The Driest Continent
Which of the following is the driest continent on the planet?
- The North Pole
Answer: C. First of all, the North Pole isn’t a continent; under that ice cap, there’s just water, and no land. Secondly, even though most people imagine Australia to be a pretty dry and barren place–conjuring up visions of the Outback–it isn’t. They have a large central and western area which is desert (about one third of the entire continent), surrounded by a ring with a semiarid climate (about another third), but outside of that, it can be subtropical and tropical and around Melbourne, quite humid. (Australia is however the driest inhabited continent.) Africa has vast areas in its northern third which are quite dry, like the Sahara Desert, but it also has a large central band where the climate is tropical. The driest continent is Antarctica (which is a continent, and technically, also a desert). Even though it’s mostly covered by water (snow and ice) the frigid air can hold only very little moisture, and only a very few inches of it fall each year.
Magic In Numbers
Which of the following statements is most correct?
- For any airplane, minimum sink and maximum endurance speeds are equal, and both are each about 3/4 that of the best glide speed.
- For any airplane, the best glide speed is also the speed for maximum range, both occur at L/D(max), and both are each in turn about 3/4 of the speed for optimum cruise (where you get the most “knots per gallon”).
- A stopped prop can increase glide ratio by up to 20%.
- Altitude has absolutely no effect on the indicated speed to use for attaining an optimum glide, although best glide speed should be decreased at lighter weights.
- Although one should increase glide speed by half the headwind component, if the gear remains extended in a retractable-gear aircraft, glide speed should actually be decreased by around ten to 15 percent.
- All are correct.
Answer: In the spirit of conveying as much truth and knowledge as succinctly as possible, the best answer is in fact choice F. The exact ratios in choices A and B are actually the fourth root of one third (not quite 0.76). For choice C, there is no one exact number for every airplane. For choice D, best glide speed goes down with the square root of weight. For choice E, best glide decreases with the fourth root of “effective flat plate area” (which is only about 15%, when this value is doubled…which is close to what happens when the gear is extended, for example in a Bonanza). But of course the most remarkable thing concerns the speeds for maximum range, maximum endurance, and minimum sink, as well as optimum cruise. They can be very useful indeed, and although they rarely appear in an airplane owners manual or a POH, they can however be quickly and easily calculated based upon a number that usually is given, namely, the best glide speed.
Now You Tell Me!
Real-life scenario: At 6000 feet, while enroute on an IFR flight plan, in visual conditions, you’re flying with passengers on what for them is their first flight in a general aviation aircraft. About three miles ahead you see a cloud deck, and as you approach, you become certain that the cloud tops are about 500 feet above you. Not wanting to make your passenger nervous, you request “higher” but the controller says he can’t oblige. What is your most expedient option?
- request a heading that will avoid the clouds, followed by another to return on course
- Cancel IFR and either divert around the clouds or climb to 8500 feet.
- Accept your fate and reassure your passengers that you have an instrument rating.
- Request an “on top” climb.
Answer: D. Like “contact approach”, “on top” is a magic word for special privileges (and the pilot has to request it). If you inform ATC that you are in “on top” conditions and ask for an “on top” climb to 8,500 feet, unless there are traffic separation issues, the controller will probably approve the request with instructions to climb as requested, report reaching on top, and/or to maintain on-top conditions at or above (or below) some particular altitude. When requesting “on top” one must remain in VFR conditions and accept the responsibility for traffic avoidance, but ATC is no longer bound by the separation rules that govern IFR aircraft, so they are free to let you climb where you want. You do have to use an appropriate VFR cruising altitude, based on your magnetic course (and it must also be above any minimum IFR enroute altitude) and you must comply with VFR cloud clearance criteria, and of course you have to maintain VFR conditions, but your route isn’t compromised. Controllers will also still provide traffic advisories and safety alerts. (However, if you will encounter IMC at any time, you must inform ATC that you want to resume your IFR flight at a “hard” IFR altitude, whereupon you will be given a new clearance.) Note that you don’t actually have to be trying to overfly a cloud layer in order to request this. You can also be between layers, or even in the clear wild blue.