effect of humidity on propellant

It makes it wet and gooey.

I will allow others to expand on that (or while thinking about that).

Depends on the motor type.

A typical BP motor with a wound paper casing will swell upon repeated exposure to high humidity levels. I recommend storing BP motors in a humidy-controlled environment.

Certain propellents (e.g., sugar rockets) are hygroscopic. They will absorb water vapor from the atmosphere. High humidity levels will exacerbate this condition.

Keep all of your motors in a cool, dry place. Keep your beer in a cool, dark place.

Bill Sullivan

"The American pe> plz tell me effect of humidity on mechanical properties of solid rocket > motor

Gawd, I love technical terms...

Yeah, the humidity causes them to expand. Also, if the humidity is excessive, or prolonged, the nozzle clay will become...

um, well, "poopy"...[1]

tah

[1] Actually the nozzle clay will begin to soften and disintegrate. Friend of mine had this happen with a bunch of motors he stored in his basement.