Lift vs. Drag – Moments That Matter - Belmont University Blogs

Dr. Jon R Roebuck, Executive Director

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For a number of years, I have held a Private Pilot’s license.  It’s an expensive hobby and thus, for me, it is a hobby rarely enjoyed.  But I love the thought of flying and if time and money were no object, I’d like to climb into the skies with a lot more regularity.  It’s just one of those thrills that you can’t really describe unless you have been there.  If you are a pilot, or even an aviation enthusiast, you would know the answer to this question: “What are the four main forces that affect flight?”  Easy. They are: gravity, thrust, lift, and drag.

Let’s talk about those last two for a moment.  Lift is created when the air pressure under the wing is greater than the pressure above it.  That’s why wings are shaped the way they are.  Bernoulli’s principle comes into play which states that the faster air flows over a surface, the less air pressure is exerted.  The curve on the top surface of the wing forces a quicker airflow, thus there is less air pressure on the top surface of the wing, which creates lift.  (I know that may be a little technical but the next time you are streaking across the sky at 600 m.p.h. give a little nod to that 18th century Swiss physicist.)  Drag is a little easier to explain.  It’s the wind resistance caused by the various surfaces when they are pulled through the air.  The “cleaner” the surface area of the plane, the less drag.  (That’s why retractable gear is almost always found on high-speed aircraft.)  Lift and drag.  One helps a plane to fly.  The other holds it back.

All of us are being affected by lift and drag.  They are the forces which can allow our spirits to soar or our hearts to sink.  And no, I’m no longer talking about airplanes and air pressure.  There are forces at work in our world that tend to give us a little lift.  Our days are brightened by the people who love, nurture, and encourage us.  Our spirits soar when we are joined to moments, organizations, or relationships that help humanity, solve social ills, or ease the suffering of others.  We long for the joy and euphoria that comes when we serve, when we heal, and when we make a difference.  We are “lifted” by repairing brokenness, by ending violence, and by easing injustice and poverty and hunger.  We not only crave the “lifting moments,” we must experience them.  A life devoid of service to others, a life devoid of acceptance and worth, a life devoid of love and encouragement is a lonely and painful life.  We are lifted by good friendships, meaningful encounters with God’s Spirit, and by the warmth and goodness of humanity when it is demonstrated.

My fear is that often in this tension between lift and drag, that the power of drag wins out.  Call it negativity, sorrow, regret, or disappointment.  Its affect is certainly felt by each of us.  There are many numbered among us who are so very disillusioned by the current political climate.  Others feel the negative pull of anger on social media.  Still others experience drag in the day-to-drudgery of what they perceive to be “meaningless” work.  Others are pulled down by the oppressive weight of loneliness, shame, or remorse.  All of us want to soar… but sometimes life “drags” us down.

So how can we overcome drag so that we can rise once again?  Great question.  Though I certainly don’t have all the answers, I do want to offer this thought.  Think in terms of what surrounds you.  Think first in terms of those things that are constantly bombarding your life.  Think social media.  Think 24-hour news cycles.  Think movies and music.  Think negative conversations and opinionated people.  Step back for a moment and consider how much flows into your heart and mind and how much you allow to dwell there.  Though you cannot always control the amount of negativity that flows around you, you CAN choose how much you want to harbor.  Maybe you need to take a cell sabbatical, or a Facebook holiday, or a relationship retreat.  Maybe you need to sever some of the ties that bind you to negativity so that you can just breathe again.

So where to find those things that can lift your life?  Look in the places that have always brought you joy and fulfillment… look in old, treasured friendships, or in reassuring passages from God’s Word, or in a book that bespeaks of what is best in our humanity, or in opportunities to give yourself away to a higher, more noble cause. Find it in those places where God Himself has secretly hidden it away for you to discover.

If you ever get to pilot a small plane, you will discover that once you overcome the drag as you speed along the tarmac, it becomes hard to keep a plane on the ground.  Planes are designed to fly… and so are you.

