Energy, Energy on a Beautiful Day

Atomic Power - On a Humid Day

Ahhh! Beautiful day! Nice hammock to think about physics! Specifically, how is it possible for a thunderstorm to have the power of numerous atomic bombs! No way you say! Get in the hammock and look at a cloud forming on a nice hot, humid day. Everything appears normal until suddenly the cloud rises upward very fast. Soon it takes on the appearance of a thunderstorm. Lets take a peek at that phenomenon.

The Adiabatic Lapse Rate per thousand feet is 4.5 degrees F. Suppose the dew point, on this beutiful day is 68 degrees F. If the temperature in our hammock is 90 degrees F the base of the clouds forming should be aprroximately 5000 feet above ground. As our fluffy friends approach 13000 feet something happens. At 13000 feet the water vapor begins to freeze!

Now think about what happens when water changes from a liquid state to a solid state - ice. Somewhere in the innermost recesses of my insane mind I remeber a rat fact from my HS Chemistry Teacher that for every gram of water that changes from a liquid to a solid, 580 calories of heat are released. Maybe somebody can tell me, on a hot, humid summer day, how many grams of water are being converted? You get the picture?

The enormous energy being released rapidly pushes the cloud formation to astronomical heights. Down here in "Humid Land" (South Carolina) tops of thunderbumpers reach 50000 to 60000 feet on a regular basis in the afternoon buildups.

Which answers the question of the day! In a single thunderstorm here is the amount of energy released from a thunderstorm.

If the quantity of water that is condensed in and subsequently precipitated from a cloud is known, then the total energy of a thunderstorm can be calculated. In a typical thunderstorm, approximately 5×10 8th power kg of water vapor are lifted, and the amount of energy released when this condenses is 1015 joules. This is on the same order of magnitude of energy released within a tropical cyclone, and more energy than that released during the atomic bomb blast at Hiroshima, Japan in 1945.

Energy, energy on a Beautiful Day...

Load Factors - G - Forces - Structural Failure

Load Factors in Flight

Load factors and safe flight. "The witness saw pieces of a plane fall out of the bottom of a nearby thunderstorm"...this is related to phrases like, "separation in flight" and "exceeded the designed stress limits of the aircraft" as frequently reported in too many accident reports.

The strength of an airplane is measured by the total load its wings can support without sustaining permanent structual damage. In curved flight - all types of turns, pullups from dives or when abrupt or excessive back elevator is used-the load factor increases because of the buildup of centrifugal force.   

Remember the steep turn instruction when you had to perform a left and right 360 degree steep turn for your instructor without losing altitude? You could feel the buildup of G-forces in your rear end and the pooling of blood trying to respond to the increased Gs. 

The increase of the load factor occurs at a startling rate once the bank of the aircraft has passed 45 degrees. At a 60 degree bank the load factor is 2 Gs. Twice what the load factor is in straight and level flight. At a bank of 70 degrees, a mere 10 degrees more, the load factor is 3 Gs and at 80 degrees the load factor increases to the structural failure stage of almost 6 Gs. 

Since most aircraft rated for "Normal Category" are limited to 3.8 Gs the danger from rapidly increasing G forces in planned and unplanned (read in a "thunderbumper") is obvious. Yes, you can rationalize that a plane is engineered for a safety factor 50 percent above the specified load limit for the Normal Category aircraft but it is foolish to insert yourself into a deadly game of G Force versus Structural Failure.

The limit above is the point at which wings and engine decide to leave the plane. Before the above limit is reached you can expect some damage to the aircraft. The more excess the more damage until you reach the engineered limit.Think about the aircraft you rent. If the G load was exceeded on a prior flight in a rented aircraft the 50 percent engineered safety factor may be considerably reduced. Structural failure may occur at a G force of 3.9 Gs, for example. Renting? Do a careful preflight.

If you encounter rough air or unusual vertical gusts, immediately slow the plane down to its specific "maneuvering speed" at which it will still continue to fly with a safe margin above a stall but, in rough air, it will sustain the least amount of structual damage. This speed is about 1.7 times the stall speed of the aircraft your flying.

Density Altitude - Hot, Humid Days

Density Altitude

If you have ever flown into a small strip in early morning and found, after a few hours, that the temperature increased to a point where the calculation of takeoff distance was necessary before takeoff?

I can remember several such instances at Dawn Patrols I attended in the Summer.

You have to  take humidity into your calculations. Water vapor can reduce the percentage of oxygen in the atmosphere. Neglecting density altitude with small, not too powerful planes can lead you to a much closer look at the trees below, upon takeoff, than you may have desired

The problem with humidity is that water vapor does not combine with aviation gas to produce ignition. Here's the important point. If water vapor partial pressure is five(5) percent of the total airpressure the available power to the plane is reduced by five(5) percent. this means your takeoff distance will be increased. Maybe too much!

At high temperatures and dew points the problem of high density altitude is compounded by a possible six(6) percent or more power penalty due to humidity. This factor is not accounted for in the Operators Manual of many antique aircraft.

If your manual allows you graphs to determine distance for takeoff, increase that distance by the humidity factor. If that seems like too much trouble, just add six(6) percent for all conditions below 90 degrees F or seven(7) percent for all conditions up to 100 degrees F.

The Compulsion Hazard - Actions that are IIrrational

Compulsion - Actions that are Irrational

The term compulsion refers to an individual's irresistible tendency to perform an action, even though he realizes it is irrational. 

For a pilot, this "compulsion" to go on in the face of weather conditions that were quickly deteriorating is a good example.

The feeling, irrational as it was, signaled that the weather condition was "circumnavigable" and that it would be better to the West. All of us have correctly thought such thoughts and made decisions based on new information from observatios or the FSS and had the decision turn out well.

Reasonable reponses to such thoughts is different from compulsion. An irrational response, one that could lead to an accident, may be compared to a physiological change you already know about; i.e., hypoxia or alcohol related.

Compulsion can be recognized if the pilot is alert. It is a feeling that is not backed up by information. The "Get-home-itis" feeling, which we have all experienced, is not a compulsion. A compulsion is more subtle. It relies on less obvious thoughts and personality factors. Those less obvious factors can lead a VFR pilot to continue flight into adverse weather conditions that are beyond his ability to handle.

This leads into a discussion of the intensity of the compulsion. The intensity is directly related to:

• The amount of success a pilot that has received praise for overcoming obstacles
• The number of times he has cut corners successfully
• What it means to him as a pilot
• The thrill of skirting danger. 

These less obvious factors may push the pilot into an irrational act based on compulsion.

What we, as pilots, need to do is recognize early that we are in emotional danger. When cold, hard facts or experience say "Do not go on!" Make the conservative decision.

If you can recognize the trap of compulsion and arrive at the "right" decision...you will be safe and a loved one will be very glad that you did.