# Trivia Testers : Up, Up and Away

Question: What is the highest altitude to which a non-rocket powered aircraft could ascend?

Answer: D. 85,000 feet is the approved ceiling of the SR-71. 100,000 feet is the probable maximum altitude of Helios, the experimental solar-powered airplane. The world altitude record for a jet airplane is held by a MiG 25 at 123,524 feet. And the right answer, D, is 160,000 feet: the theoretical maximum altitude of a very large hydrogen balloon. The X-15 attained 354,200 feet back in 1963, but it was rocket powered. (Yes, this one was a meanie: FIVE choices!)

Subject: Highest Speed for a Jet

Question: In the vicinity of which altitude can you generally expect the highest true airspeed for a jet aircraft with a service ceiling of FL 370?

• FL 180
• FL 250
• FL 330
• FL 370

Answer: B. Jet aircraft typically have two speed limiters, indicated air speed and mach speed. The highest available true airspeed occurs where the indicated speed curve, a curve that yields higher true airspeed with an increase in altitude, intersects the mach speed curve, a curve that yields a reduced true with an increase in altitude. There can be a significant variance however, depending on aircraft type. Vmo can either stay the same or increase slightly with altitude, and the maximum true airspeed occurs at an altitude where Vmo is greatest (before being reduced because of Mmo). Actually, mach speed is primarily dependent on temperature. There is also one other slight dependency (humidity), but it is so small that it is effectively ignored in mach speed calculations.

Subject: Brrrrrr!

Question: What is the origin of the term ‘wind chill’?

• The origins are in basic atmospheric physics. There is a simple quantitative relationship between rate of air flow and potential heat exchange when water changes state across a fixed cross-sectional area. However, it was the Norwegian meteorologist Jakob Bjerknes who coined the term in 1935.
• Although there was a formula used to calculate it, namely T(wc) = wind chill temp = 91.4 – (0.474677 – 0.020425 * V + 0.303107 * sqrt(V)) * (91.4 – T), where V is mph, and both T and T(wc) are in degrees F, there were several inherent errors, including the fact that the human body produces its own heat and that wind speeds are measured at weather stations 10 meters above the ground, where they can be much greater than they are at a height of five feet. (The old method estimated wind chill as colder than it really was, and a revision was implemented on Nov. 1, 2001.) The idea behind the ‘wind chill’ figure was actually fairly recent. It is generally credited to the Austrailian Meteorology Bureau, and relatively recently, too: about 1955.
• The term is credited to good old Ben Franklin. His ‘Poor Richards Almanack’ in 1733 used the term (which reflects on how basically intuitive the concept actually is).
• not that early! It is beleived that the English chemist and physicist, John Dalton, initiated the concept in about the year 1800.
• To be precise, the term goes back to 1939. Antarctic explorer Paul A. Siple coined it his 1939 dissertation, ‘Adaptation of the Explorer to the Climate of Antarctica.’ (Siple had been one of Admiral Byrd’s technical staff during his 1928-1929 explorations.) During the 1940s, both Siple and Charles F. Passel developed the wind chill index when they conducted experiments on the time needed to freeze 250 grams of water in a plastic cylinder that was exposed to the elements, hanging on a pole 33 feet high. They found that the time depended on how warm the water was, the outside temperature, and, of course, the wind speed.

Answer: E. But it was revised as described in choice B, and for the reasons given.