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Elevators are flight control surfaces, usually at the rear of an aircraft, which control the aircraft's pitch, and therefore the angle of attack and the lift of the wing. The elevators are usually hinged to the tailplane or horizontal stabilizer. They may be the only pitch control surface present, and are sometimes located at the front of the aircraft (early airplanes and canards) or integrated into a rear "all-moving tailplane", also called a slab elevator or stabilator.

Elevator control effectiveness

The elevator is a usable up and down system that controls the plane, horizontal stabilizer usually creates a downward force which balances the nose down moment created by the wing lift force, which typically applies at a point (the wing center of lift) situated aft of the airplane's center of gravity. The effects of drag and changing the engine thrust may also result in pitch moments that need to be compensated with the horizontal stabilizer.

Both the horizontal stabilizer and the elevator contribute to pitch stability, but only the elevators provide pitch control.[1] They do so by decreasing or increasing the downward force created by the stabilizer:

• an increased downward force, produced by up elevator, forces the tail down and the nose up. At constant speed, the wing's increased angle of attack causes a greater lift to be produced by the wing, accelerating the aircraft upwards. The drag and power demand also increase;
• a decreased downward force at the tail, produced by down elevator, causes the tail to rise and the nose to lower. At constant speed, the decrease in angle of attack reduces the lift, accelerating the aircraft downwards.

On many low-speed aircraft, a trim tab is present at the rear of the elevator, which the pilot can adjust to eliminate forces on the control column at the desired attitude and airspeed.[2] Supersonic aircraft usually have all-moving tailplanes (stabilators), because shock waves generated on the horizontal stabilizer greatly reduce the effectiveness of hinged elevators during supersonic flight. Delta winged aircraft combine ailerons and elevators –and their respective control inputs– into one control surface called an elevon.

Elevators' location

Elevators are usually part of the tail, at the rear of an aircraft. In some aircraft, pitch-control surfaces are in the front, ahead of the wing. In a two-surface aircraft this type of configuration is called a canard (the French word for duck) or a tandem wing. The Wright Brothers' early aircraft were of the canard type; Mignet Pou-du-Ciel and Rutan Quickie are of tandem type. Some early three surface aircraft had front elevators (Curtiss/AEA June Bug); modern three surface aircraft may have both front (canard) and rear elevators (Grumman X-29).

Research

Several technology research and development efforts exist to integrate the functions of aircraft flight control systems such as ailerons, elevators, elevons, flaps and flaperons into wings to perform the aerodynamic purpose with the advantages of less: mass, cost, drag, inertia (for faster, stronger control response), complexity (mechanically simpler, fewer moving parts or surfaces, less maintenance), and radar cross section for stealth. These may be used in many unmanned aerial vehicles (UAVs) and 6th generation fighter aircraft. Two promising approaches are flexible wings, and fluidics.

In flexible wings, much or all of a wing surface can change shape in flight to deflect air flow. The X-53 Active Aeroelastic Wing is a NASA effort. The Adaptive Compliant Wing is a military and commercial effort.[3][4][5]

In fluidics, forces in vehicles occur via circulation control, in which larger more complex mechanical parts are replaced by smaller simpler fluidic systems (slots which emit air flows) where larger forces in fluids are diverted by smaller jets or flows of fluid intermittently, to change the direction of vehicles.[6][7][8] In this use, fluidics promises lower mass, costs (up to 50% less), and very low inertia and response times, and simplicity.

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Gallery

• A drooped elevator, nearly touching the grass, on the horizontal stabilizer of this Currie Wot biplane
• The tail of an Airbus A380, showing the elevators at the rear of the horizontal stabilizer
• Pre-installed elevators for a small Airbus. The elevator is the silver surface on the right hand side of the picture, immediately below the red pipes on the factory wall.

See also

• Rudder
• Aileron

References