Basic center of gravity is critical to aircraft control but this is another important concept most pilots (and some CFIs) don’t solidly understand. And confusion about stability and basic flight dynamics seems to be at the root of many of our LOC-I accidents. To simplify all this concept for students, I call it “balancing the teeter totter.” And this is obviously a “donuts and coffee” level pilot discussion, not a “graphs and Greek letters” deep dive. My hope is to generate some awareness, surprise and more questions for further deep study. Once there is surprise – “wow, I did not know that” – there is learning and these concepts are best learned and mastered in a calm environment (not upside down).
I know from speaking presentations to assembled fliers that this question; “where is the CG?” creates consternation and confusion – and half the pilots get it wrong! So obviously this is an “opportunity for growth and learning” if you join in and participate. Ask yourself honestly and pick an option please. Experienced CFIs please use this with your students – you will be surprised. Which end is heavy (and then we will talk about why it matters).
It’s ironic that in pilot training, we spend endless hours calculating and explaining the minutia of moments and moving imaginary baggage around to get into the approved CG range, but we miss the bigger more important picture – the basics of how every familiar GA airplane works. And I can corroborate this from giving flight tests over the last 20 years. Please make your choice…where is the weight? Then click here for the answer.
The nose of the plain vanilla, part 23 GA aircraft is the heavy end and the tail of every plane you fly is “lifting” DOWN. The implication of a heavier nose for most LOC-I situations is that the pilot is (usually) the responsible party creating the LOC-I problem with excessive back pressure. To restore control, step one is to stop pulling on the yoke (which creates and maintains the excessive angle of attack) and RELEASE, to reduce the angle of attack (AOA). There is inherent stability built into a well-designed aircraft if we do not over ride it with a fearful, startled pulling force. Reducing power is also critical (for reasons we will explain later). To simplify, planes don’t stall, but pilots stall planes by pulling. (The one exception being a batched go-around – trim stall!)
So why is it the pilot initiates this problem by pulling and stalling? There is no sure answer available but it seems to be a human tendency that occurs as part of the startle/fear experience. I personally call it the “monkey pull,” since it is an atavistic survival mechanism somewhere in our (ground-based) DNA. Pull away from what is approaching? Unfortunately for flight dynamics, this instinctive reaction in LOC-I is completely wrong for aircraft control and overrides the stability built into the machine. Much of our initial flight training involves attempting to train out this fear/startle response and overcome the pulling response in emergencies. I do not think personally we can ever entirely succeed and the training gets faint if we do not practice continuously.
Adding a durable intellectual understanding of the how basic CG and angle of attack work on an aircraft (tail force down/heavy nose) is essential, but obviously often missed, in flight training. When you screw up an aerobatic maneuver (and I’m good at this) my mentors always counsel, “reduce power, and let go, the heavy end comes down.” The power part is obvious if you again click here for the CG diagram. High power (often added inappropriately in panic situations) creates induced airflow over the tail that further drives the tail down (and increases AOA). Power also compounds the LOC problem with yaw and torque.
The bigger CG picture and the inherent stability of the plane should be explained and demonstrated to all pilots in training by the professional aviation educator in a very careful and non-threatening manner. We discussed an airplane’s stability in a turn – trim and fold your arms and your plane will keep happily turning until it is out of fuel. A stable GA trainer in a stall will recover very nicely if you just reduce power and release back pressure. I personally think this is how the first stall should be demonstrated in training; start gliding power off- gently increase AOA (raise nose too high – not even above the horizon) and the plane will stall gently. Simply release back pressure and the plane starts flying…easy peasy! It is counter productive (and often permanently detrimental) to scare and confuse your new aviator with a complex procedure and wild flight attitude. We want to convey the concept and all the variations can be added later. No learning occurs in a terrified student and we perpetuate the fear that prevents proper recovery later. The first stalls can be a great confidence builder. When I do that procedure with students they breathe a sigh of relief and comment “that was a stall?” and they can’t believe it. The often also comment “All the other students told me I would hate them and be terrified…”
Next week we will dig further into AOA. For a quiz question to lead that discussion, which of these airplanes here has a higher AOA?
Did you know that EVERY aircraft actually has an AOA indicator on board? And it might be more reliable than that techno-wizardry you just paid to install? Stand by for that… Fly safely (and often)!
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6 thoughts on “The Basic Physics of Flight Control!”