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The Right Trim

We trim our airplanes multiple times each time we fly. Trim is set based on what is needed at the time, which is typically to maintain a comfortable equilibrium that maintains low control pressures.

We trim our airplanes multiple times each time we fly. Trim is set based on what is needed at the time, which is typically to maintain a comfortable equilibrium that maintains low control pressures. How to set an aircraft's trim is covered to an extent in the Pilots Operating Handbook, or POH. Setting trim this way assures that the stick (or yoke) forces will fall within the pilot's ability to control and correct during departure, and will usually get the plane headed in at least one right general direction (up).

HOW WE ADJUST OUR TRIM AND HOW OFTEN WE ADJUST OUR TRIM IS STILL IMPORTANT AFTER THE WHEELS LEAVE THE GROUND. Sometimes we don't recognize the importance of trim, because we don't think about what could happen next in our flight. In a worst case scenario, that could challenge flight safety, and even cost us our life!

EXAMPLE: You are taking to the sky in your airplane for the first time in three weeks. The weather has been oppressive, wintertime, low-ceiling IFR, and this has been the first break of safe visual conditions that has appeared in quite some time. You perform a thorough preflight of your aircraft, checking out the airframe with impressive attention to detail. After adding a quart of oil to the engine, you fire it up and taxi out to the active runway.

The runup goes off without a hitch, and you run through your pre-takeoff checklist, as outlined in your POH.

  • Flaps - Set to 0 (for this model).
  • Electric Fuel Pump - Off.
  • Trim - Set to plus 3 with no back seat passengers, 0 with back seat passengers. (You're by yourself, so you set the trim to plus 3).
  • Controls - freedom of movement verified, controls moving in a coordinated manner.

With the checklist and runup complete, it looks like you are ready to go. You check for traffic, and taxi the plane to the active runway centerline. The tower clears you for departure, and you apply power slowly and start to build speed. You reach the rotation speed; the plane lifts off the runway, and climbs back into the sky.

THEN IT HAPPENS. Your seat lock disengages, and the seat goes full aft, taking you with it! Your hands are on the yoke, and it comes back with you, all the way to the aft stop. The stall horn blares, the stall-warning light flashes, and plane is 200 feet above the runway. You're about to have a very bad day!

BUT YOU'RE IN TRIM! You immediately release your grip on the control wheel, and the nose of the plane falls back down to a better, more flight worthy angle. The angle might not be perfect -- the nose may actually pitch down through the horizon -- but the momentary zero-G and immediate attitude change prevents the impending stall! The stall horn and lights turn off, and your plane again begins to build airspeed. You grab on to the right seat, and pull your seat back forward again, carefully lock it into position and assess your position and problem. With any luck, you'll soon be back on the runway -- in a controlled manner -- so you can ... "clean up".

GRAVITY - WELL, GRAVITY SUCKS! When your seat lock disengaged and the seat went back, you went with it. Our instinctive reaction when we "fall" is to grab onto something. Usually that's a good thing. This is not the case with the control wheel, which is pulled full aft to precipitate the perfect departure stall, followed by the perfect stall-spin crash. In order to miss this plane wreck, you need to have considered ahead of time what you will do if your seat goes full aft.

TRY THIS AT HOME - AT A SAFE ALTITUDE WITH AN INSTRUCTOR ON BOARD. Set up for a departure stall; high power, low speed, gear down, trim set correctly, and then release the controls and move your seat full aft. The nose will pitch up more in most cases, but in MOST cases, control of the aircraft will not progress to a stall-spin-crash. Apart from the good amount of effort needed to pull the seat forward, you should be able to get the plane back to normal without the instructor reaching for the controls.

...And yes, it can -- and does -- happen.

While Cessna models have been received bad press (and litigation) over seat track problems, they aren't the only planes with seat tracks. The fact of the matter is simple: almost everyone's plane has seat tracks. Those seat tracks will wear over time. Unless you are trained, thinking and prepared for this type of problem, your chances for survival ... well, they suck.

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