What is Flight-Simply Speaking #2

The first “What is Flight” article introduced the concept of a liquid, such as air, when moving faster over the curved top of a wing generate less pressure or a vacuum, theBernoulli Principal. In this article we discuss the parts of a very simple fixed wing aircraft. The physics of a simple aircraft apply to the most advanced 747 but, in a smaller scale.

So far, we have a fuselage with wings that pull or lift the aircraft up, a propeller to pull the aircraft forward and, stabilizers at the back or tail of the aircraft to keep our aircraft flying straight like feathers do for an arrow.

Now, how does the aircraft turn, climb and descend? Each wing has an aileron that is controlled by the pilot. For a left turn the pilot moves the yoke or stick toward the left and the left aileron moves up into the airflow, disrupting the flow and reducing the lift while the right aileron moves down, increasing the curvature of the wing top and increasing the lift. Right wing moves up and left wing moves down, and the aircraft turns left. Simple enough except, another law of physics from Isaac Newton complicates the maneuver. “For every action there is an equal and opposite reaction”, so as the right wing generates more lift it also generates more drag on that wing resulting in a yaw or sideways force. The nose of the aircraft moves up and to the right. The pilot then uses a panel attached to the vertical stabilizer to move the nose left to coordinate the turn. His rudder pedals at his feet move the rudder disrupting the flow of air, in this case toward the left counteracting the right yaw from the aileron movements. What happened to “Flight-Simply Speaking? “

The opposition force of drag causes the aircraft to slow and descent unless the pilot uses another control by pulling back on his yoke or stick which activates another panel attached to the horizontal stabilizer called the elevator. It raises up into the airflow, forcing a downward force on the tail and an upward movement for the nose. Finally, a coordinated turn to the left has been accomplished but with the increased drag the aircraft will slow and eventually ‘stall’ or quit flying unless the pilot increases an opposite force to the drag called thrust.

An aircraft deals with three axes; vertical or yaw, longitudinal or roll, and lateral or pitch. Our wing has ailerons to generate a turn and the vertical and horizontal stabilizers have a rudder and an elevator to coordinate the turn.

Our next article will discuss the several forms of thrust, without which we could never get airborne and wing flaps that increase the lift of a wing to allow shorter take offs and slower landings. The pilot is much like a conductor of an orchestra. His players are thrust, ailerons, elevator, rudder and a few other players that we will discuss in future articles.


Art Krull                                                           

FoF Volunteer Ambassador

What is Flight-Simply Speaking

We will start with a definition which is often debatable, but I will use the following for a starting point:

Flight is the process by which an object moves through an atmosphere (or beyond it, as in the case of spaceflight) without contact with earth’s surface. It needs enough upward force to counteract gravity. 

A hot air balloon traps the raising hot air and lifts the basket up exceeding the pull of gravity. For horizontal flight, the object uses propulsion from a propeller or jet engine generating enough lift from the airfoil to counteract gravity. 

Today we will discuss the force generated by an airfoil. This is explained by the Bernoulli Principal: the pressure in a stream of fluid is reduced as the speed of the flow is increased

Marriam-Webster Dictionary

Air is considered to be a fluid. An airfoil or wing typically has a flat bottom and curved top. As the air passes over the top of the airfoil, the speed increases and the pressure decreases thus generating a vacuum that pulls the wing upward. This is the same effect from a propeller that has the shape of an airfoil. The propeller has a lower pressure on the front thus pulling the aircraft forward or upward as in a helicopter.

A hot air balloon simply uses trapped hot air to ascend and has little or no control of direction. A rocket uses an engine that produces upward thrust to ascend with some limited directional control. A baseball pitcher uses his strength to propel the ball and can change its direction by inducing a spin allowing the Bernoulli effect to curve the ball. A knuckle ball has little or no spin thus causing an uncontrolled flight path. These forces can be easily demonstrated by spinning a beach ball in various directions.

The wing generates upward force on the fuselage but provides no directional control. The directional stability is provided by the appropriately named stabilizers. A horizontal and vertical stabilizer are typically at the back of the fuselage.

Entering our gallery, at the bottom of the ramp, is an exhibit showing the Bernoulli Principal. The ball spins and stays levitated because of the pressure differentials. Just across from the exhibit is a huge vertical stabilizer. This is equally curved on both sides stabilizing the aircraft direction but not generating any forces to either side. This is an actual vertical stabilizer taken from 747 and an excellent example of how large the 747 is.

There are many aerodynamic forces affecting flight especially as noted in Isaac Newton’s Laws of Motion. Newton’s Third Law; For every action there is an equal and opposite reaction, generates a problem. This article introduced the useful element of lift. Future articles will explain how to deal with ‘the opposite and equal reaction’ often called drag and how, by modifying the shape of airfoils and stabilizes in flight, the aircrafts can climb, turn and descent.

Art Krull

FoF Volunteer Ambassador

Almost Lost My Stinson

A true life story form our friend Glenn H.
In April 1968 I pulled my Stinson 108, with a 150 horsepower Franklin engine, out of the hangar and did a preflight inspection. Prior to my solo flight I did a ground run-up checking the magneto’s for appropriate mag drop and temporarily applied carburetor heat to assure I had no carb ice. My fuel tanks were full of 37 cent a gallon 80 octane aviation fuel, I had no predetermined destination in mind, the day was clear and the air was smooth. Life was great! To escape boredom I climbed to 4,000 feet applied carburetor heat, reduced power and practiced some stalls. After the last stall I applied power and pushed the carburetor heat button in. To my surprise the engine ran very rough and produced only 1,700 RMP, which resulted in insufficient power to hold altitude. I again applied carburetor heat to no avail. I switched fuel tanks and experienced no improvement. I now realized I had a problem that I hadn’t previously encountered and didn’t have a solution. I surmised that I had a valve or cylinder problem. At this point I assessed my location and ascertained I was too far from any airport and my option was to land in a boggy field. Although a little panicky, I didn’t have any fear for my life, but knew an off-airport landing would probably total my plane and all the resulting problems of aircraft retrieval.
An in-flight magneto problem had never been a topic of conversation among my friends or in written format. To me, magneto’s were something that either worked or didn’t work. For some Devine reason I turned the magneto switch one click to the left and the engine immediately smoothed out. With a sigh of relieve I headed back to my home airport.
My A&P technician removed the offending Bendix magneto and replaced the coil. He ascertained that the offending magneto set up a crossfire which prevented the “good” mag from allowing the engine to perform properly. Magneto’s seldom fail, but when they do, they can do more than just go off line.