Weight and Balance, Cross-Country Flight Planning


Sorry for the delay in posting everyone, but with the holiday celebrations, the homework Mr. Whipple gave us (Planning a flight to International Falls, Minnesota, from Anoka City, Minnesota), the study for the quiz on Aircraft Performance when we return to class on January 4, 2012, and the impending FAA final, not to mention the new year celebrations, you can see it’s been quite hectic. I’ve been writing this post on and off since 12/19/2011, so without further ado let me begin by telling you about my last class before the holiday break.

Tonight’s Ground School Class (12/19/2011) was probably the most exciting and interesting for me, even more than the very first class I attended. After I attended my first class, I left thinking that I had made an excellent decision in having registered and tonight’s class confirmed that.

We learned the importance of Weight and Balance of a plane and plotted our first Cross Country Course to Brainerd Minnesota from Anoka City Minnesota. Actually this class was a continuation of the Airplane Performance class as Weight and Balance of the aircraft also affects performance. Mr.Whipple started by stating that a plane’s Center of Gravity (CG) is where the three axis, the longitudinal, the vertical and the lateral axis meet, and this is where the pilots are seated, and is an imaginary point. You must know that the plane is balanced within the approved limits as indicated in the POH (Pilot’s Operating Handbook). The Center of Gravity of the plane is perhaps more important than the weight as it’s more important to know where to put the weight. The location of this point is critical to the stability of the plane and the CG will move depending upon how the plane is loaded. The limits of the CG are the forward and aft center of gravity locations. The Reference Datum (RD) is an imaginary plane from which all horizontal distances are measured for balance purposes. This RD is decided by the manufacturer and can be found in the POH. It’s used in calculating the CG of the plane.

If a plane is over loaded behind the pilot, then it becomes tail heavy and this is more dangerous than if the plane is over loaded in the front. The importance of weight must not be underestimated and in relation to a properly loaded plane, an overloaded one has a longer takeoff run, higher takeoff speed, longer landing roll, reduced angle and rate of climb, shorter range and a higher stalling speed. In order to assess the weight you need to take in to consideration the weight of many things such as the weight of the plane itself, the passengers, the luggage and the fuel. Further there’s also something known as basic empty weight. Basic Empty Weight includes the weight of the plane, optional equipment, unusable fuel and full operating fluids and the full engine oil. The unusable fuel is that small amount left in the tanks that cannot be used in flight nor drained. “One other thing that needs to be mentioned”, said Mr. Whipple, “is that the weight of a plane may change during the course of its life as the owner may add accessories to the plane, for instance, new radios, seats, new instruments etc., and anything that changes the weight or the CG must be documented and as a pilot you must always use the latest weight of the plane in your calculations”.

Then Mr. Whipple proceeded with some examples of calculating weight and balance. There are three methods he showed us, Computational Method, the Tabular Method and the Graphical Method. The first method involves taking down the figures of the weight, the ARM which is the distance from the datum to the weight, and when these two figures are multiplied you get a third figure called the Moment. The total moments divided by the total weight gives you the CG in inches. You then see if the result of the CG falls within the limits stated in the POH. The second, tabular method is similar but the computational method, and involves using a series of tables provided by the manufacturer. For instance the manufacturer provides a Moment’s table, baggage arm table etc. To evaluate the CG you find your weights of baggage, passengers etc. and refer to the tables for moments, arms etc and then having calculated the figures refer to the tables to find out if they fall into the limits stated in the POH. Finally, the Graphical Method is again very similar but you refer to the graphs provided in the POH to see if the calculated figures fall within the range of the POH.

The above was an extremely brief explanation of the Weight and Balance class.

