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From: liz@poppyrecords.invalid.invalid (Liz Tuddenham)
Newsgroups: sci.electronics.design
Subject: Re: OT: Repeatably lobbing "projectiles"
Date: Sun, 24 Nov 2024 11:30:34 +0000
Organization: Poppy Records
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Don Y <blockedofcourse@foo.invalid> wrote:

> On 11/23/2024 1:49 PM, Liz Tuddenham wrote:
> > Don Y <blockedofcourse@foo.invalid> wrote:
> > 
> >> On 11/23/2024 3:50 AM, Liz Tuddenham wrote:
 [...]

> > If we are allowed to specify the shape of a projectile (within limits) a
> > ball-shaped projectile may look like the obvious choice, but it is not
> > particularly aerodynamic and may have errors induced by erratic
> > turbulence  I would suggest that the projectiles could be tear-drop
> > shaped to give them the best aerodynamics, with slightly spiralled tail
> > fins that engage with rifling in the barrel to spin stabilise it in
> > flight.
> 
> Do you think that would actually be significant on such a small scale?
> "Rifling" in a gun barrel seems to be an improvement to maintain
> controlled flight over REALLY LONG distances and at high muzzle velocities.

With a long thin projectile,  random tumbling could become a problem.
If it were spin-stabilised at least it would only be moving sideways
through the air in a predicatable and repeatable manner at the end of
the trajectory.

Perhaps a spherical projectile would be better for short distances.

>... I had assumed "water" just because it "flows" once the bag has
ruptured.
> (the ruptured bags represent minimal litter and the water will
> eventually evaporate. 

Use ice for the projectile, there would be no litter at all.  If it were
pointed and had the right aerodynamic properties it would embed
point-first in the ground and not bounce - but it could be dangerous if
it hit anything other than soft ground.
 

> What if there was a "plunger" that provided the seal, with the "payload"
> sitting ON the plunger, while loaded?  E.g., like a linear catapult.

Yes, that would work.  The critical point is that the air flow and
maximum obstructed pressure are already established before the
projectile enters the accelerating region, so there is no need for
accurate valve timing.

How about a spherical bag (toy balloon?) full of water sitting in a
polystyrene cup which maintained its shape as it was accelerated up the
barrel.  The cup and balloon would separate in the air, with the cup
falling near the launch point where it could be retrieved and re-used.

> 
> Could a "gate" behind the ONE projectile not serve the purpose of the
> second?  Or, the plunger I mentioned, above?

Yes.  I was following on from the 'row of peas' already stored in the
barrel, but if you have a magazine on the side you could load one at a
time.  That could get messy if the projectiles were water-filled bags.


-- 
~ Liz Tuddenham ~
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www.poppyrecords.co.uk