August 2021 Aviation Articles

Understanding Aircraft Wake Turbulence

You are flying into a controlled airport with the intent to land and ATC states, “ Cessna N617WT winds 160 at 5, cleared to land Runway 18, caution Wake Turbulence”. What is ATC trying to tell you with the message “caution wake turbulence” and how do you avoid the hazard associated with it?


Wake Turbulence

 

First off, to avoid wake turbulence we have to know what it is and how it is created. Simply put, wake turbulence (also known as wing tip vortices) is the product of created lift from the wings. The creation of this wing vortex generation is made by the creation of a pressure differential over the wing surface. As we know from basic lift aerodynamics, the lowest pressure occurs over the upper wing surface and the highest pressure under the wing. Due to that pressure differential, the rollup of the airflow aft of the wing resulting in swirling air masses trailing downstream of the wingtips. 

 

Aircraft Counter Control

 

Okay now we know what it is, why is it so dangerous? 

Compared to our little Cessna, large aircrafts wake can impose rolling tendencies exceeding the roll-control authority of the encountering aircraft. A lot depends on the encountering aircrafts wingspan. The larger the wingspan the larger the vortices, therefore, greater rolling tendencies are imposed. The greatest vortex strength occurs when the generating aircraft is

o    Heavy

    More lift is required 

o    Slow 

    Higher AOA is required to counteract lack of airspeed

o    Clean 

    The extension of flaps and other wing surface devices will change the characteristics of flight vortex (dirty, indicates delayed vortices)

Now that we know what it is and why it’s so dangerous, how do we avoid it?

When landing behind a larger aircraft— stay at or above the larger aircraft’s approach flight path and land beyond its touchdown point.

When departing behind a large aircraft—rotate prior to the rotation point and climb above its climb path until turning clear of the wake. 

Next time ATC gives you a caution such as “wake turbulence” you will know what you’re working with and looking out for. Make sure you exercise the proper precautions and avoidance techniques! You never know when you could encounter another large aircraft on takeoff and/or landing. Fly safe!

Why Aircraft Engines Thrive in Colder Temperatures

Since day one of flight training, we have all heard pilots say that aircraft perform better when it's colder outside. 

You may have heard the term density that has to do with this factor but may have not have seen it actually broken down and explained before. So here's why:

Temperature and Density

When air is entering an aircraft engine to be mixed with fuel, it goes through the 4 phase process of "intake, compress, combust and exhaust" in order to generate power. This is the same for both jet and piston engines. 

But how much air can actually enter the air inlet in order to enter the 4 step process?

Well, the slightly better question is how many air molecules

jet engine design

As explained by BoldMethod.com, "cold air molecules move slower and collide with less energy than hot molecules, causing cold air to become denser. As temperature drops, more air molecules enter an engine, and as temperature rises, fewer air molecules enter an engine."

The more air molecules that can enter an engine, the more power/performance that can be generated, therefore cooler temperatures are more preferred. 

Density Altitude & Performance 

Since we're discussing the density of air in relation to temperature, density altitude goes hand in hand with the topic. Density altitude is altitude relative to standard atmospheric conditions at which the air density would be equal to the indicated air density at the place of observation.

Or for better terms, simply put it is the density of the air given as a height above mean sea level (MSL). 

The higher you are above sea level, the less dense the air becomes, posing the same problem: fewer air molecules entering the engine, therefore, less fuel is mixed with it and lesser power is generated. 

So if you're flying somewhere with a high field elevation such as Jackson Hole, Wyoming for example, and you're taking off in the afternoon where temperatures are at their hottest, you may want to double-check performance numbers. High altitude and high temperature is the worst combination for your aircraft. 

This can even potentially stop you from being able to take off, where your only option is to wait out the temperature until the sun goes down and air cools off again. 

So, if you've been flying and curious why your plane seems more sluggish than a few months ago, now you know! Airplanes like the cold!

questions or comments? Write us below. 

