FLONE's question redux

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Postby SPG » Tue Nov 28, 2006 2:45 pm

Dons fireproof suit:

FLONE had a topic locked because he/she didn't really make their point very clearly. He/she was told to do the usual thing of searching, but I tried it with the words <i>barrel, chamber, ratio, diameter</i> and the search just timed out on me. So perhaps we can look at it again?

<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote">Originally posted by FLONE
[br]Specifically the reduction from chamber to barrel. With same cubic inch chambers and same barrel dimensions would the higher ratio 4" chamber generate faster projectile speeds than a lower ratio 3" chamber?
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

Now it's not very clearly written, but what FLONE's basically asking is:

Given identical volume chambers with an ideal C:B VOLUME ratio, would there be a performance difference in relation to the C:B DIAMETER ratio (I presume FLONE's talking combustions here because of their other question).

So what we're considering here is:

Chamber shape (short and fat versus long and thin)
Constriction at the breech (large difference in diameter versus small)

Worth considering I'd guess.
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Postby FLONE » Tue Nov 28, 2006 2:55 pm

Thank you. Just the connector and it's potential affect on the speed of the combustion gasses. I just re-did my question as a new topic, please forgive.
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Postby SpudMonster » Tue Nov 28, 2006 2:57 pm

That's the cocked-up problem with the search feature. General discussions bogs it down. If you go through each section in launchers and materials individully with the archives box checked, you should be able to dig up some dirt.

EDIT: Just tried it, and it times out on me as well...
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Postby Mr.Plow » Tue Nov 28, 2006 3:44 pm

Whoops, I misinterpreted his topic. My apologies.
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Postby Freefall » Tue Nov 28, 2006 3:49 pm

Rephrasing the question just to make sure I understand it fully:
"Does the ratio of barrel to chamber diameters, or more generally, the shape/contour/diameter reduction at the chamber/breech interface, have any appreciable effect on launcher performance?"

Short answer:
Yes.

Long answer:
There will be some flow separation wherever there is a sharp edge, causing some loss in efficiency. However, since the flow velocities at the breech are typically on the low side, these losses are usually insignificant. You could probably measure the difference with a chrony, but you would likely never notice a difference otherwise. Unless you're pushing for every last FPS, don't worry about it.
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Postby sgort87 » Tue Nov 28, 2006 3:57 pm

That's what I suspected and I was attempting to lead him onto it with my last post in there.

If he is actually talking about different chamber shapes of same volume, then to answer the question, it is said that a shorter 4" chamber will do better. This is only true to a certain point though. Once you get near the point where chamber diameter and chamber length meet, it slows performance.

If that is not answering your question... I am lost. You said something about a connector in your last post. Are you asking about a flow choke between the chamber and barrel? That doesn't often happen except in most cases where tennis ball barrels are used. And even in that case, it was shown in the past that choking the flow actually increased performance in terms of muzzle velocity.
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Postby FLONE » Tue Nov 28, 2006 3:58 pm

Thanks. Found an archived response by "DR"

"I believe that the reason as to why a 0.7:1 or 0.8:1 ratio works best for a metered-propane Combustion launcher is because the burning gases are "choked" as they are forced to go through a smaller opening.
This "bottleneck" of the burning gas allows the gas a sufficient amount of time to generate the maximum amount of pressure that they can."

I'll chew on this awhile. Thanks to all.
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Postby c0mpl3x » Tue Nov 28, 2006 4:26 pm

ive always wondered this too

example: 1.5" vs 2" barrels (at the same c:b ratio) on a 4" chamber, the smaller bore barrel is moving the gasses out faster (velocity increases, pressure decreases as size goes down, for a constant pressure)

this is the principle of carburetors, the fast moving air across the venturi draws the fuel in, where later in the intake tract i
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Postby FLONE » Tue Nov 28, 2006 4:42 pm

That was my thought all along, just could not spit it out as well as you did. Thank you!

<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote">Originally posted by c0mpl3x
[br]ive always wondered this too

example: 1.5" vs 2" barrels (at the same c:b ratio) on a 4" chamber, the smaller bore barrel is moving the gasses out faster (velocity increases, pressure decreases as size goes down, for a constant pressure)

this is the principle of carburetors, the fast moving air across the venturi draws the fuel in, where later in the intake tract i
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
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Postby c0mpl3x » Tue Nov 28, 2006 5:11 pm

<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote">Originally posted by FLONE
[br]That was my thought all along, just could not spit it out as well as you did. Thank you!

<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote">Originally posted by c0mpl3x
[br]ive always wondered this too

example: 1.5" vs 2" barrels (at the same c:b ratio) on a 4" chamber, the smaller bore barrel is moving the gasses out faster (velocity increases, pressure decreases as size goes down, for a constant pressure)

this is the principle of carburetors, the fast moving air across the venturi draws the fuel in, where later in the intake tract i
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">


my quote got cut off. but yeah, gasses can only expand so fast, and with a given friction can only move an object so many fps at a certain pressure. low power fuels show this fairly well
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