Airplane Performance

Wednesday’s Ground School was interesting regarding Airplane Performance. It covered three aspects regarding airplane performance and how it’s affected by various factors and what one can do to get the most out of the airplane. The three aspects covered were “Predicting Performance”, “Weight and Balance” and “Flight Computer” (i.e. the E6B). The term performance is used to describe the effectiveness of an aircraft in the jobs it was designed to accomplish.

Mr. Whipple began the lesson by stating that every plane has:

1. A Pilot’s Operating Handbook (POH).

2. The POH contains performance data for that plane.

3. The POH contains charts that show what performance can be expected.

“What must be noted here”, said Mr. Whipple, “is that these tests were carried out:”

1. By a professional pilot who is able to thoroughly test the plane in every possible situation.

2. The tests are carried out on a brand new plane.

3. The tests were carried out when there were no dents, or any other form of wear and tear on the plane that can affect performance.

So unless a brand new plane has been purchased, it is highly likely that the plane will perform less than expected in relation to what is stated in the POH. Performance is based on standard atmospheric conditions i.e. 15 C / 59 F with an atmospheric pressure of 29.92 inches of Mercury.

Since each type of plane is designed differently to emphasize different aspects such as speed, maneuverability, load-carrying capability, its ability to handle short, rough fields, aircraft designers try to build into the plane what they most would like it to do. For instance an aerobatic plane is highly maneuverable, but doesn’t really have any load carrying capability other than the pilot.

The ability to predict airplane performance is vital as this will enable the pilot to determine how much runway is required to land or to take off and under what atmospheric conditions, or how safely it can clear any obstacles when landing or taking off or how long it will take to reach a particular destination etc. As mentioned already most of this information is in the form of charts in the POH and one can use these to predict performance.

Other factors affecting performance are weight and balance, and wind. A heavier plane is difficult to lift and energy used to lift is unavailable for thrust. Similarly more energy is required to accelerate a heavier plane before taking off and to slow it down when landing. So runway requirements are greater when the plane is heavier. I hope now you can understand why weight and balance is so important?

Wind also plays a vital role in airplane performance and it can either help the pilot or cause him/her problems. Airplanes taking off or landing in a strong wind have a reduced ground roll. Ground roll is the length of runway that the airplane is on the ground before it takes off, or from the time of touch down until it comes to a full stop. Wind also plays a role in flight planning as fuel consumption is proportional to flight time. Atmospheric conditions can affect the air also and thereby affect airplane performance. For instance depending on the atmospheric conditions, the air density may decrease, increasing the apparent altitude. Airplane performance decreases with altitude, so if there’s a decrease in air density due to say temperature, humidity or pressure the performance is reduced.

Well I don’t want to go into too much detail but I think you can understand how performance can be affected and why it is important to be able to predict it. And this can be done using the aid of various charts in the POH along with the use of the E6B flight computer. The E6B computer is used in flight planning taking into consideration a given airplane, its performance, weight and balance, and the atmospheric conditions. The E6B looks like the old slide rule but its circular and a very useful tool to become familiar with. I’m still getting to grips with it, but I think I’ll be able to master it with practice; actually I have to master it as there are questions on the EB6 on the FAA written test.

So that was Wednesday’s class, and below you can find examples of the E6B computer. The one in white is made of plastic and cardboard whilst the black one is entirely metallic. I recently purchased the metallic one from Twin Cities Aviation Flight School for $32.01 including tax. The white E6B came with my pilot’s kit from Thunderbird Aviation. I purchased the metallic one because sometimes you have to use a marker on the computer during calculations and it’s easier to erase, not to mention the fact that it comes with a user’s manual. 😀




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