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GGDT v4.5

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Re: GGDT v4.5

Unread postAuthor: joestue » Sun Apr 20, 2008 5:09 pm

D_Hall wrote:So I tacked on the mass of the air for the acceleration equations. Mind you, I treat the mass as a single mass and do not account for leading shocks and such, but air mass is a second order effect to begin with. The stuff I'm ignoring is probably third order.


That's what I did to your spreadsheet last year, (for my own use), it produced significantly reduced, and more realistic figures after adding the mass of the air in front of the potato to the projectile, I added a function of the mass of air in the chamber to the projectile, and I added the mass of air behind the projectile when it is at the end of the barrel to account for all that moving air. When my friend is able to get some photos of my pneumatic cannon I will post more details of it.

For my cannon, the sealing of the projectile to the barrel was the largest factor in the few shots i was able to measure. The Launcher Range Calculator V2.1 was what I confirmed the velocity with, and it all added up.
Unfortunately i have no real numbers for you.
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Unread postAuthor: D_Hall » Sun Apr 20, 2008 5:19 pm

My spreadsheet?
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Unread postAuthor: joestue » Sun Apr 20, 2008 5:26 pm

Well maybe it wasn't yours, i found it online 2-3 years ago, i can't remember, and a while ago i deleted it, thinking the GGDT v4.4 was its replacement.

you are familiar with the launcher range calculator right?
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Unread postAuthor: D_Hall » Sun Apr 20, 2008 5:39 pm

Not horribly. I looked at it once and recoiled in horror. No offense to the author, I just happen to be a guy who once-upon-a-time wrote missile simulations for a living and when I saw the terminology and such being used... Well, I appreciated what he was trying to do but I didn't feel the need to get into a debate regarding proper methodologies and nomenclature within the world of aerodynamics.
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Unread postAuthor: judgment_arms » Sun Apr 20, 2008 5:45 pm

D_Hall wrote:...Well, I appreciated what he was trying to do but I didn't feel the need to get into a debate regarding proper methodologies and nomenclature within the world of aerodynamics.


If it’s the Launcher Range Calculator your talking about, then it's she, not he. :wink:
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Unread postAuthor: D_Hall » Sun Apr 20, 2008 6:01 pm

Ah.... The British gal, I'm guessing?

(Sorry, don't recall her name. Just recall that there was some gal in Britain who had her act together.)
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Unread postAuthor: Ragnarok » Sun Apr 20, 2008 8:18 pm

That would be the one - with whom I share parents, not to mention place and date of birth.

D_Hall wrote:I just happen to be a guy who once-upon-a-time wrote missile simulations for a living and when I saw the terminology and such being used.

Not everyone is lucky enough to be a aeronautical engineer that knows the right terms for everything. Actually, the first version of the spreadsheet was written before I even knew of GGDT.

I did a little work for the spreadsheet, although I didn't do the main body of it. IIRC, it was started a little over 2 years ago when I was 17, and really, it was a learning experience. No real idea about drag forces - just some good google skills to try and find out.

It wasn't ever really intended for public use, but because of someone asking nice about it, it got a bit of a spit & polish and was released - about 22 months back (so Joestue was doing well to find it 2 or 3 years ago :P)
Heck, the terms you're concerned about were probably just what we guessed at to try and label some of the boxes that needed a better explanation.

Still, it's known to be flawed, it has a few known errors, and as I'm the only person still around to work on it (as the other author is taking a gap year), I'm supposed to be fixing those problems and building in knowledge since acquired - but my parents are piling a mountain of tasks on me, so the time I used to have for working on it seems to have disappeared.
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Unread postAuthor: joestue » Sun Apr 20, 2008 8:34 pm

Now that I think about it, I downloaded that spreadsheet sometime before oct 2006, not 3 years ago. Ignoring the bugs, after I added the air mass to the projectile mass as explained before, the results were about the same at GGDT V4.4.

Having said that, none of it was pushed to the limit, the chamber was 1400 cu in, the barrel was 2 in dia. 6 feet long and I didn't go beyond 100 psi.
Zero dead volume, and valve was sufficiently ideal to ignore.

