Tuesday, July 14, 2009
Lowest To Highest
From below sea level to a Colorado high in a light jet
By departing VFR, we can easily follow the valley as it drops to the south if we lose an engine on climb out. With both engines running, we’ll quickly climb above the terrain where we can pick up our instrument clearance and head to a nearby fuel stop. One other thing we do is take off with zero flaps to ensure that we have extra speed before rotation. Then, if an engine fails at the worst moment, there’s plenty of airspeed to manage a continuous climb. Our charts show that the required field length with zero flaps will be right around 3,700 feet, and since the runway is 6,400 feet long, we should have plenty of pavement to get airborne.
We arrive at the airport at 5:30 a.m. under clear skies and with a temperature of 33 degrees F, so we quickly prepare for departure. At full power, the engines are running fine, but the takeoff roll feels sluggish. For good measure, I hold the plane on the pavement until we’re about 10 knots fast. On rotation, the plane feels mushy, and it seems like we’re barely 50 feet in the air as the end of the runway disappears below. Both engines continue to work perfectly as we rapidly gain speed and climb briskly to 16,500 feet, where we pick up our clearance to Montrose to take on more fuel for our final leg home. The views of the snow-capped Rocky Mountains are spectacular as we climb into the flight levels.
Being a newbie to hot and high jet flying, I was pretty conservative about weight limits for both airports, but that’s probably a good idea for everyone going into either of these two locations in any kind of airplane. The Citation Mustang handled the mission well, and in my mind, it was the real superhero.
John Hayes is a retired entrepreneur with a Ph.D. in optical engineering. He has owned numerous airplanes including an Extra 300, a TBM 700 and a Citation Mustang. He was a founder and past president of the TBMOPA, and is a founder and current president of the Citation Jet Pilots owner-pilot association. He has an ATP rating and nearly 3,500 hours.
|Jet Operations |
|Most of the thrust from a modern high-bypass turbofan comes from the large amount of air driven by the ducted fan in the front of the engine. The fan acts much like a high-speed propeller, pulling cool air around the hot core exhaust to make the engine more efficient and much quieter than a pure jet engine. A high-pressure compressor provides pressurized air to the burner, where fuel is ignited, providing hot exhaust to drive both the high-pressure compressor and fan turbines. |
Total thrust is determined by the mass of air that can be accelerated through the engine. So, like normally aspirated piston engines, turbofan engines lose thrust as the density of air goes down. That loss of thrust is quite noticeable during a climb and when ambient temperatures go up. For this reason, jet pilots should pay special attention to takeoff capabilities when the temperature goes up—particularly at high altitude.
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