Lesson Plans from a CFI for Steep Turns Part 2

Two weeks ago I shared the first half of my lesson plan for steep turns. Today I will continue to share the last part of that particular lesson plan covering Va (maneuvering speed), weight impact, load factor and accelerated stalls, lastly rate and radius of turn. So as promised, here you go!

Maneuvering-speed

Why do we maneuver at the Va speed?

Va or your designed maneuvering speed is the speed at which the airplane will stall before it exceeds its designed limit-load factor.

  • Full and abrupt aerodynamic control
  • Lower weight lower maneuvering speed
  • Heavier weight higher maneuvering speed
  • It permits an aircraft to preform maneuvering training (such as steep turns) at or below calculated airspeed. This will allow the aircraft to stall (exceed the critical angle of attack) before it develops structural damage.
  • The weight of the wings will exceed designed load limits when operating above Va resulting in structural damage.

The VA Formula

The Impact of Weight Changes

  • Heavier weight = greater AOA to produce sufficient lift to weight ratio
  • Lighter weight = less AOA needed to produce sufficient lift to weight ratio
  • Note* due to higher AOA of heavier aircraft it is closer to the C-AOA (Critical Angle of Attack)

Angle of Attack
Load Factor and Accelerated Stalls

  • Load factor has a proportional relationship between lift and weight. The measurement for load factor is Gs—acceleration of gravity.
  • Gs is a unit of measurement that is equal to the force exerted by gravity on a object at rest and indicates the force to which a object is subjected when it is accelerated. In other words, any force that is applied to an aircraft to change its flight path from a straight line produces some sort of stress on its structure. The resulting force that is created is the load factor.
  • A 60 degree bank pulls 2 Gs— the weight of the aircraft is doubled.
  • By increasing your load factor you also increase the stalling speed and make stalls possible at seemingly safe speeds.
  • We use the normal category— limit load factor 3.8 to -1.5 Gs.
  • The total lift has to increase substantially to balance the load factor or Gs
  • As load factor increases, so does stall speed exponentially. An aircraft’s stalling speed increases at the square root of the load factor. Accelerated stall!

Rate and radius of turn

Rate of Turn

  • The rate of turn (ROT) is measured in the number of degrees (expressed in degrees per second) of heading change by the aircraft.
  • Airspeed increase = ROT decreases unless bank is added
  • Bank angle increases = ROT increases unless airspeed is added
  • “It is found that the horizontal component of lift is proportional to the angle of bank—that is, it increases or decreases respectively as the angle of bank increases or decreases. As the angle of bank is increased, the horizontal component of lift increases, thereby increasing the rate of turn (ROT).” (PHAK Ch. 5)

Radius of Turn

  • The radius of a turn is directly proportional to the ROT as it is a function effected by both bank angle and airspeed.
  • Airspeed increases = radius of turn increase
  • “As the airspeed is increased in a constant-rate level turn, the radius of the turn increases. This increase in the radius of turn causes an increase in the centrifugal force, which must be balanced by an increase in the horizontal component of lift, which can only be increased by increasing the angle of bank.” (PHAK Ch. 5)

Completion Standards

Student is able to maintain the entry altitude ±100 feet, airspeed ±10 knots, bank ±5°, and roll out on the entry heading ±10° of steep turn preformed.

Whenever you create a lesson plan, don’t forget to give credit and cite your sources!

References:

PHAK Ch. 9 & 5

Private pilot Airmen Certification Standards

Airplane Flying Handbook

Commercial Pilot Practical Test Standards

If you have any questions or suggestions for improvement I’d love to read them in the comments below. 

Question for current or previous CFI’s: What advice would you give a pre-CFI regarding creating lesson plans or preparation to becoming a CFI that you wish you knew before you started instructing?

Lesson Plans from a CFI for Steep Turns

I am on a new yet exhausting journey of writing lesson plans for my CFI binder. It is very exciting to think that by the end of this year I will be able to teach other people how to fly an airplane. I have learned so much over the past 2 and a half years of flying and soon I will take that knowledge and share it with others. Someone told me once that being a CFI means that you are simply a certified learner. In the pursuit of creating lesson plans, I can say I have expanded my understanding exponentially. I mean think about it, for you to teach someone and answer the unfiltered questions and different levels of learning you have to continually learn the material for yourself to provide a deep understanding to your students.

