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Sorry for the primitive drawing skills, but this may work Maudit. It could work as a marking round, that way you can see a little burst of flour or what ever you put inside it to see (glow powder would be pretty cool...)
We did discuss something similar in another thread. I think the two main problems were:
a) not enough powder would be able to fit inside the projectile
b) the projectile may be buried too deep, too fast to expel enough powder to the surface.
Glow in the dark dye was, and still is, an option but the biggest limitation is having to shoot at night. Although no one would be on the beach at night, it's still risky in terms of visibility (goes against the cardinal rule of being able to see down range when shooting) and recovery as we may be using a quad (ATV) which can be incredibly dangerous.
I think one of the best chances of retrieving the projectile is calculating its Cd value. If that can be nailed to two decimal places (i.e., 0.08) then we could get a really good idea of the range. I will be shooting this at an angle of no more than 15 degrees for two reasons: I don't want to risk over-shooting the range and the projectile should fly straighter.
headlights on the ATV???? or an LED maglite duct taped to it.
That's one decimal place, and two sig figs.
Could you drill holes in the side of the body and install little flashing recessed LED's with small batteries in the body? You could just have them flash or stay on. But then again your limiting it to night or near night conditions. That could be really bright at least.
Ah dammit, my teachers always told me to proof read
No headlights, I guess a person could always hold a torch but the trouble is getting the ATV down to the beach from the house and back. It's only a few kilometers but some of that is on a state highway. Doing 40km with no headlights on a highway out in the country is pretty dodgy in NZ due to our narrow roads and 'hilly' terrain. It'd be fine during the day when cars can easily see us but I don't think I could convince my friend to drive at night
The trouble with LEDs, like the smoke idea, is that they would only give me a general direction the projectile is travelling. I think with good wind conditions, the projectile wont deviate much at a low angle, the hardest part will be finding where it lands.
That's why I think finding the drag of the projectile is important. If the possible impact zone is, say, 3500m ± 100m, theoretically we'd only have to search a 200m x 50m stretch of beach (which is a feat in itself).
Last edited by MrCrowley on Thu Jun 23, 2011 4:56 am, edited 1 time in total.
Double post, NO WAY!
Was lucky enough to catch this beauty flying through my living room
Facebook pretty much destroyed the quality of these pictures but oh well:
I can picture MrCrowley running around in his living room, the MiniBoy held up in the air and making rocket noises...
Was home alone today, how did you know what I was doing?
Word on the straße; we might be going up to my friends bach in the coming weeks. I finish exams on Saturday (two exams on a Saturday!) so hopefully I can figure out some tests for the dummy round before I go up North.
Was thinking I might remove the sabot locking ring for the test fire so if too much force is exerted on the sabot supports they fall off. Don't want to break the sabot before the big shoot.
I also think the cup mode with the ring is useless.
The spindle sabot mode with the petals temporary locked by the rubber washer seem to be working nice enough... theoretically
BTW, is the sabot diameter fitting the barrel all right? I intentionally kept it very close to the sizes you gave, so it can possibly be sanded a bit. In particular the petal edges, that could be sanded/rounded if necessary.
Well I suppose you could just find a way to insert a bit of "blur" right? Then it makes a nice big puff of smoke, and it looks cool.
I think I might use the ring for the cup mode on the proper shoot as a precaution. I highly doubt the petals would come loose when accelerating down the barrel at SOS, but in the off-chance they do, the ring would keep them together and uniform.
The aluminium plate fits the barrel almost perfectly, the petals need to be sanded a fraction, depending on how tight I want them to fit.
Cool! That's what I intended
Start by rounding a bit the edges, this will give you just a bit of play while keeping the petals perfectly spaced. Then more if necessary.
You should have a very low friction sabot with the UHMW... I would not be surprised the sabot goes far away! Even more if the ring is used Without the ring, I think you'll limit significantly the distance. But now it's for you to try
Finally got off my ass and sanded down the sabot to fit the barrel. It actually did fit without sanding but was a bit tight.
At the same time I inspected my piston, what a mess!
Sealing face is a bit munted.
Washers are a bit bent and one is loose.
Despite these issues, the cannon probably will still work once I put it back together. I originally took a look at the piston to add more teflon tape for the o-rings.
Ever since the cannon has been working, the piston has been opening before it should be. I've done the math and with 300PSI in the pilot, (from memory) it should take close to 1000PSI on the face of the piston to counter this and force it open but in practice, the valve would open at about 350PSI. Even if there was a leak between pilot and chamber, the pressure should equalize and the valve remain closed. There is something else at play that I can't get my head around. I've done the math numerous times, had SB15 check it, made sure to include the 'spool' valve area on the back of the piston, I can't think of why the valve would open far before it should considering the substantial area differential.
If anyone wants to double check the math:
Piston face diameter: 50mm
Piston washer diameter (that hold the o-rings in place): 50mm
Barrel porting: 47mm O.D.
Spool diameter (this is the rubber disks which seal the pilot vent): 22mm
I just had a thought that if the sealing face was smaller in diameter than the metal washers it could be the cause of the problem but even taking that in to account the valve should remain shut with 300PSI in the pilot and 450PSI in the chamber. Sh*t now I did some more math and am getting 1800PSI in the chamber required to force open the valve with 300PSI in the pilot
I even took in to account the sealing face being smaller than the metal washers which should benefit the opening of the valve (assuming the area on the sealing face that is acted on by pressure remains the same)
Maybe I've done something wrong
My other query is about the bent washer seen in the second picture. I'm curious as to how it got bent as if it was from the piston rebounding, the sealing face should be bent (which it isn't) and if it is from hitting the back of the piston housing, the other washer should also be bent (which it isn't). Maybe I never saw it before and it occurred when I had a previous sealing face on the valve, I'm sure I would've noticed the loose washer though since it can move freely.
Perhaps something to do with the momentum of the combustion gasses as the flame front propagates? Similar to a sort of water hammer effect? I must admit that I never really read much into the mechanics of piston valved hybrids, so I'm not sure if this would cause the piston to move much, or if it would just re-seat were it to be slightly opened for an instant. Food for thought anyway, as the theoretical pressure of a static gas may not be all that's at play.
I wonder how much deeper the ocean would be without sponges.
Right now I'm having amnesia and deja vu at the same time. I think I've forgotten this before.
Add me on msn!!! firstname.lastname@example.org
The problem occurs when the cannon is used as a pneumatic and occurs at all pressure ranges (e.g., if I put 100PSI in the pilot, the valve opens at like 140PSI, if I put 40PSI in the pilot, the valve would open at like 60PSI etc).
I'll have to do more testing this week to narrow the problem down.
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