Improve your landings with AOA & power techniques
Flying Angle Of Attack (AOA) combined with precise audible based feedback for AGL such as with the SeaRey associated Flare Assist Radar(1) or Garmin’s new GHA 15(2) will make you King Kong at landings. For all airplanes that permit such, Power techniques will lock this for you.
Summary of Cirrus Approach “Stabilized Approach: Energy Management” Video
Sorry, folks, this one(3) is paywalled. If you have a Cirrus Approach account, you can find it in the Takeoffs and Landings lessons. Summarizing it here, Cirrus looks at the Drag Curve recognizing this as the Thrust Required Curve then assumes you’re in balanced flight meaning your power setting is currently holding you straight and level unaccelerated. From here, they point out if you add power, your energy balance goes up. If you reduce power, your energy balance goes down. This applies to your Total Energy and can be applied to your Kinetic Energy (airspeed) and/or to your Potential Energy (altitude). Left unsaid in this is that as we’re looking to land, we actually want a negative energy balance. Hence you must re-center your reference to an energy loss rate equal to that matching your intended glide path. They show the drag polar relabeled for this energy trade situation but it doesn’t work well as it misses the dynamic element that you want to decrease your potential energy while maintaining kinetic till the flare, then decrease kinetic till zeroing out your energy.
The Cirrus Approach video is good, however, in that it makes this discussion about energy. It is also great in that it recognizes errors in terms of energy. The video breaks deviations into three categories: Total Energy Errors, Distribution Energy Errors, and Combination Energy Errors.
Total Energy Errors
Total energy errors involve errors in both potential and kinetic energy in the same direction. The total is too high or too low with the airplane being too fast & too high or too low & too slow. These sorts of errors will require both power and pitch fixes. The video notes extra concern for low & slow situations as likely these will also be on the back side of the power curve meaning the more we slow the more energy input we need just to stay balanced. As we’re low, we have little space and time to correct while as we’re slow, we need increasing power just to maintain the errors we already have so we’ll need significantly more to fix the errors.
Distribution Energy Errors
Distribution energy errors mean we have the correct amount of total energy but it is imbalanced. The video treats it like overfunding one account resulting in the other account being underfunded. You’re either low & fast or high & slow. Use your elevator to redistribute to a proper account balance. (I’d argue use your pitch Trim as opposed to pitch to do this.)
Combination Energy Errors
Combination energy errors involve both a total energy error and a distribution imbalance. You’re on-speed and either high or low, or, you’re on glide path and fast or slow.
Good News: the FAA talks a similar talk
From The Airplane Flying Handbook Chapter 4(4):
“An energy-centered approach clarifies the roles of the engine and flight controls beyond the simple ‘pitch for airspeed and power for altitude’ by modeling how throttle and elevator inputs affect the airplane’s total mechanical energy. From an energy perspective, the problem of controlling vertical flight path and airspeed becomes one of handling the airplane’s energy state — the total amount of energy and its distribution over altitude and speed. Thus, rather than asking what controls altitude and what controls airspeed, a pilot can now ask what controls total energy and what controls its distribution over altitude and airspeed.”
“The central principle encapsulating the role of the throttle and elevator for managing the airplane’s energy can be summed up as follows: coordinated throttle and elevator inputs control the airplane’s energy state. Modifying a popular adage, the principle can be restated as ‘pitch plus power controls energy state.’ This central principle serves to guide a set of general energy control rules to achieve and maintain any desired vertical flight path and airspeed targets within the airplane’s energy envelope.”
“Every pilot is an energy manager — managing energy in the form of altitude and airspeed from takeoff to landing. Proper energy management is essential for performing any maneuver as well as for attaining and maintaining desired vertical flightpath and airspeed profiles in everyday flying. It is also critical to flight safety since mistakes in managing energy state can contribute to loss of control inflight (LOC-I), controlled flight into terrain (CFIT) and approach and landing accidents. The objectives of this chapter are for pilots to: 1) gain an understanding of basic energy management concepts; 2) learn the energy role of the controls for managing the airplane’s energy state; and 3) develop the ability to identify, assess and mitigate risks associated with failure to manage the airplane’s energy state.”
Do Note the FAA quotes mentioned total mechanical energy. We tend to view mechanical as total though this is not correct, total is mechanical plus chemical while mechanical is potential plus kinetic. As chemical is not instantaneously available, generally we’re ok seeing mechanical as total though we’ll see impact of this distinction as we differentiate dives from descents and zooms from climbs.
How The Navy Sees It
The Navy also uses energy to frame its discussion around landing. First they look at three things: Meatball, Lineup, Angle-Of-Attack (AOA). The Navy will often refer to AOA by the Greek letter Alpha. Similarly, it will view yaw angles as Beta. The “meatball,” often shortened to just “ball” refers to the Fresnel Lens which gives glide path information though much more precisely than do PAPIs. The ball is also referred to as “the source” though more specifically, the source is the yellow or red light which is related to green datum lines. It is these three things and only these three things which we focus upon and manage for landing jets aboard ships. We can translate these to civilian counterparts and tie them to respective energy flavors as such:
Meatball -> Glide path -> Potential Energy
Lineup -> Lineup
AOA -> AOA if you have it, Airspeed if you don’t -> Kinetic Energy
Interlude: What is Tradition?
While a junior officer in Strike Fighter Squadron 136, I had a Department Head one day who asked me “What is Tradition?” I’d like you to take a moment and consider this yourselves.
I gave an answer that I’d bet resonates with your answers. Something along the lines of patterns of action accepted as functional from historical experience. Perhaps ways of doing things set through repeated successes. Maybe cultural influences upon our actions.
This Department Head didn’t directly answer his own question. Instead he deviated upon a story.
There was a psychologist who had a large room with twelve monkeys. Psychologists seem to enjoy tormenting monkeys. This room had a bunch of bananas hanging from the center of the ceiling though there were no beams nor ropes nor lines such that the monkeys couldn’t reach the bananas. The psychologist set a ladder in the corner. Monkeys are clever, and they’re observant, and with bananas involved, they’re motivated. They went for the ladder. As they approached the ladder, the psychologist popped open an upper floor window and sprayed them with a fire hose. Monkeys don’t like water. Especially not high pressure water. The monkeys gave up going for the ladder and with that gave up on the bananas. Now, the psychologist removes one monkey and puts a new monkey in the room. New monkey is motivated, hungry, sees the bananas, and sees the ladder. New monkey goes for the ladder. But eleven old monkeys don’t want to be hosed again, so they beat down new monkey. Eventually new monkey gives up. So the psychologist removes another old monkey and places a new monkey in the room. The cycle repeats. Eventually we get to the thirteenth swap. We now have new new monkey who gets beat by eleven new monkeys despite not a single monkey in the room even knowing about the fire hose.
That, said the Department Head, is tradition.
How Airspeed Came to Replace AOA as the Primary Datum for Landing
Let’s consider for a moment the Wright Flyer. With this we have a two propeller pusher propeller contraption in which the person sits next to the engine with their respective weights laterally balancing. We have a sort of canard in front providing stability and control.
Something interesting with the Wright’s is that they had a Yaw String. This meant they simply had a piece of yarn in front of the pilot so as to be able to see any side component of how the wind hit the airframe. Gliders use such things today while the F-14, AV-8, and U-2 aircraft all used them. This string works in lieu of a slip and skid indicator and visually shows Beta. Unlike yaw strings we may see today, the Wrights’ string was not running along a canopy. This enabled the Wrights to do something else in that they had a rod sticking straight back such that the string could be compared to the rod. This meant they could see Alpha too. They’d compare the angle up and down on the string which showed relative wind and compare to the rod which paralleled the longitudinal axis of the plane. Why did the Wright’s do this? Because they had previously done wind tunnel tests with airfoils and understood what they called and the Brits still call Angle of Incidence mattered to lift production. Angle of Incidence is what we call AOA being that angle between the chord line of the wing fixed to that seen by the rod and the incoming wind seen by the displacement of the yarn.
Shortly after the Wright flyer, aircraft evolved to be “conventional gear” meaning tail wheel aircraft with tractor pull style propellers. This was advantageous as airfields of the day were really grass circles. Short takeoff distances enabled the use of such which allowed aircraft to always takeoff and land into headwind while zeroing out crosswinds. But, being turf circles, they wanted to keep the propeller up and away from the turf. Similarly, float planes started around the same time and with these they wanted to keep the propeller up and away from water and to minimize sucking water up into the prop wash.
Consider our turning tendencies. One of these, that slipstream, has other effects. Basically it made the Yaw String and any similar ideas for AOA to include vanes unusable. As AOA was no longer measurable, they needed something else. Pitot tubes were in use on ships in the 19th century. Making an adaptation from water to air was not a big stretch.
In a sense, we’re the monkeys not knowing the Why of things. We use airspeed not realizing it was a workaround for not being able to use AOA. Even should some of us be aware there’s this workaround, we fail to realize workarounds are not solutions; they’re symptoms of problems. We might have once said “airspeed in lieu of AOA” or “airspeed as proxy for AOA” but those notions were silenced in favor of expediency in discussion and subsequently forgotten.
