Flying the Learjet: What's it Like?

The Learjet 24F

Imagine flying at 82% of the speed of sound (mach .82) at 45,000 feet. Imagine pushing the power levers up to the takeoff power setting and hearing the powerful turbojet engines spooling up behind you as you are pushed back into your seat. Upon lift-off, imagine yourself sticking the nose of this piloted bullet at about 25 degrees above the horizon and watching the vertical speed indicator needle swing up to 7,000 feet per minute as you begin to climb. If you can imagine this, then you've had a glimpse of what it is like to fly a Learjet 24.

Brief history
The Learjet has an interesting story behind its origin. The airframe was originally designed for a Swiss fighter jet in the 1950's. The Swiss military eventually rejected the prototype and that's when Bill Lear saw an opportunity. His dream was to build a small, civilian business jet and this rejected jet fighter was his answer. In 1963, Lear began producing the first Learjet 23 in Wichita, Kansas using the exact wing with its tip tanks and the same landing gear that were on the military prototype. The Learjet 24F was the last model made before the Learjet 25 came into production. Thus, the Learjet was born.

The engines
Powered by two CJ-610-8A engines with a total power of 5,900 pounds of thrust, the Learjet 24 is not lacking in performance. We often refer to it as "The lawn dart with little wings." The engines are pure stage 2 turbojet engines, as opposed to most modern jets today, which are powered by turbofan jet engines. Pure turbojet engines are not very fuel efficient, especially at low altitudes. But, the power behind these fighter-like engines is incredible. In fact, the Air Force's T-38 has this same engine, just with afterburners for supersonic flight. One day I was at the airport when I heard the rumbling and shaking of powerful jet engines. As I looked up for the airplane I was expecting to see a military jet fighter. What I saw was a Learjet 24 that had just taken off. I remember thinking, "Gosh, is that how loud we are?"

Climb performance
As I mentioned earlier, the performance in the Learjet 24 is awesome. Several times we have taken off and entered a left downwind to the runway and then crossed perpendicular over the runway for a departure. Upon crossing over the runway, about one minute after takeoff, we are 7,000 feet above the airport! If you know anything about airplane performance, then you know that this is an incredible climb rate. Because we do not have RVSM, we have to remain below 29,000 feet or fly above 41,000 feet. Air traffic controllers are sometimes reluctant to clear a non-RVSM aircraft to climb through RVSM in order to cruise "on top." However, controllers know the performance of different airplanes. They know the capabilities of a Learjet and we generally have no problem getting cleared up into the thin air. If there seems to be a question about our ability we just advise the controller that we can give them a "good climb through RVSM." That makes them happy because it gets us up and out of the way of the other airplanes that are flying in the limited separation airspace between 29,000 feet and 41,000 feet.

Usually during our climb through the "30's" we can give them somewhere between 2,000 and 3,000 feet per minute climb. Flying a jet up into the thin atmosphere is a balancing act between a good climb rate and arriving at your desired altitude with enough forward energy. If we climb too quickly (nose-high climb attitude), our forward speed suffers and upon reaching 45,000 feet, we may not be able accelerate because we used all of our kinetic energy in the climb. If we climb too slowly (a nose-low climb attitude) our forward airspeed will be high, but our vertical climb rate will be too little. This may agitate the ATC folks, burn up too much fuel, and our high speed forward momentum yields little vertical climb. On a graph, a jet's climb to the high altitudes looks like an arc that bends
with the curvature of the earth. Each aircraft's flight manual will have a performance chart that tells the pilot what climb profile will be the most efficient use of kinetic energy, especially for jets.

High altitude operations
Many Learjets, including the Learjet 24, have a certified operating ceiling of 51,000 feet. It's more of a marketing ploy than anything else. However, the airplane has to be equipped with a switch in the engines that prevents a compressor stall. The Learjet that I fly does not have the protective switch and thus we are certified up to 45,000 feet. Although it would be a thrill to fly a craft at an altitude where the only thing flying higher than you is the Space Shuttle, I'm glad we can't go that high. If anything goes wrong at that altitude, it can get pretty scary.

As it is, we fly as high as 45,000 feet and I'm sitting on the right side wearing the oxygen mask. This is actually a regulation that pilots have to follow above 41,000 feet and there's good reason for it. If we had a sudden failure in the cabin pressurization, the captain would immediately don his mask, but I would be the one who would assure that one of us is already on supplemental oxygen. Meanwhile, Jose would begin an emergency descent. It would take about 3-4 minutes to get down to 10,000 feet. If there was a rapid decompression of the cabin, useful consciousness at 45,000 feet could be less than ten seconds. You have to be on your toes when flying at such high altitudes.

