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|Eastern Air'||23 %|
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This all-moveable tail is called a:
The traditional elevator sits on the trailing edge of a horizontal stabilizer. Normally, moving the elevator generates a pressure change which moves forward to cover the entire horizontal stabilizer. This generates a large force, allowing the tail to stabilize and control the aircraft's pitch.
The pressure change generated by the elevator moves forward at the speed of sound. At transonic and supersonic speeds, airflow over your tail moves faster than the speed of sound. That supersonic flow prevents the elevator's pressure change from moving forward and affecting the entire tail. In fact, the pressure waves form a shock wave at the elevator's hinge, and the only pressure change exists directly over the elevator itself. Your elevator essentially became a lot smaller - and less effective.
The Stabilator - More Effective At High Speeds:
A stabilator moves as one piece, so pressure changes occur over the entire surface - even at supersonic speeds. Plus, you've eliminated the shock wave at the elevator hinge point, which significantly reduces drag.
By moving the entire stabilizer surface, you've increased controllability and decreased drag at high speeds.
The Drawback - No Control Feedback:
Like everything in aviation, there is a drawback to a stabilator. Since the entire surface moves as a single unit and rotates around its aerodynamic center, there's very little control pressure acting against the pilot - the elevator moves without any resistance. Without a fly-by-wire system, this makes the elevator extremely touchy and difficult to control.
You can create control feedback by adding an anti-servo tab to the rear of the stabilator. An anti-servo tab moves in the same the direction of the control surface - but it deflects even more. So, if you move the stabilator's trailing edge up, the anti-servo tab sticks up even further. Air flowing over the surface pushes back against you, adding control feel.
But Why Are They On Light Aircraft?
Why put a stabilator on a light aircraft? Piper wasn't concerned with supersonic airflow when designing the Cherokee's tail. A stabilator generates a large pitching moment without a lot of control force. They're a great alternative when an elevator would be too hard for a pilot to easily move. And, by adding a small anti-servo tab to the stabilator's trailing edge, you'll have just enough feedback to stay controllable.
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