One of my very first lesson plans is over steep turns and what better way to start sharing my newly acquired knowledge than to share it with you all? Feel free at any point to leave advice and comments to improve my lesson plan. This is not the full version as it turned out to be roughly 10 pages of material. This post will be one of a two-part series to provide that information. This first post will cover coordinated turns, uncoordinated turns, and over banking tendencies. Enjoy and let me know what you think!

Steep Turns

Purpose of Steep Turn

The purpose of this maneuver is to develop the pilot’s smoothness, coordination, orientation, control technique, and division of attention by executing maximum performance turns.

Set-up of Maneuver

CLEARING TURN

To ensure that the immediate practice area is free of conflicting air traffic and obstacles and to select an emergency landing site.

PRE-MANEUVER FLOW 

Single engine PA28-161

  1. Area Clear
  2. Fuel Selector Proper Tank
  3. Mixture Full Rich
  4. Fuel Pump On
  5. Carb Heat Off
  6. Power Set for Va, (Specific to aircraft determined Va for specific weight)

Memory Aid: GUMP

  • Gas (Fuel selector & fuel pump)
  • Under carriage (Gear up/down)
  • Mixture (Full rich/ lean)
  • Power (Va)

PA28-161 Piper Warrior III SOP (Standard Operating Procedure)

  1. Enter the maneuver on a cardinal heading at least 1,500 AGL  at Va.
  2. Execute a coordinated turn, using a 45-degree bank (50-degree bank for advanced students).
  3. As the bank angle approaches 30 degrees, simultaneously increase back elevator pressure to maintain level flight and add approximately 100 to 200 RPM as necessary to maintain entry airspeed, and apply trim to support the desired flight attitude and airspeed.
  4. Execute a steep turn in the opposite direction (advanced students must immediately execute a steep turn in the opposite direction).
  5. Begin rollout approximately one-half the bank angle in degrees before the entry heading, e.g. in a 45-degree bank, begin rollout while passing through a heading approximately 20-degrees before entry heading.
  6. Roll out of the turn at entry heading and altitude, while simultaneously relaxing back elevator pressure and reducing power to a normal cruise setting.
  7. Fuel pump off if no more maneuvers are to be practiced on that flight.

Forces in Turns
Coordinated and Uncoordinated Flight

Coordinated Flight

Centrifugal force is equal to the horizontal component of lift.

Basics of a Turn

In a turn, the lift component is broken into vertical and horizontal components.

The horizontal component of lift is a force involved with turning the aircraft to either side.

Centrifugal force is the “equal and opposite reaction” of the aircraft to the change in direction during a turn and acts equal and opposite to the horizontal component of lift.

 The vertical component of lift acts opposite to weight (gravity acting downward). “Since the lift during the bank is divided into vertical and horizontal components, the amount of lift opposing gravity and supporting the aircraft’s weight is reduced.” (PHAK Ch. 5) Consequently, more lift needs to be generated by increasing the coefficient of lift requiring back pressure on the elevator to maintain a higher A.O.A.

It is important to note that the AOA must be progressively increased to produce sufficient vertical lift to support the aircraft’s weight due to the vertical component of lift decreasing as the bank angle increases. The pilot should keep in mind that when making constant altitude turns, the vertical component of lift must be equal to the weight to maintain altitude.

Also during the turn, since the drag of the airfoil is directly proportional to its AOA, the airplane will lose airspeed proportional to the angle of bank executed. To maintain the required 45 degree (50 degrees for advanced), Va, and altitude rolling past 30 degrees added power is required to compensate added drag due to increased AOA.

