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Beginner’s Series: Four Forces of Flight

How exactly DOES an airplane fly? How is it possible for a jumbo jet weighing hundreds of tons to actually lift of the ground and fly through the air?

First, it is important to understand that anything that flies through the air, from the jumbo jet we were just talking about to the small airplane you will fly for your training, to the frisbee or the paper airplane you threw as a kid (or just earlier today, you rascal), all have the same four forces acting on them allowing them to fly.

Those four forces of flight are: lift, thrust, drag, and weight (or gravity).

And here is what the four forces of flight look like in relation to each other and an airplane:

Four Forces of Flight

Lift

Lift is generated by the wings, and opposes weight / gravity. When lift is greater than weight, the airplane climbs.  When lift is less than weight, the airplane descends.  When lift and weight are equal, the airplane maintains its altitude.

Lift is always generated perpendicular to the wings (so in a turn, lift actually “pulls” sideways as the airplane banks, and in a climb, lift actually “pulls” backwards slightly, since the nose is pointed upwards somewhat). In this way, lift actually contributes to drag (see induced drag).

Thrust

On your training airplane, thrust is generated by the propeller, which is turned by the powerplant. Thrust moves the airplane forward through the air, and it opposes drag.  When thrust is greater than drag, the airplane accelerates.  When drag is greater than thrust, the airplane decelerates / slows down. When thrust and drag are equal, the aircraft maintains its airspeed.

Thrust / Lift cooperation

Lift is often given credit for making an airplane fly; however, technically, no lift would be generated without thrust to move the airplane through the air. So in reality, excess thrust is actually what makes an airplane fly, because without that thrust, no lift would ever be generated in the first place!

Weight

Weight is simply how much the airplane weighs. Sometimes this force is referred to as gravity, since gravity pulls down on the plane in relation to its weight. Weight opposes lift. An airplane must create more lift than weight to climb to higher altitudes.

Weight always pulls down directly toward the ground - unlike lift, which can change direction as the airplane pitches (nose up / nose down) or rolls (“banks” (leans) left or right). This concept will be important when you start to learn about aerodynamics in turns, so keep this in mind!

Drag

Drag is, quite simply, a force that opposes thrust. As an airplane moves through the air, there is friction from the air itself running into the aircraft.

There are two types of drag you need to be aware of:

  1. Parasite Drag: also known as “form” drag. Parasite drag is simply the air “running into” parts of the airplane. Parts like antennas, rivets, tires, the windscreen, your arm sticking out the window, anything and everything that the winds “hits” causes parasite drag.
  2. Induced Drag: This type of drag is a little harder to wrap your head around, but it is simply drag caused as a result of the creation of lift.  Remember above, when I said that lift is created perpendicular to the wings? Well, the wings are never really “flat” against the wind, so the lift vector is always pointed slightly to the back of the aircraft.  That “backwards” lift is induced drag. The more lift being created, the more drag is created.

While drag opposes thrust, you should know and understand that it does not EXACTLY oppose thrust.  Just as weight always points directly down toward the ground, regardless of the airplane’s attitude, drag is always opposite to the airplane’s flight path. The flight path is rarely the same as where the nose is actually pointed. For example, in a climb, thrust points directly where the nose is pointing, but the aircraft is not climbing directly where the nose is pointing; it is actually “mushing” into the air somewhat, which means drag is offset slightly “above” the thrust vector. This can be difficult to imagine, so see the below image of the 4 vectors during an aircraft’s climb (exaggerated):

Four Forces in a Climb

In conclusion, and to circle back around to the initial question: “How is it possible for a jumbo jet to actually lift of the ground and fly through the air?”

Any airplane will fly if its thrust exceeds its drag, and its lift exceeds its weight. If the four engines on a Boeing 747, producing a total thrust of more than 250,000 pounds, can exceed the drag the aircraft produces, and its 196 foot long wings can produce enough lift to exceed its weight (maximum 970,000 pounds), it can fly!

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Beginner’s Series: Parts of an Airplane

When you start your flight training, you will learn lots of new terms and phrases. You’ll be expected to know what those terms refer to in relation to your airplane.

Wings, tail, engine, etc. are pretty easy to remember, but there are many new terms that you may not be familiar with. Such as:

Fuselage Empennage
Spinner Aileron
Horizontal Stabilizer Vertical Stabilizer
Cowl Cockpit

And other words that you may know but that mean something different in relation to aircraft:

Trim Strut
Elevator Rudder
Beacon Flap
etc.