AOA gives us direct feedback into how the wing is performing. Airspeed is a proxy substitute with several limitations. There’s only one critical angle giving us stall. Yet we can stall at any speed and at any pitch. There’s only one angle for maximum endurance, one for best glide (in no wind), one for maximum range (in no wind). Yet all of these vary in speed dependent on load meaning weight and angle of bank. Weight and g-loading typically seen via turning impact speeds but not AOAs. Yet our procedures and our regulations are all written around speeds. Why? Because we didn’t have access to AOA information when the rules and procedures were written. We tend to add further confusion as we often discuss airspeed and AOA interchangeably while they are not.
Something from this to explore: You’ve done constant altitude constant airspeed turns. To do these, you added back stick rolling into the turn while adding a little power to compensate for the increased drag. The back stick increased your AOA to compensate for the increased lift required. Have you tried a constant AOA level turn? To do such, roll into your turn but do not add back stick. Instead add a little more power than you would have added if doing constant speed. Your speed will tick up a few knots while your AOA will stay at the trimmed setting. Use power adjustments to maintain level. With such AOA turns, you do not cut into your stall margin during the turn. Such is how Navy jets fly in their landing patterns. Though they’ll slowly reduce power through the turn so as to increase rate of descent. Note with these, as you added more power for the turn, you need a bigger power reduction rolling wings level to avoid “ballooning” or unintended climbing. While it would be nice to see both AOA and airspeed in experimenting with these at altitude to include during slow flight, you don’t need to see the AOA to do them. The wing is trimmed to the AOA regardless of you seeing its AOA. After doing them at altitude, you can try doing them in the landing pattern. Once you understand these, you’ll realize you can fly your pattern while needing to control for less variables simultaneously. Rather than doing constant speed turns in your pattern, I would suggest you should be doing constant AOA turns. These need not be at “on-speed” AOA as flying a lower AOA faster speed gives you a larger energy package increasing your contingency options. More on this later.
LSO Rules to Live By
The Landing Signals Officer (LSO) was that person you saw with two large boards, one in each hand, that guided aircraft to landing aboard the ship. Hence LSOs are referred to as “Paddles.” As equipment matured with the introduction of angled flight decks in which one could “bolter” and continue into a go-around if one missed the wires, and with the ball, we no longer needed Paddles directing pilots. In heavy sea states, Paddles will still direct either via the radio and/or using an alternate lighting eclipsing the ball so as to appear as if the ball but really Paddles driven. For the majority of landings, Paddles observes, scores, debriefs, but most importantly acts as a backup interjecting if needed. Paddles now typically holds a double trigger device with one trigger that turns on wave off lights while simultaneously turning off the source though leaving the datums on; the other trigger lights what we call the “cut light,” which is used to tell pilots to give it a shot of power. Such illuminates as a green bar above the ball. In addition to backing up the pilot every pass at the boat, LSOs are the teachers for landing at the boat.
While we fly “Meatball, Lineup, Angle of Attack,” we have six rules for controlling the ball and AOA. As Navy aircraft do not flare(5) while we shift the focus from the three things to strictly “ball, ball, ball” at the Ramp. Touchdown on a good Navy landing should be a surprise to the pilot. Navy jets are normally landing with touchdowns at 700 fpm VVI. As such, and as you flare, the last two rules of the LSO Rules to Live By Do Not Apply to your landings. They do, however, apply to your Instrument Approaches.
Why do Navy jets land in this manner? Because we want a consistent and precise touchdown spot for the tail hook. By keeping a constant AOA through touchdown, we know the distance spacing from what the pilot sees to the hook is constant. Therefore our ball actually guides the hook to just before the wire through the pilot with parallel lines hook to wire and pilot to ball.
We need to pause here a moment to look at terminology. Consider in a military context you will not hear “cease fire.” What you would hear instead are either “HOLD! Hold Hold Hold!” Or “ABORT! Abort Abort!” Why? What happens were one to call “Cease Fire” and you only to hear half the transmission?
Similarly, we will use speed based terminology for AOA fully recognizing we are discussing AOA not speed. This is because ‘High’ and ‘Low’ will be used relative to altitude or glide path. Regarding Lineup, we have similar separation of terms with “Come Left” or “Right for Lineup.”
Our Rules:
- Always Lead the High or Fast
- Never Lead the Low or Slow
- If High and Fast, Fix the Fast then the High
- If Low and Slow, Fix the Low then the Slow
- Never Re-Center a High Ball In Close But Stop the Rising Ball
- Fly the Ball All the way to Touchdown
Let’s think a moment how we do fixes:
- Always Lead the High (Power) or Fast (Pitch (Trim))
- Never Lead the Low (Power!) or Slow (Pitch (Trim))
- If High and Fast, Fix the Fast (Pitch (Trim)) then the High (Power)
- If Low and Slow, Fix the Low (Power!) then the Slow (Pitch (Trim))
You’ll notice we did not discuss what Cirrus Approach called the Distributive Errors. These rarely get mentioned as they’re seen as common sense easy trades. Trade the High against the Slow; Trade the Fast against the Low. Yes, use your elevator most likely via a few clicks of trim. More often than not, except for round out and flare, you’ll be using pitch trim not direct elevator if such corrections be needed. You’ll see later these are really mini dives and zooms.
Let’s consider each rule for a moment looking to why we will honor such and a little further into how to do them.
Always Lead the High or Fast: We don’t want to overshoot our corrections to Low and/or Slow as under-energy is worse than over energy. Hence we chip away incrementally at the over-energy conditions.
Never Lead the Low or Slow: Similarly, as under-energy is more risky than over-energy, we want to push out of the under-energy condition without stopping; were we to try to incrementally correct, we’d remain under-energy and perhaps worse so as our counter-correction to initial correction attempt could be too large in scale while getting closer to the ground and with the case of the Low, smaller margins due to narrowing space for given angular errors on the glide path.
If High and Fast, Fix the Fast then the High: It is very hard for us to see how large our energy errors are when they’re in both kinetic and potential energies. Of these, the potential is easier to visualize as we can readily see altitude or glide path deviations. AOA can be seen in units or degrees while speed can be seen in knots but these don’t readily translate to touchdown distance extensions realtime as we fly. Hence, isolating out the kinetic error first helps us see a singular deviation. Such also helps us as correcting the kinetic will require both trimming up and power reduction plus subsequent power increase to catch. Solving this first leaves us with only one independent variable being power to correct a singular dependent variable being altitude. Fixing the Fast then the High makes correcting easier as you get closer to landing where margins get smaller. Doing so also readily reveals if you’re excessively over-energy to the point of needing to shift your landing point in the case of a long runway or go-around in normal and short field cases. Fixing the Fast first will reveal this to you sooner such that you can more slowly and deliberately thus more smoothly execute such procedures. You’ll have an easier time with such as you’ll be less likely to be in and out of ground effect and won’t have the need to jam the rudder as you can more readily match the rudder to a smoother power addition in the case of our propeller planes.
In addition to this, fixing the fast then the high gives contingency energy with the high should the fix for the fast be over done. If you get slow, you can trade against the high.
If Low and Slow, Fix the Low then the Slow: Based on the above discussion, you would think the same variable isolation would come to play. This is not the case If Low and Slow, Fix the Low then the Slow. We need to realize that you are in a flying condition. As you’re in a flying condition, you’re not going to stall except should you egregiously pull back on the stick. Let’s get away from the ground while in our known flying condition. Correct the more readily seen energy deficit first. Note this actually is single variable as you’re adding power to “climb.” Why is “climb” in quotes? Because you may be climbing though more likely you’re flattening out as we’re climbing relative to glide path not necessarily relative to the earth. Single variable get rid of one of the dangerous conditions. As we cross the glide path, now we can push forward which helps reduce the climb so as not to “balloon” excessively above glide path while simultaneously helping us to get faster. From here we can both trim to on-speed and adjust power. The counter-correction to our isolated input helps us with the second output. Note: tractor propellers may need to trim a little forward with the power addition due to increased prop wash over the elevator. Similarly, those with underslung engines may also need to do so while those with high mounted engines may need a little aft trim with power. In all these cases, it is to hold what you have in terms of AOA till climbing or flattening through, then set desired AOA. If you happen to get a little faster than you originally were, don’t worry about it, let it climb. Just don’t let it get any slower.
Never Re-Center a High Ball In Close But Stop the Rising Ball: This doesn’t apply to GA in landing as we round out and flare. It does, however, apply to our precision instrument approaches. The idea here is that as the margins narrow as we get closer to landing point, we recognize we are inadequate to the task of correcting in totality. Trying to do so sets us up to “fly through down” thus putting us under-energy with a sinking vector. “Fixing A High Ball In Close” will cause you to both land short and hard. For the instrument approach, it will cause you to fly through down thus hitting decision height early with excessive sink rate. It is better instead to only partially reduce power trying to stop from a rising ball that would arise from flying a wire parallel to but high of glide path. You want a slightly steeper glide path but one that intersects glide slope after decision height thus trying to maintain your error neither letting it grow nor too rapidly correcting setting up the fly through down. Some corrections are ok, just not in totality. If you’re a dot and a half high 100 ft above decision height, strive to be three quarters high at decision height though not less than half a dot and not more than the dot and a half.
