Friday, August 10, 2012

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.

Wednesday, August 8, 2012

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?"


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.


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.


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.

Tuesday, August 7, 2012

In Flying - How Far are You from a Stall?

Speed - Load and a Stall

The lowest of the Angle of Attack means the same thing to many of us as "Speed." Slow flight, as covered before, means high Angle of Attack.

Another factor to consider about the Angle of Attack when you fly a plane depends on its load. If you load your plane up and need to maintain the same speed you need more Angle of Attack.

When you increase the Angle of Attack to compensate for the increased load to maintain the same speed you achieved at a lighter load you lose your reserve of lift. 

A stall occurs when your plane reaches the limit of its reserve of lift. Your load can increase only to that point where the maximum reserve lift limit is reached. At that point the plane will stall at the straight and level flight and speed.

Now, how does this apply to practical flying? The centrifugal force experienced in a turn or pulling up after a dive (g-forces) act like real weight or load that brings you and your plane closer to the maximum limit of your reserve of lift

Now you understand that, in a turn or pull out from a dive, the increase in weight does several things:
  • Angle of Attack increases.
  • Reserve Lift decreases.
  • It approaches a stall even though the speed remains the same.
In straight flight speed and a sense of "lift" are the same thing. If a pilot can sense his speed he can also sense his lift. This is a definition of buoyancy. 

The tight turn centrifugal forces and g-forces in recovery from a dive can quickly turn into a stall. You must think ahead if you anticipate what can happen if you suddenly increase your load your plane carries.