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projectile testing - any volunteers?

A place to ask general spud cannon related questions.
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Unread postAuthor: jackssmirkingrevenge » Fri Oct 14, 2011 12:02 pm

Labtecpower wrote:COG test


Given the forward CG and flat base, I see no reason why it shouldn't fly straight.

The Delrin tail projectiles are probably upset by muzzle blast as they are only kept centred in the barrel near the tip at full bore diameter, also there is a more likely chance off pressure effects from muzzle blast acting orthogonally to the flight path.


Dewey suggested this may be a factor, still haven't checked it out yet. Still, I'm not so sure it's the case. One of the "tests" I did with the finned projectile was throw it sideways at a paper sheet on the floor - it always hit nose first. I would therefore think that even if the muzzle blast deflected it, it would still have time to stabilise before hitting the target.

That's why fins are good, very little drag while flying straight but high drag if the projectile wobbles off axis.

A drag stabilised projectile doesn't have to be draggy the whole time.


Indeed, my quest to eliminate fins and drag seems to be a bit of an evolutionary dead end.

Some math ahead of time would have been nice for this experiment, Could have saved JSR a log of machining.


Ah but I love machining ;) here's something I made in the meantime just for the sake of using the mill that was feeling a bit ronry, haven't worked up the courage to fire it yet.
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Unread postAuthor: Petitlu » Fri Oct 14, 2011 12:08 pm

@Dewey-1 :
thank you
they are threaded rods M14
2paissor of the tube aluminum: 0.91mm
CG: 18mm


I do not put adhesive or another thing to make hold steel and aluminum. Simply a small punch mark on aluminum. And it tube is cut to the “cut tubes”


EDIT : @jackssmirkingrevenge : super work! cheer!
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Unread postAuthor: saefroch » Fri Oct 14, 2011 3:33 pm

Dang that'd be amazing if it flies straight. Lots of wasted brass though :( Should have used crimped Al fins, and epoxied it all together.

Like seriously, I'm going to be trying making some projectiles with that crimping method, it's genius.
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Unread postAuthor: POLAND_SPUD » Fri Oct 14, 2011 3:59 pm

These projectiles may be stable but probably have reasonably high drag too, not necessarily any good for long range
Depends what you understand by reasonably high drag :)

If they are close to G8 shape that's already a huge step forward... ohh and don't forget this projectile can have very high sectional density

Personally I like the one that consists of just the cone and the tube - damn simple


I don't think we need another miniboy that's too valuable to lose - ammo has to be cheap
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Unread postAuthor: Petitlu » Fri Oct 14, 2011 4:12 pm

yes cheap, easy to make and rather precise!
Those which I recover have the tube twisted aluminum but the point out of steel is good, I change the tube and it is good for another shooting!
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Unread postAuthor: MrCrowley » Fri Oct 14, 2011 4:26 pm

POLAND_SPUD wrote:I don't think we need another miniboy that's too valuable to lose - ammo has to be cheap

I don't think MiniBoy is exactly valuable, just time consuming to make. Then again, it was never about how many of them we could make.

Speaking of the MiniBoy, I'll have to tune in to this thread later once I can sort out the CG, I believe dewey-1 already calculated the CP:
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Unread postAuthor: Petitlu » Fri Oct 14, 2011 4:35 pm

It takes time and machines it to make and toutle world does not have a tower at the house…
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Unread postAuthor: Petitlu » Fri Oct 14, 2011 4:49 pm

A style of arrow:


[youtube]http://www.youtube.com/watch?v=iO7Vpkl4Mmc[/youtube]

Image

EDIT :Sorry DP
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Unread postAuthor: al-xg » Fri Oct 14, 2011 4:51 pm

ammo has to be cheap

Ammo needs to be retrievable, unless, of course, the intent is bombarding the beach to increase the chance of finding at least one of them.

Granted you could use test projectiles to get an idea of the landing zone then optimise them in increments to estimate the final record setting landing point.


We could just use the G8 shape as intended with rifling (provided some means of projectile retrieval fits inside) but rifling was dismissed because it would waste too much energy.
If we're going to be fussy about that, then settling for draggy projectile seems a bit silly.

A dart would be a much better projectile for a range record if it wasn't for that fact that some device is intended to be housed inside it.
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Unread postAuthor: saefroch » Fri Oct 14, 2011 5:57 pm

What about housing a retrieval system in the nose and leaving the body hollow, as in JSR's successful design?
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Unread postAuthor: POLAND_SPUD » Fri Oct 14, 2011 7:47 pm

then settling for draggy projectile seems a bit silly
we don't know how well it performs
So who said it is draggy ?

You're saying 'hey let's build one projectile that will fly really really far'... what I am talking about is long range ammo that is cheap enough to be used on a regular basis

these are two different things
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Unread postAuthor: saefroch » Fri Oct 14, 2011 7:55 pm

Petitlu wrote:A style of arrow:
I doubt that this was actually stable in flight, seeing how much it bent upon impact with the target. It looks like it was tumbling, but then suddenly stopped upon hitting the wood, but the back end kept rotating.

EDIT: En anglais, on dit "lathe" pour la chose qu'on utilise pour usiner. "Tower" veut dire un structure très haute, on peut dire "pylône," je pense.
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Unread postAuthor: MrCrowley » Fri Oct 14, 2011 9:39 pm

POLAND_SPUD wrote:
then settling for draggy projectile seems a bit silly
we don't know how well it performs
So who said it is draggy ?

You're saying 'hey let's build one projectile that will fly really really far'... what I am talking about is long range ammo that is cheap enough to be used on a regular basis

these are two different things

Why even bother with long range ammo unless you intend to do what I'm doing? Why not build ammo for 'medium range' target shots, say shooting something from several hundred yards away? Or is that what this discussion already intended? :D
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Unread postAuthor: POLAND_SPUD » Fri Oct 14, 2011 10:45 pm

Why even bother with long range ammo unless you intend to do what I'm doing?
uhmm this is getting boring

1. ammo that JSR tested - a lenght of pipe and a nose cone
2. the miniboy

the latter will probably fly ~15-20% further than the former yet it costs ~20 times more $ and time to make

see my point?

that's a law of diminishing returns and maybe it would be better to choose a more practical ratio of performance/price
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Unread postAuthor: MrCrowley » Fri Oct 14, 2011 11:01 pm

F*ck, just typed out a lengthy reply for Google Chrome to glitch out. I can't be bothered replying and my previous post was a bit daft so I'll just say that you misunderstood me a bit, I wasn't referring to cheap/expensive projectiles :wink:
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