Pussy Footing Around - Detecting a Cushion

Sensing Float (Buoyancy)

In landing an airplane sensations you receive from the plane to you are very important. Short fields require sensitivity to the subtle clues that affect lift. Floating is not nice as you run out of runway.

You want a slight cushion, when you land, to flare out, check the descent of your plane and contact the ground. This is the very slight touch of your wheels in a perfect landing. The "Ahh, what a landing" reaction from pilot and passengers. 

This is "flying the edge" to some folks. To arrive at the edge and not drop off the cliff is the goal in every landing.

We talked about lift reserve before. The perfect landing results from a cushion of reserve lift that allows the plane to touchdown quickly with as little float when you pull back on the stick or wheel and stall.

When you pull back on the stick you don't want to feel a surge of lift that requires a checking of the descent from you!

At altitude you can test the effect by flying a slow glide at the very edge of a stall. When you pull the stick back a few inches the flight path of the plane does not go up. Instead the plane begins to stall and settle. The flight path goes down. In a fast glide, with lots of reserve lift, when you pull back on the stick a few inches, the plane balloons with a firm push into your bottom. Net result is an upward flight path and a much longer movement forward before the plane settles down to land.

At altitude you can't  really see the deflection of the aircraft upward. You feel it. In an actual landing flare, near the ground, the slightest ballooning or settling of the plane is very apparent to the eye. You feel the changes you make in the stick position by sensing the slight weight changes (lightness or heaviness) that occur from stick handling.

If a pull back on the stick makes you feel slightly heavier you are gliding too fast and the plane "floats" until the glide slows.

If you pull back on the stick and you feel lighter, like going down in a fast elevator, your reserve of lift is limited and you descend.

Your perception of weight change is very sensitive. You make a conscious effort to pay attention to that "sense" and act accordingly. If you are a passenger in the right seat of a small plane during the final stages of a landing you will see the pilot make small changes in the stick position (both back and forward) as he "senses" the planes descent to a perfect landing.

This gives credence to the term "flying by the seat of your pants" when landing an airplane.

In conclusion, sensing the cushion effect is important to a good approach and landing. Your senses become very sensitive as you glide lower to the ground and control movements are limited to prevent major changes in flight attitude (up and down).

The Breakdown of a Spiral Turn Before the Breakup

The Breakdown:

Something disturbs the plane in straight and level flight at cruising speed. The right wing drops slightly. The plane enters a gentle sideslip to the right. In a slip a crossflow of air initiates a dihedral response to pick up the right wing.

The vertical tail fin responds, simultaneously, by yawing the plane slightly to the right. If the plane is spirally unstable the rudder (tail fin) forces the plane around before the dihedral had time to pick the right wing up.

The rudder produces a yaw which introduces an over-banking tendency while the plane turns. In a turn to the right the left wing is moving, at the moment, faster through the air and generates more lift. At the same time the right wing is slowed a bit and generates less lift. The net result is the left wing goes up slightly and the right wing drops. The over-banking tendency cancels out the attempt of the dihedral to the right wing to return the plane to level flight. Net result the right wing stays down.

The slight sideslip to the right continues and the dihedral tries again to right the right wing to stop the sideslip. The vertical tail again over-rides the dihedral and the plane enters a new over-banking effect. This process will repeat itself unless stopped.

If this isn't stopped the plane enters a steeper bank and a tighter turn. This continues if you don't interfere. 

The g-load increases due to the centrifugal force build-up. The increase in load forces the plane to drop its nose and pick up speed. The plane has a built-in tendency to keep itself at a constant Angle of Attack. The extra load, created by the centrifugal force build-up, creates a situation where the plane can only maintain a constant Angle of Attack by picking up additional speed. The dive combines with the spiral turn to create a spiral dive.

When an increase in the bank reaches a certain point another effect forces the nose of the plane downward toward the earth. In this deep bank the earth is on the right side and the sky is on the left side. The rudder (vertical fin) continues to push the plane around to the right. It now is pushing the plane into a dive toward the earth.

In summary, this is what a plane "wants to do" once it is in a turn. The plane wants to do this even when the pilot is on the controls. 

