Quote:
Originally Posted by Peter Hudson
I have always wondered what the effect is when arrows are greased before firing? Something tells me that the speed is either maintained better or increases the hitting power when goosegrease is put on the arrows...somehow preventing friction thus increasing delivery speed to the target...suggesting it was better for armour penetration... but I have no direct evidence to quote ...it being something someone said once? Can anyone throw some light upon this ?
Regards,
Peter Hudson.
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Making a suface greasy or non-stick doesn't necessarily reduce it's friction drag (viscous drag). If it did we would coat airplanes with teflon and save a lot of money in kerosene. So any improvement that you would see will not be due to drag reduction.
Aerodynamic drag in the low subsonic speed range that arrows travel in, is due to 2 reasons: viscosity of the air and longitudinal pressure distribution over the arrow.
The viscous part is due to the air sticking to the exposed surface of the arrow. So to reduce viscous drag you need to reduce this wetted area in ratio to the arrow's mass. Or change the material to a higher density. Like kinetic armour piercing rounds APFSDS for tanks use depleted uranium or tungsten due to their high density. Of course you will need to use a stronger bow to maintain initial velocity. Coating with a lubricant will not work.
The pressure drag is due to high pressure in the front, and a low pressure wake developing in the rear. For an example of a optimized shape, look at a symmetric airfoil. Blunt in the front (required for wings but not for arrows) and long gently tapering back (always a necessity).
So, for a medieval archer to improve, I strongly recommend a research and development programme in the field of computational fluid dynamics and material science, towards the development of depleted uranium arrows of an optimized cross-section distribution. Oh, and to train more, so he can chuck the damn things with gusto. I don't know... maybe hit the gym.