so I’m pretty comfortable with that aspect of it.
 
Also the latest version of RockSim has a "Recommended motors" options that you can use to get a general idea of motors that might work for you. My typical workflow was Thrustcurve.org to narrow down the range of possibilities then RockSim to sim several options before I buy the motor(s).

But now with RockSim 10 I can start with "recommended motors" and put in different variables (rod length, reload / single use, etc.) and start from there. Here's an example for my 3.1" LOC Sandhawk with a 38mm MMT. I never though about a J435WS but looking at the table it might be something to SIM and see what it looks like.

View attachment 428853
Wow, RS shows my rocket needing K L and M motors. J motors don’t give it fast enough take off. Thanks for showing me that feature. It is nice to have.
 
Also the latest version of RockSim has a "Recommended motors" options that you can use to get a general idea of motors that might work for you. My typical workflow was Thrustcurve.org to narrow down the range of possibilities then RockSim to sim several options before I buy the motor(s).

But now with RockSim 10 I can start with "recommended motors" and put in different variables (rod length, reload / single use, etc.) and start from there. Here's an example for my 3.1" LOC Sandhawk with a 38mm MMT. I never though about a J435WS but looking at the table it might be something to SIM and see what it looks like.

View attachment 428853
In RS when I select recommended motors it shows an L850W as one of the safe motors except it doesn’t have a safe deployment speed. This is a plugged motor and I will be using electronics. Why is it saying the deployment speed isn’t safe and how do I correct this? Is there a place in the settings that something needs changed?
 
In RS when I select recommended motors it shows an L850W as one of the safe motors except it doesn’t have a safe deployment speed. This is a plugged motor and I will be using electronics. Why is it saying the deployment speed isn’t safe and how do I correct this? Is there a place in the settings that something needs changed?

I had this same issue when I first tried to simulate dual deployments. What I did was

1. add a drogue to the "rocket design components" (I use a streamer in this example)
2. When you elect the motor, click on the "Flight Events" tab
3. Select one of the recovery devices (Drogue or streamer in my case)
4. For the drogue select "deploy at apogee" for the "event description"
5. Select the main chute
6. Select "deploy at altitude" for the "event description" and enter the desired altitude (e.g. 700')
7. Click on launch

DualDeployConfig.jpg
 
Thanks. I tried that and it’s still showing unsafe deployment speed on a K560 which is plugged.
 

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