level 1 attempt. Could use a little help w/sims

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Wallace

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Before we get started want to make it clear that I have never nor ever will get along well with any form of computer, just muddle my way through basically ( Think along the lines of "A thousand monkeys at a thousand typewriters"). Well then, on to my project ... I have an Estes Scion that I built stock with the exception of a baffle and nosecone ebay. I suspect my version of Open Rocket/crappy ancient Dell 5500/self are somewhat incompatible because I cannot for the life of me get anything to sim correctly. I've un/re-installed Java and Open Rocket multiple times with no joy (never managed to get 3D to work but that's not really all that important at this point). Attached is my O.R. file with a list of single use motors that I currently have and single use H and I that should be available for my attempt. Stability is unobtainable despite my best efforts. Weight and CG are not even close and I cannot get any cooperation out of this cursed machine. Any help at all would be much appreciated. Thanks in advance.....Ok, here's a prime example. I can't upload the file because size on disc is 432 kb. I've attempted to open and compress it but nothing seems to be compatible. Ugggh...
 

Wallace

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This is about the best I can manage for now. I'll get my i.t. buddy on it hopefully when he gets off work.

20170712_100040.jpg
 

djs

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I'm not really sure what you're getting at here. From what I understand, you are saying that the CG and stability calculated by OR are nowhere near correct based on what the rocket is actually like. Is this correct? If so, you want to right click on the section marked "stage" on the design, and override the CG and mass on the rocket.
 

Nytrunner

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I see your OR weight is...... .865 oz? That doesn't sound right.

Do I read your note pad correctly and see that your model weight is 37 oz? That is pretty heavy for a scion.
Is that a 60" chute in there?

Have you tried Only overriding the Stage's mass and CG instead of the individual components? (take off all overrides then match the stage to the built model)


You're altitude results don't look too far from reality. They're a little higher than what I got from my Heavy built Leviathan (whose parts the Scion is assembled from)
 

Crash-n-Burn

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Wow, you are putting in some serious work for your L1 attempt. I applaud you for that. You entitled the thread "Level 1 attempt..." so in that context I can say that you are going above and beyond. Unless your certifiers or club are asking for all this, it isn't necessary by NAR guidelines. You could get by with a ThrustCurve.org sim, which for the H135 gave me 1954' (based on your component weights). Other motors will get you L1 cert at ~1400' if you don't want to go that high.

CP is 36.5" from tip. https://www.rocketryforum.com/showthread.php?132843-Center-of-Pressure-Estes-Scion You have your CG.

In regard to the computer issue part of this, my best guess is to sacrifice a chicken. I'm worse than useless on that one.
 

Bat-mite

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Looks like you weighed every piece of the rocket. That's good. Now, open each component in OR and go to the Overrides tab. Put in the actual weight.
 

dhbarr

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Yup, change your Stage Override weight from 0.865oz to 37 oz is my guess. Double check your overall CG override while you're in there, lotta' solid effort in there.
 

Wallace

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Thanks for all the help everyone. I've already done all suggestions. I'm fairly certain my or is corrupted. I am aware of the WAY overkill on the build but I sure am having a great time with it. The handwritten list is correct, the or file is not. I basically just need to know stability margins with the listed motors so I can adjust nose weight if necessary. I'd really like to use the I 205 but or is telling me way under 1 caliber. I actually enjoy building 'em more than I do flying. I have a 60" hemi shaped umbrella canopy that I'd like to cut to the correct diameter but I get conflicting answers on that also. Was kinda leaning towards 30ish inches. Btw, It will have a cable cutter type setup. The bt-55 in the nose contains an eggfinder mini and a quantum.
 

Wallace

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The nc currently weighs 263 grams because it contains all the electronics and an 800 Mah lipo. I used a piece of stainless brake line from my j7nk pile to make the anchor point replaceable, also put the 1/2" tube/cap setup in so I can add weight if needed because I foamed the cone....
 

djs

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Can you upload the OR file so we can take a look? Sometimes OR can be "tricky" to get to agree with you.

Currently, where is your CG at, on an empty rocket?
 

djs

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The nc currently weighs 263 grams because it contains all the electronics and an 800 Mah lipo. I used a piece of stainless brake line from my j7nk pile to make the anchor point replaceable, also put the 1/2" tube/cap setup in so I can add weight if needed because I foamed the cone....
With that, you should be stable with pretty much all motors, I would think.
 

mccordmw

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Just a suggestion here... While you hammer out how to best use sims like OR, with such a small rocket like the Scion, how about going with a more conservative approach?

Pull the ebay out of the nose
Weigh the whole thing on a scale now
Balance it to measure the CG
Use the stock chute it came with. Should be ok with that and get a good descent rate
Use the Aerotech H115 DM, drilled delay to 8s
Rely on motor eject to pop the chute

Stock, with no foamed nosecone puts the stability at about 0.9 calibers. Since you have more weight in there, you're probably ok, but check mass and CG to be sure.