This, in previous posts, is the anatomy of the "death spiral" that causes many lost lives where instrument flight skills are lacking and/or the pilot tries to fly an airplane so it makes him "feel good or more 'natural'."

Flight Controllers have testified about their inability to talk an untrained pilot out of a "death spiral." They try to put the aircraft into a flight attitude where their sensations are "more natural." In effect, they don't believe what the plane's instruments are telling the pilot about the actual attitude of the plane (a deep spiral dive).

This is a safety lesson on proper instrument pilot training. Knowing the normal tendency of a plane, in a turn, can set you up for a vestibular illusion that may end your and your passengers lives in a needless spiral dive accident.

No Controls Touched - Will a Plane Fly Straight?

Will a plane fly straight or turn away from it's cruising straight ahead attitude of flight , if you release the controls?

What does an airplane really want to do concerning the direction of its flight? 

Unfortunately, aircraft built to American specifications don't have the stability to remain straight and level with the controls released.

A pilot knows this if he experiments at a safe altitude. Release the controls and the plane will enter a turn. Pilots say the reason a plane enters a turn is because of:

• Torque
• Stiff controls
• Wing heaviness

Planes will enter a turn. Once into the turn they will keep increasing the angle of bank, the rate of turn, the speed and the rate of descent. This results in a true spiral which is an ever tightening turn combined with an ever steepening dive.

The end result, if the plane is left to its own fate, is the plane will break up in this tight corkscrew because of excessive g forces that exceed the aircrafts maximum load limits.

The spiral looks like a spin except the plane's controls will function in a normal manner and no stall is involved. You can recover from a spiral dive any time you elect to use the controls.

The entrance into a spiral begins when something disturbs the plane's right-left sense. The aircraft will respond to the disturbance in two different ways simultaneously. One is a planes vertical tail will yaw the plane around to point itself into the direction it was actually moving. At the same time its tendency to refuse to sideslip, due to the dihedral angle of its wings, will cause the plane to lift one wing and drop the other to regain its lateral balance. Both events occur together. 

The turn causes the relative wind, to blow slightly crosswise at the plane to affect both the vertical tail and the wings dihedral at the same time. A plane will respond to a disturbance depending on weather the yaw effect or the wing-righting response is quicker and more forceful.

Think about a plane that has a very small tail and a pronounced dihedral. If a gust throws the ship into a slight sideslip the right wing will pick itself up before the small tail has a chance to yaw the plane around to the right. After the disturbance the plane will resume its flight in the origiinal direction.

Now think of a plane with no dihedral and a large vertical tail fin. The gust above will cause the plane to turn entirely from the yawing. If it does recover, it will head in a different direction. 

Students think the vertical tail fin is there to keep the plane flying straight. Instead, it actually makes the plane turn.

All of the above also depends on tail length and wing span. The density of the air plays a role in the dampening effect. A gust may cause a quick response but the air density will damp the quickness. A short tail and short wings will react quickly. Slower for a long tail-long wingspan aircraft.

Designing a stable non-spiraling plane is not worth the time for aircraft designers. They design a plane to actually help a pilot in controlling the aircraft. They contend that a spirally stable airplane is hard to fly in rough air. It will tire the pilot out over a long period of time.

To a pilot, in a steep spiral turn, is that tendencies that exist in a plane with controls released will be noticeable when the pilot flies the turn.

Plane design should make stability a priority. 

For Pilot Training Which is Better - High Wing or Low Wing?

High Wing versus Low Wing Trainers

I learned in a Cessna 120 tail-dragger. With experience, the Angle of Attack is controlled by the elevator. Keep in mind the Angle of Attack is the angle the attitude of your wings makes to the relative wind.

Lift is nothing but lowness of the Angle of Attack. When the stick is in a certain position the well balanced plane will assume a certain Angle of Attack. Put the stick further back the higher the Angle of Attack.

Whether the plane goes up, stays level or goes down at that Angle of Attack does not on stick position but entirely on the throttle position.

A good visible indication of this is a commercial jet aircraft descending on a landing flight path. The attitude of the airplane doesn't change due to its Angle of Attack but it is descending. If the pilot needs to maintain a flight altitude he applies power to maintain altitude. The stick  remains in the same position. If he needs to resume the original downward flight path he reduces power. The speed of the approach remains constant.

