There’s no place like home…there’s no place like home…
Near the end of a long flight on autopilot, above an overcast at 9,000 feet, at night, a C-182 pilot suddenly realizes that he had fallen asleep, and worse, that he had mis-set his OBS with the wrong heading. Not being able to contact Center on his current or previous frequency, he frantically cycles through all frequencies in the hope of reaching somebody–anybody. Just before resigning himself to making a mayday call on 121.5, he is elated to hear that 131.8 is quite busy. Actually, he’s worse off than he could imagine. Why?
- This is the frequency used by range officers in a Military Operations Area.
- This is the air-to-air frequency often used by airliners over the North Atlantic.
- He’s flown South outside of Miami Center and into Cuban airspace.
- This is the frequency used for chase planes during a Space Shuttle launch.
Answer: B. (Did I also mention that’s it’s mid-winter?)
The Cost of Speed
What is currently the highest airspeed-to-horsepower ratio in a propeller airplane?
- generally around one-to-one (knots per horsepower)
- usually less than 1:1
- two to one
- almost three to one
Answer: D. The speed of an airplane is limited by the friction it encounters with the air through which it flies. For airplanes not powered by jet engines, the efficiency of a propeller in converting horsepower to thrust is reduced as airspeed increases. Although one form of drag called induced drag actually decreases with increasing airspeed, generally overall drag increases in proportion to the cube of the airspeed, and so airspeed increases by only the cube root of the ratio of increased to original horespower (though the climb rate is linearly related to excess horsepower). Most fixed-gear general aviation airplanes generally get somewhere in the vicinity of one (and often less) mile per hour for each horsepower that its engine is capable of producing. In aviation, as well as with ships at sea, the preferred unit of speed is the knot, which is equivalent to about 1.15 miles per hour, but this “one-to-one” ballpark figure–plus or minus around 50%–is still generally true for most small general aviation airplanes. For example, a new Cessna 172, with a 160 horsepower engine, has a maximum sea level cruise speed of 123 knots, or around 141 mph. But there are some well-known exceptions.
Incredibly, it is about three-to-one. For example, an owner-designed and built airplane powered only by a 65-hp Rotax engine has achieved a speed of 213 mph in 1992. Having the very lightest FAI land plane weight class (C1a/0, under 300 Kg. gross weight), the speed-to-power ratio of Californian Mike Arnold’s AR-5 was about 2.85 knots/HP (3.3 mph per hp). Where most small GA airplanes have an equivalent “flat plate area” (not literally a frontal cross-sectional area, but still a useful metric) somewhere around three to six square feet, this airplane had an FPA of well under one square foot. Austrian Peter Scheichenberger’s Bede BD-5B attained over 218 mph (almost 190 knots) in August 1999, so as far as FAI records go it was faster, but that was with a 74 HP Rotax (and a “knot/HP” ratio of 2.56).
To completely escape the possibility of a lightning strike in the vicinity of a thunderstorm, an aircraft would have to climb how high?
- about 10 miles: lightning strikes above 50,000 feet are virtually nonexistent
- sixty miles
- FL 600
- Since lightning only strikes downward or horizontally, any altitude above the highest clouds within a radius of approximately 20 miles would do.
Answer: B. Yes, you guessed it: 60 miles. We really don’t know all there is to know about electricity in regards to weather. Although pilots have actually seen electrical discharges emanating upward from thunderstorm clouds for many years, it has only been fairly well documented within the last decade or so. Red and blue colored flashes of light from thunderstorms reaching altitudes as high as 60 miles have been recorded by NASA researchers aboard jet aircraft. Some extend up above the ozone layer into the ionosphere, where auroras occur. Our atmosphere may in fact be exchanging electric charges with the solar plasma in space, and storms just might be driven by energy from the larger environment through which Earth itself travels. (They may also be responsible for changes in the amounts of upper atmospheric ozone, for all we know at this point.) So far, two distinctly different flashes have been identified, named sprites and blue jets. Sprites are red flashes which last only a few thousandths of a second and extend from above storm clouds up to about 60 miles high, reaching the bottom of the ionosphere. Blue jets are flashes that appear in narrow beams or sprays resembling tracks of atomic particles or rays in a cloud chamber.