Fly the Ball All the way to Touchdown: Again, not for GA due to our round out and flare. But still applicable to instrument approaches. Don’t give up on your glide slope on the precision approaches and work the minimum descent altitude on the non-precisions both all the way through till you’ve decided to go missed. If you’ve decided to land, keep working these as applicable till you’ve fully transitioned to visual. Don’t make a visual transition binary, instead initially work one third visual two thirds instrument shifting to two thirds visual and one third instrument shifting to visual plus AOA (or speed).
While working these rules, we use three-part power corrections. With turbine aircraft, these really are noticeable linked three-part corrections. Often with piston propellers due to the more immediate responsiveness and due to the need of counter and counter-counter correction being more spaced out, we may not realize these are linked. However, except near touchdown when pulling to idle, or on go around when powering up, all our power corrections will come in series of three. This is easiest to visualize from an altitude error. Consider we are high but configured with proper landing power set. We have found ourselves on a high wire paralleling desired glide path. We need first to reduce power to descend. Then we need to add power to break our descending momentum. Then we reduce again to maintain our newly established wire and assess what we may need for the next series. I find this easiest done by imagining however much I pull power initially is equal to one unit. I add that same unit when I counter-correct to break momentum then pull half a unit for a counter-counter correction. As I am chipping the high, I will shift from high wire to steep wire to high wire to not as steep a steep wire… progressing iteratively till reaching desired glide path. Each progression will have its own three-part power correction. If I were low, I would have one series solving the low but this drives me high as I don’t lead a low, at which point I’ll find myself in the similar iterative situation. One unit initial correction, one unit counter-correction, half a unit counter-counter correction with the magnitude of error setting the size of each series unit. As you’re flying piston propeller, you may not need to think much about this except on the counter correction to counter-counter correction. With these, realize you need both and you can do both before seeing effects of the counter-correction matriculate. This will be particularly important should you be correcting a low in close as you want the counter-correction to not excessively balloon but you’ll need the counter-counter correction of power added back in so as not to come down hard.
How do you know what is a “unit” of power? You don’t want to be looking at rpms, manifolds, percentages. You need to be scanning and looking outside. Here comes the importance of a tactile reference. You want part of your hand or some fingers touching a stationary part of the plane while moving the throttle or power lever such that you can tell how much you are moving said lever. In the T-45, there was a shelf outboard of the throttle that I’d rest my pinky and ring fingers upon while using the other three to move the throttle while on approaches and landing. For the F/A-18, I’d hold the left throttle with two fingers and the right with three. I’d make changes in one about the other such that left became reference for right. In the Cirrus, if left seat, I run my right pinky and ring fingers down the right side of the center console using the three remaining to hold the power lever. If right seat, I rest the pinky side of my hand on the quadrant under the power lever. In my RV which will be similar to Cessna style power knob, I extend a finger to touch the instrument panel wall. Each of these enables knowing relative scale of power movement without looking. Find yourself a stable stationary reference upon which you can feel the magnitude of your power adjustments. If you hear me say “fingers,” this is what I’m talking about, get your stationary tactile reference for power movement.
For a look at the consequences of not following the LSO Rules to Live By, look to the Crash of the F-35C in the South China Sea:
In the Under Energy Condition, the FAA and the Navy Disagree:
Note FAA disagrees with If Low and Slow, Fix the Low Then the Slow, as per Figure 4–13 of the Airplane Flying Handbook:
“Increase throttle setting significantly to gain total energy. Push elevator forward gradually to accelerate to correct airspeed and then climb.”
“Depending on the aircraft type, as full throttle is applied at the start of correction maneuver, slight forward [low slung multis come to mind] or aft [certain float and high mounted multis] elevator pressure may be needed to maintain a constant pitch attitude. As the airplane gains total energy, use the elevator to accelerate to correct airspeed and then climb.”
The FAA’s logic seems to make sense but is taken to extreme as to Why the recommendation counter to the Navy in that they say you’re higher on Induced Drag hence will add energy more slowly if you fix the Low then the Slow. But we aren’t as concerned to the rate of correction so much as the direction of proper correction. We’re looking to shallow or flatten out our Low not necessarily Climb. The Navy actually agrees with the FAA’s logic regarding Low and Slow when applied to climbs. We are talking landings, however. Our “climb” is relative to a descending glide path. In addition to climbing away from terrain, the FAA’s way would also be beneficial at high altitude near service ceiling. It’s just not a good fit for landings. It sets you up to not readily see your energy errors and for difficulty in the counter-correction.
Note we don’t care about constant Pitch here as the FAA suggests, we care about flying and constant AOA. Your Pitch should increase with constant AOA plus power. You want this to get away from the ground and add energy. AOA is flying, Pitch is not. Pitch like airspeed is a convenient crutch for approximating AOA given known other conditions but like airspeed, pitch in lieu of AOA has its drawbacks. Remember you can stall at any Speed and at any Pitch. I’ve even stalled at ninety degrees nose down.(6)
- You’re correct to recognize the lift required at ninety nose down pitch is zero, just like it is a ninety nose up, but how often are you going to be holding such vertical steady state pitches? Pitch rate also imposes an AOA demand and it is through this pitch rate requirement that you can impose need for AOA to which you can exceed critical AOA thus stalling while your nose transits through ninety degrees nose down.
- You can think Pitch as proxy for AOA and better at such than ASI if you like. After all, if you’re straight and level and trimmed to on-speed AOA, there is only one pitch you can be at. For the Hornet, this is 8 degrees. 8 degrees AOA is on-speed, hence S&L when trimmed, we see 8 degrees pitch. Similarly, when on a 3 degree straight glide path, we see 5 degrees pitch. In this way, pitch can be used to confirm functioning AOA and does so easier than does a weight speed combination. It also gives method for where to trim if you’ve lost AOA though you could also use a S&L weight speed pairing to accomplish this. Note turbulent rising sinking air and gusts can make this cross check and backup technique difficult. To use this technique in your own aircraft, you would need to know your actual on-speed AOA in degrees. It is through this sense that the FAA can be technically correct for Pitch Power combinations though really they’re getting at AOA through Pitch.
What is interesting is that in the Airplane Flying Handbook, the FAA gave two scenarios, one being landing, the other being flight around mountainous terrain. Were they not to have been applying the above points to landing and instead had they been applying such strictly to Vx climbs, then their advice would have been great as we’d want to reduce induced drag and find maximum thrust excess. But we’re talking landings in which we want to meet terrain at a desired point rather than avoid terrain. Take this as yet another reminder that Context Matters. (Every landing is a CFIT and every mid-air refueling is a mid-air collision.)
Having said this, while discussing the climb for terrain situation, the Handbook shows excess power which would lead to best rate climb Vy, not excess thrust for best angle climb Vx which is in error as we need to clear the terrain, an angle concern, not get up quickly, a rate concern. Were you to be orbiting the field, then you could go with this rate approach. But then again, orbiting the field, you could do your temperature compromised cool climb too.
Front Side v. “Back Side” v. Back Side
We should note our “Fundamental Maneuvers(7)” of Straight and Level, Climb/Descend, Accelerate/Decelerate, and Turn are an incomplete list. We also have Zoom and Dive. To Climb or Descend, we change Power thus giving excess to Climb or letting Drag dominate to Descend. To Accel/Decel, we change Pitch typically while also changing Power so as to stay Level or stay on a Constant Glide Path. Turning isn’t relevant to this discussion. Zooming and Diving, however, are Trades between Kinetic and Potential Energy. Zoom and Dive differ from Climb and Descend in this as Climbs and Descents involve trades in Chemical Energy for Potential Energy while Accelerations and Decelerations are really Chemical for Kinetic. When we Climb or Descend, we maintain our Trim Setting maintaining a Constant AOA. Our fixes for those Distributive Errors are really miniature Zooms or Dives. Shallowing or steepening VVI at constant AOA (or speed) are miniature Climbs and Descents.(8)
For the Front Side, we use Pitch to Control Glide Path and Power to Manage Speed. These are Zooms or Dives connected with Accelerations or Decelerations.
For a moment, imagine flying Front Side but at zero Power. If we’re High, we can Nose Down as we will Accelerate per this Dive trading Potential Energy for Kinetic Energy and this adds Drag as we move up the Parasitic side of the curve. Added drag helps against the over-energy state of being High. There’re limits to this as we cannot Dive through the Ground and we have a Vne. If we’re Low, we can Nose Up reducing Parasitic Drag to stretch. There’s a limit to this as we’ll eventually bleed through L/Dmax to the Back Side and thus as we’d continue to bleed adding Drag from the Induced side of curve.
Use Pitch (trim) to control AOA (or speed as proxy) and Power for Glide Path in what some mistakenly consider Back Side though what are really Power Techniques. These work on any plane in any position of the curve. To prove this, consider Cruise flying obviously Front Side. What happens if you add Power with no other changes (and no autopilot engaged)(9)?
