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Long Range Ammo idea

Post about things you have launched or thought about launching. Also post about various materials used for building cannons. No posts about explosive projectiles!
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Unread postAuthor: Insomniac » Thu Apr 19, 2012 11:34 pm

I think you are approaching this slightly the wrong way. We all know how to create a stable dart, as it is quite aerodynamically simple. Get the CG a good distance in front of the CP, and it'll fly straight.

Seeing as this is an aerofoil based design, I think this approach is doomed to fail. I think there will be a very specific CG which will work well with any given ring design, and anything outside of this range will result in instability or turn it into a dart with little benefit from the aerofoil at all.

My suggestion is to make some scale paper models. Just get a sheet of paper, fold the front edge over itself a bunch of times, then tape it into a ring. I've made these before, and they'll only fly well at a specific CG. Too far forward or back and they'll tend to flip, or turn rapidly one way or another. Add fins like you intend to in the real model and then experiment with different CGs until you find the ideal one. Then replicate this CG position on the real model.

I'm not sure how the different aerofoil will affect the ideal CG, if at all (almost flat paper vs a proper aerofoil shape), but hopefully it'll get you in the ballpark.
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Unread postAuthor: jackssmirkingrevenge » Fri Apr 20, 2012 12:28 am

Insomniac wrote:Seeing as this is an aerofoil based design, I think this approach is doomed to fail. I think there will be a very specific CG which will work well with any given ring design, and anything outside of this range will result in instability or turn it into a dart with little benefit from the aerofoil at all.


You could go for the typical CG around 35% of the length of the airfoil from the leading edge, but that would mean a very heavy (cast lead?) nose and very light tail.

If you want something that flies though, I would be more enthusiastic to make something like the stuff suggested here.

From that thread:

Image

Image

You could also have a "scissor" type single wing on one pivot.
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Unread postAuthor: Insomniac » Fri Apr 20, 2012 2:03 am

Yeah. The problem I see with a passive glider design, is that it will likely turn, loop or roll unless *very* well designed and trimmed. At high speeds, any folding wing will have to be very well engineered to reduce stress. Trimming it for level flight at high speed will also require a bit of trial and error, and I see most failed launches causing a lot of damage. The advantage of a ring, in my view, is that there are no control surfaces to trim. All you need to do is get the CG right, and a good launch, and you should see it fly quite far.
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Unread postAuthor: jackssmirkingrevenge » Fri Apr 20, 2012 2:29 am

Catapult gliders with folding wings exist and are quite successful, I made several as a young adolescent (The only sort of projectile launching I could do at the time... ) and with some basic aerodynamic knowledge trimming isn't such a chore.

Here's a blast from the past: http://www.americanjuniorclassics.com/i ... orhome.htm

a modern attempt to replicate it here: http://www.modelairplanepages.com/aj-in ... index.html

Again though, it doesn't have to look like a glider. Glide bombs provide plenty of aerodynamic inspiration, some of them have ring airfoils too:

Image

A spudgun launched replica of the Fritz-X would be awesome :D

Image

Image

Image

Although a high aspect ratio wing would be more efficient, there's no real need for complex folding fin mechanisms.

Some more inspiration, a Luftwaffe WWII "paper project", the Heinkel Wespe and Lerche:

Image

Image

Image

Image
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Unread postAuthor: POLAND_SPUD » Fri Apr 20, 2012 7:55 am

I am affraid that such a projectile (glider) would require some sort of guidance system...

If you have a guidance system on your projectile you might as well add a motor and a propeler.... but then you have a fully functioning plane, which doesn't have to be tube launched at all... :D
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Unread postAuthor: jackssmirkingrevenge » Fri Apr 20, 2012 8:23 am

POLAND_SPUD wrote:I am afraid


Don't worry, I'll protect you ;)

Why would it need a guidance system if you're just going for distance?

Trim it as a hand launched glider and load it up :D
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Unread postAuthor: POLAND_SPUD » Fri Apr 20, 2012 8:46 am

Why would it need a guidance system if you're just going for distance?
because I think you need something to keep the nose up... oh well maybe I am wrong
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Unread postAuthor: jackssmirkingrevenge » Fri Apr 20, 2012 4:50 pm

That's the point of trimming it, in order to ensure it flies well without diving to the ground or stalling.
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Unread postAuthor: Insomniac » Sat Apr 21, 2012 10:25 pm

When you say 'catapult gliders', do you mean ones that are launched to apogee with the wings folded, then glide to earth? That's a bit of a different situation than we have here, as the slow glide speed of your gliders means that the wings and surfaces don't need to be as solidly attached when in the 'glide' mode. I think if we're talking about a glider that unfolds as soon as it leaves the barrel, there will be a few significant difficulties.
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Unread postAuthor: jackssmirkingrevenge » Sun Apr 22, 2012 2:48 am

Insomniac wrote:I think if we're talking about a glider that unfolds as soon as it leaves the barrel, there will be a few significant difficulties.


... hence my references to stubby winged glide bombs that would not have moving parts :)

A model of something like the X-15 could also be made to fit in a barrel:

Image

Image

An annular wing would however give a greater surface area for a given barrel diameter.
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Unread postAuthor: Insomniac » Sun Apr 22, 2012 3:51 am

True. A conventional layout WOULD work, but I can't help thinking that an annular wing would be much easier to get flying well. But these are all guesstimates pulled out of my arse, so I could well be wrong.
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Unread postAuthor: RJB INDUSTRIES » Sun Apr 22, 2012 2:53 pm

If you can design a system that with a remote comand It close a capacitors net circuit to create a spark like happens with the marx generator, I could finish an old project

A cloud of explosive gas gets out of the bullet when at the target and next with that remote command the spark (from the maybe MGert) gets on fire....

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Unread postAuthor: jackssmirkingrevenge » Mon Apr 23, 2012 12:20 am

RJB INDUSTRIES wrote:A cloud of explosive gas gets out of the bullet when at the target and next with that remote command the spark (from the maybe MGert) gets on fire


:?

Wrong thread? Not really discussing thermobaric warheads here ;)
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Unread postAuthor: RJB INDUSTRIES » Mon Apr 23, 2012 1:52 am

Ok :lol:

But is a functional idea, i have done it before, not with the remote comand...


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Unread postAuthor: POLAND_SPUD » Mon Apr 23, 2012 7:55 am

Wrong thread? Not really discussing thermobaric warheads here
Lol why not? that's still a cool idea

though AFAIK it will deflagrate only
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