With that in mind, let’s take a look at all the parts of an airplane that you’ll need to know.  We’ll also discuss a little bit about what they do and how they work.
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Fuselage

The fuselage (sounds like "moose-ah-lodge") is the main body of the airplane. The wings, tail, and landing gear are attached to the fuselage. Basically, it holds everything else together as well as containing the passengers and baggage.

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Empennage

The empennage (sounds like "hemp-a-nudge") is what is colloquially known as the “Tail” of an airplane – the entire tail section.  The tail section (empennage) actually consists of multiple parts:

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  • Vertical Stabilizer: the “up and down” (vertical) part of the tail, to which the rudder is attached
  • Rudder: The rudder is a “control surface” which moves side-to-side, controlling the airplane’s “yaw.” Similar to the rudder of a boat.
  • Rudder Trim Tab: Most likely, your training airplane will not have rudder trim, or will have a “fixed” rudder trim tab. A fixed rudder trim tab can only be adjusted while the plane is on the ground. A fixed tab should only be adjusted by a qualified aircraft mechanic (see picture below).

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  • Horizontal Stabilizer: The “side-to-side” (horizontal) part of the tail, to which the elevators are attached.  Sometimes referred to as the “tail wing” (interestingly, this is not an incorrect term).
  • Elevator: The elevator is a “control surface” which moves up-and-down, controlling the airplane’s “pitch” (whether the nose is pointed up or down).  There are generally two elevators, one on each side of the vertical stabilizer. Each elevator is connected to one of the horizontal stabilizers, which are located on each side of the vertical stabilizer. Both elevators move the same direction when moved.
  • Elevator Trim Tab: The elevator trim tab is a small portion of the elevator that is a control surface in and of itself.  It is moved by a wheel or crank in the cockpit of the aircraft, and allows the pilot to “set” the elevator position.  Think of it as “cruise control” for the airplane, as it can be set to a specific airspeed or pitch. Once set, the airplane will always try to return to this setting when disturbed (by the pilot or atmospheric conditions). See picture, below.

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Cockpit

The cockpit is simply where the pilot sits.  It has all the controls to move and adjust the control surfaces (which include the rudder, elevators, ailerons, flaps, and trim), as well as flight instruments. Flight instruments are like the speedometer and tachometer in your car: they give the pilot important information about what the plane is doing and where it is going. Communication and navigation radios are also found in the cockpit. You will learn all about the stuff in the cockpit of your specific training aircraft. The cockpit is sometimes called the “Flight Deck” (especially on larger aircraft).

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Wings

Wings are pretty self-explanatory and easy to recognize.  They stick out from the fuselage to each side of the airplane. An airplane's wings hold some of the plane's control surfaces (ailerons and flaps, to be specific).  They also hold fuel tanks and some instrument system parts, such as the pitot tube and stall sensor. Depending on whether your airplane is a high-wing or low-wing, it may support your main landing gear or have a strut. The front (round) part of the wing is called the “Leading Edge,” and the back (pointy) part of the wing is called the “Trailing Edge.”

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Aileron

The ailerons (pronounced "ale-er-ons") are control surfaces that are attached to the wings of the airplane.  They live on the outer portion of the trailing edge of each wing, and there are two of them.  They move up-and-down, and always move opposite in relation to each other (if the right aileron moves up, the left aileron moves down). They control the “bank” or “roll” of the airplane. The airplane “banks” or “rolls” when it turns and “leans” into the turn, sort of like when you are riding a bicycle.

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Flap

The flaps are also attached to the trailing edge of the wings, one on each side, just like the ailerons. Flaps, though, are “inside” – closer to the fuselage – if they exist at all. Flaps can be extended or retracted. They can also be “partially extended,” which just means that they are not “fully extended.”  They are used to generate extra lift (and they also create A LOT of drag), and are usually only used on landing. Sometimes, you will use flaps when you are doing certain maneuvers in flight. They are also sometimes used on takeoff in very specific situations. They are generally electrically or manually driven on training aircraft (they are often hydraulic on large aircraft).

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Strut

Most high-wing airplanes have a strut, which is really just a support for the wing. It is used to save weight (and headroom in the cockpit), since having a spar strong enough to support the entire length of the wing requires thicker, stronger, and heavier metal throughout the entire length of the wing (from wingtip to wingtip).  The strut simply attaches to the fuselage (usually in front of and near the bottom of the cockpit door) and the wing itself, somewhere about 1/3 of the way out or so from the fuselage.

