The Force May Not Be With You (Centrifugal Force)

There I was, explaining steep turns to my very experienced flight instructor during my initial CFI training. All bright-eyed and confident, I knew this maneuver inside and out and I was positive that he was going to be impressed with my instructional delivery. When the topic of centrifugal force came up, I explained it just as the FAA had it laid out in their own glossary, "it is the apparent force that an object moving along a circular path exerts on the body constraining the object and that acts outwardly away from the center of rotation." Of course, I did explain try to simplify this, the effects of centrifugal force on the pilot, weight, etc. However, my instructor laughed and mentioned that centrifugal force did not exist. I was puzzled, how could the FAA lie to me? I've used their publications on countless briefings, not only because it was the perceived as the correct thing to do, but also because I trusted them. Those well-respected and knowledgeable FAA authors were the reason I knew what I knew, and their information was what I was about to impart onto others.

This bothered me for a long time, and I found it funny that years later the topic of centrifugal force came up again. This time, I was the senior instructor, and my new student mentioned that his previous instructor mentioned that centrifugal force does not exist. I realized that in the pursuit of being a knowledgeable instructor, one who strives to teach a subject correctly 100% of the time, I needed to understand why centrifugal force does not exist, and why the FAA mentions it for labeling turning forces in flight.

After much research, I found that Les Kempula, previous Embry-Riddle Aeronautical University Professor and author of the textbook "Aerodynamic Principles for Professional Pilots" explained this non-existent force best;

"Centrifugal force does not exist. The concept of centrifugal force throwing a body to the outside of a turn is not really a force at all. Rather, the tendency of a body to move to the outside of a turn is really its tendency to move in a straight line. For example, as you sit in a car while turning, the tendency of your body to move to the outside of the turn is really your body wanting to move in a straight line while external forces accelerate the car to the center of the circle. People tend to attribute this tendency to a force acting toward the outside of the turn, but in reality what is felt is the centripetal force caused by friction of the seat accelerating the body toward the center of the circle. In a banked aircraft, the horizontal component of the force pushing up on your body by the seat provides the centripetal force."

So what is happening here? Well, we use centrifugal force as a simplistic way of describing to the pilot what they are feeling during flight, not necessarily explaining the forces that are acting on an airplane. You see, explaining the physics of circular motion to a student may be complicated, and by creating a simplistic incorrect-but-not-so-harmful way of explaining this phenomena, the FAA figured that damage would be minimal. We have been teaching it this way for a long time, and I couldn't find a single NTSB, NASA, or FAA report that said a pilot did something wrong, crashed an airplane, or ended up in an accident due to the fact that they misunderstood centrifugal force.

So what is my recommendation for all this? Well of course, I want people to explain things correctly. While it may take a little bit longer, and a little bit of practice to simplify your explanation, we can cutout using the misleading explanation forever.

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#aerodynamics #steepturns #physics #centrifugal #centripetal #flightinstruction #flightinstructor