Chapter 15-Transition to Jet Powered Airplanes
Table of Contents
Jet Engine Basics
Operating the Jet Engine
Jet Engine Ignition
Thrust to Thrust Lever Relationship
Variation of Thrust with RPM
Slow Acceleration of the Jet Engine
Jet Engine Efficiency
Absence of Propeller Effect
Absence of Propeller Slipstream
Absence of Propeller Drag
Recovery from Overspeed Conditions
Mach Buffet Boundaries
Low Speed Flight
Pilot Sensations in Jet Flying
Jet Airplane Takeoff and Climb
Rotation and Lift-Off
Jet Airplane Approach and Landing
The Stabilized Approach
Touchdown and Rollout
PILOT SENSATIONS IN JET FLYING
There are usually three general sensations that the pilot transitioning into jets will immediately become aware of. These are: inertial response differences, increased control sensitivity, and a much increased tempo of flight.
The varying of power settings from flight idle to full takeoff power has a much slower effect on the change of airspeed in the jet airplane. This is commonly called lead and lag, and is as much a result of the extremely clean aerodynamic design of the airplane as it is the slower response of the engine.
The lack of propeller effect is also responsible for the lower drag increment at the reduced power settings and results in other changes that the pilot will have to become accustomed to. These include the lack of effective slipstream over the lifting surfaces and control surfaces, and lack of propeller torque effect.
The aft mounted engines will cause a different reaction to power application and may result in a slightly nose- down pitching tendency with the application of power. On the other hand, power reduction will not cause the nose of the airplane to drop to the same extent the pilot is used to in a propeller airplane. Although neither of these characteristics are radical enough to cause transitioning pilots much of a problem, they must be compensated for.
Power settings required to attain a given performance are almost impossible to memorize in the jets, and the pilot who feels the necessity for having an array of power settings for all occasions will initially feel at a loss. The only way to answer the question of ôhow much power is needed?ö is by saying, ôwhatever is required to get the job done.ö The primary reason that power settings vary so much is because of the great changes in weight as fuel is consumed during the flight. Therefore, the pilot will have to learn to use power as needed to achieve the desired performance. In time the pilot will find that the only reference to power instruments will be that required to keep from exceeding limits of maximum power settings or to synchronize r.p.m.
Proper power management is one of the initial problem areas encountered by the pilot transitioning into jet airplanes. Although smooth power applications are still the rule, the pilot will be aware that a greater physical movement of the power levers is required as compared to throttle movement in the piston engines. The pilot will also have to learn to anticipate and lead the power changes more than in the past and must keep in mind that the last 30 percent of engine r.p.m. represents the majority of the engine thrust, and below that the application of power has very little effect. In slowing the airplane, power reduction must be made sooner because there is no longer any propeller drag and the pilot should anticipate the need for drag devices.
Control sensitivity will differ between various airplanes, but in all cases, the pilot will find that they are more sensitive to any change in control displacement, particularly pitch control, than are the conventional propeller airplanes. Because of the higher speeds flown, the control surfaces are more effective and a variation of just a few degrees in pitch attitude in a jet can result in over twice the rate of altitude change that would be experienced in a slower airplane. The sensitive pitch control in jet airplanes is one of the first flight differences that the pilot will notice. Invariably the pilot will have a tendency to over-control pitch during initial training flights. The importance of accurate and smooth control cannot be overemphasized, however, and it is one of the first techniques the transitioning pilot must master.Ch 15.qxd 5/7/04 10:22 AM Page 15-16
The pilot of a sweptwing jet airplane will soon become adjusted to the fact that it is necessary and normal to fly at higher angles of attack. It is not unusual to have about 5 of noseup pitch on an approach to a landing. During an approach to a stall at constant altitude, the noseup angle may be as high as 15 to 20 . The higher deck angles (pitch angle relative to the ground) on takeoff, which may be as high as 15 , will also take some getting used to, although this is not the actual angle of attack relative to the airflow over the wing.
The greater variation of pitch attitudes flown in a jet airplane are a result of the greater thrust available and the flight characteristics of the low aspect ratio and sweptwing. Flight at the higher pitch attitudes requires a greater reliance on the flight instruments for airplane control since there is not much in the way of a useful horizon or other outside reference to be seen. Because of the high rates of climb and descent, high airspeeds, high altitudes and variety of attitudes flown, the jet airplane can only be precisely flown by applying proficient instrument flight techniques. Proficiency in attitude instrument flying, therefore, is essential to successful transition to jet airplane flying.
Most jet airplanes are equipped with a thumb operated pitch trim button on the control wheel which the pilot must become familiar with as soon as possible. The jet airplane will differ regarding pitch tendencies with the lowering of flaps, landing gear, and drag devices. With experience, the jet airplane pilot will learn to anticipate the amount of pitch change required for a particular operation. The usual method of operating the trim button is to apply several small, intermittent applications of trim in the direction desired rather than holding the trim button for longer periods of time which can lead to over-controlling.