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# *Practical* Aerodynamics; Facts Every Pilot Must Know

Pilots don’t need aerodynamics at the level of Greek Letters and many decimal places to be safe in flight. But understanding the basic physics of flight is essential. F-16 pilot and good friend AF General Mike Hall calls this “fighter pilot math;” a practical working knowledge ready for immediate use. Remember, gravity works tirelessly, day and night all year long. We are continuously using physical forces to safely stay aloft.

Â I recommend the Essential Aerodynamics course from AOPA to all of my students (and many new CFIs) since there seems to be a general ignorance that can cause accidents. At my #SnF22 forums (and most previous pilot seminars) I always give a short 5-6 question quiz on aerodynamic basics and the results are the same; pilots need better knowledge to be safe. (Try the quiz here if you haven’t, then re-engage for the answers below) Thanks to everyone for participatingđź™Ź

BTW: I am only a pilot CFI/DPE so I checked my answers with a much more qualified guy; Ron Blum. He supervised/created Flight Test and Aerodynamics departments at Cessna, Honda, Beech & Kestrel before being Chief Engineer for Mooneyâ€™s M10. I learned a lot talking with Ron!

### 1) Misunderstood Angle of Attack

These two photos depict a C-152 in climb and descent. Photo A shows a Vy climb in the “clean” configuration. Photo B shows a reduced power (pattern) descent with flaps deployed (same plane, same loading). Both have approximately the same angle of attack (notice the same airspeed of 60K). Why does this matter? Pilots seem to universally fear the nose high flight attitude and often do not pitch enough for maximum performance when they need to (timid pilot). Additionally, many pilots mistakenly believe a nose-low attitude guarantees safety, when in fact this aircraft is just as close to a stall as the nose-high aircraft. Pilots practice “predictable stalls” in training and are not ready for “surprise stalls” encountered in an upset.

Flaps deployed dramatically change the wing shape and effect, requiring a lower flight attitude. Though you cannot determine AOA from an external snapshot of a plane in flight (you need trend), internally the amount of chrome showing (how far back you have the yoke or stick) is a pretty close approximation of AOA. Watch this AOPA video of a stall with the nose pointed straight down.

### 2) Where is the CG (and why does this matter)?

In a conventional, properly loaded aircraft, the CG is forward of the center of lift yielding stability and control. This means for an average pilot, the nose is the “heavy end” of the plane (in flight the tail provides downforce). Why does this matter? Stability is designed into every airplane (see CFR Part 23) during certification and testing; “planes don’t stall, pilots stall planes” (by pulling too much) – unload to recover!

### 3)Lift is Equal on the Wings in a Stabilized Turn

In a stabilized turn, lift is equal on the wings (or your plane would still be rolling). In a 30-degree banked turn, trim the nose for hands-off level flight and fold your arms. A well-rigged plane will continue to turn happily with no input until you run out of fuel. (this is a great CFI demonstration for early learners to dissipate their fear of turns)

Why is this important? If pilots fear turning and stallsÂ  they become timid pilots, skidding their plane instead of banking. (I would guess ~50% of PPL test applicants have never done a turning stall). The nose simply falls away from the lift vector and the real takeaway is that there is usually even fewer real aerodynamic signals (no “break”). Most trainers simply start to mush and their pilots fail to realize they are even stalled!

### 4) The “Active Control” in a turn is the elevator.

See the above demonstration of trimming a stable turn, ailerons and rudder should be neutral in a medium-banked turn in a well-rigged aircraft. The elevator is turning the plane. Rolling into and out of a turn obviously requires the coordinated use of ailerons and rudder (and differential lift). Turning with just the rudder is a skid…not conducive to long life and health.

### 5) No Spin From a Coordinated Turning Stall.

See #3 above, but “stall break” in most planes is even less pronounced than level. The aircraft nose falls away from the lift vector (nose to toes). Most planes have built-in dihedral stability so many planes roll out of the turn. (No “excitement” if you are coordinated – the “big if!”). A demonstration of a stall in a slip or skid is useful for advanced pilots (try this only with a CFI please – required on the CFI initial). Pro tip: Most trainers just mush in a power-off slip when brought to a stall; yaw and roll balance out nicely.

### 6) Stall speed only increases by 19% in a 45-degree banked turn!

This seems to be one of the most misunderstood aerodynamic nuggets. Ignorance here can create timid pilots who do not bank effectively and fly the pattern way to fast. Pilots who do not bank enough also tend to skid the plane (turning flat with the rudder) and *this* is a dangerous pilot action. Unfortunately, we all normalize this kinaesthetic feeling daily driving cars.

Maintaining 1.4 Vso in the pattern actually provides a 20% margin over stall even in with a 45-degree bank (just sayin, not recommended). For a deeper analysis of turning flight see Rich Stowell’s (free) course on Community Aviation. And try some Extended Envelope Maneuvers with your favorite MCFI to tune-up your “Practical Aerodynamics.” Fly safely out there (and often).

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## Author: David St. George

SAFE Director, Master CFI (12X), FAA DPE, ATP (ME/SE) Currently jet charter captain.

## 5 thoughts on “*Practical* Aerodynamics; Facts Every Pilot Must Know”

1. Don Dillman says:

Hi David. Iâ€™m unclear on the rationale for question #1, AOA versus configuration. When flaps are extended, the camber of the wing is increased producing the same lift at reduced AOA. How can flight at the same speed, with different configurations and therefore cambers, produce the same AOA? In the description above, you recommend yoke position as a proxy for AOA, which is good. Why isnâ€™t aircraft attitude another proxy for AOA in a straight-and-level demo I.e. fly a constant speed/altitude, note the attitude reduction (and power change for increased drag from the flaps). Constant relative wind, constant IAS, lower attitude and lower AOA.

Thanks for clearing this up for me. Great review of aerodynamics.

1. David St. George says:

I have taught flying for over 30 years (with 16K dual given) but talking with Ron Blum again conveyed the complexity of precise aerodynamic terms and analysis – lots of Greek letters and endless decimal points (well beyond my understanding). I was hesitant to publish anything in this area. You are correct, the deployment of flaps entirely changes the airfoil. Experts in aerodynamics (you may be one) actually regard the engineered wing as having a whole range of AOAs due to washout, stall strips and other methods of managing AOA and assuring control.

For the purposes of simplifying this discussion though, we are regarding AOA as a sum of all these forces. Otherwise we just dig deeper and obscure some important basic principles. Remember, “experts” still can’t agree on what actually keeps a plane in flight: https://bit.ly/SAFE-lift (at least I can do that…) Hopefully, a “practical” (non-complex) discussion avoiding excessive erudition (which can obscure the “big picture”) can create some benefit? “Fighter pilot math” – practical application – always does some harm to endless analysis.

Experts also frown at the mention of the AOPA course for this same reason. In both cases we are trying to build aerodynamic understanding for *non-experts.* I included “approximate” to signal the intentional lack of precision for this discussion. As evidence of need, notice how wildly wrong most pilot answers are to even these simple questions. I personally think we need much more *basic* education for pilots to assure flight safety.

2. Don Dillman says:

Thanks very much for sharing the wisdom and rationale. Makes complete sense.

3. Dean Howard says:

The FAA does not issue Licenses (PPL). You can obtain such in many countries, but not through the FAA, only Certificates and Ratings !

1. David St. George says:

Correctđź‘Ť

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