What i'm saying is it s accurate for middle range simulations.

BTW, the launcher range calculator i downloaded at the same time i was building the cannon, dec 07, the spreadsheet version of the spud gun simulator i don't exactly remember when.
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Unread postAuthor: judgment_arms » Sun Apr 20, 2008 8:39 pm

That reminds me, its bean a while since I last badgered you last about finishing it, Ragnarok, so…:D

Is it done yet?
:D



How ‘bout now?
:D :D :D :D :D
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Unread postAuthor: Ragnarok » Sun Apr 20, 2008 8:54 pm

judgment_arms wrote:Is it done yet?

No.

How ‘bout now?

No... oh wait, what's this?.. ah crap, still no.

@Joestue: I have the feeling that you're referring to a different Launcher Range Calculator to the one everyone else is thinking of (given that the one I helped write didn't have any facilities for internal ballistics calculation) - would you mind giving more information?
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Unread postAuthor: D_Hall » Sun Apr 20, 2008 10:34 pm

Ragnarok wrote:Not everyone is lucky enough to be a aeronautical engineer that knows the right terms for everything.

I realize. And it actually gets worse. The AE folk who design aircraft have one nomenclature/methodology convention while the folks who design missiles and projectiles (ie, artillery shells and the like) have a completely different convention. Because aircraft is what everybody "sees" in the aerospace world that's what's covered in texts 99.9% of the time. The "missile conventions" (my words) are somewhat of an arcane art shared amongst a tightly cloistered community.

My point being that I'm fully aware of how rare my insight into this particular topic is. That's a large part of why I originally never said anything; I didn't want to start a big controversy (too late, I guess).

I did a little work for the spreadsheet, although I didn't do the main body of it. IIRC, it was started a little over 2 years ago when I was 17, and really, it was a learning experience. No real idea about drag forces - just some good google skills to try and find out.

As I hinted at in the earlier post... Looking at it I could see what you were trying to do and it most certainly was a valiant attempt for one who'd not yet had formal training in the topic. It was a bastardization, but much of that is because it was obvious you were starting from scratch. For what it's worth, IIRC it looks like your methodologies were more inline with the missile community than the aircraft community.

Heck, the terms you're concerned about were probably just what we guessed at to try and label some of the boxes that needed a better explanation.

Of that, I'm certain. Please don't take this the wrong way, but this is a double edge sword.

On the one hand, your self-coined terms and conventions showed drive and ingenuity.

On the other hand, your self-coined terms meant that you likely had a hodge podge of self-taught and classical aerodynamics methodologies. IE, where in doubt you used your own (which based on your nomenclature makes me suspect your mind works like a missile designer's) but where you could google you likely used classical methods (ie, aircraft methodologies).

The bad news is that while the two methodologies are mathematically equivelent, you can't just mix and match pieces of them without screwing stuff up. It is THAT can of worms that I simply did not want to deal with.

But to summarize: While I didn't want to deal with sorting out the spreadsheet, that doesn't mean that I don't respect the thought and effort that obviously went into it. If I have offended you (and by your tone clearly I have), I sincerely appologize. Offending you (or anyone else involved with it) was never my intention. Hell, I don't care if it was total bollocks, you at least made a bone fide attempt whereas most people just scratch their ass, sniff their finger, and decide that they don't know crap from Shinola.
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Unread postAuthor: Lentamentalisk » Sat Apr 18, 2009 5:51 pm

Well I am still running 4.4 for some reason, so I have the "energy eff" guy, and for some reason, I got 104.4%. Is that even possible, or is there something going wrong?

Image

edit: yes I know the thread is a year old, but it was the most recent relevant topic, and I didn't want to start a new thread entirely for this.
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Unread postAuthor: Ragnarok » Sun Apr 19, 2009 6:22 am

Firstly, it's probably easier to upgrade to 4.6

Secondly, the energy efficiency box was removed because of the fact it repeatedly gave odd readings like this.
You're asking about a bug that's already been fixed (if by dykeing it out, but that's one way to fix any problem if the thing causing it doesn't have to be there in the first place)
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