Plane & Pilot
Tuesday, February 11, 2014

Turbocharging


The benefits of getting high


Turbochargers have other duties besides high and fast, however. They provide a knowledgeable pilot the ability to operate out of airports at ridiculous elevations. The key word above is knowledgeable.

The psychological downside to turbocharging is that it may fool a pilot into thinking he's invincible. Many years ago, while delivering a new Bellanca Turbo Viking from the factory in Alexandria, Minn., to California, I stopped in Denver for the overnight on the way West. It was early July, and the following morning offered chamber-of-commerce weather conditions. If the Earth had been flat, I could have seen Hawaii. I decided to drop in to Leadville, Colo., elevation 9,927 feet MSL, the highest municipal airport in America.

After a cup of coffee with the manager and some deep-breathing exercises, I climbed back into the energetic T-Viking for the remainder of the trip West. The temperature was about 74 degrees when I pushed the throttle forward for takeoff. The Bellanca surged ahead with what seemed its usual enthusiasm, but when it came time to fly, what had been 1,500 fpm at sea level turned out to about half that at 10,000 feet MSL. True, the density altitude was up to nearly 13,000 feet, but I assumed the twin turbos out front would take care of that problem. The moral is that you can turbocharge the engine, but you can't turbocharge the wing and the prop.

In most reasonable situations, compressed power will make a big difference in both climb and cruise. I got a graphic taste of what a turbo can do for speed in 1994 when I set eight world-class C1C city-to-city speed records between Los Angeles, Albuquerque, Dallas and Jacksonville in a new Mooney Bravo. I flew the trip at FL250 all the way with the world's fastest refueling stop at Dallas Love Field. Average speed for the full, seven-hour-nine-minute-cross-country dash from LAX to JAX was 300.1 mph, but one of the intermediate legs, Los Angeles to Albuquerque, worked out at 338.4 mph.

Of course, one major benefit for my record flight was good weather and excellent winds aloft. Fully half of the world's weather tops at 18,000 feet MSL or below, so the higher you fly, the better the ride. If you operate at or above FL180 very often, you'll most often be cruising in smooth air and sunshine.
Turbochargers do, indeed, change your perspective on flying high, and for many of us, the positives far outweigh the negative.
Additional altitude can sometimes seem like an intangible asset—until the engine quits. A turbo can provide a thicker buffer of altitude in the event of an engine problem, and while there's no guarantee you'll always make the right choice of an emergency landing site, no matter what your cruise altitude, remember that the available space increases as the square of altitude. If you're flying an airplane with an L/D of 10 to one and cruising a mile above Kansas when everything suddenly becomes quiet, you'll have a theoretical emergency radius of 314 statute miles to pick a landing spot. If you're flying 20,000 feet above Kansas, your available landing area increases to just over 5,000 square miles.

There are a few negatives to flight at high altitude, but very few. Fuel burn will inevitably increase, partially because of the need to keep the engine cool. TBO also may take a hit. Mooneys are out of production these days, but when both the 201 and 231 were on the line, the 201 burned about 11 gph at max cruise, and my 231 consumed more like 13 gph.




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