An airplane, of overall length 55 ft, is designed to fly at 680 m/s at 8000-m standard altitude. a one-thirtieth-scale model is to be tested in a pressurized helium wind tunnel at 20°c. what is the appropriate tunnel pressure in atm? even at this (high) pressure, exact dynamic similarity is not achieved. why?

appropriate tunnel pressure is 384.64 ATM

Even at this (high) pressure, exact dynamic similarity is not achieved because the specific heat ratio of helium is approximately 1.66 and is not equal to that of air which is approximately 1.40

Explanation:

It is too long to type here.

Kindly check the attached file for the calculation.