Saturday, November 1, 2008
Flight Planning In The Real World
Realistic flight-planning requires far more than simply measuring the distance, figuring the book speed and fuel burn and then launching
| My first airplane, a 1947 Globe Swift, purchased in 1966 for $3,700 when I had a whopping 80 hours in my logbook, was a cute little devil. It offered quick handling and was a ball to fling around the sky, but it obviously hadn’t read its own press releases. The stock Globe GC-1B came up short in virtually every performance parameter—it wasn’t nearly as fast as advertised, didn’t climb as it was supposed to, burned more fuel than the POH suggested and couldn’t carry nearly as much weight as it “should” have. I learned the airplane’s true nature by trial and error, probably not the best method in any aeronautical pursuit.|
If you should happen to luck out and encounter tailwinds up high, plan to stay as high as possible for as long as possible to maximize your speed and minimize your time en route. If you normally plan your descents at 500 fpm, consider maintaining altitude longer and plan a descent at 1,000 fpm to your destination with reduced throttle.
Aircraft cruise speed and fuel burn normally don’t meet specs for a variety of reasons, none of them having to do with a braggadocio flight manual. It’s important to remember that your chances of reproducing book specs are poor. Cruise charts are based on highly experienced test pilots with thousands of hours flying new airplanes with perfect engine tune and propeller pitch, optimum CG near the aft limit, all vents closed and a modicum of external antennas.
Fuel burn will rarely equal or “subceed” the charts, at least not if you hope to make your engine last to TBO. Even if you don’t have an engine analyzer, the old traditional wisdom about leaning will allow you to come close to book, but probably no cigar.
When most of us old pelicans learned to fly, often without the benefit of even a single-probe EGT, we were taught to lean the engine to the onset of roughness, then push the red knob forward just enough to ensure smooth operation. On most engines, that will put you slightly on the lean side of peak. If you don’t subscribe to running lean of peak, you’ll burn a little more fuel and find it even more difficult to achieve book fuel flows.
Most airplanes today are fitted with engine analyzers that allow interrogating each cylinder for EGT and CHT, and that makes it easier to lean to the most efficient setting. Even so, you may find achieving book fuel flows to be a challenge.
The choice of power setting is more than arbitrary, no matter what kind of airplane you fly. In my Mooney, I tend to use 75% cruise whenever possible, but there are times when you can actually reduce total travel time by flying slower. A recent trip from Los Angeles to Miami (via Cross City, Fla.) is a perfect example. The GPS distance works out to just below 2,100 nm. If I use max cruise in no-wind conditions on that trip, I’m obliged to stop three times. If I come back to 55%, however, I can eliminate one stop, burn less fuel and make the trip in the same or less time.
In my case, I’m probably not smart enough to do that. I’ll nearly always opt to fly faster, even if it costs me time and money. Some pilots never learn.
|Additional Tools |
Bernoulli Aviation’s Destination Direct aids pilots by planning the intended flight path, calculating weight and balance, and determining the effects of winds aloft. The user-friendly, highly intuitive software has a comprehensive design that’s easily customizable for various pilot skills and aircraft types. Among its extensive features is the ability to connect to your GPS, allowing you to view your aircraft as it moves en route and depicting your current position in relation to other airports and navaids. Contact: Bernoulli Navigation, (618) 281-8050, www.flightplan.com.