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Propeller

The propeller is out on the nose of the aircraft, in front of the engine.  It spins around (clockwise if you are looking at it from inside the cockpit), and generates thrust, which “propels” the aircraft forward – hence its name. Think of it as a rotating wing, because, well, that’s actually what it is. Not shown in the images, but see the picture below.

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Spinner

The spinner is the cone-shaped cover in the center of the propeller.  It reduces drag and protects the hub at the center of the propeller.

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Powerplant

This is just another term for the engine. It produces power to turn the propeller and create electricity to charge the battery and run the electronic instruments and communication / navigation (com/nav) radios.

Cowl

The cowl is the part of the fuselage that covers the engine. Think of it like the hood of your car, only for your airplane. Also called “cowling.”

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Beacon

Most airplanes have a “rotating beacon” (actually, these days it is usually a flashing beacon), that is simply a red light – usually at the top of the vertical stabilizer – that flashes, pulses, or blinks. The beacon is the first electric device turned on before starting the engine and the last one turned off after shutting down the engine. Pilots and “in the know” airport visitors see a flashing beacon as a warning that an airplane is about to start its engine or move on the tarmac.  There are a few other lights on an airplane, including wingtip strobes, navigation (nav) lights – also on the wingtips – and the back of the empennage, landing lights & taxi lights, etc.

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These are the parts of an airplane that you will need to know. Knowing these terms will help you make sense of upcoming lessons and information. It will also make it easier for you to decipher the language a pilot speaks. There are other, smaller parts that you will learn more deeply as you continue through your training. All these terms may seem like a lot to learn. I promise that learning them, using them, and hearing them will make you fluent in “pilotspeak.”

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Phraseology: Make Short Approach

So you're flying into a towered airport. You've been listening to other traffic and their clearances, and you hear that there is another aircraft on an 8-mile final, and you are abeam the numbers on downwind.

What are you thinking? Are you going to have to extend your downwind? Man, that will put you WAY out farther then you normally like for flying the pattern... Can the guy on final do a 360 to give you space? SOMETHING has to give, or you'll end up trying to share the same space at the same time - never a good thing.

Just then, you hear tower: "November two-one-six-five papa, cleared to land runway one-two, make short approach."

What!?!

"Make short approach" simply means that tower wants you to cut your downwind short and turn early for your base leg (see our traffic patterns post for more information). Air traffic control generally assumes that you will cut your normal distance between the numbers and your base leg in half, but depending on your aircraft, the runway length, etc, you could "make short approach" immediately abeam the numbers or even further down the runway.

You might hear ATC ask you to "tighten your approach" instead of saying "make short approach." Also, a non-standard statement, but still one you might hear, is "direct to the numbers." ALternatively (or in addition to) any of the above phrases, ATC may also ask you to "keep your speed up," which is self-explanatory, and is another way for ATC to keep safe spacing between aircraft on approach.

The important things to keep in mind when you are asked by air traffic control to make short approach are:

  1. you will need to descend at a steeper angle than normal, meaning that your airspeed will be higher than you'd like if you are not prepared and planning ahead for that (get power out and flaps in earlier than normal to compensate).
  2. you may need more runway than you normally use
    • because of your higher airspeed from a steeper descent (see above)
    • because you may touch down further down the runway than normal
  3. there is traffic behind you, probably only within a few miles, so you'll want to clear the runway as soon as possible - don't loiter!

Above all, ALWAYS keep in mind that you are the pilot in command (PIC) - if you don't believe that you can do what ATC is asking you to do safely, don't do it! Tell them you are unable, and that you would rather do a 360, or a 270 to base, or extend your downwind. Never, ever put yourself in a situation where you are uncomfortable or unsafe, even if ATC has requested it of you.

Think of the radio as an inflight, electronic suggestion box... but not the boss. That would be you. Act like it.

Start the below video at about 1:37 to really see the "approach" being shortened...


Have you ever been asked to make short approach? How did you handle it? Did you do it? Did you request an amended clearance from ATC? What do you think about short approaches in general?

Andrew C. Hartley is a Certificated Flight Instructor in Columbus, Ohio.

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The Three Axes of an Airplane

Three axes of an airplaneAn airplane has three (3) axes about / around which it can move in flight.