Note: Gliders use “Power Techniques” too though by simultaneously adding Drag and reducing Lift through Spoilers. Spoilers are mechanized to act with the same effect as a Throttle or Power Lever with more Spoiler Control Lever Back less Spoiler Control Lever Forward. Nominal Spoiler is midrange allowing for adjustments in both directions. Trim for AOA (or speed), Spoiler in lieu of Power for Glide Path. If excessively high beyond means of maximum spoiler, use both spoiler and forward slip.
Speaking of gliders, we should make a caveat regarding “If Low and Slow, Fix the Low then the Slow.” As you can imagine, such won’t work well for a glider and is a recipe to end up significantly shorter out of energy perhaps unintentionally stalling while near the ground. But we’re not going to fix the slow first either, rather instead we’ll fix both simultaneously. Step one — Spoilers In. The immediate effect will be to shallow out starting to fix the low though such also better enables “acceleration” via mini-dive. Now push for L/Dmax. AOA is ideal though most gliders only have airspeed indicators, this is ok. You’re simultaneously fixing both speed and as best you can altitude as you’ll be moving forward from the back side of the drag (thrust required) curve to its low point. (Glider drag polars typically are expressed as sink rate vs speed hence L/Dmax is the tangent from origin as you’d see on the power required curve. Here we’re thinking forces of drag vs speed.) Note for headwind you’ll want to push a knot or two faster than L/Dmax (maybe even five knots in strong headwinds) while for tail winds, you can subtract similarly but no slower than maximum endurance glide time.
So, with gliders, you fix both simultaneously, but it will probably feel like fixing the slow then the low and unlike with powered flight, you should probably think of it this way. This feeling of fixing the slow then the low in gliders (or airplanes with lost power) is especially true as you’ll finish fixing the slow before you finish fixing the low even as the act of fixing the slow also fixes what low may be fixed. Maybe this is why the FAA answers the low and slow differently than the Navy? In the glider or without power, you’re better thinking fix the slow first if slow and low. Fixing the slow helps resolve the low but better to think it sequentially.
What is true Back Side? Consider again flying with zero Power though this time on the Back Side. If you’re High, Pull Up thus Slowing and Increasing Induced Drag thus Sinking then Dump the Nose to Accelerate reducing Drag and Catch desired Glide Path. If Low, Push the Nose gaining Speed Reducing Drag to Float further. Obviously, these are uncomfortable, hence we prefer the Power Techniques. They’re also more susceptible to mistakes, hence again, we prefer Power Techniques. Note with the back side power unavailable case, the FAA’s answer to Low and Slow is the only viable answer though it is a case of least bad not best. Use Power techniques and with them use the Navy’s LSO Rules. If you’re pulling or pushing while low to stretch a glide you may want to consider a spot with less buildings and trees short of the desired runway. If you were on best glide, push and pull both fall short.
Where is the Back Side? For jets, gliders, and (all) engine(s) out propellers, it is the left portion of the drag curve aka thrust required curve where induced drag is dominant. For propellers with operating propulsion, it is the left side of the power required curve hence the expression “back side of the power curve.” This means propellers fly on the front side for significantly more of their landing conditions than do other fixed wing aircraft except for power out. Yet piston (and electric) propellers handle much better with power techniques! See further below and think response time. For both jets and propellers, these transition points are coincident with maximum endurance flight time.
Note: I like to think of these transitions as “Reverse Demand” not ‘reverse command.’ To me, “Reverse Command” is the difference between front side and back side techniques with regards to what results when you pull or push. Reverse Demand is the increased need for throttle be it thrust or power to fly slower. See the difference? Reverse Command tells you how to pitch should you need to control altitude by speed. Reverse Demand tells you what is required to control altitude with power, thrust, or spoilers.
https://medium.com/@jamesmcclaranallen/back-side-of-the-power-curve-vs-drag-curve-8442d369d9c8
How does the Forward Slip fit with front, power, and back side techniques?
While High and with Zero Power, you can Forward Slip. Technically, this is Front Side as you’re using Parasitic Drag to Drop. It is it’s own unique case, however, as you’re distorting the Drag Curve. In the Forward Slip, you are massively amplifying the Parasitic thus pushing the intersection of Induced and Parasitic Up and Left. You likely were right of the Reverse Demand before slipping, certainly are while slipping, and shift the Reverse Command left so likely are right of it while slipping. More importantly, you’re thinking in the conduct of the forward slip fits with both Front Side and Power Techniques. You don’t need to adjust your approach to control to use the forward slip for either case. Most importantly the forward slip helps you to avoid needing to use the true Back Side Technique with the pitch up to slow, fall, dump the nose to catch.
Why Power Techniques
They’re more precise while they’re easier to fly since they tend to more easily isolate variables. One variable Pitch (trim) for AOA (or speed) and one variable Power for Glide Path. Using these techniques means those Combination Errors can be resolved sequentially via the LSO Rules to Live By rather than trying to solve them simultaneously.
Why Not Power Techniques
Engine out, obviously. But also…
Why might we like Front Side flyers? Turbines have long spool-up times resulting from inertia of the turbines and associated compressors. Front side gives us improved though still not ideal responsiveness in these sorts of planes. They can pitch for more responsive glide path while anticipating the impact of these pitch changes to speed adjusting power accordingly. They can then refine the power fixes as further speed errors propagate. As they’re working front side, they have margin for any speed concerns relative to stall while drag works in their favor as it increases or decreases in the direction they need such to go. They will have excess energy to dissipate either in landing gear absorption and/or in flare, however. But, the Navy flies turbine, how do they use power techniques? They deploy lots of drag in landing configurations such that the neutral power point is up thus engines are already spooled up and are thus more responsive. They also fly lower flatter patterns.
We can see Front Side Technique at play regardless of the side with autopilot aircraft that have no corresponding auto throttle. If you’re in Altitude Hold, VNV, or VS, throttle will control speed as “Hal” will be trimming for you behind the scene. If, however, you’re in FLC, then “Hal” tries to maintain speed hence Power controls VVI more in line with those Power Techniques. These become a factor when doing coupled Instrument Approaches with Technically Advanced Aircraft. The mind shift from Front Side while Coupled to Power Technique when Hand Flying especially in a transition to land can confuse a novice Instrument flyer as well as those new to such autopilots. With this, I highly recommend watching or rewatching Children of the Magenta(10).
The Navy Pattern
You might suspect that I find the Navy pattern to be best. I don’t believe we’ve discovered what is the best pattern. Nor do I think there is a “best,” rather patterns get adapted to specific circumstances. I say discovered as while we like to think we’ve designed patterns to optimize, the reality is we adapt what was previous thus patterns evolve. I do think the Navy way of flying is best though I would not recommend the Navy pattern due to the desire for contingency energy; naval aircraft typically have two engines providing such with ejection seats or parachutes as alternate contingency. Navy patterns lack potential energy while deliberately slowing earlier than others for easier control throughout as such reduces variables but this means little kinetic energy either. The Navy likes the low patterns as such makes for flatter base turns hence shifting the neutral power point up; it works with the extra drag devices to keep turbines spun up. Though it also evolved from needing to see the boat around radial engines. I also recognize the Navy way is incompatible with those platforms reliant upon front side technique.
Instead, what I’d like you to get from the Navy pattern is a sense of flying AOA technique meaning add a little power into your turns then a little more so as not to need to add any back stick while using power techniques throughout. Power for altitude or glide path and pitch mostly via trim for AOA or airspeed in lieu of. Note airspeed will increase in the turn though AOA will stay constant (except for large power changes with tractor propellers influencing air over the horizontal stabilators, elevator, and elevator trim or with airplanes with engines mounted with vertical displacement from cg).
As we look at the Navy patterns, we notice no base nor crosswind legs. These are continual turns. Oval not rectangle. We also notice that for the ship, the 180 is the abeam. This is because either winds are strong pushing the base turn out, or the ship is driving away creating a relative wind and thus displaces for us what was our abeam versus what would have been our abeam had we called abeam next to our actual landing position. The goal with the Navy pattern is to be configured to land and trimmed on-speed AOA no later than the abeam. The overhead break is at 800 feet AGL, after the break turn, one descends to 600 feet AGL for downwind. Should one launch directly into the pattern, get waved off (told to go around), or “bolter” missing a wire, one climbs for a 600 ft AGL crosswind turn turning throughout upwind to downwind. The base turn has several points referred to by the degrees of turn remaining to roll out on final; the 90 is when perpendicular to landing and should be treated as analogous to the start of the base to final turn. We typically treat the first half of the turn 180 through 90 as an instrument turn while looking out more for the latter half.
An effect of the ship driving away or steering into strong winds is that the glide path apparent to the pilot is not the same glide path the airplane actually flies. Typically the ship provides a 4 degree reference though this can be altered based on wind condition while the aircraft flies a 3 degree path through the air. Such comes into play for you too. Imagine flying into a headwind. Should you seek a 3 degree reference, you’ll need to be further up on power as you’ll be flying flatter than that 3 degrees as you travel over ground but through the air mass — the wind is pushing you back. You accomplish less forward travel for given VVI descent. Your apparent 3 degree glide path is only the flown glide path with no wind. Now if you happen to have tail wind, you’ll be back on the power and flying steeper. If you cannot get far enough back on the power, you may need to forward slip. Why might you accept a little tail wind? Some airports may take up to five or even ten knots before switching for other concerns like avoiding populated areas or terrain avoidance. Some airports may have down slope runways to balance against wind.