 Uncoordinated Flight

Slip

Slipping Turns

The horizontal lift component is greater than the centrifugal force

  • Aircraft yaws to the outside of turn
  • Bank angle too much for the rate of turn
  • The outside wing has a higher A.O.A, stalls first, drops and levels the wings

Recovery: decrease the bank angle, increasing the Rate of Turn, or a combination of the two changes.

Note* Slips may result in inaccurate airspeed due to the pitot tube/ mass not being Skidding Turnsaligned with the relative wind.

Skid

 

An excess of centrifugal force over the horizontal lift component

  • Turning too fast for bank angle
  • Fuselage blankets lower wing, lower wing stalls, spin is created

Recovery: reduce the rate of turn, increase bank angle or a combination of the two changes.

Over banking tendencies

  • During a steep turn maneuver, the outer wing of the aircraft moves slightly faster through the air than the inner wing. This lack of symmetrical lift between both wings, causing the aircraft to steepen its bank angle in the initial direction. To counteract this over banking tendency, apply opposite aileron as necessary to maintain your bank angle.
  • Negative static stability about the longitudinal axis.

Okay, that’s just the first portion of this lesson plan. Stay tuned for my next post that will go into Va (maneuvering speed), weight impact, load factor, and accelerated stalls, and rate and radius of turns. Your critics make me a better learner therefore a better teacher so feel free to leave any thoughts!

Your 2021 Guide to Flying Into Aspen, CO

A lot of pilots will tell you flying into Aspen, Colorado (KASE) isn't really that bad. But if this is your first time going into that airport, especially if you're single pilot, it can be a little intimidating. 

The best way to stay safe going into KASE is to be prepared. Do your homework and have a plan in your head of how you'll fly the approach inbound! Have no worry, we're here to help give advice and links to the best information the internet has to offer!

1) Youtube

One of the best inventions of the 21st century, Youtube has a lot of aviation videos ranging from general aviation discussions for student pilots, accident reviews, and then how-to guides for difficult approaches such as Aspen. From researching the internet and asking pilots their opinions, I found two helpful links:

Aspen Missed Approach - that shows two pilots coming in and having to go missed on the actual approach back in 2010. They get set up early, stay ahead of the airplane, keep talking through the approach the entire time, then make a decision to go missed and head into Eagle (KEGE) which most use as their alternate. 

Aspen LOC DME-E and Visual Approach - this is more from the single pilot standpoint to show the workload and is just another good video showing what it's like setting up for everything from a Phenom 300

Coming in on the visual it's going to look like you're gliding on top of a mountain (pictured above), then it drops off and it seems like you're way too high above the airport (1st picture). As you keep following the approach in it'll transition to looking like you're too low. Trust the approach even if your visual cues disagree and continue to stay stable. 

2) Simulator

If you can get in a full motion sim before your trip this is a great idea. If you're going to training anytime soon, ask to do a trip into there. The simulator going into Aspen is very realistic, not to mention this is the safest way to make mistakes and have an instructor with you giving you all the best tips and tricks. 

In the simulator you an also adjust temperatures and other weather factors. This can give you a chance to see how performance changes and what it feels like gaining less performance from your aircraft. High density altitude, high temperature, add a tailwind in there and it makes for a "fun" day....if you can even take the runway. 

3) Familiarization Course

Something that you can heavily review before your trip or even better review in addition to your simulator training is a familiarization course. A great presentation is one published by Code 7700: ASE Familiarization Training that also includes the departure procedures. It includes pictures, approach charts, even landmarks to help you locate the airport and an arrival training video.

4) Phone a Friend

Along with reviewing these, I also took advantage of more experienced pilots and asked for their stories before flying in! Of course it helps to ask pilots flying the same type aircraft as you so maybe they can say which power setting or airspeed works best. 

Text an instructor from training if you have their number, ask a friend if you know one, or find a forum (like a Facebook group) to start a discussion on. 

There are lots of resources out there nowadays that can help keep you safe and confident. And if you still feel uncomfortable, trust your gut and have a different crew fly it. Or fly into Eagle instead! 

Thanks for checking out this article, wishing you the best on your trips! If you have any great links or advice to add comment below!

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