Here's K'Tesh's beautiful Scion ORK file I found on this site.

The critical thing now is to weigh the whole model wo/a motor and get the balance point (the CG).

Once you figure out your L1, you can start to experiment with electronic deployment and other complexities that come with the electronics. I'm no one to talk, though. I did my L1 with a big Binder Excel, dual deployment with redundant Eggtimer Quantums, and an Eggfinder GPS. :p
 

djs

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+1 - this is a very fixable rocket file... Where are you planning on doing your L1?
 

Wallace

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Actual measuerd cg is @ 15.625 from the top of the bt, it's actually on my list, just sorta in an unlikely spot so I see how you could have missed it. I do have a stock "spare" nc and anther rocket I could use, I know from experience (life?) enough to keep my options open. I'm planning on the upcoming Bong launch. I've exchanged eMails with Mark H. about it and contacted Wildman about motors (sadly no I 205's in stock at this time) can always hope though. I will definitely be doing some testing (ground and launch) beforehand, just waiting on a few more bits that I couldn't source locally. I have a few different aerotech su motors (F's and G's) in my possesion and a 6' chunk of 10/10. Time, as usual is the problem. I know I could/possibly should keep it simple but that's beyond my control. I have always had a habit of starting with the most difficult things first. I quit fighting it a lotta years ago.
 

Wallace

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BTW, the foam was not to "stiffen" th nc. It's the only reasonable way I could bond all this stuff to plastic.

20170708_195155.jpg
 

djs

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Actual measuerd cg is @ 15.625 from the top of the bt, it's actually on my list, just sorta in an unlikely spot so I see how you could have missed it. I do have a stock "spare" nc and anther rocket I could use, I know from experience (life?) enough to keep my options open. I'm planning on the upcoming Bong launch. I've exchanged eMails with Mark H. about it and contacted Wildman about motors (sadly no I 205's in stock at this time) can always hope though.

Ok- generally the Estes pro-series rockets are stable for most/all motors, so I wouldn't worry too much about it.

I'll be at the bong launch- if you need someone to sign off on your cert, I'll be there for most/all of the day on Sat, and the morning on Sunday. Mark H can do it as well, and there are several others.

I might have a connection for an I205, but I'd definitely recommend doing your L1 on an H motor.. esp at Bong :) PM me if you're interested.
 

Wallace

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Actually turned out better than I expected. It would be a shame to not fly it.

20170709_123832.jpg
 

mccordmw

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Ok. So if I override total weight wo/motor as 1079 g (per what I see on your image), and if I override CG to be 24.19" from the tip. The stability wo/motor is 4.88 calibers. That's one heavy and nose-heavy rocket. I like to stick with a minimum thrust-to-weigh of 6:1 (others have slightly varying opinions on this). That puts you in the realm of minimum average thrust around 64 N/s (a bit higher once you add in motor weight). All the options you picked at higher, so that's good.

You OR image showed the following motors I think:

H115
H135
H165
I205

The stability in your sim (once I added the mass and CG) are:

H115 - 3.61
H135 - 3.59
H165 - 3.62
I205 - 3.24

That's pretty overstable. The sweet spot is about 1.5 calibers. If you launch this in any significant wind, it will weathercock. Try to get it off the rod as fast as possible then. I can't tell in your image, but it looks like you're using the stock launch lugs? So expect a rod of around 4'. The H165 comes off a 4' rod at a healthy 18.2 m/s. Hopefully, on a not too windy day, it won't weathercock too much then. That should fly a nice 1,350 ft. or so. Drill the delay to about 8 seconds per the sim.
 

Wallace

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Sounds absolutely reasonable. It has lugs and buttons, sort of a mid build change of plans. You're numbers are with the heavy nc, or the stocker? I do have both...
 

djs

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What are you trying to set them to?
 

Wallace

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nc weighs 263 grams loaded. total mass w/out motors is 1079.7 grams and actual cg is 15.625 from top of bt {that's what OR calls for in override}
 

Wallace

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The simple answer is I need a new(er) computer:facepalm:
 

Wallace

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outstanding! Now if I just do a "save as" I can hack away until it's unusable again and go back to your correct version. Thanks tons for the help. 22.9 fps a little fast for landing? or maybe desirable for motor eject @ altitude? I can easily do any size hemi chute up to 50" with what I have on hand. I'm kinda leaning towards the dark matter, very cool motors...
 

djs

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I don't think so... at Bong, having a smaller chute might be preferable.

I might fly an I327 dark matter motor that weekend, if I have the time.
 

DavidMcCann

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I admire your desire to sim it.

with that much nose weight.... Stuff in whatever fits, and fire it. and at bong.... I'm lead to believe you're better off coming in hard. ;)
 
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