Horizontal Stabilizer Shape
Only half a speed-brake
CC77, true. The secondary design objective would be to slope them in such an angle that they contribute to as little drag as possible. Dan's suggestion remains a viable one.
The gutters are sloped aft to keep them from filling and getting the slf damp whilst parked and doors open. Also. If level, they confuse the rain runoff.
And this is good gen from a mate who was on the Airbus design team.
Thanks Dan. Good design suggests its purpose to those who can appreciate it.
Conforming the slope to cruise airflow is one example. In the course of an airframe's life, saving drag goes directly to the bottom line...
Conforming the slope to cruise airflow is one example. In the course of an airframe's life, saving drag goes directly to the bottom line...
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On aircraft with powered control surfaces it doesn´t matter, but on aircraft with manually controlled elevator, negative camber of the horizontal stabilizer results in a "stick forward" zero elevator force, the faster you go, the higher the stick forward tendency, the aircraft is free-stick-instable. So basically you need to have either an S-sloped airfoil, or one with at least a positively combered elevator to make the aircraft stable. Symmetrical airfoils are neutral with that respect, all stick-free-stability comes from the fixed-stick-stability, which causs an elevator deflection over speed curve with enough gradient, to also produce enough stick force over speed gradient.
Positive camber plus trim tab may work as well, but is not very efficient. Additional springs in the elevator system may provide the desired force gradient as well.
Several gliders have symmetrical horizontal stabilizer airfoils up to the hinge but positively cambered elevators aft of that, often created by a the naturally concave surface of the laminar flow airfoil combined with an (easy to build) flat upper elevator surface.
The Wilga even has a fixed (negative) slat on the elevator horn.
Positive camber plus trim tab may work as well, but is not very efficient. Additional springs in the elevator system may provide the desired force gradient as well.
Several gliders have symmetrical horizontal stabilizer airfoils up to the hinge but positively cambered elevators aft of that, often created by a the naturally concave surface of the laminar flow airfoil combined with an (easy to build) flat upper elevator surface.
The Wilga even has a fixed (negative) slat on the elevator horn.
There was a long running thread on this subject about ten years ago. Can't find it at the moment.
On a naturally stable a/c, which is every large civilian type I can think of, the horizontal stabilizer has a cambered lower surface. Usually, completely flat on top. That suggests to me that in all flying conditions the stab is designed to create a downward force to balance a c of g forward of the c of p.
It is also notable that on a trimmable stabilizer the range of movement is far greater leading edge down than leading edge up.
Which also suggests that a downward force is almost always the requirement.
Storing fuel aft, either tip tanks in a swept wing or stabiliser (horizontal or vertical) is just a very efficient way of reducing the required stabiliser incidence in cruise and therefore reducing drag.
Storing fuel in the tips also aides wing bending relief but thats another topic.
On a naturally stable a/c, which is every large civilian type I can think of, the horizontal stabilizer has a cambered lower surface. Usually, completely flat on top. That suggests to me that in all flying conditions the stab is designed to create a downward force to balance a c of g forward of the c of p.
It is also notable that on a trimmable stabilizer the range of movement is far greater leading edge down than leading edge up.
Which also suggests that a downward force is almost always the requirement.
Storing fuel aft, either tip tanks in a swept wing or stabiliser (horizontal or vertical) is just a very efficient way of reducing the required stabiliser incidence in cruise and therefore reducing drag.
Storing fuel in the tips also aides wing bending relief but thats another topic.
