Introduction
Propeller-driven aircraft is more efficacious at low speeds than jet-driven aircraft, for they create higher propulsive efficiency and, consequently, greater thrust while the craft is moving at lower airspeed; however, jet-driven aircraft experience the deficiency of thrust when the craft is moving at low airspeed (Dole & Lewis, 2000, p. 207). Also, the efficiency of propeller-driven craft is higher compared to that of jet-driven craft at lower altitudes (Dole & Lewis, 2000). On the other hand, jet-driven aircraft are more effective at higher altitudes because less fuel is used (Dole & Lewis, 2000, p. 109). In addition, it is better to cruise at higher speeds at high altitudes due to the reduced drag, which also gives an advantage to jet-driven craft at greater altitudes.
Consequently, when choosing the power plant type, it is needed to consider the desired speed and altitude of the aircraft. For cargo and passenger craft that are not large, and where airspeed is not paramount, propellers are often better, especially if the ranges they are to travel are not long (so they do not need to fly long ranges at high altitudes). For military craft (which need to fly faster and require greater thrust), long-distance cargo and passenger craft (which would fly at higher altitudes for a long time), and large aircraft (which would also fly at higher altitudes to reduce the drag), jets are often better (Dole & Lewis, 2000).
Comparing Various Jet-Range Profiles
Which jet-range profile is best depends on what is needed in a particular situation.
· While maintaining a constant Mach and a constant cruising altitude, usually an aircraft utilizes a large amount of fuel to fly given distances which are not long. So, this mode is best for flying short, set distances.
· For a craft to maintain constant thrust and a constant cruising altitude, it is needed to use fuel at a steady rate to keep the thrust at the same level, and, consequently, to maintain the given altitude. However, it should be noted that throttle settings will need to be adjusted to maintain the needed level of trust, for the actual thrust will change due to the loss of weight resulting from the fuel burn (Dole & Lewis, 2000).
· While flying at constant cruising altitude and lowering Mach, it is needed to decrease the fuel consumption to reduce airspeed (Dole & Lewis, 2000). This is probably the best profile to utilize when it is required to maintain constant altitude while flying long ranges, for decreasing the fuel use will lead to a greater specific range (Dole & Lewis, 2000, p. 110).
· When flying at constant Mach while increasing the altitude in the process (cruise-climb technique), it is possible to achieve an improvement in range thanks to the decrease in weight of the craft and the lower density and temperature at high altitudes; thus, this is the best profile to use when it is permitted to increase the altitude (Dole & Lewis, 2000, pp. 111-112).
Aircraft Design Features Affecting Takeoff and Landing Performance
There are several characteristics of aircraft design that affect takeoff and landing performance, some of which are:
- Gross weight of the aircraft: greater weight increases liftoff speed and decreases acceleration; so, greater weight increases the takeoff distance. Weight change needs to be taken into account when landing; heavier craft need greater approach speed, and, therefore, longer runways (Civil Aviation Authority of New Zealand [CAA], 2011);
- The features of the wheel (the wheel bearing friction, the drag resulting from braking, the deformation of the tire, the tire pressure, etc.) (CAA, 2011; “Takeoff & Landing Performance,” n.d.);
- Wing peculiarities (e.g., flap settings, wing surface, airfoil, etc.) (CAA, 2011).
As for B-17, there were a variety of subtypes of that craft; some of them utilized the NACA 0018 wind design (Current, n.d.). Different models of B-17 could have a gross weight of nearly 40,260-56,000 lbs (“Boeing B-17 Performance,” n.d.).
References
Boeing B-17 performance. (n.d.). Web.
Civil Aviation Authority of New Zealand. (2011). Takeoff and landing performance. Web.
Current, J. D. (n.d.). American warplanes of WWII. Web.
Dole, C. E., & Lewis, J. E. (2000). Flight theory and aerodynamics: A practical guide for operational safety (2nd ed.). New York, NY: John Wiley & Sons.
Takeoff & landing performance. (n.d.). Web.