I’ve been able to get back into the air recently and start reviewing old private pilot knowledge as I prepare for my Instrument Rating. Since it’s been awhile between the two, we’ve been reviewing lately. In the car to the airport, Jake asked me about left turning tendencies. I knew the basics, but forgot the names and how this will affect my flying.
So let’s review! What are left turning tendencies? And more importantly, why do they matter?
This is caused by the engine. The more power, the more torque. The engine is putting power in turning the propeller, but it also turns the airplane. Well, hold on, the airplane is MUCH heavier than the propeller so that’s why it doesn’t rotate like the propeller. From the cockpit perspective, the propeller turns clockwise. Therefore, the engine causes the fuselage to rotate counter-clockwise (bank to the left). Since the fuselage is lighter than the propeller, it only rolls slightly to the left and requires a little right aileron to fix it and the effects are only really felt at full power.
Torque is caused by engine power.
Propeller factor. This one I find hard to visualize. The downward swinging propeller blade takes a bigger “bite” out of the air in a nose high attitude. What does that even mean? It’s basically asymmetric thrust taking place. Yeah…still not helping. Okay, so a propeller is an airfoil. In a nose high attitude, the downward swinging blade of the propeller generates more lift (thrust) due to the higher angle of attack (of the blade, not necessarily the airplane). This means in that attitude, the right side of the propeller (downward swinging blade) generates more thrust than the left side (upward swinging blade) which causes the airplane to yaw to the left.
P-Factor is caused by high pitch.
See how the blue arrow (i.e. the air) will come from the propeller and wrap around the airplane in a corkscrew fashion until it hits the tail? What would happen when a crosswind would hit the tail? You’d yaw in the opposite direction. It’s the same concept, air is hitting the tail, but it’s just from the propeller and not the wind. Due to the way majority of propellers rotate, it’ll be to the left. This only happens at slow speeds. At faster speeds the corkscrew (slipstream) is longer and also the airplane is moving faster, therefore moving out of the slipstream before it can hit the tail and cause the left turning tendency.
Experiment: Grab a friend, and on a piece of paper draw a spiral and have your friend pull the paper slowly. Then repeat drawing a spiral at the same speed but have your friend pull the paper faster. That’s how you can get a better visualization of what the spiraling slipstream looks like at slow and fast speeds.
Spiraling slipstream is caused by slow speed.
Right, right, I get it. But why does it matter?! Knowing your airplane and how it’s going to react when you have certain inputs is important. You can stay ahead of the airplane and not react to it and play catch up, but anticipate it.
When you takeoff, you’re at high power and high pitch and you start off slow. So what is a factor? Torque (power) and p-factor (pitch) and for a little bit before you gain more speed, spiraling slipstream (slow speed), so you’re going to have to use a good amount of right rudder and a little right aileron on takeoff since you have two of these forces acting upon the airplane.
Slow flight involves all three of these. You’re at a high pitch (p-factor), you’re slow (spiraling slipstream), and you have a lot of power to hold altitude (torque). It’s the perfect storm and causes LOTS of right rudder. Then what if you have to turn right? You better give it all the right rudder you can along with a small bank to remain coordinated.
But wait, Caitlin, you’re missing one more! Okay, yes, there is one more left turning tendency.
This is always mentioned during left turning tendencies and gets glossed over sometimes. And honestly, that’s not a HUGE deal, but it is important to know. Gyroscopic precession really only matters if you’re flying a tailwheel airplane and most pilots don’t train in those for their PPL nowadays.
Just due to the laws of physics, when you put a force on a spinning object it’ll deflect 90 degrees to the right. While the following is NOT correct, it helped me to think about it as a delay. You hit an object at the top (360) but by the time it reacts, that point is at the (090) mark. Speed of the spinning object has NOTHING to do with this, so that’s why that’s wrong, but it’s just what helped me remember it and understand it better.
When you takeoff a tailwheel airplane, the tailwheel will lift up before the front wheels. Lifting the tail puts a force on the top of the propeller. That force is deflecting 90 degrees and causing the airplane to yaw to the left.
Whew, and those are the four left turning tendencies! I hope this helps for a better understanding and application of them to take into your next flight!
Any questions or comments, feel free to leave a comment!