You are asked to help design a streamlined dirigible with a length of 600 m and a diameter of 100 m to cruise at 15 m/sec for excursions for retired professors. Your task is to estimate the power required for each of four engines assuming 100% efficient propellers. You are allowed to make the crude assumption for calculating the drag that the surface can be represented as one side of a flat plate formed by unwrapping a hollow cylinder with the same length a diameter. You estimate is about: a. 20 horsepower
b. 200 horsepower
c. 2000 horsepower
d. 2 horsepower

A3-mm-thick panel of aluminum alloy (k 177 w/m-k, c 875 j/kg-k and ? = 2770 kg/m) is finished on both sides with an epoxy coating that must be cured at or above t,-150°c for at least 5 min. the production line for the curing operation involves two steps: (1) heating in a large oven with air at ts,0-175°c and a convection coefficient of h, 40 w/m2. k, and (2) cooling in a large chamber with air at 25°c and a con- vection coefficient of he 10 w/m2.k. the heating portion of the process is conducted over a time interval te which exceeds the ime required to reach 150°c by 5 min (h = r + 300 s). the coating has an emissivity of ? = 0.8, and the temperatures of the oven and chamber walls are 175 and 25°c, respectively. if the panel is placed in the oven at an initial temperature of 25°c and removed from the chamber at a safe-to-touch tempera ture of 37°c, what is the total elapsed time for the two-step curing operation?