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GGDT/HGDT Request Thread

A place to ask general spud cannon related questions.
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Unread postAuthor: wyz2285 » Sat Apr 28, 2012 5:39 am

Hi, didn´t read all the posts, so if my is wrong please remove it.
I´m designing my pcp(4.5mm), and I have almost everything decided, but I don´t know that to put in the valve flow coefficient :? I read about it and I understand what it means, but how can I figure out that´s my valves flow coefficient?
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CpTn_lAw wrote::D "yay, me wanna make big multishot pnoob with 1000 psi foot pump compressor using diamond as main material. Do you think wet bread make good sealant? " :D
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Unread postAuthor: Goats spudz » Sat Apr 28, 2012 3:22 pm

wyz2285 wrote:.144 pcp(4.5mm),
Just so you know its .177
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Where's my Chuck key?

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Unread postAuthor: Lockednloaded » Sun Jun 10, 2012 4:58 pm

Can someone post an HGDT screenshot for this launcher for me?

Advanced combustion with chamber fan and single spark gap
2-1/2" x 30" chamber and 2-1/2" x 30" barrel fireing a 2-1/2" tennis ball weighing 57g with a CD of .6 fired at a 45 degree angle

Thanks in advance to anyone who can put this into HGDT for me.
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Unread postAuthor: MrCrowley » Wed Jun 13, 2012 7:10 pm

Using propane, I got a touch over 300fps muzzle velocity and a touch over 300' for distance. The distance isn't all that surprising, you'd struggle to shoot it further without adding water or sand to the ball.

Sorry but I can't post a screenshot at the moment, if you need one I can do it later.

You might get slightly better performance than what is stated. My 2" sprinkler valve cannon with 3' barrel and 3' 2" chamber could do an average velocity of 250fps over a distance of 60' at 120PSI.
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Unread postAuthor: Lockednloaded » Wed Jun 13, 2012 9:19 pm

Thanks MrC, I got SB15 to run some numbers for me and he told me that with a 25" chamber and a 35" barrel I could bump it up to 350fps. I doubt I've got enough energy here to push weighted balls a considerable distance, but I could always use some sub-caliber, denser projectiles for distance
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Unread postAuthor: Lockednloaded » Sun Jul 29, 2012 9:41 pm

Sorry for the double post :oops:
But anyway, I'm doing some commission cannon for some friends and I want to be able to give them some numbers that they should expect.

So the specs are:
2" x 30" chamber
1.5" x 48" barrel
1" modified barrel sealing sprinkler valve
100 psi and 160 psi
Potato slug (I know, very unspecific but that's what they plan on shooting)

What I'm looking for is the approximate velocity, and approximate range at a 45 degree angle.

Thanks in advance for the help, I could really use the extra cash from these little projects
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Unread postAuthor: jonesy42 » Sun Jul 29, 2012 10:25 pm

Hi,.... Not sure if this is enough info, but these are my componants/parts.
I would like to know a suitable firing chamber size for this configuration?, and
approx, what fps it would create?, (with the firing chamber installed).

Qev valve - operating pressure- 0.3bar - 15bar

Barrel/bore - 650mm x 6.03 bore diameter

regulator - 300psi max

3 way 150 psi rated pilot/trigger valve

3000psi air tank

Thanks.
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Unread postAuthor: Zeus » Sun Jul 29, 2012 11:13 pm

Ok, what we need to know is the chamber size, porting and nominal size of the QEV, and the nominal size of the pilot. Also if you can guesstimate the pilot volume, that'll help.

I ran a quick estimate, based on a 1/2" QEV and 4" of 1/2 steel for the chamber, and you've getting around 300m/s with a 0.20g air<s>crap</s>soft BB, which might be a bit optimistic. I know you can't get them easily, so the ammo used would be nice too.
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/sarcasm, /hyperbole
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Unread postAuthor: Lockednloaded » Tue Nov 27, 2012 10:42 pm

Hi, looking to make a large bore hybrid, but I want to see some performance specs first.o

14" long x 2" diameter chamber
60" long x 1.68" diameter golfball barrel
2" cam-lock burst disk holder
Single ignition point
Propane+Air Mix (5x and 2x with 150 psi and 450 psi bursting pressure respectively)
46g golfball with a Cd of .3
45 degree launch angle

If I don't have any HGDT numbers I'll probably just build a nice old pneumatic gun.
^ that might get somebody with HGDT to help me out :lol:
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Unread postAuthor: saefroch » Wed Nov 28, 2012 12:20 am

45 degree launch angle is not the optimal launch angle for a high-velocity golf ball.

Image

Image

Image

Image

Your golf ball won't have such a good fit, but it doesn't make an observable difference in the simulation.

Don't know why I'm doing this, I have homework due at 10:30 a.m. that I haven't started.
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Unread postAuthor: Lockednloaded » Wed Nov 28, 2012 12:32 am

Thanks saefroch, I'll probably use some wadding with the golf ball to keep a tight seal. I'm not particulary concerned with range, but for curiosity's sake, what is the optimal angle?

EDIT: nevermind, stop procrastinating :lol:
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Unread postAuthor: MrCrowley » Wed Nov 28, 2012 12:38 am

Range will probably be more than that, think I had to use a Cd of 0.25 to match the real-life results from a pneumatic to GGDT predictions. I don't see a golf ball going further than 600m at the velocities we're used to on Spudfiles so you might get close to that as 400m is a realistic range from a piston valved pneumatic or advanced combustion.
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Unread postAuthor: Lockednloaded » Wed Nov 28, 2012 12:48 am

So you think I could achieve significantly more than 300m even with just a 2x mix? I plan to shoot it at 2x far more often than at any higher mix, but I do want the options
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Unread postAuthor: saefroch » Wed Nov 28, 2012 12:53 am

HGDT is crashing on me, need to re-read part of the chapter to finish this homework. I'll try to have you something before I hit the hay.
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Unread postAuthor: MrCrowley » Wed Nov 28, 2012 1:01 am

Lockednloaded wrote:So you think I could achieve significantly more than 300m even with just a 2x mix? I plan to shoot it at 2x far more often than at any higher mix, but I do want the options
I measured 420m or so from a 1.5" porting piston valve pneumatic at 120PSI. Depends on the wind and things as well but you should definitely get more than 300m at 2x with that cannon. I have a 100cm golf ball barrel for my 3/4" burst disk hybrid that has a chamber volume of under 500ml and even that would out-perform the aforementioned pneumatic cannon at 3x or so (though I usually use it at 10x, bit more fun) :D
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