Plane & Pilot
Tuesday, February 11, 2014

Turbocharging


The benefits of getting high


To be of any value up high, turbo models must offer their occupants oxygen systems, and these add weight, expense and (sometimes) minor discomfort. As mentioned above, modern O2 systems have alleviated much of that problem, but oxygen will still dry out your mouth, may congest your sinuses and presents a minor fire hazard.

Oxygen and oil can be combustible, so you need to advise anyone wearing lipstick or oil-based makeup to remove it before flight. (Those T-shirts that read "Remove Before Flight" take on special meaning in a heavy-oxygen environment.)

On top of that, refilling an O2 tank isn't cheap, primarily because it requires the attention of an A&P mechanic. Total system weight is typically 35 to 40 pounds, subtracted directly from payload. If your system is portable, you might substitute medical oxygen, which is usually cheaper, but make certain the bottle will be inside the cabin where it's warm. Medical O2 contains more humidity, which could freeze the regulator if exposed to extreme cold temps.

By definition, icing may be another consideration of flying high, even in summer when it wouldn't be a hazard for normally aspirated aircraft. Many turbo models aren't approved for anti-ice systems, much less de-ice, either pneumatic boots or TKS. On many of those airplanes, the most exotic anti-ice equipment available may be pitot heat.

Plane & Pilot worked with Barry Doctor of Weather Service International in West Palm Beach, Fla., to define the risks of icing, and we'll have more to say about that in next month's issue.

The condition of the heater may not seem a critical item in summer unless you happen to be launching for cruise at FL240. Standard temperature at that height is -27 degrees F. Even if you're departing Palm Springs in July, yo­­­­u may need a properly functioning heater at high altitude.

Pilots who fly at 10,000 feet usually plan their descents for 500 to 700 fpm and assume they'll actually gain a little speed during descent. Flying high, say at 20,000 feet, you may actually lose speed, because you may drop out of your tailwind. Descents demand more time and attention if you have three or four miles of altitude to lose, and gradual descents may be impractical because of terrain considerations.

The airlines start down as much as 150 miles from their destination, partially because of their greater speed, but also a function of the need to lose 35,000 to 40,000 before landing. If you're flying at 25,000 feet and approaching an airport near sea level, even a 700 fpm descent would demand 35 minutes. If your airplane is a Mooney, 210 or Bonanza, that could translate to starting down 100 miles out.

The value of turbocharging is very much in the eye of the beholder and the size of his bank account. Few things in aviation are free, but if you're willing to absorb the higher price of acquisition, additional license requirements (instrument rating above 18,000 feet), shorter TBO, extra fuel burn and higher maintenance cost, a turbo may be just the ticket.



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