Power changes pitch the nose (pitch-power couple)
Pitch-power couple: power change pitches nose on its own, before any elevator input (TP 1102, Effect of Power).
| Power change | Nose | Uncorrected |
|---|---|---|
| Add | Rises | Starts a climb |
| Reduce | Drops | Starts a descent |
- Not a trim effect: appears even when trimmed for prior attitude.
Thrust line position:
| Thrust line | Pitch effect of power change |
|---|---|
| Through CG | None |
| Above CG (high) | Offsets nose-up tendency of power increase |
| Below CG (very low) | Tends to add nose-up moment as power rises (PHAK ch.5, Longitudinal Stability) |
Power-on descents (TP 1102, Power-on Descents):
- Add power to shallow descent: nose rises on its own. Little elevator needed to set new attitude at original airspeed.
- Close throttle for power-off descent: nose drops. Properly trimmed, aircraft settles near best-glide attitude, little further adjustment.
- Why: closing throttle reduces wing downwash, so tail-down force can no longer hold nose up (PHAK ch.5, Longitudinal Stability).
- Desirable: aircraft inherently trying to regain airspeed and re-establish balance.
Trap: unanticipated large power addition (e.g. go-around) pitches nose up on top of held attitude; without forward pressure, couple alone can carry nose past desired attitude.
References
- TP 1102 (Flight Training Manual), Effect of Power
- TP 1102 (Flight Training Manual), Power-on Descents
- PHAK ch.5, Longitudinal Stability (Pitching)
- TP 1102 Ex.6 Straight-and-Level Flight (Reducing/Increasing Airspeed, Trim)