openrocket help with apogee zephyr file

[Lt72884]

I downloaded the zephyr rocksim file from apogee. I first noticed that i couldnt do a mass over ride for the nose cone when i added the j270 as my motor. i want to add some mass since the caliber is below 1, and i like to have it about 1ish.

I noticed it said couldnt do mass over ride since the stage has mass over ride. Double clicking the upper most component in the window labeled stage, i unchecked mass over ride.

now the main isse. i added mass to the nose cone, but in order to raise my caliber to 1, i need 6.5 LBs of material. that seems like a lot of material to add...

Here is the file from their website

https://www.apogeerockets.com/Rocket-Kits/Skill-Level-3-Model-Rocket-Kits/Zephyr#motors

I tried to add the mass more in the center with same issue. This file seems odd to me. any ideas?

thanks

 

[OzHybrid]

I downloaded the zephyr rocksim file from apogee. I first noticed that i couldnt do a mass over ride for the nose cone when i added the j270 as my motor. i want to add some mass since the caliber is below 1, and i like to have it about 1ish.

I noticed it said couldnt do mass over ride since the stage has mass over ride. Double clicking the upper most component in the window labeled stage, i unchecked mass over ride.

now the main isse. i added mass to the nose cone, but in order to raise my caliber to 1, i need 6.5 LBs of material. that seems like a lot of material to add...

Here is the file from their website

https://www.apogeerockets.com/Rocket-Kits/Skill-Level-3-Model-Rocket-Kits/Zephyr#motors

I tried to add the mass more in the center with same issue. This file seems odd to me. any ideas?

thanks

The mass of the entire rocket is overridden in the "Stage" at the top. That's where you normally put the final constructed mass and measured CG position, before the motor is loaded. Then run the sim for the various motors you want to use. As you load the motor the mass and CG will be seen to correct for the motor chosen.
If you want to be able to add masses at various points the "easiest" way is to make the mass of the components correct and add up to the final weight and then add your masses where you want them. Before....... you untick the mass and cg position override, make a note of what they are. They'll be 0 when you go back.......Untick the mass and cg override in the stage at the top.

 

[neil_w]

It is always best to post *your* file, so we can look at it.

In general, when loading any file from the internet, you have to look it over carefully, and that goes double when importing a RKT file into OpenRocket. If you post your file we'll have a look (save it as an ORK file out of OpenRocket).

 

[OzHybrid]

It is always best to post *your* file, so we can look at it.

In general, when loading any file from the internet, you have to look it over carefully, and that goes double when importing a RKT file into OpenRocket. If you post your file we'll have a look (save it as an ORK file out of OpenRocket).

This is the file from the Apogee site. Should be the one he downloaded. As that one has the stage overridden as downloaded and all component masses greyed out, I'd be pretty sure that's the issue. But you are right...

 

[Lt72884]

It is always best to post *your* file, so we can look at it.

In general, when loading any file from the internet, you have to look it over carefully, and that goes double when importing a RKT file into OpenRocket. If you post your file we'll have a look (save it as an ORK file out of OpenRocket).

I agree, it's best to always upload my file, however, this is not my file it's right from their website. The issue at hand is when I adjust the mass to balance out my CP and CG to have a stability of one , it says I need to add 6 and 1/2 lb of weight to get a stability of one. That's way too high

The mass of the entire rocket is overridden in the "Stage" at the top. That's where you normally put the final constructed mass and measured CG position, before the motor is loaded. Then run the sim for the various motors you want to use. As you load the motor the mass and CG will be seen to correct for the motor chosen.
If you want to be able to add masses at various points the "easiest" way is to make the mass of the components correct and add up to the final weight and then add your masses where you want them. Before....... you untick the mass and cg position override, make a note of what they are. They'll be 0 when you go back.......Untick the mass and cg override in the stage at the top.

