When my C152 stalls with engine, it always stalls turning left. Why ?

[manucordier]

Good morning,

I just wonder why my Cessna 152 always turns left when the nose goes down while stalling with engine. However when I stall with idle power, the nose goes down and the aircraft maintains a straight flight without doing any turn. One thing to note is that the nose gets a lot higher while stalling with engine than with idle power. Thus the P-factor is stronger since the angle of attack of the proppeler's blade going down is greater (P-factor).

To summarise: my hipotesis here is that the left turn is due to P-factor which is very strong at low speed and high angle of attack (due to a higher nose).

But could spiraling slipstream or asymmetrical lift intervene as well ?

Thansk a lot.
Emmanuel Cordier.

[FlyingStone]

Exactly, the P-factor causes the aircraft to yaw to the left (of course having in mind clockwise-rotating propellers), which actually happens all the time during flight - takeoff, climb, cruise, descent and landing.

However during cruise the rudder is trimmed (via rudder trim or fixed trim tab) so force required on the rudder pedals is zero. The yaw which is produced by P-factor is actually variable with speed, since the effectiveness of rudder increases with speed - this basically means that with the same engine thrust and reducing speed, you would have to increase the opposite rudder to maintain zero side-slip angle.

That having been said, I wouldn't recommend doing powered stalls (not approach to stall) without an instructor on board, since the aircraft should not roll or yaw during stall as you say it does. Perhaps you could ask an instructor to demonstrate it to you correctly.

Here (http://www.pprune.org/private-flying/423641-keeping-wings-level-stall.html) is another good discussion on how to maintain wings-level attitude during stall.

[manucordier]

Thanks for you clear answer FlyingStone.

I wanted to see the natural reaction of the airplane while stalling with engine so I climbed 4500 feet AGL, I started the manoeuver and I did nothing to recuperate the stall until the very last moment (when the nose was down and the aircraft entering into a left turn). I then tried to follow the aircraft tendency, pushing the stick forward and the yoke to the left. I lost 500 feet of altitude before it stabilized again in straight and level flight.

It worked quite well without any problems but I'll have anyway a look at the link you just gave me to see what they say.

The thing is that the C152 seems to me an extremely stable aircraft and sometimes it gives me the impression that I could do almost anything with him (always with sufficient height above terrain of course) and it would not betray me by entering into a spin or a spiral. Am I wrong ? (I did many stalls before with instructors).

Have a good day,
Emmanuel.

[UncleNobby]

At low speed,high engine power, and high AOA you have multiple left turning tendencies...

High Engine Power
- Torque reaction - engine spinning right (viewed from the pilot seat) causes a left turning reaction

- Spiraling Slipstream - spiraling air striking the tail on the left hand side. At low speed, high power the slipstream is more compact (think of a slinky)

High AOA
- P Factor - When the aircraft is at a high AOA, the prop blade AOA is greater on the descending blade due to resultant relative wind.
BTW: I don't think its correct to say P-Factor occurs all the time. When relative wind is at 90 degrees to the prop (i.e. head on) both blades (up/down) are producing the same lift.

- Gyroscopic precession; When you pitch down (or when the nose falls) the resultant force is felt at 90 degrees and in the direction of rotation. Nosing over is like applying a force at the 12 o clock position of the prop, the resulting force is felt at the 3 o clock position (as viewed from pilots seat, blade rotating to the right).
Anytime you pitch or yaw there will be precession, but is most obvious in the situation you have described above.