In the image above, you are seeing all three of these axes:
Longitudinal axis: from the nose to the tail of the airplane
Lateral axis: from wingtip to wingtip
Vertical axis: from the bottom of the airplane to the top of the airplane

Each of these three axes meet at the center of gravity (CG) of the plane. The CG is the point at which the airplane would balance if you could lift it up by an imaginary string that attached at that exact point. You can think of the CG also as a kind of fulcrum (like on a teeter-totter) that the plane rolls and pitches around.

Anyway, back to the axes of the plane. Here's what you need to know about them and why they are important.

The Longitudinal axis (the one that runs the length of the plane from nose to tail) is the axis that stays fixed when the airplane "rolls" or "banks" - such as in a turn. In this case, the plane is rotating "about" or "around" the longitudinal axis. This is caused by the airplane's ailerons, which change the camber of the wing and increase its lift on one side,making the wing climb, and spoil the lift on the other side, making the wing drop.

The Lateral axis (the one that runs from wingtip to wingtip) stays fixed when the plane "pitches" - raising or lowering the nose (such as for a climb or a descent). The plane pitches about the lateral axis. This is done using the airplane's elevators. The elevators change the shape of the horizontal stabilizer, causing it to decrease lift (tail goes down, nose goes up) or increase lift (tail goes up, nose goes down). Some aircraft have "stabilators," where the entire horizontal surface moves instead of just the elevator, but the concept (and result) is still the same.

The last one is the Vertical axis, which runs vertically (up and down) through the fuselage. This one stays fixed when the airplane "yaws" - meaning the nose moves left or right. When the plane yaws, it is turning about the vertical axis. This is like turning a car (the car doesn't roll or pitch, it just turns, or "yaws"). This can be done by moving the rudder, which is the movable control surface on the vertical stabilizer (the upright portion of the tail). Moving the rudder right puts it into the airflow and pushes the tail to the left (and the nose to the right). Generally, the rudder is used in tandem with the ailerons to coordinate an airplane's turns, because when an airplane banks, there is a change in drag, making the nose want to move away from the turn initially. the rudder is used to "yaw" the nose the right way and keep the whole plane moving in the direction the pilot (you) want it to go.

It is possible to move an airplane about all three axes at one time, and rarely does an airplane move about just one at a time. You, as the pilot in command, will use all the control surfaces to move the plane about all of its axes and make it do what you want it to do.


Do you have any questions about the three axes of an airplane, or do you have any hints or tricks or stories to share that relate to them? Leave a comment and tell us all about it!

Andrew Hartley is a Certificated Flight Instructor in Columbus, Ohio.

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Weather Terminology: Winds

windsockHere's something dumb - "direction-erly" winds.

Have you ever heard someone say the winds are easterly today, and wondered what that meant? I always assumed that easterly winds meant that the winds were going towards the east (like an easterly facing wall, or a boat moving in an easterly direction).

But when it comes to winds, easterly actually means "from the east," - so the winds are actually moving from east to west.

WTF?

I actually discovered this because of an aviation quiz question in a magazine - probably AOPA Pilot or Flying Magazine.

I got the answer wrong, so I googled the term so I would understand it if I heard it or saw it again.  Personally, I think it is dumb.  But the more I thought about it, the more it made sense.

Here's why:

Winds in aviation are always reported using the compass direction they are coming from and then their velocity, in knots.

An example of this is on a METAR:

KCMH 021551Z 33011KT 10SM BKN042 07/M03 A2995 RMK AO2 SLP147 T00671028

In bold, above, this METAR says that winds at Port Columbus airport in Columbus, Ohio, are from 330 degrees (from the northwest) at 11 knots.

Another example of this is when you listen to ATIS or get your departure clearance from the tower - they will almost always give you the current winds in degrees and speed, just like the METAR above does.

In summary, since all other aviation winds are reported as "from" some direction, it makes sense that "westerly" winds would be "from the west."

So, below, I offer a handy "key" to direction-erly winds:

easterly = from the east

westerly = from the west

northerly = from the north

southerly = from the south

You can apply this as well, if you like, for non-cardinal directions - like north-westerly winds in the METAR example above.

Just don't try to tell the tower or your instructor that the winds are 330 degreeserly.


Anybody else out there who struggled with this kind of seeming inconsistency? Tell us about it in the comments. Erly.

Andrew Hartley is a Certificated Flight Instructor in Columbus, Ohio.

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