Next Mr. Whipple showed us how to plot a Cross Country Course using a plotter (combination of a protractor and a ruler), map, and the E6B flight computer. This was quite a detailed process and too much to describe here but briefly, we drew a line from point A (starting position – Anoka City, MN) to point B (destination – Brainerd, MN). Using the plotter we then measured the length of the line to evaluate the course in nautical miles. Then at every 15 miles or so we found a Check Point (i.e. reference point) on the map, such as a lake, or a tower, major roads, rail roads, major towns/cities etc. so that we could use them to stay on track during flight. Now the aim of flight planning is to make the path over the ground match the course line drawn on the chart, and in order to do that, you also have to take in to consideration wind direction and wind velocity so that wind corrections may be made to make adjustments to drift. One also needs to take in to consideration True and Magnetic values. So next using the protractor part of the plotter we measured the True Course from the map. This was done by placing the plotter, i.e. the protractor part of the plotter, on the course line and moving the center hole of the protractor until it was over the intersection of the nearest meridian. There are two arrows on the protractor that are pointed in opposite directions. These arrows tell you which part of the protractor should be used to measure the angle for the course heading. The outer part of the protractor has an arrow pointing left, and the inner one has an arrow pointing right. So basically you use that part of the protractor in which the arrow is pointing when placed on the intersection. In our example, the True Course angle was measured at 332 degrees.

Next we used the E6B flight computer to calculate the True Heading and the Magnetic Heading using the compass numbers found on the plane. So you need the following data to evaluate the True Heading:

Wind Direction – 300 degrees at 22 Knots (This was given to us by Mr. Whipple and you would find out such information from ATIS or other weather services).

True Course – 332 degrees (We measured this on the map)

True Airspeed – 110 Knots (Given to us by Mr. Whipple, and this is the speed of the plane)

Given the above and using the E6B flight computer we found the following information:

Wind Correction – 7L (i.e. 7 degrees Left)

True Heading – 325 Knots (This is the difference between True Course and Wind Correction).

Depending on which side of the E6B computer you end up with for the Wind Correction Angle, you add or subtract the angle to get the True Heading. If it’s on the Left as we go, i.e. 7L you subtract, and it’s on the Right, you add.

Ground Speed – 90 Knots

We entered these figures in our Navigation Log along with other data such as names of Check Points, Distance between check points (Measured on the map using the plotter), Estimated Time En Route and Fuel Remaining after each leg of the journey.

Next we had to correct for the Magnetic Variation. The compass that’s used in planes points to magnetic north, and we have to adjust the aircraft heading which is based on the compass reading i.e. Compass Heading, in order to get the True Heading. The sectional charts show the magnetic variation by a dashed magenta line with the magnetic variation on it e.g. 2 degrees East. So you have to take this into consideration when tracking the true heading of 325 degrees. In order to do this you have to either add or subtract the magnetic variation from 325 degrees. The question now arises is when do you add and when do you subtract? There are two methods which help you to make that decision and I’m going to use the easiest one. Actually, they’re both easy but one takes longer to explain than the other. A good memory aid in deciding when to add and when to subtract is to remember the following: “East is Least, West is Best”. From this, you can see that if the variation is a certain number of degrees to the East, you subtract, and if it’s to the West you add. In our example, the Magnetic Variation was 1 degree East, so we subtracted this amount from 325 to get 324 degrees, the Magnetic Heading.

Then next thing we did was to measure the distance between the Check Points using the plotter, and entered this into the Navigation Log. This would come useful in calculating the Estimated Time En Route (ETE) i.e. time of travel between each leg. You can calculate this using the formula below or the E6B and we used the latter.

ETE (minutes) = (Distance (in Nautical Miles) X 60 (minutes)) / Ground Speed (in Knots)

Finally, we calculated using the E6B the fuel used to travel each leg of the journey.

So here’s a quick summary of the above process:

1. Draw a line on the map between the starting airport and the destination airport

2. Measure in Nautical Miles the distance between the airports using a plotter

3. Every 10 -15 miles or so, find Check Points and mark them on the map

4. Find the True Course heading using the plotter and the Meridian

5. Change True Course to Magnetic Course using Magnetic Variation

6. Find Wind Correction Angle and then Magnetic Heading

7. Find the Estimated Time En Route

8. Find amount of fuel used on each leg of journey

9. Remember to enter all details in the Navigation Log

Navigation Log for Anoka to Brainerd (Double click to enlarge)

      

 

 

 

 

 

Please note that in practice, most, if not all of this Navigation Log would be completed, but since this was an example from class it is not entirely filled out.

And here’s the Sectional Map showing Anoka, Brainerd and the Check Points encircled in blue. Sorry about the picture quality but it’s the best I could do.  😀

Sectional of Anoka-Brainerd (Double click to enlarge)

 

 

 

 

 

 

 

😀 A Very Happy and Prosperous New Year Everyone! 😀

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