large combustion

Just build a cannon and want to show it off? Post it in here.

Postby fullmetaljacket » Sun Feb 11, 2007 4:41 am

Here it is, my first large combustion and biggest cannon to date:

<a href="http://img151.imageshack.us/my.php?image=cannonfullnb6.jpg" target="_blank"><img src="http://img151.imageshack.us/img151/962/cannonfullnb6.th.jpg" border="0" alt=>.</a>

The barrel's 41 inches long, the chamber (made of the same pipe as the barrel) is 28 inches long - I added some 100mm piping around the chamber for added safety as I wasn't sure what kind of pressures it could take. The barrel is a push fit in the bell end of the chamber.

This is the ignitor setup:

<a href="http://img263.imageshack.us/my.php?image=cannonignitoren3.jpg" target="_blank"><img src="http://img263.imageshack.us/img263/4253/cannonignitoren3.th.jpg" border="0" alt=>.</a>

Piezo ignitor from a cigarette lighter epoxied to a section of electrical conduit threaded coupling for easy access and a fuelling point. I'm currently using a butane/propane mix at about 4% which I meter with a syringe.

It works reliably, but I'm rather dismayed at the performance. Chamber fan, perhaps? How much better will it make the performance? assuming I stick it the barrel end of the chamber, which way should it be blowing?
fullmetaljacket
 
Posts: 1684
Joined: Mon Jun 14, 2004 1:33 pm
 

Postby fullmetaljacket » Sun Feb 11, 2007 4:42 am

Feck, the html's gone mammaries skyward, but I can't seem to edit the post?
fullmetaljacket
 
Posts: 1684
Joined: Mon Jun 14, 2004 1:33 pm
 

Postby Mr.Plow » Sun Feb 11, 2007 11:41 am

That really is uncharacteristically large for you, huh? :D

For that cannon, you really should use a chamber fan. It would increase performance by a significant margin.
Mr.Plow
 
Posts: 3932
Joined: Fri Aug 29, 2003 11:48 pm
Location: USA
 

Postby fullmetaljacket » Sun Feb 11, 2007 11:56 am

Cheers for the edit :D

Yeah I know, never felt the inclination to "go large" really - the logistics and materials tend to get a bit out of hand, it makes discreet transportation inconvenient <small>and i don't need to compensate for anything either ;)</small>. Indeed there were worries in the household that I was going to start my own revolutionary army or something.

So, chamber fan is definitely a thing to have then. I'll be putting it where the barrel joins to the chamber, which way should it be blowing? Towards the inside of the chamber, presumably...
fullmetaljacket
 
Posts: 1684
Joined: Mon Jun 14, 2004 1:33 pm
 

Sponsored

Sponsor
 
 

Postby An Apple Pie » Sun Feb 11, 2007 11:58 am

Whoa that is huge!(for you anyways)

Looks like a nice gun. It looks very clean.
I would highly suggest a chamber fan. I think that if it was towards the barrel side than it should be blowing back into the rest of the chamber. I am not entirely sure that that is right.
An Apple Pie
 
Posts: 423
Joined: Mon Apr 03, 2006 9:05 pm
Location: USA
 

Postby BewareOfDog » Sun Feb 11, 2007 4:30 pm

fmj,
The way your launcher's ignition system is configured, a chamber fan will do you little to no good; The area behind the fan is a "dead spot", where little fuel will be present.

The fan draws from the back, but with the chamber sealed the airflow does not circulate hardly at all.

<img src="http://img.villagephotos.com/p/2003-9/398596/cannonignitoren3edit.jpg">

Even with the chamber end open, when there is a projectile sealing the barrel, the airflow becomes almost stagnant.

Even if it did ignite, there's a large chance that you'll quickly fry your fan.

Nice job, though. -
What are you launching out of it?
What is the pipe's I.D?

<center><a href="http://img.villagephotos.com/p/2003-9/398596/cannonfullnb6edit.JPG"><img src="http://thumbs.villagephotos.com/19457982.jpg"></a>
...A little bit brighter. ;)
BewareOfDog
 
Posts: 4306
Joined: Fri Sep 19, 2003 12:37 am
Location: USA
 

Postby Mr.Plow » Sun Feb 11, 2007 5:14 pm

DR-
That assumes he's using a chamber fan whose blades are the exact diameter of the chamber. Because computer fans (the most prevalent type of chamber fan) are box shaped, there are gaps where air can flow into the backspace. Regardless, he can always avoid the issue entirely and choose to get a <a href="http://www.thermaltake.com/product/DCfan/Slot/slot_index.asp">slot fan</a> like Boogiman did on his <a href="http://www.advancedspuds.com/revolverx.htm">Revolver X</a>. Or he could just get a normal PC fan, but a size or so smaller than the chamber ID, to allow plenty of air to circulate.
Mr.Plow
 
Posts: 3932
Joined: Fri Aug 29, 2003 11:48 pm
Location: USA
 

Postby fullmetaljacket » Sun Feb 11, 2007 10:40 pm

I found this fan in one of my spares boxes, it's from an old hairdryer with a rectified 380 motor. Here it is pictured in a section of barrel/chamber pipe for scale (pipe I/D is 2.87")

<a href="http://img256.imageshack.us/my.php?image=p1010005yw3.jpg" target="_blank"><img src="http://img256.imageshack.us/img256/4687/p1010005yw3.th.jpg"</a>

Do you reckon it would work if I were to install it at the breech end of the chamber, blowing towards the ignition end?

I'm currently firing soup tins out of it (pictured next to the launcher in the er... "illuminated" pic, cheers :D) - the intended projectile for this project (which fits coonvenietly in the soup tin which is used as a sabot) is this <a href="http://localhost/forums/viewtopic.php?t=15007">2.75" steel ball</a> (as was discussed <a href="http://localhost/forums/viewtopic.php?t=15643">here</a>) - I fired it once at a sheet of ply, and was rather dismayed when it just split the thing as opposed to sailing right through it, hence the desire for more power.

I'm taking it to work today, hopefully I should have a few videos :D
fullmetaljacket
 
Posts: 1684
Joined: Mon Jun 14, 2004 1:33 pm
 

Postby BewareOfDog » Sun Feb 11, 2007 11:13 pm

<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote"><b>Originally posted by fullmetaljacket</b>
Do you reckon it would work if I were to install it at the breech end of the chamber, blowing towards the ignition end?
<hr height="1" noshade id="quote"></font id="quote"></blockquote id="quote">

Yes, but maybe only a few times, as the combustion gases will quickly destroy it.- Not to mention impede the flow.

Your best bet is to attach this pipe to a larger pipe, which will act as the chamber. (As an added bonus, using the entire 7 feet for the barrel would greatly increase the velocity! 8))
BewareOfDog
 
Posts: 4306
Joined: Fri Sep 19, 2003 12:37 am
Location: USA
 

Postby fullmetaljacket » Sun Feb 11, 2007 11:51 pm

Hmmm... dammit, you're going to make me build another one! hehe :D
fullmetaljacket
 
Posts: 1684
Joined: Mon Jun 14, 2004 1:33 pm
 
 
Next

Return to Finished Cannons

cron