lets inconspicuously dream of decent amounts of energy.
imagine taking an old piston engine from a car. the engine itself would be permanently turned @ 6000 rpm by an electric motor. the exhaust valves should be modified. they would close from outside, very quick flappng to outside under explosion pressure. (i mean... we dont want to accelerate the crancshaft, pressure MUST be out BEFORE the cylinder starts moving downwards again) the exhaust gas should be used to decently accelerate our potato.
repeatedly. Imagine, @ 6K rpm... with a 4tact engine we would have 12000 shots per minute on a 4 cylinder! (one per cylinder every 2 revolutions, using 4 of them)
@joule... thats difficult, forgive me, I make some assumptions and mistakes... Lets assume that engine has 300 NM torque. Lets assume that the crankshaft exceeds its center by 5cm. > The push down power of one cylinder would be 6 K newton?! Lets assume a cylinder of 500ml, having a diameter of 80mm. Think thats kinda typical for cars. So its A=Pi * radius quadrat = Pi * 4 quadrat = 3,14 * 16 = 50cm2 6000newton on 50cm2 = 120newton/cm2 == 12bar pressure inside cylinder / We have a volume of 6 liters gas to expand. [here it becomes difficult. a gas explosion would deliver 68 bar maximum. that 12+bar should result from a turbo charged engine, we would need a 5kw+ air pump in our setup... )
now comes traveler potato. lets say the ideal rocket type potato has a diameter of 5 cm and a length of 8. that 12 bar would create a certain pressure in newton to our friendly potato. A=Pi r2 = Pi 2,5cm2 = 7,85 == 8 cm2 8cm2 * 12 bar = 960 newton. now the pressure sinks while that potato moves in our ideal tube that way, that the gas has 1bar at the end of teh barrel. the pressure sinks all the time, but we can say that it should be half the maximum pressure from the start. so, over the time of acceleration, the potato would "feel" an average 480 newton. now the length of the barrel becomes important. we want to fill 6 liters of combustion gas in a tube/cylinder with A=8cm2 thats 6000/8 = 750cm. (impressive^^) so, we have 480 newton * 7,5m = 3600 newton * meter thats a very interesting 3600 Joule.
if you would shoot now for 1 minute...
1 potato weighs [8cm2 * 8cm] 64 grams. @12k potatoes per minute firing rate (ppmfr). > our minigun would spit 768 Kg potatoes per minute, delivering 43200000 Joule! > it would be 10 times stronger then the german MG3. > its potato output power [200potatoes/s*3600J] would be 720KW. [it would have more power as it had before in that shitty car, but we would have to invest some 50KW...]
that would be style. you could use that gun to dispense large amounts of food or fertilizer in farming. the further crap flies, the less you would have to drive over your fields (which comresses the ground, takes time, harms plants etc) ofc ethanol or at least propane driven in order not to poison the food/fields for a seeding machine its output temperature should be problematic.
for military use it would be to weak in terms of pressure. the pressure in a rifles barrel is 50100 times higher, at least i thinkso.
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