T-Tail
Since flight at a high AOA with a low airspeed and an aft CG position can be dangerous, many aircraft have systems to compensate for this situation.
The systems range from control stops to elevator down springs.
On transport category jets, stick pushers are commonly used.
An elevator down spring assists in lowering the nose of the aircraft to prevent a stall caused by the aft CG position.
The stall occurs because the properly trimmed airplane is flying with the elevator in a trailing edge down position, forcing the tail up and the nose down.
In this unstable condition, if the aircraft encounters turbulence and slows down further, the trim tab no longer positions the elevator in the nosedown position.
The elevator then streamlines, and the nose of the aircraft pitches upward, possibly resulting in a stall.
The elevator down spring produces a mechanical load on the elevator, causing it to move toward the nose-down position if not otherwise balanced.
The elevator trim tab balances the elevator down spring to position the elevator in a trimmed position.
When the trim tab becomes ineffective, the down spring drives the elevator to a nose-down position.
The nose of the aircraft lowers, speed builds up, and a stall is prevented.
The elevator must also have sufficient authority to hold the nose of the aircraft up during the roundout for a landing.
In this case, a forward CG may cause a problem.
During the landing flare, power is usually reduced, which decreases the airflow over the empennage.
This, coupled with the reduced landing speed, makes the elevator less effective.
As this discussion demonstrates, pilots must understand and follow proper loading procedures, particularly with regard to the CG position.
More information on aircraft loading, as well as weight and balance, is included in Chapter 10, Weight and Balance.
'PHAK' 카테고리의 다른 글
| PHAK Chapter 6-12 Canard (0) | 2021.08.12 |
|---|---|
| PHAK Chapter 6-11 Stabilator (0) | 2021.08.11 |
| PHAK Chapter 6-9 T-Tail (0) | 2021.08.09 |
| PHAK Chapter 6-8 Elevator (0) | 2021.08.08 |
| PHAK Chapter 6-7 Coupled Ailerons and Rudder (0) | 2021.08.07 |
댓글