Why do mortar shells have fins, but not artillery shells?
In: Engineering
There has been a lot of talk about rifling stabilization, but dancing around rhe real reason. The speed of the shell dictates if fins or spin are best for stability.
Artillery, such as howitzer, are long range weapons that shoot at a high arc. The shell is a high speed projectile so rifling can engage and the spin will stabilize the round, letting it fly straight and true.
A mortar is a medium range weapon that shoots at a high arc. The shell flies slower than a howitzer so spin stabilization would do less. Fins are a much more economical solution.
The modern mortar is a result of economics more than anything else. Mortars of old looked somewhat like cooking pots attached to a board. These short cannons were meant to lob explosives over fortifications. A light charge for a relatively short range. The modern ones have the ammunition completely self contained. The propellant and the payload are all on the shell. The “mortar tube” is effectively just a pipe with a nail at the bottom to strike the propellant primer. No longer does your mortar team need powder and fuses in addition to ammo, you just need to give them crates of ammo.
But because mortars have always been slow projectiles, spin stability has always been beyond it. Fins, while providing more drag, impart more stability without reducing effectiveness.
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