quick fan question

Boom! The classic potato gun harnesses the combustion of flammable vapor. Show us your combustion spud gun and discuss fuels, ratios, safety, ignition systems, tools, and more.
User avatar
covey12
Specialist 2
Specialist 2
Posts: 260
Joined: Sat Aug 23, 2008 4:36 pm

Fri Jul 23, 2010 2:21 pm

i have a lot of experience with mini combustions and large pneumatics, but have decided to make a large combustion, and regarding the chamber fan i see most people mount theirs in the chamber. does the ignition of the propellants not harm the fans? it seems like it would melt it to be but i'm probably wrong, just making sure :?:
“The object of war is not to die for your country but to make the other bastard die for his.”
User avatar
jrrdw
Moderator
Moderator
United States of America
Posts: 6569
Joined: Wed Nov 16, 2005 5:11 pm
Location: Maryland
Has thanked: 39 times
Been thanked: 22 times
Contact:

Donating Members

Fri Jul 23, 2010 2:36 pm

They must take a good bit of punishment because there is very little discussion about replacing burnt up chamber fans.
SpudBlaster15
First Sergeant 3
First Sergeant 3
Seychelles
Posts: 2400
Joined: Wed Oct 18, 2006 11:12 pm
Has thanked: 2 times
Been thanked: 10 times

Fri Jul 23, 2010 3:00 pm

Lorem ipsum dolor sit amet, consectetur adipiscing elit. Cras nec placerat erat. Vivamus dapibus egestas nunc, at eleifend neque. Suspendisse potenti. Sed dictum lacus eu nisl pretium vehicula. Ut faucibus hendrerit nisi. Integer ultricies orci eu ultrices malesuada. Fusce id mauris risus. Suspendisse finibus ligula et nisl rutrum efficitur. Vestibulum posuere erat pellentesque ornare venenatis. Integer commodo fermentum tortor in pharetra. Proin scelerisque consectetur posuere. Vestibulum molestie augue ac nibh feugiat scelerisque. Sed aliquet a nunc in mattis.
Last edited by SpudBlaster15 on Thu Jul 15, 2021 1:05 am, edited 1 time in total.
jimmy101
Sergeant Major
Sergeant Major
United States of America
Posts: 3197
Joined: Wed Mar 28, 2007 9:48 am
Location: Greenwood, Indiana
Has thanked: 5 times
Been thanked: 15 times
Contact:

Fri Jul 23, 2010 5:08 pm

The most common problem with a chamber fan isn't the temperature (SP15 hit the answer dead on), it's the loading on the fan blades, at the instant the ammo leaves the barrel (rapid decompression gets the air in the chamber moving much much faster than it ever does when the ammo is still in the barrel) and then again a few milliseconds later when cool dense air rushes back into the chamber and slams into the fan.

Put the fan pretty close to the breach so that you aren't moving massive amounts of combustion gases through the fan during firing, that'll trash the fan pretty quick. It is rarely a problem though since putting the fan anyplace other than near the breach is a real PITA so the practical place is also the best place for the fan.

I had a gun for a couple years that had a fan blade blown off. It still worked just fine, indeed the missing blade provided "tactile feedback" that the fan was indeed operating when the gun was closed up and ready to fire ... the whole gun vibrated slightly due to the out of balance fan.
Image
User avatar
jrrdw
Moderator
Moderator
United States of America
Posts: 6569
Joined: Wed Nov 16, 2005 5:11 pm
Location: Maryland
Has thanked: 39 times
Been thanked: 22 times
Contact:

Donating Members

Fri Jul 23, 2010 6:30 pm

motorfixer1
Private 4
Private 4
Posts: 91
Joined: Wed Jul 07, 2010 5:28 pm

Fri Jul 30, 2010 9:11 pm

Good answers guys very informative! Thanks
Post Reply