Since we’re looking at Navy landings, it is worth noticing how a Fast or Slow matriculates. Imagine the fast airplane on glide path. Its AOA is less, as it is straight on final, its pitch is less. As a result, its tail is higher therefore the hook is higher. This means the glide path targeting the wire may result in the hook overflying the wire as if it be High. It is to ensure the hook alines on the proper line parallel to the glide path line that really drives the Navy to be so focused on AOA. Yet such provides us with example of the over or under energy cases Fast or High and Slow or Low as really being the same sort of cases.
Note again: With tactical aircraft preferring turbine engines mounted at or near the longitudinal axis of the aircraft pushing air out the back, we have a certain luxury in that we can set the trim for on-speed AOA and it is set. This won’t be true for low mounted engines like commercial airliners or high mounted engines like some of your float planes to include Icon A5, the Lake, SeaBreeze, SeaRey, and some business jets. As we’ll see later, the trim to AOA depends upon competing airfoils but these off axis engines add a competitor to the situation. As the set trim for AOA is such a balance, tractor style propeller aircraft throwing more or less air over these airfoils also create changes to this balance, hence you can expect that with power changes, you may need to tweak your trim resetting on-speed AOA trim. In these tractor style propellers, you should accept minor variance in AOA seeking a proper on-speed range of AOA as opposed to a singular value though expect to make changes in trim with larger power changes such as rolling out of your base to final turn after having pulled then pushed power to accommodate the sudden increase of lift due to the loss of the horizontal component and addressing the “three part power correction.” Note many GA AOA systems don’t actually measure AOA, rather they measure pressure differentials over the wing giving a “Lift Reserve” approximating AOA. They’re getting directly to the same idea of what is the wing’s capacity or margin to stall but they’re not quite the same thing. This is important as AOA is susceptible to vertical gusts of wind: updrafts and downdrafts. Airspeed is susceptible to horizontal gusts of wind. Pressure differentials are susceptible to both and this means that turning into a headwind as from base to final you may see a displayed change to your “AOA” and thus want to readjust your trim to accommodate. The magnitude of pressure differential susceptibility to each, horizontal and vertical gusts, will depend upon the location of the comparison holes. Those atop and on the bottom of the leading edge of a wing will be more so to vertical. On my RV, I have a forward facing hole and one on a slant forty-five degree down; this is susceptible to both near equally. I recommend holding off final trimming for final till after you’ve completed your rollout power adjustments thus accomplishing adjustment for both this onrush of wind and for the leveling wings power changes in one trim adjustment effort. With significant headwind while entering final, you will need to come up on power so as to flatten glide path through the air mass which will impact the balance. Think some power off with leveling wings to not balloon but then power back in for headwind then check AOA and finally adjust trim. For the tractor propeller, the trim change won’t be large relative to your other trim changes but will be larger relative to non-tractor planes with on axis thrust lines accomplishing the same roll out on final. As example, for the Cirrus with electric trim, you’re used to large “runs” of trim such as leveling off, accelerating, pushing forward pressure, and running the trim forward to alleviate the pressure. During the rollout on final, however, instead of running the trim, you’ll do better to do momentary “clicks” of trim till you get your AOA back to 3 o’clock on-speed. For those aircraft with off axis engines, you may find yourselves needing more than clicks. The Icon A5 and the T-45 also use 3 o’clock as the on-speed position with their respective gauges. The T-45 trims similarly with clicks as opposed to runs fine tuning for landing.
How You Can Apply Navy AOA Pattern Techniques
To fly applying Navy techniques, you should trim for AOA in downwind. I highly recommend you do slow flight at altitude prior to attempting this. While in the slow flight, start with your traditional constant airspeed level turns noting what happens to AOA. Now do constant AOA level turns noting what happens to airspeed. Note the power addition required to stay level rolling into turn. You may need to go to thirty degrees angle of bank as opposed to twenty to truly observe this; you’re ok, you’re not going to stall as you’re keeping AOA constant and not adding any back stick pressure. Note also the power reduction rolling out so as not to balloon. Now that you’ve done this, roll into a constant AOA level turn then walk power back to set a 500 fpm descending constant AOA turn. Add power to level while still turning. Reduce power setting the descent again and roll out straight maintaining constant AOA and 500 fpm descent. Note you will need a power reduction likely followed by a slighter power addition. Now you are doing AOA the way you want to in the pattern.
What if you have no AOA indicator? That’s ok, set your landing attitude while straight and level. While straight and level, your pitch matches your AOA. Should such be hard to get right, go ahead and trim to landing speed adjusting for weight. A Mike Goulian Aviation Rule of Thumb(11) for light aircraft is to subtract one knot for every hundred pounds below max gross weight. Note this is specific to flying straight (you need not be level). You can do the same exploration in slow flight as described just above noting no back stick and noting speed will increase with AOB, this is expected.
Returning to the pattern, do a couple laps as you normally would so as to be comfortable landing. Now configure to land and slow to on-speed in the downwind. Have the plane nicely trimmed to on-speed. Turning base, add adequate power to maintain desired rate of descent, No Back Stick! Same for turning final. Remember to pull the power rolling wings level or you will balloon. Even should you need to add power for headwind, pull power for wings leveling first then add for the wind. (Gliders, power = less spoiler.) Do this for a few passes. You’ll see AOA combined with power technique works. You’ll probably find it easier to what you‘ve previously done.
If you have neither AOA nor speed information available, fall back on your pitch and power combinations (to include approximate lever positions should gauges also be unavailable). You should probably also have developed a sense of VVI, speed, and power combinations which you could also use combining VVI and power to approximate speed. Fixed pitch prop pilots may aid with tone of rpm while gliders can aid by sound of air rush. You will need to adjust from these references for headwind and tailwind. You’ll also need that power in the turn to maintain desired pitch and/or VVI — no back stick.
Why You May Not Want To Apply AOA Pattern Techniques — Blend AOA into what you previously did
There’s two answers here, one is bullshit. Except for those forced to fly front side techniques, you have no extra risk of stall by slowing fully to AOAref (or Vref if you must) in the downwind as you will not be pulling back on the stick. Except for the stick puller, this stall avoidance reason is bullshit. After all, you are maintaining a constant AOA therefore maintaining a constant buffer from stall.
The other answer is important. Contingency energy! For those flying a Cirrus, you’re fortunate enough to have Cirrus Aircraft Parachute System (CAPS). For the rest of us, we might like to be able to make an emergency glide to some sort of landing. We might even like to be able to make a compromised precautionary approach while minimizing power adjustments. Hence, after having flown a few fully AOA based patterns, I recommend you accept the point learned and shift to a compromised pattern. Yes, we accepted a bit of risk for those few laps, but the risk was minor. If you always fly this way, however, the risk accumulates; lots of minor adds to significant. So, fly your previously normal downwind through your previously normal downwind to base turn. Depending on your plane and how comfortable you are, shift to AOA prior to turning final, in the turn to final, or rolling out on final. You can still use extra power in the downwind to base turn and in the base to final turn so as not to need to pull back on the stick but fly your speeds till you reach your compromised transition to AOA point so as to maintain contingency energy. Such will also give you a little margin against startle factor as AOAref is likely at or below best glide AOA and it will help keep you consistent with others in the pattern reducing pattern “accordion” effect.
Own the Glide Path, “Energize the Ball”
Sidney Dekker and Todd Conklin mention “The Fundamental Regulator Paradox” in their book Do Safety Differently(12):
In control engineering terms, this is called ‘the fundamental regulator paradox.’ It says that if you regulate a machine so well that it bends your key data stream toward zero, and then you’ll have nothing to regulate the machine on. You start to fly blind. You won’t know what it’s doing, and what you need to do. Until it’s too late.
As we don’t have anywhere near the precision we’d like for glide path, and as we essentially look for deviations from desired glide path, we ourselves are in such a system. We subtract desired glide path from observed glide path as we assess our approaches; this means when we’re on desired glide path, we are in the realm of zero. This gets worse in our case as aircraft trends develop further out increasing their intensity while we have less precision yet these trends matriculate as we get closer while our required precision and margins narrow.
The solution here is quite simple. Rather than flying on glide path relative to our visual systems, where we don’t know exactly where we are within the on glide path cell nor our trend within this cell, add a little power shallowing out to drive to a slightly high then correct back down. Do this iteratively to ride the boundary of the on glide path and slightly high cells. In doing this we are no longer riding the zero difference from desired glide path and we know both where we are and what is our trend. With the fresnel lens, this is called “cresting the ball.” For those flying the PAPI, you can actually see the light transition through pink as you see a bit of white with a bit of red. Ride the pink of either that second or third light toggling it from red or white to pink and back to your chosen red or white (choose which way to toggle from red to pink or white to pink and upon which light to do so based on your plane and runway length available).
