Information AboutTrim Tab |
| CATEGORIES ABOUT TRIM TAB | |
| aircraft controls | |
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Trim tabs are small surfaces connected to the trailing edge of a larger Control Surface on a Boat or Aircraft . The angle of the tab relative to the larger surface can be adjusted to null out hydro- or aero-dynamic forces and stabilize the boat or aircraft in a particular desired attitude without the need for constant control inputs. When mounted on a movable surface (such as a rudder), the trim tab acts as an anti-servo tab, moving in opposition to the main surface. Because the center of effort of the trim tab is further away from the leading edge of the main surface than the main center of effort, the forces generated by the tab work over a longer lever arm. The main surface will rotate around its mounting axis until the moments from the main and trim surfaces balance each other. USES IN BOATS Boats with planing-type hulls will often have trim tabs attached to the trailing edge of the hull or transom. These are used to adjust the pitch attitude of the boat while underway. Changes in boatspeed or weight placement will usually require the trim tabs to be adjusted to keep the boat at a comfortable and efficient pitch attitude. This reduces the work of the captain by reducing the amount of manual control necessary, as well as providing for greater efficiency by keeping the ship in the ideal orientation for the conditions. Trim Tabs are most found on cruisers, sport fishing boats and center console boats rangering from 20 feet and up. In some sailboats, the trailing edge of the keel has a trimtab which is used to null out rudder forces (lee or weather helm). Sailboats intended for long-distance voyages with minimum crew often have a self-steering system which works via a trim tab (usually called an anti-servo tab) on the trailing edge of the rudder. This tab is mechanically connected to a windvane. The system automatically adjusts the boat's heading to keep it at a fixed angle of attack to the apparent wind. USES IN AIRCRAFT Virtually all airplanes (including gliders) have elevator trim tabs. Elevator trim frees the pilot from constantly adjusting the pitch controls. A pitch trim control (often in the shape of a wheel) is adjusted by the pilot to cancel out control forces for a given airspeed. When the trim control is rotated forward the nose is held down. Many newer aircraft, especially jet aircraft have electric trim controls. Many airplanes also have Rudder and/or Aileron trim systems. The picture to the right shows an aircraft with a rudder trim tab that is somewhat fixed into place and not adjustable during flight. It is angled slightly to the left to lessen the need for the pilot to push the rudder pedal constantly to overcome the left-turning tendencies of this prop-driven aircraft. Many aircraft have control wheels inside the cockpit so the pilot can adjust the rudder trim while in flight. When a trim tab is employed, it is moved into the windstream opposite of the control surface's intended deflection. For example, in order to trim an elevator to hold the nose down, the elevator's trim tab will actually rise ''up'' into the windstream. The increased pressure on top of the elevator surface caused by the raised tab will then deflect the ''entire'' elevator slab down slightly, causing the aircraft's nose to move down. The use of trim tabs significantly reduces the workload on pilots, since their attention can be focused on tasks other then control input during continuous maneuvers (ie: sustained climb on takeoff to high altitude, descent prior to landing), such as traffic avoidance, or communication with Air Traffic Control . Not only does keeping an aircraft trimmed properly reduce pilot workload,it also increases fuel efficiency by reducing Drag . For example, if an aircraft is climbing it will have a tendency to Yaw which increases Parasite Drag because the craft is not flying straight into the flight path but at a slight angle which puts more of the fuselage into the wind. TRIM TAB AS METAPHOR The engineer Buckminster Fuller is often cited for his use of trim tabs as a metaphor for leadership and personal empowerment. In the February 1972 issue of ''Playboy'', Fuller said:
The Buckminster Fuller Institute calls its member newsletter , ''Trimtab''. |
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