I enjoy reading your magazine and often use information I find in the courses I teach. However, the article "Back to the Future" (Flight International, 18-31 December 2001) contained misleading information.
The box "Fast jet basics" describes the overpressures from sonic booms in the units of "kg/m2" along with the British "lb/ft2" units.
Please be aware that pressures in the metric system are properly expressed in N/m2 (Newtons per square meter), using the Newton force unit. In fact, the accepted pressure unit is the Pascal, where 1 Pa = 1N/m2. The kilogram is a mass unit and does not follow in any expression of pressure.
I have a hard enough time teaching my students to work with the correct units. Please make my job easier and at least use the proper pressure units.
Donald Edberg
Pomona, USA
Source: Flight International
