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Wanting to build more aerodynamic projectile for disc launcher

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LAN_403

w1vlf

Sun May 11 2008, 03:13AM

Registered Member #1329 Joined: Mon Feb 18 2008, 07:31PM
Location: Harwinton Connecticut
Posts: 53

Hello,
I hae been launching a 2-1/4" dia. 1/4" thick AL disc for a while now and the best I can get is a 6 sec round trip time.

The disc althought it travels straight up off the launch pad, is spinning like a flipped coin.

As the velocity drops, the higher it goes, the projectile suddenly curves off to the left due to the spin. This happens quite reliably. I thing there is a deformity in the coil.

But heres the deal. I thought I would glue 1/2 of a tennis ball or other suitable domed object to the top of the AL slug, and then have a fiberglass tube attached to the bottom of the slug. The fiberglass tube would hang straight down and go through the hole in the coil.

The AL slug would lay directly on top of the coil. The fiberglass tube could be part of an arrow. Hopefully this would help the projectile travel up in a straight line. I am guessing the projectile would come straight down and land on the tennis ball.

Mabey an evolution would be a cone type nose instead of a dome later.

My goal is to eventually launch the "dart " for distance and accuracy.

Any comments or suggestions???

Thank you
PC
W1VLF

...

Sun May 11 2008, 03:30AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

If you want 'stable' flight, you would be better off adding some fins. Keeping in mind that an object in flight always rotates arround the center of gravity, you need something that will be a 'restoring force' to push the object back to strait flight. See

for more info.

Quantum Singularity

Sun May 11 2008, 11:43AM

Registered Member #158 Joined: Sun Feb 12 2006, 09:53PM
Location: Central Ohio
Posts: 282

I too had disks spinning violently with some of my past induction launchers, and yeah they spun worse as the coils became more deformed. In fact, thatâ€™s how I managed to sink that 5" hard drive disk in my avatar into some barn boards... at about a distance of 10' the disk had already rotated 90* so it was on edge and managed to seriously punch in.

You could try to do similar to FastMHz and make rockets similar to model rockets but with the aluminum slug attached to the base. I tried to attach some various domed plastic containers and similar before, but pretty much every attempt I tried resulted in failure at energies much over 500-1000J. I was thinking about turning down a piece of wood into a nose cone, or perhaps getting a small metal lathe and turning some aluminum stock. Thatâ€™s probably what I'll do once I get moved into my new house (though it might be some time before I can spend money again lol). You can get various diameter aluminum rod cuttings of ebay for cheap, I've got several sizes, just need the lathe.

w1vlf

Sun May 11 2008, 01:35PM

Registered Member #1329 Joined: Mon Feb 18 2008, 07:31PM
Location: Harwinton Connecticut
Posts: 53

Tristan,
First I have to say ..that is a great picture of the disc embeddded into the barn boards!!! Makes one think about force that is a our finger tips when playing with these things.

1) Did the plastic nose cone work before it destroyed it self? I mean did it help stablilize the disc and there by increase height?

Thanks for the tip on the Ebay AL stock, I have indeed purchased some, several sizes, from this my friend machined the projectiles and the winding fixtures.

PauLC

Quantum Singularity

Sun May 11 2008, 03:10PM

Registered Member #158 Joined: Sun Feb 12 2006, 09:53PM
Location: Central Ohio
Posts: 282

You might be able to come up with some sort of plastic nose cone that might work. The things I tried were just to flimsy or I didnt attach them good enough. For example I remember trying a tomato container, which is round and a hemisphere shape but it split apart upon launch. With a bit stiffer plastic that is better secured to the aluminum, it might work better. Just remember that for aerodynamics, you want a projectile thats longer than it is wide, this isnt so common around the house I've found. And with the sharp acceleration the method of attachment needs to be good.

Oh and thanks for the compliment... that disk ending up in the board (actually roof board in the garage) was an accident that could have ended much worse. Thankfully it stuck in and didnt ricochet around the building which you'd think would be a much more probably result... that launch was using one of my big maxwells and the switch didnt trigger properly to fire it, and I didnt have any kind of backup at the time so we manually bridged the switch with the chicken stick... could potentially have been near or even over full charge ~6kJ. Wont ever use the maxwells again without a quality trigger and safety and monitoring, etc, etc. (all of which I am working on though... I do plan on using the maxwells again sometime in the future, its sad that they have been sitting unused for probably 10 years now).

w1vlf

Sun May 11 2008, 05:11PM

Registered Member #1329 Joined: Mon Feb 18 2008, 07:31PM
Location: Harwinton Connecticut
Posts: 53

Hey Peter, Thanks for that link. I understand about restoring force and CG now. Also went to your page and saw that your rockets get subjected to in excess of 50G's

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