This confirms what a pilot wants to know about lift, that is how far he is from a stall.

Students need to appreciate and experience the pressures that increase  while he approaches a stall Angle of Attack. In a high-wing trainer stick movement to achieve this is much greater than in a low-wing airplane. The increased pressure you feel is  very noticeable and important. 

It is easier, in a glide, to let the stick creep backwards while in the glide. The pilot does this without realizing the slow change in position of the stick that results in a gradual increase in angle of attack. This is a drawback to high-wing trainers. An inexperienced new private pilot could approach a stall without adequate notice.

In low-wing aircraft, like the American Yankee, the range of stick movement is very small in comparison to a Cessna 120. I found out first hand when I pushed the stick forward just a couple of inches forward and I was in a fast power dive than in level flight. Same situation in a very steep climb. The Yankee, close to a stall, required only a couple of inches of back stick movement to reach that state.

A student tends to over-control. This is not good to use a quick reaction trainer if you want a student to recognize how a plane reaches a stall. It will enter a stall too quickly. This is frightening to a new learner.

You really have to "fly" a Yankee. I think this analogy pertains to the majority of low-wing aircraft.

In conclusion, a training airplane should require a wide, highly noticeable changes of stick position for small changes in Angle of Attack. The high-winged trainer would be my choice.

Sensing Angle of Attack

If Angle of Attack is associated with lift can we sense the angle of Attack?

Yes, No and Sometimes. The question should be " How reliable are our Senses to sense Angle of Attack?"

Speed

Low Angle of Attack and speed are almost the same thing in fast flight. High Angle of Attack and its relation to Load were discussed in an earlier post.

Reason

Ever play Blind Mans Bluff? There is way too many variables to trust your "reasoning" when it involves Angle of Attack. Here are several rationales,

• You "reason" since your power is on full and your planes attitude is slightly up you have good air speed.

• My power is very reduced and my nose (aircraft attitude) is down therefore I have good but not super fast air speed.

• Taking off from a high altitude airport the engine does not perform as well in the thrust department and a pilot trusting his throttle will rotate to his usual takeoff angle and the plane will stall.

If you are using your "reasoning" to judge "speed" it is wise to make sure your "reasoning" is correct and you are aware of all the factors involved.

Be aware of our old friend "g-load" where, in a tight turn, the airplane flying at a certain speed loads itself up with centrifugal force (load). This causes the plane to assume a larger Angle of Attack and gets itself closer to a stall. (Remember lift reserve?) 

The plane, at a larger Angle of Attack, the wings have more drag and slows the plane. To prevent the plane from slowing you must apply more power. This, if you think back, creates an even higher Angle of Attack and the plane edges ever closer to a stall.

You must realize and understand how dangerous this effect is. A small plane fully loaded and with the throttle set to maintain a level cruising speed will not maintain indefinitely any turn with bank at  45 degrees or more. The plane will slow down gradually as it circles as the pilots stick comes further and further back. If everything remains constant the plane will complete more turns until it stalls. This happened out of level flight at cruising speed.

An example may be a pilot taking his family out for a "spin", so to speak, to enter a tight turn to show them several things above their town that requires many turns to view completely. Things happen fast and you may suddenly see them as you hurdle down in a stall-spin accident.

Sounds

Airplanes make all sorts of big and little sounds that tells a pilot, by their pitch (high pitch=faster and low pitch=slower) that relates to speed and to the changing sound that indicates whether the plane is increasing or decreasing in speed. The problem is all planes are unique. The sounds one plane makes in different attitudes, speeds, etc. are all different. The beginning pilot hears the sounds but ignores them. The greatest danger of all is nothing at all - silence.

With experience, a pilot get away from just using the sense of sight and use his other senses to provide a "sense" of attitude that vision alone cannot.

Unfortunately the sounds of flight are not a good clue to provide the flight condition out of which a stall-spin accident develops.

Flight safety is learning from the good experience of others. Talk frequently to your instructor. Ask him how he can recognize dangerous flight situations in the air.