I did untick both of those, but it's telling me that I need to add 6 and 1/2 lb of weight in the nose cone to make a stability of 1 caliber. 6 and 1/2 lb. Seems like a lot of weight and way too high in my opinion

 

[neil_w]

I agree, it's best to always upload my file, however, this is not my file it's right from their website.

It’s your file now because you’ve changed it.

 

[OzHybrid]

OR file with override removed (this changed mass from 1000 to 1400gm(ish))
From that I had to add 106g of mass to nose to get the Cessaroni?? j270 to be 1 cal stable. I'm running OR 23.09 on Linux.

 

[Lt72884]

It’s your file now because you’ve changed it.

OR file with override removed (this changed mass from 1000 to 1400gm(ish))
From that I had to add 106g of mass to nose to get the Cessaroni?? j270 to be 1 cal stable. I'm running OR 23.09 on Linux.

odd, i wonder why its making me add 6.47 lbs

i am using aerotech j270 and version 23.09 for windows.

Thanks for your file. i will use that as a template and go from there.

I have had some odds goings on lately with OR. I actually might uninstall and reinstall.

If i have any more questions, ill be sure to post in this thread.

thank you much.

 

[OzHybrid]

odd, i wonder why its making me add 6.47 lbs

i am using aerotech j270 and version 23.09 for windows.

Thanks for your file. i will use that as a template and go from there.

I have had some odds goings on lately with OR. I actually might uninstall and reinstall.

If i have any more questions, ill be sure to post in this thread.

thank you much.

Just loaded it. Similar results, 3000ft ish.

 

[lr64]

I'm messing around with the file OzHybrid posted. 204 grams seems pretty heavy for a shock cord, and it's pretty far back, too. But moving it forward only reduces the necessary balance mass a little. The fins are a significant mass far back on the rocket. If the fins were half as heavy, you could remove a lot of the nose weight. That sounds like a lot, but solid aircraft plywood is heavy and less than optimal. Better to use something like 1/32" ply on either side of a lightweight core. That will keep most of the stiffness and strength, with much less weight. If you want equal thickness, just make the fin slightly thicker at the rood. The leading and trailing edges can be enough solid wood to allow the right shape. The rocket is subsonic, so an airfoiled shape could save a bunch of drag, while allowing it to be thicker and, if the core is light, lighter because it will allow the use of lighter skins. An 8 percent airfoil, which is fairly thin, especially at the Reynolds numbers we're talking about, would still be about 2.5 times as thick as the fin in the ork file. You could probably use 1/64" skins, or maybe double 1/64", with one layer at +/-45 degrees and the other at 0/90. That would greatly increase the torsional stiffness, combating flutter. Even better, maybe a layer of 1/64" ply at +/-45, covered by a pretty layer of veneer parallel to the spanwise direction of the fin. It could look like furniture. If you didn't feel like shaping your own cores, there are vendors who do custom cores for reasonable prices. Generally for model airplanes, but cores for tails might be appropriate here, and some outfits will cut to your specs.

An easier way to reduce the weight of the fins would be to make them from slightly thicker okoume plywood, which is considerably lighter than birch. To resist flutter, it doesn't actually have to be quite as stiff, since it's lighter.

 

[OzHybrid]

The 1/4 ply fins are what comes with the kit. The coupler also looked heavy at 207 grams.
I'm not sure why the Stage mass had been overridden to 400gm less than the summed component mass. Usually when you weigh your components/ calculate the weight it's lower than the finished rocket due to the glue factor ( and how much you used) and then when you override the stage to the real value it would be slightly heavier, not lighter.
The shock cord supplied is H/duty 1/2" and long......

 

[lr64]

Have you weighed the various components?

Incidentally, when playing around with Openrocket, it appears the apogee is not terribly sensitive to the exact weight. At least up to 1400 g empty. OTOH, keeping the weight near the CG allows better damping and therefore better dynamic stability. It seems possible one might get away with somewhat smaller fins.