is there a reason why people dont convert the cooling fans in computers into ducted fans for airplanes. it seems simple enough (though i have not tried it) all i think would be needed to do is change the motor. if anyone has tried this or has any info it is aprriciated

I dont know for sure but it seems to me that all fans are specifically designed to be run at some set speed range.. so if the pc fan would even hold together at 10 times its normal speed, would it be efficient at that speed? Probably not is my guess. However, some of the server fans at work seem really heavy duty... but then they are heavy too.... just my 2 schillings...

No but, they make great Cooling tube fans for battery charging. The highest rotational speed that I have seen is 15000 rpm. and the
motor is quite heavy. I saw a case fan with the motor mounted on the outer ring pulsing the blades might be a good electric turbine Idea if it could handle the amps. it was rated at almost 100 cfm.

Most Case fans are not balanced very well either.

Although after 15 years in the computer industry I have never experienced one shattering unless the bushings lock up and the motor
cooks the plastic, breaks pretty easy then.