The Dambusters Play Set arrives in a plastic tub. After you've inflated the paddling pool, your first task is to build the dam. The pool has a rigid plastic frame supporting the opening you're trying to fill. The sand isn't provided, but the binder is, in sachets to limit the amount of "cement" you can use. The lid from the plastic tub has a convenient convex shape to it and serves as a mould for beginner dambuilders. When the sand has set, the shape-forming parts are removed and the pool should be ready to fill.
Now the kids (and grown-ups) get to take it in turns to play dambuster. The launcher has wings to give it the approximate appearance of a Lancaster but it's actually a kind of catapult that sits on a tripod which you can carefully adjust. The stores themselves ("bombs") are plastic cylinders not dissimilar to film cannisters which need to be filled with baking soda and vinegar. Internally, the canister has a divide to delay the mixing of the ingredients - loading the cannisters is notoriously fiddly.
The launcher, as you can probably guess, imparts spin to the bomb and fires it. This is achieved using elastic bands, which need to be wound the correct number of turns (to be determined by you).
Oh, there are plenty of things to go wrong - too many bounces and you may bounce right over, too few and it might not reach. The bombs themselves will almost certainly detonate prematurely. Do you impart topspin or backspin? What is the best angle of first impact? You may need to add ballast to your bombs to help them sink, even if this means compromising on payload. You will hopefully find that a small blast in the right place can do far more damage than many large near-misses.
Inevitably, the dam will eventually break - but will it be by your bomb, an opponent's, or the misuse of the catapult in frustration? Either way, the game ends with destruction and the flooding of your garden, and yet the toy can still claim to have enormous historic and scientific educational value. Bravo!-- mitxela, Jun 23 2014 Some more info: Originally I wanted the canisters to have a lid which popped from concave to convex when at a certain depth, but even the slightest amount of pre-mixing quickly overpowers the effect of external pressure. We don't want to overengineer the bombs, they should be simple and almost disposable, so perhaps the best solution is a 'canister within a canister', where the baking soda is in the inner container, with a calibrated leak. At some point the inner container will burst and suddenly mix the remaining ingredients.
Choosing a non-toxic binder might be difficult, so it may be that this part has to be supervised. But it would add a lot of replayability if different dam shapes could be experimented with.
For imparting spin, it may be easiest to have a surface along the length of the catapult which the cylinder rolls against. This is harder to adjust but we're probably dealing with too many variables anyway.-- mitxela, Jun 23 2014 Oh yes!-- po, Jun 23 2014 Bravo!
(This is going to give [8th] an erection.)-- MaxwellBuchanan, Jun 23 2014 It would probably be relatively easy to design a canister that keeps the components separate until the spin slows down below a certain level. This wouldn't be exactly the desired effect, but it would be close.-- MechE, Jun 23 2014 Shut up, [MB].
We call this semi-Baked.
Projectile: 330ml soft drink can (aluminium) filled with Chlorosulphonic acid and a piece of thin masking tape over the filling hole. As soon as water gets in, BDHUMPFF ! a huge plume of spray shoots up (we have very clear memories of the actual highly enjoyable sound, which due to the water is felt as much as heard).
Getting the correct backspin on the Upkeep mine replica is far from easy, and the launch angle needs to be very low.
Chlorosulphonic acid is not particularly nice to handle, and the resultant shockwaves do tend to attract attention. As do the stunned fish hich float to the surface in large numbers. The fish attract seagulls, and then after ther third shot the mixture of stunned fish and stunned seagulls definitely attracts attention. Also a seagull which has been stunned can be in a remarkably bad mood when it wakes up and is inclined to exhibit abnormally agressive behaviours, the vicious bastards that they are. Sharing a small open boat with a dozen or so angry seagulls was not part of the original test programme.-- 8th of 7, Jun 23 2014 (mild jealousy)
But what were you aiming at? Did you construct your own dam?
Incidentally, I believe Wallis himself built a few tiny dams to try and calculate scaling-laws for his tests.-- mitxela, Jun 25 2014 A year or two ago I saw a very good television programme about the dambusters raid which explained a fair amount of the physics and culminated in them building a large model and bombing it from a small aeroplane - excellent stuff.-- hippo, Jun 25 2014 // But what were you aiming at? Did you construct your own dam? //
Yes.
// Incidentally, I believe Wallis //
"Sir Barnes Wallis" if you don't mind. And kneel down and bang your forehead on the floor while declaiming "I am not worthy !" when you speak His name …
// himself built a few tiny dams to try and calculate scaling laws for his tests //
Indeed he did.-- 8th of 7, Jun 25 2014 (This is going to give [8th] an erection.) — MaxwellBuchanan, Jun 23 2014
Coffee snort for the day.-- blissmiss, Jun 26 2014 Probably better to drink it. Cocoa powder might not be too bad, but just don't sneeze later.
But anyway, I think you might get to do this on the macro scale, the dambustering..
Some of the old dams are silting up, from memory the Aswan dam is getting a bit long in the tooth.-- not_morrison_rm, Jun 26 2014 A sillted dam is no good. To work properly, Upkeep needs to strike the inner face of the dam and then sink to is base. Silt accumulates against the inside face in an accretionary prism, causing the mine to move away from the damn face and greatly reducing the effectiveness.-- 8th of 7, Jun 26 2014 Hmm, deep fairly large tube that goes to the base of the dam, freeze the bottom 5 metres or so, suck out the rest of the silt..making sure to leave enough water in it to prevent major disparities viz water pressure inside/outside the tube.
If they can hit that bit, it should be able to get pretty close to the base of the dam. Or, for those with poor senses of aim the big tube is funnel shaped at the top.
Alternatively, encase the bomb in neutronium, it should sink nicely to the bottom, silt or no silt.-- not_morrison_rm, Jun 26 2014 random, halfbakery