Tutorial Review

I have started the first phase of the King Schools Private Pilot Knowledge Test Course, and in the weeks to come, I’ll be giving regular reviews. I figure this not only benefits me, since I’ll be rehashing it for this review, it will also benefit all you new folks to the wide open world of aviation, those of you new to flight simming, since the concepts of flight dynamics are used in the modeling of the aircraft, and last but surely not least, the folks at King Schools, enabling them to hopefully spread the word a bit farther on how anyone that wants to fly, can fly! So without further ado, let’s get on with the review!

The lessons are laid out in a really easy to follow and convenient format. Follow the links provided to the King Schools Home site, to view more info on there lesson packages. Like they say, there’s a good mix of fact, graphics, down-to-earth teaching concepts, and of course, a bit of humor to keep things light! They really do make it easy to learn the material. With anything that you learn though, you still must study and review and a good dose of commitment!

Here’s what we’ll cover in the first review:

1. Aerodynamic Principles
     A. Forces on an aircraft.
     B. Angle of Attack and Stalls
     C. Frost on the wings
     D. Left turning tendency

2. Practical Aerodynamics
     A. Stability
     B. Turns and Load factors
     C.   Byproducts of lift

1A - Forces on an aircraft
The four forces that are in play upon an aircraft in flight are Thrust, Drag, Lift, and Weight.

These four forces are in equilibrium, Thrust = Drag, Lift = Weight, when there is no change in either speed or direction, or during unaccelerated flight.

1B - Angle of Attack and Stalls
Bernoullis’s Law is covered here. Imagine an air hose with the middle constricted down, or narrowed. As the air is passing through the hose, it gets to this narrow spot and speeds up, due to the constriction. Pressure at this point is also the least. Now, at the point of restriction, if you sliced that hose lengthwise, you’d have what would look like a side view of a wing, a curved top and a flat bottom. Here’s where Bernoulli’s Law kicks in. Since the air passing over the top of the wing is at a low pressure (remember the constricted hose), this means that on the bottom of the wing, there will be high pressure, and this is what causes the lift of the wing, and anything attached to it, namely you and the rest of the aircraft!

Bernoulli’s Law is now applied to the concept of Angle of Attack, or AOA. AOA is determined by the Chord Line of the wing (sideways view of wing with a line drawn through it) in relation to the Relative Wind (which is the wind direction, in relation to the wing). The angle between these two lines is the AOA.

AOA determines how much lift the wing will have. When this lift is destroyed, i.e. not enough speed and too much of a climb angle, there is not enough air flowing across the wing surface, and a stall occurs. This has nothing to do with the engine cutting out, but the forward movement of the plane. The AOA at which an aircraft stalls will remain the same, regardless of the weight of the craft. The indicated airspeed at which a given airplane stalls will remain the same, regardless of the altitude.   To spin an airplane, the aircraft must be stalled. When the spin occurs, both wings are stalled, no matter which direction the spin is in.

1C - Frost on the Wings
Anything that is foreign to the smooth shape of the wing will interfere with the smooth flow of air over the wing surface. Especially dangerous is frost on the wings. Frost may prevent the aircraft from gaining enough lift at normal takeoff speed, thus not getting airborne in time to either clear the runway or that tree!

1D - Left Turning Tendency
The aircraft will have a strong left turning tendency while climbing and at takeoff. The use of some right rudder is necessary to counteract this effect. This is due to a couple of reasons. One is the P - Factor, which is the pitch of the prop blade, or the angle at which the blade “bites” the air. When the aircraft is taking off, the prop is not pointed directly forward, into the wind. The blade on the right, the descending blade, is at this point taking a big bite out of the relative wind, (remember what that is?) while the blade on the left, the ascending blade, is taking a much smaller bite. This is called Asymmetric Prop Loading, which is yawing to the left of the aircraft at high angles of attack. The prop blade on the right is giving you more thrust than the blade on the left, causing torque, which is at its greatest when you have the aircraft at high power and low airspeed, like when you’re taking off and climbing.

