SlamClick From United States of America, joined Nov 2003, 10062 posts, RR: 66
Reply 1, posted (11 years 2 months 1 week 6 days 6 hours ago) and read 3239 times:
Talking about aircraft other than FBW Airbus here...
Before takeoff we have set the stab trim for our weight, configuration and CG location. It should be right for the initial takeoff. However, I noticed in lots of swept wing planes that somewhere around 300-500' after liftoff some nose-down trim would be required. A possible explanation for that is that the fuel centroid location assumed in the W&B is based on level pitch attitude. When we go 20-25 degrees nose-up the fuel flows to the aft parts of the tanks including the outboard parts of the wings. This would have the effect of shifting the CG aft slightly.
During and after flap retraction some trim is going to be required.
For landing, it is a technique used by some pilots to trim nose-up throughout the flare and even until the nosewheel touches down. They feel they get smooth touchdowns that way. I choose not to do this normally, and I get about as many greasers as they do. Again, it is a matter of technique and not procedure.
Anyway, when not maneuvering, or, in other words in unaccelerated flight, you trim when you find yourself pulling or pushing against the yoke.
Happiness is not seeing another trite Ste. Maarten photo all week long.
BuckFifty From Canada, joined Oct 2001, 1316 posts, RR: 18
Reply 3, posted (11 years 2 months 1 week 6 days 1 hour ago) and read 2400 times:
As Slamclick says, it's a matter of technique. It makes a difference in accordance to individual pilot skill, not in a technical sense. Trimming nose up you can keep the aircraft in a more or less constant nose pitch attitude, which allows for a gradual ROD during the flare (and thus a greaser). This happens because trim adjustments are quite finite, and the rate of trim change is constant, making it easier to flare accurately. But if you have steady hands, you really don't need to do this. I reckon if you overtrim the nose up pitch in the flare, you're just asking for trouble.
And Airbii don't need stab trim, as it is done automatically during most phases of the flight, except for the flare. At that point, there's no point in using manual trim anyway, just glide the aircraft down smoothly using the sidestick.