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Tater or Fuel. What comes first?

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Tater or Fuel. What comes first?

Unread postAuthor: Tatersalad2000 » Tue Aug 11, 2009 8:04 pm

Flame away. Sorry for not already knowing this.

If there is a newbie post area...let me know.

I've spend some hours reading the archives. I'm not looking to harvest uranium so the fuel rods can create steam to drive a turbine....or a potato.

My question is: Is it best practice to load the tater first...then spray in the fuel? Or spray in the fuel...then the potato?

I read a few posts that made it sound like "compressing" the gas with the tater was the right thing to do.

I don't see that being viable...so I'm asking.

Thanks.
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Unread postAuthor: jmadden91 » Tue Aug 11, 2009 8:09 pm

They mean putting the potato in first, but only plunging it half way, then spraying the fuel, then pushing the potato the rest of the way, thus compressing the fuel. Some claim this increases performance but unless you build a hybrid compressing your fuel in this way will probably not lead to any noticeable difference. So generally its potato first, then fuel.
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Unread postAuthor: Tatersalad2000 » Tue Aug 11, 2009 8:17 pm

That was fast...thanks. Okay I'll try both methods and see if it makes any dif this weekend. I'm building my cannon this week for use this weekend.

Although there are variables involved I'm bringing a 100ft tape measure to see if I can document anything measurable.
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Unread postAuthor: jonnyboy » Tue Aug 11, 2009 8:29 pm

Although there are variables involved I'm bringing a 100ft tape measure to see if I can document anything measurable.


That's not nearly long enough look up your shooting range on a satellite imager , I find that local.live gives better crisper images than google maps. Then find your shooting spot and see if you can find any landmarks such as trees in a field etc. that you can use to gauge distance from a satellite image.

I think the general conclusion is that there is no noticeable increase in power I think I remember a topic on spudtech about this but that was before my time.
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Unread postAuthor: Tatersalad2000 » Tue Aug 11, 2009 8:46 pm

I just looked in the garage its actually a 330ft tape measure.

I'm in AZ and plan camp near some meadows near flagstaff.

I'll bring my quad and zip out to the impact points.

I'll collect what data I can relevant or not.
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Unread postAuthor: MrCrowley » Tue Aug 11, 2009 10:48 pm

I believe it is safer to load first, then spray.
Because if you spray, then load and you accidentally hit the ignition while you're loading, you could have your face or hands in the way of the barrel when the potato comes flying out. :)
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Unread postAuthor: Technician1002 » Wed Aug 12, 2009 12:03 am

MrCrowley wrote:I believe it is safer to load first, then spray.
Because if you spray, then load and you accidentally hit the ignition while you're loading, you could have your face or hands in the way of the barrel when the potato comes flying out. :)


I second that. Safety first. This applies to air cannons too.

Many pneumatic launchers have valves that are affected by outlet pressure. This includes many sprinkler valves and all barrel sealer piston valves.

I have opened my piston valve cannons by loading them. Always load any ammo that needs rammin first. The only one I load in the other order is the marshmallow shooter with the oversize barrel. Dropping in a marshmallow is unlikely to set it off.

I load, close the piston and then add air.
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Unread postAuthor: jimmy101 » Wed Aug 12, 2009 1:22 pm

If you are fueling via "spray-n-pray" then how you fuel won't make much difference. The shot-to-shot variability will be soooo big that any difference from spud-then-fuel versus fuel-then-spud will be impossible to measure. Your shots are going to vary in range by probably something like a factor of 2. :(

Go get a $2 60cc syringe from a farm animal supply store. Get a blunt needle for a buck. Use that to measure your fuel. Your gun will give the best performance it can and the shot to shot variability will be much less.

As to measuring the range ... you'll need to precisely set the launch angle. There is big difference in range for say a 20 degree launch versus a 45 degree launch. (For spud type ammos the optimal launch angle for maximum range is usually in the 35 to 40 degree range.)

I would pace out your range and put some kind of markers every 50 feet or so. You want the distance where the round hit the ground, not the distance where it came to a stop. The markers will help you determine the contact distance. "It hit 1/3 the way between marker 4 and 5, the markers are 50' apart so that is ~215 feet". A spotter a few tens of feet off to the side of the shooter will have a much better view of the contact point then the shooter does.

It is possible to get a "hybrid affect" by starting the spud in the barrel, adding fuel then ramming the spud home, which compresses the fuel and air. With a double beveled muzzle, and shooting spuds, you can probably get up near a 1.5X hyrbid ratio would would be a pretty significant increase in performance. The double beveled muzzle knife significantly increases the static friction. With my double beveled 2" barrel shooting 1/2 spuds the static friction is in the vicinty of 30 lbs (~10 PSI). So I should be able to get to a 1.66X hybrid.

But, as others have said, there are safety issues with ramming a fueled gun. (Of course, muzzle loaders do it all the time.)

Have fun and post your results.
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Unread postAuthor: psycix » Sun Aug 16, 2009 10:55 am

Safety first, always load, THEN fuel.
If it goes off while loading you might get hurt, especially when muzzleloading.
On top of that, the fuel will stay inside if there is a projectile in place.
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