Now here was something that I found very interesting, and that’s the aerodynamic compensations that are built into aircraft, that take effect at your aircrafts particular airspeed. What the manufacturers have done is taken the left wing and incorporated a greater AOA. There’s that AOA thing again! Must be pretty important! The right wing has been incorporated with a lesser AOA. The tail section is also slightly canted to the right to help compensate for that yawing to the left that I’ve been talking about. There’s one instance that comes to mind concerning one of the aircraft models that I have built, the British Supermarine Walrus, with its engine canted slightly in its mountings between the wings (it was a biplane-type seaplane) to help with this yaw factor.

2A - Practical Aerodynamics
Stability of an aircraft means that it takes little effort at cruise speed to to control the aircraft if it is inherently stable. When they talk of longitudinal stability, it means pitch stability. If you were to pull back and pitch the aircraft up, and then let go of the yoke, the aircraft will return to equilibrium, or level flight.

Longitudinal stability is determined by the location of the center of gravity in relation to the center of lift. Center of gravity is normally located forward of the center of lift. Here’s another engineering tidbit, the tail section has an aerodynamic down force built into it, to compensate for the weight being forward of the center of gravity. So the tail wants to fly downward, or the craft nose up. When you’re moving slow, there’s less airspeed moving over the tail, so the plane will want to go into a dive, since there’s not enough “downward” force on the tail to keep the nose up. I hope I’m not confusing you! King’s makes it real easy! When you speed up and pull up, the amount of air flowing over the tail is back to being enough to compensate for those center of gravity forces, and ouila! You’re back to not scaring your passengers to death!

The center of gravity in an aircraft can be changed. However, this also changes the stability characteristics of the aircraft. If you pack everything into the most aft center of gravity limit, the aircraft will be less stable no matter how fast or slow you’re going! When the weight is distributed in this manner, you may have extreme difficulty in recovering from a stall. You want to get the nose down in a hurry and if your tail end is heavy, that just isn’t going to happen so easily!

2B - Turns and Load Factors
Banking an aircraft tilts the lift of that aircraft. The horizontal component of lift is what makes the aircraft turn. When making a turn, the aircraft wants to yaw in the opposite direction. This is due to the drag over the ailerons, and can be corrected with the use of the rudder, in the opposite direction of he turn. Because of the increased load on the aircraft during a turn, the nose will want to drop, so adjustments are made by pulling back on the yoke to make small corrections.

During an approach to a stall, an increased load factor on the aircraft will cause the plane to stall at a higher speed, since the wings have to support more weight. Putting load on an aircraft increases the G forces on the aircraft. 1 G is what we feel everyday when standing still, or flying in unaccelerated flight. When making a turn, G’s increase, and the aircraft can only take so many G’s before structural damage takes place, like losing the wings! In smaller, general aviation craft, a 30 degree bank will get you 1.2 G’s, and a 60 degree bank will put you at 2.0 G’s. There are loads of charts and graphics in the course to help illustrate all these concepts. Keep in mind that the amount of excess load that can be imposed on a wing depends on the speed of the airplane.

3A - Byproducts of Lift
Wing tip vortices are discussed in detail, for they are a dangerous factor to small aircraft. Whenever an aircraft’s AOA is at its highest, wing tip vortices are at there worst. This is especially dangerous behind large, heavy aircraft when they are clean and slow. “Clean” meaning flaps and gear up. Vortices have a tendency to sink behind the aircraft and spread out when near the ground. So fly above the aircraft’s threshold when taking off behind a large aircraft. Maximum caution is required when there is a light, quartering tailwind to avoid wake turbulence. So remember when landing after a large aircraft has landed, land beyond the point where his nose wheel touches down, and when taking off after a large aircraft, pull up and above the flight path of the larger aircraft, or if possible wait a minute if there is no hurry.

This concludes my first part of the King Schools Private Pilot Knowledge Test Course! I hope you find some of this information interesting and helpful, whether you’re a new “Flight Simmer”, or you too are starting your studies for your license! Watch for more to come!

Visit King Schools at www.kingschools.com for more information on this, and other wonderful courses and products. They have quite a lot to offer!