Approach and landing
Earlier, I discussed what the takeoff is like in a Learjet, but what about the landing? Well, it's actually quite interesting.

Up until March of 2009, I had only around eight hours in a jet from when I was at Air Force Pilot Training. I had some King Air 200 experience, but most of my flying was in general aviation single-engine or twin-engine, piston aircraft. As a crew member in the Learjet 24, I am required to have knowledge of the systems and be able takeoff and land in the airplane.

The essentials to landing any airplane is pretty much universal. Whether its a Bonanza A-36 or a Learjet, it's all about airspeed control on final, having a stable, configured aircraft on approach, and flaring above the runway for a nice touchdown. Our final approach speeds, called Vref, are usually between 115 and 120 knots. That's not too far off from the final approach speed in a Beechcraft Baron, which is between 100 and 105 knots. So, the speeds weren't to drastically different for me.

During my initial training at
Flight Safety International in Wichita, Kansas, I made about a half dozen takeoff and landings in their Level C simulator. The biggest thing that threw me for a curve was the flare. I was not prepared for the reverse effect (from what I was used to) when reducing the power to idle over the runway. In propeller aircraft, reducing the power to idle during the flare above the runway causes the nose of the airplane to pitch down. The pilot's response to this is to give some back pressure (pull back on the wheel) and allow the aircraft to settle onto the runway. However, in an airplane where the engines are mounted aft of the center of gravity and near the tail, like in a Learjet, a reduction of power results in the nose pitching up. To illustrate this, you could lightly hold a toy airplane in one hand with only two fingers and grasp it on the underbelly right at its balancing point (as if you are going to launch it for flight). With your other index finger, give it a push from behind right on the tail. The toy plane will pitch down because the "thrust" (your finger) is coming from behind the center of gravity.

The same thing is true in the Learjet. Thrust is coming from the rear of the aircraft and is essentially pushing the nose down. If you take away the thrust, the nose will rise. During the flare in most jets, a pilot does not pull the controls back after reducing power. The nose rises on its own with a reduction of power. In fact, in some jets, the pilot needs to push the control column forward a little to prevent the nose from rising too high. In the Learjet, reducing power to idle over the runway produces the perfect amount of nose pitch-up that it really flares on its own. The pilot just needs to control the lateral stability to keep the airplane centered in the middle of the runway. Then, as it decelerates, the aircraft gently (hopefully) settles onto the runway.

Our thirty-year-old Learjet has a nose wheel steering button that you engage anytime while taxiing. The steering button is actually just like in the Air Force's T-37 that I flew some. At taxi speeds, you either hold a button down or depress the steering lock button. This button electrically connects the nose wheel to your rudder peddles. Otherwise, your rudder peddles will not control the nose wheel without the steering engaged. This takes some getting used to.

When rolling out on the runway after a landing, you can't engage the steering button until you are nearly at a taxiing speed. So how do you control the airplane as you slow down on the runway? With differential braking. This went completely against what I had been used to for the previous twelve years. As an instructor, I would harp on my students for getting on the brakes too soon during the landing roll-out; that's a great way to burn up brakes quickly. However, after taking a look at the beefy brakes on the Learjet 24, you can see why it's completely doable. Now, here I am using the left or right brake in the last part of my landing to keep the Learjet on the runway centerline. That's just the way it is in a Learjet 24.

I am constantly learning new "tricks" about flying this high performance jet. Jose, the captain I fly with, is very experienced and is always teaching me techniques for flying a jet. Things progress quickly in a jet and a lot of real estate passes below you very quickly as you move along during your flight. You definitely have to be "thinking ahead of the airplane" and consider what is coming up next. If you get off of your game in a Learjet, the aircraft does not care. It will keep on truckin' and it will leave you behind in a heartbeat. That's a bad place to be as a pilot.

1 comment:

Anonymous said...

"Thrust is coming from the rear of the aircraft and is essentially pushing the nose down."

Thrust pushes the nose down not because it's coming from the rear, but because the thrust vector is above the vertical center of gravity. The horizontal location of the engines w.r.t. center of gravity has nothing to do with it.