If you then multiply that acceleration by the amount of time in the turn (for example, 60 seconds in a standard rate turn), you get a 200 knot change in velocity leftward. Let’s take an example where we do the math with a particular aircraft in a particular turn and discover that the acceleration turns out to be 3.33 knots per second leftward. Newton’s 2nd law of motion is F = ma (force equals mass times acceleration), which we can rewrite as a = F/m (acceleration equals force divided by mass). The upward and downward forces cancel out. Note that it is simply a force from right to left. If you average all the forces throughout the turn, you get something like the picture on the right as the average force. With reference to the air you are flying through, a well-executed turn will always be a circle. Taking us back to high-school physics, this is a centripetal force, and it causes the aircraft to fly a nice, circular path in the turn. Remember how good it felt when at the completion of a perfectly performed steep turn you felt the bump of passing through your own wake? In a coordinated turn, the sideward force is always perpendicular to the direction of motion. You may already intuitively know that airplanes turn in a circle from your Private Pilot training. Gliders and helicopters use a piece of yarn outside the cockpit in the airstream to help pilots keep their turns coordinated. In other words, the yawing of the aircraft will match the change in direction of flight, and the aircraft will neither slip nor skid. In a coordinated turn, the airflow should remain straight down the airframe. This causes the vertical stabilizer to yaw the aircraft in the direction of the turn. The sidewards force from horizontal component of lift changes the direction of the aircraft’s movement sidewards. Rudder input is used to keep the turn coordinated. Once the aircraft has stabilized at the new airspeed, the turn is straightforward. The following video shows the relationship between drag, thrust and airspeed in our standard (constant power) turn. Any increase in lift causes an increase in drag, which in turn will cause the aircraft to slow down unless you add power. This is why you were taught to add power to maintain airspeed in a steep turn. If we do not add power, the aircraft will slow down enough for total drag on the aircraft and the thrust from the engine to balance each other again. The increase in lift causes an increase in induced drag. Remember that in steady flight, thrust and drag balance each other out. This is necessary to keep the aircraft at a constant altitude. The vertical component of lift continues to counteract the force of gravity so the aircraft can stay in the air.īecause the vertical component of lift decreases as the aircraft banks, the pilot pulls back on the controls to increase the total lift from the wings in order to maintain a balance between the vertical component of lift and the force of gravity. The bank angle causes the lift from the wings to provide both horizontal and vertical forces. The horizontal component of lift causes the aircraft to change direction (accelerate) sidewards. The recommended procedure to enter a normal turn is to roll to the appropriate bank angle for the turn and apply back pressure on the controls to maintain altitude. This should be a nice refresher of your Private Pilot ground training with a little bit of high-school physics thrown in. And to make sure we are on the same page, let’s walk through the dynamics of a standard turn in a no-wind situation. For this discussion, I will define a “standard turn” as level (constant-altitude), constant-rate, coordinated, and with constant power. The first step in breaking things down is to eliminate as many variables as possible. Second, there are so many interdependent variables involved in flight (altitude, attitude, air density, wind, thrust, drag, aircraft configuration, etc.) it is really easy to mix them up. First, to really grasp the underlying issues at play here requires going back to high school physics, which is a painful memory for many of us. This is a challenging topic to discuss for a couple reasons. Rather, let’s take the MasterFlight approach to this problem: break it down and put it back together with recommended procedures and techniques.
Mac McClellan (former editor-in-chief of Flying magazine and current editor of EAA’s Sport Aviation) re-ignited the controversy about whether or not turning downwind can be dangerous because it will cause a loss of airspeed due to the inertia of the aircraft. Many pilots responded to disagree with McClellan’s post, and I won’t copy all those discussions here. In a recent post on his blog, Left Seat, J.