Re: Temperature and Mach number
Shouldn´t the IAS and Mach number also depend on the composition of air, for equal temperature and static pressure?
Yes, the ratio of nitrogen to oxygen in air is roughly constant. As are the quantities of minor ingredients like argon and carbon dioxide.
But what about water?
The molecular mass of water is 18, while that of nitrogen is 28 and for oxygen, 32. This means that for equal total static pressure and temperature, moist air should hold less oxygen and nitrogen, and have lower density, than dry air. Less density means less lift and IAS for equal TAS.
The effects on sound speed should be yet more complicated...
For one thing, water vapour has lower molecular mass, which should mean faster speed of sound.
For another, there are the issues with water having an additional rotational degree of freedom, and more allowed vibrations, which IIRC ought to mean slower speed of sound...
And then I cannot quite figure out what happens to sound in wet adiabatic conditions...
Anyway, the speed of sound in water varies in a weird manner - goes through maximum at a certain temperature... But since it is so huge, I do not think planes should worry about Mach numbers in water - coming near water at such speeds, they have worries in air already, and no chance on water contact.
Froude numbers is quite another matter!