Note you may start out on a PAPI or VASI yet in small general aviation aircraft, you may shift to a visual point short of the landing point targeted by these systems. Yes, they will now all turn red, and this can be ok so long as you don’t make such a transition too early and if you’re with another pilot, you communicate your shift. Having all red is not ‘accepting a low’ if you’re using a different intended aim point and desired touchdown point short of the lighting system’s.
Regarding visual aim points, as your eyeball is much more precise than are most visual lighting systems excluding the fresnel lens systems, and as your margin for landing point is much larger than that required for landing on ships, I generally don’t think you need to worry about “cresting the ball” with visual aim points. If you desired to do this technique, however, what you would do is simply select a secondary aim point just beyond your desired aim point. Add power such that your aircraft adjusts to this new aim point then reduce to settle back to the original aim point. Now you can iterate between these two points. Again, I don’t think this necessary except possibly for transitioning into unfamiliar turbo and turbine engine aircraft to which you’re not yet used to their responsiveness (or lack thereof) to power application or, if flying front side or true back side, their responsiveness to elevator input.
Ultimately “Energizing the Ball” proactively controls glide path as opposed to reacting to trends after they become apparent.
A Float Plane Pilot’s Technique on Flaring
“Chip and Hold, Chip and Hold, Chip and Hold Hold Hold.”
The first time I flew a T-38, I pranged it on landing. I was used to sitting a bit higher, so when I flared, I unwittingly flared high. The energy bled out, then the plane dropped.
We haven’t really discussed the flare other than to say it negates two of the LSO Rules to Live By. Yet the flare finalizes your energy dissipation terminating your flight.
For those of you flying your aircraft regularly, you should develop a clean consistent round out. You know intrinsically when it is about right and how much to pull back to hold while that energy bleeds out. If you haven’t been flying regularly, however, or if you switch back and forth between different airplanes, you may have trouble figuring out the flare. Be it too high, too low, insufficient nose up, flat or worse nose down, a tendency to balloon, a tendency to drop, we can fix you.
Realize many factors affect your flare. Seat height changes your perspective. If you sit eight feet up in one kind of airplane and only two feet up in another, your flare likely gets skewed. CG matters as it impacts the feel and sensitivity of the pull. Gusty winds affect you.
Once upon a time and a while after hurting that T-38, I had a conversation with a float plane instructor who had to face uncertain height above surface in landing. Clear smooth water makes for difficult understanding of how high you are above. Height on step on the water as on landing touchdown differed from at mooring in the water while, as he flew amphibians, wheels down on the ground seating was higher than wheels up floats on the water. So, rather than seeking a smooth analog motion, he’d approach his flare in discreet pieces keeping a ratchet in mind. “Chip and Hold, Chip and Hold, Chip and Hold Hold Hold.” Picture your descent and take a chip out of it shallowing but still descending. Hold then make the next chip. Like a ratchet, this is one-way. Yes, you’ll bleed speed but it will be a slow bleed and you won’t stall. Hold your stick or yoke open handed such that you cannot wrongly push over forward. You can still trim into your flare(13) (you don’t have to trim into it though); you’re just doing the flare in steps instead of one smooth motion. If you flare too high, extend your hold. If you flare too low, shorten your hold even eliminating it going straight into your second chip. If you get to your third chip and do the holds while still not getting down, you can add some power to cushion so as not to drop, or if short field, Go Around. The Holds of the Chip and Hold give you opportunity to fix flare errors.
Chip and Hold gives some capacity toward dealing with wind gusts though in such conditions I recommend half flaps just as I would for crosswinds. Half flaps for crosswinds means you need less crab or less sideslip to compensate while half flaps with gusts means you’re more ready to go around should a gust excessively balloon you.
As an aside, these three YouTubes seem reasonable in discussing flaring (or, if you prefer, round-out through flaring):
- https://www.youtube.com/watch?v=OsjYNFCxNPc
- https://www.youtube.com/watch?v=iIW91SOSvVg
- https://www.youtube.com/watch?v=wPzT8SD3cU8(14)
Context and Circumstances Matter
Please see The Contrarian Aviator(15) regarding Complicated versus Complex environments and thoughts concerning Pattern Entries. Note not just the blog but also the comments to the blog carry valuable discussion.
Mathematical “Proof” We Trim for AOA
To call this a proof is a bit of a misnomer. Why? Because we’re playing off the definition of a longitudinally stable airplane. A longitudinally stable airplane is one in which it tends to return to the trimmed condition following a gust or disturbance. Thus we aren’t really proving a fact of nature here so much as showing consequences of deliberate design. We are reverse engineering as opposed to proving. Most aircraft including planes and gliders to which this discussion really applies are deliberately made to be statically longitudinally stable.(16)
“The static longitudinal stability of an aircraft is appreciated by displacing the aircraft from some trimmed angle of attack. If the aerodynamic pitching moments created by this displacement tend to return the aircraft to the equilibrium angle of attack the aircraft has positive static longitudinal stability.” — Aerodynamics for Naval Aviators
“The certification testing standards do not specify trim requirements for a steep turn. The decision whether to use trim depends on the airplane characteristics, speed of the trim system, and preference of the instructor and learner. As the bank angle transitions from medium to steep, increasing elevator-up trim and smoothly increasing engine power to that required for the turn removes some or all of the control forces required to maintain a higher angle of attack. However, if trim is used, pilots should not forget to remove both the trim and power inputs as the maneuver is completed.” — FAA Airplane Flying Handbook
“Longitudinal stability (pitching). Stability about the lateral axis. A desirable characteristic of an airplane whereby it tends to return to its trimmed angle of attack after displacement.” — FAA Pilot’s Handbook of Aeronautical Knowledge
Imagine for a moment we have an airfoil though not attached to a plane. Run a rod forward of the spar of this airfoil, attach the rod to a stand, and expose the airfoil to wind. It will zero out its angle of attack streamlining or weathervane with the wind. It is only by attaching it to other structure that will cause it to maintain other than zero angle. This other structure is the rest of our airframe. In regards to longitudinal stability, our airframe has two contributing airfoils.
Consider our four forces of flight. We have thrust balancing drag with lift balancing weight. Yet this is oversimplified. We know a backward portion of lift contributes to drag as induced drag. We know thrust can have a vertical component. And weight is not our only down force. In reality we have the sum of up forces balanced by the sum of down forces as we have the forwards balancing the afts.
Consider for a moment how we achieve our longitudinal stability. It is an inverted teeter-totter or seesaw. Our center of lift is the fulcrum while the weight presses down on one side and our horizontal stabilizer presses down with equal moment on the other side. Keeping this in mind, we can now define weight in terms of a lift equation but from a different airfoil than the wing hence a different coefficient of lift. Aerodynamics for Naval Aviators refers to this other coefficient of lift as the pitching moment coefficient.
Coefficients of lift account for airfoil shape and air flow about the foils aka angle of incidence aka angle of attack. We control the pitching moment coefficient with the elevator which we control by trim. Due to the hard structure of the airplane or glider, this forces a specific angle of attack upon the wing due to the airflow portion of the coefficient of lift. All other factors either cancel out or are locked into a constant for the given aircraft. Airspeed cancels out while AOA remains and depends upon horizontal stabilizer AOA which depends upon elevator position which depends on elevator trim.
Lift = Weight + empennage Force Down
Weight * length A = empennage Force Down * length B
Lift = coefficient of lift * half wing area * velocity squared * air density
empennage Force Down = pitching moment coefficient * half stabilizer area * velocity squared * air density
Weight = length B / length A (pitching moment coefficient * half stabilizer area * velocity squared * air density)
Lift = length B / length A (pitching moment coefficient * half stabilizer area * velocity squared * air density) + (pitching moment coefficient * half stabilizer area * velocity squared * air density)
Lift = pitching moment coefficient * half stabilizer area * velocity squared * air density * (length B / length A + 1)
Coefficient of Lift * half wing area * velocity squared * air density = pitching moment coefficient * half stabilizer area * velocity squared * air density * (length B / length A + 1)
velocity squared and air density cancels from both sides, leaving
coeffieinct of lift * half wing area = pitching moment coefficient * half stabilizer area * (length B / length A + 1)
All other values are fixed for a given aircraft in given configuration thus reduce to
coefficient of lift = k * pitching moment coefficient
Holding configuration constant means the shape of the airfoils is locked leaving
AOA = k1 * elevator trim
We trim to reduce stick forces and we trim for AOA, not airspeed. We trim for the air flow around the respective airfoils.(17)
You can see this in long flights in which you trim an initial cruise “airspeed.” As you burn fuel, you will climb. To prevent such, your options are to pull power to stop the climb in which case you will slow to and maintain a new slower speed as you are actually trimmed to an AOA while needing less lift because you are now lighter due to the fuel burn reducing your weight, or you can trim forward setting a new lower AOA and accelerating to a new new cruise speed, or you can accept the climb. You’re stuck with the airflow pattern about the airframe due to your pitch trim setting the AOA until you change the trim thus changing the AOA.
