Why Some Aircraft Have T-Tails?

Aircraft can come in many shapes and sizes, accommodating particular design requirements, applications, and needs. When observing various aircraft, you may have noticed that some airliners feature a lower tailplane while others may have what is known as a T-tail. While differing from a majority of designs found on commercial airliners, these T-tails serve a significant role in flight.

Across all aircraft designs, the tail serves to establish stability and control throughout a flight operation. The vertical stabilizer comes in the form of small wing-like structures that protrude from the main tail near the end of the fuselage. The horizontal stabilizer, meanwhile, will feature the elevators and flight control surfaces that enable attitude management. For most commercial airliners, the horizontal stabilizer is in line with the fuselage, placed at the base of the tail. The T-tail structure, meanwhile, features the horizontal stabilizer at the top of the tail fin.

T-tail structures are not entirely common, often being found on models such as the Boeing 717 (formally the McDonnell Douglas MD-95) and the Boeing 727. Both of these aircraft feature fuselage-mounted engines, that of which is common to T-tail aircraft design. Numerous small to midsize jets also feature T-tails in the modern day, including the Bombardier CRJ Series, the BAe 146, Embraer ERJ, and various Learjet and Gulfstream business jets. One may even find T-tails on some military and transport aircraft, allowing for an increased clearance for the benefit of loading operations.

In theory, there is little difference between standard tail designs and T-tail designs as both enable the tail to function as intended with the use of all needed flight control systems. Nevertheless, T-tail placement is due to the properties of airflow, such designs ensuring that tail structures are situated far from the disturbed airflow present behind the wings and engines. As such, T-tail designs are necessary when the aircraft has fuselage mounted engines.

With a high horizontal stabilizer also comes various improvements in terms of short-field performance. When airflow is disturbed around a low placed stabilizer, such aircraft may become fairly difficult to manage while traveling at low speeds. With increased control during low speed operations, short take-off and landing capabilities are enhanced.

While such benefits can be very advantageous, larger modern jets still maintain the more conventional tail design. This is due to various reasons, one of which is the fact that the lower horizontal stabilizer is much easier to install and maintain. Additionally, such aircraft typically feature strong engines and operate on standard sized runways, meaning that the short-field performance increases provided by T-tail designs are not as beneficial.

One of the biggest reasons for the lack of T-tails on such aircraft, however, is for the avoidance of deep stall conditions. While traveling at a high angle of attack, the disruption of airflow caused by the high horizontal stabilizer can cause a loss of pitch control. While many modern T-tail aircraft now have ample modifications to warn of impending stalls, a lower tail configuration would avoid this issue entirely.

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1. alex marsh
2. Posted on September 20, 2021
aerospace

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