SpudFiles

Hey Brainy People (complement sure to foster good relations!!)
Anyway , a good friend and I have a little on-going competition in witch
we should design a projectile that contains some kind of functioning "Hang Time Device".
This said projectile would be launched from a COMBUSTION cannon.
The barrel i.d. is 18 mm, The chamber is around 200cc ( it takes 8cc of butane to fire well, I made two of the same gun-except my chamber is 5mm longer http://www.spudfiles.com/forums/collect ... t9941.html
Look at the aluminium one in the pic.

I need to design a projectile that launches a parachute or ribbon at approx max altitude(the comp IS hangtime), I have thought of a bi-carb- vinegar fuse to 'pop' a cap that would release a parachute, it would be activated at launch through the "g" forces of combustion.

ANY ideas are very welcome Except ideas that may contain Mercury.

P.s. I could not decide if i should put this in ammo or general, if it should be moved please do so Mods

How about an electronically fired device (say a hot wire that burns through a string holding down a spring-loaded parachute) that is triggered by a losse piece of mercury in a tube that closes the circuit the minute the trajectory goes from up to down, technically at the peak.

Stop screwin' with me bro, i have not the intelligence of a mountain goat!
It would work- however mercury? i played with that as a kid a i am now mad enough!!
I need simple, say.. kitchen recipes for this one my friend
Off top- how is your Hybrid getting along?

Edit: Poo, i did say ANY ideas didn't i!!

Stay with me, have a look at the diagram - it's a bit complicated to make but not really when you think about it, does it make more sense now?

The hybrid's currently basking in the sunshine as the epoxy cures, it should be ready for testing on Saturday morning

Makes much sense, however i can't get mercury.
I like the idea, i just need a different trigger mech.
We are also limited by our 18mm rounds

Edit- how about a bb as the contact? I would have to weight the round nice but...

Novacastrian wrote:Makes much sense, however i can't get mercury

Break a thermometer though a BB will do nicely as long as it reliably touches both contacts.

You do have a point though, 18mm is a bit tight for this sort of mechanism.

Instead of making your own little capsule to hold the mercury, why not go to an electronics shop and get yourself one of these? They only cost a dollar or so.

Here's my design for a parachute (or any payload really) ammo. Spudblaster15 built it and it worked, but the rubber bands he used on it were too strong so to get it to work he had to remove them.
Larger fins would eliminate this problem.

EDIT: I think I may have found a flaw in your design jack. If the air resistance on the projectile is too great, then it may decelarate enough for the mercury to experience negative G's, making it rise to the top of the little tube it is in, and set off the parachute. If this happens making the ammo more aerodynamic might help.

You could also use a wind-up tommy timer mechanism as used in this water rocket.

Yeah, but your design and mine both will work with different powered launchers, as they are activated at apogee. A tomy timer takes a little trial and error to get it working right, and will only work for a certain launcher. Using different fuel, or adding a longer barrel means you need to wind it a different number of times.

You should google "water rocket parachute" for many ways to deploy a parachute. The "Tomy Timer" is perhaps the most common method but there are several others. The design posted by Insomniac is sometimes called an "air brake" deployed 'chute.

The problem I've never been able to come up with a good solution for is getting the round to be small enough to fit in a spudgun barrel. I thought that perhaps a sabot and a long rod, which will also act to stabilize the round in flight kind of like a bottle rocket, would be the way to go. Here is my air brake idea from a couple years ago, never tested it though.


Another possibility (stolen from water rockets) is to just put the 'chute in a nose cone that simply sits on top of the rest of the round. If you can get the round to slide backwards at apogee, air drag (or the 'chute trying to expand) will pull/push the nose off. The nose is connected to the 'chute with a string and drag on the nose deploys the chute. See for example http://hometown.aol.com/waterrocketguy/ezd.html

Another possibility, is omit the 'chute and design the rocket so that when falling it flies horizontally. The high drag makes it fall slowly. There are two designs that I know of that do this. One uses a long tube mounted on the rockets nose with a ping pong ball resting on the end of the tube. The PP is attached to the rocket with a long string. On ascent air drag keeps the PP on the nose and the rocket is aerodynamically stable. At apogee the PP falls off but is retained by the string a foot or two away from the rocket body. The PP trashes the aerodynamic stability of the rocket and it falls with the rocket body horizontal.

The second method uses a very long pointy rocket body, called a "backslider" or "Barroman Body". The long skinny shape gives very curios aerodynamics. At high velocities it flies nose first. At low velocities it flies sideways. So, to apogee it flies fast and stable in the normal "rocket" orientation. After apogee it falls with the body parallel to the ground and very slowly. See http://hometown.aol.com/waterrocketguy/backslider.html

The advantage of the Backslider and PP designs is that you get a very aerodynamic (low drag) rocket shape that maximizes the altitude the rocket will reach. The falling velocity might be greater than with a big 'chute but you might be able to offset the greater fall rate with a higher apogee.

A 'chute shell that worked well would be really cool. Keeps us posted on how it goes. (Attach a photoflash board hacked to fire repetitively and fire the round at night )

Thanx for all of your ideas, i will have a play and see what happens