Extra Concerns for using AOA:
How does your instrument work?
We’ve mentioned above that AOA is sensitive to vertical gusts while airspeed is sensitive to horizontal gusts yet lift reserve or lift capacity measures vary depending on where the holes for comparative pressures reside. There are other concerns such as singular static ports when slipping impacting airspeed (and VVI and altitude), similar blanking could occur with AOA vanes as well as with pitot tubes depending upon the location of respective probe, direction of slip or skid, and magnitude of slip or skid. Small ranges of display can also make AOA or lift reserve displays seem more erratic or jumpy.
Range of display can reduce how you might use AOA. Consider a stall warning horn is essentially a binary AOA or a binary lift reserve. Granted, some may start growling before whining before howling, though the range of this occurrence doesn’t give much beyond warning to stop pulling or to unload a bit. And the growling might get missed with attentional blindness or through desensitization to it. Such a device lacks adequate range to give AOAref. Other devices may similarly limit usefulness. Remember AOA is good for AOAref and also for best range (no wind), best glide (no wind), best endurance, best glide time. It is only good for these, however, should you be able to read the respective values on your gauge.
Precision can be an issue. Remember AOA has a nonlinear relationship with airspeed. Typically we associate the low end kinetic with landing but some platforms such as the T-38 have high landing speeds. Were one to use AOA with the T-38, they’d be safe from Approach Turn Stalls and safe from circling approach stalls, but they could often carry extra energy as the precision of their AOA is inadequate thus meaning while on an AOAref the speed could vary by as much as ten knots. Their AOA system would be sufficient for a plane landing at slower speed as such wouldn’t need precision but using strictly AOA with the T-38 means lots of potential to land hot or more likely float and land long with the floating and long landing enhanced by ground effect. This, in turn, creates hazards for overrun or for increased go arounds. Despite what you’ve been told, go arounds are not free. Each go around incurs a minor risk while risks accumulate through multiple go arounds. We like our wave-offs / go arounds / rejected landings / diverts as typically they trade gaining a minor risk purchase against an obvious immediate more major risk sold off. They are a net reduction, they are not a total reduction.
Depending on how your sensor is mounted, you may have different AOAref values for full flaps, half flaps, no flaps. The Cirrus, the T-45, and the F/A-18 all have the same AOAref regardless of flaps buy my RV with its Lift system(18) differs. (Note I also rotated the gauge ninety degrees clockwise such that high slow was up rather than left.)
Secondary effects due to empennage effects amplified with tractor propellers:
We’ve mentioned through this discussion tractor propellers prop wash changes with power and changes the trimmed AOA balance. To emphasize this point, consider the trim stall demonstration. In this, we have an airplane trimmed to land and jam on full power. The prop wash significantly increased the tail down hence nose up of the empennage thus rapidly changing the wing’s angle and changing the balance between empennage and wing. Thus we have immediate pitch rate and a new higher AOA trimmed balance both moving us to stall. Similarly, engine position below cg will rock us up. Above cg will rotate us nose down. Power can change AOA balance depending on airplane design.
Other landing considerations:
Aerodynamics for Naval Aviators tells us inlets forward of the cg as well as tractor style propellers with their area forward of the cg is destabilizing.
“Power effects on static directional stability are similar to the power effects on static longitudinal stability. The direct effects are confined to the normal force at the propeller plane or the jet inlet and, of course, are destabilizing when the propeller or inlet is located ahead of the c.g. The indirect effects of power induced velocities and flow directions changes at the vertical tail are quite significant for the propeller driven airplane and can produce large directional trim changes. As in the longitudinal case, the indirect effects are negligible for the jet powered airplane. The contribution of the direct and indirect power effects to static directional stability is greatest for the propeller powered airplane and usually slight for the jet powered airplane. In either case, the general effect of power is destabilizing and the greatest contribution will occur at high power and low dynamic pressure as during a wave-off.”(19)
Obviously, yes, your turning tendencies are greatest at high power and slow speed and are of concern in the go around. I look at this differently, however. I see destabilizing here as pilot-out-of-the-loop bare airframe response. As for the propeller, however, I see pilot-in-the-loop as really shifting the neutral point from no rudder to increasing right rudder. So long as the power leaves you some excess right rudder so as to be able to make corrections, power isn’t destabilizing pilot-in-the-loop. There is concern that advancing the power too quickly gets ahead of the pilot and rudder at which point you’re in the pilot-out-of-the-loop unstable situation. Assuming you’re matching the rudder to power and as needed sufficiently slow about advancing the power, and if your specific plane can get rudder limited, allow time to accelerate so as to gain rudder authority, you’re not unstable.
With this in mind, I like to compare front wheel drive vehicles and rear wheel drive vehicles. Front wheel pull from the front and thus are stabilizing, or at least dampening neutralizing, while rear wheel push from behind and are destabilizing. You can experiment with pulling a pencil versus pushing it across the table. Pull from the front, push from the rear, as any disturbance occurs, see what happens. Or consider pulling a cart versus pushing, think about pulling a trailer versus backing it up pushing.
Why do I bring this up? Because keeping a little power pulling from the front can actually help you in gusty crosswind conditions presuming adequate runway for increased rollout. Such can also help the novice tail-wheel or rusty regaining proficiency conventional gear pilot. A little power can also cushion should flare be too high and should not be feared for destabilizing effects. What is deemed directionally destabilizing can actually help stabilize.
With this, I’d like to take a moment to think about winds and other varying landing conditions.
We have mentioned with headwind and tailwind, should we follow our visual apparent three degree glide path, we’ll actually be flying flatter or steeper through the air mass respectively and therefore need to adjust our neutral power point up or back. In the case of back, should it reach idle, we may need to forward slip. This is one way to handle it and is probably the way you will prefer to do it. Alternately, you could fly a steep apparent glide path in headwind or shallow apparent glide path with tail wind so as to keep flying a normal glide path through the air mass with normal neutral power point.
Regarding crosswinds, you have two basic techniques from which to choose. You can crab and kick out the crab for alignment at the end, or you can side slip. I’ll note the F/A-18 calls for crab with only kicking out half the crab though they have robust landing gear absorbing the other half. For swept wings and for really long wings, you may favor the crab and kick. Cirrus calls for such too, though I will side slip in the Cirrus thank you very much. I also side slip in my RV. And I have side slipped in the Hornet. Yes, it has swept wings though not excessively so though it does say top rudder is only effective in light cross. Anyway, with the side slip, remember to keep the inputs through touchdown. It is ok to land on one wheel. If you have a tail wheel and are doing wheel landings, one wheel is fine. Three point becomes two point. Though realize sometimes and in some places the wind intensity decreases as you close to the runway, so play out your inputs in these cases.
For the side slip, I like to roll out on final first starting with a crab. Then I set the wings and set opposite rudder as two discrete steps. This way I avoid temptation to skid. Rollout, then wing into wind, then counter with top rudder.
Cirrus tells us full flaps even in crosswinds. I think this is garbage. Half flaps not only puts you a step closer to go around procedure, it increases your velocity which means that component balancing out the wind takes less crab angle to obtain or takes less angle of bank for horizontal lift to counter hence needs less rudder to compensate for the side slip. Half flaps is to your advantage should runway length permit with crosswinds. Hornets too go to half flaps in heavy crosswind and even with heavy headwind. (They also use half flap for single engine or suspect engine issues. Puts them a step closer to their loss of thrust go around procedure while having less drag.) Side note, folks often land with the Cirrus half flaps as on instrument approaches should one break out below 500 AGL, they don’t want you reconfiguring from the half flap used on the approach.
How about gusts? You may have heard “add half the gust,” and that has good merit to it. Though since we’re using AOA, consider trimming to 4 o’clock instead of 3 o’clock. Gusts in crosswinds, I’d really consider that half flaps. Ready to go around. More rudder capacity preserved. Full flaps or half flaps, consider raising the flaps after touchdown so as to reduce your capacity for flight should a gust hit you while also getting more weight on the wheels for both better braking and more control. Caveat, tail wheel, you might want to go for the wheel landing so as to maintain more aerodynamic directional stability after touchdown slowly blending into the three wheel instability. As your tail settles might be a better cue to raise flaps. Though in all cases not at the expense of working your feet for both controllability and braking.
How about short field with obstacle, confined water with obstacle, or rough water? Consider after rolling out on final going to 2 o’clock AOA realizing you’ll bleed quicker in round out and flare so perhaps a little shorter holds in the chips and holds. Steeper pattern as needed for obstacle with neutral power back accordingly though note forward slip even prior to reaching idle can be a big help. With the forward slip you’ll drop with all that parasitic drag but taking the slip out immediately cleans your flying. You can do this all the way to round out and flare at which point you also catch ground effect so you won’t plump down.
Short field with no obstacle should be practiced with a long landing point so as to imagine a threshold to target. Aim short of imaginary threshold or actual threshold, then add power as you round out and flare in ground effect so as to drive in ground effect. Chop the power crossing the threshold. But, why go to a field so short? If you do, be sure you can take off from it before going. Similar thoughts for confined water no obstacle.
