Landing... AOA, Trim vs Throttle

[Lex Talionis]

To clarify..

 

Trim (talking about pitch as thats the finicky one), for those aircraft that have it *active*, operates on the same aerodynamic principles resulting in the same effects regardless the aircraft. From a Cessna 152 to a T-45, to the F-18 when configured, trim is the same. The aircraft will fly whatever AOA you trim for. In aircraft that do not have AOA indexers, that AOA results in an aerodynamic equilibrium with a subsequent airspeed. So you can also say you trim for an airspeed.

 

Power control's VSI. To little power and the aircraft will not have the energy to maintain the AOA/airspeed it is trimmed for so you will descend lookingfor the energy to maintain that AOA/AS. To much power and the inverse is true, just right and it will maintain level. The aircraft will seek what it is trimmed for, power will dictate if it will find that AOA/airspeed in a climb, descent, or level. Trim can be thought of as a means to set where aerodynamic equilibrium occurs between the wing and horizontal stab.

 

Mis conceptions include, trimming for an attitude, trimming for an altitude, trimming to climb/descent , etc

 

Trim for an AOA /airspeed, thats all.

 

- hope this helps.

Edited June 3, 2019 by Lex Talionis

[euthyphro]

Not to get too technical but does your trim adjust to the given thrust in order to maintain a specific AOA (middle of the E bracket) ? Is this why we can change thrust but the AOA stays the same?

 

 

Still this seems counter intuitive given the range of pitch the aircraft can take and still maintain the same AOA.

 

 

That video is excellent BTW.

 

 

Lex, I did join your Discord page... Thanks!!!

[Lex Talionis]

That is a bit backward.

 

The aircraft seaks to keep aerodynamic equilibrium between the horizontal stab and the wing about the aerodynamic center. Trim changes the angle of the horizontal stab, which in turn forces the wing to hit the relitive wind, that is then defined as AOA X. That aerodynamic equilibrium happens at any power setting, the aircraft will seek that equilibrium. AOA is relitive to the wind as it hits the wings, has nothing to do with pitch to the horizon.

 

Thrust does not change the trim. If you have enough power to maintain lvl flight , the wing is flying at whatever AOA it is trimmed for and it just so happensit is creatingenough lift to remain lvl. When you pull power you need to increases AOA to obtain the same amount of vertical lift required to reamin lvl. OR, if you do not want to remain level, let go of the stick and the nose will drop decreasing the AOA back to what it is trimmed for. The inverse holds true.

 

It can be quite confusing, even some instructor's have a hard time understanding why it works even though they understand how to use it as the front seat stick actuator meet puppet.

 

Glad to hear it, great to have ya :)

Edited June 3, 2019 by Lex Talionis