page title:    understanding it
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page created 30.06.2002 - 11:34, last modified 27.09.2002 - 12:15 by

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understanding it     part of the aerobatic figure hammerhead

   understanding the hammerhead

The hammerhead is an interesting maneuver because three forces, slipstream, torque, and gyroscopic precession caused by the aircraft's propeller come into play to a greater extent than in most other aerobatic maneuvers. The effect of these forces is especially pronounced in high-performance competition aircraft.


The beginning of the hammerhead is similar to the beginning of a loop; it can be thought of as performing a quarter loop, which would place the aircraft on the vertical upline. The minimum speed for a hammerhead is the loop entry speed, though the faster the entry speed, the longer the vertical upline, and the more well-defined and distinctive the hammerhead. In a Decathlon, a good entry speed is 160 mph, or about the same airspeed used for the reverse half Cuban eight.


The interesting forces become apparent as the aircraft begins to run out of energy along the upline. The slipstream is usually drawn out behind the aircraft becomes tighter and tighter as the aircraft slows. The slipstream forces the fuselage and tailplane to the right as it tightens, which causes the left wing to drop, so it has to be countered with slight right rudder.



As the aircraft slows on the upline, the wing produces progressively less lift. There comes a point when the engine torque effect overcomes the wing's lifting effect and causes the aircraft to roll left. This has to be countered with slight right aileron.



As the aircraft becomes practically motionless, the slipstream becomes so tight around the fuselage that it buffets the airframe, much as it does on the ground during engine runup. This usually is the signal to begin to pivot with the rudder.



As the nose rotates when the aircraft pivots, there are two forces to contend with. The outside wing generates more lift than the inside wing because it is traveling faster in the pivot and gyroscopic precession is created by the twisting from right to left of the rotating propeller disk. The greater lift on the outside (right) wing wants to roll the airplane left, and gyroscopic precession wants to push it over on its back. Aileron opposite to the direction of the pivot overcomes the outside wing's extra lift, and slight forward stick counters gyroscopic precession.



A word of caution on this control configuration, especially for pilots of all Pitts and Eagle aircraft. Forward stick and full rudder deflection coupled with high power and negligible airspeed is the recipe for an inverted flat spin, and if forward stick is excessive, the aircraft will spin in a flash. In aircraft susceptible to this phenomenon, it is imperative to obtain expert instruction in the recognition of and recovery from the inadvertent inverted spin from a hammerhead, and to manage altitude conservatively.


Care must be taken not to exceed redline and G limit on the pullout after the aircraft has been established in straightline flight on the vertical downline and has built up speed.

last modified 27.09.2002 - 12:15 by ,
article created 30.06.2002 - 12:03

about the hammerhead
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hammerhead information
 -  the hammerhead
 -  flying it
 -  common errors

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