For soft fields, consider 4 o’clock AOA. Then catch ground effect similar to the no obstacle short field though you need not aim short except should the soft also be short. Rather than chopping the power, ease it to idle. For glassy water, you can do something similar but you may not want to ease fully to idle as you may be higher than you think. Consider cushioning as if you flared high. Also think beforehand can you attempt to mark the water with some flotsam?
(1) https://flareassistradar.com/
(3) https://learning.cirrusapproach.com/courses/371/stages/297/lessons/318
(5) In this sense I am combining “flare” to be “round-out” and “flare” inclusively. Some treat both as one as flare while others treat these as two separate distinct portions of landing. Think about it whichever way is easier for you in your landings. Point here is Navy jets land in what some describe as controlled crashes with no change in the approach to touchdown attitude. “Chip-and-Hold” as discussed below as a method applies to combining round-out and flare into one concept. If you were to break such into two distinct pieces, the first couple “chip-and-holds” would associate with round-out while the latter gets to the flare.
(6) to answer Ed Wischmeyer as to Why AOA sometimes leads Pitch though Pitch sets AOA, it is this pitch rate concern. If steady state, pitch will yield the significant contribution to relative wind hence Pitch driving though not fully setting AOA but AOB still plays as do environmental lifts, sinks, and if not zero pitch gusts also play yet significantly, Pitch Rate will have AOA leading Pitch. How else are you going to change pitch if not via that elevator while the elevator versus wing balance is what drives AOA… https://podcasts.apple.com/us/podcast/pilots-discretion-from-sportys/id1571051265?i=1000630813005 as to his comments regarding needing to be on steady conditions for validity of AOA, consider that the Navy doesn’t just use AOA to land, it also uses it while fighting… as does the Air Force.
(7) Chapter 3 FAA Airplane Flying Handbook provides the Four Fundamentals as straight-and-level, turns, climbs, and descents. It gives three moments being Pitch, Roll, Yaw about the three axes though calls the moments movements. To confuse this more, the manual also refers to six motions of flight with bank, pitch, yaw, and horizontal, vertical, lateral displacements all being motions. Despite how the FAA sees these, we have five fundamental maneuvers for flight being straight-and-level, turns, accelerate/decelerate, climbs/descents, and zooms/dives. I’ll often ask “what are the six fundamental maneuvers of flight?” to generate discussion despite the FAA only writing of four while I have five groupings. The answer most commonly given is actually the three moments. By including the distinctions for zoom and dive versus climb/descent decel/accel, we get into flavors of energy trades which makes for better understanding of flying. John Boyd and Wolfgang Langewiesche would both approve. https://www.faa.gov/sites/faa.gov/files/regulations_policies/handbooks_manuals/aviation/airplane_handbook/04_afh_ch3.pdf
(8) I’ve an observation to share with you regarding Close Air Support (CAS). CAS is an attack activity in which strike aircraft bomb in close proximity to friendly troops. As such it is fairly high risk for accidental “fratricide” and to help alleviate this, the attacking aircraft no longer owns its own weapons release. Instead a Forward Air Controller (FAC) working with the ground troops owns the release. The FAC has to verbally state over the radio “Cleared Hot” to the attacking aircraft for each release run. My observation is that in training, more complicated and more dynamic dive deliveries result in fewer inadvertent releases than do straight and level GPS or laser guided weapon releases. This is to say the more complicated and more dynamic events tend to have less violations of the most important safety rule in the CAS situation.
For the Instrument Flyers, consider the discussion for non-precision approaches and Constant Descent Final Approach (CDFA) versus “Dive-and Drive.” They’ll argue constant descent is safer as it is stable. They’ll point to the poetically though inaccurately named “dive-and-drive” as unsafe and unstable. They’ll convince you of this through Kahneman-esque System 1 understanding in which the argument sounds smooth hence never engages a more skeptical and questioning System 2. “Dive-and-Drive” sounds pleasing to the ear so we accept the name which in turn means we accept the image of Diving which we see as unstable.* Yet you don’t dive-and-drive, you Descend-and-Drive in the properly named ‘StepDown’ as you’re trimmed to an AOA (or airspeed in lieu of). A Dive, the opposite of Zoom, is trading Potential Energy for Kinetic Energy. A Descent is a reduction of Potential Energy while keeping Kinetic Energy constant. They’ll argue the CDFA requires less actions, that is true two instead of three flight path changes being descend from Final Approach Fix (FAF) and Missed Approach (MAP) missing the level off in between these two from a slightly steeper descent. Yet I’ve seen far more Minimum Descent Altitude busts with the LNAV+V and VOR+V aka CDFAs than I have Descend-and-Drive. The only way to avoid these is to add margin for the “Derived Decision Altitude” (DDA) in which one adds to the MDA to create a notional DA. Add thirty feet to your MDA to get your DDA in light general aviation (GA) airplanes. This means you may as well add a hundred feet and a half mile to the weather minimums for said approach as you’re not going to see the field at published minimums in a timely manner to land with the CDFA technique. It also means you’re adding the risk of doing an actual MAP while adding the risk of doing the “DRAFT” and flying to your alternate. Sure, there’s risk for being lower longer while on the Descend-and-Drive StepDown, but it is not as bad as you think as you know you’re above MDA cleared safe altitude. This is especially true for light aircraft, read low inertia, that have fast engine response times like GA pistons do (and possible future electrics will). If you’re in a heavy with long spool-up times, CDFA is probably for you. That does not mean such should be transferred to light and responsive aircraft as a one-size-fits all “best” safety practice. While you may have planned fuel for the alternate on your IFR event, imagine the situation when you are VFR with clear forecast throughout, hence your fuel reserve reflects such, yet that area fog is developing un-forecast. That fog probably also impacts your likely diverts. Best learn your Cynefin. Context matters. There often isn’t one best practice. Maybe CDFA is fine for your planned IFR to non-precision approach while maybe you want to Descend-and-Drive in the late IFR pickup. Perhaps you’re near the bases approaching the FAF, so descend-and-drive gets you out sooner. Though perhaps you’re above a layer hence CDFA may reduce your time in IMC. Context please.
* I’ll bet you can’t find an attack pilot who views diving as unstable. They need stability in their dives for their attacks to be successful.
(9) You Climb.
(10) https://www.youtube.com/watch?v=5ESJH1NLMLs
(12) page 45 https://www.amazon.com/Do-Safety-Differently-Sidney-Dekker/dp/B09RM3Z17V
(13) Though she uses speed in lieu of AOA while trimming off in lieu of AOA, her technique has merit and more-so for the loss of prop wash over the tail with power reduction into the round out and flare which she left out of her discussion. https://www.mikegoulianaviation.com/wp-content/uploads/2022/02/2021-10-PrassunaProTip.pdf
(14) Jason is advocating a power idle approach; I don’t do this. The value of this video is in breaking the landing into distinct parts as a tool to better talk about errors in debriefing landing. His uses phases requiring differing actions. The Navy will use distance gates as its means of breaking landings into pieces for ease of debrief. Jason’s is nice as in General Aviation aircraft, you do have different actions to do in each piece.
(15) https://www.dailykos.com/stories/2022/6/16/2104524/-The-Contrarian-Aviator-Sometimes-Turns-Right noting both the blog and comments to it; duplicated though missing the comments yet with a new forward https://medium.com/@jamesmcclaranallen/the-contrarian-aviator-sometimes-turns-right-89da7d61d132
(16) As an aside, a recent computer based ground school program developed by Cirrus for Private Pilot training asked which control surfaces affected longitudinal stability. It mistakenly took ailerons as the “correct” answer as these control the moment about the longitudinal axis. This answer is wrong as it is the horizontal stabilizer that really controls longitudinal stability while its associated control surface of the elevator with its trim are the only proper answers. Longitudinal stability is about the lateral axis as all the longitudinal motion is seen in the longitudinal plane. Directional stability is about the vertical axis with its motion in the directional plane. Lateral stability is about the longitudinal axis with lateral stability observed in the lateral plane more easily seen by wing tips than fuselage. Note lateral and directional stabilities are coupled, deviations in one result with deviations in both. Longitudinal stability modes are the short period and phugoid and are seen by watching the nose or tail scribe paths through the longitudinal plane being the plane defined by the longitudinal axis and vertical axis. Directional stability would be seen on the directional plane described by the lateral and longitudinal axes. Lateral stability would be seen on the lateral plane described by the lateral and vertical axes. But as directional and lateral are tied, we typically look to rolling yawing balance and motions up and down and left and right, circular, oval of wingtips versus nose motions.
(17) Trimming for AOA is true in direct mechanical and hydraulic aircraft. Fly-by-wire planes may differ. Most such will transition in values from AOA in the low end to airspeed in the midrange to mach at the high end. Not all follow such, however, as the F/A-18 trims to g when both flaps up and at low through medium AOA. With flaps down or at high AOA, it will trim to AOA. This means in cruise flight the Hornet has little feel for accelerations and decelerations.
(19) pgs 287 & 290, Aerodynamics for Naval Aviators