Harpoon Gun

[Axt]

<img src="http://ww1.ft100.com/~45653/guns.ft100.com/images/harpoongunfront.jpg" alt=" - " />

The problem is with the trajectory of the harpoon. What happens is it travels approx. 15m then typically the rear kicks up and it plunges into the ground, sometimes it will fly off to the side but never straight.

The harpoon is all Al construction and seals the bore via tassels. Its tethered with fishing line on a reel.

Any ideas as to why it doesnt fly straight?

<small>[ January 11, 2003, 11:37 PM: Message edited by: Axt ]</small>

[Flake2m]

We discourage newbies from posting new topics, though I am prepared to explain. :rolleyes:

The harpoon dosen't travel striaght because of the weight distribution. The front end of the hapoon would be heavier then the back.

<small>[ January 12, 2003, 08:32 AM: Message edited by: Flake2m ]</small>

[Axt]

The front is heavier then the back.

Note that although the pic shows a brass "catch" to carry the line out it is now plastic as the brass was too heavy and would take half the velocity off as soon as it was hit.

It does the exact same thing even when there is no "catch" and untethered.

<small>[ January 12, 2003, 12:51 AM: Message edited by: Axt ]</small>

[A-BOMB]

The pic take to long to load on my cable modem. Though it does look nice.

<small>[ January 12, 2003, 01:19 AM: Message edited by: A-BOMB ]</small>

[Energy84]

Although the harpoon may be balanced or even a little nose heavy, it's like trying to fly an arrow backwards because there are no fins on the back.
I think that if you were to keep the shaft aluminum but changed to point to something heavier that it might help. But you'd still have problems I think over long distances.
The reason why real harpoons work I think is because they have a heavier line attached to the back, making it fly straight. Pretty much the same way that a tail on a kite keeps the nose pointing into the wind.

[Fl4PP4W0k]

I agree with Energy84, you need to have the line heavier as to balance the harpoon in flight.

If a heavier line isnt an option... have you thought about flexible\folding fins?
For example, have three fins made from bendy plastic at the rear of the harpoon; to load - insert the harpoon with a slight rotation so that the fins get folded around the shaft. Hard to explain... though its fairly simple.

This way, when the harpoon flies out, the bendy fins flip back into their (somewhat) original shape - aiding the harpoon in flight.

[Axt]

Thanks for the replies.. Sorry the image size is quite large for such a small pic..

Heres a scan of the rear -

<img src="http://ww1.ft100.com/~45653/guns.ft100.com/images/tassels.jpg" alt=" - " />

As you can see my plan was to stabalise it via the use of tassels, but obviously this didnt work.

Energy84, from what you have said, the large broardhead could be acting like the flights on an arrow, this probably explains it. Since I dont think I should make the point nor the line heavier the first thing i'll try is to do away with the broardhead and use a sharpend barbed stake.

Fl4PP4W0k, I cant add fins to the rear as the "catch" must slide down the shaft when fired, although it may be possible to add them onto the "catch" so they are grapped as carried away at the muzzle, the bad thing with this is is dead weight that will take away considerable velocity.

[Energy84]

By the look of that rear, it should fly straight. How coarse are those fibers though? They might be too fine and just get pushed back really easily by the air. If they are coarse though I would have to say that the airspeed just isn't great enough for them to be effective, but if the airspeed were so low then the broad point would not have much effect.
My guess then is that the fibers on the back are too fine. Can you lengthen them by any chance? I would probably start off with fibers about a foot long and see if it flys straight. With that much length it should forsure. Then just trim them back about half an inch to an inch at a time and watch closely for any indication of instability.
I once fired a ski pole out of my 6' potato cannon with a shopping bag attached to the back end. The ski pole flew beautifully and stuck about 8" into the ground 200 yards downrange. :D
Good luck.